632
FXUS66 KPQR 130515 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
1015 PM PDT SUN APR 12 2026
UPDATED AVIATION DISCUSSION.
SYNOPSIS
A TRANSITION TO A COOLER, MORE PROGRESSIVE PATTERN
IS UNDERWAY THIS AFTERNOON AS FLOW ALOFT GRADUALLY TURNS WEST TO
NORTHWEST. SCATTERED SHOWERS CONTINUE AT TIMES THROUGH EARLY
NEXT WEEK. CONFIDENCE REMAINS HIGH IN A STRONGER FRONTAL SYSTEM
ARRIVING LATE TUESDAY INTO WEDNESDAY, BRINGING WIDESPREAD
PRECIPITATION AND A SHIFT TOWARD CASCADE SNOW IMPACTS. A WINTER
STORM WATCH HAS BEEN ISSUED FOR THE CASCADES FROM LATE TUESDAY
INTO EARLY THURSDAY AS A RESULT OF INCREASING CONFIDENCE. COOLER
OVERNIGHT TEMPERATURES FOLLOW, WITH INCREASING FROST CONCERNS
BY MID TO LATE WEEK.
SHORT TERM...NOW THROUGH TUESDAY
THIS AFTERNOON, A BROAD
UPPER-LEVEL LOW THAT SUPPORTED RECENT CONVECTIVE ACTIVITY IS
SHIFTING INLAND ACROSS THE NORTHERN CALIFORNIA, NEAR THE OR/CA
BORDER. IN ITS WAKE, FLOW ALOFT WILL GRADUALLY SHIFT TO ONSHORE
WEST-NORTHWESTERLY FLOW OVERNIGHT, RESULTING IN COOLER
TEMPERATURES AND A TRANSITION AWAY FROM THUNDERSTORMS. CURRENT
OBSERVATIONS SHOW SCATTERED SHOWERS LINGERING OVER PARTS OF
SOUTHWEST WASHINGTON AND NORTHWEST OREGON, WITH ADDITIONAL BANDS
EXPECTED THROUGH THE REMAINDER OF TODAY AS WRAP-AROUND MOISTURE
PERSISTS.
TEMPERATURES TODAY HAVE COOLED COMPARED TO RECENT DAYS, WITH
INLAND HIGHS GENERALLY IN THE 50S TO LOW 60S. SHOWER
PROBABILITIES REMAIN ELEVATED, RANGING FROM 60-95% ACROSS MOST
OF NORTHWEST OREGON AND ELEVATED TERRAIN IN SOUTHWEST
WASHINGTON. LOWER PROBABILITIES, AROUND 20-40%, ARE EXPECTED
ALONG THE NORTH OREGON AND SOUTH WASHINGTON COAST DUE TO THE
UPPER-LEVEL LOW CONTINUING TO DISTANCE ITSELF AS IT MOVES
SOUTHEASTWARD.
ON MONDAY, A WEAK SHORTWAVE IS EXPECTED TO MOVE INTO THE REGION
FROM THE NORTHWEST, MAINTAINING WIDESPREAD SHOWER ACTIVITY.
PRECIPITATION PROBABILITIES REMAIN IN THE 60-90% RANGE, HIGHEST
ACROSS THE CASCADES, COAST RANGE, AND FOOTHILLS WHERE
OROGRAPHIC LIFT WILL ENHANCE PRECIPITATION. BY LATE MONDAY INTO
TUESDAY MORNING, A TRANSIENT RIDGE BEGINS TO BUILD OVERHEAD.
WHILE THIS MAY NOT FULLY ELIMINATE SHOWER CHANCES, IT SHOULD
LEAD TO DECREASED COVERAGE ACROSS THE INTERIOR LOWLANDS, WITH
ACTIVITY BECOMING MORE CONFINED TO ELEVATED TERRAIN SUCH AS THE
COAST RANGE, CASCADES, AND ADJACENT FOOTHILLS.
ATTENTION THEN TURNS TO AN APPROACHING PACIFIC FRONTAL SYSTEM.
BY TUESDAY AFTERNOON, INCREASING SOUTHERLY FLOW AHEAD OF THE
FRONT WILL BRING LOCALLY BREEZY CONDITIONS, WITH GUSTS GENERALLY
IN THE 20-35 MPH RANGE, STRONGEST ALONG THE COAST. THE BULK OF
PRECIPITATION AND IMPACTS ASSOCIATED WITH THIS SYSTEM ARE
EXPECTED TO HOLD OFF UNTIL TUESDAY NIGHT INTO WEDNESDAY.
LONG TERM...TUESDAY NIGHT THROUGH SATURDAY
ENSEMBLE AND
DETERMINISTIC GUIDANCE REMAIN IN STRONG AGREEMENT THAT A COLD
FRONT WILL SWEEP THROUGH THE REGION TUESDAY NIGHT INTO WEDNESDAY
MORNING (ARRIVING ANY TIME BETWEEN 11 PM TUE AND 11 AM WED),
BRINGING WIDESPREAD PRECIPITATION. CONFIDENCE HAS INCREASED IN
MODERATE RAINFALL AMOUNTS, WITH 24-HOUR TOTALS GENERALLY RANGING
FROM 0.7 TO 1.2 INCHES ACROSS THE WILLAMETTE VALLEY AND
PORTLAND METRO (10-30% CHANCE TO EXCEED 1.2 INCHES), 0.9 TO 1.7
INCHES ALONG THE COAST AND COAST RANGE (5-15% CHANCE TO EXCEED
1.7 INCHES), AND 0.9 TO 2.0 INCHES ACROSS THE CASCADES (10-20%
CHANCE TO EXCEED 2.0 INCHES).
COOLING TEMPERATURES ALONG AND BEHIND THE FRONT WILL LOWER SNOW
LEVELS TO NEAR OR BELOW CASCADE PASS ELEVATIONS, INCREASING THE
LIKELIHOOD OF WINTER TRAVEL IMPACTS. CURRENT PROBABILISTIC
GUIDANCE INDICATES A 60-90% CHANCE OF 12+ INCHES OF SNOWFALL AT
THE CASCADE PASSES BETWEEN TUESDAY AFTERNOON AND THURSDAY
AFTERNOON (48 HOURS). AS A RESULT, A WINTER STORM WATCH HAS BEEN
ISSUED FOR HEAVY SNOW POSSIBLE ABOVE 3500 FT IN THE SOUTH
WASHINGTON CASCADES, NORTH OREGON CASCADES, CASCADES OF MARION
AND LINN COUNTIES, AND CASCADES OF LANE COUNTY FROM 5 PM TUESDAY
THROUGH 5 AM THURSDAY. TOTAL SNOW ACCUMULATIONS BETWEEN 9 TO 18
INCHES POSSIBLE, WITH THE HIGHEST AMOUNTS IN THE HIGH CASCADES
FROM MARION TO LANE COUNTY. ROADS, AND ESPECIALLY BRIDGES AND
OVERPASSES, WILL LIKELY BECOME SLICK AND HAZARDOUS, AND WINDS
MAY GUST AS HIGH AS 45 MPH.
IN ADDITION TO CASCADE SNOWFALL, COOLER AND POTENTIALLY CLEARER
CONDITIONS BEHIND THE SYSTEM WILL BRING RENEWED FROST CONCERNS
TO THE INTERIOR VALLEYS. THE FIRST OPPORTUNITY APPEARS WEDNESDAY
NIGHT INTO THURSDAY MORNING, WITH A 60-80% CHANCE OF FROST
ACROSS MUCH OF THE INTERIOR LOWLANDS, EXCEPT FOR A 25-45% IN THE
METRO AND AT THE COAST. ADDITIONALLY, THERE IS A 60-90% CHANCE
OF FREEZING TEMPERATURES IN THE UPPER HOOD RIVER VALLEY. SIMILAR
CONDITIONS MAY DEVELOP AGAIN THURSDAY NIGHT INTO FRIDAY
MORNING, THOUGH WITH SLIGHTLY LOWER PROBABILITIES (10-20%
LOWER). WHILE FROST POTENTIAL STARTS FOR MOST AREAS THURSDAY
MORNING, THE UPPER HOOD RIVER VALLEY WILL HAVE FROST POTENTIAL
SOONER AND LONGER, WITH A 25-65% CHANCE OF FROST WEDNESDAY
MORNING, 85-95% THURSDAY AND FRIDAY MORNING, AND 60-80% SATURDAY
MORNING. CHANCES OF FROST LOWER TO 10-20% BY SUNDAY MORNING FOR
THE UPPER HOOD RIVER VALLEY. TEMPERATURES GRADUALLY WARM INTO
THE WEEKEND, REDUCING FROST CONCERNS. ~12
AVIATION
LIGHT SHOWERS CONTINUE TO TAPER OFF AS AN UPPER LEVEL
LOW SHIFTS EASTWARD. CONDITIONS HAVE TRENDED TOWARD VFR AS CIGS
INCREASE ABOVE 3000 FEET AT MOST TERMINALS BUT AREN'T EXPECTED TO
PERSIST THROUGH THE NIGHT AS A SHORTWAVE DROPS SOUTHEAST OVER THE
PACNW. SHOWER ACTIVITY IS EXPECTED TO INCREASE BETWEEN 8-12Z
MONDAY AS THIS DISTURBANCE PASSES OVERHEAD. SCATTERED SHOWERS
PERSIST THROUGH MOST OF MONDAY BUT WILL BE LIGHT. THIS DISTURBANCE
WILL ALSO INCREASE PROBABILITIES FOR SUB- VFR CONDITIONS FOR ALL
TERMINALS. INLAND TERMINALS HAVE A 40-70% CHANCE FOR MVFR CIGS
UNTIL 12Z AND COASTAL TERMINALS HAVE A BATTER CHANCES AT 60-80%
THROUGH 20Z. WINDS REMAIN WEST TO NORTHWEST THROUGH THE PERIOD.
KPDX AND APPROACHES...VFR CONDITIONS EXPECTED TO DROP BACK TO MVFR
AS A DISTURBANCE PASSES OVERHEAD. SHOWER ACTIVITY ALSO EXPECTED TO
INCREASE BUT WILL BE SCATTERED ENOUGH TO NOT BE IN A PREVAILING
GROUP AT THIS TIME. LIGHT WESTERLY WINDS EXPECTED THROUGH THE
PERIOD. -19
MARINE
NORTH TO NORTHWESTERLY WINDS ARE EXPECTED TO CONTINUE
INTO MONDAY, ALBEIT NOT PARTICULARLY STRONG WITH GUSTS STAYING
BELOW 20 KNOTS. SIGNIFICANT WAVE HEIGHTS HOLD IN THE IN THE 4 TO
7 FOOT RANGE THROUGH THIS TIME PERIOD AS WELL. FOCUS THEN TURNS
TO THE NEXT WEATHER SYSTEM THAT WILL CAUSED INCREASED WINDS AND
SEAS TUESDAY AND WEDNESDAY. THERE IS HIGH PROBABILITY (85-95%
CHANCE) IN SMALL CRAFT ADVISORY WIND GUSTS GREATER THAN 21 KTS
WITH A 10-25% CHANCE OF A BRIEF PERIOD OF GALE FORCE GUSTS OVER
34 KTS AS A ROBUST COLD FRONT PASSES THROUGH THE WATERS TUESDAY
AFTERNOON AND EVENING. AN INCREASING WESTERLY SWELL ALONG WITH
THE WINDS WILL CAUSE SEAS TO BUILD TO AROUND 8-11 FEET AT 9-10
SECONDS. WINDS BEGIN DECREASING WEDNESDAY WHILE THE SEAS REMAIN
ELEVATED, DECREASING ON THURSDAY. -03
PQR WATCHES/WARNINGS/ADVISORIES
OR...WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH LATE
WEDNESDAY NIGHT FOR ORZ126>128.
WA...WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH LATE
WEDNESDAY NIGHT FOR WAZ211.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
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X.COM/NWSPORTLAND
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