FXUS66 KPDT 100551
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
950 PM PST WED DEC 9 2009
.SHORT TERM...CLEAR SKIES ACROSS THE FORECAST AREA THIS EVENING.
SATELLITE SHOWS AN AREA OF STRATOCUMULUS CLOUDS OVER EASTERN
WASHINGTON. THIS COULD MOVE ACROSS THE NORTHEASTERN PORTION OF THE
FORECAST AREA NEAR DAYTON. OTHERWISE EXPECT SKIES TO REMAIN CLEAR
FOR THE OVERNIGHT PERIOD. TEMPERATURES WILL BE COLD...HOWEVER LOOKS
AS THOUGH THEY WILL BE A FEW DEGREES WARMER THAN THE PAST FEW
NIGHTS. 00Z SOUNDINGS ACROSS THE PACIFIC NORTHWEST SHOW THE AIRMASS
IS WARMING AND WILL CONTINUE TO WARM OVER THE NEXT 2 DAYS. THIS WILL
INCREASE TEMPERATURES A FEW DEGREES EACH DAY...MORE WARMING IS
EXPECTED AT THE MID AND HIGHER ELEVATIONS AS THE COLUMBIA BASIN WILL
BE UNDER A STRONGER LOW LEVEL INVERSION. SKIES WILL REMAIN MOSTLY
CLEAR THROUGH THURSDAY NIGHT. AN APPROACHING LOW PRESSURE SYSTEM
SHOULD START INCREASING CLOUDS ON FRIDAY WITH A CHANCE OF SNOW
FRIDAY NIGHT INTO SATURDAY. 94
.AVIATION...06Z TAFS. VFR CONDITIONS THE NEXT 24 HOURS WITH CLEAR
SKIES AND WINDS 5KT OR LESS.
&&
.PREV DISCUSSION... /ISSUED 135 PM PST WED DEC 9 2009/
SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT...THE REGION CONTINUES TO
BE UNDER A DRY NORTHERLY FLOW THIS AFTERNOON. A FEW HIGH CLOUDS
CONTINUE TO MOVE ACROSS THE FAR EASTERN PORTION OF THE FORECAST AREA
AND EXPECT MOSTLY CLEAR SKIES OVER THE REGION TONIGHT. THIS WILL
AGAIN LEAD TO COLD OVERNIGHT LOW TEMPERATURES. 500 MB HEIGHTS WILL
GRADUALLY INCREASE TOMORROW AND 850 MB TEMPERATURES WILL ALSO
INCREASE. THIS WILL LEAD TO HIGH TEMPERATURES TOMORROW BEING A FEW
DEGREES WARMER THAN TODAY. LOWER LEVEL FLOW WILL SWITCH TO THE
SOUTHWEST THURSDAY AND FRIDAY AHEAD OF A WEATHER DISTURBANCE
APPROACHING THE NORTHERN CALIFORNIA/SOUTHERN OREGON COAST. THIS WILL
HELP INCREASE TEMPERATURES FURTHER IN CENTRAL OREGON AND THE HIGHER
ELEVATIONS ON FRIDAY...WHILE COOLER TEMPERATURES REMAIN TRAPPED OVER
THE LOWER ELEVATIONS IN THE COLUMBIA BASIN AND SURROUNDING VALLEYS.
MODELS ARE IN DISAGREEMENT WITH THE TRACK OF THE OFFSHORE
SYSTEM...WITH SOME TAKING THE ENERGY INTO CALIFORNIA...WHILE OTHERS
(SUCH AS THE GFS) TAKE IT THROUGH OREGON. HAVE LEANED MORE TOWARD
THE GFS SOLUTION WITH WARMER AIR ALOFT AND INCREASING PRECIPITATION
CHANCES MOVING INTO CENTRAL OREGON BY FRIDAY NIGHT. WITH
TEMPERATURES BELOW FREEZING AT THE SURFACE...PRECIPITATION WILL
START OUT AS SNOW FOR CENTRAL AND NORTH CENTRAL OREGON...BUT MAY
INCLUDE A MIX OF SLEET AND FREEZING RAIN DUE TO THE WARMING LAYER
ALOFT. FURTHER NORTH AND EAST...MODEL SOUNDINGS SHOW THAT
TEMPERATURES AT THE SURFACE AND ALOFT WILL REMAIN BELOW FREEZING
WITH SNOW BEING THE PRECIPITATION TYPE. A SPECIAL WEATHER STATEMENT
HAS BEEN ISSUED FOR THE POSSIBILITY OF WINTER PRECIPITATION THIS
WEEKEND. FUTURE MODEL RUNS WILL NEED TO BE WATCHED AS THE THREAT OF
WINTRY PRECIPITATION WOULD DECREASE IF THE WEATHER DISTURBANCE MOVES
THROUGH CALIFORNIA INSTEAD OF OREGON. DMH
LONG TERM...SATURDAY THROUGH WEDNESDAY...VERY INTERESTING AND
COMPLEX WEATHER SITUATION SETTING UP FOR THIS WEEKEND INTO EARLY
NEXT WEEK. MODELS ARE IN GENERAL AGREEMENT ON MOVING A LARGE SCALE
TROUGH INTO CA OVER THE WEEKEND. BUT WHERE THERE IS IS SOME
DISAGREEMENT IS THE PIECE OF ENERGY THAT THE GFS BREAKS OFF AND
MOVES ALONG AN E-W FRONTAL BOUNDARY ACROSS NORTHERN OREGON WITH
ENHANCED LIFT AND SNOWFALL. THE GFS HAS BEEN CONSISTENT WITH ITSELF
FOR AT LEAST A FEW RUNS NOW WHICH GIVES THIS SOLUTION CREDENCE. THE
EURO IS FARTHER SOUTH WITH THE PRECIP FIELDS AND THE CANADIAN IS IN
BETWEEN THE TWO BUT SOMEWHAT SIMILAR TO THE GFS. AFTER MUCH
CONSIDERATION HAVE DECIDED TO FORECAST AN ENHANCED AREA OF SNOW
ACROSS NORTHERN OREGON AND EXTREME SOUTHERN WASHINGTON FOR SATURDAY
AND SATURDAY NIGHT. THIS CAN BE TWEAKED NORTH OR SOUTH AS THINGS
BECOME MORE CLEAR. THERE IS THE POTENTIAL FOR SEVERAL INCHES OF SNOW
WITHIN THIS BAND WHEREVER IT SETS UP. A TEMPORARY BREAK IN THE
ACTION IS EXPECTED ON SUNDAY WITH TEMPERATURES POSSIBLY WARMING UP
ABOVE FREEZING IF THINGS CAN MIX OUT...BUT THIS IS NOT A CERTAINTY.
THE GFS AND CANADIAN SHOW ANOTHER ARCTIC INTRUSION ON MONDAY PRIOR
TO THE ARRIVAL OF A MOIST PACIFIC SYSTEM WHICH COULD LEAD TO A GOOD
DOSE OF SNOWFALL ACROSS THE LOWER ELEVATIONS AND MOUNTAINS IF IT
PANS OUT. BY MID WEEK...FLOW IS EXPECTED TO BECOME MORE WESTERLY AND
TEMPERATURES SHOULD GRADUALLY MODERATE BUT ONLY INTO THE 30S LOWER
ELEVATIONS. OVERALL THE CONFIDENCE IN THESE SPECIFIC SCENARIOS
PLAYING OUT EXACTLY AS DESCRIBED IS BELOW NORMAL...BUT THE POTENTIAL
FOR SOME SIGNIFICANT WINTER WEATHER DEFINITELY EXISTS FROM SATURDAY
THROUGH TUESDAY OF NEXT WEEK. 78
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 5 22 11 24 / 0 0 0 0
ALW 10 24 14 26 / 0 0 0 0
PSC 6 26 11 24 / 0 0 0 0
YKM 1 22 8 23 / 0 0 0 0
HRI 4 24 11 24 / 0 0 0 0
ELN 1 23 7 23 / 0 0 0 0
RDM -6 26 7 32 / 0 0 0 10
LGD 1 23 9 25 / 0 0 0 0
GCD 0 23 11 28 / 0 0 0 10
DLS 7 25 15 27 / 0 0 0 0
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&
THREAT INDEX
THURSDAY : GREEN
FRIDAY : GREEN
SATURDAY : 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/
