FOUS30 KWBC 230808
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Sat May 23 2026

Day 1
Valid 12Z Sat May 23 2026 - 12Z Sun May 24 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF EASTERN
TEXAS AND WESTERN LOUISIANA...

Convection across the Southern Plains early this morning will
likely remain active in the post 1200 UTC period Saturday in an
overall favorable convective pattern over the Southern Plains into
the Lower MS Valley. There is a strong signal for widespread
heavy precip day 1 across eastern/southern TX into southern LA as
additional shortwave energy moving east northeastward from far
northeast Mexico into southern and eastern Texas early Saturday
enhances large scale uvvs. HREF and RRFS neighborhood probabilities
are high for 1 and 2"+ totals day 1 in the slight risk area.
Several of the latest CAMS, ARW2, GEM, NAMNEST and FV3LAM show
potential for a period of training of cells across the Upper TX
coast into southwest LA late morning into this afternoon. Across
these areas, the HREF and RRFS neighborhood probabilities are high
for 3"+ totals and the HREF probabilities high for 5"+ totals.
There is potential for these heavier totals affecting the urban
areas from Houston to Lake Charles, where an upgrade to a moderate
risk was considered and will be re-evaluated after viewing the 1200
UTC hi-res guidance as per collaboration with affected NWS WFOs.

No significant changes made to the marginal risk area from the
Southern Appalachians into the Southeast. Southwest mid to upper
level flow with embedded shortwaves will continue across these
areas day 1. With PW values remaining well above average, 2 to
2.5+ standard deviations above the mean, additional widespread
scattered convection will likely produce locally heavy rainfall
totals. Both the HREF and RRFS show scattered areas of fairly high
probabilities for 1"+/hr rainfall totals Saturday afternoon,
supporting potential for isolated runoff issues.

Over the Upper OH Valley region, a marginal risk area was added for
potential for additional scattered convection and locally heavy
rains into this afternoon. This additional scattered heavy precip
will fall across areas that have received 1-2" of rain over the
past 24 hours, raising soil moisture and stream flows and lowering
FFG values. Isolated runoff issues possible across these areas.

Oravec


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 INTO SOUTHWESTERN LOUISIANA...

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 3
Valid 12Z Mon May 25 2026 - 12Z Tue May 26 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE
SOUTHERN APPALACHIANS...

A small slight risk area was introduced in the vicinity of the
Southern Appalachians from north Georgia into the Upstate of SC and
far southwestern NC. A very broad region of much above average PW
values, 2 to 2.5+ standard deviations above the mean, will stretch
from the Central gulf coast, northeastward across the South,
Tennessee Valley, Southern Appalachians and into the Southern Mid-
Atlantic during day 3. Similar to the day 2 period, broad south
southwesterly mid to upper level flow with embedded shortwaves will
support additional widespread scattered convection across these
areas. While locally heavy rains are likely across a large region
in this anomalous PW axis, there is model signal for concentration
of heavy precip into the upslope regions of the Southern
Appalachians, with a small slight risk area depicted here. Included
the Atlanta metro in the slight risk area given the sensitivity to
potential urban issues. There may be additional slight risk areas
in this anomalous PW axis depicted in future updates, but low
confidence with placement at this time.

Oravec
$$
--- MultiMail/DOS
 * Origin: Project Scorpio TEST (618:250/6)