627
FXUS66 KPDT 280506
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
906 PM PST THU FEB 27 2020
UPDATE
HIGH PRESSURE WILL DOMINATE THE AREAS WEATHER WITH DRY
CONDITIONS TONIGHT. MINOR CHANGES WERE DONE TO SKY AND TEMPS THAT
ARE FORECAST TO FALL INTO THE 30S WITH 20S IN THE MOUNTAINS.
AVIATION
VFR CONDITIONS WILL PERSIST AT ALL TAF SITES FOR THE
NEXT 24 HOURS. MEANWHILE BRIEF WIND GUSTS BETWEEN 20 TO 25 KTS ARE
POSSIBLE AT TAF SITE KDLS AFTER 23Z.
PREV DISCUSSION
/ISSUED 210 PM PST THU FEB 27 2020/
SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT...THE ATMOSPHERE WILL
REMAIN DRY AND STABLE FOR THE NEXT 24 HOURS AS HIGH PRESSURE ALOFT
REMAINS OVER THE REGION. IT WILL BE WARMER TONIGHT COMPARED TO LAST
NIGHT, BUT I DECREASED THE VALUES GIVEN BY GRIDDED GUIDANCE DUE TO
MOSTLY CLEAR SKIES AND LIGHT WINDS RESULTING IN STRONG RADIATIONAL
COOLING. FRIDAY'S TEMPS WILL BE IN THE 50S TO MID 60S FOR MOST OF
THE REGION--ABOUT 10-15 DEGREES ABOVE SEASONAL AVERAGE.
A SHORTWAVE TROUGH OFF THE GULF OF ALASKA WILL FLATTEN THE RIDGE AS
IT TRAVELS ACROSS WA/OR FRIDAY NIGHT. THE TROUGH AND ITS ASSOCIATED
SURFACE COLD FRONT WILL STRETCH APART AS IT MAKES IT WAY ACROSS THE
REGION, THEREFORE THE AMOUNT OF PRECIPITATION WILL BE LIGHT. QPF
AMOUNTS WILL RANGE FROM A TRACE TO AROUND 0.15 INCH (HIGHER ALONG
THE CASCADE CREST). SNOW LEVELS WILL LOWER FROM 5000-6000 FEET
FRIDAY AFTERNOON DOWN TO NEAR 2000 FEET EARLY SATURDAY MORNING, BUT
ONLY LIGHT AMOUNTS OF SNOW ARE EXPECTED. WINDS WILL INCREASE AND
THERE WILL BE AREAS WITH SUSTAINED WINDS OF AROUND 20-30 MPH GUSTING
TO 40-45 MPH FRIDAY NIGHT AND SATURDAY, MAINLY THE HORSE HEAVEN AND
RATTLESNAKE HILLS. THE AIR MASS WILL BE SLIGHTLY UNSTABLE WITH
TOWERING CUMULUS CLOUDS DEVELOPING, BUT ANY POTENTIAL FOR
THUNDERSTORMS WILL BE OVER NORTHEAST WA. IT WILL BE MUCH COOLER ON
SATURDAY COMPARED TO FRIDAY WITH HIGHS IN THE 30S IN THE MOUNTAINS
AND 40S TO LOWER 50S IN THE LOWER ELEVATIONS. HOWEVER, THESE
TEMPERATURES ARE ACTUALLY CLOSE OR SLIGHTLY BELOW SEASONAL AVERAGE.
THE TROUGH WILL TAKE A POSITIVE TILT AND TRAVEL SOUTH INTO THE GREAT
BASIN SATURDAY NIGHT, FOLLOWED BY A COLDER AND DRIER NORTHERLY FLOW
ALOFT. OVERNIGHT TEMPERATURES IN THE 20S ARE FORECAST FOR MOST OF
THE FORECAST AREA SATURDAY NIGHT. WISTER
LONG TERM...SUNDAY THROUGH THURSDAY. TILTED, ELONGATED TROUGH
WILL BE EXITING THE REGION TO THE SOUTH SUNDAY MORNING, BRINGING DRY
NORTHERLY FLOW ALOFT. AS THE UPPER LEVEL TROUGH CONTINUES TO DIG
SOUTH AND EASTWARD SUNDAY EVENING, FLOW ALOFT WILL TURN TO THE
NORTHWEST, BRINGING FAVORABLE UPSLOPE FLOW INTO THE CASCADE, BLUE,
AND WALLOWA MOUNTAINS. EMBEDDED IN THIS NORTHWEST FLOW, A SERIES OF
SYNOPTIC SYSTEMS WILL IMPACT THE FORECAST AREA STARTING LATE MONDAY.
AHEAD OF AN UPPER LEVEL SHORTWAVE AND JET MAX, PRESSURE GRADIENTS AT
THE SURFACE WILL TIGHTEN AND A 850MB JET MAX WILL DEVELOP OVER THE
LOWER COLUMBIA BASIN. BREEZY WESTERLY WINDS WILL START TO DEVELOP
UNDER THIS PATTERN MONDAY AFTERNOON, DIMINISHING SLIGHTLY OVERNIGHT,
AND STRENGTHENING AGAIN AT SUNRISE. WINDS WILL DIMINISH AGAIN BY
TUESDAY EVENING. AT THIS TIME, MODELS ARE NOT SIGNALING ADVISORY
LEVEL WINDS, BUT WILL KEEP AN EYE ON THEM AS WE GET CLOSER TO THIS
EVENT. SHORTWAVE WILL MOVE NORTH OF THE REGION MONDAY EVENING,
PULLING A GOOD POOL OF MOISTURE BEHIND IT. THIS MOISTURE PULL WILL
HELP TO SUSTAIN UPSLOPE SNOW SHOWERS IN THE WA/OR CASCADES, WITH
LIGHT SNOW SHOWERS POSSIBLE IN THE BLUE AND WALLOWA MOUNTAINS.
THOUGH SNOW SHOWERS WILL CONTINUE THROUGH WEDNESDAY MORNING,
PRELIMINARY SNOW ACCUMULATIONS ARE NOT REACHING ADVISORY LEVELS.
BEYOND TUESDAY EVENING, MODELS BEGIN TO DISAGREE ON GENERAL FLOW
REGIME, WITH GFS BRIEFLY BUILDING A DRY RIDGE OVER FORECAST AREA
WHERE ECMWF KEEPS A WET WESTERLY FLOW. HOWEVER, THERE IS GENERAL
CONSENSUS IN A UPPER LEVEL SHORTWAVE TROUGH AND ATTENDANT COLD FRONT
DROPPING DOWN FROM GULF ALASKA AND IMPACTING THE REGION EARLY
THURSDAY MORNING, WITH A WARMER SOUTHWEST FLOW ALOFT SETTING UP
BEHIND THE FRONTAL BOUNDARY THURSDAY EVENING. THERE WILL GENERALLY
BE A WARMING TREND THROUGH WEDNESDAY, WITH MAINLY MOUNTAIN SNOW
SHOWERS AND SLIGHT CHANCES OF LOWER ELEVATION RAIN WITH EACH PASSING
SYSTEM. LAWHORN/82
PRELIMINARY POINT TEMPS/POPS
PDT 35 65 39 50 / 0 0 20 10
ALW 38 63 40 51 / 0 0 20 20
PSC 34 64 40 55 / 0 0 0 10
YKM 32 61 33 52 / 0 0 10 10
HRI 34 64 40 53 / 0 0 10 10
ELN 32 56 32 47 / 0 0 20 20
RDM 27 65 30 45 / 0 0 10 20
LGD 29 54 34 43 / 0 0 20 30
GCD 34 62 32 43 / 0 0 10 30
DLS 36 61 40 50 / 0 0 40 30
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
97/97
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