930
FXUS66 KPDT 281209
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
509 AM PDT FRI AUG 28 2026
KEY MESSAGES
- VERY LOW TO SLIGHT CHANCE (5-15%) OF THUNDERSTORMS TODAY (BLUE
MOUNTAINS) AND SATURDAY (CASCADE AND BLUE MOUNTAINS).
- HIGH CONFIDENCE (99%) THAT A LOW-PRESSURE SYSTEM WILL TRACK
OVER THE PACIFIC NORTHWEST SATURDAY INTO EARLY SUNDAY,
RESULTING IN BELOW-NORMAL TEMPERATURES AND WIDESPREAD BREEZY
WESTERLY WINDS.
- PERIODS OF ELEVATED FIRE WEATHER CONDITIONS THROUGH THE
WEEKEND DUE TO THE BREEZY WINDS, BUT LOW CONFIDENCE (<40%) IN
WIDESPREAD RED FLAG CONDITIONS.
- LOW-MEDIUM PROBABILITY (20-50%) OF NEAR-FREEZING MORNING LOW
TEMPERATURES IN COLD-PRONE VALLEYS OF CENTRAL AND NORTHEAST
OREGON SUNDAY AND MONDAY.
DISCUSSION
SATELLITE IMAGERY EARLY THIS MORNING SHOWS SOUTHWESTERLY FLOW
ALOFT, WITH A SHORTWAVE TROUGH NOTED UPSTREAM JUST OFFSHORE IN
THE PACIFIC. MEANWHILE, A CLOSED LOW IS LOCATED OVER FAR
SOUTHEAST ALASKA, MOVING SOUTHEAST ALONG THE COAST. THE LATTER
LOW WILL BE THE PRIMARY DRIVER OF OUR WEATHER OVER THE WEEKEND.
TODAY, DIURNALLY BREEZY WINDS ARE EXPECTED (99% CONFIDENCE)
THROUGH THE CASCADE GAPS. WEAK FORCING AND INSTABILITY OVER THE
BLUE MOUNTAINS (MAINLY ELKHORNS, NORTHERN BLUES, AND WALLOWA
COUNTY) MAY FACILITATE ISOLATED SHOWERS AND THUNDERSTORMS THIS
AFTERNOON AND EVENING, WITH STRONGER SYNOPTIC-SCALE FORCING
ASSOCIATED WITH THE AFOREMENTIONED LOW ALONG THE ALASKA COAST
LEADING TO ISOLATED SHOWERS OVERNIGHT INTO EARLY SATURDAY ALONG
THE BLUE MOUNTAINS AND THEIR ADJOINING FOOTHILLS AS IT
APPROACHES THE PACIFIC NORTHWEST. POPS ARE QUITE LOW (5-15%)
DURING THIS PERIOD.
ENSEMBLE NWP IS IN EXCELLENT AGREEMENT (99% CONFIDENCE) THAT THE
LOW WILL TRACK INLAND OVER THE PACIFIC NORTHWEST ON SATURDAY,
THEN EXIT TO THE EAST THROUGH SUNDAY. WIDESPREAD BREEZY WESTERLY
WINDS ARE FORECAST ON SATURDAY, STRONGEST THOUGH THE CASCADE
GAPS. NBM PROBABILITIES SUGGEST MEDIUM (30-70%) CHANCES OF
REACHING ADVISORY-LEVEL WIND GUSTS THROUGH OUR MOST WIND-PRONE
AREAS SUCH AS THE KITTITAS VALLEY AND THE EASTERN COLUMBIA RIVER
GORGE AND VICINITY. DESPITE THE BREEZY WINDS, CHANCES OF
WIDESPREAD RED FLAG CONDITIONS ARE LOW (<40%) DUE TO BELOW-
NORMAL TEMPERATURES.
RAIN SHOWERS ARE LIKELY (55-75% POPS) ALONG THE WASHINGTON
CASCADE CREST LATER TONIGHT INTO SATURDAY AS THE LOW SWINGS
INLAND. CHANCES OF PRECIPITATION ARE LOWER (10-40%) OVER THE
BLUE MOUNTAINS SATURDAY AFTERNOON, BUT STILL NOTEWORTHY. CHANCES
OF THUNDERSTORMS ARE LOW (5-15%) FOR THE CASCADES AND BLUE
MOUNTAINS ON SATURDAY.
LOOKING AHEAD, THERE ARE LOW-MEDIUM CHANCES (20-50%) OF NEAR-
FREEZING MORNING TEMPERATURES (LOWER TO MIDDLE 30S) IN COLD-
PRONE VALLEYS OF CENTRAL AND NORTHEAST OREGON SUNDAY AND MONDAY
IN THE WAKE OF THE COLD UPPER LOW. NBM PROBABILITIES ARE LIKELY
TOO AGGRESSIVE SUNDAY MORNING DUE TO SOME LINGERING BREEZINESS,
THOUGH FORECAST PWATS AND TEMPERATURES ALOFT ARE SUPPORTIVE OF
CHILLY CONDITIONS. THINKING THE COLDEST TEMPERATURES IN VALLEYS
WILL FALL ON MONDAY MORNING WITH LIGHT WINDS AREAWIDE UNDER A
SHORTWAVE RIDGE, SOMETHING NBM PROBABILITIES DO NOT HIGHLIGHT
WELL.
ANALYSIS OF ENSEMBLE CLUSTERS SUGGESTS A CONTINUED TROUGHING
PATTERN FOR THE PACIFIC NORTHWEST BY THE MIDDLE OF NEXT WEEK
WITH ALL FOUR CLUSTERS EXHIBITING SOME FLAVOR OF TROUGH/UPPER
CLOSED LOW AND NEAR-NORMAL OR BELOW-NORMAL 500-HPA HEIGHTS.
WILL THE REGION SEE ITS FIRST WIDESPREAD WETTING RAIN WITH THE
FALL-LIKE PATTERN? NBM PROBABILITIES ARE QUITE OPTIMISTIC FOR
THE 48-HR PERIOD ENDING 5AM FRIDAY. IN GENERAL, IT SHOWS 40-70%
CHANCES OF 0.10" OF PRECIPITATION FOR NON-MOUNTAIN AREAS WITH
50-90% CHANCES ACROSS THE MOUNTAINS (HIGHEST CHANCES FOR THE
WASHINGTON CASCADES).
AVIATION /12Z TAFS THROUGH 12Z SATURDAY/
VFR CONDITIONS ARE FORECAST AT ALL SITES THROUGH THE PERIOD.
SMOKE ACROSS CENTRAL OREGON TERMINALS PRESENTS THE BEST CHANCE
OF SUB-VFR VSBYS/CIGS THIS MORNING, BUT CONFIDENCE WAS TOO LOW
(<50%) TO HAVE A MENTION IN THE 12Z TAFS.
WINDS WILL BE DIURNALLY BREEZY, STRONGEST THROUGH THE SITES
DOWNWIND OF OR WITHIN THE CASCADE GAPS (DLS, RDM, BDN) WITH SOME
BREEZES EXPECTED TO ARRIVE AT PDT LATER THIS EVENING.
MOSTLY CLEAR SKIES ARE FORECAST OUTSIDE OF FEW-SCT CUMULUS AND
BANDS OF CIRRUS THAT ARE CURRENTLY DRAPED ACROSS FAR EASTERN
OREGON AND NORTHWEST OREGON TO CENTRAL WASHINGTON.
PRELIMINARY POINT TEMPS/POPS
PDT 82 47 73 45 / 0 0 0 0
ALW 84 54 75 50 / 0 10 0 0
PSC 85 51 78 45 / 0 0 0 0
YKM 85 53 76 48 / 0 0 0 0
HRI 85 52 76 47 / 0 0 0 0
ELN 77 47 69 43 / 0 0 0 0
RDM 82 39 72 34 / 0 0 0 0
LGD 86 47 75 40 / 0 0 0 0
GCD 89 49 77 41 / 0 0 0 0
DLS 82 56 74 51 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...AIR QUALITY ALERT UNTIL NOON PDT TODAY FOR WAZ026-522-523.
OR...AIR QUALITY ALERT UNTIL NOON PDT TODAY FOR ORZ041-505-506-
509>511.
DISCUSSION...86
AVIATION...86
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