991
FXUS66 KPDT 061102
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
402 AM PDT MON APR 6 2026
KEY MESSAGES
- ABOVE-NORMAL TEMPERATURES TODAY.
- LOW (5-15 PERCENT) CHANCE OF THUNDERSTORMS TODAY, MAINLY OVER
THE BLUE MOUNTAINS.
- WIDESPREAD BREEZY TO WINDY CONDITIONS MONDAY NIGHT THROUGH
TUESDAY.
DISCUSSION
THE UPPER-LEVEL RIDGE THAT IS PARKED OVER THE PACIFIC NORTHWEST
EARLY THIS MORNING WILL FLATTEN THROUGH THE DAY. A WEAK
SHORTWAVE IS WRIGGLING THROUGH THE RIDGE, AND IT WILL BE
FOLLOWED BY MORE SIGNIFICANT HEIGHT FALLS LATER THIS MORNING AND
AFTERNOON AS A STRONGER WAVE EVIDENT IN WATER VAPOR IMAGERY
TREKS SOUTHEAST ALONG THE BRITISH COLUMBIA COAST BEFORE DIVING
INLAND ACROSS THE NORTHERN TIER. MEANWHILE, A DEEP CLOSED LOW IS
CUTTING OFF FROM THE JET STREAM WELL OFFSHORE IN THE PACIFIC
AROUND 34.5N, 143.0W; I'LL TALK MORE ABOUT THE IMPLICATIONS OF
THE CUT-OFF LOW LATER IN THE DISCUSSION.
CONFIDENCE IS VERY HIGH (90 PERCENT) THAT AFTERNOON HIGH
TEMPERATURES WILL BE WELL ABOVE NORMAL TODAY. IF FORECAST HIGHS
IN THE MIDDLE TO UPPER 70S AND ISOLATED LOWER 80S VERIFY, THEY
WILL GENERALLY FALL IN THE TOP 5 OR 10 WARMEST APRIL 6THS DURING
THE PERIOD OF RECORD AT ALL OF OUR CLIMATE SITES.
GLANCING AT PROBABILISTIC OUTPUT, THERE IS A HIGH (65-90
PERCENT) CHANCE THE EASTERN COLUMBIA RIVER GORGE, YAKIMA VALLEY,
LOWER COLUMBIA BASIN OF WASHINGTON, AND LOWER ELEVATIONS OF
NORTH-CENTRAL OREGON WILL REACH 80 DEGREES. ELSEWHERE, CHANCES
OF REACHING 80 DEGREES ARE LOWER AT 50 PERCENT OR LESS, HIGHEST
FOR THE WALLA WALLA VALLEY AND LOWER COLUMBIA BASIN OF OREGON.
GUIDANCE CONTINUES TO SHOW LOW (5-20 PERCENT) CHANCES OF
SHOWERS AND VERY LOW (5-15 PERCENT) CHANCES OF THUNDERSTORMS
THIS AFTERNOON AND EVENING. LATEST 00Z CAMS ARE ADVERTISING A
MODESTLY UNSTABLE ATMOSPHERE WITH MUCAPE/SBCAPE OF 250-500
J/KG, LOCALLY HIGHER, OVER THE MOUNTAINS. BEST CHANCES OF
SHOWERS AND THUNDERSTORMS WILL BE OVER THE BLUES, BUT CANNOT
RULE OUT MORE ISOLATED ACTIVITY FOR THE CASCADES OF BOTH OREGON
AND WASHINGTON. THUNDERSTORMS, IF ANY, SHOULD BE OF THE AIR MASS
VARIETY DUE TO WEAK EFFECTIVE SHEAR OF 15-25 KTS. MY ANALYSIS
OF STORM MOTION WAS INCORRECT YESTERDAY, AND FOR THAT I
SINCERELY APOLOGIZE. BASED ON LATEST 00Z HREF AND REFS FORECAST
SOUNDINGS, STORM MOTION OF 15-20 KTS TO THE EAST OR EAST-
SOUTHEAST IS EXPECTED, RATHER THAN THE LETHARGIC 5-10 KTS THAT I
STATED IN YESTERDAY'S DISCUSSION. GUSTY OUTFLOW WINDS ARE STILL
EXPECTED TO BE THE PRIMARY HAZARD WITH CONVECTION. 00Z HREF AND
REFS SUGGEST UP TO 40 KT GUSTS WITH THE MOST ROBUST CELLS, AND
DCAPE OF 500-800 J/KG IN FORECAST SOUNDINGS SUPPORTS THESE SUB-
SEVERE OUTFLOW WINDS. IN ADDITION TO OUTFLOW WINDS, ANY
THUNDERSTORMS THAT DEVELOP WILL BE CAPABLE OF PRODUCING SMALL
HAIL.
WINDS TONIGHT (MONDAY NIGHT) AND TUESDAY ARE STILL THE BEST
CHANCE OF A HEADLINE-WORTHY EVENT FOR THE NEXT WEEK. THAT SAID,
THE MORNING PEAK IN THE 850-HPA JET IS NOT OPTIMAL FOR REALLY
STRONG WINDS DURING THE AFTERNOON. STILL EXPECTING (90 PERCENT
CONFIDENCE) WIDESPREAD BREEZY TO WINDY WESTERLY TO
NORTHWESTERLY WINDS, BUT CONFIDENCE IN REACHING ADVISORY-LEVEL
WIND GUSTS (45 MPH OR GREATER) IS TOO LOW TO ISSUE ANY WIND
HEADLINES. FROM A PROBABILISTIC STANDPOINT, THE NBM HAS NOT
EXHIBITED MUCH DAY-TO-DAY CHANGE, AND STILL GENERALLY PAINTS
LOW-MEDIUM (30-70 PERCENT) CHANCES OF REACHING ADVISORY
CRITERIA THROUGH THE CASCADE GAPS AND ACROSS WIND-PRONE PORTIONS
OF THE COLUMBIA BASIN AND SURROUNDING LOWLANDS.
LOOKING AHEAD, THERE IS SIGNIFICANT UNCERTAINTY IN THE
EVOLUTION OF THE 500-HPA PATTERN WEDNESDAY THROUGH THE REMAINDER
OF THE WEEK AND INTO THE WEEKEND AS ENSEMBLE GUIDANCE STRUGGLES
TO RESOLVE THE BOTH THE TRACK OF THE OFFSHORE CUT-OFF LOW IN
THE PACIFIC AS WELL AS AN ADDITIONAL TROUGH/LOW. 12Z RUNS KEEP
THE CLOSED LOW IN THE VICINITY OF THE OR/CA BORDER OR
NORTHERN/CENTRAL CALIFORNIA WEDNESDAY THROUGH FRIDAY. THE TREND
TOWARDS A SPLIT FLOW PATTERN HAS RESULTED IN AN UPWARD TREND IN
FORECAST TEMPERATURES AND WOULD KEEP ABOVE-NORMAL TEMPERATURES
IN PLACE FOR THE DURATION OF THE WEEK. A SLIGHT CHANCE TO CHANCE
(15-40 PERCENT) OF SHOWERS IS FORECAST THURSDAY AND FRIDAY
ALONG THE CASCADES OF CENTRAL OREGON AND ACROSS THE BLUE
MOUNTAINS, BUT THUNDERSTORM CHANCES ARE STILL LOW (LESS THAN 15
PERCENT). BY THE WEEKEND, ALL ENSEMBLE CLUSTERS SHOW SOME FLAVOR
OF A TROUGH OR CLOSED LOW RETURNING TO THE PACIFIC NORTHWEST,
THOUGH THERE IS A LARGE AMOUNT OF SPREAD IN SCENARIOS. THIS DOES
PLACE THE MAJORITY OF THE FORECAST AREA UNDER SLIGHT CHANCE TO
CHANCE (15-50 PERCENT) POPS, LOWEST FOR THE LOWER COLUMBIA
BASIN AND CENTRAL OREGON, HIGHEST FOR THE MOUNTAINS. 86
AVIATION /12Z TAFS THROUGH 12Z TUESDAY/
VFR CONDITIONS ARE FORECAST FOR ALL SITES THROUGH THE PERIOD.
THERE IS A VERY LOW (5-10 PERCENT) CHANCE OF ISOLATED SHOWERS
AND THUNDER AT RDM/BDN THIS AFTERNOON. ELSEWHERE, PRECIPITATION
CHANCES ARE LESS THAN 5 PERCENT. WINDS WILL INCREASE TO 10-15
KTS AT DLS/RDM/BDN THIS AFTERNOON AND EVENING, WITH 10 KTS OR
LESS FORECAST AT OTHER SITES. GUSTS OF 15-25 KTS ARE FORECAST AT
DLS/RDM/BDN WITH 15 KTS OR LESS FOR ALL OTHER SITES. 86
PRELIMINARY POINT TEMPS/POPS
PDT 75 47 64 34 / 0 0 0 0
ALW 75 50 63 37 / 0 0 0 0
PSC 80 48 67 35 / 0 0 0 0
YKM 77 41 65 34 / 0 0 0 0
HRI 79 49 67 35 / 0 0 0 0
ELN 72 38 55 32 / 0 10 0 0
RDM 75 36 67 30 / 0 0 0 0
LGD 74 43 62 32 / 10 0 0 0
GCD 74 41 65 32 / 20 20 0 0
DLS 77 47 63 37 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...NONE.
DISCUSSION...86
AVIATION...86
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