July 6 Severe Thunderstorm Watch And Flash Flood Potential

Monday July 6 2020

The atmosphere is primed to dump a lot of rain on some areas today. The high temperatures in the 90s and dew points in the mid 70s would bee enough. But there is a boundary to our north once again trying to wobble south to act as a trigger.  But the availability of moisture and slow moving storms can lead to some areas with 3 to 4 inches of rain.

Severe Thunderstorm Watch and Flash Flood Watch

Severe Thunderstorms (pink shading): Storms may produce winds over 60 mph, large hail larger than a quarter, dangerous lightning, and an isolated tornado.

Flash Flood Watch (green): Slow moving storms may produce over 2 inches of rain per hour with totals up to 4 inches in some spots.

 

WPC Outlook

The initial risk for Flash Flooding was forming around Philadelphia. The expansion into northeastern Maryland and New Jersey.

• Chance for 1″/hour  rainfall = 90%
• Chance for 2″/hour  rainfall = 40-60%
• Isolated areas 3″+/hour rainfall

 

Storms Erupted Early

Doppler Radar Snapshot

Storms formed around metro Philadelphia shortly after noon. They seemed to blossom in place and spread Southeast. This is one of the complexes expected to drop southward into Maryland in a few hours.

 

Regional Radar Loop

 

Satellite Loop

Watch the explosion of clouds near Philadelphia. In the last few frames you can see the development of clouds moving south in New Jersey towards Delaware.

As the cloud tops grow higher, the upper level winds will steer the system to the south and southwest.

The next few hours the complex will drop into our region.

Wind Forecast

Convergence is when two opposing air forces meet up in the atmosphere. This is the boundary we will see move our way into the evening.

 

Radar Simulations –> Sliders

Nether of these models are perfect. The timing is off between them and both were slow with the Philadelphia development.

*Both DO SHOW CONVERGENCE OVER MARYLAND: That complex dropping into Maryland along with some storms moving in from the west. Where this meets up there will be extremely heavy rain that can last a couple of hours. That is where the fooding will develop.

This should continue to move south into southern Maryland tonight, and gradually weaken after the sun goes down.

HRRR Model

NAM 3Km Model