977
FXUS66 KPQR 111751
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1021 AM PDT SAT APR 11 2026
UPDATED AVIATION DISCUSSION.
SYNOPSIS
YET ANOTHER DAY OF UNSETTLED CONDITIONS IS
EXPECTED TO START THE WEEKEND WITH CONTINUED SHOWER AND
ISOLATED THUNDERSTORM ACTIVITY STREAMING SOUTH TO NORTH OVERHEAD.
WE'LL TRANSITION TO SLIGHTLY COOLER CONDITIONS SUNDAY INTO
EARLY NEXT WEEK AS FLOW TURNS MORE WEST-NORTHWESTERLY BUT
SHOWERS CHANCES PERSIST. COME THE MIDDLE OF NEXT WEEK CONFIDENCE
CONTINUES TO INCREASE IN A POTENT COLD FRONTAL SYSTEM USHERING
IN WIDESPREAD PRECIPITATION WHILE SHIFTING IMPACTS TO CASCADE
PASS SNOWFALL AND COOLER OVERNIGHT TEMPERATURES FOR THE END OF
NEXT WEEK AS WELL.
SHORT TERM...NOW THROUGH SUNDAY NIGHT
EARLY THIS MORNING
SATELLITE AND RADAR IMAGERY DEPICT SEVERAL CONSOLIDATED BANDS
OF SHOWER ACTIVITY STREAMING SOUTH TO NORTH ACROSS WESTERN
OREGON AND SOUTHWESTERN WASHINGTON ALL THANKS TO THE SAME
SYNOPTIC FEATURE WHICH PROVIDED SOME EXCITEMENT IN THE FORM OF
THUNDERSTORM ACTIVITY YESTERDAY (FRIDAY). THIS UPPER-LEVEL
SHORTWAVE HELPING TO DRIVE THE CURRENT PRECIPITATION WILL
CONTINUE TO EJECT NORTHWARD OVER THE NEXT SEVERAL HOURS WITH
MODELS INDICATING AT LEAST A NOTICEABLE DECREASE IN SHOWER
ACTIVITY BY MID TO LATE MORNING, ESPECIALLY ACROSS THE CENTRAL
WILLAMETTE VALLEY UP THROUGH SW WASHINGTON.
IF YOU'RE HOPING FOR A REPEAT PERFORMANCE THIS AFTERNOON IN
REGARD TO THUNDERSTORM CHANCES, YOU MAY BE IN LUCK AS THE SET-UP
TODAY HAS SEVERAL SIMILARITIES TO WHAT OCCURRED YESTERDAY,
ALBEIT NOT AS ENTICING IN MOST ASPECTS. DETERMINISTIC AND
ENSEMBLE MODELS SHOW ANOTHER CLOSED UPPER-LEVEL LOW PRESSURE
SYSTEM OVER THE FAR EASTERN PACIFIC SLOWLY MARCHING TOWARDS THE
NORTHERN CALIFORNIA COASTLINE KEEPING US UNDER BROAD AND MOIST
SOUTHERLY FLOW HIGHLIGHTED BY ANOMALOUSLY HIGH PWAT VALUES
AROUND 0.8-0.9IN. THIS KEEPS US IN A FLOW PATTERN WHICH
TRADITIONALLY GIVES US A BETTER SHOT AT THUNDERSTORMS WEST OF
THE CASCADE CRESTS. WHILE THE OVERALL SYNOPTICS ARE FAVORABLE,
THE MOST IMPORTANT AND UNFORTUNATELY MOST UNCERTAIN ASPECT OF
THE FORECAST REVOLVES AROUND THE AMOUNT OF CLEARING WE RECEIVE
THROUGHOUT THE DAY - MORE CLEARING LIKELY LEADS TO HIGHER CAPE
VALUES AND THUS DEEPER/STRONG CONVECTION. GENERALLY, THE HREF
AND DETERMINISTIC MODELS LIKE THE GFS/NAM PROJECT MUCAPE VALUES
PEAKING IN THE 300-600 J/KG RANGE LATER TODAY WHICH SHOULD BE
SUFFICIENT FOR THUNDERSTORM DEVELOPMENT, ALTHOUGH THESE VALUES
ARE A BIT LOWER THAN WHAT OCCURRED YESTERDAY. THE AMOUNT OF
WIND SHEAR ALOFT TO SUPPORT STORM ORGANIZATION IS ALSO A BIT
LOWER AS WELL WITH EFFECTIVE SHEAR AROUND ~20-25 KNOTS. WITH ALL
THIS IN MIND THE STORM MODE SHOULD GENERALLY FALL INTO THE
"POP-UP" VARIETY WITH A 15-30% CHANCE OF THIS ACTIVITY OCCURRING
FROM ROUGHLY THE US-26 CORRIDOR SOUTHWARD. HIGHEST RELATIVE
CHANCES ARE OVER TERRAIN FEATURES LIKE THE CASCADES, COAST
RANGE, AND ATTENDANT FOOTHILLS WHERE CONVECTION IS MORE LIKELY
TO INITIATE BETWEEN 1PM TO 8PM. IMPACTS INCLUDE LIGHTNING,
SMALL HAIL, HEAVY RAIN, AND LOCALLY GUSTY/ERRATIC WINDS IN ANY
STORMS WHICH DO OCCUR. IT'S WORTH POINTING OUT GIVEN THE
MARGINAL DEPTH AND FAIRLY SKINNY CAPE PROFILE SHOWN IN MODEL
SOUNDINGS, A GREATER DEGREE OF CLOUD COVER THAN ANTICIPATED WILL
ALMOST CERTAINLY KEEP ACTIVITY FROM ELECTRIFYING (YOU WANT CAPE
TO EXTEND THROUGH THE -10 TO -20C MIXED PHASED REGION OF THE
ATMOSPHERE) THUS LEAVING US WITH JUST EFFICIENT RAINFALL
PRODUCING SHOWERS. ONCE WE GET TOWARDS SUNSET AND DAYTIME
HEATING WANES, SO TO WILL CONVECTION WITH JUST LINGERING SHOWERS
OVERNIGHT.
ON SUNDAY, THE UPPER-LEVEL LOW PRESSURE FEATURE STIRRING UP THE
UNSETTLED WEATHER TRACKS FURTHER EAST TRANSITIONING THE REGION
INTO MORE OF A WESTERLY FLOW PATTERN AND EFFECTIVELY ENDING MOST
THUNDERSTORM POTENTIAL OUTSIDE OF A SLIGHT CHANCE (AROUND
10-15%) OVER THE FAR SOUTHERN PORTION OF THE LANE COUNTY
CASCADES NEAR THE CREST-LINE. STILL, DON'T EXPECT A RETURN TO
COMPLETELY DRY WEATHER AS MODELS ARE IN MODERATE TO GOOD
AGREEMENT SHOWING SHOWERS PERSISTING DUE TO WRAP-AROUND MOISTURE
ON THE NORTHERN PERIPHERY OF THE BROADER CIRCULATION - POPS OF
70-95% OVER THE CASCADES AND FOOTHILLS AND 30-60% ELSEWHERE.
WITH THE LOSS SOUTHERLY FLOW NEAR THE SURFACE, TEMPERATURES
ALSO COOL BACK INTO THE UPPER 50S TO LOW 60S INLAND, CLOSER TO
SEASONAL NORMALS FOR EARLY TO MID APRIL. -99
LONG TERM...MONDAY THROUGH FRIDAY
ENSEMBLE GUIDANCE
INDICATES BROAD WEST-NORTHWEST TO NORTHWEST FLOW ALOFT FOR EARLY
NEXT WEEK HELPING TO STEER A WEAK EMBEDDED SHORTWAVE INTO THE
REGION ON MONDAY. AS A RESULT SHOWERS CHANCES (50-90%) WILL BE
MAINTAINED. BEYOND THIS SHORTWAVE FEATURE SHOWER ACTIVITY
DECREASES MONDAY NIGHT INTO TUESDAY AS A TRANSIENT RIDGE BRIEFLY
BUILDS OVERHEAD. OUR ATTENTION THEN TURNS TO THE NEXT PACIFIC
FRONTAL SYSTEM ARRIVING FROM THE GULF OF ALASKA LATE TUESDAY
INTO EARLY WEDNESDAY MORNING. CONFIDENCE IS HIGH COOLER
TEMPERATURES ALOFT ASSOCIATED WITH THIS SYSTEM WILL LOWER SNOW
LEVELS TO NEAR OR BELOW CASCADE PASS ELEVATIONS, RAISING THE
CONCERN FOR POTENTIAL TRAVEL IMPACTS RETURNING. A STARK CHANGE
FROM THE RATHER WARM CONDITIONS WE'VE SEEN THE LAST COUPLE OF
WEEKS. THE LATEST NBM PROBABILISTIC GUIDANCE INDICATES A 60-90%
CHANCE OF 6+ INCHES OF SNOWFALL AT THE CASCADE PASSES (GOV CAMP,
SANTIAM, WILLAMETTE PASS) OVER THE 48 HOURS BETWEEN 5PM TUESDAY
AND 5PM THURSDAY. AS FOR 12+ INCHES OF SNOWFALL, THERE IS A
40-60% CHANCE DURING THIS SAME TIME PERIOD. SHOULD THESE
PROBABILITIES AND CURRENT FORECAST SNOWFALL AMOUNTS HOLD,
SNOWFALL RELATED HIGHLIGHTS WOULD BE NEEDED FOR OUR OREGON AND
WASHINGTON CASCADE ZONES.
ADDITIONALLY, COOLER AND POTENTIALLY CLEARER CONDITIONS BEHIND
THE SYSTEM MAY INTRODUCE RENEWED FROST CONCERNS ACROSS PORTIONS
OF THE INTERIOR VALLEYS BY MID TO LATE WEEK. WEDNESDAY NIGHT
INTO THURSDAY MORNING IS THE FIRST OF THESE SUCH NIGHTS WITH NBM
GUIDANCE SUGGESTING A 30-70% CHANCE FOR AREAS FROST (<36F WITH
PARTIAL CLEARING) ACROSS MOST INLAND LOCATIONS AND A 60-80%
CHANCE FOR FREEZING TEMPERATURES IN THE UPPER-HOOD RIVER VALLEY.
A SIMILAR SET-UP IS ANTICIPATED THURSDAY NIGHT INTO FRIDAY
MORNING AS WELL. AT LEAST THE TREND IS TO MODERATE BACK TOWARDS
NORMAL TEMPERATURES FOR THE FOLLOWING WEEKEND. -99/12
AVIATION
MIXED FLIGHT CONDITIONS ARE EXPECTED THROUGH SATURDAY
AS UNSETTLED WEATHER CONTINUES DUE TO AN UPPER LEVEL LOW PRESSURE
SYSTEM OFF OF THE NORTHERN CALIFORNIA COAST. SCATTERED SHOWERS
CONTINUE THROUGH THE DAY MOVING FROM SOUTH TO NORTH. SHOWERS HAVE
BEEN CAUSING PERIODS OF LOWER FLIGHT CONDITIONS TO MVFR/IFR CIGS AND
VIS. MVFR CIGS OUTSIDE OF SHOWERS ARE FORECAST TO BECOME
PREDOMINATELY VFR BY 19Z SAT. THUNDERSTORM CHANCES RETURN AFTER 18-
20Z SAT, ENDING AROUND 03Z SUN. BEST CHANCES ARE IN THE CENTRAL AND
SOUTHERN WILLAMETTE VALLEY INTO THE ADJACENT CASCADES WITH A 25-30%
CHANCE, AND A 15-25% CHANCE ELSEWHERE. STRONG SHOWERS OR
THUNDERSTORMS COULD PRODUCE GUSTY OUTFLOW WINDS, BRIEF HEAVY RAIN,
SMALL HAIL, AND LIGHTNING. OUTSIDE OF CONVECTIVE OUTFLOW, WINDS WILL
BE VARIABLE AND MAINLY LESS THAN 7 KTS.
LATEST GUIDANCE SUGGESTS WIDESPREAD MVFR CONDITIONS RETURN BETWEEN
09-14Z SUN AHEAD OF ANOTHER ROUND OF SHOWER ACTIVITY.
KPDX AND APPROACHES...MAINLY VFR CONDITIONS THROUGH SATURDAY, THOUGH
ISOLATED SHOWERS COULD LOWER FLIGHT CONDITIONS TO MVFR/IFR. THERE'S
A 15-20% CHANCE FOR THUNDERSTORMS, MAINLY BETWEEN 23Z SAT TO 04Z
SUN. HOWEVER, CONFIDENCE IN TIMING AND PLACEMENT REMAINS ONLY LOW.
MVFR CONDITIONS FORECAST TO RETURN AFTER 09-12Z SUN AHEAD OF ANOTHER
ROUND OF WIDESPREAD SHOWERS. -03
MARINE
HEADED THROUGH THE WEEKEND CONDITIONS REMAIN RATHER
BENIGN AS FAR AS THE SEA STATE AND WINDS ARE CONCERNED WITH
SIGNIFICANT WAVE HEIGHTS HOLDING IN THE 4 TO 7 FOOT RANGE WITH
WINDS GUSTS BELOW 20 KNOTS ACROSS THE INNER AND OUTER WATERS.
WE'LL LIKELY SEE SOUTH/SOUTHWEST WINDS SLOWLY BECOME MORE
NORTH/NORTHWEST TODAY INTO THIS EVENING BEFORE PERSISTING THROUGH
AT LEAST MONDAY NIGHT. LOOKING TOWARDS THE MIDDLE OF NEXT WEEK
IN THE TUESDAY AND WEDNESDAY TIME PERIOD A DECENTLY ROBUST
FRONTAL BOUNDARY WILL LIKELY (75-85% CHANCE) RESULT IN SMALL
CRAFT ADVISORY WIND GUSTS AND SEAS BUILDING TO AROUND 7 TO 10
FEET. WAVE HEIGHTS AND WINDS THEN SLOWLY DECREASE INTO THE END OF
THE WEEK. -99
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
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