Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
335 PM EDT Fri May 9 2025
Day 3
Valid 12Z Sun May 11 2025 - 12Z Mon May 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS
OF THE SOUTHEAST...

20Z Update: The primary change for the forecast was a general
expansion of the SLGT risk area further northeast into SC to
account for the heavier rainfall threat protruding inland given
the strong uni-direction component advecting rich Gulf moisture
poleward between the closed upper reflection over the Mississippi
Valley and the surface ridge over the Western Atlantic. Cold front
from the north will also hit a roadblock as it motions south,
likely becoming more quasi-stationary across North GA and the SC
Piedmont before being pushed back as a warm front. This will likely
coincide with a stronger low-level convergence signature up into
those areas by the afternoon and beyond on Sunday into Monday.
Considering the nature of the persistent moisture advection regime
and enhanced theta_E pattern, expecting widespread thunderstorm
development with rates likely reaching between 1-3"/hr within the
heaviest cores. Antecedent soil conditions should moisten with the
day prior, so the overlap will create a better threat for natural
runoff, not including the urban threat that is customary in these
setups. The previous SLGT risk was maintained with those expansions
to reflect the latest trends.

Kleebauer


..Previous Discussion..

A wave of upper level energy will pivot around the upper low across
the Southeast, sparking another wave of convection from the Gulf
Coast to the Southeast Atlantic Coast. Models are showing a more
organized area of surface low pressure moving into the Southeast
with significant rainfall totals on the eastern side. Widespread
totals of 1.5-2.5 inches are expected with locally high amounts
above 3 inches. Considering this will be the second day in a row
with heavy rainfall in the Southeast, areas with saturated soils
from the day before may be slightly more prone to flood impacts
with additional heavy rain on Sunday. The most favorable flash
flood conditions will be across North Florida and southern and
central Georgia where 1000+ J/kg MUCAPE and 30+ knots of effective
bulk shear with support organized convection. Additionally,
precipitable water values in excess of 1.5 inches will support
efficient rain rates in strong thunderstorms. A Marginal Risk area
is in effect for much of Alabama, Georgia, South Carolina, and
North and Central Florida, with an embedded Slight Risk area over
North Florida and southern and central Georgia.

Dolan

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