546
FXUS66 KPDT 190512
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1012 PM PDT TUE AUG 18 2026
KEY MESSAGES
- BREEZY WINDS AND LOW RELATIVE HUMIDITY PRODUCING ELEVATED TO
CRITICAL FIRE WEATHER CONDITIONS THROUGH THIS EVENING
- DRYING AND WARMING TREND INTO FRIDAY AS UPPER LEVEL HIGH
PRESSURE BUILDS OVER THE REGION, WITH ELEVATED FIRE WEATHER
CONCERNS DUE TO DRY AND UNSTABLE CONDITIONS
- BREEZY WINDS DEVELOPING SATURDAY, WITH UNCERTAINTY IN
TIMING/EXTENT OF THUNDERSTORMS/SHOWERS FRIDAY THROUGH SUNDAY
MORNING
DISCUSSION
VISIBLE SATELLITE IMAGERY SHOWS MOSTLY CLEAR
SKIES ACROSS THE FORECAST AREA THIS AFTERNOON, THOUGH SEVERAL
SMOKE PLUMES ARE VISIBLE ACROSS THE CASCADE EAST SLOPES AND
IN THE NORTHERN BLUE MOUNTAINS. MEANWHILE, WATER VAPOR IMAGERY
SHOWS AN UPPER LOW OFFSHORE WESTERN CONUS WHILE A SHORTWAVE
TROUGH SLIDES INTO WESTERN MT.
THE SHORTWAVE TROUGH PASSAGE THROUGH THE REGION HAS RESULTED IN
A STRENGTHENING OF THE CROSS CASCADE PRESSURE GRADIENT TODAY.
BREEZY GAP WINDS EXTENDING INTO THE COLUMBIA BASIN WILL PERSIST
THROUGH THE EVENING, THEN DECREASE WITH THE WEAKENING OF THE
SURFACE PRESSURE GRADIENTS OVERNIGHT. THOUGH SEVERAL DAYS OF
THUNDERSTORMS MOVED THROUGH THE AREA, DRY CONDITIONS HAVE
SETTLED BACK INTO THE REGION, AND COMBINED WITH THE BREEZY
WINDS, WILL BRING ELEVATED TO CRITICAL FIRE WEATHER CONDITIONS
THROUGH THE EVENING.
TOMORROW THROUGH THURSDAY, UPPER LEVEL RIDGING WILL BUILD INTO
THE PACNW RESULTING IN A WARMING AND DRYING TREND WITH LIGHT
WINDS. DAYTIME TEMPERATURES WILL RISE INTO THE LOWER TO UPPER
90S IN THE LOWER ELEVATIONS BY THURSDAY, WITH THURSDAY NIGHT
LOWS ONLY COOLING INTO THE LOWER TO MID 60S ACROSS MUCH OF THE
AREA (COOLER IN CENTRAL OR AND MOUNTAIN VALLEYS/BASINS). RISING
LAPSE RATES (AND MIXING HEIGHTS) UNDER THE UPPER RIDGE WILL
BRING ELEVATED FIRE WEATHER CONCERNS ACROSS THE HIGH TERRAIN, AS
THE COMBINATION OF DRY AND UNSTABLE CONDITIONS MAY LEAD TO
INCREASED FIRE BEHAVIOR THROUGH THURSDAY.
FRIDAY THROUGH SUNDAY, ECMWF AND GFS ENSEMBLE MEMBERS ARE IN
GOOD AGREEMENT THAT THE UPPER LOW OFFSHORE WESTERN CONUS WILL
BECOME AN OPEN WAVE AS IT LIFTS INTO THE PACNW, BRINGING WITH IT
ROUNDS OF ISOLATED TO WIDELY SCATTERED THUNDERSTORMS, BREEZY TO
LOCALLY GUSTY WINDS, AND COOLER TEMPERATURES. HOWEVER, AGREEMENT
ON TIMING, INTENSITY, AND LOCATION ARE POOR. GFS ENSEMBLE MEAN
SHOWS IT'S MEMBERS (AND THE DETERMINISTIC) FAVORING THE UPPER
TROUGH COMING INLAND LATE FRIDAY EVENING AND OVERNIGHT,
TRIGGERING NOCTURNAL ISOLATED THUNDERSTORMS ACROSS THE FORECAST
AREA DURING THAT TIME PERIOD. MEANWHILE, ECMWF MEMBERS (AND IT'S
DETERMINISTIC/CONTROL) FAVOR A LATER PASSAGE BY ABOUT 6 TO 12
HOURS, WITH ISOLATED THUNDERSTORMS DEVELOPING VERY EARLY
SATURDAY MORNING ACROSS THE CASCADE EAST SLOPES, THEN LATE
EVENING THUNDERSTORMS DEVELOPING OVER THE BLUES AND WALLOWA
COUNTY. BOTH SOLUTIONS DO FAVOR BREEZY WINDS DEVELOPING THROUGH
THE CASCADE GAPS SATURDAY, WITH ECMWF MEMBERS FAVORING STRONGER
WINDS THEN THOSE OF THE GFS MEMBERS. FORECAST CONFIDENCE IS AT
LEAST MODERATE (45-60%) IN THE UPPER TROUGH PASSAGE OCCURRING
THROUGH THE WEEKEND, HOWEVER THERE IS LOW CONFIDENCE (20-25%)
IN FORECAST DETAILS.
BY NEXT MONDAY, THERE IS MODERATE CONFIDENCE (55-60%) IN UPPER
LEVEL RIDGING BUILDING BACK OVER THE REGION WITH DRY AND WARM
CONDITIONS WITH LIGHT WINDS. LAWHORN/82
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
VFR CONDITIONS PERSIST THROUGH THE PERIOD WITH THE EXCEPTION OF
RDM WHICH IS SEEING MVFR CONDITIONS AND A VIS OF 5SM DUE TO LOW
LEVEL SMOKE. THE SMOKE AT BDN IS EXPECTED TO PERSIST THROUGH
09Z.
BREEZY WINDS ARE EXPECTED DLS THROUGH 00Z. WINDS WILL BE
GENERALLY LIGHT ELSEWHERE AT LESS THAN 12 KNOTS SUSTAINED WITH
ELEVATED SMOKE IN THE REGION.
FIRE WEATHER
BREEZY WINDS THROUGH THE CASCADE GAPS WILL OVERLAP
WITH LOW RH IN THE OR COLUMBIA BASIN, EASTERN GORGE, AND AROUND
WARM SPRINGS THROUGH THIS EVENING. HOT, DRY, AND UNSTABLE
CONDITIONS WILL DEVELOP WEDNESDAY THROUGH THURSDAY AS HIGH
PRESSURE BUILDS OVERHEAD. FRIDAY INTO THE WEEKEND, THERE IS
INCREASING POTENTIAL FOR A RETURN OF ISOLATED THUNDERSTORMS ACROSS
THE AREA, WITH BREEZY TO LOCALLY WINDY CONDITIONS THROUGH THE
CASCADE GAPS AND COLUMBIA BASIN. LAWHORN/82
PRELIMINARY POINT TEMPS/POPS
PDT 54 91 57 93 / 0 0 0 0
ALW 62 92 64 95 / 0 0 0 0
PSC 57 93 58 96 / 0 0 0 0
YKM 59 93 62 97 / 0 0 0 0
HRI 59 93 60 95 / 0 0 0 0
ELN 59 89 59 93 / 0 0 0 0
RDM 47 93 51 95 / 0 0 0 0
LGD 53 94 57 97 / 0 0 0 0
GCD 55 96 57 98 / 0 0 0 0
DLS 60 92 62 97 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...AIR QUALITY ALERT UNTIL 1 PM PDT WEDNESDAY FOR ORZ041-505-506-
509>511.
DISCUSSION...82
AVIATION...90
FIRE WEATHER...82
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