569
FXUS66 KPQR 220456
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
956 PM PDT MON APR 21 2025
UPDATED AVIATION DISCUSSION
SYNOPSIS
ISOLATED SHOWERS WILL TAPER OFF THIS AFTERNOON,
WITH RETURN TO DRY WEATHER. AREAS OF FROST IS EXPECTED TONIGHT
AS TEMPERATURES COOL INTO THE LOW TO MID 30S ACROSS MUCH OF THE
AREA. TAKE NECESSARY PRECAUTIONS FOR SENSITIVE OUTDOOR PLANTS.
EXPECT WARMING TEMPERATURES AND MOSTLY CLEAR SKIES THROUGH
THURSDAY. PATTERN CHANGE RETURNS FRIDAY AS AN APPROACHING SYSTEM
RETURNS COOLER TEMPERATURES AND CHANCES FOR PRECIPITATION.
SHORT TERM...NOW THROUGH WEDNESDAY NIGHT
RADAR IMAGERY AND
MESOANALYSIS AS OF 3 PM PDT DEPICTS NORTHWEST FLOW ALOFT WITH
ISOLATED SHOWERS ACROSS PORTIONS OF NORTHWEST OREGON AND
SOUTHWEST WASHINGTON. MOST OF THE SHOWER ACTIVITY HAS BEEN NORTH
OF TILLAMOOK ALONG THE COAST AND NORTH OF AURORA IN THE
WILLAMETTE VALLEY. EXPECT THESE SHOWERS TO TAPER OFF THROUGHOUT
THE AFTERNOON WITH CLEARING SKIES.
TONIGHT, CALM WINDS AND MOSTLY CLEAR SKIES WILL LEAD TO COLDER
OVERNIGHT TEMPERATURES VIA EFFICIENT RADIATIONAL COOLING.
TUESDAY MORNING LOW TEMPERATURES ARE FORECAST BETWEEN 33 TO 36
DEGREES ACROSS MOST AREAS WEST OF THE CASCADES EXCEPT ALONG THE
COAST AND INNER PORTLAND METRO AREA. THESE COLDER TEMPERATURES
ALONG WITH SUFFICIENT SURFACE MOISTURE WILL LEAD TO AN INCREASED
POTENTIAL FOR FROST FORMATION, ESPECIALLY OVER GRASSES AND
ELEVATED METAL SURFACES. THE CURRENT FROST ADVISORY REMAINS IN
EFFECT BETWEEN 12 AM TO 9 AM TUESDAY FOR ALL AREAS WEST OF THE
HIGH CASCADES, EXCEPT FOR THE COAST AND INNER PORTLAND METRO.
URBAN HEAT ISLAND EFFECTS ARE LIKELY LEADING TO THOSE WARMER
FORECAST TEMPS IN THE PORTLAND METRO AREA.
MEANWHILE, THE ORIGINAL FROST ADVISORY IN THE UPPER HOOD RIVER
VALLEY HAS BEEN UPGRADED TO A FREEZE WARNING, ALSO IN EFFECT
FROM 12 AM TO 9 AM TUESDAY. TUESDAY MORNING LOWS IN THIS AREA
ARE FORECAST BETWEEN 28 TO 32 DEGREES. THE PROBABILITY FOR A
HARD FREEZE OCCURRING (TEMPS FALLING BELOW 28 DEGREES) IN THIS
AREA IS AROUND 5-15%. THE COLDEST TEMPERATURES ARE FORECAST
ABOVE 1000 FEET ELEVATION, BETWEEN ODELL AND PARKDALE. TAKE
STEPS NOW TO PROTECT SENSITIVE OUTDOOR PLANTS FROM THE COLD. TO
PREVENT WATER PIPES FROM FREEZING, WRAP OR DRAIN OR ALLOW THEM
TO DRIP SLOWLY.
THE FROST/FREEZE THREAT SHOULD END BY MID-MORNING TUESDAY AS
DAYTIME HEATING PROGRESSES. THE UPPER LEVEL PATTERN TURNS INTO
DRY NORTHERLY FLOW, WITH RIDGING BUILDING OVER THE NE PACIFIC
AND A SHORTWAVE TROUGH DROPPING INTO THE INTERMOUNTAIN WEST. NO
PRECIPITATION EXPECTED IN OUR AREA WITH THIS SHORTWAVE TROUGH.
HIGH CONFIDENCE FOR TEMPERATURES WARMING UP INTO THE MID 60S
ACROSS THE WILLAMETTE VALLEY TOMORROW AND LOW 70S BY WEDNESDAY
WITH MOSTLY SUNNY SKIES AS UPPER LEVEL RIDGING BUILDS OVER THE
PACIFIC NORTHWEST. -ALVIZ
LONG TERM...THURSDAY TO SUNDAY
CONDITIONS GENERALLY REMAIN
WARM AND DRY ON THURSDAY AS THE UPPER LEVEL RIDGE PROGRESSES
EASTWARD. THURSDAY LOOKS TO BE THE WARMEST DAY OF THE WEEK, WITH
INLAND HIGHS FORECAST TO PEAK IN THE MID TO UPPER 70S.
PROBABILITIES FOR REACHING 80 DEGREES OR WARMER ARE AROUND
15-35%, MAINLY FOR THE PORTLAND METRO AREA.
A PATTERN SHIFT ARRIVES THURSDAY NIGHT INTO FRIDAY, AS THE
MAJORITY OF ENSEMBLE MEMBERS FROM THE GEFS, EPS, AND GEPS ARE IN
AGREEMENT OF AN UPPER LEVEL TROUGH APPROACHING THE PACIFIC
NORTHWEST. THERE IS STILL SOME UNCERTAINTY WITH THE EXACT TRACK
AND MAGNITUDE OF THE LOW, HOWEVER, THERE IS INCREASING
CONFIDENCE FOR A RETURN OF COOLER TEMPERATURES AND WIDESPREAD
PRECIPITATION CHANCES TOWARD THE END OF THE WEEK. ON FRIDAY, NBM
PROBABILITIES FOR 24 HOUR PRECIPITATION ENDING 5 AM SATURDAY OF
0.25 INCH OR GREATER IS AROUND 15-30% ALONG THE COAST AND
WILLAMETTE VALLEY, AND AROUND 40-60% FOR THE COAST RANGE AND
CASCADES. COOLER TEMPS AND PRECIPITATION CHANCES REMAIN
THROUGH SUNDAY AS BROAD TROUGHING PROGRESSES THROUGH THE
WESTERN U.S. -ALVIZ
AVIATION
GOING THROUGH THE REST OF TONIGHT AND TUESDAY EXPECT
MAINLY VFR CONDITIONS AS NORTHWEST FLOW TURNS NORTHERLY ALOFT.
SATELLITE CURRENTLY INDICATES SOME LOW CLOUD COVER BUILDING ALONG
THE WEST SLOPES OF THE CASCADES THIS EVENING WHICH IS A FEATURE
WE'LL NEED TO KEEP A CLOSE EYE ON. THE SUBSECTION OF HIGH
RESOLUTION GUIDANCE WHICH SHOWS THIS DEVELOPMENT SUGGEST THESE
LIKELY MEANDER FURTHER WESTWARD NEAR/AFTER SUNRISE WHICH WOULD
DROP KTTD DOWN TO MVFR CIGS FOR A PERIOD OF TIME - POTENTIALLY PDX
AND KUAO AS WELL. HIGH CONFIDENCE IN WIDESPREAD VFR CIGS/VIS
MIDDAY THROUGH THE AFTERNOON HOURS AT ALL SITES. WINDS REMAIN
ONSHORE AT LESS THAN 10 KT, BECOMING LIGHT AND VARIABLE OVERNIGHT.
EXPECT THESE WINDS TO INCREASE ALONG THE COAST AND IN THE
CENTRAL/SOUTHERN WILLAMETTE VALLEY FOR TUESDAY AFTERNOON WITH
GUSTS UP TO 18-25 KNOTS POSSIBLE.
PDX AND APPROACHES...HIGH CONFIDENCE VFR CIGS HOLD THROUGH MOST
OF THE OVERNIGHT HOURS. WE'LL HAVE TO WATCH 12-18Z FOR LOW
CLOUDS OVER THE WEST SLOPES OF THE CASCADES TO POTENTIALLY DRIFT
WESTWARD NEAR THE TERMINAL WHILE DISSIPATING. WOULD GIVE PDX A
~40% CHANCE TO SEE AT LEAST AN HOUR OF MVFR CIGS DURING THE
PERIOD. OTHERWISE VFR CONDITIONS PREVAIL. -SCHULDT
MARINE
STRONG HIGH PRESSURE OFFSHORE ALONG WITH A SURFACE
LEVEL THERMAL TROUGH DEVELOPING AND STRENGTHENING OVER THE
SOUTHERN AND CENTRAL OREGON COAST WILL MAINTAIN NORTHERLY WINDS
ACROSS ALL WATERS THROUGH THE MIDDLE OF THE WEEK. CENTRAL OREGON
COASTAL WATERS WILL SEE INCREASING WINDS THIS EVENING INTO
TUESDAY MORNING WITH GUSTS OF 20-25 KTS AT TIMES. A SMALL CRAFT
ADVISORY REMAINS IN EFFECT FOR ZONE PZZ273. AS THE THERMAL
TROUGH STRENGTHENS OVER THE COAST, THESE WINDS ARE EXPECTED TO
SPREAD NORTH ALONG THE NORTHERN OREGON AND SOUTHERN WASHINGTON
COASTAL WATERS LATE TUESDAY INTO WEDNESDAY NIGHT, WITH GUSTS
25-30 KTS POSSIBLE AT TIMES. HAVE ADDED A SMALL CRAFT ADVISORY
FOR ZONES PZZ253, PZZ252, AND PZZ272 STARTING 2 PM TUESDAY. THE
NORTHERN OR, SOUTHERN WA ZONES MAY NEED A SMALL CRAFT ADVISORY
AT SOME POINT BUT GUSTY WINDS AREN'T EXPECTED TO PERSIST IN
THESE ZONES TOMORROW. STRONGEST WINDS ARE EXPECTED TO EBB AND
FLOW DIURNALLY, STRONGEST IN THE LATE AFTERNOON TO OVERNIGHT
HOURS, BACKING OFF IN THE MORNING HOURS. SEAS ARE EXPECTED TO
PERSIST AROUND 6 TO 8 FT AROUND 10 SECONDS THROUGH THE MIDDLE OF
THE WEEK.
-BATZ/HEC
PQR WATCHES/WARNINGS/ADVISORIES
OR...FROST ADVISORY UNTIL 9 AM PDT TUESDAY FOR ORZ104>109-113>119-
123>125.
FREEZE WARNING UNTIL 9 AM PDT TUESDAY FOR ORZ121.
WA...FROST ADVISORY UNTIL 9 AM PDT TUESDAY FOR WAZ203>205-208.
PZ...SMALL CRAFT ADVISORY FROM 2 PM TUESDAY TO 2 AM PDT WEDNESDAY FOR
PZZ252-253-272.
SMALL CRAFT ADVISORY UNTIL 2 AM PDT WEDNESDAY FOR PZZ273.
WWW.WEATHER.GOV/PORTLAND
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