12:00 PM (Thurs) | ***A remarkable cold air outbreak on the way for Friday night/Saturday…powerful winds to 50 mph will accompany the cold blast…rain-changing-to-snow scenario for interior sections***

Quite an amazing outbreak of significantly colder-than-normal air will encompass much of the northeastern quadrant of the US by the early part of the weekend. Map courtesy NOAA, tropicaltidbits.com

Overview

A remarkable cold air outbreak is coming to the northeastern quadrant of the nation for Friday night and Saturday and it will be accompanied by a rain-changing-to-snow event for many interior sections of the Mid-Atlantic/Northeast US.  This cold blast is likely to result in some of the coldest daily temperatures ever recorded both at the surface and in the upper atmosphere and, in some cases, monthly temperature records may be set.  In addition, some spots might see their latest measurable snowfall in the Friday night/Saturday time period. Some interesting notes…in Philadelphia, there has not been a temperature in the 30’s on May 9th or later in more than fifty years (1966) and it could happen on both Saturday (9th) and Sunday (10th) mornings. In Buffalo, the predicted temperature of -40°C this weekend at the 500 millibar level would shatter the previous record of -35.7°C for the entire month of May. In Baltimore, there has not been a measurable snowfall in the month of May since 1872 and the latest on record there is May 9th (1923). 

In addition to the cold and potential snow, winds will become an important factor as well on Saturday with gusts past 50 mph on the table in the Mid-Atlantic/Northeast US and this will raise the chance for scattered power outages.  Looking ahead, the overall weather pattern that has resulted in multiple cold air outbreaks from Canada into the central and eastern US during the past several weeks is likely to finally break down during the third week of May, but we’ll have to endure some pain before we get to those expected warmer-than-normal conditions. 

An extremely anomalous upper-level low will move on top of the Mid-Atlantic/Northeast US by the early part of the weekend representing the core location of a remarkably cold air mass for this time of year. Map courtesy NOAA, tropicaltidbits.com

Details

Generally speaking, there are two requirements for significantly colder-than-normal weather this time of year in the Mid-Atlantic region and they include thick cloud cover and low-level easterly winds which bring the still quite cold ocean air into the area from the western Atlantic.  Indeed, temperatures peaked on Wednesday at 52 degrees for highs in Lancaster, PA which was the lowest high temperature ever recorded there and in State College, PA, the high of 43 degrees was the lowest in the month of May since 1989.  These two examples were pretty representative of the chill experienced throughout the rest of the Mid-Atlantic region on Wednesday. The chill of mid-week will ease considerably on Thursday with the return of sunshine and a change of the low-level flow of air from east-to-west and high temperatures will be in the low-to-middle 60’s in many spots. The weather will become quite a bit more active later Friday as a strong cold front advances this way from the Upper Midwest and low pressure begin to develop over the Tennessee Valley.

06Z EPS total snowfall forecast map for the upcoming event with quite an impressive display for this time of year. (Note- this computer forecast model map of total snowfall is based on a 10:1 ratio of snow-to-liquid and it is likely to end up being a higher ratio than that during this upcoming event which would mean less snow than depicted here). Map courtesy Weather Bell Analytics, ECMWF

This low pressure system will push along the southeastward-advancing cold frontal boundary zone on Friday and rain is likely return to the Mid-Atlantic region during the afternoon and evening hours.  As colder air wraps into the system on Friday night, the rain is likely to change to snow in a good part of the Mid-Atlantic/Northeast US; especially, across interior higher elevation locations of upstate PA, NY and New England where accumulations are possible.  In fact, there can be a changeover from rain-to-snow showers later Friday night all the way into the suburban locations just to the north and west of Route I-95 in the DC-to-Philly-to-NYC corridor. This low pressure system will intensify dramatically by the time it reaches the Gulf of Maine on and a deepening pressure gradient will result in powerful winds to go along with the unusual cold.  In fact, the low pressure reading expected for this storm on Saturday could rival the lowest ever recorded in Maine during the month of May.  Winds on Saturday can gust to 50 mph or so in the Mid-Atlantic region/Northeast US raising the chance for scattered power outages. 

Low pressure will intensify rapidly on Friday night and Saturday and become a powerful storm by the time it reaches the Gulf of Maine. The pressure gradient will tighten markedly on Saturday between this low and high pressure over the middle of the country resulting in wind gusts to 50 mph or so in the Mid-Atlantic/Northeast US. Map courtesy NOAA, tropicaltidbits.com

By the late morning and mid-day hours on Saturday, an extremely anomalous upper-level low will slide over the Northeast US and the quite amazingly cold air aloft will create a very unstable environment.  As a result, while the low pressure and frontal-induced precipitation may have ended, a re-development of snow showers is quite possible during the late morning and mid-day hours on Saturday in the unstable atmosphere and this could take place all the way into the I-95 corridor.  Mother’s Day (Sunday) will get off to a very cold start for this time of year and it’ll stay quite a bit colder-than-normal; however, the afternoon will be much more bearable when compared to Saturday as the winds should be far less noticeable and there should be some sunshine although it might fade behind increasing clouds ahead of the next system.

Cold air outbreaks have dominated the scene for several weeks in the central and eastern US, but there is light at the end of the tunnel. It looks like the third week of May will bring about a transition in the overall weather pattern to one that features warmer-than-normal weather for much of the central and eastern US - and the Atlantic Basin tropical season will not be too far behind. Map courtesy NOAA, tropicaltidbits.com

Looking ahead, the overall weather pattern that has resulted in cold air outbreaks from Canada into the central and eastern US during the past several weeks looks like it may finally break down during the third week of May.  It should remain generally colder-than-normal for much of next week in the Mid-Atlantic/Northeast US, but then a transition to warmer weather looks likely once we get past the middle of the month.  The temperature at Philadelphia has not reached the 80 degree mark yet this year and the latest that that has happened for the first time in a given year was May 20th in 1984 – something of interest to monitor in coming days.  Once we transition to a warmer weather pattern during the second half of the month, the Atlantic Basin tropical season may not be too far behind as, often times, the tropical season begins rather early when there is a chilly spring in the central and eastern US. 

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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