352
FOUS30 KWBC 191550
QPFERD
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1150 AM EDT THU MAR 19 2026
DAY 1
VALID 16Z THU MAR 19 2026 - 12Z FRI MAR 20 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON STATE...
..16Z UPDATE
NO CHANGES WERE MADE FOR THIS UPDATE WITH ANOTHER DAY OF STEADY,
LOCALLY HEAVY, RAINFALL EXPECTED FOR WESTERN WASHINGTON. THE 12Z
HREF GUIDANCE DID NOT SHOW SIGNIFICANT CHANGES FROM THE 00Z CYCLE
AND AN ADDITIONAL 2-4 INCHES OF RAIN THROUGH FRIDAY MORNING STILL
LOOKS REASONABLE WITHIN THE FAVORED SOUTHWEST FACING SLOPES OF THE
OLYMPICS INTO THE CASCADES (LOCALLY HIGHER POSSIBLE). HOURLY
RAINFALL IS LIKELY TO REMAIN BELOW 0.5 INCHES AND OF CONCERN FOR
FLASH FLOODING, BUT AN ISOLATED THREAT WILL STILL EXIST, WITH
ELEVATED RIVERS/STREAMS AND SOIL MOISTURE A CONCERN GIVEN
ANTECEDENT RAINFALL OVER THE PAST SEVERAL DAYS.
OTTO
..PREVIOUS DISCUSSION FOLLOWS
AN ATMOSPHERIC RIVER OF MOISTURE AND RAINFALL ORIGINATING FROM THE
TROPICS NEAR HAWAII (A.K.A. PINEAPPLE EXPRESS) WILL BE DIRECTED AT
THE OLYMPICS AND CASCADES OF WESTERN WASHINGTON STATE ON THURSDAY.
THE PLUME WILL BE GUIDED BY A LARGE AND VERY ANOMALOUSLY STRONG
UPPER LEVEL HIGH/RIDGE OVER THE SOUTHWEST, AND A SERIES OF LOWS,
BOTH OVER THE PACIFIC AND THE GULF OF ALASKA. THE PLUME ITSELF WILL
BE ANOMALOUS IN THAT THE MOISTURE CONTENT WILL BE BETWEEN 3 AND 4
SIGMA ABOVE NORMAL FOR MARCH FOR WESTERN WASHINGTON AS PWATS EXCEED
AN INCH.
HEAVY RAIN WILL IMPACT MUCH OF WESTERN WASHINGTON THROUGH THE DAY
ON THURSDAY. A BRIEF DIMINISHING OF THE RAIN IS EXPECTED THROUGH
THE FIRST HALF OF THURSDAY NIGHT BEFORE A WEAK WAVE OF LOW PRESSURE
MOVES INTO SOUTHERN BRITISH COLUMBIA, AND ANOTHER ROUND OF HEAVIER
RAIN MOVES IN AFTER MIDNIGHT. TOTAL RAINFALL AMOUNTS WILL BE IN THE
2-4 INCH RANGE IN THE OLYMPICS AND NORTHERN CASCADES. THIS RAIN
WILL BE ON TOP OF ALREADY SATURATED SOILS FROM PRIOR RAIN EVENTS,
SO MUCH OF THE NEW RAINFALL WILL QUICKLY CONVERT TO RUNOFF.
ISOLATED FLASH FLOODING IS PROBABLE, ESPECIALLY IN URBAN AND
FLOOD-PRONE AREAS.
WEGMAN
DAY 2
VALID 12Z FRI MAR 20 2026 - 12Z SAT MAR 21 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON STATE...
A WEAK WAVE OF LOW PRESSURE WILL MOVE ASHORE INTO VANCOUVER ISLAND
VERY EARLY FRIDAY MORNING. THE MOISTURE ASSOCIATED WITH ITS
TRAILING FRONT WILL CONTINUE THE HEAVY RAIN INTO WESTERN WASHINGTON
FROM OVERNIGHT THURSDAY NIGHT. THE LOW WILL DISSIPATE IN SOUTHERN
BRITISH COLUMBIA DURING THE DAY THURSDAY, BUT THE ASSOCIATED
RAINFALL WILL LIKELY CONTINUE FOR MUCH OF THE DAY FRIDAY. ONCE THE
CENTER OF THE LOW REFORMS OVER THE PLAINS IN ALBERTA, THE FLOW WILL
WEAKEN ENOUGH TO END ANY UPSLOPE INTO WESTERN WASHINGTON, AND
ENDING THE RAINFALL EVENT. NEVERTHELESS, EXPECT AN ADDITIONAL 1-2
INCHES OF RAIN INTO THE OLYMPICS AND ANOTHER 2-3 INCHES INTO THE
WASHINGTON CASCADES BEFORE THE RAIN ENDS. GIVEN PLENTIFUL EARLIER
RAINS FROM DAY 1/THURSDAY, THERE IS SOME POTENTIAL FOR FLOODING TO
BE ONGOING AT THE START OF THE PERIOD. IN WHICH CASE, ADDITIONAL
RAINFALL COULD WORSEN ONGOING FLOODING AND/OR INITIATE NEW
FLOODING. A SLIGHT RISK UPGRADE COULD BE NEEDED WITH FUTURE UPDATES
IN THE NORTHERN CASCADES.
WEGMAN
DAY 3
VALID 12Z SAT MAR 21 2026 - 12Z SUN MAR 22 2026
THE PROBABILITY OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE IS LESS
THAN 5 PERCENT.
WEGMAN
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
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