FOUS30 KWBC 160825
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
425 AM EDT Sun Mar 16 2025

Day 1
Valid 12Z Sun Mar 16 2025 - 12Z Mon Mar 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE EAST COAST FROM SOUTH CAROLINA THROUGH SOUTHERN NEW ENGLAND, 
AND FOR PORTIONS OF NORTHERN CALIFORNIA AND SOUTHWEST OREGON...

...East Coast...

A progressive cold front and negatively tilted longwave trough 
will traverse much of the East Coast today, as the upper-level 
pattern becomes a bit less amplified (shortwave over the Southeast 
cutting off from northern/polar stream with ridging building over 
central CONUS). Convection in association with the front looks to 
generally result in areal average totals of 1.0-1.5" (per latest 
WPC QPF), but the latest CAMs (00z HREF suite) suggests relatively 
high odds (30-50%+) for localized totals in excessive of 2" (per 
40-km neighborhood probabilities). The inherited Marginal risk area
was expanded a bit to generally encompass where 2" exceedance probs
are 30%+ (but excluding FL and much of southeast GA, as FFGs are 
particularly high here). While this is a lower-end Marginal risk 
for most places, the risk is maximized over coastal NC where 3" 
exceedance probs are 40-60%. 

...Southwest Oregon into Northern California...

A relatively weak and narrow atmospheric river (AR) will continue
to bring moderate to heavy rainfall to the OR/CA coastal border
region with additional forecast localized totals today of 2-5".
Most of this rainfall will be spread out over a 12-18 hour period
with peak rates staying under 1"/hr due to a lack of instability
(though 1"/hr rates may be reached for a brief period near the
CA/OR border along the coast where the HREF indicates MU CAPE up to
nearly 500 J/kg). Maintained the inherited Marginal risk, though a
future targeted upgrade to Slight risk remains possible (depending
on the evolution of rainfall this morning and any upticks in QPF in
the 12z HREF suite).

Churchill


Day 2
Valid 12Z Mon Mar 17 2025 - 12Z Tue Mar 18 2025

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

Churchill


Day 3
Valid 12Z Tue Mar 18 2025 - 12Z Wed Mar 19 2025

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

Churchill

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