087
FXUS66 KPDT 010201 CCA
AFDPDT
AREA FORECAST DISCUSSION...CORRECTION
NATIONAL WEATHER SERVICE PENDLETON OR
701 PM PDT MON MAR 31 2025
EVENING UPDATE
AN UPPER LOW PRESSURE SYSTEM CONTINUES TO PUSH
SHOWERS AND THE OCCASIONAL ISOLATED THUNDERSTORM ACROSS THE
FORECAST AREA THIS LATE AFTERNOON. BEST ACTIVITY HAS BEEN CENTERED
ACROSS THE COLUMBIA BASIN INTO THE BLUE MOUNTAIN FOOTHILLS, WHERE
A COLD CORE ALOFT HAS RESULTED IN DECENT LOW TO MID LEVEL LAPSE
RATES. MOST RECENT MESOANALYSIS ACROSS THE REGION ALSO SHOWS A
VORTICITY MAXIMUM IN THE COLUMBIA BASIN, HELPING STORMS TO
DEVELOP. A LACK OF SHEAR ALOFT, HOWEVER, HAS RESULTED IN THESE
STORMS ONLY STICKING AROUND FOR ABOUT 30 MINUTES BEFORE
DISSIPATING. THIS TREND WILL CONTINUE INTO THE EARLY EVENING, BUT
EXPECT ACTIVITY TO DIE DOWN AFTER SUNSET. OTHERWISE, LOCALLY
BREEZY TO BREEZY CONDITIONS WILL CONTINUE IN THE COLUMBIA BASIN
THROUGH THIS EVENING, WITH LIGHT WINDS OVERNIGHT. UPDATED
PRECIPITATION AND THUNDERSTORM CHANCES ACROSS THE COLUMBIA BASIN,
WITH REST OF FORECAST ON TRACK.
PREV DISCUSSION
/ISSUED 500 PM PDT MON MAR 31 2025/
UPDATED AVIATION DISCUSSION...
SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT
CURRENT RADAR SHOWS ISOLATED TO SCATTERED SHOWERS THROUGHOUT THE
CWA. AN OCCASIONAL THUNDER SHOWER IS POPPING UP AROUND THE
PENDLETON/LA GRANDE AREA ALL AFTERNOON AND WILL CONTINUE TO SEE
THOSE COME THROUGH FOR THE REST OF THE AFTERNOON. CAPE VALUES ARE
AROUND 500 J/KG TO SUPPORT SOME GRAUPEL/SMALL HAIL REPORTED IN THE
PENDLETON AND YAKIMA AREA EARLIER THIS AFTERNOON. SATELLITE SHOWS
BKN TO OVC SKIES ACROSS THE CWA, ALLOWING SOME FUEL TO DEVELOP
SCATTERED SHOWERS.
GOING FORWARD, HEAR ARE THE KEY MESSAGES THROUGH WEDNESDAY NIGHT:
1) LOW ELEVATION RAIN TO CONTINUE THROUGH TUESDAY AM. LIGHT
MOUNTAIN SNOW TO CONTINUE THROUGH WED PM.
2) PATTERN BECOMING MORE DRY AND WARMER AS WE HEAD THROUGH MID-
WEEK.
AN UPPER LEVEL TROUGH IS CURRENTLY PLACED OVER THE REGION WITH SW
SURFACE LEVEL WINDS, ALLOWING FOR MOISTURE ADVECTION TO ENTER THE
AREA. THIS IN RETURN IS BRINGING IN SCATTERED SHOWERS AND AN
OCCASIONAL THUNDERSTORM TO POP UP AND INCREASE MOUNTAIN SNOW
ACCUMULATIONS. PRECIPITATION IN THE LOWER VALLEYS WILL DROP OUT AS
THE OVER HEAD TROUGH MOVES TO THE EAST. ADDITIONAL MOUNTAIN SNOW
ACCUMULATIONS ARE NOT MUCH TO ISSUE ANY HIGHLIGHTS, WITH WA
CASCADES AND THE BLUE MOUNTAINS RECEIVING 2-4" (70-90%
CONFIDENCE), WITH THE OREGON CASCADES RECEIVING A SLIGHTLY HIGHER
AMOUNT OF 3-5" (60-80% CONFIDENCE).
A SECOND SYSTEM THAT'S ACCOMPANIED WITH ANOTHER SHORTWAVE WILL
PASS SHORTLY AFTER THE FIRST SYSTEM TUES PM, BUT WILL BE WEAKER
WITH LESS MOISTURE ATTACHED WITH LESS FAVORABLE WESTWARD WINDS.
THIS IS PRIMARILY A LIGHT MOUNTAIN SNOW EVENT WITH LOWER
ACCUMULATIONS THAN THE FIRST SYSTEM WITH NO MORE THAN AN
ADDITIONAL 3" OF ACCUMULATION (50-70% CONFIDENCE).
LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...KEY MESSAGES
- LINGERING MOUNTAIN PRECIP CHANCES WEDNESDAY NIGHT-EARLY THURSDAY
THEN DRY CONDITIONS INTO MONDAY
- WARMING TREND WITH HIGHS 10-15 DEGREES ABOVE AVERAGE BY SUNDAY
AND MONDAY
ALTHOUGH AN SOMEWHAT AMPLIFIED, PROGRESSIVE PATTERN WILL BE IN
PLACE, AN EVOLVING LONGWAVE UPPER-LEVEL RIDGE WILL PROMOTE QUIESCENT
CONDITIONS. MEANTIME, AREA WILL SEE WARMING TEMPERATURES INTO THE
WEEKEND BEFORE THE NEXT UPPER-TROUGH INFLUENCES THE AREA. AN UPPER-
LEVEL RIDGE WILL BE INITIALLY OVER THE EASTERN NORTH PACIFIC
EXTENDING ACROSS THE GULF OF ALASKA EARLY WEDNESDAY NIGHT WITH A
UPPER TROUGH DOWNSTREAM AMD CYCLONIC FLOW DOMINATING THE WESTERN TWO-
THIRDS OF THE CONUS. THIS UPPER-LEVEL RIDGE OVER THE EASTERN PACIFIC
WILL BE SHIFTING AND BUILDING ACROSS THE OFFSHORE WEST COAST THROUGH
FRIDAY BEFORE PUSHING EAST TO BE OVER THE INTERIOR NW/NORTHERN
INTERMOUNTAIN WEST SUNDAY. OVERALL, DECENT MODEL AGREEMENT IS SEEN
BETWEEN ENSEMBLE MEANS AND CLUSTERING SCENARIOS WITH THE VERY
STRONG, ANOMALOUS RIDGE BUILDING INTO WESTERN CANADA FRIDAY AND THIS
WEEKEND. LATEST ECMWF MEAN 500 MB HEIGHTS ARE FORECAST TO FALL WELL
ABOVE CLIMO FOR THIS TIME OF YEAR ACROSS THE WESTERN PROVINCES AND
THE NORTHWEST TERRITORIES AS THE UPPER RIDGE EVOLVES FROM THE PACNW
COAST TO NORTHERN INTERMOUNTAIN WEST THIS WEEKEND. LOOKING AHEAD,
THE REGIME BECOMES SUPPORTIVE FOR A WARMING TREND FRIDAY ONWARD. A
SOUTHERLY FLOW BECOMES WELL ESTABLISHED SATURDAY IN TANDEM WITH EPS
850 HPA MEAN TEMPERATURE ANOMALIES APPROACHING AND REACHING 5 C.
THIS SHOULD SUPPORT HIGHS RETURNING INTO THE LOWER 70S SUNDAY AND
MONDAY, MOST WIDESPREAD ON SUNDAY, WITH HIGHS READING 10-15 DEGREES
ABOVE NORMAL.
THE DRY PERIOD IS FOLLOWED BY THE RIDGE BREAKING DOWN MONDAY WITH
CLUSTERING SCENARIOS SHOWING THIS POTENTIAL SCENARIO (40% CHANCE)
WITH A LEADING SHORTWAVE TROUGH MOVING INTO THE PACIFIC NW. OF
WHICH, THE DISTURBANCE’S ATTENDANT MOISTURE PLUME WOULD BE DIRECTED
LARGELY OUT OF THE SSW BASED ON THE SYNOPTIC FLOW. THE FOCUS FOR
MOISTURE TRANSPORT ANTICIPATED TO BE LARGELY FOCUSED ACROSS THE
OR/WA CASCADES WITH LIMITED PROBABILITIES SEEN WHEN IT COMES TO
MOISTURE PENETRATING INLAND BY THE ECMWF (20-40% CHANCE FOR IVT >150
KG/MS VIA INLAND TRANSECT). THE SYSTEM’S ATTENDANT COLD FRONT AND
ITS PASSAGE WILL KNOCK TEMPERATURES DOWN SOME, HOWEVER, CONFIDENCE
IS LOW OVERALL IN THIS (LESS THAN 40%) AND LOOKS LIKE THE FRONT
WOULDN’T BE STRONG WITH THE LATEST GUIDANCE. FURTHER, LOOKS LIKE
MOUNTAIN SNOW IMPACTS WILL BE LIMITED OWING TO THE AIR MASS AND
ELEVATED SNOW LEVELS STEMMING FROM THE WARMING TREND THIS WEEKEND.
AVIATION...00Z TAFS
PREDOMINANTLY VFR CIGS/VSBYS AT ALL TAF
SITES FOR THE NEXT 24 HOURS. HOWEVER, BRIEF, LOCALIZED MVFR
CONDITIONS MAY ACCOMPANY CONVECTIVE SHOWERS THIS AFTERNOON AND
AGAIN TUESDAY AFTERNOON. WINDS WILL BE DIURNALLY DRIVEN,
DECREASING IN MAGNITUDE OVERNIGHT AT ALL SITES BEFORE RAMPING BACK
UP TUESDAY AFTERNOON. PLUNKETT/86
PRELIMINARY POINT TEMPS/POPS
PDT 34 55 38 53 / 20 10 20 10
ALW 36 54 39 53 / 20 10 20 20
PSC 36 60 38 59 / 30 10 10 0
YKM 33 58 33 58 / 20 10 0 0
HRI 34 59 38 58 / 20 10 10 0
ELN 36 55 36 54 / 30 10 0 0
RDM 27 51 29 49 / 20 20 10 0
LGD 27 49 32 47 / 40 30 40 20
GCD 27 48 31 46 / 40 40 50 20
DLS 35 58 40 55 / 20 10 10 10
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
EVENING UPDATE...82
SHORT TERM...95
LONG TERM....80
AVIATION...86
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