015
FXUS66 KPDT 051018
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
318 AM PDT SUN APR 5 2026
KEY MESSAGES
- ABOVE-NORMAL TEMPERATURES THROUGH MONDAY.
- LOW (5-15 PERCENT) CHANCE OF THUNDERSTORMS MONDAY.
- WIDESPREAD BREEZY TO WINDY CONDITIONS MONDAY NIGHT THROUGH
TUESDAY.
DISCUSSION
AN UPPER-LEVEL RIDGE IS IN PLACE OVER THE PACIFIC NORTHWEST
EARLY THIS MORNING, THOUGH BROKEN HIGH CLOUD IS EVIDENT ON
SATELLITE IMAGERY AS A WEAK SHORTWAVE APPROACHES FROM THE
SOUTHWEST. ENSEMBLE NWP GUIDANCE IS IN EXCELLENT AGREEMENT THAT
THE RIDGE AXIS WILL CONTINUE TO SHIFT OVERHEAD TODAY, RESULTING
IN VERY HIGH CONFIDENCE (95 PERCENT) THAT TEMPERATURES WILL
REMAIN ABOVE NORMAL. FROM A DETERMINISTIC STANDPOINT, WIDESPREAD
AFTERNOON HIGH TEMPERATURES IN THE 70S, AND ISOLATED LOWER 80S,
ARE ADVERTISED BY THE NBM TODAY AND MONDAY. GLANCING AT
PROBABILISTIC OUTPUT, THERE IS A HIGH (70-95 PERCENT) CHANCE THE
EASTERN COLUMBIA RIVER GORGE, YAKIMA VALLEY, LOWER COLUMBIA
BASIN, AND LOWER ELEVATIONS OF NORTH-CENTRAL AND CENTRAL OREGON
WILL REACH 80 DEGREES MONDAY.
DRY CONDITIONS ARE EXPECTED (95 PERCENT CONFIDENCE) UNDER THE
RIDGE TODAY, BUT GUIDANCE IS SHOWING LOW (10-20 PERCENT)
CHANCES OF SHOWERS AND VERY LOW (5-15 PERCENT) CHANCES OF
THUNDERSTORMS MONDAY AS A WEAK SHORTWAVE WRIGGLES INTO THE
PACIFIC NORTHWEST FROM THE PACIFIC AND A CLOSED LOW AND
ATTENDANT COLD FRONT SLIDE SOUTHEAST INTO BRITISH COLUMBIA AND
NORTHWEST WASHINGTON. CAMS ARE SHOWING A WEAKLY UNSTABLE
ATMOSPHERE (MUCAPE/SBCAPE 250-500 J/KG) OVER THE MOUNTAINS,
PRIMARILY THE BLUES, BUT ALSO PORTIONS OF THE CASCADES OF BOTH
OREGON AND WASHINGTON. THUNDERSTORMS, IF ANY, WILL BE OF THE AIR
MASS VARIETY DUE TO WEAK SHEAR (15-25 KTS EFFECTIVE) AND SLOW
STORM MOTION OF 5-10 KTS TO THE EAST OR EAST-SOUTHEAST IS
ANTICIPATED. GUSTY OUTFLOW APPEARS TO BE THE PRIMARY HAZARD WITH
THIS CONVECTION, AND CAMS ARE OUTPUTTING UP TO 35 KTS WITH THE
MOST ROBUST CELLS. FORECAST SOUNDINGS SUGGEST DCAPE OF 500-800
J/KG WHICH WOULD SUPPORT THESE SUB-SEVERE OUTFLOW WINDS.
BY TUESDAY, ENSEMBLE GUIDANCE GENERALLY DEPICTS A CLOSED LOW IN
THE PACIFIC APPROACHING THE OR/CA COAST WHILE THE
AFOREMENTIONED CLOSED LOW TREKS ACROSS THE NORTHERN TIER. THE
TREND IN GUIDANCE HAS BEEN FARTHER NORTH AND EAST WITH THE
LOW FROM CANADA, RESULTING IN FORECAST TEMPERATURES THAT ARE
NEAR TO ABOVE NORMAL TUESDAY AND WEDNESDAY.
WINDS MONDAY NIGHT AND TUESDAY ARE STILL THE BEST CHANCE OF A
HEADLINE-WORTHY EVENT FOR THE NEXT WEEK. THE NBM SUGGESTS A LOW-
MEDIUM (30-60 PERCENT) CHANCE OF REACHING OR EXCEEDING
ADVISORY-LEVEL WIND GUSTS (45 MPH OR GREATER) 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 AS ENSEMBLE GUIDANCE STRUGGLES TO RESOLVE THE TRACK
OF THE OFFSHORE CUT-OFF LOW IN THE PACIFIC. LATEST 00Z RUNS
HAVE TRENDED LESS PROGRESSIVE AND ENSEMBLE MEANS 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.
DELVING INTO SOME ANALYSIS OF UNCERTAINTY IN THE 500-HPA
PATTERN, ENSEMBLE CLUSTER ANALYSIS SHOWS ROUGHLY 30-40 PERCENT
OF MEMBERS KEEP THE CLOSED LOW IN A POSITION THAT IS FAVORABLE
FOR SHOWER AND THUNDERSTORM DEVELOPMENT FOR A SMALL PORTION OF
OUR CWA ACROSS CENTRAL AND EASTERN OREGON WEDNESDAY THROUGH
FRIDAY, BUT THE BULK OF THE ACTIVITY WOULD REMAIN IN SOUTH-
CENTRAL OREGON AND NORTHERN CALIFORNIA. THE REMAINDER OF THE
ENSEMBLE MEMBERS ARE STILL ADVERTISING A MORE PROGRESSIVE
PATTERN WITH THE LOW DIVING SOUTHEAST INTO CALIFORNIA SOONER
AND/OR PLACE THE LOW FARTHER SOUTH. 86
AVIATION /12Z TAFS THROUGH 12Z MONDAY/
VFR CONDITIONS ARE FORECAST FOR ALL SITES INTO MONDAY, WITH
BROKEN HIGH CLOUD COVER. WINDS WILL BE DIURNALLY AND TERRAIN-
DRIVEN WITH SUSTAINED WINDS OF 12 KTS OR LESS FORECAST FOR ALL
SITES. THAT SAID, CONFIDENCE IS HIGH (70 PERCENT) THAT
PDT/RDM/BDN WILL OBSERVE PERIODIC AFTERNOON GUSTS IN THE 15-20
KT RANGE, SIMILAR TO YESTERDAY. 86
PRELIMINARY POINT TEMPS/POPS
PDT 72 45 76 48 / 0 0 0 0
ALW 72 49 74 50 / 0 0 0 0
PSC 74 46 80 48 / 0 0 0 0
YKM 72 46 78 42 / 0 0 0 0
HRI 73 45 79 49 / 0 0 0 0
ELN 68 44 73 40 / 0 0 0 0
RDM 74 39 75 38 / 0 0 0 0
LGD 69 42 74 43 / 0 0 10 10
GCD 71 42 73 41 / 0 0 10 10
DLS 74 49 78 47 / 0 0 0 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...NONE.
DISCUSSION...86
AVIATION...86
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