Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1152 AM EDT Mon Apr 27 2026
Day 3
Valid 12Z Wed Apr 29 2026 - 12Z Thu Apr 30 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM CENTRAL AND
SOUTHEAST TEXAS TO THE CENTRAL GULF COAST...

The threat of excessive rainfall and flash flooding seems to be
increasing in the most recent set of model guidance, due to a
continuation of strong instability and the arrival of a plume of
unusual amounts of mid-level moisture. Backward trajectory
analysis indicates that moisture around 3km above the surface
originated in the tropical central Pacific, advected into the
southern U.S. by an anomalously strong subtropical jet (300mb winds
around 60+ knots) extending about 6000 mi. from the Marshall
Islands, to just south of Hawaii, all the way to Texas. This should
push PW values over the whole region above 1.7 inches, and above 2
inches in portions of Texas, which is quite unusual. For instance,
a 2+ inch PW has only been observed on an upper air sounding at
Corpus Christi 3 times prior to May 1st (36 year period of record;
since 1990). Although model QPF is not exceptionally high at this
point, that may largely be a function of a lack of high-res
guidance from convection-allowing models. The environment (when
also considering strong bulk shear to around 50 knots) would favor
organized thunderstorms with very high rain rates, potentially in
excess of 2 inches per hour. Given that the previous outlook had
probabilities below 5 percent, the main change with this update is
to introduce a Marginal Risk, but a further upgrade may be
required, especially across parts of Texas.

Lamers

Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt