Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1239 PM EST Sat Mar 7 2026

Day 1
Valid 16Z 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...

16z update:
Very little change was required with respect to reasoning and
overall 12z HREF probability forecasts. Overall RADAR/Satellite
trends suggest, a typical, slightly faster propagation which is
limiting some of the overall totals and keeping the overall
coverage of excessive rainfall and localized flash flooding on the
lower side of Slight Risk category. Yet, there remain a few signals
particularly upstream along the upwind edge, where slightly
increased instability, slightly reduced and more unidirectionally
aligned steering profiles over east-central Texas suggest a few
highly isolated but higher thunderstorm rates are possible;
suggesting higher totals.

Upstream over the mid to lower MS River Valley, the squall line is
starting to be more progressive in nature. So the best potential
for localized flash flooding will be for areas that will see the
widely scattered pre-frontal cells that move more northeast ward
parallel to the squall-line; intersect or merge as the line goes
through resulting in small localized maxima of 2-3" totals in
1-2hrs. As such, the broad Slight Risk areas remain in place across
much of MS/LA/S AR and E TX; while the surrounding Marginal Risk
extends through the lower Rio Grande Valley as well as through the
Ohio/Tennessee River Valleys into the Central Appalachians into
western New York...where quick hitting 1-2" totals cross recently
saturated areas and lower FFG values.

Gallina


~~~Prior Discussion~~~
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


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt