FXUS66 KPDT 080542 AAA
AFDPDT
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
942 PM PST MON DEC 7 2009
UPDATED AVIATION DISCUSSION.
.UPDATE...VERY COLD DRY AIR CONTINUES TO STREAM INTO THE AREA
TONIGHT FROM ALBERTA ON A NORTHEASTERLY FLOW AND A VERY CHILLY NIGHT
IS UNDERWAY. TEMPERATURES HAVE ALREADY DIPPED INTO THE SINGLE DIGITS
ABOVE ZERO IN MOST OF THE AREA. CENTRAL AND NORTH CENTRAL OREGON AND
THE EASTERN MOUNTAINS HAVE LOCATIONS BELOW ZERO WHILE THE COLUMBIA
BASIN HAS LOCATIONS STILL AT 10 TO 15 ABOVE. HOWEVER...EVEN THERE
DEW POINTS ARE BELOW ZERO AND EXPECT TEMPERATURES WILL DROP TO THE
LOW SINGLE DIGITS ABOVE ZERO LATER TONIGHT. SKIES HAVE CLEARED OUT
EXCEPT ALONG THE CASCADES AND IN PORTIONS OF CENTRAL OREGON. HAVE
REDUCED CLOUD COVER A BIT TO BETTER REFLECT CURRENT CONDITIONS
THOUGH THE RESULTS MAY BE MINOR IN FORECAST PRODUCTS. HAVE ALREADY
LOWERED TEMPS TONIGHT ONCE AND WILL DO SO AGAIN. HAVE TAKEN CURRENT
DEW POINT TEMPERATURES AS A STARTING POINT AND ADJUSTED UPWARD AS
NEEDED. WINDS REMAIN LIGHT EXCEPT FOR 10 TO 20 MPH WINDS IN THE
GRANDE RONDE VALLEY. EXPECT THAT THEY WILL DROP TO 5 TO 10 MPH LATER
TONIGHT. HAVE ALREADY ADDRESSED THIS IN THE EARLIER UPDATE. SECOND
UPDATE OUT SOON. PERRY
&&
.AVIATION...06Z TAFS...VFR CONDITIONS WILL BE PREVALENT FOR THE NEXT
24 HOURS. SKIES WILL BE FEW-SCT ABOVE 15000 FEET...POSSIBLY WITH BKN
SKIES AT TIMES IN THE NORTH AFFECTING KYKM AND KPSC. AN EXCEPTION
WILL BE IN CENTRAL OREGON WHERE AN UPSLOPE FLOW AND SNOW COVER WILL
LEAD TO A POSSIBLE SCT-BKN STRATUS DECK AT 3000-4000 FT AGL THROUGH
08/21Z AFFECTING KRDM. HAVE KEPT SCT035 TO ACCOUNT FOR THIS. WINDS
WILL REMAIN UNDER 10 KTS FOR THE NEXT 24 HOURS. PERRY
&&
.PREV DISCUSSION... /ISSUED 330 PM PST MON DEC 7 2009/
SHORT TERM...TONIGHT THROUGH THURSDAY...A HIGHLY AMPLIFIED TROUGH
STRETCHING FROM NORTH CENTRAL CANADA SOUTHWESTWARD INTO CALIFORNIA
HAS FUNNELED BITTERLY COLD ARCTIC AIR INTO THE REGION. EVEN
THROUGH THE TROUGH WILL SHIFT TO THE EAST OVER THE NEXT SEVERAL
DAYS...NORTHERLY FLOW ALOFT WILL ENSURE THAT THIS COLD DRY AIR
REMAINS IN PLACE THROUGH THE MIDDLE OF THE WEEK. TONIGHT WILL LIKELY
BE THE COLDEST NIGHT THIS WEEK WITH LOW TEMPERATURES RANGING FROM
TEN BELOW ZERO IN CENTRAL OREGON TO TEN ABOVE ZERO IN THE LOWER
COLUMBIA BASIN. TUESDAYS HIGH TEMPERATURES WILL BE SIMILAR TO WHAT
THEY WERE TODAY. HOWEVER...FROM TUESDAY NIGHT ONWARD...TEMPERATURES
WILL SLOWLY MODERATE AS THE LARGE SCALE FLOW SHIFTS TO THE NORTHWEST
DUE TO BUILDING HIGH PRESSURE IN THE EASTERN PACIFIC. BY
THURSDAY...DAYTIME TEMPERATURES WILL HAVE WARMED SLIGHTLY...REACHING
INTO THE MID TO UPPER 20S ACROSS EASTERN OREGON AND INTO THE MID 20S
OVER MUCH OF SOUTH CENTRAL WASHINGTON. DESPITE THE EXTREME
COLD...SKIES WILL GENERALLY BE MOSTLY CLEAR AND WINDS WILL BE LIGHT
THROUGHOUT THE PERIOD. 82
LONG TERM...THURSDAY NIGHT THROUGH MONDAY. COLD AND DRY CONDITIONS
WILL CONTINUE THURSDAY NIGHT AND FRIDAY. THERE ARE SEVERAL
CHALLENGES FOR THE REMAINDER OF THE FORECAST PERIOD. MEDIUM-RANGE
MODELS ALL SHOW A SHORTWAVE TROUGH AND WARM AIR ADVECTION (WAA)
ALOFT BRINGING PRECIPITATION INTO CENTRAL OREGON FRIDAY NIGHT THEN
OVER THE REMAINDER OF THE REGION ON SATURDAY. THE DIFFERENCES LIE
IN THE POSITION AND STRENGTH OF THE SURFACE LOW. THE GFS IS
STRONGER AND FARTHER NORTH WITH THE SURFACE LOW ON SATURDAY COMPARED
TO THE ECMWF...THUS THE WARM FRONT IS STRONGER AND THE QPF IS MORE
IMPRESSIVE. THIS WILL MAKE A BIG DIFFERENCE ON PRECIPITATION TYPE
OVER THE BASIN AND SURROUNDING VALLEYS. AT THIS TIME...LEANING
TOWARDS THE MORE CONSISTENT ECMWF WITH WEAKER WAA. BELIEVE THERE
COULD BE A WINTER MIX OF SNOW...SLEET...AND FREEZING RAIN IN THE LOW
ELEVATIONS ON SATURDAY AND SATURDAY NIGHT SO WILL INCLUDE THIS IN
THE FORECAST AND THE HAZARDOUS WEATHER OUTLOOK. THE SURFACE LOW AND
A WEAK COLD FRONT MOVING ACROSS OR/WA WILL ALLOW PRECIPITATION TO
RETURN TO ALL SNOW BY SUNDAY...BUT THERE WILL ALSO BE SOME DRYING BY
LATE SUNDAY. ANOTHER WARM FRONT IS PROGGED TO BRING PRECIPITATION TO
THE REGION ON MONDAY. DUE TO SLIGHT MODEL INCONSISTENCIES...WILL
HOLD OFF ON MENTIONING FREEZING PRECIP FOR MONDAY AND SEE WHAT
FUTURE MODELS HAVE IN STORE. JOHNSON
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT -2 18 8 22 / 0 0 0 0
ALW 3 20 12 24 / 0 0 0 0
PSC 0 22 8 24 / 0 0 0 0
YKM -2 20 3 24 / 0 0 0 0
HRI 1 21 6 23 / 0 0 0 0
ELN -3 20 4 24 / 0 0 0 0
RDM -4 16 1 23 / 0 0 0 0
LGD -4 17 5 20 / 0 0 0 0
GCD -1 19 5 21 / 0 0 0 0
DLS 2 22 9 28 / 0 0 0 0
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&
THREAT INDEX
TUESDAY : GREEN
WEDNESDAY : GREEN
THURSDAY : 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
$$
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