677
FXUS66 KPDT 202346
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
446 PM PDT TUE MAY 20 2025
UPDATED AVIATION DISCUSSION
SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT
LAST NIGHT'S
SHORTWAVE HAS MOVED OFF TO THE EAST AND A ZONAL WESTERLY FLOW HAS
SET UP OVER THE PACIFIC NORTHWEST TODAY. AN UPSLOPE FLOW INTO THE
MOUNTAINS WILL KEEP A SLIGHT CHANCE OF VERY LIGHT MOUNTAIN SHOWERS
INTO EARLY THIS EVENING BUT OVERNIGHT AND TOMORROW LOOK TO BE DRY.
BREEZY WEST WINDS THROUGH THE CASCADE GAPS WILL CONTINUE FROM AT
15 TO 20 MPH WITH GUSTS TO 30 MPH AND THE WEST TO NORTHWEST AT 10
TO 15 MPH WITH GUSTS OF 20 TO 25 MPH IN THE COLUMBIA BASIN THROUGH
EARLY EVENING THEN DECREASE OVERNIGHT. DESPITE AN APPROACHING
SHORTWAVE, PRESSURE GRADIENTS ARE MUCH LIGHTER ON WEDNESDAY AND
WINDS WILL TURN NORTHERLY AT 10 MPH OR LESS. THE ZONAL FLOW WILL
WARM TEMPERATURES 6 TO 10 DEGREES OVER MOST OF THE AREA BUT THE
NORTHERLY WINDS WILL ONLY ALLOW A COUPLE OF DEGREES OF WARMING IN
THE COLUMBIA BASIN. HIGHS WILL BE IN MID 60S TO LOWER 70S WITH
UPPER 50S TO MID 60S IN THE MOUNTAINS.
WEDNESDAY NIGHT, MODELS CONTINUE TO SHOW A FAST MOVING WAVE ARRIVING
IN THE EVENING IN CENTRAL OREGON THEN PROGRESSING THROUGH THE
EASTERN MOUNTAINS OVERNIGHT BEFORE EXITING THE AREA THURSDAY
AFTERNOON. THE WAVE LOOKS A LITTLE WEAKER THAN ON PREVIOUS MODEL
RUNS BUT SHOULD STILL GENERATE LIGHT RAIN SHOWERS IN CENTRAL
OREGON INITIALLY THEN OVER THE EASTERN MOUNTAINS. RAINFALL AMOUNTS
IN THE ABOVE MENTIONED AREAS WILL BE A TENTH OF AN INCH OR LESS.
THE WASHINGTON PORTION OF THE AREA WILL SEE LITTLE IF ANY RAIN.
NBM PROBABILITIES SHOW A 25 TO 50 PERCENT CHANCE OF GETTING A
TENTH OF AN INCH OF RAIN IN THE EASTERN MOUNTAINS. THE NBM ALSO
SHOWS ENOUGH INSTABILITY THURSDAY AFTERNOON AS THE WAVE MOVES OVER
THE EASTERN PORTIONS OF THE AREA TO PUT A 15-20 PERCENT CHANCE OF
THUNDERSTORMS OVER THE BLUE MOUNTAINS AND WALLOWA COUNTY THOUGH
ANY CELLS THAT DEVELOP WOULD BE FAIRLY WEAK. WITH THE WAVE
CROSSING THE AREA AND HEAVIER CLOUD COVER, TEMPERATURES IN THE
SOUTHERN HALF OF THE AREA WILL DROP 3 TO 5 DEGREES WHILE FURTHER
NORTH IN THE COLUMBIA BASIN, TEMPERATURES WILL SEE LITTLE CHANGE
FROM WEDNESDAY.
IN THE WAKE OF THE DEPARTING WAVE, MODELS SET UP A SHALLOW TROUGH
ALONG THE COAST WITH A SOUTHWEST FLOW OVER OUR AREA THURSDAY NIGHT.
WHAT FEW SHOWERS THAT LINGER WILL END IN THE EARLY EVENING. PERRY/83
LONG TERM...FRIDAY THROUGH TUESDAY
KEY MESSAGES...
- SCATTERED MOUNTAINS SHOWERS AND LOW THUNDERSTORM CHANCES (UP TO
20%) IN THE FAR EASTERN MOUNTAINS AND WALLOWA FRIDAY WITH DRY
CONDITIONS THIS WEEKEND,
- ABOVE AVERAGE HIGHS BY AS MUCH AS 10-15 DEGREES SUNDAY-TUESDAY
WITH THE WARMEST CONDITIONS SUNDAY/MONDAY, AND
- UNSETTLED WEATHER WITH BEST CHANCES (20-50%) IN THE CASCADES AND
EASTERN MOUNTAINS.
THE LARGE SCALE PATTERN EARLY FRIDAY WILL FEATURE A QUASI-ZONAL MID-
LEVEL FLOW WITH AN EMBEDDED SHORTWAVE TROUGH CROSSING THE REGION.
THIS WILL BE FOLLOWED BY THE AMPLIFICATION OF AN UPPER-LEVEL TROUGH
IN THE EASTERN NORTH PACIFIC AND AN UPPER RIDGE DOWNSTREAM ACROSS
THE NORTHERN INTERMOUNTAIN WEST THIS WEEKEND. INITIALLY, GUIDANCE IS
IN FAIR AGREEMENT WITH LOW SPREAD SEEN AMONGST ENSEMBLE GUIDANCE
UNTIL SUNDAY WHEN THE UPPER TROUGH BEGINS TO DE-AMPLIFY. THEREAFTER
THE UPPER-LEVEL RIDGE WILL PROGRESS TO BE OVER THE ROCKIES EXTENDING
NORTH INTO SASKATCHEWAN MONDAY-TUESDAY WITH THE AREA UNDER SOUTHWEST
FLOW. OF WHICH, AN EMBEDDED DISTURBANCE OR TWO EMERGING OUT OF THE
EASTERN NORTH PACIFIC IS ANTICIPATED TO PROMOTE LOW CHANCES (20-50%)
IN AFTERNOON MONDAY/TUESDAY AS THE UPPER TROUGH DE-AMPLIFIES.
ON FRIDAY, THE CONVECTIVE PARAMETER SPACE IS NOT STRONGLY FAVORABLE
FOR THUNDERSTORM CHANCES BETWEEN THE MARGINAL MOISTURE IN THE LOWER
TROPOSPHERE AND SURFACE, AS SEEN IN PROXIMITY SOUNDINGS, IN TANDEM
WITH 6.5-7 C/KM MID-LEVEL LAPSE RATES. THIS EXPECTATIONS MATCHES
WHAT ARE SEEING WHEN IT COMES TO GUIDANCE THUNDERSTORM PROBS WITH
CHANCES AS HIGH AS 20% IN EASTERN GRANT AND WALLOWA COUNTIES.
OTHERWISE, THE AREA WILL SEE A WARMING TREND BEGIN FRIDAY THAT PEAKS
SUNDAY/MONDAY AS A WARMER AIR MASS TAKES HOLD. WHILE THERE IS SOME
DISAGREEMENT LATE SUNDAY, THE SENSIBLE WEATHER IMPACTS ARE ISOLATED
AND CONFINED TO THE UPPER CASCADES. ENSEMBLE CLUSTERING SHOWS A
CHANCE (1 OUT OF 5) WHERE A FASTER/EASTWARD SOLUTION WITH THIS
TROUGH WILL PROMOTE A SLIGHT INCREASE IN MOUNTAIN SHOWERS ON SUNDAY.
LOOKING INTO EARLY NEXT WEEK, GUIDANCE IS LARGELY SUPPORTIVE OF THE
UPPER RIDGE SHIFTING AND BUILDING PROGRESSING EASTWARD. AS NOTED IN
INITIAL FORECASTS, CLUSTERING SCENARIOS SHOWED THE POTENTIAL FOR THE
UPPER RIDGE TO LINGER AND BE DISPLACED WEST LONGER. THUS PROMOTING
POTENTIALLY WARMER TEMPS THAN CURRENTLY FORECAST ON MONDAY AND
TUESDAY. OF WHICH, CLUSTERING DPROG/DT SHOWS THIS OUTCOME, LINGERING
RIDGE, BECOMING MORE UNLIKELY (COMPARED TO PAST RUNS MONDAY. THAT
SAID, MONDAY BOAST SIMILAR CHANCES FOR 90S OR HIGHER IN THE LOWER
BASIN (10-20%) COMPARED TO SUNDAY; TUESDAY HAS THESE CHANCES LINGER
AS WELL (~10%). MEANTIME, AN EJECTING DISTURBANCE FROM THE UPPER
TROUGH WILL PROMOTE LINGERING CHANCES IN THE CASCADES AND IN THE
AFTERNOON/EVENING MOUNTAINS, 10-50%, MONDAY AND TUESDAY. LOWEST
CHANCES WILL BE IN NORTH CENTRAL OR AND THE WESTERN/CENTRAL LOWER
BASIN WHERE DRY CONDITIONS ARE MORE LIKELY THAN NOT TO PREVAIL.
AVIATION...00Z TAFS
VFR CONDITIONS TO PREVAIL THROUGH THE
PERIOD. SCT-BKN CIGS AOA 6KFT AGL WILL CONTINUE TO IMPACT SITES
THROUGH THIS EVENING, WITH CIGS BECOMING FEW-BKN AOA 20KFT AGL
OVERNIGHT AND TOMORROW. WINDS OF 12-17KTS WITH GUSTS TO AROUND
25KTS WILL CONTINUE TO IMPACTS SITES DLS/PDT/RDM/BDN/ALW/PSC
THROUGH 3-6Z, WITH LIGHT DIURNALLY DRIVEN WINDS DEVELOPING
OVERNIGHT INTO TOMORROW TOMORROW MORNING. WINDS WILL BE 12KTS OR
LESS AND FROM THE NORTH TO NORTHWEST AT SITES DLS/PDT/RDM/BDN/PSC
TOMORROW AFTERNOON, WITH WINDS FROM THE SOUTHEAST AT SITE YKM AND
VARIABLE AT SITE ALW. LAWHORN/82
PRELIMINARY POINT TEMPS/POPS
PDT 41 69 47 67 / 0 0 40 50
ALW 45 68 49 66 / 0 0 30 50
PSC 42 71 48 72 / 0 0 20 30
YKM 39 70 50 71 / 0 0 10 20
HRI 42 71 49 72 / 0 0 30 40
ELN 39 68 46 69 / 0 0 10 20
RDM 32 70 41 65 / 0 0 40 20
LGD 34 66 44 62 / 0 0 40 60
GCD 34 70 44 64 / 0 0 50 50
DLS 42 72 50 70 / 0 0 30 30
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...83
LONG TERM....80
AVIATION...82
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