Ramblings of Meteorologist Jim Sullivan

For some reason, I posted the forecast for this event as another page and not a post. Here’s the link to that page:

https://ohwxramblings.wordpress.com/december-18-19-2015-lake-effect-snow-event/

Based on storm reports and some estimation based off of radar/terrain, here is my best guess on how much snow fell during the event:

Here was my forecast:

The biggest bust may have been in Geauga County, due to banding getting farther south than expected Saturday morning. This resulting in 1-3″ and 3-6″ type snows getting farther south than expected. The heavy snow also got a bit farther south than expected across Ashtabula and Crawford Counties. Overall I’m happy with the forecast, as with the exception of central/southern Geauga County the differences from actual are fairly minor/cosmetic. Not perfect, but not terrible either, which is all I sometimes home for with lake effect snow.

There was some interpolation/estimation to fill in the map, as spotter reports are often spaced pretty far apart. Used radar/satellite loops and elevation maps to estimate as needed.

For record keeping purposes, here is a post I made on Neoweather’s Facebook page this afternoon regarding the expected lake enhanced rain/snow tonight in NE Ohio

An upper level low pressure combined with a trough of low pressure in the low levels of the atmosphere will combine with moisture and instability off of the relatively warm waters of Lake Erie to cause rain to develop this evening across the lakeshore counties and Snowbelt east of Cleveland that changes to snow tonight and ends Thursday morning. The potential exists for a period of moderate to heavy snow overnight tonight inland from Lake Erie in the Snowbelt that produces accumulating snow and a period of hazardous travel. Travel conditions should improve during the AM rush…but locations from the hills in southern and eastern Cuyahoga County points east could see some lingering impacts during the early portions of the AM rush.

Rain showers will increase in coverage across portions of our coverage area this evening, mainly from Cuyahoga County points east. These showers could be mixed with a little graupel or soft hail, but will primarily fall as rain initially. The heaviest precipitation before midnight will be mainly focused on parts of Lake, Geauga and Ashtabula Counties. After midnight, the trough of low pressure will start slowly shifting southeast, which will start pushing precipitation into the rest of the lakeshore as far west as Erie County, including the Cleveland metro. The rain will likely start changing to snow away from the lake by midnight as colder air works in. Temperatures during the snow may stay a little above freezing, which means it will be a very wet snow.

A period of moderate to heavy snow appears to be a decent possibility in inland portions of the Snowbelt for a few hours during the pre-dawn hours on Thursday. Temperatures will again be a little above freezing in the snow, but the heavy nature of the snow could cause slick roads to develop in parts of the Snowbelt east of town at times after midnight. The heaviest snow in the Snowbelt will likely occur between 2AM and 6AM Thursday. As the precipitation moves southeast across the Cleveland metro, light to moderate bursts of snow are also possible away from the lake in parts of Lorain, Cuyahoga, northern Medina and northern Summit Counties. Again, the lakeshore will stay mainly rain or a mix.

The window for snow will be fairly brief (only a few hours), but the potential for moderate to heavy snow should allow for 1-3” of slushy snow to fall in the inland portions of the Snowbelt east of Cleveland; that’s eastern Cuyahoga, Geauga, inland Ashtabula, northern Trumbull and possibly far southern Lake Counties. Some portions of northern Geauga County and inland Ashtabula County could see locally up to 3-4” of wet snow if the changeover to snow occurs quickly enough. In the Cleveland area, a light dusting could occur inland from the lake…and the hills in southern Cuyahoga, northern Medina, northern Summit and northern Portage Counties could see a slushy accumulation up to an inch. Elsewhere, a few snow showers could occur and a dusting can’t be ruled out, but there won’t be any accumulations to write home about outside of the Snowbelt.

The amount of snow won’t be a ton and this will all end quickly Thursday morning, but a period of slick travel with low visibility due to snow seems like a decent possibility during the wee hours of Thursday morning in parts of the Snowbelt away from Lake Erie, with a lot of other areas seeing some snowflakes. Plan accordingly if you are an early commuter east of Cleveland. Conditions will again improve quickly during the rush hour Thursday morning. –Jim

It was a very warm first week of November in the central and eastern US, with many record highs (including some monthly records) broken from Florida all the way up to Michigan. The weather pattern still isn’t a cold one, with three of our main teleconnections for North America pointing to a cool west and warm east, however this will change some as we head towards the end of the week; the question is, will this be enough of a change to allow for a good shot of below normal air to occur with possible snow, or will it just be enough of a change to knock temperatures back closer to normal after last week’s very warm conditions?

As we head towards mid-week, a very potent shortwave associated with a 150kt+ jet streak will eject out of the Rockies into the Plains and cause a strong lee cyclone to form and track towards the Great Lakes. The strong jet streak combined with a tight temperature gradient between cold with the trough moving out of the Rockies and persisting warmth over the southern and eastern US will allow this low to become quite deep as it tracks into the Great Lakes, possibly fostering an outbreak of severe thunderstorms and causing a large area of gusty winds behind the system:

If time permits I’ll have a post detailing this system Tuesday night (assuming it still looks to be a potentially potent severe threat), but the main impact in the bigger picture this storm will have is to re-enforce ridging over eastern Canada and then undercut it, causing a bit of a west-based –NAO block to form:

The parallel GFS ensembles (they’ll be operational at some point) show a decent little ridge over eastern Canada and the Davis Strait, which is enough to slow the trough down over the eastern US and force it a bit farther south. There MAY be enough cold air with this solution for perhaps some minor lake effect snow off of the Great Lakes and some upslope snow showers in the mountains in northern New England, but overall the –NAO is not very strong or well located for big East Coast storms moving forward, and there’s no real 50/50 low either…so essentially the upper low/trough continues to eventually move east under the ridge:

You can see by day 9 that the trough has moved northeast away from the US, showing that although there is a modest –NAO block, which doesn’t hurt, it really isn’t significant enough to have a major impact on the pattern in the day 6-10 timeframe…although it may slow down/amplify the trough enough for a couple days of below average temps over the Northeast. The 0z ECM and 12z GGEM ensembles agree with this evolution.

By this point in 9 days, the look from the GFS ensembles has improved some from current; although it’s not a classic block, there is some west based –NAO ridging, and higher heights over Siberia and the Davis Strait are extending into the Arctic and at least allowing the AO to trend to more neutral values; this downward AO trend is more a result of tropospheric influences than it’s due to any stratospheric activity, as the stratospheric polar vortex is currently very strong and strengthening (which isn’t uncommon for November). The next opportunity for some upwelling and weakening of the stratospheric vortex may come later this month (and I’ll try to look at that more next weekend). The Canadian and Euro ensembles in the day 8-9 timeframe do overall show a similar look:

The ESRL GFS ensemble based teleconnection graphs do show the improvement in the NAO department over the next 7-10 days, but also show the issue, that is also plainly visible on the images above too:

Although the Atlantic and Arctic improve slightly, the Pacific remains rather putrid for eastern US cold for at least the next 10 days. The PNA remains negative, indicative of higher heights near the Aleutians and lower heights along the west coast, while the EPO remains positive, indicative of troughing over the Gulf of Alaska and Alaska, which floods much of the continent with mild Pacific air. The WPO being positive isn’t as much of a kiss of death if the low height anomaly with it ends up a little farther south or west towards northeast Asia, however this isn’t the case over at least the next 10 days. Basically, these indices are telling us that a small black hole will form over Alaska and the Gulf of Alaska over the next week and a half at least, which will flood the continent with mild Pacific air…so any marginal NAO help probably won’t be able to overcome this and allow for sustained cold in the east. In fact, it wouldn’t surprise me with such a strongly negative PNA that the week of the 16^th at least starts warmer than average in the east after a few days of cooler weather centered on next weekend.

Last week I discussed how tropical forcing was becoming stronger from the Indian Ocean, and this has remained the case this week. This supports higher heights over a good portion of the northern Pacific and troughing over the western US. There is a bit of change this week as some convection has begun re-flaring in the Pacific just east of the Dateline, although the Indian Ocean convection has generally been stronger and more persistent this week. Here’s what the global jet stream looks like:

It’s again important to explain how/why tropical convection can alter the hemispheric weather pattern: more persistent convection releases latent heat along the equator, causing higher heights north of the convection and a stronger jet stream due to a tighter pressure gradient aloft. When the jet stream gets east of the persistent convection and attendant higher heights you get an area of divergence, which tends to support storminess, which pulls warm air north east of this region and causes a ridge aloft. Extra-tropical forcing can also affect the jet stream, tropical convection/forcing is just an (important) part of a larger equation.

On the above image, which is essentially current (it’s a 12 hour forecast), you can see a stronger jet north of the persistent Indian Ocean convection, and some attempt at ridging over the central Pacific, which does support western US troughing as discussed last week. The increasing convection just east of the Dateline may also be supporting a stronger jet over the north-central Pacific, which supports storminess over Alaska. If this storminess is persistent it can cause a fairly persistent upper low to develop over Alaska/the Gulf of Alaska, which the three ensembles all suggest happening over the next 7-10 days. From here, it’s important to try to predict what convection in the tropics will do over the next couple of weeks to find out if a more improved Pacific pattern may try to develop:

It’s evident that over the last 2-3 weeks that Indian Ocean convection has flared up significantly, to the point where it suppressed the El Nino related convection over the Pacific, as discussed last week. The Indian Ocean convection appears to have edged east over the last week, while there are some signs per the time longitude plot and above images that the El Nino convection may be trying to fire back up. It will be interesting to see if the Indian Ocean convection really weakens or holds steady. Although it has edged east slightly over the last week, an argument can likely be made that the Indian Ocean convection is more of a standing wave than a propagating MJO, as it has moved very slowly.

The GFS and Euro ensembles both appear to agree on the convection over the Indian Ocean trying to weaken over the next week, although to what extent it weakens is disagreed upon. The convection has persisted more than either model expected a week ago. The GFS ensemble solution shows the Indian Ocean convection completely weakening, which would likely allow El Nino forcing to take back over during the next 1-2 weeks. The GFS ensemble does then show another flare-up developing in the 10-14 timeframe in a potentially more favorable area if you want cold in the eastern US. The European ensemble shows the convection remaining over the Indian Ocean but perhaps weakening some. The Euro makes a bit more sense to me as the convection isn’t a propagating wave, and if El Nino convection does try flaring back up over the next week or so it may try to suppress convection elsewhere. In general, I’m not really hot on the idea of convection becoming more focused near the Dateline in the near future, which is the eastern US cold sweet spot.

One interesting feature to note, is that the GFS (shown) and Euro ensembles have both been persistent in their idea of retracting the Pacific jet for a few days around November 20^th, perhaps as a result of convection in the tropics shifting around some. If this occurred, it would suggest the low over Alaska shifting west towards the Aleutians, causing the PNA to rise and the EPO to fall in about two weeks. As far as my interpretation goes, I don’t think tropical forcing supports this persisting for an extended period of time, but both ensembles have shown this for a few days. This could support a cool down in the central US (that possibly works east) Thanksgiving week.

Both ensembles (GFS ensemble shown) begin extending the jet again after a few days, which would make sense if convection increases in the central Tropical Pacific in associated with the El Nino and very warm waters there. This leads me to believe that any Pacific driven cooldown around Thanksgiving would be short lived.

The parallel GFS ensembles do attempt to show a brief improvement in the Pacific pattern around the 20^th as the Alaskan low retrogrades west, which would possibly support ridging over Alaska/western Canada and allow some cold into the central US, but note how the low starts shifting back west towards Alaska towards the end of the run, which would likely allow Pacific air to start blasting into North America again shortly after Thanksgiving.

In general, I’m thinking that after the east warms back up for the first few days of this week that a few days of below average temperatures do occur across parts of the Great Lakes, Ohio Valley, New England and northern Mid Atlantic as a west based –NAO occurs and causes a trough to slow down and amplify some as it tracks across the Northeast. The Western US should be mild in this timeframe.

As we head into the week of the 16^th I expect near normal temperatures and stormier conditions to return to the west (especially the northwest), with milder weather compared to normal over the central and eastern US.

Between the potential for modest NAO help and some ensemble suggestion for a brief Pacific pattern improvement, it wouldn’t surprise me if Thanksgiving week is a bit cooler than average over the central and eastern US and warmer than average over the west, but I expect El Nino forcing to allow for a Gulf of Alaska to return to start December, resulting in a mild start to the month.

As we flip the calendar to November, many of the teleconnections are pointing to warmth in the eastern US and cooler conditions in the west. Lower than average heights over the North Pole are indicative of a +AO, with lower heights over Greenland and the adjacent N. Atlantic associated with a fast flow south of Greenland and Iceland, associated with a +NAO, with high heights over the Aleutian Islands and lower heights near the US West Coast, associated with a –PNA. The lower heights over western Canada into Alaska can also qualify as a +EPO. All of these teleconnection signs point to a trough over the western US and a ridge over the eastern US over the next several days, with the European ensembles showing this by midweek:

This would result in active weather continuing in the west, where they desperately need the rain, with warm and mainly dry weather over the east. The European and GFS ensembles are in good agreement in ejecting the trough out of the west and providing for a brief cool down in the Midwest, Great Lakes and Northeast to end the work-week and into next weekend, however, the PNA stays negative and the AO/NAO stay largely positive, suggesting this cool down will be transient and not particularly intense:

The European ensembles do indeed build the western US trough and eastern US ridge back into place by the time we start NEXT work-week (the week of November 9^th):

It appears that for those excited for winter in the east that they’ll have to wait until later in November for any hope. The GFS ensembles are in agreement, keeping all three main teleconnections unfavorable until at least mid-November, with very few members deviating from this. Yes, the NAO and AO start trending down towards mid-month, but this isn’t a strong enough signal (on its own) to forecast a cold second half of November:

This November warmth may come as a surprise to many, as believe it or not, most strong El Nino events since 1950 have featured a cold November in the central and eastern US:

This begs the question, why is this discrepancy occurring this November, and how long will it continue? The likely explanation for this departure from a “normal” El Nino pattern for at least the first half of November likely has to do with MJO activity in the Indian Ocean:

After the bulk of the last 90 days featuring no MJO activity, which is quite typical in stronger El Nino events, as tropical forcing is dominated by consistent convection over the central and eastern Tropical Pacific in strong El Ninos with subsidence and limited convection elsewhere, the last week or so has featured an MJO “flare-up” in the western Indian Ocean. MJO activity here is actually more typical in La Nina events, when the waters in the central and eastern tropical Pacific are cooler than normal, so it’s not a surprise that MJO activity typically associated with a La Nina (the opposite of El Nino) forces quite a different North American weather pattern than what we’d expect with an El Nino.

You can visualize the difference in convective forcing over the last week by examining outgoing longwave radiation (OLR) plots; lower OLR is associated with more clouds and precipitation (in the tropics, this usually means thunderstorms that can affect tropical forcing), while higher OLR is associated with fewer clouds and precipitation:

The strongest tropical forcing occurring near and east of the International Dateline enhances the jet stream over the central Pacific (due to latent heat released from the convection increasing geopotential heights in the Tropics and tightening the pressure gradient north of this area), forcing a low south of Alaska (due to favorable upper level divergence in the left-exit quadrant of the enhanced jet), forcing a ridge over central and western N. America. The last 90 day 500mb pattern matches this idea fairly well (although not perfectly over eastern N. America):

Over the last week, the OLR anomalies clearly show the more active convection over the Indian Ocean (and somewhat less impressive convection over the eastern Pacific), which changes where the tropical forcing occurs and alters the large scale weather pattern across the entire Northern Hemisphere, as the jet becomes more enhanced over Asia, and not the Pacific:

The 500mb pattern over the last week, while not perfectly resembling the look above, does have the general idea:

There is still some sign of typical El Nino forcing, with a low over the Aleutians, however it is significantly diluted from what you’d expect in a typical El Nino pattern (typically in strong El Ninos, this low is stronger and farther southeast in November).

In attempting to determine how long this trough west/ridge east pattern will continue into November, the key likely lies in determining how (or even if) the current MJO activity will propagate east, and when more convectional El Nino tropical forcing will return.

The GFS and European ensembles have slightly different ideas over the next two weeks; both models do suggest the MJO will weaken some, however, the GFS maintains the more active convection over the western Indian Ocean and keeps the MJO safely outside of the “circle of death,” while the European slowly propagates the MJO east will weakening it. The European solution would likely result in more typical “El Nino” forcing returning in 2-3 weeks, while the GFS would belabor that process.

Given that strong, basin wide El Nino events (with the exception of 1987-88) tend to feature limited MJO activity, the European solution makes more sense, and would likely result in near normal temperatures in the eastern US for the last week to 10 days of November, with warmer than normal temperatures building into the west (especially the Northwest, compared to normal) and perhaps northern Plains (so, the pattern would start to take on the typical canonical strong El Nino look by the end of the month).

However, this MJO activity will have to be monitored closely as we head through November to see if it will in fact just weaken, returning us to El Nino dominated tropical forcing. It isn’t normal to have a basin wide El Nino that is this strong, period, however the very warm waters along the west coast of North America and in the Indian Ocean may be indicators that typical very strong El Nino progression may not work out “perfectly” this winter, as I discussed extensively in my winter outlook.

As for AO/NAO help, at this point it’s a waiting game to see if we can start getting an attempt at enhanced heat flux from the troposphere to the stratosphere in November as Dr. Cohen’s Snow Advance Index suggests, along with other research. Any AO/NAO help later in November would likely have to come from tropospheric influences.

I’ll attempt to update these longer range, large scale pattern posts once a week or a little more frequently, but that’s dependent on how busy I am on a week to week basis.

Definitely think there’s some interesting potential for a low CAPE/high shear severe weather event from portions of Ohio and West Virginia points east across Virginia, Pennsylvania, New York, Maryland, Delaware, New Jersey and perhaps parts of New England late Wednesday afternoon straight through to very early Thursday. Although the previous SPC D3 outlook basically punted another day, I suspect they’ll start introducing severe probs for a fairly large area, and depending on how things evolve I could see a decent slight risk area (potentially even an enhanced) being needed for some of the areas outlined above.

Here is a look at my winter outlook for last year (along with links to previous outlooks):

https://ohwxramblings.wordpress.com/2014/10/12/jim-sullivans-2014-2015-winter-outlook-for-the-us-and-southern-canada/

Maps and Brief Summary:

This winter will be strongly affected by a very strong “El Nino” in the Tropical Pacific. This will likely result in a warm December, an up and down January, and a cold February in the Eastern US. The western US will become warmer as the winter moves on. Precipitation will be abundant across the Deep South in response to the El Nino. I expect the El Nino to contribute to continued rain/snow chances in California through December, before conditions gradually dry up in January and especially February.

There could be an active storm track from the southern Plains east towards the East Coast. Locations like the Great Lakes may stay north of the big storms, while locations like the Ohio Valley are near the northern edge of the active storm track later in winter.

The following are maps depicting departures from normal for the winter months across the country for temperatures, and general precipitation patterns. Remember a warm month overall can still have some cold days, and vice versa.

December:

January:

February:

Technical Discussion:

This will be my 6^th winter outlook; I’ve had two decent outlooks (2009-2010, 2014-2015), two outlooks that had varied success in different regions of the country but could’ve been much better (2012-2013, 2013-2014), and one that I’d consider subpar/not very helpful (2010-2011). I guess it’s good that I consider my most recent outlook to be one of my better ones.

I do arrive at a set of analogs at the end, which I do partially base my monthly maps off of, however extensive reasoning is provided herein on how I came to my conclusions.

Let’s Start With Sea Surface Temperatures:

Current sea surface temperatures as we head into October show several distinct features; a basin-wide and strong (bordering on “super”) El Nino in the Tropical Pacific, impressive warm waters well north of the ENSO regions from near Hawaii all the way to California, an abnormally warm Indian Ocean, very warm waters compared to normal, surrounding the Aleutian Islands, warm waters (that have cooled some recently) south of Alaska and off of the west coast of Canada, and an overall very warm Atlantic, with the exception of a large cold pool across the N. Atlantic.

Closer Look at El Nino:

The western Nino regions (3, 3.4 and 4) have all featured warmer than average waters since summer of 2014, although the eastern region (1+2) did cool during the winter of 2014-15. All Nino regions except for 4 (which was quite warm already) warmed strongly starting in the spring of 2015, and after a brief “leveling off” in the warming late in the summer, have warmed again in September. Nino 4 has the smallest warm SST anomaly, however this is quite typical, an anomaly of around +1C for Nino 4 is impressive. Regions 1+2, 3 and 3.4 all have SST anomalies of +2C or greater, which pushes them into the “super El Nino” range. These very warm waters haven’t persisted long enough for this El Nino to be officially classified as a super El Nino yet, although that may just be a matter of time.

A look at the 850mb winds over the equatorial Pacific shows that there have been persistent weaker than normal trade winds (denoted by the warm colors) since last Spring, with a few well defined westerly wind bursts (WWB). These weaker trades are important, as they help the warmer pool of water normally located closer to Australia and the Pacific Maritimes to spread farther east and limit upwelling of cooler waters. Westerly wind bursts are especially proficient at encouraging further warming, and usually help downwell warmer waters. There is a robust WWB occurring at present across much of the eastern equatorial Pacific, which is likely accounting for the recent warming discussed above. This suggests that the El Nino is not done strengthening as we head through October.

One distinct characteristic of an El Nino is a deepening of the thermocline east of the International Dateline. The thermocline has deepened considerably farther east over the last two months, all the way to the S. America coast. This suggests that El Nino’s effects are not confined to just the central and western Nino regions, this is a basin wide event (NOT a modoki or anything close). This is important as it has an impact on where the strongest tropical forcing may be located this winter. It’s also notable that the recent WWB has had a noticeable effect on deepening the thermocline in the central Pacific over the last two weeks.

http://www.esrl.noaa.gov/psd/enso/mei/

When comparing the 2015 El Nino to past strong El Nino events, using the Multivariate ENSO Index, which incorporates factors other than just sea surface temperatures when determining ENSO strength, it can be seen that for the August/September period, the only El Nino stronger than 2015 was the 1997-98 super El Nino. The only two El Ninos to peak higher than 2015 at any time of year are 1982-83 and 1997-98. Those two El Ninos are the only two “super” El Ninos since 1950 (MEI of +3 SD or greater), and both of those events had a secondary MEI peak in mid-winter.

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ensoyears.shtml

Another method of determining Nino strength, called the Ocean Nino Index, relies strictly on sea surface temperature anomalies in the ENSO regions. The most recent tri-monthly value for JAS was +1.5, making this a strong El Nino. Weekly values have been generally +2 for quite some time, so it’s likely that the next two tri-monthly values continue to increase. The threshold for a “super” El Nino using the ONI is an anomaly of +2.0C or greater; that has only been done three times, in the 1972-73, 1982-83 and 1997-98 El Nino events. The JAS ONI value was the third highest since 1950, behind 1997 and 1987. 1987 did not get any stronger after JAS, while 1997 intensified into the early winter.

Either way, given the recent WWB near the Dateline and the continued deepening of the thermocline in the equatorial Pacific, further intensification of this El Nino is likely in the near future. A peak very close to or possibly stronger than 1982-83 is possible, although a peak matching or exceeding 1997-98 is a bit more of a stretch.

This very strong El Nino is a very good indicator of the general pattern that will likely be in place this winter across the CONUS; tropical forcing is usually focused in the central/eastern Pacific, east of the Dateline, which forces a persistent low pressure somewhere near or south of Alaska, which drives the polar jet northward across the west coast of the continent, causing warmer and somewhat drier conditions across much of the northern US in an El Nino winter. El Ninos also strengthen the sub-tropical jet, bringing increased moisture to the southern US and usually cooler weather to the Deep South.

Typically, stronger El Ninos match the above “perfect El Nino” pattern better than weaker ones, as the forcing with weaker El Ninos may not overwhelm other factors. However, not all El Ninos come in the exact same flavor (or else I’d be done with my outlook right now):

http://www.jamstec.go.jp/frcgc/research/d1/iod/enmodoki_home_s.html.en

This webpage from JAMSTEC explains the difference between a “Modoki” El Nino, one that has the warmest anomalies in the central Pacific, closer to the Dateline, with cooler waters off of the S. American Coast, and a normal El Nino, that has warmer waters farther east. The location of the warmest waters can have a big impact on where persistent tropical convection that ultimately drives the jet stream’s response to an El Nino occurs.

There are really three different types of El Nino: Modoki, basin wide, and east based:

All three different types, on average, yield a different positioning of the Gulf of Alaska low, and a different CONUS wintertime weather pattern:

Note how a central based/Modoki El Nino tends to have a weaker GOA low that is generally farther southwest, while the east based lows, in the means, are stronger and progressively farther northeast, flooding more of the CONUS with mild Pacific air, resulting in the negative anomaly moving farther southeast off the East Coast. These composites were made using all El Ninos since 1950 regardless of strength, however the Modoki and basin wide events have a reasonably large sample size and produced reasonably strong composite anomalies when blended together. Two of the three east-based El Ninos were strong-super, not a coincidence.

The difference in the GOA low position is due to differences in the intensity and location of the strongest tropical forcing in different El Nino winters. In an attempt to further diagnose this difference in forcing to use it as an aid in forecasting this winter, I looked at a few different methods to quantify the tropical forcing in the different El Ninos:

The first method was to look at 250mb height anomalies during DJF; the reasoning behind this is tropical convection gives off a tremendous amount of latent heat, which will thicken the atmosphere and raise the geopotential heights of the upper atmosphere. This is important because this tightens the pressure gradient immediately north of the higher heights and strengthens the jet stream, altering the downstream weather pattern. This first exercise was actually rather interesting, as it seemed as though the strongest anomalies in all three types of El Nino were located near 130W; it was the strength of the anomalies and eastward extent that differed. East based El Ninos had the strongest anomalies at 130W, with the anomalies extending farther east, likely suggesting that the convection along the equator in the Pacific in those El Ninos was more robust and also occurred farther east than the basin wide and especially modoki events. This may also be a by-product of the east based and basin wide El Ninos on average being stronger than Modoki events (with east based events being stronger than basin wide on average). With east based events, weak positive height anomalies extended well west towards the Indian Ocean; this was not the case with basin wide or Modoki events.

The second method was to examine outgoing longwave radiation (OLR) anomalies in the Pacific during the three types of El Nino during DJF. This helps show where tropical forcing is more prevalent because the colder cloud tops associated with thunderstorms radiates less outgoing longwave radiation; so a dearth of outgoing longwave radiation indicates more persistent thunderstorms. This method was similar to the 250mb height anomaly method in that the Modoki El Nino forcing was generally weaker than the basin wide and east based events, however the difference in this method is that the east based forcing shows up as being centered much farther east than the other two, unlike the height anomaly method where the max anomalies were near the same longitude (130W). It’s notable that the positive OLR anomalies (associated with less convection than normal) across the Maritimes into the Indian Ocean are much more distinct with east based events than basin wide or Modoki ones, indicated a lack of MJO activity overall with east based events.

A third proxy I used was 850mb zonal wind anomalies. This does two things; it determines where warmer/colder waters are likely to persist in the equatorial Pacific (westerly anomalies/weaker trades suggest warmer waters, vice versa with easterly anomalies/stronger trades), and also suggests where more persistent tropical convection is likely to be, as low level convergence along the eastern edge of the westerly anomalies promotes more active convection. Much as the case with the 250mb height anomalies and OLR anomalies, east based events feature stronger anomalies farther east, while basin wide are markedly farther west and a bit weaker, while modoki events on average feature the farthest west and weakest anomalies.

So, with all of this said, let’s start comparing to this year:

Height anomalies for September and first half of October:

September 1-October 18 OLR anomalies:

September 1-October 18 850mb zonal wind anomalies:

(note that I tweaked the scale some to show that while the anomalies near 150E are very strong, that strong anomalies extend well east of the Dateline)

Another method of looking at the position of the 200mb and 850mb anomalies:

A few things of note: The strongest negative OLR anomalies are located near the Dateline, much farther west than the DJF means for any type of Nino, however stronger anomalies along the equator do extend rather far east in a fashion most similar to basin wide events. The 250mb height anomalies are pushing 60m, close to the DJF mean for east based events, and stronger than the basin wide events mean. Also, the positive anomalies extend well east towards S. America, most like east based events. There’s also a stout positive height anomaly from NE Asia towards western Alaska. The 850mb zonal wind anomalies are centered much farther west than the east-based DJF composite; in fact, the max anomalies are centered near the DJF modoki composite, however the implied convergence at the eastern edge of the westerly anomalies is located farther east, closer to the basin wide DJF composite. The strongest 200mb velocity potential has been located along and a bit east of the Dateline, and has gradually nudged west over the last couple of months.

Before we go any farther, it’s important to note that these height/OLR anomalies for 2015 are for September-October, NOT DJF. First, I’m going to recreate the 250mb height anomaly, OLR anomaly and 850mb zonal wind anomaly for the three types of El Nino events for S-O:

250mb height anomalies:

OLR anomalies:

850mb zonal wind anomalies:

When comparing this September-October (so far) to the composites above, the 250mb height anomalies in the mid-latitudes are actually closest to the modoki composite; it’s very notable that really NO other El Nino since 1950 has had such high 250mb geopotential height anomalies over the tropics. The OLR and zonal wind anomalies are somewhat mixed in the comparisons; the strongest OLR anomalies in September-October are centered smack dab over the dateline, which is actually farther west than the strongest OLR in any of the September-October El Nino composite anomalies. However, the negative OLR anomalies extend farther east, so overall it has more of a basin wide event forcing look. The 850mb zonal wind anomalies are similar; the strongest westerly anomalies are well west of the dateline, centered somewhere between the modoki and basin wide strongest composite westerly anomalies, however per the time-longitude plot above, this is skewed a bit by a strong, but brief WWB in early October east of the Dateline. Overall, the strongest westerly 850mb anomalies have been west of the Dateline, most similar to basin wide events. In general, it seems like forcing is currently mirroring basin wide events the best this fall, however, as noted above it’s not a perfect match.

Now, I’m going to look at all moderate-super El Ninos (per ONI) since 1950 to determine which El Ninos had similar September-October patterns to this one, and determine what kind of El Nino they were and how their upcoming winters turned out. It was actually tough to find similar analogs to this year, with very few years that looked anywhere close to the N. American pattern we have seen thus far this fall during a moderate-super El Nino. Another complicating factor was this year’s odd convection placement along the equator; there’s a clear max in convection centered at the Dateline, however a lesser but still abnormal amount of convection has occurred rather far east.

After looking over all moderate-super El Nino Septembers and Octobers, I determined that 1957, 1986 and 1987 were the “closest” matches to our current tropical forcing. With this said, the overall pattern in the mid-latitudes doesn’t really match what we’ve seen this fall thus far. Because 1986 was the first year of a two year El Nino and was strengthening through DJF (very unlikely in this second year El Nino), I tossed it out. The overall OLR composite for September and October for 1957 and 1987 is “OK”:

The following DJF mean OLR anomaly looks close to what you’d expect for a basin wide El Nino event, with the GOA low positioning also close to what you’d expect for a basin wide event:

After the review above, my best guess at this time is that the Gulf of Alaska low placement will be somewhat close to what is “typical” for basin-wide El Ninos. This makes sense; this is clearly NOT anything near a Modoki based on the exhaustive review done thus far, but warm SST anomalies along with the location of the most persistent tropical forcing are most certainly farther west than east based events, despite very warm SST anomalies in the eastern Nino regions.

It is worth noting that per the MEI, this is the strongest basin-wide El Nino since at least 1950, and if the ONI continues rising as it should per the recent weekly ENSO region weekly anomalies, there’s a good chance this will beat 1972-73 for the strongest basin wide El Nino per the ONI as well. So, we’re already in potentially uncharted territory when looking at just the El Nino strength and type.

Other factors heading into this winter are also rather unusual, and will be investigated now. The very warm waters off of the western N. American coast, in the sub-tropics and in the northern Pacific are very impressive. These waters aren’t paramount to tropical forcing that is a significant driver of the wintertime jet stream strength/position, but seem somewhat important.

The first area examined specifically will be the area of very warm waters extending from south of Hawaii east-northeast towards California. This year’s waters are off the charts warm in this area, with widespread anomalies of +2-4C right now. There are a few possible things I can think of this effecting: It could possibly weaken trade winds farther east (weaker temperature and pressure gradient between the EQ and the sub-tropics in this area), possibly forcing convection farther east. It may also allow additional moisture into the Southwest US. To examine this area, I looked at all moderate or stronger basin wide El Ninos since 1950 (per ONI), and looked for years that also had warmer waters in this region. No year has waters as anomalously warm as this year, however a few did have generally warmer waters in this same area. Her is the September-October SST difference map in the four Ninos I have with warmer waters from Hawaii up to near California compared to the rest of the basin wide, moderate plus El Nino events since 1950:

When looking at the difference of several potentially key DJF variables between years that featured warm waters from near Hawaii to California, a few interesting features were evident:

It is worth noting that these years ignore all other variables. This is just the difference in moderate or strong El Nino winters between ones that had the warmer HI-CA waters compared to years that didn’t. It’s possible that other variables are affecting some of these differences.

One interesting difference is an apparent tendency to pull tropical forcing a bit farther west in years where the warm water is present; the Pacific jet is stronger overall, but strongest over the central Pacific, with stronger trade winds and less OLR (indicative of more clouds/convection) along and west of the Dateline, potentially indicative of more MJO activity, which is normally limited during stronger El Nino winters. This results in the heights over the Aleutians being lower (GOA low farther west) and heights along the west coast being a bit higher (overall a slightly more favorable +PNA look). There is also a distinct tendency for a strongly west based –NAO. The look also looks potentially wetter for CA (stronger westerly 850mb winds, a stronger jet, lower OLR).

The overall tendency appears to be for winters that have a more favorable N. Pac orientation and NAO for troughing over the eastern US…however, the sample size is small, and it’s quite possible other factors influenced/caused these differences. It IS worth noting that my two tropical forcing “analogs” (1957-58, 1987-88) and 1986-87 (not one of my forcing analogs, tossed due to being a first year Nino that strengthened during winter) are in the list of moderate or stronger basin wide El Nino winters that had warm water from HI to CA.

The next area/factor examined specifically will be the very warm N. Pacific waters and strongly positive Pacific Decadal Oscillation (PDO). The PDO is a pattern of north Pacific SSTs that tend to persist for around 30 years. A warm phase of the PDO features colder waters of the north-central and northwest north Pacific, with warm waters off of the west coast of N. America, while a cold phase of the PDO features warmer waters of the northwest and north-central north Pacific, with colder waters off of the west coast of N. America.

http://research.jisao.washington.edu/pdo/

We had been in a 10-15 year old cold PDO phase, but have seen a strong rise over the last couple of years, which isn’t uncommon during El Nino events that occur during an otherwise cold PDO. Sea surface temperatures in the PDO region are not nearly warm enough to force convection that completely re-shapes the jet stream, however, PDO trends may be more indicative of persistent weather patterns, and although the sea surface temperatures here aren’t nearly as significant as over the tropics, they may cause small differences in the track/intensity of mid-latitude cyclones in this region that does have some impact on the overall pattern.

September’s PDO value came in a +1.94, per the University of Washington, which is the highest it has been since March. There are only two moderate or stronger, basin wide El Nino events since 1950 that had a September PDO of greater than +1.50 per the University of Washington dataset (or greater than +1 for that matter); 1957 and 1987. These are ironically the two best tropical forcing “analogs,” and are also two of the four moderate or stronger basin wide El Nino events since 1950 that featured warm water from HI to CA. When looking at difference maps as done above between the moderate or stronger basin wide El Nino events with strong warm September PDOs and the rest of the moderate or stronger basin wide El Nino events, some similar trends are noted:

One initial warning here is that we are starting to deal with small sample sizes (two years), and that factors other than PDO may influence some of these differences. However, some trends that are again apparent is for stronger trade winds east of the Dateline, perhaps suggesting tropical forcing will be located somewhat farther west than most basin wide El Nino events. The 250mb zonal wind difference also suggests a stronger jet over the Pacific, although in this instance the jet is even stronger in the west coast of North America. There is also a tendency for a more strongly west based –NAO in 1957-58 and 1987-88 compared to the rest of the basin wide moderate or strong El Nino winters…again however, this is a two year sample, and should be used with caution.

The next factor examined is the very warm Indian Ocean; much of the basin is experiencing SST anomalies of near or above +1C; since 1950, only 3 moderate or stronger basin wide El Nino events have featured a warm overall Indian Ocean (and most not as warm as this year), when looking at September-October Indian Ocean SSTs. The years are: 1987-88, 2002-03 and 2006-07. Here are the difference maps compared to basin wide moderate or stronger El Nino winters that had normal or cooler than normal Indian Oceans:

A few interesting trends; again, much like warm HI to CA SSTs and strong +PDO years, the jet is stronger across the northern Pacific; however, in this instance, the OLR is lower west of the Dateline, indicating more convection than the rest of the basin wide Nino years in this areas, perhaps due to a more active MJO than what normally occurs in El Nino years (which is potentially a direct result of the warm Indian Ocean supporting lower pressures and more convection than what would occur farther west in a typical El Nino). There’s also a strong high latitude blocking signal across N. America, although it’s possible other factors such as the stratosphere or solar influences are at work here. There is an overall trend for the GOA low to be centered a good bit farther west in these winters than in typical basin wide El Nino winters.

As a note, 1987 is the only September-October moderate or stronger basin wide El Nino since 1950 that featured a similar N. Atlantic SST configuration to 2015. That seems to be a top analog based on global SST patterns.

Moving on and looking more specifically at high latitude blocking now, there is a clear trend in all moderate-super El Nino winters since 1950 (regardless of east based, basin wide or modoki) for a progressively more negative NAO and to an extent AO as the winter progresses (along with a trend for the GOA to retrograde through the winter). This signifies that there is a strong chance that tropical forcing associated with stronger El Nino events tends to favor a –NAO. The question is, why, and will a –NAO be favored later this winter as well?

When taking the basin wide events (which we will be dealing with this winter) and subtracting all other moderate to strong events from it, the –NAO signal becomes weaker! Granted, a great –NAO winter like 2009-10 is removed in this process. Also, there’s a tendency for higher heights in the PNA/EPO domains, potentially due to removal of east based super El Nino events in 1982-83 and 1997-98. There is still a –NAO signal in the means for basin wide events for January and February, although the above implication is that removing the modoki events likely weakens the overall –NAO signal for moderate to strong El Nino winters:

QBO/Stratosphere Stuff:

The Quasi Biennial Oscillation refers to phases of more westerly or easterly winds in the stratosphere over the Tropics. Easterly phases are typically associated with a weaker winter time stratospheric polar vortex (and a better likelihood of sudden stratospheric warming events, leading to potentially periods of deep –AO blocking), while westerly phases tend to be associated with a stronger winter time stratospheric polar vortex (and a lower likelihood of the vortex getting disrupted in winter, potentially leading to periods of +AO conditions). There are exceptions to the rule, but the correlation is fairly well understood.

As seen on the above graph, there are westerly winds descending through the stratosphere right now, suggesting that the winter QBO will be positive or westerly. There have been 5 moderate to strong El Nino winters since 1950 that featured a +QBO (per 30mb wind anomalies), per these data sources:

http://www.cpc.ncep.noaa.gov/data/indices/qbo.u30.index

https://climatedataguide.ucar.edu/climate-data/qbo-quasi-biennial-oscillation

There was a pretty strong signal for retrogression of the GOA low through the winter and a developing –NAO by February. The February pattern looks quite favorable, even with the super east based El Nino of 1982-83 in that composite.

When removing the modoki and east based El Nino winters from the composites, the overall message doesn’t change a ton; a fairly warm December with a GOA low flooding the CONUS with Pacific air, with no AO or NAO help, followed by a retrogression of the GOA low for January and February allowing for West Coast ridging, with a declining AO and NAO for February. The AO decline is much more noticeable in this composite than the one including all moderate-strong +QBO winters.

Another factor that influences the potential for high latitude blocking during winter is solar activity; I’m not extremely well versed on how this process works so I won’t try to explain it, but in general, the best combination for a deep, -AO winter is a solar minimum and –QBO. Monthly solar radio flux data from the sun can be found here back into the 1940’s:

http://www.spaceweather.gc.ca/solarflux/sx-6-mavg-en.php

We are currently coming off of a weak solar maximum; slightly weaker than the maximum in the early 1970’s; radio flux output will likely be in the neighborhood of 85-105 if the current rate of decline continues into this winter. Out of the +QBO basin wide ENSO years above, 1988 is an OK but not great solar match, as the radio flux was very similar to what’s expected this winter, however 1987-88 was near the beginning of a significant ramp up towards the next solar maximum near 1990. 2002-03 is also not the best match, as the radio flux values are higher, however, 2002-03 was a winter that also occurred in the declining phase of the solar cycle. 2006-07 occurred before the most recent solar minimum, with numbers slightly lower than what will likely occur this winter. If we see a ramp up in solar activity, 2002-03 could become a better analog; if we see a decrease, 2006-07 could become a better analog from a +QBO/ENSO/solar perspective.

Overall, the current solar activity doesn’t appear extremely helpful or unhelpful in attempting to get high latitude blocking this winter.

Peaking at “newer” research done by others:

https://www.aer.com/science-research/climate-weather/arctic-oscillation

Dr. Judah Cohen has done extensive research that suggests that the late winter AO state is strongly correlated to October snowcover advance in Eurasia south of 60N (especially in Siberia); the reasoning is found in the graph above. The “Snow Advance Index” did very well in predicting AO state until the last two winters (with the 2014-15 winter being a fairly large failure); there is valid meteorology behind the idea, so although the index failed to properly predict last winter’s AO state, it is still worth looking at for this winter.

The above plots, found Dr. Cohen’s blog linked above, it can be seen that so far, through the first half or so of October, Eurasian snowcover is advancing quicker than normal, but a bit behind the last two years.

The GFS has been persistently showing a significant amount of snow south of 60N across Eurasia over the next 10 days. Considering the model has been showing this fairly consistently, and considering the current Eurasian pattern features a few upper lows/troughs well south of 60N, likely supporting snow, and considering the thus far decent (but not as good as last year) snow advance this month, it seems more likely than not that the SAI will finish higher than normal, suggesting a more –AO winter is potentially more likely. It remains to be seen whether it’s well above normal or just a bit above, but currently this factor doesn’t look to hurt things.

Research done by Al Marinaro (wxmidwest) suggests that the winter NAO state in El Nino winters is correlated to N. Pacific sea level pressure in October. This correlation makes sense when thought through, as El Nino winters in general appear to favor a –NAO, with some exceptions, generally based on where/how strong the tropical forcing is. This may be an early way of diagnosing the tropical forcing, and seeing if it’s in a favorable location for a winter –NAO.

SO FAR, through October 18^th, the N. Pacific SLP appears to be averaging lower than 1013mb, which would favor a –NAO. The catch is it’s a bit early. The “good” news is, the European ensembles insist on a very active weather pattern in the N. Pac, with a persistent Aleutian low through the remainder of October with a recurving typhoon perhaps deepening the feature quite a bit:

It appears possible that the N. Pac SLP in Al Marinaro’s box will be quite a bit below 1013mb on the mean for the month of October, which tends to correlate to a –NAO in an El Nino winter.

In Conclusion:

We are essentially in uncharted territory since at least 1950 in terms of a basin wide El Nino event of this strength, when combined with a warm Indian Ocean, very warm waters compared to Hawaii to California and a very warm N. Pacific. However, there is evidence that the warm Indian Ocean may act to cause somewhat more MJO activity that what is common during stronger El Nino winters, and in general, the warmer waters elsewhere in the East Pacific tended to pull the Aleutian low farther west when compared with other moderate to strong basin wide El Nino events. This suggests that a +PNA may become more likely as the winter goes on, after Pacific air likely floods a good portion of the CONUS in December.

In general, basin wide El Nino winters favor a negative NAO as you head farther into winter, although not as strongly as modoki events. The three moderate to strong basin wide El Nino events since 1950 that had a +QBO as we’ll have this winter featured decent AO/NAO blocking by February, after a warm December and up and down January. Research done on October snow advance in Eurasia by Dr. Judah Cohen and on October N. Pacific sea level pressure by Al Marinaro both suggest that trends this month also support a –AO/NAO this winter.

In general, a rising +PNA could limit California/west coast rainfall by later in winter. Hopefully they’re very active before then, as they desperately need the rain. The eastern US looks cold/active for the second half of winter, after a potentially very slow start.

The potential bust factor here revolves around how the Nino behaves. Other basin wide El Nino events with such a warm Indian Ocean (1987-88, 2002-03) saw more MJO activity than normal for stronger EL Nino winters, which likely contributed to a favorable pattern for eastern US snow. If this event becomes more strongly east based, this may not be able to occur. Another overall question mark is if all of the correlations discussed, small sample size for some of them notwithstanding, hold up with such a strong El Nino. We may learn quite a bit this winter…hopefully not at the expense of this forecast.

Analogs, based on good SST matches globally and QBO:

1957-58, 1987-88 (2), 2002-03, 2006-07