356
FXUS66 KPDT 021115
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
415 AM PDT WED SEP 2 2026
KEY MESSAGES
- WIDESPREAD SHOWER CHANCES TODAY THROUGH EARLY THURSDAY, WITH
PERIODS OF MOUNTAIN RAIN SHOWERS
- ISOLATED THUNDERSTORM CHANCES (15-25%) WILL DEVELOP OVER
NORTHEAST OR TODAY, THEN ACROSS CASCADES AND BLUES THURSDAY
AND FRIDAY
- BELOW NORMAL TEMPERATURES THROUGH EARLY NEXT WEEK, WITH
FREEZING TEMPERATURES IN MOUNTAIN VALLEYS THURSDAY AND FRIDAY
NIGHTS
DISCUSSION
WATER VAPOR SATELLITE IMAGERY TONIGHT SHOWS AN
UPPER SHORTWAVE TROUGH ACROSS THE PACNW AND NORTHERN CA, WITH
THE TROUGH BEGINNING TO PIVOT NORTHEAST. PER AREA RADAR,
ISOLATED SHOWERS/THUNDERSTORMS HAVE BEEN DEVELOPING ALONG THE
BASE OF THE CASCADE EAST SLOPES, WITH THIS ACTIVITY MOSTLY IN
WA.
TODAY THROUGH THIS WEEKEND, THE PACNW WILL BE UNDER THE
INFLUENCE OF UPPER LEVEL LOW PRESSURE THAT WILL BRING A COUPLE
ROUNDS OF RAIN SHOWERS TO THE LOWER ELEVATIONS, WITH MORE
PERSISTENT CHANCES ACROSS THE MOUNTAINS (CONFIDENCE 70-90%).
TEMPERATURES ACROSS THE REGION WILL BE NEARLY 10-15 DEGREES
BELOW AVERAGE EACH DAY, WITH AFTERNOON HIGH TEMPERATURES AT
THEIR LOWEST IN THE MID 60S AND LOW 70S THURSDAY AND FRIDAY
(CONFIDENCE 70-85%). STARTING WITH TODAY, A NEGATIVELY TILTED
UPPER SHORTWAVE TROUGH WILL LIFT NORTHEAST ACROSS THE REGION
FOLLOWED BY THE ARRIVAL OF AN UPPER CLOSED LOW OFFSHORE THE
PACNW. THESE SYSTEMS WILL PRODUCE THE BEST CHANCES OF
PRECIPITATION EAST OF THE CASCADES, WITH THE MAIN RAIN CHANCES
SPREADING NORTHEAST ACROSS THE FORECAST THIS AFTERNOON THROUGH
THE EVENING. PRIOR TO THAT, THE SHORTWAVE PASSAGE WILL RESULT IN
ISOLATED THUNDERSTORM CHANCES ACROSS THE NORTHERN BLUES AND
WALLOWA COUNTY THIS AFTERNOON. THROUGH TONIGHT, THERE IS A
50-90% CHANCE OF 0.1 INCHES OF PRECIP IN THE LOWER ELEVATIONS,
WITH THE HIGHEST CHANCES ALONG THE BLUE MOUNTAINS FOOTHILLS AND
CENTRAL OR. AS FOR THE MOUNTAIN ZONES, THERE IS GENERALLY A
50-80% CHANCE OF 0.5 INCHES OF RAIN FALLING IN THE NEXT 24
HOURS, WITH THOSE CHANCES NEAR 100% ALONG THE OR CASCADE CREST.
THURSDAY THROUGH THE WEEKEND, THERE IS GOOD CONSENSUS AMONGST
ENSEMBLE MEMBERS THAT THE UPPER CLOSED LOW WILL PARK ITSELF
OVER THE PACNW, WITH THE CENTER OF THE LOW REMAINING WEST OF THE
CASCADE CREST THROUGH THIS PERIOD (CONFIDENCE 60-85%). DURING
THIS TIME, PERSISTENT RAIN SHOWER CHANCES (30-60%) WILL REMAIN
OVER THE CASCADES AND EASTERN MOUNTAINS EACH DAY, WITH SHORTWAVE
IMPULSES FRIDAY AND THE LOW PASSAGE SUNDAY/MONDAY PRODUCING
LIGHT RAIN CHANCES (15-40%) IN THE LOWER ELEVATIONS. ISOLATED
THUNDERSTORMS WILL BE POSSIBLE OVER THE MOUNTAINS THURSDAY AND
FRIDAY AS WEAK INSTABILITY DEVELOPS IN THESE AREAS WITH
ADDITIONAL SUPPORT FROM THE COLD CORE OF THE LOW ALOFT. AS FOR
PRECIPITATION AMOUNTS, THE CASCADES AND BLUES WILL SEE 0.1 TO
0.25 INCHES OF DAILY PRECIP (CONFIDENCE 65-90%), WITH LOCALLY
HIGHER AMOUNTS WHERE THUNDERSTORMS DEVELOP.
SUNDAY INTO MONDAY, ENSEMBLE AND DETERMINISTIC MEMBERS SHOW THE
UPPER CLOSED LOW BEGINNING TO PUSH EAST, WITH THE LOW OVER THE
FORECAST AREA DURING THE DAY SUNDAY. WHILE LIGHT TO MODERATE
RAIN SHOWERS ARE FORECAST ACROSS THE AREA, THE UPPER LOW BEING
OVERHEAD WILL ALSO RESULT IN SLIGHT CHANCES (15-25%) OF ISOLATED
THUNDERSTORMS AREA-WIDE.
MONDAY AND TUESDAY, ENSEMBLE MEMBERS ARE IN AGREEMENT THAT THE
PACNW WILL REMAIN UNDER UPPER LEVEL TROUGHING, HOWEVER DISAGREE
ON THE PLACEMENT OF THE UPPER TROUGH AXIS. MEMBERS THAT FAVOR
THE TROUGH AXIS TO THE EAST OF THE REGION KEEP THE FORECAST AREA
MAINLY DRY, WHILE MEMBERS DEPICTING A TROUGH AXIS OVERHEAD OR
WEST OF THE CASCADE CREST RESULTS IN LIGHT PRECIPITATION OVER
THE AREA. AT THIS TIME, CONFIDENCE IS LOW (20-30%) IN FORECAST
DETAILS EARLY NEXT WEEK. LAWHORN/82
AVIATION /12Z TAFS THROUGH 12Z THURSDAY/
VFR CONDITIONS TO
PREVAIL THROUGH THE PERIOD. ISOLATED SHOWERS/THUNDERSTORMS HAVE
ALREADY DEVELOPED IN THE AREA AHEAD OF AN APPROACHING UPPER
WEATHER SYSTEM, WITH PROB30 CHANCE THAT SHOWERS WILL IMPACTS
SITES PDT/ALW/PSC THROUGH THIS MORNING, WITH PERIODIC SHOWERS AT
SITE YKM. LATER THIS AFTERNOON AND EVENING, WIDESPREAD RAIN
IMPACTS WILL DEVELOP AT ALL SITES, WITH RAIN ENDING AROUND 2Z-3Z
AT SITES YKM/RDM/BDN/DLS, AROUND 6Z FOR SITE PSC, AND LATE
OVERNIGHT FOR SITES PDT/ALW. CONFIDENCE IN MVFR OR LOWER
CIGS/VSBY DEVELOPING WITH PRECIP IS LOW (25-30%). BREEZY WINDS
(12-17KTS WITH GUSTS TO AROUND 25KTS) WILL DEVELOP AT MOST SITES
THIS AFTERNOON AND EARLY EVENING, BUT WILL OTHERWISE BE LIGHT
IN THE MORNING AND OVERNIGHT. LIGHT WINDS WILL PREVAIL AT SITE
DLS THROUGH THE PERIOD. LAWHORN/82
PRELIMINARY POINT TEMPS/POPS
PDT 74 45 68 43 / 50 90 30 30
ALW 76 50 69 49 / 60 90 40 40
PSC 77 47 73 44 / 30 70 10 10
YKM 74 48 69 46 / 30 60 20 10
HRI 76 47 71 44 / 40 80 10 20
ELN 69 43 65 41 / 40 60 30 20
RDM 63 36 63 32 / 90 80 20 50
LGD 72 46 65 43 / 80 100 70 70
GCD 72 45 64 42 / 60 100 70 70
DLS 71 49 67 48 / 90 80 40 40
PDT WATCHES/WARNINGS/ADVISORIES
WA...AIR QUALITY ALERT UNTIL 10 AM PDT THIS MORNING FOR WAZ026-522-
523.
OR...AIR QUALITY ALERT UNTIL NOON PDT TODAY FOR ORZ041-505-506-
509>511.
DISCUSSION...82
AVIATION...82
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