316
FXUS66 KPDT 161740
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
940 AM PST THU JAN 16 2025
UPDATE
SHORT TERM...
MADE ADJUSTMENTS TO TEMPERATURES, ESPECIALLY IN THOSE AREAS WITH
FOG OR STRATUS, AS FORECAST HIGH TEMPERATURES WILL LIKELY BE TOO
HIGH. THESE AREAS WILL LIKELY BREAK OUT THIS AFTERNOON, BUT DUE TO
THE CLOUD COVER AND STRATUS, TEMPERATURES WILL NOT MOVE MUCH
UNTIL THEY DO. THEREFORE HIGH TEMPERATURES WILL LIKELY END UP
BEING LOWER THAN ORIGINAL FORECASTS.
OTHERWISE, CURRENT FORECASTS LOOK REASONABLE.
PREV DISCUSSION
/ISSUED 928 AM PST THU JAN 16 2025/
AVIATION...18Z TAFS...VARIABLE CONDITIONS THIS MORNING AS LOW
CLOUDS AND FOG LINGER ACROSS MOST TAF SITES, SAVE FOR BDN/RDM.
SOME RELIEF IS EXPECTED THIS AFTERNOON AS A WEAK WEATHER SYSTEM
MOVES THROUGH THE AREA, CAUSING AN UPTICK IN WINDS FOR MOST SITES,
HOWEVER CONFIDENCE IS WAVERING ON WHETHER OR NOT THESE WINDS WILL
BE STRONG ENOUGH TO MIX OUT THE LOW CLOUD DECK. WINDS IN YKM,
ALW, AND PSC IN PARTICULAR COULD BE TOO WEAK TO SEE IMPROVEMENTS
BEYOND MVFR. WITH CALM CONDITIONS EXPECTED TO SETTLE BACK IN THIS
EVENING, WHEREVER CLOUDS DO NOT MIX OUT, THEY WILL PERSIST HEADING
INTO FRIDAY. PDT AND DLS ARE MOST LIKELY TO SEE IMPROVEMENT, WITH
BDN AND RDM STAYING VFR THROUGH THE PERIOD. EVANS/74
PREV DISCUSSION... /ISSUED 401 AM PST THU JAN 16 2025/
SHORT TERM...TODAY THROUGH SATURDAY NIGHT...
KEY MESSAGES:
1. PATCHY FOG AND LOW STRATUS THIS MORNING.
2. LIGHT MOUNTAIN SNOW TODAY INTO FRIDAY MORNING.
3. BREEZY WINDS ACROSS THE GRANDE RONDE VALLEY TODAY.
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWS A SUBSTANTIAL
STRATUS CLOUD DECK EXTENDING ACROSS THE COLUMBIA BASIN, BLUE
MOUNTAIN FOOTHILLS, NORTH-CENTRAL OREGON, AND THE YAKIMA/KITTITAS
VALLEYS UNDER DRY CONDITIONS. THIS LOW STRATUS DECK HAS REACHED
THE GROUND SURFACE IN SOME AREAS IN THE FORM OF PATCHY FOG AND
FREEZING FOG, WHICH HAS OCCURRED ALONG THE BLUE MOUNTAIN
FOOTHILLS. VISIBILITIES OF ONE HALF MILE HAVE BEEN OBSERVED VIA
AREA WEBCAMS AND WEATHER STATIONS (PRIMARILY SOUTH OF MILTON-
FREEWATER AND OVER CABBAGE HILL ALONG THE I-84 CORRIDOR), WHICH
HAS WARRANTED THE ISSUANCE OF A SPECIAL WEATHER STATEMENT UNTIL 4
AM - WHICH WILL LIKELY BE EXTENDED UNTIL MID-TO LATE MORNING.
PATCHY FREEZING FOG HAS ALSO BEEN OBSERVED ACROSS NORTH-CENTRAL
OREGON AND THE KITTITAS VALLEY, BUT CURRENTLY ONLY IN ISOLATED
AREAS BETWEEN MORO AND SHANIKO ON HIGHWAY 97, AND IN THORP PRAIRIE
SOUTH OF CLE ELUM. THESE CONDITIONS ARE A RESULT FROM AN UPPER
LEVEL RIDGE AND SURFACE HIGH PRESSURE THAT IS CURRENTLY OVER THE
AREA, BUT WILL BE LOSING THEIR INFLUENCE THROUGH THE MORNING AND
AFTERNOON. FOG AND FREEZING FOG IS EXPECTED TO DISSIPATE THROUGH
THE MORNING AS A RESPONSE. THE UPPER LEVEL RIDGE HAS ALREADY BEGUN
TO WEAKEN AS AN UPPER LEVEL TROUGH CONTINUES TO DROP THROUGH
CENTRAL BRITISH COLUMBIA BEFORE DRIVING THROUGH EASTERN WASHINGTON
AND OREGON THIS EVENING INTO FRIDAY MORNING.
THIS UPPER LEVEL SYSTEM AND ATTENDANT COLD FRONT WILL SHIFT THE
FLOW ALOFT FROM THE WEST TO THE NORTHWEST BY THIS AFTERNOON AND
EVENING. THE FLOW ALOFT THAT IS CURRENTLY FROM THE WEST WILL
ATTRIBUTE TO UPSLOPE SNOW CHANCES (30-50%) ACROSS THE WASHINGTON
CASCADES THIS MORNING AND AFTERNOON, PRIMARILY AT AND ABOVE 5000
FEET. THE COLD FRONT WILL BE DRAPED ACROSS THE AREA DURING THE
LATE MORNING AND EARLY AFTERNOON BEFORE DEPARTING TO OUR SOUTH
LATER THIS EVENING. BEHIND THE COLD FRONT, FLOW ALOFT WILL SHIFT
OUT OF THE NORTHWEST AND ALIGN WITH THE NORTHERN BLUE MOUNTAINS TO
ALLOW UPSLOPE SNOW SHOWERS AFTER 4 PM. SNOW CHANCES (30-50%) OVER
THE NORTHERN BLUES WILL PEAK TONIGHT BETWEEN 7 PM AND MIDNIGHT,
BEFORE SLOWLY DISSIPATING OVERNIGHT INTO THE EARLY MORNING HOURS
ON FRIDAY. AS THIS SYSTEM IS APPROACHING FROM THE NORTH, VERY
LITTLE MOISTURE IS ASSOCIATED WITH IT AS ONLY 1-2 INCHES OF
SNOWFALL IS ANTICIPATED OVER THE WASHINGTON CASCADES AND THE
NORTHERN BLUE MOUNTAINS. CONFIDENCE IN THESE SNOW AMOUNTS IS HIGH
(80%) AS THE HREF ADVERTISES A 30-60% CHANCE OF 1 INCH OR MORE OF
SNOW ACROSS THE WASHINGTON CASCADES AND NORTHERN BLUE MOUNTAINS,
WHICH DROPS TO ONLY A 10% CHANCE WHEN INCREASING THE SNOW AMOUNT
TO 2 INCHES OR MORE. HIGH PRESSURE AND THE UPPER LEVEL RIDGE
OFFSHORE BEGINS TO REBUILD ON FRIDAY, KEEPING CONDITIONS DRY INTO
THE EARLY PART OF THE WEEKEND.
THE COLD FRONTAL PASSAGE LATER TODAY WILL ALSO LEAD TO BREEZY
WINDS ACROSS THE EAST SLOPES OF THE WASHINGTON CASCADES, SIMCOE
HIGHLANDS, GORGE, AND THE BLUE MOUNTAIN FOOTHILLS, WITH THE
HIGHEST WINDS EXPECTED TO OCCUR OVER THE GRANDE RONDE VALLEY AS A
PRESSURE GRADIENT SETS UP ALONG THE BLUE MOUNTAINS. THE GFS AND
SREF SUGGEST A PRESSURE GRADIENT OF BETWEEN 6.5-7.5 MB BETWEEN
BAKER CITY (KBKE) AND MEACHAM (KMEH), WHICH IS ABOVE THE NORMAL
ADVISORY THRESHOLD OF 6 MB. HOWEVER, CURRENT OBSERVATIONS ARE
TRENDING 1-1.5 MB BELOW GFS AND SREF GUIDANCE. FURTHER CONFIDENCE
IS GLEANED FROM THE HREF AND NBM, WHICH SUGGESTS A 40% AND 30%
CHANCE OF ADVISORY-LEVEL WIND GUSTS (45 MPH OR GREATER),
RESPECTIVELY. THUS, SUSTAINED SOUTH WINDS OF 20-30 MPH WITH GUSTS
OF UP TO 40 MPH WILL BE POSSIBLE, PEAKING DURING THE LATE MORNING
AND EARLY AFTERNOON HOURS. THESE WIND VALUES WILL ALSO OCCUR OVER
THE AFOREMENTIONED AREAS OF THE EAST SLOPES OF THE WASHINGTON
CASCADES, SIMCOE HIGHLANDS, GORGE, AND THE BLUE MOUNTAIN
FOOTHILLS, BUT WILL BE EXPERIENCED IN ISOLATED AREAS. WINDS WILL
BE SUBSIDING THROUGH THE AFTERNOON AND EVENING IN THE WAKE OF THE
DEPARTING COLD FRONT. 75
LONG TERM...SUNDAY THROUGH THURSDAY...MODELS ARE CONFIDENT IN
HAVING A LARGE RIDGE OF HIGH PRESSURE OFFSHORE THROUGH THE LONG TERM
PERIOD WITH OUR AREA UNDER A GENERALLY NORTH TO NORTHWEST FLOW ON
THE EAST SIDE OF THE RIDGE. MODELS DO HAVE DIFFERENCES AS TO THE
STRENGTH OF THE RIDGE AT TIMES, ESPECIALLY ON TUESDAY AS THEY DIFFER
ABOUT WHETHER A SHORTWAVE FLATTENS THE RIDGE INTO A MORE WESTERLY
FLOW OR NOT. THOSE MODELS ALSO KEEP A FLATTER RIDGE THROUGH THURSDAY
AND THIS ALLOWS FOR A POSSIBLE SHORTWAVE TO BRING A SLIGHT CHANCE OF
VERY LIGHT SNOW SHOWERS TO THE CASCADES, NORTHERN BLUE MOUNTAINS AND
THE WALLOWA MOUNTAINS. THE EXTREME FORECAST INDEX HIGHLIGHTS COLD
TEMPERATURES SUNDAY THROUGH WEDNESDAY MORNING WITH VALUES OF -0.77
TO -0.88. OTHER THAN THAT, NO UNUSUAL WEATHER IS EXPECTED IN THE
LONG TERM PERIOD. OVERALL, FORECAST CONFIDENCE IS GOOD DROPPING TO
AVERAGE BY THURSDAY.
SUNDAY WILL SEE THE RIDGE WELL ESTABLISHED OFF THE COAST WITH A DEEP
TROUGH FROM THE ROCKIES EASTWARD. A WEAK SHORTWAVE WILL BE PASSING
WELL TO OUR EAST AND THIS WILL TIGHTEN PRESSURE GRADIENTS SOMEWHAT.
NORTH TO NORTHEAST SUSTAINED WINDS WILL ONLY BE AROUND 10 MPH BUT
GUSTS WILL REACH ABOUT 20 MPH. THE MAIN IMPACT WILL BE TO KEEP HIGH
TEMPERATURES IN THE 30S WITH OVERNIGHT LOWS COOLING TO THE TEENS
WITH LOWS 5 TO 15 IN THE MOUNTAINS.
MONDAY THROUGH WEDNESDAY THE RIDGE PERSISTS OVER THE AREA WITH
CONTINUED DRY WEATHER. TEMPERATURES COOL MONDAY TO THE MID 20S TO
MID 30S THEN WARM TO THE MID 30S TO LOWER 40S BY WEDNESDAY.
BY THURSDAY, MODELS DIFFER AS TO JUST HOW FAR OFFSHORE THE RIDGE
WILL CENTERED. ABOUT A THIRD OF THE MODEL ENSEMBLE MEMBERS HAVE THE
RIDGE FURTHER OFFSHORE AND FLATTER AND HAVE A SHORTWAVE MOVING NORTH
OF THE AREA AND BRINGING A SLIGHT CHANCE OF VERY LIGHT SNOW SHOWERS
TO THE HIGHER MOUNTAINS WHILE THE REST OF THE AREA IS DRY.
TEMPERATURES WARM A FEW DEGREES TO THE MID 30S TO MID 40S.
PERRY/83
PRELIMINARY POINT TEMPS/POPS
PDT 41 27 38 22 / 0 10 0 0
ALW 42 28 38 23 / 0 10 0 0
PSC 42 28 40 25 / 0 0 0 0
YKM 39 26 41 20 / 0 0 0 0
HRI 46 29 40 25 / 0 0 0 0
ELN 39 25 37 21 / 0 0 0 0
RDM 52 23 36 18 / 0 0 0 0
LGD 44 27 36 17 / 0 20 10 0
GCD 49 25 36 15 / 0 10 0 0
DLS 47 32 44 28 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...FREEZING FOG ADVISORY UNTIL 11 AM PST THIS MORNING FOR ORZ507.
WA...NONE.
SHORT TERM...77
LONG TERM....83
AVIATION...74
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