Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 PM EDT Mon May 10 2021
 
Day 3
Valid 12Z Wed May 12 2021 - 12Z Thu May 13 2021 

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE GULF 
COAST REGION...

21Z Update...Models still in agreement on sending the deepest 
moisture/instability out over the Gulf during this time period. No 
significant changes made to day 3 QPF, thus no changes made to 
previous Marginal Risk area. 

Chiari/Campbell

Previous Discussion...

The threat of heavy to excessive rainfall will be lingering into 
Wednesday along the Gulf coast given a moist airmass in place and 
the presence of a front to help focus storms.  However, the 
approach and passage of a broad, low amplitude synoptic-scale 
trough should usher the deepest moisture/instability out over the 
Gulf ahead from west to east.

Before that happens, a corridor of precipitable water values in 
excess on 1.75 inches should extend from coastal regions of the 
South Texas to the Upper Texas coast and eastward into portions of 
Mississippi/Alabama and Georgia. Given the resulting instability 
and moisture convergence along the front, scattered storms capable 
of producing heavy rainfall will linger until the front and 
associated upper level trough moves through.  With decreasing 
precipitable water values and a less uniform low-level flow 
pattern, thinking is that rainfall amounts/rates will not be as 
high as in previous days.  In due time, any convection should be 
moving into areas which have higher FFG.  Thus thinking is that a 
Marginal Risk should be sufficient for now...although later shifts 
can evaluate the need for a Slight Risk area given a clearer look 
at how the pattern evolves.

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