FOUS30 KWBC 220733
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Sat Mar 22 2025

Day 1
Valid 12Z Sat Mar 22 2025 - 12Z Sun Mar 23 2025

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

Wegman


Day 2
Valid 12Z Sun Mar 23 2025 - 12Z Mon Mar 24 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON STATE AS WELL AS FOR PORTIONS OF THE LOWER
MISSISSIPPI AND TENNESSEE VALLEYS...

...Western Washington State...

The trailing cold front of a low moving into British Columbia will
move into the Pacific coast of Washington State on Sunday. The
front will usher in a period of strong westerly fetch off the
Pacific. This will keep a steady supply of moist upslope flow into
the Olympics and Washington Cascades. 3 to 5 inches of rain are
expected into those ranges Sunday and Sunday night. The inherited
Marginal Risk was largely unchanged, with the greatest chances of
isolated flash flooding on the west facing slopes of those ranges.
The Skokomish River remains the river with the highest potential
for flooding given its low thresholds for flooding. Further, the
soils are already near saturation in this area given the multiple
rounds of rain the area has seen over the last several weeks, so
most of the rainfall expected should convert to runoff.

...Portions of the Lower Mississippi and Tennessee Valleys...

A slow-moving cold front will move southeastward across portions of
the Mid-South Sunday afternoon through Sunday night. The front will
be supported by an LLJ of Gulf moisture, which will be aligned
southwest to northeast, or parallel to the frontal interface. This
will support some training convection, despite only modest Gulf
moisture. The potential for some training over areas that got heavy
rain a few days ago could lead to isolated instances of flash
flooding, especially in low-lying flood-prone areas and urban
areas. FFGs are quite high across the Mississippi Valley but
decrease markedly across the Tennessee Valley due to recent heavy
rain. However, the further north you go, the less instability there
will be, which will effectively cap how strong the storms will be.
The front will have enough forward speed to also limit the
potential for training as well. Given all of these above factors,
there have been few changes to the ERO for this area.

Further northeast into West Virginia, the latest forecast rainfall
has come down significantly from previous forecasts. Due to a lack
of instability. the rainfall is not expected to remain heavy for
long as individual cells track northeastward along the front.
Despite very low FFGs, expect much of the rainfall in this area to
be stratiform, greatly limiting the flash flood potential, despite
some topography the rain will have to overcome to cause flooding.
With the broader forecast now under a half inch in much of northern
West Virginia, the inherited Marginal Risk in this area has been
downgraded.

Wegman


Day 3
Valid 12Z Mon Mar 24 2025 - 12Z Tue Mar 25 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
CENTRAL GULF COAST...

The front that moved across the Lower Mississippi Valley on Sunday
will continue to the Gulf Coast on Monday before stalling. There
remains some potential for instability and modest moisture (by Gulf
Coast standards) to support heavy rainfall from training storms,
but the primary flash flooding threat will be in the urban areas
from New Orleans east through Pensacola and the Florida Panhandle.
The inherited Marginal Risk area was trimmed on the northern end
where high FFGs and a meager expected rainfall should preclude any
flash flooding concerns into interior southern Alabama and Georgia. 

Wegman

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