Another Nor’ Easter Wednesday-Thursday. Accumulating Snows Somewhere, but Where?

A current look at the upper level pattern shows a pattern coming together supporting another Nor’Easter with impacts to the eastern Mid-Atlantic through New England Wednesday and Thursday of this week.

A ridge of high-pressure along the west coast of the US is combining with a modest –NAO ridge over eastern Greenland and 50/50 low (the remnants of Sandy) to keep a trough over the eastern US. A piece of shortwave energy, circled in red, is rounding the base of this trough today and will move off the east coast tomorrow. Off the east coast, this trough will phase with the next incoming piece of energy and result in a deepening storm off the Mid-Atlantic coast:

When one looks at the above map, valid early Wednesday morning off the American GFS model, it is apparent that the two pieces of energy, one off the southeast coast, and another rounding the base of the trough over the US, are close to “phasing,” or combining with one another.

Another look at the map reveals why this storm will track farther off the east coast than earlier model projections:

  1. The western US ridging is gradually weakening and is displaced east by a large incoming piece of energy towards the northwest US.
  2. The remnants of Sandy, acting as a “50/50” low are displaced west, closer to 60W, not near the more traditional 50N, 50W position.
  3. The –NAO is quickly weakening, with little ridging over Greenland at this point.

So, while the storm will phase and deepen close enough to the US coastline for impacts to be felt, the trough will be pulling out to the east as it happens, meaning impacts will be somewhat limited and will struggle to reach well inland.

With that said, what are some potential impacts?

When looking at wind gust potential Wednesday evening, due to a tight pressure gradient between the decently strong Nor’Easter tracking well off the Mid-Atlantic coast and just off of Cape Cod and a large high pressure stretching from northern New England towards the Ohio Valley, the potential exists for 50-60MPH wind gusts near the coast line. Right now the low will likely track far enough east to limit impacts from New Jersey points south, however the potential will exist for 50+MPH wind gusts from Long Island towards Southern and Coastal New England.

These winds will be able to pile up 2-4’ of water along the coast from NJ northward towards much of New England. Although these values are much less than what occurred with Sandy, Sandy significantly damaged dune protection along the coastline and the infrastructure remains weak in the Sandy damage area, meaning that potential additional power outages from wind and coastal flooding appear likely Wednesday into Thursday from coastal NJ northward towards coastal New England, including Long Island and New York City.

Snowfall:

The airmass ahead of the upcoming Nor’Easter will be seasonably cool across much of the east coast. However, due to the weakening –NAO and weakening western US troughing, the cold air may be dis-lodged fairly easily as the storm brings in warm air off the ocean.

Recent GFS and Euro runs show differences in temperatures across the region on Wednesday:

GFS:

Euro:

The GFS has much less cold air over the eastern US than the Euro, with the Euro showing a large area of sub-freezing 850mb (5000’) temperatures over the eastern US. The question is which camp wins out?

When looking at the upper level projections from the two models valid Wednesday morning (with surface features imposed on top) one can see that the Euro is a bit farther east with the initial low pressure area…and a bit stronger with ridging over Northern New England, which is pumping cold air down the Appalachians. The Euro is a bit more amplified with western US ridging and a tad deeper with the eastern US trough.

As we roll the models forward to Thursday morning we see key differences in the track and strength of the low pressure area. The Euro shows a slightly deeper area of low pressure, with the retreating high pressure north of the system remaining stronger than the GFS depiction. The GFS also tucks the low much closer to the east coast, allowing the warm flow off the Atlantic to eat away at the cold air from New England south into the Mid Atlantic.

Which solution was right? In my previous post and earlier in this post I argued that the pattern argues for a farther east solution. The Euro has the UKMET on its side with the farther east track, with the Canadian model slower and farther west, but also well south, allowing a more dominant northerly flow to persist over the Mid-Atlantic and New England.

Given the synoptic reasoning discussed above, I’d give the nod to the slightly farther east and faster solution. Right now the Euro, UKMET and Canadian generally show 850mb temps of 0 to -3C across the region during the storm. This argues for higher elevation snows and rain closer to the coast.

As for snow amounts, things are always a bit hairy this far out.

The most recent GFS run, which did trend a bit east with the storm from the afternoon run posted above, shows strong mid-level frontogenesis setting up from the coastal Mid-Atlantic into southern and eastern New England Wednesday afternoon through Wednesday night, setting up the potential for moderate to heavy precipitation rates.

Indeed, the model shows very strong upward motion at around 18,000 feet above the ground in that region at that timeframe, gradually moving north and west and weakening Wednesday night. Thus, this seems like a short to medium duration (8-12 hours) moderate to heavy precip event near the coast, with lighter amounts farther west. Models are generally spitting out up to one inch of liquid near the coast from Long Island into Southern New England with amounts of .5-.75” extending up to 100 miles inland. However, the trend is for lighter amounts in general and will trend the forecast in this direction.

Given I expect the higher elevations to be mostly snow from the Mid Atlantic northward, this argues for a swath of 6-12” type snow amounts in the higher terrain, generally above 750’ in New England to 1000’+ over the Mid Atlantic. Near the coast, as the storm pulls away, lower elevations may change to snow in the Mid-Atlantic. However, heavier snow amounts will likely lie in the more elevated suburbs of the major I-95 cities from DC-Baltimore points northeast along that corridor. In New England, a coastal front will likely set up and keep much of southeastern NH, eastern MA and RI rain until the storm pulls away, when a brief changeover is possible. Again though, given the general eastward trend with this system, I will temper the westward extent of snows for this forecast.

With that said, my take on snow amounts:

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