112
FXUS66 KPDT 241751 AAA
AFDPDT
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
1051 AM PDT THU APR 24 2025
UPDATED AVIATION DISCUSSION
SHORT TERM...TODAY THROUGH SATURDAY
1. PATTERN SHIFT TODAY WILL BRING PRECIPITATION ACROSS THE OR
CASCADES
2. ISOLATED THUNDERSTORMS BOTH FRIDAY AND SATURDAY AFTERNOON
CURRENT SATELLITE SHOWS VERY CLEAR SKIES OVER THE REGION THIS
MORNING. WITH THE LACK OF CLOUDS, TEMPERATURES WILL DECREASE HEDGING
INTO SOME ISOLATED AREAS OF FREEZING. ESPECIALLY ALONG THE FOOTHILLS
OF THE BLUES AND PORTIONS OF THE COLUMBIA BASIN. A FREEZE WARNING
HAS BEEN ISSUED FOR THE FREEZE THROUGH 9 AM.
MODELS SHOW THE UPPER LEVEL RIDGE TO REMAIN OVER THE REGION THROUGH
MUCH OF THE DAY TODAY. TEMPERATURES WILL REMAIN WARM UNDER THE
INFLUENCE OF THE RIDGE WITH TEMPERATURES CRESTING THE 70S ACROSS
MUCH OF THE CWAS MID AND LOWER ELEVATIONS. BY THIS AFTERNOON AND
THROUGH THE EVENING AND UPPER LEVEL LOW WILL CONTINUE TO MOVE
SOUTHEAST AND BEGIN TO UNDERCUT THE REGION BRINGING WITH IT A MINUTE
AMOUNT OF PRECIPITATION TO THE FAR CORNER OF DESCHUTES COUNTY.
MODELS SHOW THE UPPER LEVEL LOW TO CONTINUE TO MOVE SOUTHEAST AND BY
TOMORROW BEING JUST OFFSHORE OF CALIFORNIA. THE WRAP AROUND FROM THE
UPPER LEVEL LOW WILL CONTINUE TO BRING IN WARM AIR ADVECTION AS WELL
AS INSTABILITY AND MOISTURE. BEGINNING AT OR NEAR 11 AM, 10-20% OF
THE NBM RAW ENSEMBLES SHOW PROBABILITIES OF THUNDERSTORMS ALONG THE
EASTERN MOUNTAINS. CAMS SOUNDING DATA ALSO SHOWS THE AREAS ALONG THE
EASTERN MOUNTAINS TO BE A BIT UNSTABLE AS THE DAY WARMS UP WITH
MUCAPE VALUES RANGING BETWEEN 250-300 J/KG, LIS OF -2 TO -3, LAPSE
RATES WELL ABOVE NORMAL AT 9-9.5 C/KM. THIS IS ENOUGH TO ALLOW FOR
SOME ISOLATED THUNDERSTORMS TO POP UP ALONG THE EASTERN MOUNTAINS
THROUGH THE AFTERNOON AND EVENING ON FRIDAY. THIS SET UP CONTINUES
THROUGH TO SATURDAY WITH NBM RAW ENSEMBLES INCREASING SLIGHTLY IN
PROBABILITIES OF THUNDER TO 20-30%, WITH THE CAMS SOUNDINGS SHOWING
AN INCREASE IN MUCAPE VALUES TO 300-450 J/KG, LIS OF -3 TO -4 AND
LAPSE RATES 8.5-9 C/KM. WITH THAT SAID, CANNOT RULE OUT THE
LIKELIHOOD OF ISOLATED THUNDERSTORMS POPPING UP ALONG THE EASTERN
MOUNTAINS BOTH FRIDAY AND SATURDAY AFTERNOON. BENNESE/90
LONG TERM...SUNDAY THROUGH THURSDAY
SENSIBLE WEATHER CONCERNS
THROUGH THE EXTENDED FORECAST WILL REVOLVE AROUND THE PASSAGE OF AN
UPPER LOW PRESSURE SYSTEM TO THE SOUTH AND EAST OF THE FORECAST AREA
SUNDAY, FOLLOWED BY AN UPPER SHORTWAVE TROUGH PASSAGE TUESDAY.
OTHERWISE, UPPER LEVEL RIDGING WILL DEVELOP BETWEEN AND AFTER THE
SYSTEMS MONDAY AND AGAIN WEDNESDAY THROUGH THURSDAY NEXT WEEK.
AN UPPER LEVEL LOW SOUTH OF THE FORECAST AREA WILL CONTINUE TO PUSH
EAST ACROSS THE GREAT BASIN AND TOWARDS THE ROCKIES SUNDAY. WHILE
THE BRUNT OF THE PRECIPITATION AND BEST INSTABILITY WILL STAY SOUTH
AND EAST OF THE FORECAST AREA, THERE IS A 40-70% CHANCE THAT SURFACE
CAPE WILL INCREASE TO AND ABOVE 150 J/KG SUNDAY AFTERNOON ACROSS
WALLOWA COUNTY. THE INCREASED SURFACE INSTABILITY, COMBINED WITH
MODEST MID-LEVEL LAPSE RATES (7-8C/KM) WILL ALLOW FOR A FEW ISOLATED
THUNDERSTORMS TO DEVELOP AMONGST THE SHOWER ACTIVITY ACROSS WALLOWA
COUNTY IN THE AFTERNOON. THE SHOWERS/THUNDERSTORMS WILL PUSH EAST OF
WALLOWA COUNTY IN THE EVENING SUNDAY WITH THE EASTWARD PUSH OF THE
UPPER LOW TO OUR SOUTH.
ENSEMBLE GUIDANCE IS IN GREAT AGREEMENT THAT DRY CONDITIONS WILL
DEVELOP ACROSS THE AREA AS UPPER LEVEL RIDGING ATTEMPTS TO BUILD TO
INTO THE PACNW LATE SUNDAY THROUGH MONDAY AFTERNOON. BY MONDAY
AFTERNOON, THERE IS MOD-HIGH CONFIDENCE (60-80%) THAT THE UPPER
RIDGE WILL FLATTEN AS A SHORTWAVE TROUGH APPROACHES THE PACNW. THE
UPPER SHORTWAVE WILL GLIDE ACROSS THE PACNW TUESDAY, RESULTING IN
INCREASING RAIN AND HIGH MOUNTAIN SNOW SHOWERS ACROSS THE CASCADES,
BLUES, AND EASTERN MOUNTAINS. A FEW SHOWERS MAY ALSO DEVELOP ALONG
THE BLUES MOUNTAIN FOOTHILLS, THOUGH 12 HOUR PROBABILITIES OF AT
LEAST 0.01 INCHES OF PRECIP ARE BETWEEN 20% AND 40% ENDING LATE
TUESDAY EVENING. OVERALL, THERE IS GREAT AGREEMENT THAT UPPER LEVEL
RIDGING WILL BUILD BACK OVER THE PACNW WITH DRY CONDITIONS OVERNIGHT
TUESDAY THROUGH WEDNESDAY. HOWEVER, ENSEMBLE CLUSTER SOLUTIONS
WEDNESDAY INTO THURSDAY DEPICT UNCERTAINTY IN THE STRENGTH OF THE
RIDGE AND THE LOCATION OF THE RIDGE AXIS AS IT PASSES OVER THE
REGION. NAMELY, 48% PERCENT OF THE ENSEMBLE MEMBERS (FROM THE GFS,
ECMWF, AND CANADIAN) DEPICT THE UPPER RIDGE AXIS EXITING INTO THE
NORTHER ROCKIES, ALLOWING DEEP SOUTHWEST FLOW TO DEVELOP OVER THE
PACNW AND FOR LIGHT SHOWERS TO DEVELOP AT LEAST OVER THE CASCADE
CREST THURSDAY. THOUGH GUIDANCE HAS DIFFICULTY THIS FAR OUT WITH
DEPICTING CONVECTION, IF THESE MEMBERS DO VALIDATE FOR THURSDAY NEXT
WEEK, WOULD EXPECT INCREASING INSTABILITY AT THE SURFACE AND FOR AT
LEAST ONE OR TWO ISOLATED THUNDERSTORMS TO DEVELOP IN AREAS OF
SHOWERS (CONFIDENCE 10-20%).
OTHERWISE, THERE IS FAIRLY GOOD AGREEMENT AMONGST ENSEMBLE MEMBERS
THAT SURFACE PRESSURE GRADIENTS WILL REMAIN TIGHTENED THROUGH
TUESDAY, WITH SUNDAY HAVING THE STRONGEST GRADIENTS THROUGH THE
EXTENDED FORECAST. THIS WILL RESULT IN BREEZY TO LOCALLY GUSTY WINDS
(GUSTS 35-45MPH) DEVELOPING THROUGH THE CASCADE GAPS SUNDAY, WITH
THE STRONGEST GUSTS OF 40-50MPH THROUGH THE KITTITAS VALLEY
(CONFIDENCE 70-90%). MONDAY THROUGH TUESDAY, WIND GUSTS WILL MAINLY
BE BETWEEN 30-40MPH THROUGH THE CASCADE GAP AREAS EACH AFTERNOON
(CONFIDENCE 55-70%). THE LOWER COLUMBIA BASIN WILL ALSO SEE BREEZY
CONDITIONS(GUSTS 25-35MPH) THROUGH THIS PERIOD (CONFIDENCE 60-80%).
LAWHORN/82
AVIATION...18Z TAFS
VFR CONDITIONS TO PREVAIL THROUGH THE PERIOD.
HIGHER CIRRUS WILL BE MOVING INTO THE AREA FROM THE SOUTHWEST LATE
THIS AFTERNOON AND EVENING AND INCREASING FROM FEW TO SCT ABOVE 20K
FEET AGL OVERNIGHT. KRDM AND KBDN WILL BECOME BKN AT 12K-15K FEET
AGL AFTER 10Z-12Z. WINDS WILL GENERALLY BE LIGHT, LESS THAN 12 KTS,
THROUGH THE PERIOD WITH WIND DIRECTIONS DIURNALLY DRIVEN. THE
EXCEPTIONS ARE KRDM AND KBDN ARE EXPECTED TO HAVE NORTHERLY WINDS OF
10-12 KTS GUSTING TO 20 KTS FROM 21Z-05Z. PERRY/83
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...90 LONG TERM....82 AVIATION...83
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