Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
853 PM EDT Sun May 24 2026
Day 1
Valid 01Z Mon May 25 2026 - 12Z Mon May 25 2026
...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FROM PARTS OF THE
GULF COAST INTO THE SOUTHEAST US AND ACROSS THE UPPER OHIO
VALLEY...
01Z Update...
Changes were made to each of the Slight Risk areas but the changes
were fairly modest and done to better reflect trends in the radar
and satellite imagery. The primary threat overnight looks to be in
parts of the Upper Ohio Valley, parts of the Southeast US and
to a lesser extent across portions of Texas. Over the eastern part
of the country, Low and mid level flow was tapping deep moisture
and drawing that moisture where soils have become saturated. In
these areas...the amount of additional rainfall needed to renew
flooding or result in new flooding can be realized is fairly
minimal. In Florida...some overlap between areas of heavy rainfall
on Saturday and the where additional rainfall may occur later this
evening suggests the threat of excessive rainfall will linger into
the late evening hours.
On-going convection over Texas should be tapering off by
late evening. Until then...there is a chance that sufficiently high
rainfall rates will occur to challenge the 1- and 3-hour flash
flood guidance before the threat wanes.
Bann
16Z Update...
The forecast overall remains on track with some tweaks made to
reflect the latest trends on 12Z CAMs. Satellite shows mostly
cloudy and overcast skies across a large portion of the eastern
third of the CONUS. Large sums of anomalous moisture remain in
place in the South and into both the OH Valley and Mid-Atlantic.
However, it is where there are breaks in the clouds that will
promote a more unstable atmosphere over soils that are highly
saturated (WV, eastern OH, western PA) or near the remnant MCV in
approaching central AL that remain the focus as showing the best
potential for scattered areas of flash flooding. The Slight Risk in
the OH Valley was expanded south more into eastern KY where 12Z
HREF probabilities show low chances (20-35%) for localized rainfall
totals >3". Some zones in eastern KY sport 3-hr FFGs <2", and NASA
SPoRT-LIS 0-10cm soil percentiles are >80% in some cases.
12Z soundings are painting a busy picture in the Mid-South and Ohio
Valley. The BMX soundings show a weak capping inversion with over
1,500 MUCAPE and a 1.87" PW ahead of the approaching MCV. Farther
north, the BNA sounding is highly saturated and shows an even
weaker capping inversion. This air-mass in the TN Valley will
advect north and east into the OH Valley this afternoon, setting
the stage for highly efficient thunderstorms from central TN to as
far north and east as the central Appalachians and western PA.
Strong differential heating is also underway in central GA and
southern SC along the stationary front, which will once again be
another trigger for additional strong thunderstorms this afternoon.
Latest 12Z HREF brought QPF up in the windward side of the central
Appalachians in eastern WV, with some low-to-moderate chance
probabilities (30-50%) for >3" of rainfall this afternoon and
evening. There are also moderate chance probabilities (40-60%) for
rainfall totals >3" from the SC/GA border to the coastal plain of
NC. Localized flash flooding is possible in these areas this
afternoon and evening.
...Central TX...
A Marginal Risk was introduced for the midday update. 12Z HREF
probabilities show low chances (10-30%) for localized rainfall
totals topping 3" this afternoon and lingering into this evening.
There is a remnant mid-upper level circulation over the heart of TX
that coincides within an area seeing strong surface-based heating
and PWs approaching 1.5". Storm motions will be very slow with
ECMWF area-averaged soundings showing mean cloud-layer winds within
the Marginal Risk area less than 5 kts. The lack of shear should
make these storms more pulse like in nature and shorter in duration,
but given the saturated soils in the region (NASA SPoRT-LIS shows
>80 percentile 0-10cm soil moisture the farther south you go in
central TX) and these storms potentially packing a punch in a brief
period of time (1-hr HREF PMM precip rates up to 1.5"), the
potential exists for isolated cases of flash flooding this
afternoon and evening.
Mullinax
---Previous Discussion---
The well defined MCV moving from southeast LA into far southern MS
early this morning expected to continue to push northward day 1
across central AL and into north GA. While the organized convection
associated with this MCV may weaken early day 1, there is potential
for convection to re-fire ahead of this MCV later this afternoon
in the axis of much above average PW values, 2 to 2.5+ standard
deviations above the mean expected to stretch from the Central Gulf
Coast, northeastward through the Southern to Central Appalachians,
Southeast and Mid-Atlantic. We added a slight risk from central AL
into north GA to account for this convective potential.
Farther to the southwest...we made some significant changes to the
previous slight risk area across southern MS and southern LA. We
suppressed the slight, keeping it just for far southeast LA. The
best instability in the wake of the northeastward moving MCV will
be over the northern Gulf, suggesting the heaviest precip with the
next round of convection also being offshore. We kept the New
Orleans metro area in the slight as model consensus is for a narrow
axis of heavy rains to extend into far eastern LA.
Across FL...the marginal risk was extended south into portions of
north central to southwest FL. Model consensus is for another round
of active convection forming Sunday afternoon in a general north to
south axis. Slow moving cells will again have potential for produce
locally heavy rainfall amounts and isolated runoff issues. There
will be potential for overlap of yesterday's heavy rainfall amounts
with Sunday afternoon's. The biggest runoff threat will continue to
be in more urbanized regions.
Over the Upper Ohio Valley...added a slight risk area from
northeast KY into eastern OH, northwest WV and far southwest PA.
Both the HREF and RRFS are showing fairly high probabilities,
25-50%+ for 3 hour precip amounts exceeding FFG values this
afternoon into early evening. Favorable right entrance region jet
dynamics in the above mentioned axis of anomalous PW values will
support potential for heavy precip and localized runoff issues.
Oravec
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
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