708
FXUS66 KPQR 010506
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1006 PM PDT MON MAR 31 2025
SYNOPSIS
UPPER LEVEL TROUGHING SUPPORTS SEASONABLY COOL AND
SHOWERY CONDITIONS THROUGH WEDNESDAY. UPPER LEVEL RIDGING WILL
THEN BRING AN EXTENDED PERIOD OF DRY WEATHER FROM THURSDAY
ONWARD, WITH TEMPERATURES GRADUALLY WARMING EACH DAY. THE
WARMEST TEMPS ARE EXPECTED THIS WEEKEND WITH WIDESPREAD HIGHS IN
THE 70S. ALSO OF NOTE IS THE POTENTIAL FOR FROST WEDNESDAY
NIGHT AND/OR THURSDAY NIGHT.
SHORT TERM...NOW THROUGH WEDNESDAY NIGHT
MONDAY NIGHT
THROUGH WEDNESDAY NIGHT...THE SHORT TERM FORECAST IS HIGHLIGHTED
BY SEASONABLY COOL AND SHOWERY WEATHER THROUGH WEDNESDAY, WITH
HIGH TEMPS IN THE LOW TO MID 50S ACROSS THE LOWLANDS EACH DAY.
THERE WILL BE A BRIEF BREAK FROM SHOWERY ACTIVITY MONDAY NIGHT
THROUGH TUESDAY MORNING AS A WEAKENING UPPER LEVEL LOW SHIFTS
SOUTHEASTWARD INTO SOUTHWEST OR AND NORTHERN CA, BRINGING
RELATIVELY DRIER NORTHERLY FLOW TO SOUTHWEST WA AND NORTHWEST
OR. SHOWERY ACTIVITY WILL RETURN TUESDAY AFTERNOON WITH DAYTIME
HEATING, HOWEVER MODEL SOUNDINGS SUGGEST THESE RAIN SHOWERS WILL
BE QUITE SHALLOW AND WEAK WITH EQUILIBRIUM LEVELS AROUND 700 MB
OR LOWER. TEMPERATURES AT THIS LEVEL ARE AROUND -10 DEGREES
CELSIUS, SUGGESTING IT WILL BE DIFFICULT FOR MIXED-PHASED CLOUDS
CAPABLE OF CHARGE SEPARATION AND/OR HAIL. NBM PROBABILITIES FOR
THUNDER ARE LOW AT 5-10%, WHICH HELPS BACK THIS UP. OVERALL NOT
EXPECTING THUNDERSTORMS OR HAIL ON TUESDAY UNLESS IT IS WITH
ONE OR TWO ISOLATED CELLS THAT MANAGE TO OVERPERFORM AND PRODUCE
ONE OR TWO LIGHTNING FLASHES. MUCH OF THE DAY WILL BE DRY ASIDE
FROM LIGHT HIT-OR-MISS RAIN SHOWERS IN THE AFTERNOON.
OVERNIGHT LOWS TREND COOLER WEDNESDAY NIGHT WITH THE POTENTIAL FOR
PATCHY FROST. HIGH PRESSURE WILL YIELD CALM WINDS AND CLEARING SKIES
OVER THE AREA, RESULTING IN AN IDEAL SETUP FOR RADIATIONAL COOLING.
FORECAST LOWS CURRENTLY RANGE BETWEEN 34-38 DEGREES ACROSS THE
LOWLANDS. FOR FROST FORECASTING, WE TYPICALLY LOOK FOR 2-M SURFACE
TEMPERATURES NEAR 35F OR COLDER ON CLEAR/CALM NIGHTS WITH DRY
NORTHERLY FLOW JUST ABOVE THE SURFACE/ALOFT, AS THIS TENDS TO FAVOR
FROST FORMATION RATHER THAN FOG. GIVEN GOOD MODEL AGREEMENT THIS
PATTERN WILL BE IN PLACE WEDNESDAY NIGHT, HAVE DECIDED TO INTRODUCE A
MENTION OF FROST IN THE FORECAST FOR LOWLAND LOCATIONS EXPECTED TO
SEE LOWS NEAR 35F OR COLDER. NBM PROBABILITIES FOR LOW TEMPS OF 35F
OR COLDER RANGE FROM 40-70% ACROSS THE CENTRAL AND SOUTHERN
WILLAMETTE VALLEY, CASCADE FOOTHILLS AND COWLITZ VALLEY.
PROBABILITIES ARE LESS THAN 5-10% AT THE COAST, AND 5-15% FOR THE
PORTLAND/VANCOUVER METRO AREA (EXCEPT 40-60% FOR HILLSBORO, FOREST
GROVE AND BANKS). IF CONFIDENCE INCREASES FOR WIDESPREAD LOWS BETWEEN
33-35, WILL LIKELY NEED TO ISSUE A FROST ADVISORY FOR SOME ZONES NOW
THAT THE GROWING SEASON IS UPON US. THIS OUTCOME IS MOST LIKELY TO
OCCUR FOR OUTLYING RURAL AREAS. -TK
LONG TERM...THURSDAY THROUGH SUNDAY NIGHT
THE PATTERN WILL START
TO TRANSITION ON THURSDAY AS UPPER LEVEL RIDGING BEGINS TO DEVELOP
OVER WESTERN WASHINGTON/OREGON, AFTER WHAT LOOKS TO BE A POTENTIALLY
FROSTY START TO THE DAY FOR SOME LOCATIONS WITH CHILLY MORNING LOWS
IN THE 30S. THIS WILL BE ESPECIALLY TRUE FOR OUTLYING RURAL AREAS
WHERE PROBABILITIES FOR LOWS OF 35F OR COLDER ARE HIGHEST (40-50%,
EXCEPT 70% FROM CORVALLIS TO JUNCTION CITY). PROBABILITIES FOR THE
PORTLAND/VANCOUVER METRO RANGE FROM 15-35%, 35% IN SALEM AND 50% IN
EUGENE-SPRINGFIELD.
DESPITE CHILLY MORNING TEMPS, EXPECT AFTERNOON HIGHS WELL INTO THE
50S TO NEAR 60 DEGREES ACROSS THE LOWLANDS. DRY NORTHERLY FLOW WILL
SUPPORT BREAKS OF SUNSHINE, MAKING FOR A RATHER MILD AND PLEASANT
SPRING DAY. IF YOU PREFER WARMER TEMPERATURES, YOU'RE IN LUCK COME
FRIDAY THROUGH SUNDAY. THIS IS WHEN MODELS AND THEIR ENSEMBLES SHOW
GOOD AGREEMENT FOR THE AFOREMENTIONED UPPER LEVEL RIDGE TO BECOME
HIGHLY AMPLIFIED OVER THE REGION, RESULTING IN WIDESPREAD HIGH TEMPS
IN THE 70S FOR THE UPCOMING WEEKEND. IN FACT, HIGHS IN THE LOWER 80S
CANNOT BE RULED OUT ON SUNDAY ACCORDING TO THE NBM. THIS IS WHEN
THERE IS A 5-20% CHANCE FOR HIGHS OF 80 DEGREES OR WARMER, WITH THE
HIGHEST PROBABILITIES IN PORTLAND. THIS EXCLUDES THE COAST WHERE
PROBABILITIES ARE NEAR ZERO. CONDITIONS WILL ALSO BE DRY FRIDAY
THROUGH SUNDAY, MAKING FOR IDEAL CONDITIONS FOR OUTDOOR ACTIVITIES.
-TK
AVIATION
VFR FLYING CONDITIONS WILL CONTINUE INTO TONIGHT
ACROSS THE REGION AS A WEAKENING SURFACE LOW MOVES ONSHORE TO
THE SOUTH IN SOUTHWESTERN OREGON, BRINGING LIGHT RAIN SHOWERS
TO SOUTHERN TERMINALS INCLUDING EUG/ONP, WHILE DRIER WEATHER
PREVAILS TO THE NORTH. LATEST SATELLITE IMAGERY SHOWS A BREAK
IN THE CLOUD DECK GENERALLY ALONG THE COLUMBIA RIVER ON THE
NORTHERN FLANK OF THE CLOUD SHIELD ASSOCIATED WITH THE
APPROACHING LOW. THIS GAP IN CLOUD COVER MAY ALLOW FOR THE
DEVELOPMENT OF RADIATION FOG, MOST LIKELY NEAR BODIES OF WATER,
INCLUDING ALONG THE COLUMBIA RIVER ITSELF, AS WELL AS WITHIN
SHELTERED VALLEYS. TERMINALS WITH THE HIGHEST CHANCES, 40-60%
LIKELIHOOD, OF SEEING FOG/MIST RESTRICTING VIS TO 1SM OR LESS
INCLUDE PORTLAND-AREA SITES (PDX/HIO) AND SITES IN THE NORTHERN
WILLAMETTE VALLEY (UAO). NEARBY TERMINALS INCLUDING TTD/SLE WILL
SEE A LOWER CHANCE OF IFR VIS (10-30%), AND HAVE THEREFORE
INCLUDED MVFR VIS AT THIS TIME. FOG/MIST CHANCES WILL PEAK
OVERNIGHT AND CONTINUE PAST DAWN, FROM ROUGHLY 12-16Z TUE,
BEFORE VFR CONDITIONS RETURN AS ANY FOG DISSIPATES. IF THE CLOUD
DECK CURRENTLY OVER THE SOUTHERN WILLAMETTE VALLEY IS ABLE TO
PUSH FARTHER NORTH, CHANCES FOR FOG DEVELOPMENT WILL BE MUCH
LOWER AND VFR CONDITIONS WILL INSTEAD BE FAVORED. TO THE SOUTH
AT EUG/ONP, SCATTERED RAIN SHOWERS WILL CONTINUE OVERNIGHT, WITH
MVFR CIGS FAVORED AFTER 12Z TUE. WINDS THROUGH THE PERIOD WILL
REMAIN LESS THAN 10 KT AT INLAND SITES, TURNING FROM SOUTHEAST
TO NORTH TUESDAY MORNING, AND FINALLY TO THE NORTHWEST TUESDAY
AFTERNOON. ALONG THE COAST, NORTHWEST WINDS MAY GUST TO 20 KT
AFTER 20-21Z TUE. ADDITIONAL LIGHT RAIN SHOWERS WILL DEVELOP
WITHIN MOIST NORTHWEST FLOW AFTER 20-22Z TUE.
PDX AND APPROACHES...VFR CONDITIONS EXPECTED THROUGH THE FIRST
HALF OF THE OVERNIGHT PERIOD AS CLOUDS LARGELY CLEAR ON THE
NORTHERN FLANK OF A SURFACE LOW MOVING INLAND IN SOUTHWESTERN
OREGON. THIS CLEARING MAY ALLOW FOR AREAS OF FOG TO FORM,
ESPECIALLY ALONG THE COLUMBIA RIVER, YIELDING A 50-60% CHANCE OF
IFR VIS FROM 11-16Z TUE. IF THE CLOUD DECK CURRENTLY OFF TO THE
SOUTH IS ABLE TO ADVANCE FARTHER TO THE NORTH, THESE CHANCES WILL
BE MITIGATED. ANY VIS RESTRICTIONS WILL LIFT AFTER SUNRISE AS
FOG DISSIPATES. ADDITIONAL RAIN SHOWERS AFTER 20-22Z TUE ARE
NOT EXPECTED TO IMPACT FLYING CONDITIONS. -PICARD
MARINE
CONDITIONS ARE STILL FAIRLY ACTIVE ACROSS THE COASTAL
WATERS THIS AFTERNOON WITH WAVE HEIGHT AROUND 7-10 FT AT 8
SECONDS WITH WINDS OCCASIONALLY GUSTING TO 25 KNOTS. SMALL CRAFT
CONDITIONS LIKELY PERSIST INTO THE EVENING HOURS BEFORE WINDS
DECREASE. HOWEVER, SEAS WILL GRADUALLY INTO TUESDAY MORNING DUE
TO THE ARRIVAL OF A FRESH SOUTHWESTERLY SWELL WITH SEAS PEAKING
8-13 FEET - HIGHEST SOUTH OF CAPE FOULWEATHER. FORTUNATELY SEAS
THEN DISSIPATE THROUGH THE REST TUESDAY INTO WEDNESDAY BOTTOMING
OUT 4-6 FT LATE WEEK THANKS TO A RIDGE OF HIGH PRESSURE
BUILDING OVERHEAD. EXPECT WINDS TO TURN NORTHERLY THURSDAY INTO
FRIDAY AS WELL. -SCHULDT
BEACH HAZARDS
MINOR COASTAL FLOODING DUE TO TIDAL OVERFLOW
WILL BE POSSIBLE ALONG THE NORTH OREGON COAST AND SOUTH
WASHINGTON COAST LATE TONIGHT INTO TUESDAY MORNING DUE TO A
FAIRLY ROBUST HIGH TIDE IN COMBINATION WITH LINGERING SURGE FROM
THIS PAST WEATHER DISTURBANCE. WITH A TOTAL TIDE OF ~10.5-11.2
FEET IN THIS REGION, FLOODING UP TO ONE FOOT ABOVE GROUND LEVEL
WILL BE POSSIBLE FOR THE LOWEST LYING COASTAL AREAS LIKE ALONG
PORTIONS OF HIGHWAY 101 NEAR RAYMOND. ANY THREAT FOR TIDAL
OVERFLOW END BY 7-8AM TUESDAY MORNING. -SCHULDT
PQR WATCHES/WARNINGS/ADVISORIES
OR...COASTAL FLOOD ADVISORY FROM 2 AM TO 6 AM PDT TUESDAY FOR
ORZ101.
WA...COASTAL FLOOD ADVISORY FROM 2 AM TO 6 AM PDT TUESDAY FOR
WAZ201.
PZ...SMALL CRAFT ADVISORY FROM 5 AM TO 11 AM PDT TUESDAY FOR PZZ210.
SMALL CRAFT ADVISORY UNTIL 5 AM PDT TUESDAY FOR PZZ251>253-
271>273.
WWW.WEATHER.GOV/PORTLAND
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