9:30 AM (Friday) | *Strong-to-severe thunderstorms a threat on Saturday/Saturday night; especially, to the north of the PA/MD border*

Upper-level energy will be a contributing factor on Saturday in the formation of strong-to-severe thunderstorms across the Mid-Atlantic/Northeast US. Map courtesy NOAA, tropicaltidbits.com

Overview

Temperatures will spike on Saturday in the Mid-Atlantic region after a comfortably warm day on Friday and the sudden warm up will be accompanied by plenty of instability in the atmosphere.  Multiple waves of energy in the upper part of the atmosphere will shift eastward on Saturday from the Northern Plains across the Ohio Valley and into the Mid-Atlantic/Northeast US. In addition, there will be a frontal boundary zone extending all the way from the Northern Plains into the eastern Great Lakes and this too will help to create some instability.  As a result, strong-to-severe thunderstorms will be possible in the Mid-Atlantic region on Saturday afternoon and evening; especially, to the north of the PA/MD border.

The wave of energy that will play a key role in tomorrow’s weather across the Mid-Atlantic/Northeast US is causing showers and strong thunderstorms today in the Upper Midwest (circled region). Map courtesy NOAA, University of Wisconsin

Discussion

Temperatures today will be warm in the Mid-Atlantic region, but humidity levels will remain quite comfortable for this time of year with dew points generally in the upper 50’s.  A warm front will lift northward through the region in the overnight hours and this will set the stage for a significant warm up on Saturday with the lower 90’s likely for afternoon highs in much of the urban corridor from DC-to-Philly-to-NYC and it will become noticeably more humid as well. 

NOAA’s Storm Prediction Center has a slight risk of severe weather in the Mid-Atlantic/Northeast US on Saturday; especially, to the north of the PA/MD border.

An area of showers and thunderstorms is likely to start the day on Saturday already in existence across the eastern Great Lakes, western New York and across parts of upstate Pennsylvania.  This batch of early day showers and storms will trek eastward during the morning hours and it’ll allow for the possibility of strong-to-severe thunderstorm activity in the I-95 corridor region as early as mid-day or early afternoon.  The threat for showers and embedded strong-to-severe thunderstorms will continue through the afternoon and into the evening hours across the Mid-Atlantic region as additional waves of energy slide to the east from the Ohio Valley. However, cloud cover associated with the initial batch of rainfall makes it somewhat difficult at this point in time in determining how unstable the atmosphere may be later tomorrow into early tomorrow night. The quicker it clears out, the better the chance for daytime heating to make the atmosphere unstable for afternoon/evening storm development.

Given the higher humidity levels expected on Saturday and a rather strong mid-level jet streak, the primary weather hazards with any thunderstorm will be heavy rainfall and damaging gusts. While hail is a possibility with any strong storm, its chances will likely be somewhat limited given the relatively high melting layer expected in the atmosphere.  Another short-wave upper-level trough will rotate around the main upper-level low on Sunday and this small-scale feature will continue the threat for showers and thunderstorms in the Mid-Atlantic region.  However, the mid-level strong jet streak should be east of here on Sunday limiting the chances for damaging wind gusts in any thunderstorm that forms.  The main upper-level low associated with this weekend’s instability will meander in the in the Mid-Atlantic/Northeast US during the first half of next week and this positioning will likely result in a few more rounds of showers and storms. 

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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