FOUS30 KWBC 220909
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
509 AM EDT Fri May 22 2026

Day 1
Valid 12Z Fri May 22 2026 - 12Z Sat May 23 2026

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL OVER THE UPPER
OHIO VALLEY AND THE SOUTHERN APPALACHIANS...

Shortwave energy embedded in broad southwesterly mid to upper
level flow from the western to central Gulf Coast, northeastward
through the TN/OH Valleys will persist through the upcoming day 1
period. These height falls/broad diffluent upper flow will enhance
uvvs in a large region of much above average PW values/anomalous
850-700 mb moisture flux, 2 to 2.5+/2-3+ standard deviations above
the mean respectively from the Gulf Coast northeastward into the
Ohio Valley. There is fairly good model consensus for the potential
for widespread moderate to heavy rainfall total in this anomalous
PW axis day 1. Simulated radars suggest cells will be fairly
progressive to the northeast. However, with potential for short
term training of cells and/or repeat rounds of convection, there
will be potential for runoff issues. Slight risk areas maintained
over the Upper OH Valley from northeast KY into southern OH where
FFG values are relatively low, and in the upslope region of the
Southern Appalachians from far northeast GA into the Upstate of SC
and western NC where heavy precip likely to focus in the region of
southerly low level flow. The slight risk areas fit well with the
axes of the HREF and RRFS means 2 and 3"+ probabilities.

Across the Southern Plains, a marginal risk area was introduced for
potential for additional convection Friday evening into the early
hours of Saturday. Additional shortwave energy expected to push
eastward into the Southern High Plains, supporting potential for
some organization to the associated convection late Friday into the
early hours of Saturday. Low confidence on details, with isolated
runoff issues possible where convection become organized.

Oravec


Day 2
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...

Additional shortwave energy expected to move from far northeast
Mexico into southern and eastern Texas early Saturday, likely
setting the stage for another round of organized convection.
Building instability early Saturday, Mucape values reaching
2000-300 j/kg ahead of these height falls, in an axis of PW values
1.5-2.5 standard deviations above the mean, will support potential
for an organized line of convection to push across eastern and
southern TX Saturday morning into afternoon. The previous risk
areas were narrowed to better reflect the latest model qpf output
and the max RRFS 2 and 3"+ probability axes for the day 2 time period.

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 2. 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 fairly high probabilities for
1"+/hr rainfall totals Saturday afternoon, supporting potential for
isolated runoff issues.

The marginal risk was also expanded northward from the previous
issuance into far eastern KS and large portions of MO to cover
areas the RRFS, GEM and FV3LAM are showing heavy rainfall totals day 2.

Oravec


Day 3
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 SOUTHERN LOUISIANA...

A slow moving upper trof expected to amplify somewhat day 3 as it
pushes from eastern Texas into the Lower MS Valley. Similar to the
day 2 and day 3 period, there will continue to be an axis of much
above average PW values stretching from the Gulf Coast
northeastward into the Southeast/Southern to Central Appalachians.
There is a lot of spread day 3 with the QPF details, but still a
signal for widespread moderate to heavy rain potential in this
anomalous PW axis. A slight risk was maintained from the Upper TX
coast into southern LA, close to the WPC and NBM qpf max. This
covers the urban areas from Houston to New Orleans.

The marginal risk area was extended farther northeast through the
Southern to Central Appalachians where scattered convection likely
in the anomalous PW axis, supporting locally heavy rainfall
amounts and potential for isolated runoff issues.

Oravec
$$
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