FOUS30 KWBC 131126
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
726 AM EDT Sat Jul 13 2024

Day 1
Valid 12Z Sat Jul 13 2024 - 12Z Sun Jul 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF 
THE EASTERN SEABOARD, UPPER MIDWEST, PINEY WOODS, AND FOUR CORNERS REGIONS...

...Missouri... Early morning convection has been more expansive 
than earlier guidance, and will likely continue for the first 
several hours of the D1 period. See MPD#614 for more information. 

...Eastern Seaboard...

In coordination with PHI/Mt. Holly, NJ forecast office, the 
inherited Slight was downgraded to a Marginal with this forecast 
update. A slow-moving front and disturbance located along the east 
coast will gradually move north this morning. Associated showers 
and storms will continue today, but the guidance has come down 
somewhat on the amounts as the primary area of rain shifts 
northeast more quickly this afternoon. There should be widely 
scattered instances where a few storms may produce an inch or 2 of 
rainfall through this morning, but given both antecedent dry 
conditions and general disorganization of the rainfall, expect only
isolated instances of flash flooding today. The disturbance will 
drift further east away from the coast by tonight, largely ending 
the flash flooding threat.

...Upper Midwest...

Showers and storms may train/backbuild from Minnesota south and
east into the Chicagoland region today as southwesterly flow of
moisture runs into storms tracking southeastward today. There is
considerable disagreement as to where these storms will track and
how much training will occur, with a broad ensemble consensus
suggesting 2 separate lines of fairly fast moving storms moving
across the region today. Given the urbanization on the western
shore of Lake Michigan and some southward trending...expanded the
Marginal to include the Chicagoland region.

...Piney Woods of Southeast Texas...

Widely scattered but slow moving storms may cause isolated flash
flooding in portions of southeast Texas again later today due in
part to some sensitivity of the soils post-Beryl.

...Four Corners...

Monsoonal moisture may cause slow moving storms to form along the
terrain which may cause isolated flash flooding from the Mogollon
Rim over to the Sangre de Cristos of central NM. There has been
little change in the overall coverage and intensity of the storms
in the guidance in the Marginal Risk area, but a notable decrease
further south into southern Arizona, so the Marginal Risk was
trimmed a bit.

Wegman

Day 2
Valid 12Z Sun Jul 14 2024 - 12Z Mon Jul 15 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF 
THE NORTHERN PLAINS AND THE GREAT LAKES AS WELL AS FOR PORTIONS OF 
THE SOUTHWEST...

...Northern Plains and Great Lakes...

On Sunday the axis of rainfall across the region will shift a bit
towards the east across the Great Lakes on the periphery of the
building ridge across the middle of the country. Organization of
the storms remains poor in the guidance, so any areas where a
little training may result in higher rainfall totals remains
obscured. Thus, while a small area of Slight risk impacts may be
embedded in the Marginal risk region, uncertainty is too great to
separate out the area of that risk at this time. Further, since
there's good agreement that there will be more rain in portions of
the area (Wisconsin) today, should higher rainfall totals occur
then those areas may be able to be highlighted with a Slight with
future updates.

...Southwest...

Atmospheric moisture will increase across the region as compared to
today by Sunday. This will result in both an increase in coverage
and intensity of the resultant storms across this area today. That
said, the trends in the guidance have been flat. There's somewhat
higher certainty that storms will concentrate along the Mogollon
Rim of Arizona, so that region is in a higher-end Marginal with
potential for an upgrade to a Slight with future updates. Meanwhile
the signals for heavy rain have decreased in far southern Arizona.

Wegman

Day 3
Valid 12Z Mon Jul 15 2024 - 12Z Tue Jul 16 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF 
THE UPPER GREAT LAKES AND FOUR CORNERS REGION...

...Upper Great Lakes...

"Ridge running" storms will continue across the upper Great Lakes
again on Monday. The storms should be fast-moving which will
greatly limit the flash flooding potential, but antecedent
conditions after potentially multiple afternoons of storms for some
areas may support a future Slight risk for this area. Nonetheless
there remains too much uncertainty for such an upgrade at this
time.

...Four Corners...

Monsoonal flow may shift a little bit east away from northwestern
Arizona and southern Utah and focus closer to the AZ/NM border
while extending north across much of central Colorado. Storms that
form will once again likely be tied to the terrain, which with burn
scars may result in locally significant flash flooding if the
storms are strong enough and remain stationary, but with still
minimal organization there is not enough certainty to upgrade to a
Slight at this time, but the potential is there for future updates.

Wegman
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