FOUS30 KWBC 061600
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1100 AM EST Fri Mar 6 2026

Day 1
Valid 16Z Fri Mar 06 2026 - 12Z Sat Mar 07 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE LOWER MISSISSIPPI VALLEY, INCLUDING THE ARKLATEX...

...16Z Update...
Minor adjustments overall made to the overnight forecast thinking.
Based on the 12Z HREF suite, the inhereted Slight Risk was 
extended slightly northward into the Missouri Ozarks which 
partially overlaps with an area of recent heavy rainfall. 
Otherwise, the Marginal Risk in the Ohio Valley was removed as both
the HREF and RRFS suggest the threat of exceeding an inch of rain 
(around the 1 HR FFG for the area) is below 5%. 

Asherman

...Previous Discussion...

...ArkLaTex to Lower Mississippi Valley...

Highly amplified pattern across the western United States will
shift eastward today and tonight setting up a broad axis of
convective development downstream over the Southern Plains up into
the Midwest to the Mississippi Valley. Instability and moisture
being drawn northward from the Gulf gets in place ahead of an
approaching cold front that provides a focus for another round of
storm later today and tonight with heavy rainfall expected in a
well defined warm sector situated from the eastern half of Texas
into the Missouri Valley where precipitable water anomalies
pushing 2 or 3 standard deviations above normal for the time frame
should be in place. Ensemble bias corrected QPF from 06/00 remained
over 2 inches across the ArkLaTex with the convergence signal
strongest over the three-state region as the nocturnal Low Level
Jet is forecast to nose into the area promoting the most favorable
axis for organized convection and eventual cell mergers after
sunset. The previously issued Slight Risk was maintained with only
minor adjustments based on latest model guidance.

...Midwest...

Amplified pattern to the west will have impacts on the evolution
and related threat of excessive rainfall over the Upper Midwest as
a wavy boundary to the south lifts to the north as a warm front
later today and tonight. The combination of vertical wind shear and
the approach upper level shortwave will result in a deepening
surface low over Kansas later today which draws increasing moisture
and instability into the Upper Midwest later today and
tonight....resulting in convection capable of producing heavy 
rainfall over the Missouri River Valley and points east. Any risk 
for excessive rainfall should be offset a bit by quick storm 
motion. 00Z HREF and RRFS both ramp up the probability for 1 inch 
of accumulation early in the Day 1 period which moves off to the 
northeast and dissipates this morning...followed by redevelopment 
this evening in central and northeast Iowa. Provided an apron 
around this area to account for uncertainty in where the convection
redevelops. As a result...the previous Marginal risk was largely 
maintained with only minor adjustments.

Bann

Day 2
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...

The previously issued Slight risk across portions of Texas into
Mississippi was maintained given a consistent signal in the
numerical guidance of a corridor of heavy rainfall. 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. However, the 06/00Z guidance from both the
HREF and RRFS still maintain be an opportunity for some along axis
training even with some southward propagation. The HREF probability
was notably more aggressive with its neighborhood probabilities for
1 inch per hour rate than was the RRFS...especially at the start
of the Day 2 period but eventually converge on similar values on
Saturday afternoon. At that point the RRFS begins to increase
probabilities of 1 and 2 inch probabilities ahead of the front as
it sags southward (after the last forecast hour from the HREF). Thus
think there is enough going for this event to justify maintaining a
broad Slight risk with this update.

A Marginal risk was also extended as far north as western NY.
Plenty of moisture will advect northward along this corridor, with
as much as 500-1000 j/kg of CAPE as well. 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 OH Valley, and some snow pack and frozen
ground over NY...these higher rates could be enough to locally
result in excess runoff and minor flood concerns.

Bann

Day 3
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 as a cold front makes its
way southward on Sunday. Model guidance showed a corresponding
decrease in QPF and spaghetti plots from the SREF and the GEFS
maintaining a few members with probabilities of 2 inches in the 24
hour period ending at 12Z Monday from eastern Texas eastward. This
reflected a downward trend in the deterministic QPF. During the
latter half of the period...Gulf moisture starts to return
northward over southwestern Texas later in the period...so made a
westward expansion of the Marginal risk area.

Bann
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