Area Forecast Discussion
Issued by NWS Pendleton, OR

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000
FXUS66 KPDT 260526
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1030 PM PDT MON MAY 25 2015

.SHORT TERM...SCATTERED SHOWERS MOVING THROUGH THE COLUMBIA BASIN
THIS EVENING...ROTATING AROUND THE UPPER LOW OVER EASTERN WASHINGTON.
THESE SHOULD DIMINISH OVER THE NEXT FEW HOURS. OTHERWISE APPEARS
MOST OF THE ACTIVITY WILL REMAIN NORTH OF THE FORECAST AREA FOR
TONIGHT. THE UPPER LOW IS NEARLY STATIONARY...ONLY MOVING TO SOUTHEAST
WASHINGTON BY TUESDAY AFTERNOON. THE AIRMASS IN THE VICINITY OF
THE LOW REMAINS UNSTABLE AND EXPECT SCATTERED SHOWERS AND
THUNDERSTORMS TO DEVELOP TOMORROW AFTERNOON. MAIN AREAS IMPACTED
WILL BE FROM THE WASHINGTON CASCADES ACROSS THE COLUMBIA BASIN TO
THE NORTHEAST OREGON MOUNTAINS. BY WEDNESDAY THE LOW WILL BE OVER
IDAHO. UNSTABLE NORTHWESTERLY FLOW ALOFT WILL KEEP SCATTERED
SHOWERS AND THUNDERSTORMS GOING FOR THE WASHINGTON CASCADES ACROSS
THE BASIN INTO NORTHEAST OREGON AGAIN. 94

.AVIATION...06Z TAFS. FEW REMAINING SHOWERS MOVING ACROSS THE
COLUMBIA BASIN LATE THIS EVENING WITH CEILINGS 050-080. SHOWERS AND
ISOLATED THUNDERSTORMS WILL INCREASE IN COVERAGE TUESDAY AFTERNOON
AND EVENING FOR YKM DLS PSC PDT ALW. CLEAR TO PARTLY CLOUDY SKIES
FOR RDM BDN THE NEXT 24 HOURS. 94

&&

.PREV DISCUSSION... /ISSUED 409 PM PDT MON MAY 25 2015/

SHORT TERM...TONIGHT THROUGH THURSDAY...AN UPPER LEVEL LOW NEAR THE
BRITISH COLUMBIA/WASHINGTON BORDER WILL DRIFT SOUTHEAST TONIGHT
THROUGH WEDNESDAY. WITH THE LOW OVER EASTERN WASHINGTON TODAY
ONSHORE FLOW WILL CONTINUE WITH BREEZY/WINDY CONDITIONS THROUGH THE
CASCADE GAPS, COLUMBIA RIVER GORGE, AND UPPER KITTITAS VALLEY. THIS
FLOW IS RELATIVELY STABLE, SO SHOWERS AND THUNDERSTORMS WILL BE
LIMITED THIS EVENING. SOME BUILDUPS HAVE DEVELOPED ON THE EAST
SLOPES OF THE WA CASCADES, AND GRANT COUNTY TO THE BLUES AND WALLOWA
COUNTY. EXPECT ISOLATED TO SCATTERED SHOWERS WITH ISOLATED
THUNDERSTORMS OVER THE EAST SLOPES AND NORTHEAST MOUNTAINS (MAINLY
THE BLUES EAST TO WALLOWA COUNTY). A FEW SHOWERS MAY PERSIST ACROSS
OUR NORTHERN ZONES OVERNIGHT AS THE LOW MOVES CLOSER INTO EASTERN
WASHINGTON. AS THE LOW DRIFTS ALONG THE WA/OR/ID BORDER TUESDAY
AFTERNOON/EVENING THE AIR MASS OVER SOUTHEAST WASHINGTON AND
NORTHEAST OREGON WILL BECOME MORE UNSTABLE. A WEAK WAVE WILL ROTATE
AROUND THE LOW AND ENHANCE SHOWERS IN SOUTHEAST WASHINGTON, THE
LOWER COLUMBIA BASIN, AND NORTHEAST OREGON. WEDNESDAY WRAP AROUND
MOISTURE AND INSTABILITY MAY TRIGGER SHOWERS AND AFTERNOON
THUNDERSTORMS ACROSS THE EASTERN EDGE OF WASHINGTON AND OREGON.
DAYTIME HEATING MAY TRIGGER A FEW SHOWERS AND THUNDERSTORMS ALONG
THE WASHINGTON CASCADES AS WELL. THURSDAY WEAK RIDGING WILL DEVELOP
ALONG THE COAST. DRY NORTHERLY FLOW WILL BE OVER EASTERN WASHINGTON
AND OREGON BUT DAYTIME HEATING AND OROGRAPHIC EFFECTS MAY TRIGGER A
FEW SHOWERS AND THUNDERSTORMS ALONG THE WASHINGTON CASCADES AND THE
BLUES AND WALLOWAS. COONFIELD

LONG TERM...THURSDAY NIGHT THROUGH SATURDAY NIGHT...A RIDGE OF HIGH
PRESSURE TO THE SOUTH AND A LOW PRESSURE SYSTEM TO THE NORTH WILL
PROVIDE SPLIT FLOW TO THE AREA THURSDAY NIGHT INTO FRIDAY.  THIS
FLOW WILL TRANSITION TO SOUTHWEST FLOW BY SATURDAY AS THE TWO
SYSTEMS PROGRESS EAST.  ISOLATED THUNDER POSSIBILITIES ON
FRIDAY...MAINLY ALONG THE EAST SLOPES OF THE CASCADES...AND THE
EAGLE CAPS.  SATURDAY WILL BE A BETTER CHANCE OF THUNDERSTORMS DUE
TO THE TRANSITION TO SOUTHWEST FLOW.  THUNDERSTORMS WILL BE MAINLY
OVER THE NORTHEAST MOUNTAINS ON SATURDAY EVENING. WEBER

SUNDAY THROUGH MONDAY NIGHT...AN ACTIVE WEATHER PATTERN WILL LIKELY
BE OVER THE REGION THROUGH MUCH OF THIS PERIOD. MOST GUIDANCE IS IN
GENERALLY GOOD AGREEMENT THAT A MOIST SOUTH TO SOUTHWEST FLOW WILL
SET UP OVER THE AREA OUT AHEAD OF A SLIGHTLY NEGATIVELY TILTED
TROUGH. THERE REMAINS SLIGHT TIMING AND POSITION DISCREPANCIES
WITHIN THE GUIDANCE FOR THIS TROUGH...WITH THE LATEST 12Z ECMWF
STILL DROPPING THE FEATURE FURTHER SOUTH THAN THE 12Z GFS. WITH
THESE DIFFERENCES IN MIND DECIDED TO JUST GO SLIGHT CHANCE TO CHANCE
POPS FOR SHOWERS AND THUNDERSTORMS OVER MUCH OF THE FORECAST AREA
DURING THIS TIME. WILL NEED TO KEEP A CLOSE EYE ON THIS SYSTEM AS
SOME OF THE LATEST GUIDANCE WOULD PLACE THE CWA IN THE FAVORABLE
LEFT EXIT REGION OF A 100KT JET AT THE 300MB LEVEL BOTH SUNDAY AND
MONDAY AFTERNOON. OTHERWISE TEMPERATURES REMAIN RATHER WARM ON
SUNDAY AFTERNOON...LIKELY ABOUT 10 DEGREES ABOVE AVERAGE BEFORE
COOLING OFF CLOSER TO AVERAGE BY MONDAY WITH THE INCREASED CLOUD
COVER AND PRECIPITATION CHANCES. 77

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  50  75  51  77 /  20  20  20  20
ALW  56  77  57  79 /  20  30  20  30
PSC  54  80  55  84 /  20  20  20  20
YKM  53  77  54  82 /  20  30  30  20
HRI  52  80  53  82 /  20  10  20  20
ELN  54  76  53  81 /  20  40  30  20
RDM  39  76  42  76 /  10  10  10  10
LGD  46  71  48  71 /  20  40  20  30
GCD  44  75  45  73 /  10  10  10  30
DLS  54  77  56  83 /  10  20  20  10

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&

FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT...
WWW.WEATHER.GOV/PENDLETON

$$

94/


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