Precipitation Forecast

000
FOUS30 KWBC 170019
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
819 PM EDT Mon Mar 16 2026

Day 1
Valid 01Z Tue Mar 17 2026 - 12Z Tue Mar 17 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC AND NORTHEASTERN U.S...

Only modest changes were needed to the ongoing Marginal Risk 
across portions of the Mid-Atlantic and much of the Northeast. The 
strong cold front is crossing the Mid-Atlantic States presently,
and in random spots, showers and thunderstorms have been popping up.
Ahead of the front, a deep warm, moist air mass is being rapidly 
advected northward. Thus, storm motions have been very fast, moving
at 50-60 mph. MU CAPE was eroded by early afternoon convection, 
broadly sitting in the 100-500 J/kg range. Frontogenesis has been 
occasionally doing the heavy lifting, with hourly rain amounts 
occasionally exceeding 1", with local amounts to 2", occurring 
thus far.  Snowmelt potential remains the reason for the Marginal 
Risk for upstate New York and northern New England. In southern New
England (MA/CT/RI), enough instability exists to support a similar
maximum potential (hourly to 1", local totals to 2"). Left the 
Marginal Risk in place as a course of least regret.

Roth


Day 2
Valid 12Z Tue Mar 17 2026 - 12Z Wed Mar 18 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WASHINGTON STATE...

...19Z Update...

Only subtle changes made to the Marginal Risk ERO based on the
latest (12Z) guidance, including the HREF neighborhood
probabilities of QPF exceedance. Across the more elevated Cascades,
additional runoff from snowmelt will enhance the short-term runoff
rates.

Hurley

...Original Discussion...

Active pattern across the Gulf of Alaska will lead to another AR
contribution into portions of the Pacific Northwest as the main
IVT surge will adjust south into WA state after impacting
neighboring British Columbia the day prior. Looking at IVT values
between 500-700 kg/ms across northwest WA state with the surge
propagating far enough inland to impact the Northern Cascades.
Rainfall amounts between 2-3" will be common in the hardest hit
areas, mainly into the Olympic Peninsula, Chehalis River valley,
as well as the Cascades to the east of Seattle. Rates will lack
vigor to the point for a more substantial impact, so the threat is
mainly due to prolonged moderate to locally heavy rain prospects
falling over relatively moist soil layer present after being
impacted for weeks leading in. The previous MRGL risk was generally
unchanged with the threat leaning towards the lower-end of the risk
threshold. Areal hydrologic concerns are still viable with river
and small stream flooding the most notable potential impacts.

Kleebauer


Day 3
Valid 12Z Wed Mar 18 2026 - 12Z Thu Mar 19 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WASHINGTON STATE...

...19Z Update...

Expanded the Marginal Risk area across the coastal and Cascade
Ranges in WA, more closely matching the Day 2 outlook given the
continuation of the event (similar QPF profile) over mostly the
same area.

Hurley


...Original Discussion...

Occluded low over the Gulf of Alaska a strong mid-level ridge
positioned across the Southwest U.S. will lead to a continued
transport of modest IVT into WA state for the D3 period. AR
dominated pattern will enhance rainfall prospects for the northern
half of WA leading to cumulative rainfall totals breaching 4" in
spots within the Northern Cascades, Olympics, and adjacent coastal
areas of northwest WA. Real concern is the growing hydrologic
factors with river flooding coupled with moderate rainfall posing a
problem for areas around the main rivers and tributaries for the
aforementioned areas. Flash flood threat remains low due to the
rates anticipated with the rainfall as hourly rainfall will remain
<0.5"/hr for a majority of Wednesday. However, the coupling of the
previous days rain and the already saturated soils will likely lead
to some hydro concerns mid-week, so maintained the previous MRGL
risk inherited with only some minor tweaks at the southwest edge of
the risk.


Kleebauer


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt