FOUS30 KWBC 240801
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
301 AM EST Mon Feb 24 2025

Day 1
Valid 12Z Mon Feb 24 2025 - 12Z Tue Feb 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE NORTHERN
OREGON COAST RANGE INTO THE OLYMPIC RANGE AND OVER THE SOUTHERN
WASHINGTON CASCADES...

...Pacific Northwest...

A vigorous shortwave trough supporting a 985 mb surface low will
race into the coast of the Pacific Northwest tonight. Its leading
cold front will move into the Oregon and Washington coasts today
and spread inland through tonight. Upslope flow into the Olympics,
coastal ranges, and Cascades will all locally enhance the rainfall
rates...which at times may exceed an inch per hour. NASA Sport 
soil moisture imagery shows the soils across nearly all of 
Washington, Oregon, and Idaho are at or near saturation in the 
surface layer. This should allow the rainfall from the front moving
into the region today to mostly convert to runoff. Integrated 
Vapor Transport values will peak around 500 kg/ms across coastal 
Washington. These values are far from impressive, so those very 
favorable antecedent soil moisture will play a major role in the 
potential for flooding. Part of the reason for the lower IVT values
is the predominant south to southwesterly flow, which is at an 
oblique The typical urban areas, low- lying and flood- prone areas,
and narrow valleys will be at greatest risk for flash flooding, 
especially south and west facing slopes.

Snow levels will rise to as high as 7,000 ft. ahead of and through
frontal passage for southwest Washington and all of western Oregon
through the day. As colder air moves in post-frontal passage, the
snow levels will crash to around 3,500 ft area-wide. The lower snow
levels will allow much of the heaviest precipitation falling into
the mountains to remain as snow, and thus reduce the flooding risk
through the overnight. Dynamic cooling on the windward side of the
mountains may further reduce the amount of precipitation that
converts to runoff due to locally reduced snow levels.

No significant changes were made to the inherited Slight and
Marginal risk areas across the Pacific Northwest. The low is
already well-formed and will continue intensifying as it approaches
the Pacific Northwest tonight. A few very minor tweaks were made to
exclude some of the higher elevations from the flood risk areas due
to falling snow levels tonight.

...Southeast Florida...

A positively tilted trough traversing the Gulf this morning will
intensify as it becomes more neutrally tilted, thus increasing the
divergence ahead of the trough. A few persistent thunderstorms are
making their way in the general direction of the Florida Keys this
morning. The latest HRRR guidance suggests the heaviest
thunderstorms will pass south of the Marginal Risk area that covers
from West Palm Beach to Miami. Nonetheless heavy rain and potential
for training are still possible, prompting the continuance of the
Marginal Risk in this area with no changes. This remains a very
low-end Marginal Risk threat with much of South Florida in a dry
period, and should any flooding occur, it will likely be in poor-
drainage and urban areas.

Wegman


Day 2
Valid 12Z Tue Feb 25 2025 - 12Z Wed Feb 26 2025

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

Wegman

Day 3
Valid 12Z Wed Feb 26 2025 - 12Z Thu Feb 27 2025

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

Wegman

$$
--- SBBSecho 3.20-Linux
 * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (618:250/1)