000
FXUS66 KPDT 220515
AFDPDT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
1020 PM PDT TUE MAY 21 2013

.SHORT TERM...STRONG UPPER LEVEL LOW IS MOVING INTO THE PACIFIC
NORTHWEST TONIGHT. A SHORT WAVE ROTATING THROUGH THE LOW IS
CURRENTLY MOVING OVER THE NORTHERN HALF OF THE FORECAST AREA. THIS
FEATURE IS PRODUCING AN AREA OF HEAVIER RAIN AND ISOLATED
THUNDERSTORMS. THIS PRECIPITATION WILL CONTINUE TO MOVE NORTHWARD
OVER THE NEXT SEVERAL HOURS. OTHERWISE EXPECT MOSTLY CLOUDY SKIES
TONIGHT WITH SCATTERED SHOWERS. FREEZING LEVELS ARE LOWERING QUICK
WITH THE COLD ADVECTION AND WE WILL HAVE SNOW SHOWERS OVER THE
HIGHER TERRAIN. THE UPPER LOW WILL BE DIRECTLY OVER THE FORECAST
AREA WEDNESDAY. COLD AIR ALOFT SHOULD PRODUCE ENOUGH INSTABILITY FOR
RAIN SHOWERS AND MOUNTAIN SNOW SHOWERS. ISOLATED AFTERNOON
THUNDERSTORMS ARE POSSIBLE IF THE CLOUDS DECREASE ENOUGH TO ALLOW
FOR SOME SUNSHINE. TEMPERATURES WILL BE WELL BELOW NORMAL WITH HIGHS
IN THE 50S. LITTLE CHANGE IN THE WEATHER PATTERN THURSDAY AND FRIDAY
WITH THE UPPER LOW CONTINUING TO PRODUCE SHOWERS AND COOL
TEMPERATURES.  94

.AVIATION...06Z TAFS. AREA OF STEADY RAIN WILL CONTINUE TO IMPACT
YKM PSC ALW FOR SEVERAL MORE HOURS. OTHERWISE SCATTERED SHOWERS
ACROSS THE TAF SITES FOR THE NEXT 24 HOURS. CEILINGS WILL BE
030-060. WINDS 10-25KT.

&&

.PREV DISCUSSION... /ISSUED 321 PM PDT TUE MAY 21 2013/

SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT...AN UPPER LOW WILL
CONTINUE TO MOVE INTO THE PACIFIC NORTHWEST LATE THIS AFTERNOON AND
TONIGHT. THE COLD FRONT ASSOCIATED WITH THIS SYSTEM HAS PUSHED
THROUGH MOST OF OUR AREA, EXCEPT THE EASTERN HALF OF WALLOWA COUNTY.
THIS FRONT SHOULD BE THROUGH WALLOWA COUNTY BY 5 PM. WILL CONTINUE
TO INDICATE A THREAT OF ISOLATED THUNDERSTORMS, THOUGH THE THREAT
SEEMS TO BE DIMINISHING. STORMS WILL BE POSSIBLE FROM GRANT COUNTY
NORTH TO THE BLUES AND EAST TO WALLOWA COUNTY LATE THIS AFTERNOON,
AND OVER WALLOWA COUNTY THIS EVENING. A BAND OF STEADY SHOWERS JUST
BEHIND THE FRONT CONTINUES TO SLIDE NORTHEAST AND EAST THROUGH THE
AREA. THIS BAND CURRENTLY RUNS FROM EASTERN GRANT AND BAKER COUNTIES
NORTH-NORTHWEST INTO WALLA WALLA AND FRANKLIN COUNTIES. THIS BAND
SHOULD LARGELY BE THROUGH THE AREA BY SUNSET THIS EVENING. WITH THE
UPPER LOW OVER THE REGION TONIGHT, WILL CONTINUE TO SEE BANDS OF
SHOWERS ROTATE THROUGH THE AREA. THERE REMAINS SOME UNCERTAINTY AS
TO THE TIMING AND TRACK OF THESE BANDS, BUT DATA INDICATES SOME
DECENT PRECIP OVER MANY LOCATION OVERNIGHT INTO WEDNESDAY MORNING.
SNOW LEVELS WILL FALL TO AROUND 4500 FEET THIS EVENING, THEN DOWN TO
2500 TO 3000 FEET BY DAYBREAK WEDNESDAY. THE ONE AREA THAT LOOKS TO
SEE ENOUGH PRECIP FOR SOME DECENT LATE SEASON SNOW IS THE BLUE
MOUNTAINS. WILL ISSUE A LOW END ADVISORY FOR THE BLUE MOUNTAIN ZONES
AS MUCH FOR IMPACT POTENTIAL AS FOR THE ACTUAL SNOW AMOUNTS. OTHER
AREAS THAT MAY SEE SNOW SHOULD SEE AN INCH OR LESS.

THE UPPER LOW WILL REMAIN OVER THE REGION WEDNESDAY AFTERNOON
THROUGH THURSDAY NIGHT. AS SUCH THE AREA WILL REMAIN WITHIN A COOL
AND UNSETTLED WEATHER PATTERN WITH WAVES ROTATING AROUND THE LOW
CAUSING PERIODS OF SHOWERS. SNOW LEVELS LOOK TO SLOWLY RISE THROUGH
THIS PERIOD, THOUGH SOME SPOTTY SNOW WILL BE POSSIBLE LATE AT NIGHT
INTO THE HOURS AROUND DAYBREAK. DAYTIME HEATING AND COLD AIR ALOFT
COULD CREATE LAPSE RATES STRONG ENOUGH TO SUPPORT STRAY AFTERNOON
AND EVENING THUNDERSTORMS WEDNESDAY AND THURSDAY. AT THIS TIME WILL
CONTINUE TO MENTION STORMS ONLY ON THURSDAY AS THERE APPEARS TO
BETTER FOCUSING ON THIS DAY. 90

LONG TERM...FRIDAY THROUGH TUESDAY NIGHT...UPPER LEVEL LOW WILL
CONTINUE TO CIRCULATE OVER THE AREA. EXPECT A CONTINUED CHANCE TO
LIKELY SHOWERS ALONG THE MOUNTAINS OF NORTHEAST OREGON AND EAST
SLOPES OF THE CASCADES...AS THE LOW REMAINS OVER THE AREA.
CONFIDENCE IS STILL FAIRLY HIGH WITH THE OVERALL PATTERN...BUT THERE
IS SOME DIVERGENCE WHEN IT COMES TO FAVORING THUNDER ALONG THE
MOUNTAINS OF NORTHEAST OREGON. RIGHT NOW THE BEST AGREEMENT THAT
WOULD SUPPORT THUNDERSTORMS IS FOR SUNDAY AFTERNOON. SO HAVE KEPT
THUNDER IN THE FORECAST FOR THE OCHOCO JOHN DAY...BLUE AND WALLOWA
MOUNTAIN AREAS...AS WELL AS THE GRANDE RONDE VALLEY. OTHERWISE HAVE
BACK OFF TO JUST SHOWERS FOR THE OTHER TIME PERIODS. AS WE GET
CLOSER TO THE NEAR TERM...IT MAY BE BETTER PINPOINTED AND WE CAN ADD
THE THUNDER AS NEEDED. ALTHOUGH THE MODELS KEEP THE CIRCULATION OVER
THE AREA FOR MOST OF THE EXTENDED...HENCE KEEPING A SLIGHT CHANCE
SHOWERS OVER THE LOWER ELEVATIONS AND A CHANCE TO LIKELY SHOWERS
OVER THE MOUNTAINS...THE CIRCULATION DOES APPEAR TO WEAKEN GRADUALLY
AFTER SATURDAY. THIS WILL ALLOW FOR WARMER AIR TO INTRUDE AND RETURN
LOWER ELEVATION TEMPERATURES INTO THE MID TO UPPER 70S FOR THE
REMAINDER OF THE EXTENDED. WEBER

AVIATION...00Z TAFS...MVFR AND VFR CONDITIONS ARE EXPECTED OVER THE
NEXT 24 HOURS. UPPER LEVEL LOW WILL CONTINUE TO CIRCULATE OVER THE
INTERIOR PACIFIC NORTHWEST.  EXPECT LOWERED CIGS...ON AND OFF
SHOWERS...AND BREEZY CONDITIONS AT ALL TAF SITES OVER THE NEXT 24
HOURS.  WINDS WILL GENERALLY BE 15 TO 25KTS. EXPECT BREEZY TO WINDY
CONDITIONS THIS AFTERNOON AS WELL AS TOMORROW AFTERNOON AT MOST TAF
SITES.  WEBER

&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  40  56  37  62 /  60  50  20  30
ALW  43  57  41  65 /  60  50  20  30
PSC  46  62  38  69 /  70  50  20  30
YKM  41  58  35  64 /  60  40  20  30
HRI  44  62  35  67 /  60  40  20  30
ELN  45  56  37  64 /  60  50  30  40
RDM  30  53  29  57 /  60  40  20  30
LGD  39  51  33  58 /  60  50  30  30
GCD  35  54  33  59 /  60  40  20  30
DLS  44  56  41  65 /  60  50  30  40

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 10 AM PDT WEDNESDAY ABOVE 4000
     FEET FOR THE ORZ502-503.

WA...WINTER WEATHER ADVISORY UNTIL 10 AM PDT WEDNESDAY ABOVE 4000
     FEET FOR THE WAZ030.

&&

THREAT INDEX
WEDNESDAY : GREEN
THURSDAY : GREEN
FRIDAY : GREEN

GREEN: NONE OR LIMITED NEED FOR WATCHES, WARNINGS, OR ADVISORIES.
YELLOW: A FEW WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.
RED: NUMEROUS WATCHES, WARNINGS, OR ADVISORIES POSSIBLE OR IN EFFECT.

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

$$

94