Wednesday, January 20, 2016

The oncoming MidAtlantic blizzard still on track and my pick for the most miserable weather

The latest forecasts for the MidAtlantic blizzard are on track for an extremely heavy snowfall event starting in the DC area by afternoon on Friday.   With no melting expected after the snow flakes land on the ground, I'm expecting roads will quickly become snow-covered within an hour of first snow except where roads have been treated.  And I'd expect more roads to be treated than with todays light snow, big impact event.  But look at how quickly the SREF members pile on the snow within a couple hours of onset.  The heaviest rates appear to occur with the strong surge of elevated warm air advection along the front end of this system Friday night.  I don't imagine any road treatment, except for aggressive plowing, will be able to stay ahead of the accumulating snow.  Considering that everyone will be expecting impassible conditions Friday night, I don't expect big traffic jams and numerous trapped people and thus plowing will not be seriously inhibited.

Forecast SREF snowfall accumulation at Washington DC.

At least the winds will not be strong Friday night and visibilities will be restricted mainly by snow to 1/8 mi.  Don't expect them to stay light by Saturday, however.  While snowfall rates will diminish, roads exposed to fields could experience local whiteout conditions.

The 4km NAM does show one area where strong winds may begin earlier - the Shenandoah valley.  Downslope or gap winds could enhance blowing snow and drop visibilities pretty quickly Friday night in some areas.  Would this impact I-81?  It would be interesting to find out.

Forecast 10 m winds from the NAM 4km model.

By Saturday the storm will be at its peak across the DC area and into Philadelphia to the New Jersey Coast.  What I find impressive is the continuing variability in the thickness and precipitation fields from the short range ensemble from late this afternoon.  The precipitation fields are quite varied amongst the SREF members, with the front precip edge ranging from southern to northern Pennsylvania.  Likewise the snowfall accumulation forecasts are equally variable, more so from points along the northern fringe of the expected precipitation.  Just like last year, I'll be thinking of the challenge facing NWS forecasters from State College to New York City when they have to come up with a snowfall forecast.
SREF forecast of 3 hour precipitation and sea level pressure  for Saturday morning from the Wednesday afternoon run.

If I picked a spot where conditions would be most horrid, it may not be with the purely heaviest snowfall rates that may fall from the Shenandoah to northwest Maryland but instead, the northern New Jersey Coast.  This area on Saturday will likely face the highest chance of blizzard conditions while at the same time the NOAA storm surge model depicts water level departures of more than 4 ft and waves over 20 ft high.

Forecast likelihood of blizzard conditions and >2"/hour snowfall rates for Saturday morning.

Storm surge forecast by Saturday evening Jan 24.

Wave height forecasts from the Wavewatch model Saturday night

High tide at Barnegat, NJ Saturday afternoon could feature wave spillover into houses and boardwalks while wet wind driven snow plasters the sides of houses and covers roads with a gluey mess where the surge fails to reach at the same time bringing down power lines.  Doesn't that sound wonderful?

Waterlevel forecast from SUNY Stonybrook for Barnegat, NJ

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