Subj : HVYRAIN: Excessive Rainfa
To   : All
From : Mike Powell
Date : Fri Apr 11 2025 09:17:00

FOUS30 KWBC 110800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Fri Apr 11 2025

Day 1
Valid 12Z Fri Apr 11 2025 - 12Z Sat Apr 12 2025

....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC...

A slow-moving, amplifying upper level trough parked over the
eastern half of the country will direct a southerly jet streak
along the coast. This jet streak will work to cause the trough to
become more negatively tilted with time, though it will really be
neutrally tilted. Regardless, the jet streak combined with the cold
air in the trough and a developing upper-low-esque circulation in
the upper levels will support the development of a slow moving
coastal low along the Carolinas this morning. As divergence
increases and the low continues to pick up Gulf Stream moisture,
the precipitation shield will expand over much of the Delmarva west
to the I-95 corridor. For most areas, this will mean a prolonged
period of steady rainfall starting this morning and continuing well
into Friday night.

Cool air will be a feature of this low, so much of the rain will be
a windy, cold rain. This does not favor much in the way of
convective activity, which will limit rainfall rates. Any upper
level instability will remain over VA and NC, with little getting
any further north than the DC Metro. Given the lack of instability
and ongoing longer-term drought, and the eastward shift in the axis
of heaviest rainfall in the comma-head/cold sector of the storm,
the inherited Marginal Risk was trimmed out of PA and NJ due to
lack of instability, as well as trimmed out of southwest VA and
western NC. The heaviest rain is currently expected along and east
of the I-95 corridor, so it's in this area where the Marginal
remains in place. 

Wegman


Day 2
Valid 12Z Sat Apr 12 2025 - 12Z Sun Apr 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Sun Apr 13 2025 - 12Z Mon Apr 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman

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