12:10 PM | **Another Arctic blast by the weekend and possible accumulating snow**

12Z NAM snowfall map for Saturday system (through Saturday 7PM); map courtesy tropicaltidbits.com, NOAA

Overview
Low temperature records were broken this morning in parts of the Mid-Atlantic region and Northeast US (e.g., Dulles and BWI Airports bottomed out at 24 degrees) and this is by no means the end of the unusual cold weather. Temperatures will modify some this afternoon and turn much milder on Thursday, but more Arctic air is poised to pounce on the region by the weekend and freezing conditions are quite likely in parts of the Mid-Atlantic on both weekend mornings.  In addition to the upcoming late week and weekend cold, accumulating snow is a threat as a very energetic upper-level pattern develops in the Northeast US. Waves of energy will rotate around a deep upper-level trough of low pressure at the end of the week and the result could be a storm near the Mid-Atlantic coastline by Saturday. Tomorrow’s noticeably milder weather will come at a price as there will be periods of rain – perhaps a thunderstorm or two – and some of the rain can come down hard at times.  

12Z 12-km NAM forecast map for Saturday morning (blue=snow, green=rain); map courtesy tropicaltidbits.com, NOAA

Significant rain event and milder Thursday/Thursday night
It’ll turn much milder tomorrow as a cold front approaches the eastern US and rain can develop as early as the pre-dawn hours in the I-95 corridor.  Periods of rain are quite likely on Thursday and Thursday night with some downpours and there can be some thunderstorm activity mixed in. Temperatures are likely to reach the 60 degree mark for highs by tomorrow afternoon, but that should be the highest level seen over the next several days.

Upper-level energy as of Saturday morning should help spin off surface low pressure

Friday-Saturday and the accumulating snow threat
Deep upper-level trough of low pressure will form in the Northeast US at the end of the week and several waves of energy will rotate around potentially causing mischief in the Mid-Atlantic region for the early weekend.  At the same time this upper-level low forms over the Northeast US, an “omega” blocking situation will form downstream over the Atlantic Ocean. As a result of the upper-level blocking pattern, the upper low over the Northeast US will tend to become “negatively tilted”, very slow-moving, and one particular short wave of energy that is expected to rotate around looks especially strong and it is likely to generate surface low pressure near the Mid-Atlantic coastline on Saturday.  Cold air will be well entrenched in the region and this could very well result in snow for the DC-to-Philly-to-NYC corridor – perhaps even with accumulations. In fact, this is the type of system that can produce a swath of accumulating snow over a 50-100 mile wide band from the Ohio Valley to the east coast generally in a northwest-to-southeast fashion. The 12Z (12-km) NAM forecast map for early Saturday is shown above along with the total snowfall map from that same model over the next 84 hours.  The GFS and Euro computer forecast models are in general agreement that the snow threat on Saturday is legitimate.  Stay tuned.  

Meteorologist Paul Dorian
Vencore, Inc.