FXUS66 KPDT 021729 AAA
AFDPDT
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PENDLETON OR
929 AM PST WED DEC 2 2009
UPDATED AVIATION DISCUSSION
.SHORT TERM...HIGH PRESSURE WILL DOMINATE THE WEATHER PATTERN OVER
THE NEXT COUPLE OF DAYS. SKIES WILL BE MOSTLY CLEAR BUT THERE WILL
BE INCREASING PATCHY FOG DEVELOPING. THE LIGHT EASTERLY FLOW WILL
CONTINUE TO BANK CLOUDS UP AGAINST THE CENTRAL OREGON CASCADES
RESULTING IN LOW CLOUDS AND FOG FOR CENTRAL OREGON TODAY AND
OVERNIGHT. COULD BE A LITTLE IMPROVEMENT ON THURSDAY BUT STILL
EXPECT PARTLY TO MOSTLY CLOUDY SKIES AND PATCH FOG. TEMPERATURES
OVERNIGHT WERE IN THE TEENS AND 20S. EXPECT ABOUT THE SAME TO OCCUR
TONIGHT. TODAYS HIGHS WILL BE AT OR SLIGHTLY BELOW YESTERDAYS HIGHS
WHICH MEANS 30S PUSHING NEAR 40 IN THE LOWER BASIN.
&&
.AVIATION...18Z TAFS...LINGERING LOW CLOUDS OVER THE KRDM AREA WILL
GRADUALLY THIN THIS AFTERNOON...OTHERWISE EXPECT CLEAR SKIES AND
VERY LIGHT WINDS UNTIL MID EVENING. THEN EXPECT STRATUS AND FOG TO
FORM MOST AREAS AFTER 08Z. A PERIOD OF IFR IS EXPECT ALL AREAS...
EXCEPT KYKM...AFTER 08Z. FOG AND STRATUS MAY LINGER A LITTLE LONGER
INTO THURSDAY MORNING THAN THIS MORNING BUT SHOULD NOT LAST ALL DAY
ON THURSDAY. 78
&&
.PREV DISCUSSION... /ISSUED 230 AM PST WED DEC 2 2009/
SHORT TERM...TODAY THROUGH FRIDAY MORNING...A SHARP RIDGE OF HIGH
PRESSURE CENTERED JUST OFF OF THE WEST COAST HAS BROUGHT A COOL
NORTHWESTERLY FLOW TO THE REGION. THIS GENERAL FLOW PATTERN WILL
LAST THROUGH THURSDAY EVENING...RESULTING IN MOSTLY CLEAR SKIES.
SUBSIDENCE ASSOCIATED WITH THIS AREA OF HIGH PRESSURE WILL ALSO
CAUSE FAIRLY STRONG SURFACE INVERSIONS...LEADING TO PATCHY OVERNIGHT
AND MORNING FREEZING FOG IN THE LOWER COLUMBIA BASIN AND SURROUNDING
VALLEYS. IN CENTRAL OREGON...LOW STRATUS HAS ALSO DEVELOPED UNDER
THE INVERSION. WITHOUT A STRONG ENOUGH WEATHER DISTURBANCE TO MIX
OUT THE TRAPPED LOW LEVEL MOISTURE...THESE LOW CLOUDS COULD PERSIST
THROUGH FRIDAY MORNING. 82
LONG TERM...FRIDAY AFTERNOON THROUGH NEXT MONDAY...BIG CHANGES ARE
ON THE WAY IN THE EXTENDED PERIOD BEGINNING THIS COMING FRIDAY INTO
THE WEEKEND. ALL MEDIUM TO LONG RANGE MODELS ARE IN AGREEMENT WITH
SIGNIFICANT COLD EARLY SEASON ARCTIC AIR TO MOVE DOWN OUT OF CANADA
INTO THE REGION AND ACROSS MOST OF THE WESTERN USA. THE FIRST WAVE
WILL BE A PUSH OF ARCTIC AIR BUT NOT MUCH MOISTURE ON FRIDAY SO WILL
ONLY INCLUDE SOME ISOLATED FLURRIES OR LOW ELEVATION RAIN SHOWERS ON
FRIDAY. A SECONDARY SURGE OF COLD ARCTIC AIR WILL THEN MOVE INTO THE
REGION ON SATURDAY WITH A LARGE CLOSED UPPER LOW PRESSURE SYSTEM
ALSO DROPPING DOWN FROM THE NORTH. DEPENDING ON THE TRACK OF THIS
UPPER LOW...AS WELL AS ANY CORRESPONDING SURFACE LOW PRESSURE OR
DEFORMATION ZONE...THERE COULD MEAN A DIFFERENCE TO CONSIDERABLE
ACCUMULATING SNOW OR JUST SIMPLY VERY COLD AIR WITH LIGHT SNOW
SHOWERS OR FLURRIES WITH THE INITIAL PUSH OF COLD AIR. AT THE
PRESENT TIME THE UPPER LOW IS PROGGED TO REMAIN OVER LAND AND MOVE
SOUTH ACROSS THE CWA AND INTO THE GREAT BASIN. IN THIS SCENARIO CAN
EXPECT ONLY LIGHT AMOUNTS OF PRECIPITATION AND MAINLY IN THE
MOUNTAINS. IN ANY CASE SIGNIFICANTLY COLDER AIR WILL MOVE INTO THE
FORECAST AREA WITH THE COLDEST AIR OF THE SEASON. HIGH TEMPERATURES
BY SUNDAY AND MONDAY WILL STRUGGLE TO GET OUT OF THE 20S TO AROUND
30. WILL KEEP A SLIGHT CHANCE TO CHANCE OF SNOW SHOWERS OVER THE
BLUE MOUNTAINS...FOOTHILLS AND THE CASCADES EACH PERIOD...MAINLY DUE
TO UP SLOPE AND THE PUSH OF ARCTIC AIR CAUSING LIFT OF WARMER AIR
THAT IT WILL REPLACE. IN THE LATTER PART OF THE EXTENDED FORECAST
PERIOD...IE LATER NEXT WEEK...THE GFS AND ECMWF AND DGEX MODELS ALL
PROG AN UPPER LOW FROM THE PACIFIC TO APPROACH THE COAST CAUSING THE
FLOW ALOFT TO TURN TO THE SOUTHWEST. THIS MAY BRING A SNOW TO SLEET
TO FREEZING RAIN EVENT TO THE CWA...ESPECIALLY IN THE COLUMBIA BASIN
AND YAKIMA/KITTITAS VALLEYS AS WELL AS THE COLUMBIA RIVER GORGE.
WILL NEED TO MONITOR THAT CLOSELY THE NEXT FEW DAYS AS THE FORECAST
BECOMES MORE CERTAIN. 88
AVIATION...12Z TAFS...MOST OF THE LOW CLOUDS AND STRATUS/FOG HAVE
BEEN PUSHED SOUTH BY COLDER AND DRIER AIR FROM THE NORTH. THE ONLY
LOCATION LEFT TO ENCOUNTER LOW CEILINGS AND/OR VISIBILITY IS TAF
KRDM WHERE MVFR OR IFR CONDITIONS MAY STILL OCCUR TODAY...ESPECIALLY
THIS MORNING AT TIMES. ELSEWHERE VFR CONDITIONS ARE EXPECTED WITH
PERHAPS JUST A FEW HIGH CLOUDS. WINDS WILL REMAIN LIGHT AND UNDER 10
KTS THROUGH THE NEXT 24 HOURS. 88
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 37 17 37 22 / 0 0 0 0
ALW 39 20 38 27 / 0 0 0 0
PSC 42 16 37 21 / 0 0 0 0
YKM 41 15 39 20 / 0 0 0 0
HRI 41 15 38 20 / 0 0 0 0
ELN 39 15 38 22 / 0 0 0 0
RDM 39 27 39 20 / 0 0 0 0
LGD 39 14 36 22 / 0 0 0 0
GCD 39 20 40 24 / 0 0 0 0
DLS 42 23 42 24 / 0 0 0 0
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&
THREAT INDEX
TODAY : 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
$$
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