575
FXUS66 KPDT 202123
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
123 PM PST THU FEB 20 2020
SHORT TERM
TONIGHT THROUGH SATURDAY...THE LONG PERSISTENT RIDGE OF HIGH
PRESSURE OVER THE REGION IS STARTING TO SLOWLY BREAK DOWN AND MOVE
EASTWARD. AS IT DOES, THE FLOW WILL BECOME MORE ZONAL OVER THE
AREA, HIGH CLOUDS WILL INCREASE THROUGH FRIDAY AND A WEAK AND DRY
TROUGH WILL MOVE OVER THE AREA ON FRIDAY AS WELL. THEN, BY
SATURDAY CLOUDS WILL CONTINUE TO LOWER AND THICKEN AS AN AREA OF
LOW PRESSURE WILL APPROACH THE REGION FROM THE NORTHWEST. IT LOOKS
LIKE ANY PRECIPITATION FROM THIS SYSTEM WILL WAIT UNTIL AFTER THE
SHORT TERM PERIOD FOR MOST AREAS, THOUGH SOME LIGHT RAIN OR RAIN
AND SNOW CAN NOT BE RULED OUT OVER THE CASCADE CREST AND THE
EXTREME NORTHWESTERN AREAS BY LATE SATURDAY AFTERNOON/SATURDAY
EVENING. SNOW LEVELS WILL INITIALLY BE FAIRLY HIGH, MAINLY
3000-4000 FT NORTH AND 3500-4500 FEET SOUTH.
FRIDAY MORNING STILL LOOKS COLD (THOUGH PROBABLY NOT AS COLD AS
THE LAST FEW), AND WITH INCREASING CLOUDINESS, SATURDAY MORNING
WILL LIKELY BE ON AVERAGE 4 TO 5 DEGREES WARMER. HIGHS THE FRIDAY
WILL BE A COUPLE OF DEGREES ABOVE NORMAL AND ON SATURDAY, SHOULD
BE EVEN A BIT WARMER THAN FRIDAY.
LONG TERM
SUNDAY...SYSTEM IS STILL ON TRACK TO IMPACT THE REGION LATE
SATURDAY NIGHT INTO MONDAY. FROM A SYNOPTIC VIEW, NORTH PACIFIC
ENERGY WILL MOVE NE TOMORROW NIGHT INTO SATURDAY WHERE IT IS
EXPECTED TO INTERACT WITH A MODEST TROUGH DIGGING SOUTH INTO THE
GULF OF ALASKA. IN GENERAL, MODELS AGREE ON A MEDIUM STRENGTH
ORGANIZED LOW PEAKING IN STRENGTH ALONG THE BRITISH COLUMBIA COAST
SATURDAY NIGHT BEFORE WEAKENING AS IT MOVES INLAND ON SUNDAY.
WHERE MODELS SEEM TO DISAGREE MOST IS IN TIMING, THE STRENGTH OF A
WARM NOSE NUDGING ACROSS THE INLAND NORTHWEST, AND IN TOTAL QPF
FOR THE SYSTEM. THESE DISAGREEMENTS IN DETAILS MAY BE RELATED TO
PHASING ISSUES WITH THE MARITIME PACIFIC ENERGY AND THE ARCTIC
TROUGH. SOME MODELS OR RUNS HAVE ADVERTISED A FASTER, OPEN WAVE
SYSTEM WITH MODEST QPF BUT A LIMITED WARM NOSE WHILE THE TREND WE
ARE SEEING TODAY, PARTICULARLY FROM THE 12Z GFS, IS FOR A SLOWER
SYSTEM WITH HIGHER QPF BUT ALSO WARMER TEMPS/HIGHER SNOW LEVELS.
DESPITE THE CONTINUED UNCERTAINTY IN DETAILS, THE BROAD STROKES OF
THE SYSTEM ARE CLEAR: INCREASED MOISTURE AND CLOUD COVER WILL
BEGIN PRECIPITATING ALONG THE WASHINGTON CASCADE CREST BY SUNDAY
MORNING. WINDS WILL BE BREEZY IN THE GRANDE RONDE VALLEY AS
SOUTHERLY WINDS ARE CHANNELED INTO THE LOW. SNOW IS LIKELY TO
BEGIN IN THE BLUE MOUNTAINS BY SUNDAY AFTERNOON WHILE THE BASIN
HOLDS ONTO RAIN CHANCES SUNDAY INTO SUNDAY NIGHT. SNOW LEVELS
BEGIN QUITE HIGH LATE SATURDAY INTO SUNDAY, RANGING FROM 3000FT IN
THE WA CASCADES TO NEAR 4000 IN THE BLUE MTNS, BUT THESE WILL
GRADUALLY FALL THROUGH THE DAY SUNDAY TO 2000FT BY MONDAY. MOST
MOUNTAIN PASSES ARE LIKELY TO EXPERIENCE AT LEAST MINOR IMPACTS
FROM ACCUMULATING SNOW. A FRONTAL PASSAGE WILL INCREASE WINDS
THROUGH THE COLUMBIA BASIN, CENTRAL OREGON, AND THE KITTITAS
VALLEY ON SUNDAY.
MONDAY THROUGH FRIDAY...PRECIP CHANCES DWINDLE FOR THE BASIN ON
MONDAY WHILE MORE UNSTABLE AIRMASS BEHIND THE FRONT CONTINUES TO
PROMOTE SNOW FOR THE BLUE AND WALLOWA MOUNTAINS THROUGH MUCH OF THE
DAY. A RIDGE BUILDS IN TUESDAY YIELDING CLEAR AND COOL CONDITIONS.
IT'S NOT CLEAR WHEN THIS RIDGE BREAKS DOWN NEXT WEEK AS SOME MODEL
SOLUTIONS MAINTAIN SOME AMOUNT OF MID LEVEL RIDGING THROUGH MUCH OF
THE WEEK WHILE OTHERS FLATTEN THE FLOW INTO MORE WESTERLY WINDS,
WHICH WOULD PROMOTE SOME CLOUD COVER AND POSSIBLE HIGH MOUNTAIN
SNOW. REGARDLESS, THE MID-WEEK PERIOD OF NEXT WEEK IS EXPECTED TO
HOLD RELATIVELY BENIGN WEATHER.
AVIATION
00Z TAFS...VFR CONDITIONS WILL CONTINUE THROUGH THE TAF PERIOD AND
BEYOND. WINDS WILL GENERALLY BE LIGHT, THOUGH A BRIEF WIND GUST IN
THE 10 TO 15 KT RANGE CAN NOT BE RULED OUT THROUGH THIS EVENING.
OTHERWISE, MAINLY INCREASING HIGH CLOUDS ARE EXPECTED.
PRELIMINARY POINT TEMPS/POPS
PDT 29 52 33 54 / 0 0 0 0
ALW 30 51 35 55 / 0 0 0 0
PSC 29 50 34 54 / 0 0 0 0
YKM 28 49 33 53 / 0 0 0 0
HRI 30 52 33 55 / 0 0 0 0
ELN 27 44 31 49 / 0 0 0 0
RDM 28 55 30 56 / 0 0 0 0
LGD 23 41 28 49 / 0 0 0 0
GCD 24 46 29 53 / 0 0 0 0
DLS 31 51 35 55 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
77/76/77
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