228
FXUS66 KPQR 012218
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
315 PM PDT TUE APR 1 2025
SYNOPSIS
COOL AND SHOWERY CONDITIONS WILL REMAIN IN PLACE THROUGH
WEDNESDAY AS UPPER LEVEL TROUGHING REMAINS OVER THE REGION, WITH
HIGH TEMPERATURES IN THE 50S. CHILLY OVERNIGHT LOWS BRING FROST
POTENTIAL WEDNESDAY NIGHT AND THURSDAY NIGHT, ALBEIT FOG IS FAVORED
OVER FROST WEDNESDAY NIGHT WHILE FROST IS FAVORED OVER FOG THURSDAY
NIGHT. EXPECT WARMER AND DRIER CONDITIONS WITH HIGHS NEAR OR ABOVE 70
DEGREES FRIDAY INTO THE WEEKEND.
SHORT TERM...NOW THROUGH THURSDAY NIGHT
SATELLITE AND SURFACE
WEATHER OBSERVATIONS FROM EARLY TO MID TUESDAY AFTERNOON SHOWED
SCATTERED LIGHT RAIN SHOWERS DEVELOPING OVER SOUTHWEST WA AND
NORTHWEST OR IN RESPONSE TO DAYTIME HEATING. EXPECT SHOWERS TO
DECREASE IN COVERAGE TUESDAY EVENING AS HEATING WANES, ALBEIT SOME
ISOLATED SHOWERS WILL LIKELY REMAIN. MOST SHOWERS SHOULD BE LIGHT,
HOWEVER THE STRONGEST SHOWERS COULD PRODUCE BRIEF PERIODS OF MODERATE
RAIN. MODEL SOUNDINGS CONTINUE TO SUGGEST THESE SHOWERS WILL BE
VERTICALLY SHALLOW WITH A MINIMAL THREAT OF HAIL AND/OR THUNDER.
THERE COULD BE A FEW CELLS THAT OVERPERFORM AND PRODUCE ONE OR TWO
FLASHES OF LIGHTNING AND/OR HAIL SMALLER THAN THE SIZE OF PEAS,
HOWEVER THE PROBABILITY FOR THUNDER IS GENERALLY LESS THAN 15%. NOTE
SOME LOCATIONS WILL STAY DRY THROUGH THE REMAINDER OF THE DAY DUE TO
THE HIT-OR-MISS NATURE OF THESE SHOWERS.
SHOWERS WILL BECOME MORE WIDESPREAD ON WEDNESDAY AS A SHORTWAVE
TROUGH AND ASSOCIATED VORT MAX TRAVERSES THE REGION IN NORTHWEST
FLOW. SIMILAR TO TUESDAY, THUNDER IS UNLIKELY TO OCCUR WITH THESE
SHOWERS DUE TO A LACK OF SURFACE-BASED INSTABILITY. IF A FEW BREAKS
IN CLOUD COVER OCCUR, THERE COULD BE A VERY ISOLATED WEAK
THUNDERSTORM OR TWO THAT PRODUCE ONE OR TWO FLASHES OF LIGHTNING AND
SMALL HAIL, HOWEVER PROBABILITIES FOR THUNDER REMAIN LESS THAN 15%.
EXPECT PRECIPITATION AMOUNTS BETWEEN A TENTH AND A QUARTER INCH
ALONG THE COAST AND AROUND A TENTH OF AN INCH OR LESS INLAND. MINIMAL
SNOW ACCUMULATIONS ARE EXPECTED FOR THE CASCADE PASSES, WITH SNOW
LEVELS HOVERING AROUND 2500-3000 FEET.
MODELS SUGGEST SHOWERS WILL LINGER OVER THE AREA WEDNESDAY EVENING
BEFORE BECOMING ISOLATED AND MAINLY CONFINED TO THE COAST AND
MOUNTAINS WEDNESDAY NIGHT. THE NBM DOES SUGGEST CLOUD COVER WILL
ATTEMPT CLEARING OUT AFTER MIDNIGHT, HOWEVER SOME MODEL SOUNDINGS
SHOW A DEEP LAYER OF CLOUD COVER LINGERING THROUGH THE NIGHT,
PARTICULARLY THE NAM. THE HREF ENSEMBLE MEAN FOR CLOUD COVER ALSO
SHOWS MINIMAL BREAKS IN LOW CLOUD COVER. GIVEN THE SHOWERY ACTIVITY
THAT IS SET TO OCCUR WEDNESDAY MORNING THROUGH THE EVENING, THE
GROUND WILL BE WET OVERNIGHT. THIS WILL TEND TO FAVOR THE FORMATION
OF FOG RATHER THAN FROST IN THE LOWLANDS, ASSUMING CLOUD COVER CLEARS
OUT ENOUGH TO ALLOW FOR AIR TEMPS TO COOL DOWN TO THE DEW POINT
TEMPERATURE. WHILE FROST CANNOT BE COMPLETELY RULED OUT IN THE
WILLAMETTE VALLEY AND CASCADE FOOTHILLS, IT APPEARS IT WOULD BE QUITE
PATCHY IN COVERAGE. AS SUCH, FROST ADVISORIES LIKELY WON'T BE NEEDED
WEDNESDAY NIGHT UNLESS THE FORECAST CHANGES. THURSDAY STILL LOOKS TO
BE A DAY OF TRANSITION AS DRY NORTHERLY FLOW DEVELOPS BEHIND THE
DEPARTING UPPER LEVEL TROUGH, BRINGING MAINLY DRY CONDITIONS WITH
SEASONABLE TEMPERATURES.
FROST IS MORE LIKELY TO OCCUR THURSDAY NIGHT AS THE GROUND WILL BE
RELATIVELY DRIER AT THAT POINT, SURFACE DEW POINT TEMPERATURES WILL
BE SLIGHTLY LOWER, WINDS WILL BE CALM AND SKIES WILL BE COMPLETELY
CLEAR THROUGH THE NIGHT WITH WIDESPREAD LOWS IN THE MID 30S. SUSPECT
AT LEAST SOME ZONES WILL EVENTUALLY NEED A FROST ADVISORY, BUT WILL
HOLD OFF FOR NOW UNTIL CONFIDENCE IN EXACT OVERNIGHT LOWS IS HIGHER.
-TK
LONG TERM...FRIDAY THROUGH MONDAY NIGHT
AFTER ANOTHER CHILLY START
TO THE DAY ON FRIDAY WITH POTENTIAL AREAS OF FROST, EXPECT RAPIDLY
WARMING TEMPS THROUGH THE AFTERNOON THANKS TO PLENTIFUL SUNSHINE AND
AN INCOMING UPPER LEVEL RIDGE OVER THE COASTAL WATERS. THE NBM 50TH
PERCENTILE SEEMS REASONABLE FOR HIGH TEMPS ON FRIDAY, SUGGESTING
WIDESPREAD HIGHS WELL INTO THE 60S, EXCEPT AROUND 70 DEGREES IN THE
PORTLAND/VANCOUVER METRO. THIS MAKES SENSE AS THE METRO WILL BE UNDER
THE INFLUENCE OF LOW-LEVEL OFFSHORE FLOW WITH EASTERLY WINDS
INCREASING THROUGH THE WESTERN COLUMBIA RIVER GORGE INTO THE EASTERN
METRO.
MODELS AND THEIR ENSEMBLES SHOW THE RIDGE AXIS MOVING INLAND OVER
WESTERN WA/OR ON SATURDAY WHILE LOW-LEVEL OFFSHORE FLOW REMAINS IN
PLACE. AS SUCH, TEMPS WILL BE EVEN WARMER ON SATURDAY WITH WIDESPREAD
HIGHS IN THE LOW TO MID 70S. EVEN COASTAL LOCATIONS WILL LIKELY FLIRT
WITH 70 DEGREES THANKS TO OFFSHORE FLOW. PROBABILITIES FOR HIGHS OF
80 DEGREES OR WARMER HAVE DECREASED TO 0-1% ON SATURDAY, SUGGESTING
HIGHS IN THE UPPER 70S IS A REASONABLE HIGH-END SOLUTION.
DESPITE HIGH CONFIDENCE IN THE FORECAST FOR FRIDAY AND SATURDAY,
FORECAST CONFIDENCE REMAINS LOW ON SUNDAY. THE UNCERTAINTY ON SUNDAY
IS BEING DRIVEN MAINLY BY MODEL TIMING DIFFERENCES IN THE BREAKDOWN
OF THE AFOREMENTIONED RIDGE AND SUBSEQUENT ARRIVAL OF THE NEXT UPPER
LEVEL TROUGH AND ASSOCIATED CLOUD COVER AND RAIN AHEAD OF IT. THE
GEFS/GEPS ENSEMBLE MEAN FOR 6-HR QPF BOTH SHOW MEASURABLE RAIN
BEGINNING OVER WESTERN WA/OR SOMETIME SUNDAY MORNING, WHILE THE ENS
MEAN HOLDS OFF UNTIL THE AFTERNOON/EVENING. TO COMPLICATE MATTERS
FURTHER, ALL THREE ENSEMBLE SYSTEMS HAVE SOME MEMBERS SHOWING RAIN
HOLDING OFF UNTIL SUNDAY NIGHT. THIS IS RESULTING IN A VERY LARGE
DEGREE OF MODEL SPREAD FOR HIGH TEMPS SUNDAY, WHICH THE NBM 10TH-90TH
PERCENTILE SHOWS WELL, DEPICTING HIGH TEMPS RANGING ANYWHERE FROM THE
UPPER 50S TO NEAR 80 DEGREES. IF RAIN MOVES IN EARLY IN THE DAY,
HIGHS WILL LIKELY BE IN THE UPPER 50S TO LOWER 60S. IF RAIN MOVES IN
DURING THE MIDDLE PART OF THE DAY, HIGHS WOULD LIKELY BE IN THE MID
60S TO AROUND 70 DEGREES. IF RAIN HOLDS OFF UNTIL SUNDAY NIGHT,
EXPECT HIGHS IN THE MID TO UPPER 70S.
DESPITE BEING FURTHER OUT IN TIME, MODEL SPREAD ACTUALLY DECREASES ON
MONDAY COMPARED TO SUNDAY. THIS IS DUE TO HIGHER CONFIDENCE THE
AFOREMENTIONED RIDGE WILL FOR SURE BE TO OUR EAST BY MONDAY AT THE
LATEST, RESULTING IN A RELATIVELY COOLER WEATHER PATTERN WITH CHANCES
FOR SHOWERS. 6-HOURLY POPS CURRENTLY RANGE BETWEEN 40-60% THROUGH THE
DAY MONDAY. -TK
AVIATION
A WEAK UPPER LEVEL TROUGH OVER THE REGION WILL
CONTINUE TO SUPPORT SCATTERED LIGHT SHOWERS THIS AFTERNOON WITH
PREDOMINANTLY VFR CONDITIONS AT THE TERMINALS. THERE IS A 10% CHANCE
THAT A SHOWER PRODUCES A BRIEF DIP INTO MVFR OR IFR THRESHOLDS AT
ANY GIVEN TERMINAL THROUGH ~02Z WEDNESDAY. VFR CONDITIONS SHOULD
CONTINUE INTO THE OVERNIGHT HOURS BEFORE A REINFORCING SHOT OF COOL
AIR ALOFT SUPPORTS WIDESPREAD SHOWERS AND OCCASIONAL DIPS INTO MVFR
RETURNING TO THE REGION BETWEEN BETWEEN 09-15Z WEDNESDAY. THIS STORM
SYSTEM WILL BE SPREADING SOUTHEASTWARD ACROSS THE REGION SO SHOWERS
WILL INCREASE FIRST ALONG THE COAST AND MORE NORTHERN TERMINALS
OVERNIGHT. AS THE LOWER ATMOSPHERE DESTABILIZES WITH DAYTIME HEATING
ON WEDNESDAY, THERE IS A 90% CHANCE THAT MOST LOCATIONS RETURN TO
VFR CONDITIONS BY 20Z WEDNESDAY.
PDX AND APPROACHES...A WEAK UPPER LEVEL TROUGH OVER THE REGION WILL
CONTINUE TO SUPPORT SCATTERED LIGHT SHOWERS THIS AFTERNOON WITH
PREDOMINANTLY VFR CONDITIONS. THERE IS A 10% CHANCE THAT A SHOWER
PRODUCES A BRIEF DIP INTO MVFR OR IFR THRESHOLDS THROUGH ~02Z
WEDNESDAY. VFR CONDITIONS SHOULD CONTINUE INTO THE OVERNIGHT HOURS
BEFORE A REINFORCING SHOT OF COOL AIR ALOFT SUPPORTS MORE WIDESPREAD
SHOWERS AND OCCASIONAL DIPS INTO MVFR RETURNING TO THE REGION
BETWEEN BETWEEN 09-15Z WEDNESDAY. THERE IS A 90% CHANCE THAT VFR
CONDITIONS RETURN BY 20Z WEDNESDAY.
MARINE
HIGH PRESSURE OVER THE NORTHEAST PACIFIC AND LOWER
PRESSURE INLAND WILL LEAD TO MODEST WESTERLY, NORTHWESTERLY AND
NORTHERLY WINDS THROUGH THE WORK WEEK. SEAS WILL STEADILY DECREASE
THROUGH THE END OF THE WEEK. HIGH PRESSURE WILL SHIFT OVER THE
WATERS EARLY IN THE WEEKEND BEFORE GIVING WAY TO A COLD FRONT LATE
IN THE WEEKEND. THERE IS A 20% CHANCE THAT GALE FORCE SOUTHERLY WIND
GUSTS OCCUR AHEAD OF THE FRONT SOMETIME ON SUNDAY, BUT A GREATER
THAN 90% CHANCE THAT SEAS WILL CLIMB INTO THE TEENS BY LATE SUNDAY
OR EARLY MONDAY AS A SOUTHWESTERLY TO WESTERLY SWELL PUSH INTO THE
WATERS.
FINALLY, WE ARE IN A PERIOD OF STRONGER EBB CURRENTS. THE WEDNESDAY
MORNING EBB IS IN OUR VERY STRONG CATEGORY AND THE THURSDAY MORNING
EBB IS IN THE STRONG CATEGORY.
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 6 AM TO 10 AM PDT WEDNESDAY FOR
PZZ210.
WWW.WEATHER.GOV/PORTLAND
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