Wednesday 12:30 PM **Wind gusts past 50 mph possible this afternoon and early evening…accumulating snow threat continues for Saturday...some similarities in current pattern to April 1982**

Much of the eastern two-thirds of the nation will feature significantly below-normal temperatures on Saturday afternoon as depicted by the 06Z GEFS 2-meter temperature anomalies; courtesy NOAA, tropicaltidbits.com

Overview
A very active weather pattern is bringing the I-95 corridor intense winds today associated with a strong cold frontal system and there may be another round of springtime accumulating snow this Saturday for parts of the region.  Winds could gust past 50 mph this afternoon and early evening following the passage of a strong cold front as a fresh cold air mass rushes into the region.  On Thursday, it’ll be blustery and quite cold for this time of year and the winds will start off the day quite strong though they will likely diminish during the mid and late afternoon hours. A “clipper-type” low pressure system will then bring rain and snow showers to parts of the I-95 corridor on Friday and also push a cold front through the region. This front will usher in very cold air for this time of year and low pressure will form along the stalling frontal boundary zone and likely generate some accumulating snow in the DC-to-Philly-to-NYC corridor.

Discussion
A strong cold front is whipping through the I-95 corridor at mid-day and winds will soon shift to a northwesterly direction and can gust past 50 mph during the afternoon and early evening hours with isolated power outages a possibility.  A line of showers and embedded strong thunderstorms is pushing quickly to the east and will reach the coastline within a couple of hours.  Temperatures will fall this afternoon following the passage of the strong cold front and drop sharply overnight to near 30 degrees by early tomorrow morning in DC, Philly and NYC.  

Thursday promises to be a blustery and cold day in the I-95 corridor with possible scattered snow flurries and it happens to be Opening Day for the Phillies in South Philadelphia and the Nationals in DC - not exactly great baseball weather.  A “clipper-like” low pressure system will then trek southeastward on Friday across the Great Lakes and it'll push some rain and snow shower activity into the I-95 corridor and there can even be a coating of snow in some spots north of the PA/MD border.  A cold front will trail from the low pressure system and its passage will usher in much colder air for the weekend which will be way below-normal for this time of year - perhaps 20+ degrees below-normal. This air mass is so cold, in fact, some places in the Upper Midwest will see their coldest weather ever recorded in the month of April with single digits likely for lows in places like upstate Minnesota.

12Z GFS forecast map for Saturday afternoon, April 7th, with snow shown in blue; courtesy NOAA/EMC, tropicaltidbits.com

This frontal system will stall out just to the south and east of here on Saturday and low pressure will form along the frontal boundary zone and ride to the northeast.  The exact storm track is still in some question as is the location of the rain/snow line and this will have a crucial impact on potential snowfall amounts.  With the influx of the very cold air on Saturday, temperatures are likely to ultimately be supportive of snow all the way down into the DC metro region (DC hasn't seen an inch of snow in April since 1924), but precipitation could start out as rain or a wintry mix before the likely changeover to snow.  

As far as accumulations are concerned, a few inches of snow are on the table for the I-95 corridor, but it is still a bit early to pinpoint the exact storm track and timing of the changeover to snow.  Furthermore, the eventual strength of Friday's "clipper-like" system will also play a role in the Saturday event as a stronger "front running" system could sap some energy from the following second wave of low pressure.  As is always the case with late winter and early spring snow events, elevation can play a critical role in total accumulations with higher locations likely receiving more snowfall than nearby lower elevation spots. More cold air outbreaks are likely to follow into at least the middle of the month and there may very well be additional snow threats in this on-going active and cold weather pattern including perhaps as soon as the early part of next week.  

The Madden-Julian Oscillation (MJO) index is currently moving from phase 7 into phase 8 (right plot) which is quite similar to the pattern seen in April 1982 (left plot, April shown in red); maps courtesy Weather Bell Analytics (Joe Bastardi), NOAA

April 1982 and some similarities to this weekend's setup
Can we get accumulating snow and 25 degrees below-normal temperatures in the Mid-Atlantic region during the month of April…absolutely, and one such example of this took place on April 6-7, 1982 and there are a few similarities with that overall pattern and the setup expected this weekend.  The April 6-7, 1982 storm turned out to be an all-out blizzard for New York City and much of the Northeast US and delayed the baseball season in many cities from Baltimore-to-Boston. It resulted in significant snow of more than a foot in many places from Pennsylvania-to-New England and winds gusted to 70+ mph in spots during the storm.  Also, record cold poured in on the back side of the storm with many spots falling to 25 degrees below normal for that time of year shortly after the storm had passed.  

The 500 mb height anomaly pattern during the blizzard of April 6-7, 1982 (left) and the 06Z GEFS forecast map for this weekend with both featuring well below-normal heights centered over the Northeast US and the Pacific Northwest coastline; courtesy NOAA, tropicaltidbits.com

Three similarities from the overall weather pattern in April 1982 and the atmospheric conditions expected this weekend have to do with a tropical disturbance known as the Madden-Julian Oscillation, the 500 mb height anomaly pattern and the below-normal cold.  The MJO is a tropical disturbance that propagates eastward around the global tropics with a cycle on the order of 30-60 days.  Research and empirical observations have found that the location or “phase” of the MJO is linked with certain temperature and precipitation patterns around the world.  In April 1982, the MJO was primarily in phase 7 during the storm time period of April 6-7 and was on its way into phase 8. The current forecast of the MJO has the index moving from phase 7 into phase 8 - somewhat similar to 1982.  

The April 6-7, 1982 snowstorm featured well below-normal temperatures (left map) in much of the eastern two-thirds of the country as well as in California and the forecast map for this Saturday from the 06Z GEFS is quite similar (right map); courtesy NOAA

In addition to the MJO, the temperature pattern across the nation this weekend will be quite similar to that of April 6th, 1982 with below-normal temperatures dominating the eastern two-thirds of the nation.  Also, the 500 mb height anomaly pattern in April 1982 featured two areas across the US with well below-normal heights with one centered over the Northeast US and another centered along the Pacific Northwest coastline – somewhat similar to the 500 mb pattern expected this weekend.

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com 

Extended morning video discussion: