974
FXUS66 KPDT 181050
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
250 AM PST SAT JAN 18 2025
SHORT TERM...TODAY THROUGH MONDAY NIGHT
KEY MESSAGES:
1. COOLING TREND THROUGH MONDAY MORNING.
2. FRIGID TEMPERATURES SUNDAY NIGHT AND MONDAY.
CURRENT RADAR AND INFRARED SATELLITE IMAGERY SHOWING DRY
CONDITIONS UNDER MOSTLY CLEAR SKIES. THIS IS IN RESPONSE TO THE
UPPER LEVEL RIDGE LOCATED OFFSHORE, WHICH WILL BE THE DOMINANT
SYNOPTIC FEATURE THROUGHOUT THE PERIOD. THESE FEATURES, COUPLED
WITH LOW WINDS, HAVE ALLOWED EFFECTIVE RADIATIONAL COOLING TO
OCCUR AS MORNING TEMPERATURES WILL DROP INTO THE LOW TO MID-20S
ACROSS THE BASIN AND FOOTHILLS, AND IN THE UPPER TEENS TO LOW 20S
OVER CENTRAL OREGON. THE PRIMARY CONCERN THROUGH THE PERIOD
RESIDES WITH INCOMING COLD TEMPERATURES AS A RESULT OF OUR
LOCATION ALONG THE FRONT SIDE OF THE UPPER LEVEL TROUGH -
ATTRIBUTING TO PERSISTENT NORTH NORTHWEST FLOW ALOFT. THIS FLOW
ALOFT WILL ADVECT COLDER AIR INTO THE REGION AS HIGH TEMPERATURES
TODAY ARE EXPECTED TO REACH INTO THE MID-TO UPPER 30S ACROSS THE
COLUMBIA BASIN, BLUE MOUNTAIN FOOTHILLS, AND CENTRAL OREGON, WHICH
IS ABOUT 5 DEGREES BELOW NORMAL. OVERNIGHT TEMPERATURES INTO
SUNDAY MORNING WILL DROP ANOTHER 2-4 DEGREES FROM SATURDAY
MORNING, WITH VALUES IN THE UPPER TEENS TO LOW 20S ACROSS THE
COLUMBIA BASIN AND BLUE MOUNTAIN FOOTHILLS.
AM UPPER LEVEL TROUGH WILL DROP DOWN THE FRONT SIDE OF THE RIDGE
ON SUNDAY, PROVIDING CLEARING SKIES THROUGH THE DAY AND CAUSING
FLOW ALOFT TO SHIFT FROM THE NORTHWEST TO THE NORTH. THIS WILL
MORE EFFICIENTLY BRING COLDER, ARCTIC AIR INTO THE REGION AS
AFTERNOON TEMPERATURES PEAK IN THE MID-30S ACROSS THE COLUMBIA
BASIN AND FOOTHILLS - WHICH IS ABOUT 8 DEGREES BELOW NORMAL.
NORTHERLY FLOW ALOFT WILL BE RESPONSIBLE FOR SUNDAY NIGHT INTO
MONDAY BEING THE COLDEST PERIOD IN THE FORECAST, AS MONDAY MORNING
LOW TEMPERATURES ARE EXPECTED TO BE IN THE MID-TO UPPER TEENS
ACROSS THE COLUMBIA BASIN, BLUE MOUNTAIN FOOTHILLS, AND CENTRAL
OREGON. THESE LOW TEMPERATURES ARE ABOUT 10 DEGREES BELOW NORMAL.
CONFIDENCE IN THESE TEMPERATURES IS MODERATE (70%) AS THE NBM
SUGGESTS A 60-80% CHANCE OF MORNING TEMPERATURES STAYING IN THE
TEENS ACROSS MUCH OF THE BASIN, WITH THE ONLY EXCEPTION FOR AREAS
CLOSE TO THE COLUMBIA RIVER (TRI-CITIES, HERMISTON, THE DALLES).
FOR THESE AREAS, THE NBM HINTS AT LESS THAN A 10% CHANCE OF
MORNING TEMPERATURES STAYING IN THE TEENS. FURTHER CONFIDENCE IS
GLEANED FROM ENSEMBLE MEMBERS, AS ALL ECMWF MEMBERS KEEP LOW
TEMPERATURES IN THE LOW 20S FOR PASCO. ALSO OF NOTE, ECMWF
GUIDANCE HAS BEEN TRENDING SLIGHTLY WARMER OVER THE LAST 5 MODEL
RUNS IN REGARDS TO LOW TEMPERATURES AT PASCO, INITIALLY FROM 20
DEGREES FROM THE 12Z RUN ON JANUARY 15TH TO 23 DEGREES WITH THE
MOST RECENT 00Z RUN. HIGH TEMPERATURES ON MONDAY WILL AGAIN DROP
ANOTHER 1-3 DEGREES FROM SUNDAY, WITH VALUES PEAKING IN THE LOW TO
MID-30S ACROSS THE COLUMBIA BASIN AND BLUE MOUNTAIN FOOTHILLS.
ANOTHER RESULT FROM THE NORTHERLY FLOW ALOFT WILL BE CLEAR SKIES,
WHICH ARE EXPECTED BOTH SUNDAY AND MONDAY. 75
LONG TERM...TUESDAY THROUGH SATURDAY
ENSEMBLE NWP GUIDANCE IS IN
LOOSE AGREEMENT THAT A QUICK-HITTING, LOW-AMPLITUDE SHORTWAVE TROUGH
WILL CLIP THE PACNW ON TUESDAY. SHOULD THE SHORTWAVE MATERIALIZE, IT
IS UNLIKELY TO PRODUCE MEASURABLE PRECIPITATION (<5% CHANCE AREA-
WIDE).
WEDNESDAY, ENSEMBLE MEAN 500-MB HEIGHTS FROM ALL THREE GLOBAL
ENSEMBLE SYSTEMS INDICATE A BROAD TROUGH DOWNSTREAM (EAST OF THE
ROCKIES) ACCOMPANIED BY A RIDGE OF HIGH PRESSURE JUST OFFSHORE OF
OR/WA. HOWEVER, NOTEWORTHY DIFFERENCES ARE PRESENT UPSTREAM IN THE
NORTHEAST PACIFIC AND GULF OF ALASKA. WHILE ENSEMBLE MEANS RETAIN
THE UPPER-LEVEL RIDGE THROUGH THURSDAY — A SCENARIO FAVORED BY 51%
OF ENSEMBLE MEMBERS —, A SUBSET OF MEMBERS (15%) ADVERTISE A
SHORTWAVE TROUGH BY THURSDAY AFTERNOON, AND A FURTHER 34% SUGGEST AT
LEAST SOME SUPPRESSION OF THE RIDGE. THIS TROUGH WOULD FACILITATE
PRECIPITATION ACROSS THE CASCADE CREST AND BLUE MOUNTAINS.
FRIDAY, A BREAKDOWN OF THE RIDGE IS MORE LIKELY AS 36% OF ENSEMBLE
MEMBERS SUGGEST A TROUGH AND BELOW-NORMAL 500-MB HEIGHTS OVER THE
PACNW, WHILE ONLY ABOUT 25% OF MEMBERS KEEP THE RIDGE IN PLACE. SOME
FLAVOR OF TROUGHING IS EVEN MORE LIKELY FOR SATURDAY (ROUGHLY 70% OF
MEMBERS). THE RETURN TO A TROUGHING PATTERN, HOWEVER BRIEF, SUPPORTS
AREA-WIDE PRECIPITATION CHANCES FRIDAY INTO SATURDAY. THAT SAID,
PRECIPITATION WILL LIKELY BE LIGHT — NBM PROBABILITIES OF EXCEEDING
0.1" FOR THE LOWLANDS RANGE FROM 10-40%, AND 30-70% FOR THE
MOUNTAINS. MORE SIGNIFICANT PRECIPITATION IS UNLIKELY — LESS THAN 5%
FOR THE LOWLANDS, AND 10-40% FOR THE MOUNTAINS.
SO FAR THIS WINTER, THE LOWLANDS HAVE RECEIVED LITTLE SNOW RELATIVE
TO NORMAL. WILL THAT FINALLY CHANGE? WELL, DURING THE 48-HR PERIOD
BETWEEN 4AM FRIDAY AND 4AM SUNDAY, THERE IS A 20-45% CHANCE OF
MEASURABLE SNOW (0.1") FOR THE LOWLANDS. PROBABILITIES OF 1" AND 2"
OF SNOW DROP TO 5-15% AND 10% OR LESS, RESPECTIVELY. WITH REGARD TO
MOUNTAIN SNOWFALL, NBM PROBABILITIES ARE CURRENTLY NOT SUPPORTIVE OF
HIGH CONFIDENCE IN REACHING ADVISORY AMOUNTS; FOR EXAMPLE, THERE IS
A 20-50% CHANCE OF 6" FOR THE WA/OR CASCADE CREST AND THE NORTHERN
BLUE MOUNTAINS. THE PROBABILITY OF WARNING-LEVEL TOTALS IS LOW (20%
OR LESS) FOR ALL MOUNTAIN ZONES.
NBM PROBABILITIES OF ADVISORY-LEVEL WIND GUSTS (45 MPH OR GREATER)
ARE LOW (25% OR LESS) LATE THURSDAY THROUGH FRIDAY. PLUNKETT/86
AVIATION...12Z TAFS
VFR CONDITIONS ARE LIKELY (80% CHANCE OR
GREATER) FOR ALL SITES THROUGH THE PERIOD. SUSTAINED WINDS OF 10 KTS
OR LESS ARE FORECAST FOR ALL SITES. PLUNKETT/86
PRELIMINARY POINT TEMPS/POPS
PDT 36 21 33 16 / 0 0 0 0
ALW 36 25 34 18 / 0 0 0 0
PSC 37 25 37 21 / 0 0 0 0
YKM 36 20 36 16 / 0 0 0 0
HRI 37 25 36 20 / 0 0 0 0
ELN 33 18 32 16 / 0 0 0 0
RDM 38 16 35 12 / 0 0 0 0
LGD 32 18 34 11 / 0 0 0 0
GCD 35 17 36 11 / 0 0 0 0
DLS 41 26 39 23 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...75
LONG TERM....86
AVIATION...86
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