Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
847 PM EDT Sat May 23 2026
Day 2
Valid 12Z Sun May 24 2026 - 12Z Mon May 25 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE UPPER
TEXAS COAST, SOUTHERN LOUISIANA, AND SOUTHERN MISSISSIPPI...

20Z Update...

The Slight Risk was adjusted to mimic the latest WPC QPF which
showed increased precipitation over southeast LA and southern MS.
This is due to the growing sentiment, across various guidance
members, that the closed 700mb low over the Upper TX coast will
remain slow moving and maintain a prolonged fetch of anomalous
moisture. ECMWF SATs shows a continuous >400 kg/m/s IVT fetch
(above the 90th climatological percentile) over southern LA for
much of the day. The Lower MS Valley also resides downwind of a
negatively-tilted 200-500mb trough axis that enhances vertical
ascent atop the upper troposphere. Instability will be the biggest
question mark in south-central LA, but soils have grown
increasingly saturated thanks to rainfall in recent days (and
during the day Saturday, too). The best instability should reside
just east of NOLA on north into southern MS where MUCAPE in excess
of 2,000 J/kg is expected. Rainfall rates in excess of 2"/hr are
likely in the heavier thunderstorms when accounting for >2" PWATs.
For these reasons, the Slight was expanded more into southeast LA
and southern MS.

Elsewhere, there was a change in guidance with a more expansive
area of showers and storms to the west. The frontal boundary
approaching from the Midwest is a little slower, allowing for
scattered storms to form over the eastern Corn Belt on south to
western TN. With sufficient instability present and these areas
still dealing with overly saturated soils, decided to expand the
Marginal Risk westward. In addition, the Marginal Risk was
expanded eastward to cover eastern NC and southeast VA. The
stationary front in the Southeast lifts north as a warm front on
Sunday, putting the southeast VA Tidewater region and eastern NC
squarely in the warm sector. PWs approaching 2" and MLCAPE between
500-1,000 J/kg will be more than enough to support rainfall rates
of 2-3"/hr, along with warm cloud layers as deep as 12,000ft. There
remains uncertainty in the placement of the heaviest rainfall, but
given these rates and some urbanized areas present, the Marginal
Risk was expanded to these regions.

Mullinax

---Previous Discussion---

A slow moving upper trof expected to amplify somewhat day 2 as it
pushes from eastern Texas into the Lower MS Valley. This will
likely help fire another round of convection in the vicinity of the
Upper TX coast, eastward into southern LA. At the moment, it
appears the best instability ahead of this next closed low will be
suppressed southward into the northern Gulf in the wake of the
active day 1 convection. This may support the heaviest rains being
shunted southward and off the coast day 2, as suggested by the RRFS
mean and the FV3LAM. There is still a lot of model spread, but WPC
qpf has trended south, with the heaviest offshore. Subsequently,
the previous slight risk area has been trimmed on the north end,
confined to the far Upper TX coast into southwest LA. There may be
overlap of the day 1 and day 2 heavy rain areas over the Upper TX
coast into southwest LA. However, at the moment, the risk level was
maintained as slight as there is still model spread with the day 2
heaviest qpf axis.

No significant changes made to the previous broad marginal risk
area extending northeastward from the Central Gulf Coast, across
the South and into the Southern to Central Appalachians.  Similar
to the day 1 period, there will continue to be an axis of much
above average PW values stretching across these areas, with
embedded shortwaves in the broad southwesterly mid to upper level
flow, supporting widespread scattered convection, locally heavy
rains and isolated runoff issues.

Oravec

Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt