11:45 AM | **Severe weather threat late today/early tonight from DC-to-Philly-to-NYC…"training" of thunderstorms could result in localized flash flooding...very wet pattern continues into next week**

 12Z NAM (3-km) forecast maps of simulated IR brightness from Tuesday 2PM to Wednesday 4AM with explosive development of thunderstorms indicated for later today and then possible "training" of thunderstorms in the overnight hours; courtesy NOAA/EMC, tropicaltidbits.com

12Z NAM (3-km) forecast maps of simulated IR brightness from Tuesday 2PM to Wednesday 4AM with explosive development of thunderstorms indicated for later today and then possible "training" of thunderstorms in the overnight hours; courtesy NOAA/EMC, tropicaltidbits.com

Overview
Severe thunderstorms capable of producing damaging wind gusts, hail, frequent lightning and even a few tornadoes are likely late today/early tonight in parts of the Mid-Atlantic region and Northeast US.  In addition to these particular weather threats, there are signs that “training” of thunderstorms may take place in some sections later tonight where multiple storms track over the same areas potentially leading to excessive rainfall amounts and localized significant flash flooding issues. Yesterday’s severe weather outbreak was focused in areas to the south of the PA/MD border, but today’s threat should be highest from eastern Pennsylvania to southern New England.  This overall very wet weather pattern looks like it will continue right into next week for much of the eastern third of the nation. 

 High-levels of "available potential energy" predicted by the 13Z HRRR in the I-95 corridor at 4PM; courtesy NOAA/EMC, tropicaltidbits.com

High-levels of "available potential energy" predicted by the 13Z HRRR in the I-95 corridor at 4PM; courtesy NOAA/EMC, tropicaltidbits.com

Details
A strong cold front over the Great Lakes will move southeastward today and reach the local area during the evening hours. With daytime heating and increasing humidity levels across the area, instability will develop ahead of the approaching frontal system during the afternoon hours. Model forecasts for later today suggest “potential energy” levels of sufficient quantities to develop and maintain severe thunderstorms in parts of the Mid-Atlantic region with possible large hail, damaging wind gusts to 70 mph, and even a few isolated tornadoes.   Storms are likely to first develop this afternoon across northern Pennsylvania and southern New York and then move southeastward towards the DC-to-Philly-to-NYC corridor with the greatest chance for severe weather north of the PA/MD border although it certainly can make it as far south as the Baltimore and DC metro regions.

 13Z HRRR forecast map at 7PM (left) and midnight (right) with indications of a "squall line" at the earlier time and then possible "training" of thunderstorms in the overnight hours; courtesy NOAA/EMC, tropicaltidbits.com

13Z HRRR forecast map at 7PM (left) and midnight (right) with indications of a "squall line" at the earlier time and then possible "training" of thunderstorms in the overnight hours; courtesy NOAA/EMC, tropicaltidbits.com

As the storms progress southeastward early tonight, there may be some re-development on the upstream (west-to-southwest) side of a squall line and this could result in “training” of storms where multiple storms travel over the same general regions.  If this indeed takes place, rainfall amounts can pile up in a hurry on the order of several inches leading to significant flash flooding issues.  By tomorrow, this cold front will stall out just to the south and east of here and it will turn much cooler on Wednesday in the DC-to-Philly-to-NYC corridor.

 Excessive rainfall amounts predicted by NOAA over the next seven days given the combination of tropical moisture and close proximity of a frontal boundary zone

Excessive rainfall amounts predicted by NOAA over the next seven days given the combination of tropical moisture and close proximity of a frontal boundary zone

Excessive rainfall threat continues into next week
With the frontal system remaining in close proximity, additional showers and thunderstorms are likely from mid-week through the weekend and even into the early part of next week.  To make matters worse, tropical moisture from the Southeast US will push northward and get intertwined into our overall wet weather pattern here in the Mid-Atlantic. A weak sub-tropical low pressure system will sit over the eastern Gulf of Mexico during the next few days and several waves of energy will spin off this low and lift northward along the east coast. Each one of these disturbances can result in new rounds of showers and thunderstorms for the Mid-Atlantic region through the remainder of this week and into the early part of next week.

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com