AREA FORECAST DISCUSSION
FXUS66 KOTX 242355
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
355 PM PST TUE NOV 24 2009
.SYNOPSIS...
A WEAK FRONTAL SYSTEM WILL BRING SOME VERY LIGHT PRECIPITATION TO
THE AREA TONIGHT. THE THANKSGIVING HOLIDAY WILL BE CLOUDY WITH
LIGHT PRECIPITATION MOVING IN FROM THE WEST LATE IN THE DAY. ON
FRIDAY A COLD FRONT WILL PASS THROUGH WITH ANOTHER REASONABLE
CHANCE OF MOUNTAIN SNOW AND VALLEY RAIN OR SNOW. CONDITIONS WILL
REMAIN CLOUDY AND UNSETTLED INTO NEXT WEEKEND.
&&
.DISCUSSION...
TONIGHT THROUGH WEDNESDAY NIGHT...THE REGION WILL BE UNDER A
SHORTWAVE RIDGE THIS PERIOD WITH LOW LEVEL WINDS BACKING FROM WEST
TO SOUTHWEST...PUSHING WARMER AIR INTO THE FORECAST AREA. THERE WILL
BE SUFFICIENT MOISTURE RIDING ALONG THE RIDGE TO KEEP THE THREAT OF
PRECIPITATION ALONG THE CASCADE CREST AND ACROSS THE NORTHERN THIRD
OF THE FORECAST AREA THROUGH WEDNESDAY NIGHT. PERSISTENT MOIST
ISENTROPIC UPGLIDE WILL COMBINE WITH OROGRAPHIC ASCENT TO BRING A
SWATH OF LIGHT PRECIPITATION FROM THE CASCADES...SPREADING CROSS THE
NORTHERN ZONES. PRECIPITATION WILL BE LIGHT...WITH SOME AREAS NORTH
OF I-90 SEEING SPRINKLES BUT NO MEASURABLE PRECIP. SNOW LEVELS WILL
BE ON THE RISE WITH ACCUMULATION SNOW LIMITED TO THE HIGH MTS. LOW
LEVEL MOISTURE WILL BE ABUNDANT AND LIGHT WINDS TONIGHT WILL FOSTER
PATCHY FOG IN SOME OF THE NORTHEAST VALLEYS AS WELL AS SOME OF THE
WESTERN VALLEYS. THE SPOKANE AREA WILL LIKELY SEE LOW STRATUS FORM
IN LIGHT UPSLOPE FLOW AND SOME FOG FORMATION IS POSSIBLE. DOWN
SLOPING WINDS WILL KEEP THE FOG AND LOW STRATUS OUT OF THE PALOUSE
AND EASTERN BASIN. FOG WILL BE MORE WIDESPREAD WEDNESDAY NIGHT AS
WINDS LIGHTEN FURTHER. DAYTIME TEMPERATURES WILL BE MILD WITH HIGHS
NEAR 50 DEGREES FOR THE SOUTHERN VALLEYS. OVERNIGHT TEMPERATURES
WILL BE NEAR SEASONAL NORMALS. /KELCH
THANKSGIVING THROUGH SATURDAY...THE 12Z RUNS OF THE MEDIUM RANGE
MODELS HAVE COME INTO BETTER AGREEMENT WITH THE LOW PRESSURE
SYSTEM EXPECTED TO ARRIVE THURSDAY NIGHT INTO FRIDAY. THE
GFS...ECMWF...AND THE BULK OF THE GFS ENSEMBLE MEMBERS FORECAST
THE TRACK OF THE SURFACE LOW FROM NORTHWEST WASHINGTON THROUGH
SOUTHERN BRITISH COLUMBIA. THIS TRACK WILL KEEP EASTERN WASHINGTON
AND NORTHERN IDAHO IN THE WARM SECTOR THROUGH FRIDAY MORNING. NOT
UNTIL MID DAY FRIDAY ARE SNOW LEVELS EXPECTED TO FALL BELOW 3000
FEET. BY FRIDAY AFTERNOON...MODERATE SNOW ACCUMULATIONS WILL HAVE
THE POTENTIAL TO COMPLICATE HOLIDAY TRAVEL THROUGH THE PASSES IN
THE CASCADES AND NORTHERN IDAHO.
THE POTENTIAL FOR A SECONDARY SHORTWAVE FRIDAY NIGHT INTO SATURDAY
MORNING MAY COMPLICATE HOLIDAY TRAVEL FURTHER. THE 18Z GFS AND THE
12Z ECMWF ARE IN GOOD AGREEMENT THAT A PROGRESSIVE SHORTWAVE WILL
TRACK ACROSS THE COLUMBIA BASIN IN THE NORTHWEST FLOW. SINCE THIS
WAVE WILL BE WELL BEHIND OUR COLD FRONT...SNOW LEVELS WILL LIKELY
BE DOWN TO THE VALLEY FLOORS IN THE BASIN...PALOUSE...AND SPOKANE
VICINITY. WITH 500MB TEMPERATURES PROGGED TO BE -30C OR
COLDER...CONVECTIVE BANDING ALONG AND NORTH OF THE MID LEVEL LOW
CENTER COULD CONTRIBUTE TO LOCALIZED AREAS OF SIGNIFICANT SNOW.
SINCE THE TRACK OF THIS FEATURE IS HIGHLY UNCERTAIN...
PRECIPITATION CHANCES HAVE BEEN LIMITED TO 30 PERCENT OR LESS.
HOWEVER...THIS QUICK MOVING UPPER LEVEL SYSTEM BEARS WATCHING
FRIDAY NIGHT INTO SATURDAY MORNING. /GKOCH
SUNDAY THROUGH TUESDAY...MODELS AGREE ON AN UPPER LEVEL RIDGE
RESIDING OVER THE WESTERN US SUNDAY. ALL MODELS SHOW THE UPPER
LEVEL ENERGY AND JET REMAINING TO THE NORTH IN CANADA...BUT HAS
SOME DECENT QPF ALONG THE US/CANADIAN BORDER. KEPT A SLIGHT CHANCE
MENTION IN THE MOUNTAINS THROUGH THE PERIOD TO ACCOUNT FOR
OROGRAPHIC FLOW. MONDAY/TUESDAY MODELS ARE HINTING AT A TROUGH MOVING
ACROSS THE US/CANADIAN BORDER. TRENDED CHANCE OF PRECIP UP TOWARDS
CLIMO FOR EXTREME EASTERN WA AND NORTH ID. TEMPERATURES WILL BE
AROUND AVERAGE FOR THIS TIME OF THE YEAR. /NISBET
&&
.AVIATION...
A WEAK RIDGE OF HIGH PRESSURE WILL BUILD OVER EASTERN WASHINGTON AND
NORTHERN IDAHO TONIGHT AND TOMORROW. SOME LIGHT RAIN AND SNOW
SHOWERS WILL LINGER OVER THE MOUNTAINS OBSCURING THE MOUNTAINS. LOW
CLOUDS WILL LIKELY FORM IN THE SPOKANE AND COEUR D`ALENE AREAS
BETWEEN 09Z AND 12Z AND LINGER THROUGH TOMORROW AFTERNOON. CEILINGS
WILL RANGE FROM 500 FEET TO 2000 FEET. LOW CEILINGS WILL ALSO IMPACT
THE WENATCHEE AREA THROUGH TOMORROW AFTERNOON. /GKOCH
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 34 45 34 42 36 39 / 10 0 10 10 40 60
COEUR D`ALENE 34 45 33 42 35 39 / 10 10 10 10 40 60
PULLMAN 34 47 34 46 35 38 / 10 0 0 10 30 50
LEWISTON 36 51 37 49 39 45 / 10 0 0 10 10 30
COLVILLE 33 44 34 41 34 41 / 20 20 30 30 50 60
SANDPOINT 31 41 32 38 35 37 / 20 10 20 10 30 70
KELLOGG 33 45 32 41 35 35 / 30 10 10 10 30 80
MOSES LAKE 33 48 33 44 34 45 / 10 0 10 20 40 20
WENATCHEE 35 46 35 43 34 44 / 10 10 30 20 30 10
OMAK 34 45 34 42 32 41 / 20 10 40 50 50 30
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...NONE.
&&