530
FXUS66 KPQR 131116
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
416 AM PDT MON APR 13 2026
SYNOPSIS
SCATTERED LIGHT SHOWERS CONTINUE AT TIMES TODAY.
HOWEVER, OUR FOCUS REMAINS ON A STRONGER FRONTAL SYSTEM
ARRIVING LATE TUESDAY INTO WEDNESDAY BRINGING WIDESPREAD
PRECIPITATION TO THE REGION AND A PERIOD OF HEAVY CASCADE
SNOWFALL. A WINTER STORM WATCH REMAINS IN EFFECT LATE TUESDAY
INTO EARLY THURSDAY ABOVE 3500FT. WHILE SHOWERS IN THE WAKE OF
THE FRONT DECREASE MID TO LATE WEEK, COOLER OVERNIGHT
TEMPERATURES QUICKLY FOLLOW WITH INCREASING FROST CONCERNS. AT
LEAST TEMPERATURES TREND HIGHER AND CONDITIONS DRIER FOR
SATURDAY.
SHORT TERM...NOW THROUGH WEDNESDAY NIGHT
TODAY A WEAK
SHORTWAVE WEATHER DISTURBANCE IS EXPECTED TO MOVE THROUGH THE
REGION HELPING TO MAINTAIN WIDESPREAD LIGHT SHOWER ACTIVITY.
GIVEN THE BROAD WNW FLOW, SHOWERS WILL BE MOST LIKELY ACROSS
THE CASCADES, COAST RANGE, AND FOOTHILLS WHERE OROGRAPHIC LIFT
WILL ENHANCE ACTIVITY. BY LATE THIS AFTERNOON 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 USHER IN LOCALLY BREEZY CONDITIONS, WITH GUSTS
GENERALLY IN THE 20-35 MPH RANGE, STRONGEST ALONG THE COAST.
CONFIDENCE IS HIGH BY THE EVENING HOURS THE COLD FRONTAL
BOUNDARY AND STEADIER STRATIFORM PRECIPITATION WILL BE UNDERWAY
CONTINUING TO SWEEP OVERNIGHT INTO WEDNESDAY MORNING. RAINFALL
AMOUNTS APPEAR MODEST DURING THIS PERIOD, WITH 24-HOUR TOTALS
GENERALLY RANGING FROM 0.7 TO 1.2 INCHES ACROSS THE WILLAMETTE
VALLEY AND PORTLAND METRO, 0.9 TO 1.8 INCHES ALONG THE COAST AND
COAST RANGE, AND 1.0 TO 2.0 INCHES ACROSS THE CASCADES.
HOWEVER, FOR THE LATTER REGION, ESPECIALLY AT PASS LEVEL, THE
PRECIPITATION WILL LIKELY BE FALLING AS SNOW.
THAT BRINGS US TO THE PRIMARY IMPACT ANTICIPATED WITH THIS
WEATHER DISTURBANCE. COOLING TEMPERATURES ALONG AND BEHIND THE
FRONT WILL LOWER SNOW LEVELS 2500-3500FT BY SUNRISE WEDNESDAY
MORNING ACROSS MOST OF THE SOUTH WASHINGTON AND OREGON CASCADES
SIGNIFICANTLY INCREASING THE LIKELIHOOD OF WINTER TRAVEL
IMPACTS. THE LATEST NBM PROBABILISTIC GUIDANCE INDICATES A
55-90% CHANCE OF 12+ INCHES OF SNOWFALL AT THE CASCADE PASSES
BETWEEN TUESDAY AFTERNOON AND THURSDAY AFTERNOON (48 HOURS),
HIGHEST AT SANTIAM PASS. AS A RESULT, THE WINTER STORM WATCH
REMAINS IN EFFECT 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 10 TO 20 INCHES
ARE EXPECTED, WITH THE HIGHEST AMOUNTS IN THE HIGH CASCADES
FROM MARION TO LANE COUNTY. WHILE THE WARM ANTECEDENT CONDITIONS
MAY INITIALLY STAVE OFF ROAD ACCUMULATION AFTER THE SWITCH TO
SNOW, THERE IS HIGH CONFIDENCE A PERIOD OF 1-1.5+ IN/HR SNOWFALL
RATES WEDNESDAY MORNING WILL OVERCOME ANY WARM PAVEMENT
CONDITIONS. AS SUCH, TRAVEL RELATED IMPACTS OVER THE MOUNTAIN
PASSES WILL BE POSSIBLE THROUGH WEDNESDAY AND WEDNESDAY NIGHT -
BE PREPARED TO WINTER DRIVING CONDITIONS IF YOU PLAN TO CROSS
THE CASCADES DURING THE MIDDLE OF THE WEEK.
IT'S ALSO WORTH POINTING OUT ONCE WE SHIFT TO THE POST-FRONTAL
SHOWER REGIME WEDNESDAY AFTERNOON DURING WHICH THE CORE OF THE
UPPER-LEVEL LOW PASSES OVERHEAD, CONVECTION MAY BE STRONG
ENOUGH FOR SOME WEAK THUNDERSTORM ACTIVITY. THE MAIN TIME
PERIOD OF FOCUS IS 2PM TO 7PM WEDNESDAY WHEN HEATING BETWEEN
SHOWER BANDS MAY BE MAXIMIZED. WITH DETERMINISTIC MODELS
SUGGESTING CAPE VALUES AROUND 100-300 J/KG ACTIVITY WILL BE OF
THE WEAKER POP-UP VARIETY WITH INFREQUENT LIGHTNING, SMALL
HAIL/GRAUPEL, MODERATE AND LOCALLY GUSTY WINDS THE MAIN IMPACTS
SHOULD ANY OCCUR (10-20% CHANCE). -99
LONG TERM...THURSDAY THROUGH SUNDAY
WITH THE FRONTAL BOUNDARY
WELL OUT OF THE REGION COME EARLY THURSDAY, IMPACTS SHIFT TO
COOLER AND POTENTIALLY CLEARER CONDITIONS BEHIND THE SYSTEM
BRINGING RENEWED FROST CONCERNS TO THE INTERIOR VALLEYS. THE
FIRST OPPORTUNITY APPEARS NEAR SUNRISE THURSDAY MORNING, WITH A
50-80% 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 70-90% 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 (ONLY 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 25-50%
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. ENSEMBLES HINT AT A TRANSIENT RIGHT OF HIGH PRESSURE
MOVING OVERHEAD TO START THE WEEKEND FOLLOWED BY ANOTHER LOW
PRESSURE SYSTEM SOMETIME THE SECOND HALF OF THE WEEKEND INTO THE
FOLLOWING WEEK, ALTHOUGH BEYOND THE LARGER SCALE PATTERN THE
EXACT DETAIL AND IMPACTS REMAIN UNCERTAIN AT THIS TIME. -99/12
AVIATION
EARLY THIS MORNING CONDITIONS ARE A MIX OF VFR TO IFR
ACROSS THE REGION WITH BROAD NORTHWESTERLY FLOW ALOFT. A WEAK
DISTURBANCE PROGRESSING OVERHEAD IS EXPECTED TO INCREASE LIGHT
SHOWERS, ESPECIALLY ALONG THE COAST AND OVER TERRAIN FEATURES LIKE
THE COAST RANGE, AND CASCADES. THIS DISTURBANCE WILL ALSO
INCREASE PROBABILITIES FOR SUB-VFR CONDITIONS FOR ALL TERMINALS.
INLAND TERMINALS HAVE A 30-75% CHANCE FOR MVFR CIGS UNTIL 18-19Z,
HIGHEST AT KTTD, AND COASTAL TERMINALS HAVE CHANCES CLOSER TO
60-80% THROUGH 18-20Z. AFTER THIS POINT VFR CONDITIONS REMAIN
FAVORED, ALTHOUGH ANY OF THE AFOREMENTIONED SHOWERS MAY PUSH
CIGS/VIS BACK TO MVFR TEMPORARILY. WINDS REMAIN WEST TO NORTHWEST
THROUGH THE PERIOD.
KPDX AND APPROACHES...MVFR CONDITIONS IN PLACE EARLY THIS MORNING
WILL TREND TOWARDS VFR BY 16-17Z, ALTHOUGH SHOWERS AT ANY POINT
TODAY MAY PUSH CIGS BACK TO MVFR - 20-30% CHANCE FOR MVFR
CONDITIONS FROM 17-21Z. LIGHT WESTERLY WINDS ARE EXPECTED THROUGH
THE PERIOD. -99
MARINE
EXPECT WNW WINDS TO PERSIST TODAY INTO THE EVENING HOURS
AS CONDITIONS STAY FAIRLY BENIGN WHILE SIGNIFICANT WAVE HEIGHTS
HOLD IN THE IN THE 4 TO 7 FOOT RANGE. OUR FOCUS THEN TURNS TO THE
NEXT WEATHER SYSTEM IN THE FORM OF A COLD FRONTAL BOUNDARY
INCREASING BOTH WINDS AND SEAS STARTING ON TUESDAY. SMALL CRAFT
ADVISORY WIND GUSTS INCREASE ACROSS BOTH THE INNER AND OUTER
WATERS IN THE MORNING HOURS, PEAKING IN THE LATE AFTERNOON AND
EVENING HOURS AS THE FRONT ARRIVES. WHEN THIS OCCURS, THERE'LL BE
A ~6HR PERIOD WHEN GUSTS COULD (30-40%) EXCEED 34 KNOTS AND REACH
INTO GALE FORCE CATEGORY - SOMETHING TO WATCH. LATER TUESDAY INTO
WEDNESDAY A FRESH 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 FURTHER ON
THURSDAY. WAVE HEIGHTS REVERT BACK INTO THE 4 TO 7 FEET RANGE
FRIDAY AND SATURDAY BEFORE POTENTIALLY INCREASING AGAIN LATER NEXT
WEEKEND WITH THE ARRIVAL OF ANOTHER WEATHER SYSTEM. -99/03
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...SMALL CRAFT ADVISORY FROM 8 AM TUESDAY TO 5 AM PDT WEDNESDAY
FOR PZZ210-252-253-272-273.
SMALL CRAFT ADVISORY FROM 5 AM TUESDAY TO 5 AM PDT WEDNESDAY
FOR PZZ251-271.
WWW.WEATHER.GOV/PORTLAND
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