656
FXUS66 KPQR 090503 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
1003 PM PDT SUN MAR 8 2026
UPDATED AVIATION DISCUSSION
SYNOPSIS
SHOWERS WILL INCREASE IN COVERAGE MONDAY MORNING
AND AFTERNOON BEHIND A COLD FRONTAL PASSAGE. ALTHOUGH SHOWERS
CONTINUE MONDAY NIGHT INTO TUESDAY, OVERALL COVERAGE AND
INTENSITY WILL BE ON THE DECREASE. TEMPERATURES ALOFT WILL BE
TRENDING COOLER SUNDAY NIGHT THROUGH TUESDAY MORNING, PUSHING
SNOW LEVELS DOWN TO AROUND 1000-1500 FT LATE SUNDAY NIGHT INTO
MONDAY MORNING AND THEN TO AROUND 500 FT MONDAY NIGHT INTO
TUESDAY MORNING. THIS WILL RESULT IN SOME ACCUMULATING SNOW FOR
ELEVATIONS ABOVE 500-1000 FT WITH TRAVEL IMPACTS EXPECTED,
ESPECIALLY OVER THE CASCADE PASSES. LITTLE TO NO IMPACTS ARE
EXPECTED BELOW 500 FT WHERE PRECIPITATION WILL FALL MAINLY IN
THE FORM OF RAIN OR A RAIN/SNOW MIX. BECOMING WET AND BREEZY
WEDNESDAY THROUGH FRIDAY WITH THE ARRIVAL OF A MODERATE
ATMOSPHERIC RIVER, HOWEVER RIVER FLOODING IS UNLIKELY AT THIS
TIME (90-95% CHANCE RIVER FLOODING WILL NOT OCCUR).
SHORT TERM...SUNDAY NIGHT THROUGH TUESDAY
THE SHORT TERM
FORECAST IS HIGHLIGHTED BY COOL AND SHOWERY WEATHER WITH
LOWERING SNOW LEVELS, RESULTING IN SOME TRAVEL IMPACTS FOR
ELEVATIONS ABOVE 500-1000 FEET, ESPECIALLY OVER THE CASCADE
PASSES WHERE SNOW ACCUMULATION WILL BE MOST SIGNIFICANT. EXPECT
MAINLY RAIN OR A RAIN/SNOW MIX FOR ELEVATIONS BELOW 500 FT WITH
LITTLE TO NO TRAVEL IMPACTS. THE DETAILS BEHIND THIS MESSAGING
ARE DISCUSSED BELOW.
EARLY SUNDAY AFTERNOON, SURFACE WEATHER OBSERVATIONS DEPICTED A WEAK
SOUTHWEST-NORTHEAST ORIENTED COLD FRONT DRAPED ACROSS WESTERN WA AND
THE COASTAL WATERS OFF THE SOUTH WA/NORTH OR COAST. SURFACE WINDS
WERE SOUTHERLY AHEAD OF THIS FRONT WITH MILD TEMPERATURES, CLOUDY
SKIES AND SPOTTY LIGHT SHOWERS. SKIES WERE PARTLY CLOUDY BEHIND THIS
FRONT WITH NORTHWEST SURFACE WINDS AND SLIGHTLY COOLER TEMPERATURES.
THIS FRONT HAS BEEN SLOW MOVING THUS FAR, BUT WILL EVENTUALLY SAG
SOUTHWARD ACROSS WESTERN OREGON SUNDAY EVENING INTO SUNDAY NIGHT. BY
EARLY MONDAY MORNING, NORTHWEST OR AND SOUTHWEST WA WILL BE SOLIDLY
WITHIN THE COOLER AND MORE UNSTABLE POST-FRONTAL ENVIRONMENT,
BRINGING INCREASING SHOWERS MONDAY MORNING AND AFTERNOON. BEYOND
MONDAY AFTERNOON, THE LATEST SUITE OF CAM GUIDANCE IS NOW IN GOOD
AGREEMENT SHOWERS WILL BECOME LIGHTER AND DECREASE SIGNIFICANTLY IN
COVERAGE MONDAY NIGHT INTO TUESDAY MORNING, ESPECIALLY OVER THE
WILLAMETTE VALLEY AND PORTLAND METRO. NOTE THIS IS ALSO WHEN SNOW
LEVELS WILL BE LOWEST, BOTTOMING OUT CLOSE TO 500 FEET. HOWEVER,
SINCE SHOWERS WILL BE DECREASING BY THEN WITH PRECIPITATION RATES
BECOMING LIGHTER, ACCUMULATING SNOW AND TRAVEL IMPACTS ARE NOT
EXPECTED FOR ELEVATIONS BELOW 500 FT. THE NBM V5.0 SEEMS TO REFLECT
THIS EXPECTATION BEST, SUGGESTING THERE IS ONLY A 1-5% CHANCE FOR 0.1
INCHES OF SNOW OR MORE ACROSS THE WILLAMETTE VALLEY AND
PORTLAND/VANCOUVER METRO. PROBABILITIES ARE SLIGHTLY HIGHER IN THE
COWLITZ VALLEY AT AROUND 10-15%. NBM V4.3 PROBABILITIES ARE
RELATIVELY HIGHER THAN V5.0, BUT SEEM MISLEADINGLY HIGH BASED ON THE
LIGHT AND SHOWERY NATURE OF THE PRECIPITATION WHEN TEMPERATURES ARE
COLDEST, AS WELL AS TEMPERATURES BEING MARGINAL WHEN PRECIPITATION
IS OCCURRING. THE MOST LIKELY OUTCOME IS FOR OCCASIONAL LIGHT RAIN
SHOWERS BELOW 500 FT, POSSIBLY MIXING WITH WET SNOW FOR BRIEF
PERIODS OF TIME UNDER HEAVIER SHOWERS, BUT WITH ANY SNOW LIKELY
MELTING AS SOON AS IT REACHES THE GROUND.
THAT BEING SAID, ACCUMULATING SNOW IS MUCH MORE LIKELY FOR ELEVATIONS
ABOVE 500-1000 FT WHERE TEMPERATURES WILL BE COLDER AND SHOWERS WILL
BE MORE PERSISTENT. TRAVEL IMPACTS WILL BE MOST SIGNIFICANT OVER THE
CASCADE PASSES WHERE ANYWHERE FROM 4 TO 10 INCHES OF TOTAL SNOW IS
EXPECTED FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON, EXCEPT NEAR
ONE INCH AT WILLAMETTE PASS. THE HIGHEST SNOW AMOUNTS ARE EXPECTED IN
THE SOUTH WA CASCADES, ON MOUNT HOOD, AND ALONG HIGHWAY 26 NEAR
GOVERNMENT CAMP. UP TO ONE FOOT OF TOTAL SNOW IS EXPECTED FOR
ELEVATIONS ABOVE 5000 FEET IN THE SOUTH WA/NORTH OR CASCADES. IT IS
ALSO WORTH MENTIONING HIGHWAY 26 IN THE NORTH OREGON COAST RANGE WILL
LIKELY SEE A DUSTING OF WET SNOW, EXCEPT CLOSER TO AN INCH OR TWO
ABOVE ABOVE 1500-2000 FEET OVER A 36-HOUR PERIOD ENDING AT 5PM
TUESDAY. HOWEVER, SOME MELTING OF SNOW WILL OCCUR IN BETWEEN SHOWERS,
ESPECIALLY DURING DAYLIGHT HOURS. THIS SHOULD HELP MITIGATE OVERALL
TRAVEL IMPACTS, BUT ROADS MAY BECOME SLICK AT TIMES ON HIGHER
PORTIONS OF HIGHWAY 26, ESPECIALLY MONDAY MORNING AND AGAIN MONDAY
NIGHT/TUESDAY MORNING. -23
LONG TERM...TUESDAY NIGHT THROUGH SATURDAY NIGHT
THE LONG TERM
FORECAST IS HIGHLIGHTED BY WET AND BREEZY CONDITIONS WEDNESDAY
THROUGH FRIDAY WITH THE ARRIVAL OF A MODERATE ATMOSPHERIC RIVER,
HOWEVER RIVER FLOODING IS UNLIKELY AT THIS TIME (90-95% CHANCE RIVER
FLOODING WILL NOT OCCUR). FORECAST DETAILS BECOME MORE UNCERTAIN OVER
THE WEEKEND, ESPECIALLY IN REGARDS TO PRECIPITATION AMOUNTS AND EXACT
TEMPERATURES.
BEGINNING WITH THE TUESDAY NIGHT AND WEDNESDAY TIMEFRAME, MODELS AND
THEIR ENSEMBLES ARE IN GOOD AGREEMENT FOR WIDESPREAD RAIN TO BEGIN
OVER WESTERN WA AND MUCH OF NORTHWEST OR WITH NBM POPS INCREASING TO
AROUND 90% OR HIGHER. THIS RAIN WILL BE WITH THE ARRIVAL OF AN
ATMOSPHERE RIVER EMBEDDED WITHIN ZONAL FLOW ALOFT, WHICH LOOKS TO HIT
NORTHWEST OR HARDEST BEFORE SLOWLY SAGGING SOUTHWARD AS A MODERATE
ATMOSPHERIC RIVER (IVT VALUES BETWEEN 500-750 KG/M/S PER THE GEFS AND
EPS) FOR SOUTHWEST WA AND NORTHWEST OR. WHILE MODEL ENSEMBLE GUIDANCE
IS IN FAIRLY GOOD AGREEMENT REGARDING THE STRENGTH OF THIS SYSTEM,
AGREEMENT IS NOT AS GREAT REGARDING THE EXACT DURATION RAIN WILL
LAST. IN OTHER WORDS, IT IS NOT CLEAR YET WHETHER THE HEAVIER RAIN
WILL END THURSDAY NIGHT, FRIDAY, FRIDAY NIGHT, OR SATURDAY. AS SUCH,
THERE IS STILL A VERY LARGE DEGREE OF MODEL SPREAD IN REGARDS TO
TOTAL RAIN AMOUNTS. FOR EXAMPLE, THE NBM 10TH-90TH PERCENTILE FOR
72-HR QPF AMOUNTS ENDING AT 5AM SATURDAY RANGES FROM UNDER ONE INCH
IN THE LOWLANDS AND UNDER 2 INCHES IN THE MOUNTAINS TO 3-4 INCHES IN
THE LOWLANDS AND 4-7 INCHES IN THE MOUNTAINS. DEPENDING ON HOW
QUICKLY PRECIPITATION FALLS OVER A GIVEN WATERSHED OR URBAN AREA AND
THE DURATION OF PRECIPITATION, THESE HIGHER END SOLUTIONS COULD
RESULT IN SOME RIVER FLOODING AND URBAN FLOODING (HOWEVER THIS WOULD
REPRESENT THE WORSE CASE SCENARIO WITH A 10% CHANCE OF OCCURRING;
HEFS GUIDANCE FOR RIVER FLOODING BACKS THIS UP AND SHOWS
PROBABILITIES UNDER 10%, AND UNDER 5% FOR SLOWER-RESPONDING RIVERS).
LOWER TO MIDDLE END QPF SOLUTIONS WOULD RESULT IN NO HYDRO CONCERNS
AT ALL. AS OF RIGHT NOW, THE MOST LIKELY OUTCOME IS FOR MINIMAL TO NO
FLOODING CONCERNS, HOWEVER THIS SYSTEM WILL NEED TO BE MONITORED
CLOSELY OVER THE COMING DAYS.
HEADING INTO NEXT WEEKEND, UNCERTAINTY INCREASES REGARDING EXACT
TEMPERATURES AND PRECIPITATION AMOUNTS. FOR EXAMPLE, THE NBM
10TH-90TH PERCENTILE FOR 24-HR QPF AMOUNTS FROM 5AM SATURDAY TO 5AM
SUNDAY RANGE FROM NO PRECIPITATION AT ALL TO AROUND 1 INCH, EXCEPT TO
AROUND 1.5-3 INCHES IN THE MOUNTAINS. NBM 6-HOURLY POPS GRADUALLY
DECREASE DURING THAT TIME AS WELL, LOWERING TO NEAR 40-50%. IN
ADDITION, NBM SPREAD FOR MAX TEMPERATURES RANGES FROM THE UPPER 40S
TO NEAR 60 DEGREES. THIS IS MAINLY DUE TO UNCERTAINTY REGARDING HOW
AMPLIFIED A RIDGE OVER THE WESTERN CONUS WILL BE OVER THE WEEKEND. IN
FACT, WPC'S 500 MB EOF PATTERNS SUGGEST NEARLY 60% OF MODEL VARIANCE
CAN BE EXPLAINED BY THIS, AND AROUND 26% CAN BE EXPLAINED BY THE
EXACT POSITION OF THE RIDGE AXIS. IF THE RIDGE WINDS UP CENTERED OVER
WESTERN WA/OR AND IS AMPLIFIED ENOUGH, WE WILL TREND WARMER AND DRIER
WITH SPRING-LIKE TEMPERATURES. IF THE RIDGE FLATTENS, WE WILL TREND
COOLER AND WETTER THAN AVERAGE WITH MORE ZONAL FLOW ALOFT. -23
AVIATION
PREDOMINATELY VFR FLIGHT CONDITIONS WITH OCCASIONAL
MVFR CONDITIONS FOR MOST TERMINALS THROUGH 10Z MONDAY. THIS WILL
BE THE RESULT OF A LULL IN SHOWER ACTIVITY FOR THE MAJORITY OF THE
AIRSPACE WITH THE EXCEPTION BEING ALONG THE COAST NORTH OF KTMK
AS SHOWERS WILL CONTINUE TO LINGER 10Z MONDAY. OTHERWISE, THE LULL
IN SHOWERS WILL CEASE OF THE REMAINDER OF THE AIRSPACE STARTING
AROUND 10Z-15Z MONDAY. THEN, SHOWERS WILL PERSIST THROUGH THE
MAJORITY OF THE TAF PERIOD, ACROSS THE AIRSPACE AND WILL RESULT
IN A 30-50% CHANCE FOR MVFR CONDITIONS. WINDS GENERALLY REMAIN
BELOW 10 KNOTS BUT A FEW GUSTS OUT OF THE WEST/NORTHWEST UP TO 20
KNOTS WILL BE POSSIBLE ALONG THE COAST AFTER 18Z MONDAY.
KPDX AND APPROACHES...VFR CONDITIONS THROUGH MUCH OF MONDAY.
ANOTHER FRONT AROUND 08Z-10Z MONDAY WILL BRING A 30-50% CHANCE FOR
MVFR CONDITIONS NEAR THE TERMINAL THROUGH THE REMAINDER OF THE
TAF PERIOD. NORTHWEST WINDS LESS THAN 10 KT EXPECTED. /42
MARINE
LATE THIS AFTERNOON A WEAK FRONTAL BOUNDARY CONTINUES TO
MOVE ACROSS THE COAST WATERS WITH WINDS QUICKLY TURNING
NORTHWESTERLY IN ITS WAKE. THESE WINDS COMBINED WITH A
NORTHWESTERLY SWELL AND LOW PRESSURE SYSTEM IN THE GULF OF ALASKA
PUSH SEAS IN THE 9-11 FT AT 12 SECONDS TONIGHT INTO MONDAY. EXPECT
THE GREATEST IMPACT OVER THE NORTHERN OUTER WATERS WHERE A SMALL
CRAFT ADVISORY IS IN EFFECT THROUGH TUESDAY AFTERNOON.
HEADED INTO THE MIDDLE OF THE WEEK, A SECONDARY LOW PRESSURE
SYSTEM AND ACCOMPANYING WARM FRONT WILL SKIRT OVER VANCOUVER
ISLAND ON WEDNESDAY INCREASING THE NORTH-SOUTH PRESSURE GRADIENT.
A SOUTHERLY WIND REVERSAL IS EXPECTED AND FOLLOWED BY A
SUBSTANTIAL INCREASE IN BOTH SUSTAINED WINDS AND GUSTS.
CONFIDENCE IS RISING IN GALE FORCE WIND POTENTIAL WEDNESDAY
AFTERNOON AND EVENING WITH THE NBM PROJECTING A 40-60% CHANCE FOR
HOURLY WIND GUSTS TO EXCEED 34 KNOTS DURING THIS PERIOD. SEAS
LIKELY RESPOND AS WELL, RISING UP INTO THE 14-17 FT RANGE AT 10-11
SECONDS WHICH WOULD LEAD TO A HAZARDOUS SEAS STATE. AT LEAST A
COASTAL JET IS NOT FORECAST, BUT WIND GUST SPEEDS WILL HOVER RIGHT
AROUND 34-40 KT. DUE TO STRONGER WINDS ALOFT, THEY COULD MIX DOWN
AND AREAS AROUND THE COLUMBIA RIVER BAR HAVE AROUND A 10% CHANCE
OF WIND GUSTS OF 50 KT OR GREATER. CONDITIONS GRADUALLY SETTLE
DOWN THURSDAY THROUGH THE END OF THE WEEK BUT THE OVERALL PATTERN
REMAINS ACTIVE MOVING FORWARD. -99
PQR WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY FROM 5 AM MONDAY TO 5 PM PDT TUESDAY FOR
ORZ126.
WA...WINTER WEATHER ADVISORY FROM 5 AM MONDAY TO 5 PM PDT TUESDAY FOR
WAZ211.
PZ...SMALL CRAFT ADVISORY UNTIL 5 PM PDT TUESDAY FOR PZZ271-272.
WWW.WEATHER.GOV/PORTLAND
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