FXUS66 KPDT 282349 AAA
AFDPDT
AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE PENDLETON OR
349 PM PST SAT NOV 28 2009
UPDATED AVIATION DISCUSSION
.SHORT TERM...TONIGHT THROUGH TUESDAY...A RIDGE WILL REMAIN IN PLACE
OVER THE PACIFIC NORTHWEST FOR THE NEXT FEW DAYS. A FRONT IS RIDING
OVER THE TOP OF THE RIDGE BUT THE MAIN ENERGY AND MOISTURE IS BEING
SENT INTO BRITISH COLUMBIA. HAVE KEPT A SLIGHT CHANCE OF RAIN AND
SNOW TONIGHT ALONG THE WASHINGTON CASCADE CREST BUT CURRENT RADAR
RETURNS ON NEIGHBORING RADARS ARE LOOKING FAIRLY WEAK SO DO NOT
EXPECT MUCH PRECIPITATION TO REACH OUR AREA. THE MAIN IMPACT WILL BE
MOSTLY CLOUDY SKIES OVER THE NORTHERN HALF OF THE AREA. THE CLOUD
COVER WILL TEND TO INHIBIT FOG DEVELOPMENT AND KEEP TEMPERATURES UP
SO HAVE RAISED OVERNIGHT TEMPERATURES A DEGREE OR TWO FROM LAST
NIGHT. AS FOR FOG...MODEL SOUNDINGS STILL HINT AT THE POSSIBILITY SO
HAVE KEPT PATCHY FOG AND FREEZING FOG ALONG RIVERS IN THE COLUMBIA
BASIN. TOMORROW WILL HAVE FAIR WEATHER WITH HIGH PRESSURE IN PLACE
AND NO DISTURBANCES MOVING THROUGH. TEMPERATURES WILL RISE A FEW
DEGREES WITH A WARMER AIR MASS IN PLACE. GENERALLY LIGHT WINDS WILL
CONTINUE. SUNDAY AND SUNDAY NIGHT WILL SEE CONTINUED FAIR WEATHER AS
THE RIDGE REMAINS ENTRENCHED. FOG WILL LIKELY BE MORE WIDESPREAD SO
HAVE SPREAD PATCHY FOG OVER THE ENTIRE COLUMBIA BASIN...COLUMBIA
GORGE AND SURROUNDING VALLEYS. HAVE KEPT NIGHT TIME TEMPERATURES UP
A DEGREE OR TWO AND DAYTIME TEMPERATURES DOWN A COUPLE OF DEGREES
DUE TO THE FOG. BY MONDAY...MODELS SHOW A DISTURBANCE MOVING THROUGH
BUT DIFFER SOMEWHAT ON THE DETAILS. IN GENERAL THEY SHOW A FRONT
APPROACHING THE COAST MONDAY. THE ECMWF SPLITS OFF A LOW WHICH HEADS
TO OUR SOUTH WHILE THE FRONT WEAKENS AND MOVES MAINLY NORTH OF US.
THE NAM AND ECMWF DO NOT FORM A LOW BUT SEND A WEAKENING FRONT
THROUGH THE AREA. HAVE PUT SHOWERS INTO THE CASCADES MONDAY NIGHT
AND INTO THE EASTERN MOUNTAINS TUESDAY. PRECIPITATION AMOUNTS LOOK
LIGHT IN ANY EVENT AND MOST OF THE POPULATED AREAS LOOK DRY. HAVE
KEPT FOG OUT OF THE FORECAST MONDAY NIGHT AND TUESDAY AS THE FRONT
SHOULD STIR UP THE ATMOSPHERE ENOUGH TO MIX OUT THE INVERSION AND
PREVENT FOG FORMATION. PERRY
.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...DECENT AGREEMENT THAT
THE UPPER RIDGE WILL BOUNCE BACK UP ACROSS THE WESTERN U.S. AFTER
THE WEAK SYSTEM MONDAY/TUESDAY. THUS WILL CONTINUE DRY CONDITIONS
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. AT THIS TIME WILL LOOK FOR
SOME PATCHY BASIN FOG AND LOW CLOUDS TO REDEVELOP WEDNESDAY NIGHT AS
WARM AIR AROUND 850 MB ADVECTS INTO THE REGION TO STRENGTHEN
INVERSIONS. UNCERTAINTY IN FORECAST TRENDS INCREASES SUBSTANTIALLY
FROM THURSDAY ONWARD. A DISTURBANCE LOOKS TO MOVE INTO THE REGION
EITHER THURSDAY OR FRIDAY. THE DEPTH...SPEED AND FORM THIS
DISTURBANCE WILL TAKE ALSO HAS BEEN CHANGING WITH EACH OPERATIONAL
RUN OF THE VARIOUS MID-RANGE MODELS. DUE TO THIS UNCERTAINTY WILL
INTRODUCE SOME SLIGHT CHANCE POPS TO THE MOUNTAINS THURSDAY THROUGH
FRIDAY...WHILE CONTINUING SIMILAR POP FORECASTS CURRENTLY OUT FOR
FRIDAY NIGHT AND SATURDAY. WILL SHOW A GRADUAL COOLING OF TEMPS
(MAINLY HIGHS) THURSDAY THROUGH SATURDAY TO HINT AT THE POSSIBILITY
THAT A COOLER NORTH FLOW MAY SET UP BEHIND THIS DISTURBANCE. ALSO
WILL REMOVE MENTION OF BASIN FOG FRIDAY AFTERNOON AND SATURDAY DUE
TO THE POTENTIAL AIR MASS CHANGE AND A LACK OF ATMOSPHERIC
STABILITY. 90
&&
.AVIATION...00Z TAFS...VFR CONDITIONS SHOULD PREVAIL AT ALL TAF
SITES THROUGH THIS EVENING WITH CIGS AT 11000 FT AGL OR HIGHER. CIGS
SHOULD THICKEN AND LOWER TO BETWEEN 5000 AND 9000 FT AGL AFTER 29/06
UTC AT ALL SITES EXCEPT KRDM. THIS CLOUD COVER SHOULD HAMPER
DEVELOPMENT OF LOW LEVEL INVERSIONS...STRATUS AND FOG IN THE
COLUMBIA BASIN AND COLUMBIA RIVER GORGE FOR A GOOD PORTION OF THE
OVERNIGHT PERIOD. THIS THICKER CLOUD COVER WILL BREAK UP OR THIN
AFTER 29/12 UTC. THUS WILL HINT AT SOME FOG AND LOW CLOUDINESS AT
KPSC...KYKM AND KALW AT SOME POINT AROUND OR AFTER 12 UTC. WILL KEEP
MENTION OF MVFR CIGS AT KDLS GOING FOR NOW. WILL GO WITH A FOG MIX
OUT TIME OF AROUND 29/18 UTC AT MOST AFFECTED SITES...THOUGH IT
COULD EASILY TAKE LONGER. SUSTAINED WINDS SHOULD RUN 10 KTS OR LESS
THROUGH THE PERIOD. 90
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 32 47 33 45 / 0 0 0 10
ALW 36 49 36 45 / 0 0 0 10
PSC 31 47 30 45 / 0 0 0 0
YKM 30 48 29 46 / 0 0 0 10
HRI 29 47 29 45 / 0 0 0 0
ELN 33 49 31 45 / 10 0 0 10
RDM 24 49 26 48 / 0 0 0 0
LGD 28 45 31 44 / 0 0 0 0
GCD 29 46 32 48 / 0 0 0 0
DLS 34 49 33 47 / 10 0 0 10
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
&&
THREAT INDEX
SUNDAY : GREEN
MONDAY : GREEN
TUESDAY : 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
$$
83/90/90
