Much of US will see below normal temps this weekend, similarities to storm of 1982 – cold expected throughout April

sc-todays-date
US north east April 5th 2018 storm

Much of the eastern two-thirds of the nation will feature well below-normal temperatures on Saturday afternoon as depicted by the 06Z GEFS 2-m 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 much 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 dry 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 showers to the I-95 corridor on Friday and push a cold front through the region. This front will usher in very cold air for this time of year by early Saturday and low pressure will form along the stalling frontal boundary zone and likely generate 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.

After a windy, dry and cold day on Thursday, a “clipper-like” low pressure system will then trek southeastward across the Great Lakes region on Friday and push some rain shower activity into the I-95 corridor with snow showers possible across interior sections of the Northeast US. A cold front will trail from the low pressure system and its passage will usher in much colder for the weekend which will be way below-normal (20+ degrees below normal here on Saturday). This air mass is so cold, in fact, some places in the Upper Midwest will see their coldest weather ever in the month of April with single digits likely for lows in places like upstate Minnesota.

Saturday afternoon, April 7th,

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

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. It is still a bit early to pinpoint the exact timing of the changeover to snow which will have a big impact on potential snowfall accumulation amounts, but several inches are on the table in much of the I-95 corridor. 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 possibly receiving noticeably more snowfall than nearby lower elevation spots. More cold air outbreaks are likely to follow into at least the middle of April and there may very well be additional snow threats in this on-going active and cold weather pattern including as soon as the early-to-middle part of next week.

The Madden-Julian Oscillation

© maps courtesy Weather Bell Analytics (Joe Bastardi), NOAA
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);

April 6-7 1982 and some similarities to this weekend’s setup

Can we get accumulating snow in the Mid-Atlantic region during the month of April…absolutely, and one such example took place on April 6-7, 1982 and there are a couple of similarities with that storm and the atmospheric setup expected this weekend. The April 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.

500 mb height anomaly pattern

© NOAA, tropicaltidbits.com
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

Two similarities from the storm in April 1982 and the atmospheric conditions expected this weekend have to do with a tropical disturbance known as the Madden-Julian Oscillation as well as the 500 mb height anomaly pattern. 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.

April 6-7, 1982 snowstorm

© NOAA
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)

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:

Leave a Reply

Your email address will not be published. Required fields are marked *