354
FXUS66 KPDT 281112
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
412 AM PDT THU MAY 28 2026
KEY MESSAGES
- SCATTERED THUNDERSTORMS CAPABLE OF STRONG/DAMAGING GUSTS AND
ISOLATED LARGE HAIL WILL IMPACT THE FORECAST AREA THIS
AFTERNOON AND EVENING
- HEAVY DOWNPOURS EMBEDDED WITHIN THUNDERSTORMS WILL BRING AN
EXCESSIVE RAINFALL THREAT TO THE CASCADE EAST SLOPES TODAY
- BREEZY TO LOCALLY GUSTY WINDS THROUGH THE CASCADE GAPS AND
LOWER COLUMBIA BASIN FRIDAY
DISCUSSION
TODAY THROUGH FRIDAY: SATELLITE IMAGERY TONIGHT
SHOWS A CLOSED LOW OVER THE CA/NV BORDER, WITH MID TO UPPER
LEVEL CLOUD COVER SWINGING ACROSS THE FORECAST AREA. OTHERWISE,
WINDS ARE LIGHT WITH DRY CONDITIONS ACROSS THE AREA.
TODAY WILL SEE INCREASED CONVECTIVE ACTIVITY ACROSS THE PACNW
AS THE NEEDED INGREDIENTS FOR CONVECTION WILL COMBINE WITH A
MID-LEVEL WAVE ROUNDING THE CA/NV CLOSED LOW INTO THE PACNW.
THE DEEP CLOSED LOW TO THE SOUTH WILL CONTINUE TO PLACE A SOUTH
TO SOUTHEAST FLOW INTO THE FORECAST AREA. THIS WILL LEAD TO
INCREASED SURFACE BASED INSTABILITY AREA-WIDE, WITH MEAN SURFACE
BASED CAPE VALUES FROM THE HREF AND REFS BETWEEN 800-1500 J/KG,
WITH LOCALLY HIGHER VALUES (~2000 J/KG) ACROSS THE MOUNTAINOUS
TERRAIN. LOW LEVEL LAPSE RATES ARE FORECAST BETWEEN 8-9.5 C/KM
WITH 0-6KM SHEAR BETWEEN 30-45 KTS THROUGH THIS AFTERNOON AND
EVENING. THIS COMBINED WITH THE MID-LEVEL WAVE WILL RESULT IN
SCATTERED THUNDERSTORM ACTIVITY ACROSS THE FORECAST AREA, WITH
THUNDERSTORMS DEVELOPING ACROSS CENTRAL OR AS EARLY AS 12PM, AND
ACROSS PORTIONS OF NORTHEAST OR AND SOUTHEAST WA BETWEEN
2PM-3PM. CAMS INDICATE THAT THE SHEAR AND MID-LEVEL WAVE WILL
CONTINUE TO SUPPORT THUNDERSTORM ACTIVITY INTO THE LATE EVENING
HOURS AS THE ACTIVITY ADVECTS NORTHWARD INTO SOUTH CENTRAL AND
SOUTHEASTERN WA. THE CONVECTIVE PARAMETERS IN PLACE THIS
AFTERNOON WOULD ALSO SUGGEST THE POTENTIAL FOR THUNDERSTORMS TO
PRODUCE DAMAGING WINDS AND LARGE HAIL. THE STORM PREDICTION
CENTER HAS ISSUED A SLIGHT RISK FOR STRONG THUNDERSTORMS ACROSS
MUCH OF THE FORECAST AREA.
THUNDERSTORMS THIS AFTERNOON WILL ALSO TAP INTO PWATS AROUND
0.9-1.3 INCHES, RESULTING IN THE POTENTIAL FOR HEAVY DOWNPOURS
TO ACCOMPANY ANY STORM. BOTH THE HREF AND REFS SHOW A 45-65%
CHANCE FOR RAIN RATES TO EXCEED 0.25" PER HOUR ALONG THE CASCADE
EAST SLOPES THIS AFTERNOON, WITH A 40-60% CHANCE OF 1" BETWEEN
5PM-11PM AS WELL. THIS WILL LEAD TO AN INCREASED RISK OF FLASH
FLOODING ALONG THE OR CASCADE EAST SLOPES. A MARGINAL EXCESSIVE
RAINFALL RISK HAS ALSO BEEN ISSUED ALONG THE CASCADE CREST AND
EAST SLOPES IN OR AND IN WA.
OTHERWISE, TEMPERATURES WILL WARM ACROSS THE LOWER ELEVATIONS INTO
THE 80S, EXCEPT UPPER 80S TO LOWER 90S IN THE LOWER COLUMBIA
BASIN THIS AFTERNOON.
FRIDAY THROUGH WEDNESDAY: FRIDAY, THE UPPER LOW TO THE SOUTH
WILL SWING ACROSS THE GREAT BASIN AND BECOME AN OPEN WAVE TROUGH
IN RESPONSE TO AN UPPER TROUGH SWINGING INTO BC. THE TROUGH AXIS
AND DIFLUENT FLOW ALOFT WILL RESULT IN SCATTERED SHOWERS ACROSS
THE CASCADES, CENTRAL OR, AND THE EASTERN MOUNTAINS THROUGHOUT
THE DAY, WITH ISOLATED THUNDERSTORMS POSSIBLE ACROSS THE EASTERN
MOUNTAINS. AN INCREASING PRESSURE GRADIENT ACROSS THE CASCADE
CREST WILL RESULT IN BREEZY TO LOCALLY GUSTY WINDS (SUSTAINED
WINDS 20-30 MPH WITH GUSTS 30-45 MPH) DEVELOPING THROUGH THE
CASCADE GAPS AND INTO PORTIONS OF THE COLUMBIA BASIN FRIDAY
AFTERNOON.
SATURDAY THROUGH SUNDAY, ENSEMBLE GUIDANCE IS IN GOOD AGREEMENT
THAT THE UPPER TROUGH WILL SLOWLY SWING NORTH IN THE NORTHERN
ROCKIES, WITH ISOLATED LIGHT SHOWER ACTIVITY LIMITED TO THE
HIGHER TERRAIN OF THE NORTHERN BLUES AND THE EAGLE CAPS DURING
THIS PERIOD. THE REMAINDER OF THE FORECAST AREA WILL STAY DRY
WITH BREEZY WINDS (SUSTAINED 15-25MPH WITH GUSTS 25-40MPH)
THROUGH THE CASCADE GAPS.
MONDAY INTO WEDNESDAY, WEAK HIGH PRESSURE ALOFT WILL BUILD INTO
THE REGION BEHIND THE TROUGH EXIT TO THE NORTH, RESULTING IN
WIDESPREAD DRY CONDITIONS AND LIGHT WINDS. TEMPERATURES WILL
ALSO BE ON A WARMING TREND, WITH WIDESPREAD 80S RETURNING BY
TUESDAY (CONFIDENCE 55-65%). LAWHORN/82
AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
VFR CONDITIONS TO
PREVAIL THROUGH THIS MORNING, WITH MVFR OR LOWER CONDITIONS
POSSIBLE THIS AFTERNOON AND EVENING. THUNDERSTORM ACTIVITY IS
EXPECTED TO DEVELOP THIS AFTERNOON AND EVENING ACROSS THE
REGION, WITH A 30-50% CHANCE OF THUNDERSTORMS IMPACTING SITES.
THUNDERSTORMS WILL BE CAPABLE OF HEAVY DOWNPOURS THAT MAY BRING
MVFR OR LOWER VSBY/CIGS, STRONG OUTFLOW WINDS (VARIABLE
DIRECTIONS WITH GUSTS 50KTS OR GREATER), HAIL, AND FREQUENT
LIGHTNING. MOST SITES WILL SEE STORM ACTIVITY CEASE THROUGH THE
EVENING, HOWEVER MODEL GUIDANCE INDICATES LIGHT RAIN SHOWERS
CONTINUING AT SITES RDM/BDN THROUGH PERIOD. PREVAILING WINDS
WILL MOSTLY BE LIGHT OVERNIGHT, EXCEPT WINDS AT SITE DLS WILL BE
12-15KTS WITH GUSTS TO AROUND 22KTS. LAWHORN/82
HYDROLOGY
THE WEATHER PREDICTION CENTER HAS ISSUED A MARGINAL
RISK OF EXCESSIVE RAINFALL ALONG THE CASCADE CREST AND EAST
SLOPES THROUGH LATE TONIGHT. PWATS WILL INCREASE TO BETWEEN
0.9-1.3 INCHES (BETWEEN 75TH TO 99TH PERCENTILE FOR MAY) BY
THIS AFTERNOON AND EVENING ALONG THE CASCADES, ALLOWING HEAVY
DOWNPOURS TO DEVELOP. TRAINING STORMS AND/OR EXCEPTIONALLY HEAVY
RAIN RATES (0.3 TO 0.5 INCHES/HR) IN THIS AREA COULD LEAD TO
FLOODING AND FLASH FLOODING.
PRELIMINARY POINT TEMPS/POPS
PDT 85 51 69 43 / 10 60 10 0
ALW 86 57 71 48 / 10 60 10 0
PSC 93 55 75 46 / 0 60 10 0
YKM 93 57 73 43 / 0 80 40 0
HRI 89 54 70 44 / 0 60 10 0
ELN 89 54 65 40 / 0 80 50 0
RDM 80 42 61 32 / 80 90 50 0
LGD 84 49 71 42 / 40 60 50 10
GCD 81 43 68 38 / 60 40 60 10
DLS 91 56 67 45 / 10 70 40 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...NONE.
DISCUSSION...82
AVIATION...82
HYDROLOGY...82
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