FOUS30 KWBC 201825

QPFERD



Excessive Rainfall Discussion

NWS Weather Prediction Center College Park MD

225 PM EDT Fri Mar 20 2026



Day 1

Valid 16Z Fri Mar 20 2026 - 12Z Sat Mar 21 2026



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

WESTERN WASHINGTON STATE...



...16Z update...



Moderate to locally heavy rain continued over western Washington

this morning out ahead of a cold front located ~100 miles west

of the coast as of 15Z. An additional 1 to 2 inches of rain (peak

amounts) are expected through the late evening within the Cascades

and up to a half inch or so for the Coastal Ranges/Olympics.

Ongoing river flooding and wet antecedent conditions continue to be

the main driver for the Marginal Risk, but the risk area can

likely be removed with the next update at 01Z as IVT values lower

with the cold frontal passage.



Otto



...previous discussion follows...





At the beginning of the forecast period, a stubborn atmospheric

river is forecast to weaken as a surface low and attendant cold

front progress eastward into the Pacific Northwest. Even so,

moderate IVT values on the order of 500-700 kg/m * s directed into

the WA coastline from 12-18Z should maintain the threat of locally

heavy rainfall ahead of the front. While hourly rainfall rates will

likely remain below 0.5 inches per hour, isolated instances of

excessive rainfall remain possible in upslope regions of the

Olympics and Cascades owing to antecedent rainfall over the last

few days.



Asherman



Day 2

Valid 12Z Sat Mar 21 2026 - 12Z Sun Mar 22 2026



The probability of rainfall exceeding flash flood guidance is less

than 5 percent.



Pereira



Day 3

Valid 12Z Sun Mar 22 2026 - 12Z Mon Mar 23 2026



The probability of rainfall exceeding flash flood guidance is less

than 5 percent.



Pereira



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