Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
339 AM EDT Sun May 11 2025
Day 3
Valid 12Z Tue May 13 2025 - 12Z Wed May 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID-ATLANTIC...

The slow-moving upper low and occluded surface low will continue
to move north, triggering showers and storms across the Mid-
Atlantic on Tuesday. A deep stream of moisture ahead of the system
will push PWAT values above 1.5 inches, and there will be enough
instability (MUCAPE > 1500 J/kg) across portions of North Carolina
and Virginia to support high rain rates in showers and storms. It
seems likely that rain rates could reach or exceed the 1-2 inch per
hour FFGs in Central Virginia (especially in upslope and urban
areas), and possibly the 2.5-3 inch per hour FFGs in southern
Virginia and northeastern North Carolina as well. Models have been
picking up on a faster trend with this system, but there is some
uncertainty in how fast or slow it will move. This will affect the
location of the heaviest rainfall in the warm sector and
along/ahead of the cold front. The general consensus is for the
highest totals to fall over Virginia and northern North Carolina,
but some models are advancing heavy rain even further north.

To account for the faster trend in guidance, the inherited Slight
and Marginal Risk areas from the previous Day 4 ERO have been
shifted north, with the Marginal extending up into portions of
Pennsylvania and New Jersey. The southern edge of the Slight Risk
area has been trimmed up to match QPF trends, and it was extended
east to coastal Virginia where urban areas tend to be more
sensitive to heavy rain and flooding. It's possible that the
location of the Slight Risk will shift in future updates as the
speed of the system becomes more certain.

Dolan

Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt