654
FXUS66 KPDT 211016
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
316 AM PDT TUE APR 21 2026
KEY MESSAGES
1. INCOMING SYSTEM WILL BRING INCREASED RAINFALL TO THE CWA TUESDAY
AND WEDNESDAY
2. CHANCES OF THUNDERSTORMS TUESDAY AND WEDNESDAY AFTERNOONS
3. BREEZY TO WINDY CONDITIONS WEDNESDAY
DISCUSSION
CURRENT NIGHT TIME SATELLITE SHOWS SOME SPLIT FLOW OCCURRING ACROSS
THE PACNW WITH SOUTHEAST FLOW TO THE SOUTHWESTERN PORTION OF THE
REGION AND SOUTHWEST FLOW ALONG THE EAST AND NORTH EASTERN PORTION
OF THE REGION. MUCH OF THE CLOUD COVER IS CURRENTLY OVER CENTRAL OR
WITH RADAR SHOWING SOME LIGHT RETURNS IN THAT AREA AS WELL. GROUND
OBSERVATIONS SHOW THAT THERE RAIN IS NOT CURRENTLY AFFECTING CENTRAL
OR AT THIS TIME BUT IS EXPECTED TO MOVE OVER THE AREA AFTER 10 AM.
MODELS SHOW THE LOW THAT IS CAUSING THE SOUTHEAST FLOW WILL CONTINUE
TO MOVE TO THE EAST AND BRINGING INCREASED CHANCES OF RAINFALL TO
THE REGION. MUCH OF THE RAINFALL WILL BEGIN ALONG THE SOUTHERN AND
EASTERN PORTION OF THE REGION TUESDAY BEFORE BECOMING WIDESPREAD
AFTER 5 PM. 24 HOUR QPF TOTALS BETWEEN 5 AM TUESDAY TO 5 AM
WEDNESDAY IS 0.08-0.10 THROUGH CENTRAL AND NORTH CENTRAL OR AS WELL
AS THE KITTITAS VALLEY WITH 10-25% OF THE NBM RAW ENSEMBLES IN
AGREEMENT. ALONG THE FOOTHILLS OF THE SOUTHERN AND NORTHERN BLUES,
YAKIMA VALLEY AND THE COLUMBIA BASIN, QPF AMOUNTS BETWEEN 0.20-0.30
INCHES ARE LIKELY WITH 30-50% OF THE NBM RAW ENSEMBLES IN AGREEMENT.
HIGHEST RAINFALL TOTALS WILL BE ALONG THE EASTERN MOUNTAINS ANS
ALONG THE HIGHER CRESTS OF THE BLUES WITH 0.70-0.99 INCHES WITH 30-
40% OF THE NBM RAW ENSEMBLES IN AGREEMENT. NOT ONLY WILL THERE BE AN
INCREASE IN PRECIPITATION, BUT MODELS SHOW AN INCREASE IN
INSTABILITY AS THE MOISTURE MOVES INTO THE REGION.
MODELS SHOW THE LOW TO USHER IN EVEN MORE PRECIPITATION ON WEDNESDAY
AS IT ADVECTS MORE MOISTURE INTO THE REGION. NBM QPF 24 HOUR TOTALS
SHOW CENTRAL AND NORTH CENTRAL OR, PORTIONS OF THE GORGE, YAKIMA AND
KITTITAS VALLEY SEEING ONLY 0.02-0.05 INCHES WITH 30-50% RAW ENSEMBLE
AGREEMENT. RAIN AMOUNTS WILL INCREASE AS YOU MOVE EST WITH THE
SOUTHERN BLUES, COLUMBIA BASIN OF OR AND WA AND PORTIONS OF THE
EASTERN MOUNTAINS WILL SEE QPF AMOUNTS BETWEEN 0.10-0.50 WITH 35-65%
OF THE RAW ENSEMBLES IN AGREEMENT. FOOTHILLS OF THE NORTHERN BLUES
AND THE EASTERN BASIN COULD SEE BETWEEN 0.60-0.80 INCHES WITH 50-70%
AGREEMENT. LASTLY, THE RIDGES OF THE NORTHER BLUES COULD SEE BETWEEN
0.80-1.90 INCHES WITH 50-70% AGREEMENT. HOWEVER, SNOW LEVELS WILL
BEGIN TO DECREASE ACROSS THE EASTERN PORTION OF THE REGION TO BELOW
5000 FEET WEDNESDAY SO ABOVE THIS THE PRECIPITATION WILL FALL AS
SNOW WITH 50% ENSEMBLE AGREEMENT OF 6+ INCHES OF SNOWFALL IS
POSSIBLE BETWEEN 5 AM WEDNESDAY AND 5 AM THURSDAY.
FORECAST SOUNDINGS SHOW SFCCAPE VALUES BETWEEN 150-300 J/KG, 7.1
C/KM LAPSE RATES AND 30 KT BULK SHEAR ALL ADD UP TO THE
PROBABILITIES OF THUNDERSTORMS ALONG THE EASTERN MOUNTAINS AND
PORTIONS OF CENTRAL OR AND WA CASCADES. IN HOUSE CALCULATIONS SHOW A
20-30% PROBABILITY OF THUNDERSTORMS ALONG THOSE AREAS AS WELL AS
HREF PAINTBALL SHOWING HIGH CONCENTRATIONS OF THE MEMBERS IN
AGREEMENT ON LOCATION OF THE THUNDERSTORMS. SPC ALSO HAS THE REGION
IN A GENERAL THUNDERSTORM OUTLOOK FOR TUESDAY. MOVING INTO WEDNESDAY
CAMS MODEL NAM SHOWS SFCCAPE VALUES OF 150-250 J/KG APPEARING AGAIN
WITH LAPSE RATES AROUND 7 C/KM AND BULK SHEAR AROUND 30 KTS AGAIN
WITH PAINTBALL MEMBERS SHOWING THE HIGHEST CONCENTRATION BEING OVER
GRANT AND COOK COUNTIES THEN MOVING OFF TOWARDS WALLOWA LATER IN THE
EVENING.
WEDNESDAY, DETERMINISTIC MODELS SHOW A VERY TIGHT SURFACE PRESSURE
GRADIENT BUILDING ALONG THE CASCADES AND SPILLING OVER INTO THE
BASIN. MANY AREAS WILL SEE BREEZY TO WINDY CONDITIONS WEDNESDAY
THROUGH WEDNESDAY NIGHT. IN HOUSE MODEL GUIDANCE SHOWS A VERY TIGHT
PRESSURE GRADIENT FORMING ACROSS THE REGION BRING 30 MPH SUSTAINED
WINDS KITTITAS VALLEY, FOOTHILLS OF THE SOUTHERN AND NORTHERN BLUES
OF WA AND OR, THE GORGE, SIMCOE HIGHLANDS, LOWER COLUMBIA BASIN OF
OR AND NORTH CENTRAL OR WITH 40-70% OF THE HREF RAW ENSEMBLES IN
AGREEMENT. THE AFOREMENTIONED AREAS WILL ALSO SEE 30-70%
PROBABILITIES OF 45-50 MPH GUSTS.
IN THE LONG TERM AFTER WEDNESDAY, MODELS BEGIN TO FALL OUT OF
AGREEMENT WITH THE NEXT INCOMING SYSTEM. SOME MODELS, GFS AND EURO
DO SHOW A WEAK REX BLOCK WANTING TO SET UP OFF THE COAST WITH A BIT
OF A HINT OF THE UPPER LEVEL LOW RETROGRADING BACK INTO THE AREA.
MODELS ARE IN AGREEMENT THAT THE REGION WILL PRIMARILY BE DOMINATED
BY NORTHERLY FLOW ALOFT WHICH WILL KEEP THE REGION MOSTLY DRY AND
COOL OVER THE WEEKEND. 90
AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/
VFR CONDITIONS WILL PERSIST THROUGH MUCH OF THE FORECAST PERIOD
BEFORE ALL SITE MINUS RDM/BDN SEE MVFR CONDITIONS DUE TO LOW
CIGS AFTER 07Z. SHOWERS WILL BEGIN TO APPROACH TAF SITES
BETWEEN 17Z-22Z WITH MOSTLY LIGHT SHOWERS. RDM/BDN WILL CONTINUE
TO SEE WINDS BELOW 10 KTS WHILE THE REMAINING TAF SITES WILL
SEE BREEZY WINDS BETWEEN 13-18 KTS WITH GUSTS NEARING 30 KTS
AFTER 16Z. 90
HYDROLOGY
WITH THE AMOUNT OF RAINFALL AND SNOWFALL EXPECTED THROUGH
WEDNESDAY, SOME RIVER FORECASTS SHOW A FEW RIVERS TO EXCEED
ACTION STAGE BY THURSDAY. THESE RIVERS ARE AS FOLLOWS: GRANDE
RONDE AT TROY, NACHES NEAR CLIFFDELL AND NACHES, WALLA WALLA
NEAR TOUCHET. 90
PRELIMINARY POINT TEMPS/POPS
PDT 72 44 53 39 / 40 90 90 40
ALW 73 45 52 41 / 20 90 100 50
PSC 78 49 63 43 / 10 70 80 20
YKM 76 50 65 43 / 20 50 40 10
HRI 74 46 58 41 / 20 80 80 20
ELN 70 45 56 40 / 30 50 40 10
RDM 61 36 53 28 / 50 50 40 0
LGD 74 41 47 39 / 40 100 100 70
GCD 69 39 47 34 / 70 100 90 50
DLS 66 49 59 43 / 30 40 60 0
PDT WATCHES/WARNINGS/ADVISORIES
WA...NONE.
OR...NONE.
DISCUSSION...90
AVIATION...90
HYDROLOGY...90
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