FXUS66 KOTX 260013
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
400 PM PST WED NOV 25 2009
.SYNOPSIS...
WEAK HIGH PRESSURE WILL KEEP THE INLAND NORTHWEST MAINLY DRY
WEDNESDAY NIGHT AND THANKSGIVING DAY. THE EXCEPTION WILL BE THE
CASCADES AND OKANOGAN VALLEY WHERE THERE WILL BE A CHANCE OF LIGHT
RAIN AND HIGH MOUNTAIN SNOW. THE NEXT STORM SYSTEM WILL BRING
MOUNTAIN SNOW AND VALLEY RAIN TO MOST OF THE REGION THURSDAY NIGHT
AND FRIDAY. PRECIPITATION AMOUNTS ARE EXPECTED TO BE LIGHT.
&&
.DISCUSSION...
FOR TONIGHT LIGHT PRECIPITATION WILL MAKE A SLOW ADVANCE INTO THE
NORTHWEST PORTION OF THE FORECAST AREA. BY THANKSGIVING MORNING
THE LEADING EDGE SHOULD BE FROM BLEWITT PASS TO REPUBLIC AND
NORTHPORT. SNOW LEVELS WILL REMAIN HIGH AND THE AMOUNTS ARE
EXPECTED TO BE LIGHT AWAY FROM THE CASCADE CREST. THE HIGH
PRESSURE TO THE SOUTH OF THE REGION WILL INFLUENCE THE WEATHER
ACROSS THE REST OF FORECAST AREA. MID AND HIGH CLOUDS WILL SLOW
THE RADIATIONAL COOLING... BUT STILL EXPECTING LOW CLOUDS AND FOG
TO DEVELOP AFTER 06Z FROM THE WENATCHEE AREA EAST ACROSS PORTIONS
OF THE BASIN AND INTO THE SPOKANE/COEUR D'ALENE AREA. THE RIVER VALLEYS
FROM THE EAST SLOPES ALL THE WAY TO THE SILVER VALLEY OF NORTH
IDAHO WILL ALSO EXPERIENCE LOW CLOUDS AND PATCHY FOG. A REPEAT OF
THE LOW VISIBILITIES ON WEDNESDAY BETWEEN 15Z AND 18Z ARE A GOOD
BET ON THURSDAY AS WELL. JL
THURSDAY THROUGH FRIDAY NIGHT...QUASI-STALLED FRONTAL ZONE DRAPED
OVER THE WEST SIDE OF A DEFLATING RIDGE THAT IS ALSO SLOWLY
MIGRATING TO THE EAST REMAINS IN CLOSE ENOUGH PROXIMITY TO THE
CASCADES AND BRITISH COLUMBIA BORDER TO KEEP MINOR POPS OVER THOSE
LOCATIONS THURSDAY. SHORTWAVE SPINS UP ONE OR MORE INFLECTION
POINTS OFF THE WEST SIDE AND OFFSHORE ON THIS SAME BAROCLINIC BAND
ALLOWING FOR SOME REORIENTATION OF THE FRONTAL FEATURE BEFORE ITS
EXPECTED PASSAGE AS A COLD FRONT AS EARLY AS OVERNIGHT THURSDAY
NIGHT WITH THE IDEA THAT ITS MOST SUBSTANTIAL IMPACT WILL BE FELT
FRIDAY IN TERMS OF THE HIGHEST POPS AND WIND SHIFT SPREAD FROM
WEST TO EAST. WEAK SHORTWAVE RIDGING ALONG WITH THE SHIFT TO
WESTERLY WINDS WHICH DOWNSLOPE OFF THE CASCADES ALLOW FOR A SPREAD
OF SIGNIFICANTLY DRIER POPS FROM WEST TO EAST IN THE WAKE OF THE
FRONT PASSAGE FRIDAY INTO FRIDAY NIGHT. /PELATTI
SATURDAY...IN THE WAKE OF FRIDAY NIGHT'S SHORTWAVE
PASSAGE...A FLAT RIDGE OF HIGH PRESSURE WILL BUILD ACROSS THE PAC
NW. THE RIDGE AXIS WILL SET UP JUST SOUTH OF THE CWA BACKING 850MB
FLOW FROM THE NW TO THE W/SW. THIS WILL TAP INTO THE A RICH >1.00"
PWAT PLUME OFF THE COAST AND BRING INCREASING PRECIPITATION
CHANCES TO THE CASCADES...NORTHEAST MTNS...AND IDAHO PANHANDLE AS
INCREASING ISENTROPIC ASCENT ALONG THE 285-295K SFC COUPLED WITH
FAVORED OROGRAPHIC ASCENT TRANSLATE ACROSS THE REGION. THERE IS
MODEST AGREEMENT AMONGST THE NAM/GFS/GEM WITH LESS REGARDING THE
EC...THUS FORECAST WILL TREND TOWARD THE CONSENSUS.
SUNDAY INTO MONDAY...THE NEXT PACIFIC STORM SYSTEM WILL
APPROACH THE REGION LEADING TO INCR SOUTHWESTERLY FLOW AND
CONTINUED WARM ADVECTION. THIS WILL LIFT THE BEST MOISTURE AND
ISENTROPIC OMEGA NORTHWARD BACK INTO SOUTHERN BC WITH DRIER
CONDITIONS ACROSS THE REGION OUTSIDE LINGERING OROGRAPHIC SHOWERS
ALONG THE NORTHERN MTNS. THERE IS FAIRLY GOOD AGREEMENT AMONGST
THE GFS/EC/GEM THROUGH THE PERIOD WITH RESPECT TO THE
PRECIPITATION FIELDS BUT LARGER DIFFERENCES REGARDING
TEMPERATURES. THIS IS LARGELY DUE TO THE FACT THAT THERE WILL BE A
BIG SURGE OF WARM AIR MOVING ACROSS THE REGION AHEAD OF THE
INCOMING SYSTEM WITH 850MB TEMPERATURES WARMING ABOVE ZERO CELSIUS
AS FAR NORTH AS SPOKANE AND OMAK...NEARING +5 ACROSS THE
SOUTHWESTERN BASIN. THE CHALLENGE THEN DETERMINING WHAT KIND OF
MIXING WE WILL SEE AND WHETHER THE WARMER MIDLEVEL TEMPERATURES
CAP THE SFC WITH STRATUS AND FOG OR MIX DOWN AND JUMP AFTERNOON
HIGHS FROM THE 30'S TO 40'S/50'S. BASED ON CLIMATOLOGY AND LACK OF
STRONG MSLP GRADIENTS...THE FORECAST WILL TREND TOWARD THE LATTER
AND KEEP TEMPS CLOSER TO CLIMO.
THE PACIFIC STORM SYSTEM WILL MOVE ACROSS THE REGION MONDAY
NIGHT INTO TUESDAY DRAGGING A STRONG FRONTAL SYSTEM THROUGH
RESULTING IN THE NEXT BEST CHANCE FOR REGION-WIDE
PRECIPITATION...IE VALLEY RAIN/MOUNTAIN SNOW. THE WINDOW FOR
PRECIPITATION IN THE VALLEYS WILL NOT BE LONG AND WITH MODERATE
WESTERLIES INDICATED IN THE FORECAST MODELS...AREAS IN THE LEE OF
THE CASCADES MAY EXPERIENCE VERY LITTLE TO NO PRECIPITATION WITH
THIS SYSTEM. THE ONE CONCERN WITH THIS WAVE WILL BE WIND
POTENTIAL...ESPECIALLY ACROSS THE LOWER BASIN AND PALOUSE AS THE
12Z GFS IS ALREADY SHOWING 850MB WINDS OF 35-50KTS COUPLED WITH
THE STRONG CAA ACROSS THE AFOREMENTIONED AREAS.
WEDNESDAY INTO THE END OF THE WEEK...MODELS BEGIN TO DIVERGE
IN THIS PERIOD BUT ARE SUGGESTING IN ONE FORM OR ANOTHER THAT THE
RIDGE WILL BEGIN TO REBUILD. THE DISCREPANCY WITHIN THE GUIDANCE
IS THE EASTWARD EXTENT OF THE RIDGE. THERE IS SOME POSSIBILITY
THAT THE RIDGE AXIS WILL REMAIN WEST OF THE CASCADES AND BACKDOOR
COLD FRONTS WILL SNEAK IN FROM THE EAST. ALTHOUGH BOTH SUGGEST
SUFFICIENT CONFIDENCE FOR A DRY FORECAST...THE UNCERTAINTY REMAINS
IN TEMPERATURES AND FOG/STRATUS POTENTIAL. /SB
&&
.AVIATION...
FOG AND STRATUS WILL ONCE AGAIN BE THE MAIN CONCERN ALONG THE
KGEG-KCOE CORRIDOR. LIFR STRATUS WHICH NEVER DISSIPATED THIS
AFTN N OF KCOE HAS ALREADY SLOSHED BACK INTO THE TERMINAL AND
WILL LIKELY REMAIN THERE THROUGH TOMORROW AFTN. FOR
KGEG-KSFF..EXPECT THE INCR HIGH CLDS MOVING INTO REGION WILL NOT
BE ENOUGH TO RETARD OVERNIGHT COOLING AND RETURN TO IFR/LIFR
FG WILL RETURN AFT 15Z. MVFR STRATUS WILL ALSO REMAIN BANKED
INTO THE EAST SLOPES...KEAT UNTIL THE ARRIVAL OF LIGHT PCPN
AFT 20Z THURSDAY. /SB
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 34 42 36 41 30 36 / 0 0 50 50 20 20
COEUR D'ALENE 34 43 35 41 31 38 / 0 0 50 80 40 20
PULLMAN 35 45 36 40 30 37 / 0 0 30 70 40 30
LEWISTON 38 49 39 47 34 41 / 0 0 30 50 30 30
COLVILLE 36 41 34 42 31 39 / 20 20 60 60 20 10
SANDPOINT 31 37 35 38 31 34 / 10 10 50 80 40 30
KELLOGG 34 41 35 37 29 33 / 0 0 40 90 50 50
MOSES LAKE 31 45 34 46 29 42 / 10 10 40 20 10 10
WENATCHEE 37 44 34 45 33 43 / 20 20 40 10 10 10
OMAK 36 44 33 44 28 42 / 50 50 60 30 20 10
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...NONE.
&&
$$
