802
FXUS66 KPQR 121817
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1117 AM PDT SUN APR 12 2026
UPDATED AVIATION DISCUSSION.
SYNOPSIS
A PATTERN CHANGE IS IN STORE TODAY INTO EARLY NEXT
WEEK AS THE FLOW ALOFT TURNS MORE WEST TO NORTHWEST ALLOWING FOR
CONDITIONS TO TREND A LITTLE COOLER, ALTHOUGH SHOWERS PERSIST AT
TIMES. CONFIDENCE IS HIGH IN THE ARRIVAL OF A MORE POTENT FRONTAL
SYSTEM LATER TUESDAY INTO WEDNESDAY USHERING IN WIDESPREAD
PRECIPITATION AND A SHIFT TOWARD CASCADE SNOWFALL IMPACTS. COOLER
OVERNIGHT TEMPERATURES FOLLOW TO END THE WEEK - WE MAY NOT BE OUT OF
THE WOODS WHEN IT COMES TO MORNING FROST JUST YET.
SHORT TERM...NOW THROUGH TUESDAY
TODAY MARKS THE TRANSITION
BACK TO A MORE PROGRESSIVE WEATHER PATTERN AS AN UPPER-LEVEL LOW
PRESSURE SYSTEM WHICH SAT OFF THE NORTHERN CALIFORNIA COASTLINE
YESTERDAY WHILE FACILITATING A FAIRLY CONVECTIVE ENVIRONMENT
NOW PUSHES INLAND. STILL, MODELS ARE IN GOOD AGREEMENT DEPICTING
WRAP AROUND MOISTURE AND ADDITIONAL BANDS OF SHOWER ACTIVITY
PIVOTING INTO THE REGION AS THE DAY PROGRESSES. BUT UNLIKE THE
PAST COUPLE OF DAYS, THE RETURN OF ONSHORE WNW FLOW NEAR THE
SURFACE SHOULD EFFECTIVELY END ANY ADDITIONAL THUNDERSTORM
CHANCES WEST OF THE CASCADE CRESTS THANKS IN PART TO THE COOLER
TEMPERATURES WITH HIGHS IN THE 50S TO LOW 60S INLAND - A 4 TO 8
DEGREE DROP FROM YESTERDAY. ANTICIPATE PRECIPITATION
PROBABILITIES OF 60-95% OVER MOST OF NORTHWEST OREGON AND
ELEVATED AREAS OF SOUTHWEST WASHINGTON. NORTH OF TILLAMOOK INTO
THE SOUTH WASHINGTON COAST IS THE MAIN EXCEPTION, WITH JUST A
20-40% CHANCE OF PRECIPITATION AS IT REMAINS FURTHER AWAY FROM
THE CORE OF THE UPPER-LEVEL LOW SPINNING MOISTURE OUR WAY.
HEADED THROUGH MONDAY A WEAK EMBEDDED SHORTWAVE FEATURE IS
EXPECTED QUICKLY SWING INTO THE REGION FROM THE NORTHWEST,
MAINTAINING PERSISTENT CHANCES (60-90%) FOR SHOWERS, HIGHEST
ACROSS THE CASCADES, COAST RANGE, AND FOOTHILLS WHERE TERRAIN
FEATURES WILL HELP TO INITIATE AND MAINTAIN MORE FREQUENT
ACTIVITY. AT LEAST AMONG ENSEMBLE AND DETERMINISTIC GUIDANCE
THERE IS GOOD AGREEMENT IN A WEAK HIGH PRESSURE RIDGE FEATURE
BUILDING OVERHEAD LATE MONDAY INTO TUESDAY MORNING, AND WHILE IT
WON'T COMPLETELY END OUR SHOWER CHANCES, IT'LL HELP ENSURE MOST
OF THE LINGERING ACTIVITY REMAINS PINNED TO TERRAIN FEATURES
WHILE THE INLAND VALLEYS TREND MOSTLY DRY. CONFIDENCE IS HIGH
COME TUESDAY AFTERNOON A DECENTLY STRONG COLD FRONTAL BOUNDARY
BEGINS PUSHING INTO THE REGION. BEYOND SOME LOCALLY BREEZY
CONDITIONS DURING THE AFTERNOON OF GUSTS 20-35 MPH OUT OF THE SOUTH
(HIGHEST AT THE COAST), THE BULK OF THE IMPACTS ACCOMPANYING THIS
SYSTEM HOLD OFF UNTIL TUESDAY NIGHT AND WEDNESDAY. SPOILERS: MUCH
NEEDED MODERATE TO HEAVY SNOW LIKELY RETURNS TO THE CASCADES FOR A
PERIOD OF TIME. -99
LONG TERM...TUESDAY NIGHT THROUGH SATURDAY
ENSEMBLE AND
DETERMINISTIC GUIDANCE IS IN EXCELLENT AGREEMENT SHOWING A COLD
FRONT SWEEPING THROUGH THE REGION TUESDAY NIGHT INTO WEDNESDAY
MORNING WITH WIDESPREAD PRECIPITATION ACROSS THE REGION. THE
LATEST GUIDANCE HAS BEGUN TO SHOW LESS UNCERTAINTY REGARDING 24
HOUR RAINFALL TOTALS WHEN THE MEAT OF THE FRONT PASSES OVERHEAD
TUESDAY EVENING THROUGH WEDNESDAY MORNING, WITH QPF VALUES AROUND
0.6-1.10 INCHES IN THE WILLAMETTE VALLEY THROUGH THE PORTLAND METRO,
0.8-1.5 ALONG THE COAST/COAST RANGE, AND 0.90-2.0 INCHES IN THE
MOUNTAINS. COOL TEMPERATURES ALONG AND BEHIND THE FRONTAL BOUNDARY
HELP TO RAPIDLY PUNCH SNOW LEVELS BELOW CASCADE PASS ELEVATIONS,
RAISING THE POTENTIAL FOR WINTER-LIKE TRAVEL IMPACTS. CURRENT
PROBABILISTIC GUIDANCE INDICATES A 85-95% CHANCE OF 6+ INCHES OF
SNOWFALL AT THE CASCADE PASSES BETWEEN TUESDAY AND THURSDAY EVENING
(48 HOURS), WITH A 50-70% CHANCE OF 12 INCHES OR MORE. IF THESE
TRENDS CONTINUE, WINTER WEATHER HIGHLIGHTS MAY BECOME NECESSARY FOR
PORTIONS OF THE CASCADES.
IN ADDITION TO THE CASCADE SNOWFALL, COOLER AND POTENTIALLY
CLEARER CONDITIONS BEHIND THE SYSTEM MAY INTRODUCE RENEWED FROST
CONCERNS ACROSS PORTIONS OF THE INTERIOR VALLEYS BY MID TO LATE
WEEK. THE FIRST OPPORTUNITY APPEARS WEDNESDAY NIGHT INTO
THURSDAY, WITH A 30-70% CHANCE OF FROST ACROSS MUCH OF THE
INTERIOR LOWLANDS (LOWEST AROUND THE PORTLAND-VANCOUVER METRO)
AND A 50-90% CHANCE OF FREEZING TEMPERATURES IN THE UPPER HOOD
RIVER VALLEY (CHANCES FROM ODELL TO PARKDALE). SIMILAR
CONDITIONS MAY DEVELOP AGAIN THURSDAY NIGHT INTO FRIDAY MORNING,
BUT WITH SLIGHTLY LOWER CHANCES. TEMPERATURES BEGIN TO TREND
WARMER INTO THE WEEKEND EVENTUALLY LESSENING THESE FROST/FREEZE
RELATED CONCERNS. -99/12
AVIATION
LIGHT SCATTERED SHOWERS HAVE DEVELOPED ACROSS NW OR
AND SW WA AND WILL CONTINUE ACROSS THE REGION INTO SUNDAY EVENING,
SLOWLY DISSIPATING FROM THE INTERIOR LOWLANDS BETWEEN 04-10Z SUN.
SHOWERS CONTINUE BEYOND THIS OVER THE CASCADES AND COAST RANGE.
EXPECT LOWERED FLIGHT CONDITIONS AT MOST TERMINALS TODAY, MAINLY
MVFR CIGS AND/OR VIS, THOUGH SOME SHOWERS ARE PUSHING CIGS AND/OR
VIS TO BRIEF IFR FLIGHT LEVELS. ALONG THE COAST, NORTH OF TMK WILL
BE MAINLY DRY WITH PERIODS OF VFR CIGS. AS DAYTIME HEATING PRODUCES
MORE MIXING, VALLEY TERMINALS ARE LIKELY TO BECOME MAINLY VFR
GENERALLY AFTER 19-22Z SAT, THOUGH EXPECT FLUCTUATIONS BETWEEN VFR
AND MVFR IN SHOWERS. GUIDANCE INDICATES WIDESPREAD MVFR CIGS RETURN
AFTER 04-08Z SUN. WINDS REMAIN RELATIVELY LIGHT LESS THAN 10 KTS,
MAINLY WESTERLY ALONG THE COAST AND SOUTHERLY INLAND, SHIFTING
WESTERLY AFTER 21Z SAT - 03Z SUN.
KPDX AND APPROACHES...MVFR CONDITIONS PERSIST, SHOULD BECOME VFR BY
19-22Z SUN. HOWEVER, SCATTERED SHOWERS THROUGH THE EVENING COULD
PRODUCE BRIEF PERIODS OF MVFR/IFR CIGS OR VIS. SHOWERS DISSIPATE BY
04-06Z MON, THEN WIDESPREAD MVFR CIGS RETURN. WINDS SOUTHERLY AROUND
8-10 KTS, BECOMING WESTERLY AFTER 03Z MON. -03
MARINE
NORTHERLY WINDS ARE EXPECTED TO CONTINUE INTO EARLY NEXT
WEEK ALBEIT NOT PARTICULARLY STRONG WITH GUSTS STAYING BELOW 20
KNOTS THROUGH MONDAY. SIGNIFICANT WAVE HEIGHTS HOLD IN THE IN THE
4 TO 7 FOOT RANGE THROUGH THIS TIME PERIOD AS WELL. OUR FOCUS THEN
TURNS TO OUR NEXT WEATHER SYSTEM IN THE FORM OF A ROBUST FRONTAL
BOUNDARY ARRIVING LATER TUESDAY INTO WEDNESDAY MORNING WHICH
LIKELY (85-95% CHANCE) RESULTS IN SMALL CRAFT ADVISORY WIND GUSTS
OVER 21 KTS AND SEAS BUILDING TO AROUND 7 TO 10 FEET. HOWEVER,
THERE IS A 10-25% FOR A BRIEF PERIOD GALE FORCE WIND GUSTS
TUESDAY EVENING. WAVE HEIGHTS AND WINDS THEN SLOWLY DECREASE
THURSDAY INTO THE END OF THE WEEK. -99/03
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
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