FOUS30 KWBC 070830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
330 AM EST Sat Mar 7 2026

Day 1
Valid 12Z Sat Mar 07 2026 - 12Z Sun Mar 08 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF 
THE SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY...

Maintained the Slight risk area from the Southern Plains into the 
Lower Mississippi Valley and the Upper Texas coast...with an 
expansion that effectively brought the Slight Risk area to the 
Upper Texas coast and nearby Louisiana given the 07/00Z HREF and 
RRFS probabilities for 24 hour rainfall 2-inch and 3-inch 
thresholds. There were even a few neighborhood probabilities 
exceeding 10 percent at the 5 inch threshold. Of course the actual 
extent and magnitude of the flash flood risk remains a bit 
uncertain relating to how quickly activity propagates off to the 
south and east. Some guidance supports a rather quick southward 
propagation of convection, which could keep the flash flood risk 
more isolated in nature. The HREF guidance tended to side with the 
faster solution and the RRFS was slower and was more aggressive 
with its probabilities for 1- and 2-inch per hour rates. At this
point...tended to favor the HREF guidance and associated models 
although can not entirely rule out the faster solutions. 

A Marginal risk surrounding the Slight Risk area extended north and
east as far as western New York. There should be plenty of moisture
advectiving northward along this corridor, with as much as 
500-1000 j/kg. Thus while areal averaged rainfall is not that 
impressive, there will be an opportunity for locally heavy rates. 
With saturated conditions over portions of the Ohio Valley, and 
some snow pack and frozen ground over New York...any enhanced
rainfall rates could be enough to result in isolated/locally excess
runoff and minor flood concerns.

Bann


Day 2
Valid 12Z Sun Mar 08 2026 - 12Z Mon Mar 09 2026

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

Deep moisture...instability and the risk of excessive rainfall 
should be confined to a shrinking area south of an approaching 
cold front on Sunday. Model guidance showed a corresponding 
decrease in QPF and spaghetti plots from the SREF and the GEFS 
maintaining a few members kept neighborhood probabilities of 1 inch
or greater confined from Louisiana into Georgia with greatest 
clustering from southern Mississippi into central and southern 
Alabama with QPF spaghetti plots showing few members at 2 inch 
amounts in 24 hours from either the SREF ir GEFS. In this portion 
of the Marginal risk...there was good agreement between WPC and the
CSU machine learning first-guess ERO. The WPC Marginal Risk area 
extended west along the Louisiana and Upper Texas coast if 
deference to the HREF and RRFS runs which lingered some 1+ in per 
hour rainfall along the coast and even some 2 inch per 6 hour 
lingering through at least 08/18Z. In addition...Gulf moisture 
starts to return northward over southwestern Texas later in the 
period...also supporting a westward expansion. 

Bann


Day 3 Valid 12Z Mon Mar 09 2026 - 12Z Tue Mar 10 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST UNITED STATES...

The front which had been moving from west to east in the Day 1 and
Day 2 period will slow its forward motion and become oriented along
a west to east axis on Monday and the start to inch northward
Monday afternoon and Monday night. There is a wide range of
solutions in where convection could fire along that boundary which
limits confidence. However...confidence is higher in the occurrence
of showers and thunderstorms occurring rather than details of where
that could happen given precipitable water values approaching 1.75
inches ready to to be lifted isentropically above the front as low
level flow becomes southerly. The area should become better focused
in subsequent outlooks.


Bann
$$
--- SBBSecho 3.28-Linux
 * Origin: Capitol City Online (618:250/1)