12/29/17: Meteorological Discussion on Upcoming Clipper/Lake Effect Snow

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Unfortunately, another snow event where I don’t have time to do more than a text-only write-up…pretty interesting forecast yet again…

Snow should push onshore into northeastern Ashtabula and Erie County near the lakeshore by around noon Friday as winds on the lake come around to west with WSW winds on land behind the passage of a vort max and surface trough/possible meso-low over the lake.  This general wind pattern with W winds over the lake and WSW winds on land focusing convergence near the coast in Erie, Ashtabula, and possibly NE Lake Counties will persist all of Friday afternoon and into the early evening before winds shift more SWrly and push the convergence out over the lake.  This will still be a good 7 or 8 hours of potential banding near the lakeshore in eastern Ashtabula and Erie Counties (possibly brushing NE Lake and western Ashtabula County) Friday afternoon into the evening.  Thermodynamics during the afternoon will be decently supportive with moderate instability, EL heights of 10-11k feet, and good moisture to around 7k feet including in the DGZ.  EL heights drop off some towards evening due to mid-level warm air advection ahead of the incoming clipper.  With the decent thermodynamics/moisture, strong convergence near the shore, weak shear in the mixed layer, and near-optimal snow growth have to think snow rates of around 2″ per hour will accompany the heart of the snow band Friday afternoon and early evening.  The band will mainly hug the shore and not move a ton, and may produce 6-12″ of snow near the lake in Erie County and also northeast Asthabula County, dropping off quickly farther inland.  There may be an inch or two as far southwest as northeastern Lake County.

The clipper snow doesn’t look extremely impressive in N OH Friday evening and Friday night.  There will be some lift in the form of upper-level divergence evident at 500mb (which is above the level of non-divergence in winter), some mid-level positive vorticity advection, and weak isentropic lift/warm-air advection evident at times at 700mb and 850mb.  This will generally cause a decently long period where light snow will be possible.  Forecast soundings currently suggest that the strongest lift may be above the DGZ during the synoptic snow keeping ratios somewhat in check, and the sources for lift aren’t extremely strong, so I tend to think amounts with the clipper in northern OH/NW PA will only be 1-2″.  There may be pixie dust or small flakes falling for a while which will be nice, but they won’t add up a ton.

Winds will come back around to the W or WNW over the lake by Saturday morning which will bring lake effect back into the picture.  Lingering synoptic moisture to over 10k feet through most of the morning and outstanding thermodynamics with EL heights of 10-12k feet (higher at ERI) and steep lapse rates to go along with convergence near the shoreline will support an intense lake effect snow band.  In addition, a potent vort max will pass overhead late morning and early afternoon, adding some large-scale lift.  Given nearly optimal snow growth, rates of 2 to locally 4” per hour will be possible in the heart of the band.  Band placement will be important, as some areas may see a lot of snow quickly in the Saturday morning/early afternoon timeframe.  To start the day, winds will be W over the lake and WSW on land…a familiar pattern…which will likely drive the band onshore over northeastern Ashtabula County and the Erie County lakeshore.  It may be snowing in parts of Lake County but likely won’t be that heavy at this juncture.  Winds will continue to slowly gain a more northerly component and by mid-morning are expected to be WNW over the lake and slightly south of due west of land.  With an approaching vort max (which seems to tend to keep winds more “backed” or southerly around the lake) and shoreline convergence, don’t think the band will push inland too fast, but may get into far NE Cuyahoga and northern Geauga by mid-morning, with heavier snow spreading into Lake County and the rest of northern Asthabula County.  Snow may start spreading a bit farther inland over Erie County by mid-morning.  The vort max passes around noon which should nudge the surface trough farther south as the winds likely gain more of a northerly component behind the vort max.  This should allow the band to gradually resume a more southward drift during the early afternoon.

I don’t expect the band to get too far south, as the vort max really only grazes the region with no big height falls with it, so there shouldn’t be a huge push of northerly winds Saturday afternoon…but likely enough to get the band into a good chunk of Cuyahoga County (possibly into the central part of the county) and more inland portions of the Snowbelt.  The thermodynamic environment will remain very favorable and with good snow growth to go along with some pre-seeding from Lake Michigan, though the shoreline induced convergence will likely weaken some and there will be a brief period of sinking motion during the early to mid-afternoon behind the vort max.  This should cause the band to become less organized and weaken a bit, though it probably won’t completely go away.  Ice cover over the western basin is over 80% which will limit moisture flux some, however, the ice is still not that thick and still has some cracks, which typically still allows a half decent moisture flux.  Given the strong instability and high EL heights, I think that while the ice will somewhat limit the band intensity over Lorain and Cuyahoga Counties where the fetch of open water is much diminished that it won’t completely prohibit some decently intense snow.

Another potent vort max and surface trough (with much colder air behind it) approaches late afternoon and early evening and passes around mid-evening Saturday.  These features tend to back surface winds a bit more than modelled, which suggests winds may be around 280 degrees as this vort max and trough approach.  The lift and moisture ahead of the vort max and likely upstream moisture from Lake Michigan, along with increasing convergence near the shoreline should allow a decent band to re-develop.  This band will likely develop across northern Lorain County and northern/central Cuyahoga County east into southern Lake County and Geauga County and swing south by mid-evening behind the vort max as winds then quickly go more NNW.  Though there may not be an organized convergence band over NW PA, Lake Huron moisture and increased lift should still result in a nice burst of snow.  Instability will be extreme by this point with ample moisture/good snow growth remaining in place, so the band could produce a quick few inches over parts of the Cleveland metro and into the Snowbelt, likely a bit inland form the lake, as well as in parts of NW PA especially in the higher terrain.  A brief period of good moisture behind the winds turning to the NNW may briefly allow upslope snow to continue through late evening, though colder air will start hurting snow growth.  Given the stronger vort max/surface trough passage and cold push of air, the snow band could detatch from the lake and push inland as a strong snow squall that drops a quick 1-2” of snow.  Lake Michigan moisture may contribute to a risk of squalls well west of the NE Ohio Snowbelt as well Saturday evening as the trough moves through.

Behind the trough the thermodynamics remain impressive with EL heights over 10-11k feet and extreme instability over the lake, but the airmass dries considerably for the remainder of Saturday night and through Sunday night.  This will likely limit snow outside of a Lake Huron connection.  With well-aligned winds, extreme instability, and this connection going over the open part of our lake, it may produce heavy snow.  NAM soundings show the DGZ remaining in the clouds in the Huron connection through Sunday supporting high ratios.  Models tend to bring these connections too far west, but with a NNW flow think it should get into at least Asthabula County for a decent period of time Saturday night through much of Sunday and may briefly drift into Geauga/Lake Counties late Saturday night when winds have their strongest northerly component.  Winds back Sunday night which should push the connection east.  Given the winds don’t move a ton, are well aligned, and instability is extreme, this Huron connection may drop a general 3-6” over far eastern Lake/Geauga, Asthabula, and western Erie/Crawford Counties, with locally much higher amounts possible if the band stalls for any decent length of time.  With extreme instability and wind fields getting a bit light late Saturday night into Sunday, meso-low formation may be possible with the band which could move it around at times and also bring locally enhanced snow rates.  Outside of the Huron connection, a short fetch, limited moisture hurting snow growth, but extreme instability and fairly light/well-aligned winds may allow modest snow showers to continue in the higher terrain as far west as the secondary Snowbelt.  This may add a local inch or two after midnight Saturday night through Sunday in the higher terrain west of the Lake Huron connection.

For total amounts, think there’s ample opportunity for snow for 12”+ along the lakeshore in northeast Ashtabula County and Erie County, PA.  Given a couple shots at banding, local amounts of 18-24” seem doable in Erie County within 10 miles of the lake.  Elsewhere, expect the rest of the core Snowbelt (parts of the eastern suburbs, inland Lake, northern Geauga, inland Ashtabula, inland Erie and northern Crawford) to see a general 6-12” of snow given banding likely getting in off and on Saturday mid-morning through evening, with some light upslope enhanced snow then continuing through Sunday.  Wherever the Huron band sets up, the potential for over a foot will exist.  Farther west/south, given 1-2” of clipper snow, potential squalls enhanced by moisture from Lake Michigan and the vort maxes, and likely a squall pushing south off of Lake Erie Saturday evening, think most areas can see over 4”…so will go 4-7” for much of the Cleveland and Akron metro down to Youngstown.  Given how unstable the airmass is before adding in the lakes, good snow ratios, sources of synoptic lift, and then moisture from the lakes, I have to think it’ll be a snowy Saturday and Saturday evening at times in these areas.  The moisture from Lake Michigan may also get wrung out in the central highlands at times adding some modest additional accums there on top of 1-3” of clipper snow.

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