270
FXUS66 KPQR 131757 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
1057 AM PDT MON APR 13 2026
UPDATED SHORT TERM AND AVIATION DISCUSSIONS
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. AS A
RESULT HAVE UPGRADED THE WINTER STORM WATCH TO A WINTER STORM
WARNING FROM LATE TUESDAY INTO EARLY THURSDAY ABOVE 2500FT.
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.
MORNING UPDATE
HAVE UPGRADED THE WINTER STORM WATCH TO A
WINTER STORM WARNING. THE INCOMING SYSTEM LOOKS TO BRING 12 TO
20 INCHES OF SNOWFALL TO THE CASCADES STARTING TUESDAY AFTERNOON
THROUGH EARLY THURSDAY MORNING, FOR ELEVATIONS ABOVE 2500 FT.
IN ADDITION WE ARE KEEPING AN EYE ON THE INCOMING SYSTEM AS
THERE IS A LOW CHANCE (~5%) OF SOME WET SNOW ACCUMULATIONS ABOVE
1000 FT DURING THE SAME TIME PERIOD. SO, IF YOU ARE PLANNING ON
GOING OVER THE CASCADE PASSES IN THE NEXT FEW DAYS, PLEASE KEEP
AN EYE ON ROAD CONDITIONS AS WELL AS ANY INFORMATIONAL POSTS
MADE BY LOCAL OFFICIALS. /42
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, HAVE UPGRADED THE WINTER
STORM WATCH TO A WINTER STORM WARNING FOR ELEVATIONS ABOVE
2500 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 12 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
NORTHWEST FLOW ALOFT WITH DIMINISHING SHOWERS TODAY. A
MIX OF VFR TO MVFR CONDITIONS EXPECTED TO BECOME PREDOMINATELY VFR
BY 22Z THIS AFTERNOON, WITH ONLY A 10-20% CHANCE OF MVFR OCCURRING
WITH PASSING SHOWERS THROUGH THIS EVENING. WESTERLY SURFACE WINDS
AROUND 10 KT OR LESS CONTINUE TODAY. A COLD FRONT WILL APPROACH
THE REGION FROM THE NORTHWEST TUESDAY MORNING, BRINGING INCREASING
CHANCES FOR RAIN AND LOWER CEILINGS TO THE AREA ON TUESDAY.
CHANCES FOR MVFR CONDITIONS BEGIN TO INCREASE AGAIN AFTER 12Z TUE
AT THE COAST WHILE WINDS ARE EXPECTED TO BECOME MORE SOUTHERLY
AHEAD OF THE FRONT.
KPDX AND APPROACHES...PREDOMINATELY VFR CONDITIONS EXPECTED
THROUGH AT LEAST 18Z TUESDAY. THERE IS AROUND A 20-30% CHANCE FOR
MVFR CIGS WITH PASSING SHOWERS THROUGH 22Z THIS AFTERNOON.
NORTHWEST WINDS AROUND 4-6 KT EXPECTED TO BECOME SOUTHERLY BY 08Z
TUESDAY. /DH
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 WARNING FROM 5 PM TUESDAY TO 5 AM PDT THURSDAY
FOR ORZ126>128.
WA...WINTER STORM WARNING FROM 5 PM TUESDAY TO 5 AM PDT THURSDAY
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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