Flood Watch Expanded Into Central Maryland

Wednesday September 22

Heavy rain is on the way. We’ve already discussed that, and perhaps you have already had one of those heavy showers move by your place.

The Flash Flood Watch has been expanded through central Maryland for tonight through Thursday. This has been expected, and includes all counties in Maryland west of the Chesapeake Bay.

Flash Flood Watch

Counties in Maryland added to the Watch include: Carroll, Howard, Montgomery, Baltimore, Harford, and Cecil.

Basically along and west of I-95.

Among the weather discussion today, a few things have jumped out:

“A low level jet stream is pumping in tropical moisture”

Jet Stream This Evening

Significant upslope in the mountains with training convection due to strong unidirectional flow.

Rising air in the mountains is enhancing the cloud development.

“A steady wind at cloud level is helping to bring in more moisture”

Infrared Stellite Loop

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Click to see: Live Radar And Weather Maps

“Rain falling over the same areas may produce 3 to 5+ inches of rain in the mountains”

Excessive Rainfall Risk

This map is for Wednesday. The heavy rain will shift east Thursday, to include metro areas. This is when local 1 to 2+ inches may fall.

Rainfall Potential —> slider

Compare three model forecast maps

Afternoon Weather Map

Timing The Rain…

This is a slow moving front. Rain showers have developed ahead of the main event, but the front itself is now expected to cross central Maryland/south central Pennsylvania Thursday Morning.

Rain Animation ECMWF Model

Wednesday Evening To Friday Morning

While the bulk affects central areas Thursday morning and early afternoon, the front will finally cross the coast Friday morning.

FROPA- Frontal Passage

8 AM Thursday- NAM 3 Km