Heavy Rain and Strong Winds: July 21 Storm Update And Flood Watch

Heavy Rain and Strong Winds: July 21 Storm Update And Flood Watch

Saturday 21 2018

The rain has has ready moved in and there is no avoiding this strong storm. The only debate now will be the track of Low Pressure and where the heaviest rain will fall. At this time it looks like the heavier rain and strongest winds in metro Baltimore will be between 8 PM Saturday and 2 AM Sunday. But that means a few hours earlier in southern Maryland and the beaches, and a little later into southern PA. But the precise track of the core Low will determine if the worst flooding will be east or west of the Chesapeake Bay.  The HRRR Model shows the worst case scenario, but the NAM 3 Km here is also pretty intense for most of the region. That is what will be tracked today.

This post is for three main points:

  1. Rain Timeline
  2. Storm Track/Heavy Rainfall
  3. Strongest Winds

I want to compare each element separately

Rain Timeline

Both models shows moderate rain increasing this afternoon and evening. The heaviest rain will reach

  • 2 PM to 6 PM: Beaches
  • 7 PM to Midnight: Central Southern Maryland/Western Bay
  • 8 PM to 2 AM: Southern PA

Radar Loop 8 AM to Noon

Here we see the developing storm and flow of rain to the north. The heavier rain is shaded yellow and orange

Radar Simulation

HRRR Model —> slider

This tracks the Low Pressure farther west

 

NAM 3 Km Model —> slider

This tracks the Low Pressure farther west

 

 

Storm Track/Heavy Rainfall

The storm track between the two high resolution models shown here is about 60 to 100 miles. The HRRR Model is farther west, bringing the heaviest rain band west of Baltimore and Washington to include Frederick. The NAM 3 Km (first to pick up on this storm hitting us hard) has the Low tracking over Ocean City and then curving northwest in the northern Delmarva to Harrisburg. That brings the stripe of heavy rain farther east of the cities. Check the estimated rain totals out here.

 

 

Even if we verify the lower end, the flooding potential is res and widespread. This may need to be expanded west depending on the track of the Low…

 

Strongest Winds

I have picked the 11 PM plot that shows the closest approach of the Low Pressure.

The HRRR Model plot fathers west brings the strongest winds over southern and central Maryland.  The NAM keeps that strongest winds along the beaches.

 

 

Sunday: Afternoon Storms May Turn Severe

The southerly flow will continue but the set up will be different. Instead of an organized larger storm, we will see clusters or cell develop in the afternoon. These will push south to north and some may turn severe

 

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July 21st, 2018|Tags: , , , , |