FOUS30 KWBC 150736
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
336 AM EDT Fri May 15 2026

Day 1
Valid 12Z Fri May 15 2026 - 12Z Sat May 16 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 2
Valid 12Z Sat May 16 2026 - 12Z Sun May 17 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Convection developing along a warm front draped across the Ohio
Valley could form over more sensitive urban areas on Saturday
afternoon. Soils across the Ohio Valley have sufficiently dried out
from the last round of organized heavy rain, so any flood threat
would likely be tied to the urban areas. The CAMs that cover this
time period are mostly suggesting any convection will quickly
develop into fast-moving line segments. Further, where those line
segments form is highly uncertain. Thus, the area will be monitored
for a potential future Marginal Risk, but for now uncertainty is
too great to draw one in at this time.

Wegman


Day 3
Valid 12Z Sun May 17 2026 - 12Z Mon May 18 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE UPPER MIDWEST/UPPER MISSISSIPPI VALLEY...

A digging longwave upper level trough will eject several rounds of
shortwave energy northeastward ahead of the trough from the central
Plains and into the Upper Midwest on Sunday. The nose of a stout
low-level jet will provide ample moisture for any storms that 
develop to feed on. Morning rain will douse the area as the dying 
remnants of an MCS move across the Marginal Risk area. There will 
likely be a break in any rainfall for much of the day as the 
atmosphere recharges and instability advects north ahead of an 
approaching area of low pressure. Numerous showers and 
thunderstorms will form in a line very late in the day, near 
sunset, with the storms moving sufficiently parallel/along the line
to introduce a training threat across the Marginal Risk area. Much
of the heaviest rain and the greatest flash flooding threat will 
occur Sunday evening before the surface low pressure propagates 
into Minnesota and allows the convection to have a faster push 
towards the east. The increasing forward speed of the line will 
diminish the flooding threat somewhat after midnight, through 
convection ahead of the low could still affect portions of northern
Minnesota well into the overnight. Dry antecedent soil conditions 
should generally mitigate the flooding risk, so the inherited 
Marginal Risk was left largely unchanged. Some trimming on both the
west and east sides were done to highlight the increasing 
confidence that the axis of heaviest rainfall will occur generally 
across Minnesota, potentially spilling over to adjacent areas of 
the neighboring states.

Wegman
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