135
FXUS66 KPDT 190032
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
530 PM PDT FRI SEP 18 2020
SHORT TERM
SATELLITE INDICATES UPPER LEVEL LOW JUST BEGINNING TO
PUSH INTO CASCADES. SHOWERS AND A FEW STORMS ARE EVIDENT IN RADAR
AND SATELLITE, PRIMARILY ALONG CASCADE CREST AND WESTWARD AT THIS
TIME, THOUGH THE ACTIVITY IS BEGINNING TO ENCROACH INTO US-97
CORRIDOR. THIS EVENING THROUGH TONIGHT, ISOLATED STORMS ARE
EXPECTED TO CONTINUE. THIS ACTIVITY WILL FOCUS ON WHERE
INSTABILITY IS MARGINAL TO DECENT AND LIFT FROM UPPER LOW IS
EXPECTED TO TRACK, MOSTLY IN OREGON AND POSSIBLY INTO SOUTHERN
CASCADES OF WASHINGTON. PRIMARY RISKS WILL BE SOME GUSTY OUTFLOW
WINDS, LOCALLY INTENSE LIGHTNING, AND POSSIBLE FLOODING SHOULD A
CELL FAVORABLY TRACK OVER A BURN SCAR AREA. OUTSIDE OF CONCERNS
FOR BURN SCAR FLOODING, PRECIPITATION TOTALS LOOK BENEFICIAL,
RANGING FROM NEARLY A QUARTER INCH OR MORE ALONG CASCADE CREST AND
EVENTUALLY PORTIONS OF WALLOWA MTNS TO A TENTH INCH OR SO FOR
LARGE PORTION OF BLUE/OCHOCO MTNS AND UPPER FOOTHILLS OF BLUE
MTNS TO POSSIBLY ONLY A TRACE FOR DRIER PORTIONS OF MID-COLUMBIA
REGION. WINDS MAY BECOME A TOUCH BREEZY THROUGH GORGE AND EAST
SLOPES OF WASHINGTON CASCADES AS THE SURFACE BOUNDARY WORKS ACROSS
THE REGION LATE THIS EVENING. OVERNIGHT, STORM CHANCES LINGER FOR
SOUTHERN BLUE MTNS AND WALLOWA. TOMORROW MORNING, SHOWERS TAPER
OFF FOR BLUE MTNS AND EVENTUALLY FAR EAST OREGON AS SYSTEM MOVES
OUT. UPPER LEVEL NW FLOW TOMORROW SHIFTS MORE WESTERLY ON SUNDAY
WITH COOLER TEMPERATURES AND DRYING CONDITIONS. CONFIDENCE IS HIGH
WE WILL SEE BLUE SKIES BY SUNDAY, THOUGH NARROW PLUMES OF SMOKE
MAY STILL TRACK OVER LOCAL AREAS.
LONG TERM...MONDAY THROUGH FRIDAY
MONDAY WILL START OFF UNDER
AN ACTIVE UPPER LEVEL PATTERN, WITH THE FLOW REGIME GENERALLY WEST
TO WEST SOUTHWEST THROUGH THE EXTENDED PERIOD. MODELS IN FAIRLY
GOOD AGREEMENT THAT A SHORTWAVE WILL PASS OVER THE FORECAST AREA
MONDAY WITH LOCALLY BREEZY CONDITIONS IN THE COLUMBIA GORGE AND
SOME DEVELOPMENT OF MID TO HIGH LEVEL CLOUD COVER OVER THE
FORECAST AREA. BEHIND THE SHORTWAVE EXIT TUESDAY, A WEAK REX BLOCK
PATTERN WILL PASS OVER THE FORECAST AREA WITH DRY CONDITIONS AND
SEASONABLY COOL TEMPERATURES. EARLY WEDNESDAY, THE NEXT SYSTEM
ARRIVES IN THE FORM OF SLOW MOVING FRONTAL BOUNDARY SWINGING
AROUND AN UPPER LEVEL LOW OVER THE GULF OF ALASKA. FRONTAL
BOUNDARY WILL STALL AS IT INTERACTS WITH THE CASCADES WEDNESDAY,
AND FINALLY CROSS THE FORECAST AREA OVERNIGHT WEDNESDAY INTO
THURSDAY WITH CHANCE TO SLIGHT CHANCE RAIN SHOWERS ACROSS THE
FORECAST AREA, AND LOCALLY BREEZY CONDITIONS DEVELOPING IN THE
AFTERNOON AND EVENING AHEAD OF AND BEHIND THE FRONTAL BOUNDARY.
BEHIND THE FRONTAL BOUNDARY, A SHORTWAVE TROUGH WILL ROUND THE
LARGER UPPER LOW THURSDAY AND CROSS THE FORECAST AREA OVERNIGHT
THURSDAY INTO FRIDAY. MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE
SCALE AND TIMING OF THIS LATE WORK WEEK SYSTEM, AND INDICATE A
CONTINUATION OF NOCTURNAL RAIN SHOWERS THURSDAY NIGHT/FRIDAY
MORNING, WITH LOCALLY BREEZY WINDS IN THE AFTERNOON FRIDAY.
LAWHORN/82
AVIATION...00Z TAFS. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
WILL MOVE ACROSS THE REGION THIS EVENING DECREASING OVERNIGHT.
WESTERLY WINDS WILL BE INCREASING AND WILL CLEAR MUCH OF THE SMOKE
FROM THE TAF SITES.
PRELIMINARY POINT TEMPS/POPS
PDT 51 74 48 75 / 30 10 0 0
ALW 54 75 51 76 / 40 10 10 0
PSC 57 78 53 78 / 20 0 0 0
YKM 53 75 48 76 / 20 0 0 0
HRI 55 78 50 78 / 20 0 0 0
ELN 51 71 48 74 / 30 10 10 0
RDM 43 70 39 76 / 40 10 0 0
LGD 48 69 44 74 / 60 30 10 0
GCD 47 70 43 78 / 60 20 0 0
DLS 57 75 54 79 / 20 10 0 0
PDT WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
SHORT TERM...76
LONG TERM....82
AVIATION...94
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