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11:20 AM | **Strong-to-severe thunderstorm threat later today in the I-95 corridor**

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Weather forecasting and analysis, space and historic events, climate information

11:20 AM | **Strong-to-severe thunderstorm threat later today in the I-95 corridor**

Paul Dorian

A stability index known as the “Surface-based Lifted Index” shows a large area of “-6” in the I-95 corridor region and this reflects large instability; courtesy NOAA

A stability index known as the “Surface-based Lifted Index” shows a large area of “-6” in the I-95 corridor region and this reflects large instability; courtesy NOAA

Overview

An active weather pattern is setting up for the I-95 corridor for later today/early tonight extending all the way from the Carolinas to New England.  There is an approaching vigorous wave of energy in the upper part of the atmosphere that will combine with diurnal heating and an advancing surface frontal boundary zone to destabilize the atmosphere over the next few hours and the result will likely be widespread showers and thunderstorms between about 2 and 9 PM in the I-95 corridor.  Any storm that forms later today can produce torrential rainfall, flash flooding and perhaps even damaging wind gusts. Looking ahead, a second frontal system will pass through the region early Friday and it’ll be followed by a much more comfortable air mass for the weekend with noticeably lower humidity levels.

12Z NAM 4PM forecast map at 500 mb with vigorous energy aloft in the Mid-Atlantic; courtesy NOAA, tropicaltidbits.com

12Z NAM 4PM forecast map at 500 mb with vigorous energy aloft in the Mid-Atlantic; courtesy NOAA, tropicaltidbits.com

Details

Satellite imagery clearly shows plenty of clear skies at mid-day in the I-95 corridor and this will allow for significant diurnal heating which will act to destabilize the lower part of the atmosphere.  In fact, the latest map of the stability index known as the “Surface-Based” Lifted Index (LI) features quite unstable conditions already set up in the I-95 corridor with values as low as -6 (i.e., large instability region).  The LI is an index used to assess low-level parcel (in)stability of the troposphere and the more negative the value, the more unstable the atmosphere.

Lots of clear-to-partly cloudy skies at mid-day in the I-95 corridor which will allow for diurnal heating to destabilize the atmosphere as energy arrives in the upper part of the atmosphere; courtesy NOAA/GOES, College of DuPAge

Lots of clear-to-partly cloudy skies at mid-day in the I-95 corridor which will allow for diurnal heating to destabilize the atmosphere as energy arrives in the upper part of the atmosphere; courtesy NOAA/GOES, College of DuPAge

As temperatures continue to rise this afternoon and strong upper-level energy enters the picture from the northwest, expect showers and thunderstorms to explosively increase in coverage and intensity.  The approaching wave of energy aloft even takes on a slightly “negative-tilt” later today which promotes enhanced upward motion and this increases the chances for strong-to-severe thunderstorm activity.  Short-term high-resolution forecast models depict a rather widespread area of showers/thunderstorms by the late afternoon and the threat will continue through the evening hours.  Any storm that forms later today can produce heavy rainfall and flash flooding conditions given the fact that grounds are already well saturated. Indeed, flash flood watches have been posted in some areas that received heavy rainfall on Tuesday (e.g., Philly metro region, interior NJ) and I would expect severe thunderstorm watches will be posted later today by the National Weather Service for much of the I-95 corridor.

13Z High-Resolution Rapid Refresh (HRRR) forecast map at 4PM with numerous showers/storms depicted in the Mid-Atlantic region; courtesy NOAA, tropicaltidbits.com

13Z High-Resolution Rapid Refresh (HRRR) forecast map at 4PM with numerous showers/storms depicted in the Mid-Atlantic region; courtesy NOAA, tropicaltidbits.com

Looking ahead

The good news is that after the active weather expected here for later today and tonight, things will tone down some on Thursday with a lessening chance of showers and thunderstorms and then a very nice air mass for August will arrive on Friday with noticeably lowering humidity levels.  The comfortable air mass will stay around through the upcoming weekend with pleasant temperatures and humidity levels for this time of year.

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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