FXUS66 KPDT 251024
AFDPDT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
225 AM PST FRI DEC 25 2009
.SHORT TERM...TODAY THROUGH SUNDAY...HIGH PRESSURE WILL REMAIN IN
CONTROL OF THE WEATHER OVER THE REGION ON THIS CHRISTMAS DAY AND
WILL CONTINUE INTO THE WEEKEND. IT WILL SLOWLY SHIFT EASTWARD WHICH
WILL CAUSE AN INCREASE IN MID LEVEL SUBSIDENCE AND STRENGTHEN THE
SURFACE BASED INVERSIONS...ESPECIALLY OVER THE COLUMBIA BASIN AND
ADJACENT VALLEYS/LOW LANDS. AS SUCH THE STRATUS AND FOG LAYER
CURRENTLY OVER THE FORECAST AREA WILL LIKELY EXPAND OVER THE NEXT
TWO DAYS. DENSE FOG HAS RECENTLY BEEN RECORDED OVER LOCATIONS WHERE
THE STRATUS LAYER MEETS THE TERRAIN IN LOCATIONS SUCH AS REDMOND AND
BEND IN CENTRAL OREGON AND LIKELY IN OTHER LOCATIONS AS WELL. IN THE
LOWEST ELEVATIONS IT WILL BE MAINLY A LOW STRATUS CLOUD LAYER WHILE
ON THE EDGES THERE WILL BE MORE DENSE FOG AS THE STRATUS LAYER MEETS
THE TERRAIN. THIS WILL MOSTLY AFFECT HIGHWAYS AND OTHER ROADWAYS
THAT RISE IN ELEVATION AS THEY CROSS A MOUNTAIN RANGE OR PASSES SUCH
AS INTERSTATE 84 ON CABBAGE HILL AND HIGHWAY 395 AND 97 IN CENTRAL
AND EASTERN OREGON WHICH BOTH CROSS AT LEAST SEVERAL MOUNTAIN RANGES
OR HIGH PLATEAUS. MAY NEED TO ISSUE A DENSE FOG ADVISORY BUT FOR NOW
HAVE COVERED IT WITH NOWCASTS AND IN THE ZONES/GRIDS. IN THE
FOG/STRATUS FREE AREAS CAN EXPECT MOSTLY CLEAR SKIES EXCEPT FOR SOME
HIGH THIN CLOUDS AT TIMES AND SLOWLY MODERATING TEMPERATURES OF A
DEGREE OR TWO EACH DAY THROUGH SATURDAY. ON SUNDAY A WEAK PACIFIC
WEATHER SYSTEM WILL TRY TO PENETRATE THE UPPER RIDGE BUT WILL WEAKEN
AS IT MOVES INLAND. HOWEVER THERE STILL MAY BE A FEW LIGHT RAIN OR
SNOW SHOWERS OVER THE CASCADE EAST SLOPES...MAINLY IN CENTRAL AND
NORTH CENTRAL OREGON. ELSEWHERE WILL REMAIN PRECIPITATION FREE
THROUGH SUNDAY. 88
.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...VERY FEW CHANGES WERE
MADE TO THE EXTENDED FORECAST BECAUSE GREAT UNCERTAINTY STILL EXISTS
AMONG THE MODELS. HOWEVER...PRECIPITATION CHANCES HAVE BEEN LOWERED
ON SUNDAY NIGHT AND MONDAY SINCE BOTH THE ECMWF AND THE GFS INDICATE
THAT WEAK HIGH PRESSURE WILL REMAIN OVER THE AREA DURING THIS
PERIOD. ALTHOUGH A FEW SHOWERS MAY BE POSSIBLE ALONG THE CASCADE
CREST OR IN CENTRAL OREGON...CONFIDENCE IS LOW THAT THERE WILL BE
MUCH...IF ANY...MEASURABLE PRECIPITATION. THE PRESENCE OF MID-LEVEL
RIDGING WILL ALSO ENSURE THAT THE SURFACE INVERSIONS REMAIN IN PLACE
OVER THE COLUMBIA BASIN...THUS FOG AND LOW STRATUS CAN BE EXPECTED
TO PERSIST THROUGH AT LEAST MONDAY MORNING.
THE GFS BECOMES MORE ZONAL BY TUESDAY...BRINGING A SERIES OF WET
DISTURBANCES THROUGH THE REGION DURING THE LATER HALF OF THE WEEK.
THE ECMWF BRINGS ONE SYSTEM INTO THE AREA ON TUESDAY NIGHT...THEN
BUILDS A STRONG RIDGE OVER THE REGION ON WEDNESDAY BEFORE BRINGING A
MORE POTENT SYSTEM INLAND ON FRIDAY. GIVEN SUCH UNCERTAINTY HAVE
KEPT A CHANCE OF RAIN OR SNOW IN THE FORECAST TUESDAY THROUGH
FRIDAY. 82
&&
.AVIATION...12Z TAFS...STRONG LOW LEVEL INVERSIONS...WITH TOPS
RANGING FROM NEAR 3000 FT AT KALW...KPSC AND KPDT TO NEAR 4000 FT AT
KYKM...KDLS AND KRDM...WILL PERSIST THROUGH THE NEXT 24 HOURS. THUS
WIDESPREAD MVFR OR LOWER CONDITIONS CAN BE EXPECTED AT ALL TAF
SITES. LOCAL LIFR AND VLIFR CONDITIONS ARE POSSIBLE AT ANY
TIME...ESPECIALLY AT KRDM. SURFACE WINDS WILL REMAIN LESS THAN 10
KTS. 82
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 27 19 29 17 / 0 0 0 0
ALW 26 20 29 19 / 0 0 0 0
PSC 29 20 31 19 / 0 0 0 10
YKM 28 18 31 16 / 0 0 0 10
HRI 30 19 30 17 / 0 0 0 10
ELN 28 17 30 18 / 0 0 0 10
RDM 37 14 37 20 / 0 0 0 10
LGD 31 15 31 16 / 0 0 0 0
GCD 36 17 36 16 / 0 0 0 10
DLS 33 22 35 21 / 0 0 0 10
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL 4 PM PST SATURDAY FOR ORZ041>044-
049-501-504-505.
WA...AIR STAGNATION ADVISORY UNTIL 4 PM PST SATURDAY FOR WAZ024-
026>029-501-502.
&&
THREAT INDEX
TODAY : GREEN
SATURDAY : GREEN
SUNDAY : 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
$$
88/82/82
