447
FXUS66 KPDT 170319
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
719 PM PST SAT NOV 16 2024
UPDATE
LATEST RADAR IMAGERY SHOWS PRECIPITATION SPREADING
ACROSS THE FORECAST AREA EARLY THIS EVENING. IT IS CURRENTLY
SNOWING ALONG THE EAST SLOPES OF THE WASHINGTON CASCADES PER
TRAFFIC CAMERAS. IT WILL SNOW OVER THE HIGHER MOUNTAINS OF THE WA
CASCADES THROUGH AROUND 06Z BEFORE A TRANSITION TO RAIN OCCURS AND
UNTIL AROUND 12Z OVER THE HIGHER ELEVATIONS OF THE NORTHERN BLUES.
THE CURRENT WINTER HIGHLIGHTS REMAIN IN EFFECT. THE BEST CHANCE TO
REACH WARNING LEVEL SNOW WILL BE AFTER THE RAIN CHANGES TO SNOW
BEHIND A COLD FRONTAL PASSAGE SUNDAY AFTERNOON. EVEN THEN IT MAY
BE TOUGH TO REACH CRITERIA IN THE NORTHERN BLUES, ALTHOUGH THERE
WILL STILL BE SEVERAL INCHES OF SNOWFALL. WINDS IN THE GRANDE
RONDE VALLEY WILL BE BUMPING UP NEAR ADVISORY LEVELS LATE TONIGHT
AND DURING THE DAY SUNDAY. THE PRESSURE GRADIENT BETWEEN BKE AND
MEH INCREASES TO 6-7 MB BUT THERE IS LITTLE UPPER WIND SUPPORT.
THE LATEST HREF HAS ROUGHLY 30-50% CHANCES FOR WINDS EXCEEDING 45
MPH IN LADD CANYON BUT 10% OR LESS FOR WINDS OVER 50 MPH. WITH
THAT IN MIND NUDGED UP THE WINDS IN THE GRIDDED FORECAST BUT WILL
HOLD OFF ON ISSUING A WIND ADVISORY FOR NOW. 78
PREV DISCUSSION
/ISSUED 215 PM PST SAT NOV 16 2024/
SHORT TERM...
TONIGHT THROUGH MONDAY NIGHT....AN APPROACHING WEATHER SYSTEM AND
UPPER LEVEL TROUGH WILL BRING UNSETTLED WEATHER THROUGH MUCH OF
THE SHORT TERM PERIOD. SNOW WILL DEVELOP OVER MUCH OF THE
MOUNTAINS AND HAS DEVELOPED OVER PORTIONS OF THE WASHINGTON
CASCADES ALREADY. AS A WARM FRONT MOVES ACROSS THE REGION, THIS
SNOW WILL CHANGE TO RAIN OVERNIGHT. RAIN WILL THEN CHANGE BACK TO
SNOW ON SUNDAY. SNOW LEVELS WILL RISE FROM BETWEEN 2000 AND 3000
FEET CURRENTLY TO BETWEEN 5000 AND 8000 FEET OVERNIGHT. SNOW
LEVELS WILL BEGIN TO FALL SUNDAY AFTERNOON TO BETWEEN 2500 AND
3500 FEET IN THE CASCADES, AND BY MONDAY MORNING WILL BE BETWEEN
2000 AND 3000 FEET EVERYWHERE.
SNOW ACROSS THE CASCADES AND NORTHERN BLUE MOUNTAINS COULD BE
QUITE HEAVY FOR A TIME AND WINTER STORM WARNINGS HAVE ALREADY BEEN
ISSUED. IN THE NORTHERN BLUE MOUNTAINS, AMOUNTS OVER 10 INCHES
ARE LIKELY ABOVE 4000 FEET. IN THE WASHINGTON CASCADES, AMOUNTS
AROUND 10 INCHES ARE LIKELY AT PASS LEVEL. IN THE OREGON CASCADES,
8 TO 15 INCHES ARE POSSIBLE ALONG THE CREST WITH LOWER AMOUNTS
ELSEWHERE.
THE TROUGH AXIS LOOKS TO PASS OVER THE REGION MONDAY MORNING AND
THERE COULD BE A BIT OF A LULL BEFORE MORE MOISTURE AND A DECENT
SHORTWAVE MOVES OVER THE MOUNTAINS LATER MONDAY INTO MONDAY NIGHT
IN WESTERLY FLOW. WINDS ARE EXPECTED TO GUST IN THE 30 TO 35 MPH
RANGE ON SUNDAY AS THE TROUGH PASSES OVER, ESPECIALLY IN THE
NORMALLY BREEZY LOCATIONS AND PORTIONS OF THE MOUNTAINS.
THE ECMWF EFI IS KEYING IN ON QPF OVER THE OREGON CASCADES, WITH
VALUES BETWEEN 0.8 AND 0.9 ON SUNDAY. TOTAL QPF VALUES ACROSS
BOTH THE OREGON AND WASHINGTON CASCADES ARE OVER 2 INCHES AT THE
HIGHEST PEAKS AND 1 TO 2 INCHES LOWER DOWN, THOUGH SOME OF THE QPF
WILL FALL AS RAIN AND SOME AS SNOW. THERE IS ALSO 1 TO 2 INCHES
OF QPF ACROSS THE BLUE MOUNTAINS, WITH OVER 2 INCHES AT THE
HIGHEST PEAKS. THE ECMWF EFI ALSO HAS 0.7 TO 0.8 ACROSS THE BLUES,
WITH A SMALL AREA OF 0.8 TO 0.9.
NBM PROBABILITIES OF WINDS >=39 MPH ARE 70 TO 90% ON SUNDAY,
ACROSS THE COLUMBIA BASIN, SIMCOE HIGHLANDS, PORTIONS OF THE BLUE
MOUNTAINS AND CASCADES. HOWEVER, WIND PROBABILITIES OF WIND GUSTS
>=47 MPH ARE 50 PERCENT OR LESS, FOR THE MOST PART.
LONG TERM...
TUESDAY THROUGH SATURDAY...WE HAD PREVIOUSLY BEEN ADVERTISING A
POTENTIALLY DRY PATTERN VIA PERSISTENT RIDGING ACROSS THE REGION,
HOWEVER MODELS HAVE SHIFTED AND NOW DEPICT A WET AND ACTIVE
PATTERN FOR MOST OF NEXT WEEK. IT SHOULD BE NOTED THAT THERE ARE
SOME HOLDOUTS ACROSS ENSEMBLE MEMBERS IN DEPICTING RIDGING OR A
MORE BENIGN PATTERN OVERALL, BUT THE CONSENSUS AS OF NOW IS TOWARD
THAT OF PERSISTENT SW FLOW, WHICH WILL GRADUALLY INCREASE TEMPS
AND SNOW LEVELS OVER THE COURSE OF NEXT WEEK, BUT NOT BEFORE THE
COLD AIR EXPECTED TO MOVE IN THIS WEEKEND TAKES ITS TOLL ON THE
PRECIP FORECAST.
A BROAD LOW CENTERED OFF THE BC COAST WILL PROVIDE THE FORECAST AREA
WITH AN OUTBREAK OF COLD AIR TO START OFF THE WORK WEEK NEXT WEEK,
BASED ON ITS ORIENTATION WITH A TROUGH AXIS SITUATED OVERHEAD LATE
MONDAY. EARLY TUESDAY MORNING WILL BE COLD AS A RESULT, WITH LOWS IN
THE TEENS AND 20S, BEFORE THIS LOW SHIFTS SOUTHWARD AND LIFTS A WARM
FRONT THROUGH THE FORECAST AREA TUESDAY EVENING INTO WEDNESDAY
MORNING. THIS FRONT HAS THE POTENTIAL TO BE SIGNIFICANT FOR SEVERAL
REASONS: 1) THERE WILL BE NO SHORT SUPPLY OF MOISTURE, ESPECIALLY
ACROSS THE MOUNTAINS, GIVEN THE SW FLOW ALOFT FEEDING THE FRONT, AND
2) THESE TYPES OF SETUPS TEND TO COME WITH THE THREAT OF ICY PRECIP.
TEMPS WILL INCREASE AS THIS WARM FRONT LIFTS THROUGH, BUT THE COLD
AIR FROM THE PRIOR NIGHTS WILL POOL INTO THE COLUMBIA BASIN,
RESULTING IN WARM AIR OVERRIDING COLD AIR. WANT TO EMPHASIZE THAT
MUCH IS STILL UP IN THE AIR WITH REGARDS TO THIS SYSTEM, AND
CONFIDENCE ON EXACT IMPACTS IS LOW (<30%), BUT CONFIDENCE IS MORE
MODERATE (50%) ON, AT THE VERY LEAST, HEAVY MOUNTAIN SNOW,
ESPECIALLY IN THE CASCADES, AND WINDY CONDITIONS ALONG THE FRONT.
THE MAIN COMPLICATING FACTORS WOULD BE 1) HOW EFFICIENTLY DO THESE
WINDS MIX OUT THE COLD POOL IN THE BASIN AND ADJACENT VALLEYS, AND
2) TIMING, AS THIS WOULD GREATLY IMPACT PRECIP TYPE GIVEN DAYTIME
HEATING.
SNOW LEVELS WILL GRADUALLY INCREASE THE REST OF THE WEEK AS MOST
ENSEMBLE MEMBERS KEEP SW FLOW ALOFT IN PLACE, TO THE POINT WHERE
PASS-LEVEL SNOW CEASES TO BE A CONCERN AFTER WEDNESDAY. STILL, POPS
ARE PERSISTENT AT 30% PLUS FOR THE REMAINDER OF THE PERIOD,
INDICATIVE OF MOST MODELS LEANING TOWARDS A WET SOLUTION FOR NEXT
WEEK. NOT EXPECTING NONSTOP PRECIP FOR THE PERIOD, BUT GUIDANCE
DOESN'T RELENT MUCH ONCE THE WARM FRONT LIFTS THROUGH LATE TUESDAY
INTO WEDNESDAY, ESPECIALLY FOR THE MOUNTAINS. UNCERTAIN IF HYDRO
CONCERNS MAY MATERIALIZE AFTER THIS WEEKEND'S MOUNTAIN SNOWFALL, BUT
IT DOES LOOK LIKE WE'LL SEE A SHARP SHIFT IN SNOW LEVELS FROM MONDAY
THROUGH NEXT WEEKEND. EVANS/74
AVIATION
00Z TAFS...CONDITIONS WILL BEGIN TO DETERIORATE TONIGHT AS A
FRONT MOVES THROUGH THE FORECAST AREA AND BRINGS RAIN TO ALL TAF
SITES. EXPECT AT LEAST MVFR CONDITIONS AT TIMES BETWEEN 00Z AND
08Z, MOVING WEST TO EAST, DUE TO REDUCED VISIBILITIES AND LOWER
CEILINGS. CONDITIONS WILL IMPROVE DURING THE OVERNIGHT PERIOD AS
RAIN LETS UP, WITH WINDS PICKING UP AHEAD OF THE NEXT ROUND OF
RAIN, EXPECTED TO ARRIVE BY LATE MORNING SUNDAY. THE STRONGER
WINDS MAY HELP IMPROVE CIGS AND VSBYS, BUT SUB-VFR CONDITIONS ARE
STILL POSSIBLE. RAIN MAY BE A LITTLE MORE PERSISTENT FOR PDT AND
ALW DUE TO TERRAIN EFFECTS, BUT CONFIDENCE IN THIS IS LOW TO
MODERATE. WIND GUSTS BY LATE SUNDAY MORNING MAY APPROACH 30 KTS AT
SOME SITES. EVANS/74
PRELIMINARY POINT TEMPS/POPS
PDT 37 53 31 44 / 90 80 50 40
ALW 39 52 34 46 / 100 90 60 60
PSC 42 56 38 50 / 70 60 20 10
YKM 30 52 25 47 / 80 40 10 10
HRI 40 56 35 49 / 70 60 20 10
ELN 31 49 26 44 / 90 60 30 20
RDM 36 52 26 40 / 60 60 50 50
LGD 33 42 26 39 / 100 100 90 80
GCD 31 49 26 39 / 100 100 90 80
DLS 40 52 35 48 / 70 90 60 70
PDT WATCHES/WARNINGS/ADVISORIES
OR...WINTER STORM WARNING UNTIL 10 PM PST MONDAY FOR ORZ502.
WINTER STORM WARNING FROM 10 AM SUNDAY TO 10 PM PST MONDAY FOR
ORZ509.
WA...WINTER STORM WARNING UNTIL 10 PM PST MONDAY FOR WAZ030-522.
SHORT TERM...78
LONG TERM....74
AVIATION...74
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