615
FXUS66 KPQR 151118
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
418 AM PDT WED APR 15 2026
SYNOPSIS
THE BACK EDGE OF A COLD FRONTAL BOUNDARY WHICH
HAS SPREAD AMPLE PRECIPITATIION AND MOUNTAIN SNOWFALL ACROSS
THE PACIFIC NORTHWEST QUICKLY PROGRESSES THROUGH THE REGION THIS
MORNING FOLLOWED BY A SHOWERY AIRMASS AND A 15-30% CHANCE FOR
THUNDERSTORMS THIS AFTERNOON. A WINTER STORM WARNING REMAINS IN
EFFECT FOR THE CASCADES THROUGH TONIGHT. CONCERNS SHIFT TO
COOLER OVERNIGHT TEMPERATURES AND POSSIBLE FROST/FREEZE
CONDITIONS TO ROUND OUT THE WEEK. AFTER A BRIEF STINT OF DRY
AND WARMER WEATHER SATURDAY, PRECIPITATION CHANCES RETURN BY
EARLY NEXT WEEK ALTHOUGH FORECAST CONFIDENCE SUNDAY ONWARD IS
LOW.
SHORT TERM...NOW THROUGH THURSDAY NIGHT
EARLY THIS MORNING
SATELLITE AND RADAR OBSERVATIONS SHOW OUR LATEST WEATHER
DISTURBANCE IN THE FORM OF A COLD-FRONTAL BOUNDARY AND THE WIDE
BAND OF STRATIFORM PRECIPITATION DROPPING NW TO SE ACROSS
WESTERN OREGON. SNOW-LEVELS ARE EXPECTED TO QUICKLY BOTTOM OUT
AROUND 1500-2000FT IN THE COLD AIRMASS BEHIND THE FRONTAL
BOUNDARY BY LATE MORNING WITH SNOWFALL CONTINUING TO BE THE
PRIMARY IMPACT WITH THIS DISTURBANCE FOCUSED OVER THE CASCADES.
WE'RE STILL WATCHING FOR A POTENTIAL FOR 1-3 HR PERIOD OF
DYNAMIC COOLING ARTIFICIALLY LOWERING SNOW LEVELS CLOSER TO
~1000FT AROUND SUNRISE THIS MORNING, PARTICULARLY IN COAST RANGE
AND SOUTHWEST WASHINGTON SOUTHWARD THROUGH PORTIONS OF
CLACKAMAS COUNTY. HOWEVER, AS FAR AS TRAVEL IS CONCERNED, IT'LL
BE CHALLENGING TO GET ACCUMULATION ON ROADWAYS AT THIS ELEVATION
SHOULD A PERIOD OF WET SNOW OR A RAIN/SNOW MIX OCCUR. THE
CHANCES FOR A LIGHT SLUSH-UP GETS HIGHER ONCE YOU REACH 1500FT,
PARTICULARLY IN THE CASCADE FOOTHILLS/VALLEYS, BUT DUE TO THE
WARM ANTECEDENT CONDITIONS MOST IMPACTS REMAIN 2000-2500FT+.
THE HEAVIER PRECIPITATION EARLY TO MID MORNING HELPING TO DRIVE
THESE LOWER SNOW LEVELS WILL ALSO HELP TO BOOST SNOWFALL RATES
AT PASS LEVEL, LIKELY REACHING 1-1.5+ IN/HR UNTIL THE FROST
PASSES. IF YOU PLAN TO TRAVERSE ACROSS THE MOUNTAIN PASSES
TODAY, PLEASE PREPARE FOR WINTER-LIKE TRAVEL CONDITIONS.
ONCE WE GET INTO THE MIDDAY AND AFTERNOON HOURS WE'LL HAVE
TRANSITION TO A MORE CONVECTIVE AND SHOWERY POST FRONTAL
ENVIRONMENT THANKS TO THE CORE OF A UPPER LEVEL LOW MOVING
OVERHEAD. MOST MODELS STILL SHOW CONVECTIVE AVAILABLE POTENTIAL
ENERGY (CAPE) VALUES PEAKING AROUND 200 TO 500 J/KG THIS
AFTERNOON LEADING TO A 15-30% CHANCE FOR THUNDERSTORM
DEVELOPMENT ACROSS THE CWA. THE MAIN TIME PERIOD OF FOCUS IS
11AM TO 7PM TODAY WHEN HEATING BETWEEN SHOWER BANDS IS
MAXIMIZED. CONVECTIVE ALLOWING MODEL (CAM) SOUNDINGS ARE SHOWING
A SKINNY CAPE PROFILE AND ALONG WITH COOLER TEMPERATURES ALOFT,
THIS DOES SUPPORT TINY HAIL/GRAUPEL DEVELOPMENT WITH ANY
THUNDERSTORMS THAT DEVELOP AND GIVEN THAT WHEN SPRING TIME
THUNDERSTORMS DEVELOP WITHIN OUR CWA, THEY HAVE A TENDENCY TO
PRODUCE A LOT OF TINY PEA SIZE HAIL. ALSO BE ON THE LOOKOUT FOR
INFREQUENT LIGHTNING, GUSTY WINDS, AND HEAVY RAIN ASSOCIATED
WITH ANY ACTIVITY. WITH THE LOSS OF DAYTIME HEATING
THUNDERSTORM CHANCES DECREASE WEDNESDAY NIGHT ALTHOUGH SHOWERS
LIKELY PERSIST.
AT THIS POINT THE AXIS OF THE UPPER-LEVEL LOW PULLS TO OUR EAST
WITH INCREASING HEIGHTS ON NORTHERLY FLOW ALOFT BY SUNRISE
THURSDAY MORNING HELPING TO DECREASE SHOWER ACTIVITY. THE
LINGERING COOLER TEMPERATURES ALOFT AND PARTIAL CLEARING BY
SUNRISE SHOULD ALLOW OVERNIGHT LOWS TO DROP BELOW NORMAL
BOTTOMING OUT IN THE MID 30S ACROSS THE LOWLANDS. BELOW
FREEZING TEMPERATURES ARE EVEN FORECAST FOR THE HIGHER COAST
RANGE/CASCADE VALLEYS, INCLUDING THE HOOD RIVER VALLEY, AND
POTENTIALLY IN THE CASCADE FOOTHILLS MAINLY AROUND AND SOUTH OF
OR-22. GIVE THE MODERATE TO HIGH CONFIDENCE IN THESE LOW
TEMPERATURES PANNING OUT, HAVE ISSUED FROST ADVISORIES FOR MUCH
OF THE REGION INCLUDING A FREEZE WATCH FOR THE UPPER HOOD RIVER
VALLEY AND A COUPLE OF THE AFOREMENTIONED OREGON CASCADE
FOOTHILL ZONES. A FEW SHOWERS LIKELY LINGERING THROUGH THURSDAY,
INCREASING IN THE AFTERNOON DUE TO DAYTIME HEATING, HOWEVER, THE
BULK OF THE ACTIVITY WILL BE PINNED TO TERRAIN FEATURES IN THE
CASCADES AND COAST RANGE. SIMILAR FROST/FREEZE CONDITIONS MAY
DEVELOP AGAIN THURSDAY NIGHT INTO FRIDAY MORNING AND ADDITIONAL
HIGHLIGHTS MAY BE NEEDED FOR THIS PERIOD. EVEN THOUGH
TEMPERATURES WARM SLIGHTLY ALOFT THURSDAY NIGHT COMPARED TO
WEDNESDAY NIGHT/THURSDAY MORNING, WEAK PRESSURE GRADIENTS
COMBINED WITH A BUILDING RIDGE OF HIGH PRESSURE ALOFT AND BETTER
CLEARING MAY PROVE TO BE A BETTER SET-UP FOR FROST DEVELOPMENT.
-99/42
LONG TERM...FRIDAY THROUGH TUESDAY
LOOKING TOWARDS THE
WEEKEND CONFIDENCE IS HIGH AMONG BOTH DETERMINISTIC AND
ENSEMBLE GUIDANCE IN A RIDGE OF HIGH PRESSURE CONTINUING TO
BUILD ALOFT ALLOWING TEMPERATURES TO GRADUALLY WARM AND REDUCE
FROST CONCERNS. HOWEVER THE PATTERN REMAINS RATHER PROGRESSIVE
AS MODELS SHOW THE RIDGE QUICKLY FOLLOWED BY ANOTHER LOW
PRESSURE SYSTEM ON SUNDAY ORIGINATING FROM THE GULF OF ALASKA.
WPC CLUSTER GUIDANCE DOES FAVOR THIS LOW DROPPING ALMOST
STRAIGHT SOUTHWARD ACROSS THE EASTERN PACIFIC FAVORING THIS LOW
HOLDING JUST OFF THE OR/WA COAST. HOW FAR THIS LOW HOLDS OFF THE
COAST WILL HEAVILY MODULATE CONDITIONS LOCALLY. SHOULD IT STAY
MORE TO OUR WEST, WARMER CONDITIONS AND BROAD SOUTHERLY FLOW
WOULD BE FAVORED, THAT SAID, ANY MOISTURE RIDING SOUTH TO NORTH
WITHIN THIS FLOW PATTERN COULD SPELL THE RETURN OF CONVECTION.
THUS FORECAST CONFIDENCE SUNDAY ONWARD INTO THE MIDDLE OF NEXT
WEEK IS LOW. -99/42
AVIATION
AS WE MOVE THROUGH THE MORNING HOURS STEADIER RAIN
WILL TRANSITION TO SHOWERS BEHIND THE FRONTAL BOUNDARY MOVING
OVERHEAD - KAST HAS ALREADY SEEN AN IMPROVEMENT BACK TO VFR AS A
RESULT. EXPECT A SOUTH TO NORTHWEST WIND SWITCH WHEN THE FRONT
PASSES THIS MORNING AS WELL. HOWEVER, AS BANDS OF SHOWERS MOVE
OVERHEAD, ESPECIALLY DURING THE AFTERNOON AND EVENING HOURS, BRIEF
DROP TO MVFR OR IFR CAN BE EXPECTED. ON THE WHOLE THERE IS A
20-40% CHANCE FOR MVFR CONDITIONS AT THE COAST THIS AFTERNOON WITH
A 15-25% INLAND. IT'S ALSO WORTH HIGHLIGHTING THERE IS ALSO A
20-30% CHANCE FOR THUNDERSTORMS FOR ALL TERMINALS AFTER ROUGHLY
18-21Z TODAY WITH LIGHTNING AND GUSTY/ERRATIC WINDS THE PRIMARY
IMPACTS. CHANCES FOR THESE STORMS QUICKLY DROP OFF AROUND 4-6Z
THUR.
KPDX AND APPROACHES...MVFR CONDITIONS AND BREEZY SOUTHERLY WINDS
LIKELY PERSIST UNTIL 14-16Z THIS MORNING WHILE THE PRIMARY
PRECIPITATION BAND SITS OVERHEAD. AFTER HIS POINT WINDS GAIN A
WESTERLY COMPONENT WHILE RAINFALL TURNS MORE SHOWERY, BUT AT LEAST
IT TRENDS MORE TOWARDS VFR THE REMAINDER OF THE TAF PERIOD. KEEP
IN MIND THERE WILL BE A 20-25% CHANCE FOR THUNDERSTORMS LOCALLY
AFTER ~20Z THROUGH -4Z THIS EVENING. ANY ROBUST SHOWERS OR STORMS
MAY BRIEFLY DROP CONDITIONS TO MVFR/IFR. -99
MARINE
A COLD FRONTAL BOUNDARY IS QUICKLY PROGRESSING ACROSS
THE COASTAL WATERS EARLY THIS MORNING WITH WINDS SWITCHING
NORTHWESTERLY IN ITS WAKE. EXPECT GUSTS BETWEEN 20-30 KNOTS THE
REMAINDER OF THE DAY AS AN AREA OF LOW PRESSURE DROPS ALONG THE
CANADIAN COAST TOWARD THE REGION. THIS FEATURE WILL ALSO BRING A
15-25% CHANCE OF THUNDERSTORMS OVER THE WATERS INTO THE EVENING
HOURS. SEAS ARE EXPECTED TO PERSIST AT AROUND AROUND 9 TO 10 FT,
BUILDING SLIGHTLY TO AROUND 10 TO 12 FT TONIGHT AS A FRESH NORTHWEST
SWELL MOVES THROUGH THE WATERS. THE SMALL CRAFT ADVISORY REMAINS
IN PLACE THROUGH THURSDAY MORNING FOR BOTH THE INNER AND OUTER
WATERS, INCLUDING THE COLUMBIA RIVER BAR. HIGH PRESSURE THEN
BUILDS OVER THE WATERS THURSDAY INTO THE WEEKEND AS NORTHERLY
WINDS RETURN AND SEAS GRADUALLY SUBSIDE TO AROUND 3 TO 6 FT FRIDAY
INTO SATURDAY. IT APPEARS THERE'S A 40-60% CHANCE FOR NORTH WINDS
TO GUST ABOVE 21 KNOTS INTO SMALL CRAFT CRITERIA ON SATURDAY.
LOOKING AHEAD THERE IS POTENTIAL FOR ANOTHER WEATHER SYSTEM TO
IMPACT THE WATERS LATER THIS WEEKEND, POSSIBLY INCREASING WINDS
AND SEAS. -99/DH
PQR WATCHES/WARNINGS/ADVISORIES
OR...FROST ADVISORY FROM 1 AM TO 9 AM PDT THURSDAY FOR ORZ104>107-
109-114>118-123.
FREEZE WATCH FROM LATE TONIGHT THROUGH THURSDAY MORNING FOR
ORZ121-124-125.
WINTER WEATHER ADVISORY UNTIL 11 AM PDT THIS MORNING FOR
ORZ123.
WINTER STORM WARNING UNTIL 5 AM PDT THURSDAY FOR ORZ126>128.
WA...FROST ADVISORY FROM 1 AM TO 9 AM PDT THURSDAY FOR WAZ204-205-
208.
WINTER STORM WARNING UNTIL 5 AM PDT THURSDAY FOR WAZ211.
PZ...SMALL CRAFT ADVISORY UNTIL 5 AM PDT THURSDAY FOR PZZ210.
SMALL CRAFT ADVISORY UNTIL 11 AM PDT THURSDAY FOR PZZ251>253-
271>273.
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