Mesoscale Precipitation Discussion 0535
NWS Weather Prediction Center College Park MD
817 PM EDT Fri Jun 27 2025

Areas affected...Northwest Georgia, Northern Alabama

Concerning...Heavy rainfall...Flash flooding possible

Valid 280016Z - 280430Z

Summary...Clusters of showers and thunderstorms will continue to
drift across Georgia and Alabama through the next several hours.
Rainfall rates may pulse up to 2-3"/hr at times during collisions,
potentially leading to instances of flash flooding.

Discussion...An impressive cluster of thunderstorms has developed
over northern GA this evening, while a secondary cluster of
slightly less intensity is drifting northward over central AL.
These thunderstorms are blossoming despite a weakly forced
environment in response to robust thermodynamics characterized by
PWs of above 1.75 inches overlapping MLCAPE of 2500 J/kg. Despite
modest ascent and negligible shear, leading to pulse type
convection, the robust environment is supporting rapid updraft
growth on outflow boundaries and during storm mergers, resulting
in the clusters currently analyzed on the regional radar mosaic.
Radar-estimated rainfall rates have been extreme in northern GA,
more than 2.5"/hr, leading to rainfall of more than 2 inches in
the past hour at some of the local mesonet stations, and multiple
FFW issuances from WFO FFC.

The CAMs are struggling to handle the coverage of convection this
evening, leading to lower than typical confidence for the next few
hours. Although it is likely that convective overturning and a
loss of daytime heating/destabilization should result in a gradual
downturn of thunderstorm activity (coverage and intensity), the
environment for NW GA and northern AL appears favorable for a few
more hours of thunderstorms with intense rainfall rates, despite
minimal agreement in the CAMs about coverage or placement of
convection. Multiple outflow boundaries noted on the national
radar composite are all functioning as initiation points for
additional cells, and these may merge over northern AL. Where this
is progged to occur, MLCAPE is well over 2000 J/kg, and mean 0-6km
winds are just 5 kts with chaotic and collapsed Corfidi vectors.
This suggests that as storms develop along these boundaries, or
due to storm mergers, they will continue to support impressive
rainfall rates for which the HREF suggests have a 10-20% chance of
exceeding 2"/hr, leading to 15-min rainfall that may reach 0.75"
according to the HRRR (3"/hr rates). The slow and chaotic motion
of these will cause some places to get repeating rounds or a
longer duration of rain, causing as much as 3" of rain in a few
areas.

0-40cm soil moisture across much of AL and NW GA is saturated
above the 95th percentile, leading to FFG that is as low as
1.5-2"/3hrs, especially over northern AL. The intensity of the
anticipated rainfall, combined with the slow motion of developing
storms, could exceed these thresholds through around 04Z leading
to instances of flash flooding.

Weiss

ATTN...WFO...BMX...FFC...HUN...MEG...

ATTN...RFC...ALR...ORN...NWC...

LAT...LON   34908671 34808519 34558399 34098355 33358340
            32758353 32538403 32528487 32878597 33288754
            33528795 34208832 34898810