FOUS30 KWBC 090822
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
422 AM EDT Mon Mar 9 2026

Day 1
Valid 12Z Mon Mar 09 2026 - 12Z Tue Mar 10 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE LOWER MISSISSIPPI VALLEY & SOUTHEAST...

Model agreement has started to increase QPF-wise and the present
Marginal Risk area was adjusted to fit the broad pattern of
potentially heavy rainfall advertised by the 09/00Z runs of both
the HREF and REFS guidance. Precipitable water values approaching 
1.75" return somewhat northward as low level flow begins to back
and accelerate in the lower levels. It appears that enough 
moisture, instability, and effective bulk shear will be present 
near the lower level section of a frontal zone for hourly amounts 
to approach or even exceed 2 inches. Flash flood guidance has 
lowered due to heavy rainfall on Saturday and Saturday night/early
Sunday morning to partially saturated soils. However, the 
mesoscale guidance signal for 3"+ is low enough at the present time
to remain in the Marginal Risk category as any flash flooding 
impacts appear no better than isolated to widely scattered.

Bann


Day 2
Valid 12Z Tue Mar 10 2026 - 12Z Wed Mar 11 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL UNITED STATES FROM THE PLAINS TO THE SOUTHERN GREAT LAKES...

Gulf moisture gets drawn northward over parts of the central U.S. 
from Texas into the Upper Mississippi Valley and southern Great 
Lakes region in response to circulation around an upper level low 
over the Southwest U.S.. This moisture will encounter a southward 
moving cold front from the Upper Midwest and an area of low 
pressure along the front over Kansas or Nebraska on Tuesday. This 
combination should result in convection being capable of producing 
some heavy rainfall rates that results in run off or flooding 
concern across the southern & central Plains and somewhere in the 
neighborhood of the Midwest and/or Ohio Valley. The better 
instability...and higher rainfall rates...look to be over the 
southern part of the outlook area given better instability and due 
to increasingly diffluent flow aloft as the Southwestern U.S. upper
low approaches. Farther north...the concern for excessive rainfall
comes from stronger synoptic scale forcing due to the approach of 
an amplifying trough in the northern stream.

Based on increasing numerical guidance agreement from the 
09/00Z runs...felt confident enough to separate the one Slight 
risk area from yesterday's Day 2 outlook into two Slight risk areas today.

Some places within each Slight Risk received heavy to excessive 
rainfall in the past few days which has added to soil saturation 
across portions of the Midwest, the Ohio Valley and the Mid-
Mississippi Valley. Not enough confidence yet to expand the area
deeper into the Midwest/Ohio Valley due to the lack of any notable mid-
level capping but the possibility remains. 

Bann


Day 3
Valid 12Z Wed Mar 11 2026 - 12Z Thu Mar 12 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN MISSISSIPPI VALLEY/SOUTHEAST UNITED STATES AND PARTS 
OF THE COASTAL PACIFIC NORTHWEST...

...Southern US...
Maintained a Marginal Risk area over portions of the southern 
states as an upper low propagates eastward on Wednesday. The upper 
level support for heavy rainfall should be waning with time as the
upper low undergoes slow weakening and filling. Even so...enough
low level moisture will be in place as mid-level lapse rates
steepen and increases instability at the time of maximum heating.

...Pacific Northwest...
Persistent on-shore flow of deep moisture into parts of coastal
Washington and northern Oregon should result in occasional moderate
rainfall...mainly in the west face of the coastal ranges. Amounts
on the order of 2.5 inches to 3.5 inches in 24 hours is forecast
which could result in isolated flooding ot run off problems in
areas of poor drainage.

Bann
$$
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 * Origin: Capitol City Online (618:250/10)