FXUS66 KOTX 111134
AFDOTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
335 AM PST THU MAR 11 2010

.SYNOPSIS...
COOL WET WEATHER WILL RETURN TO THE INLAND NORTHWEST BEGINNING
TODAY AND LASTING INTO EARLY SATURDAY. BY SUNDAY AND INTO EARLY
NEXT WEEK TEMPERATURES WILL RISE ABOVE NORMAL WITH MAINLY DRY
CONDITIONS.

&&

.DISCUSSION...
TODAY AND TONIGHT...THE NEXT STRONG AND MOIST PACIFIC STORM SYSTEM
IS READILY EVIDENT ON SATELLITE AND BEGINNING TO INVADE THE
FORECAST AREA. LATEST MODELS ARE IN GOOD OVERALL AGREEMENT WITH THE
CHARACTER OF THIS STORM. VORTICITY AND JET DYNAMIC SUPPORT WILL BE
RELATIVELY WEAK WITH GENERALLY NEBULOUS SURFACE FRONTAL
FEATURES. THE MAIN PRECIPITATION MECHANISM WILL BE A VERY WELL
DIRECTED AND DEEP PACIFIC MOISTURE FEED ENHANCING ISENTROPICALLY
OVER THE FORECAST AREA THROUGH TODAY AND INTO THIS EVENING.
ANTICIPATE AN ONSET OF LIGHT STRATIFORM SNOW THIS MORNING OVER THE
WESTERN ZONES...WITH PRECIPITATION SPREADING EAST AS THE DAY WEARS
ON. JUST ABOUT EVERY LOCATION NORTH OF INTERSTATE 90 WILL
EXPERIENCE AN ONSET OF PRECIPITATION TODAY...ALTHOUGH OVER THE
EASTERN ZONES VALLEY RAIN AND MOUNTAIN SNOW WILL LIKELY HOLD OFF
UNTIL MID TO LATE AFTERNOON WITH MAINLY THICKENING AND LOWERING
CLOUDS PRIOR AS THE ATMOSPHERIC MOISTENING PROCESS MATURES.

BASED ON MODEL SOUNDINGS CROSS CHECKED FOR PLAUSIBILITY AGAINST
CURRENT TEMP/DEW POINT OBSERVATIONS...AND LIKELIHOOD OF A MORNING
ONSET...THERE IS HIGH CONFIDENCE THAT INITIALLY ALL PRECIPITATION
WILL BE SNOW IN THE FAR WESTERN/DEEP BASIN ZONES REGARDLESS OF
ELEVATION. HOWEVER...AT THE LOWER ELEVATIONS OF THE COLUMBIA AND
OKANOGAN RIVER VALLEYS THERE PROBABLY WILL NOT BE ANY SIGNIFICANT
ACCUMULATION BEYOND GRASSY SURFACES BEFORE A CHANGEOVER TO RAIN
OR A WET MIX LATER THIS MORNING. HOWEVER...ELEVATED TERRAIN ON
THE SHOULDERS OF THE OKANOGAN VALLEY MAY EXPERIENCE 1 TO 3 INCHES.
A SNOW ADVISORY WILL BE ISSUED WITH THE MORNING PACKAGE FOR ABOVE
1500 FEET ELEVATION TO COMPLIMENT THE INHERITED ADVISORIES FOR THE
OKANOGAN HIGHLANDS AND THE EAST SLOPES CASCADES...WHICH STILL
APPEAR PLAUSIBLE AND WARRANTED.

TONIGHT THE OVERALL FLOW WILL BECOME MORE SOUTHERLY AS A DEEP
PARENT TROUGH IN THE GULF OF ALASKA APPROACHES THE COAST. THIS
WILL EFFECTIVELY ALLOW SNOW LEVELS TO RISE SIGNIFICANTLY AND LEAD
TO A UNIVERSAL VALLEY RAIN AND MOUNTAIN SNOW EVENT THROUGH THE
REST OF THE EVENT...WITH ADDITIONAL PRECIPITATION TONIGHT MAINLY
CONCENTRATED OVER THE MOUNTAINS NORTH OF THE BASIN WHERE
OROGRAPGHY WILL BE A DOMINANT FACTOR...AS WELL AS IN THE CASCADES
WHICH WILL BE STUCK IN THE INCREASINGLY MERIDIONAL MOISTURE AXIS.
/FUGAZZI

FRIDAY THROUGH SUNDAY NIGHT...THE WEATHER WILL REMAIN QUITE
ACTIVE FRIDAY AND FRIDAY NIGHT AS A DEEP AREA OF LOW PRESSURE
CONTINUES TO SPIN OFF THE WA COAST FEEDING SUBTROPICAL MOISTURE
INTO THE INLAND NW. THE SYSTEM WILL TRACK INLAND FRIDAY NIGHT
USHERING A STRONG COLD FRONT ACROSS THE REGION AND CONTINUED
HIGH PRECIPITATION CHANCES. HIGH PRESSURE WILL STRENGTHEN OVER THE
WEEKEND BRINGING A DRYING TREND ALONG WITH NEAR TO ABOVE NORMAL
TEMPERATURES.

WATER VAPOR IMAGERY THIS EVENING SHOWS A LARGE COLD CORE
TROUGH BECOMING ESTABLISHED OVER THE GULF OF ALASKA WITH AN
ATMOSPHERIC RIVER OF NEAR 1.00" PRECIPITABLE WATER AIMED TOWARD
THE PAC NW. THE FEATURE OF NOTE FOR DRIVING OUR WEATHER FRIDAY
AND FRIDAY NIGHT WILL BE THE SWIRL EVIDENT ALONG 155W/45N. OVER
THE NEXT 24 HOURS...WE EXPECT THE JET STREAK DOWNSTREAM OF THE
MAIN TROUGH AXIS TO WEAKEN AS ANOTHER 150KT UPPER-LEVEL SPEED MAX
DIVES DOWN THE BACKSIDE OF THE TROUGH. THIS WILL RESULT IN A
SIGNIFICANT DEEPENING OF THE WAVE WITH GFS/NAM/EC SHOWING A
SECONDARY AREA OF STRONG CYCLOGENESIS AND EVOLUTION OF A DOUBLE
BARREL SFC LOW STRETCHING FROM 140W TO THE WA COAST. THIS
DEEPENING OF THE CYCLONE CLOSE TO THE COAST WILL RESULT
IN TIGHTENING PRESSURE GRADIENTS AND MODERATE SOUTHERLY FLOW WILL
BECOME ESTABLISHED OVER THE INLAND NW. 85H WINDS WILL BE ON THE
ORDER OF 40KTS ALONG THE SOUTHERN COLUMBIA BASIN AND NORTHERN BLUE MTNS
TO 25KTS ALONG THE CANADIAN BORDER. THIS MILD SOUTHERLY FLOW WILL
CONTINUE TO SUPPORT ISENTROPIC UPGLIDE WITHIN THE 290-300K REGION-
WIDE. EVEN THOUGH MOISTURE TRANSPORT IS NEARLY UNIFORM ACROSS THE
REGION...LOCALIZED LOW- LEVEL DRYING DUE TO DOWNSLOPING EFFECTS
WILL KEEP POPS LOWEST TO THE SOUTH AND HIGH ALONG AND NORTH OF A
LINE FROM WENATCHEE TO COLVILLE. I ANTICIPATE WE WILL SEE A FEW
BREAKS IN THE CLOUDS ACROSS SE WASHINGTON DOWN INTO THE CAMAS
PRAIRIE AND PALOUSE. WITH 85H TEMPERATURES CLOSING IN ON +5
CELSIUS...TEMPERATURES HAVE BEEN RAISED SEVERAL DEGREES. THE
MODERATE SOUTHERLY FLOW WILL ALLOW FOR A CONTINUED CLIMB IN SNOW
LEVELS...ESPECIALLY OVER THE NORTHWEST WHERE 3500' TEMPERATURES
WILL BE WARMING NEAR 0 CELSIUS. THIS WILL LIKELY END THE THREAT
FOR SNOW ACCUMULATIONS IN ALL VALLEYS.

THE LOW WILL TRACK INLAND FRIDAY NIGHT USHERING A STRONG COLD
FRONT ACROSS THE REGION. THERE IS GOOD AGREEMENT AMONGST THE
FORECAST MODELS AND CONFIDENCE IS GENERALLY HIGH. THE COLD FRONT
WILL BE ALONG THE CASCADES NEAR 00Z THEN CLOSING IN ON THE ID
PANHANDLE 06Z BEFORE SLOWING AND TRICKLING INTO WESTERN MONTANA
NEAR 12Z. THE SLOWING IS LARGELY DUE TO THE SYNOPTIC SCALE WAVE
UNDERGOING MERIDIONAL STRETCHING WHILE MOVING ONSHORE.
THIS IS OLD NEWS HERE IN THE INLAND NW AS NEARLY ALL SYSTEMS
HAVE ACTED IN THIS MANNER...HOWEVER IN CONTRAST TO THE WEAK
FRONTS OF LATE...THIS WILL FRONT WILL BE MOVING INTO AN ABNORMALLY
MOIST AIR MASS...HAVE PLENTY OF INITIAL MOMENTUM AND
BAROCLINICITY TO BRING MODERATE PCPN AMTS FROM WEST TO EAST.
THIS IS REALLY EVIDENT VIA ALL GUIDANCE WHICH SHOWS A DRASTIC
COOLING OF 85H TEMPERATURES FROM NEAR +5 CELSIUS OVER THE CAMAS
PRAIRIE AND CENTRAL ID MTNS TO -3 CELSIUS BY 12Z SATURDAY. AS A RESULT
THERE IS THE POTENTIAL FOR POST-FRONTAL UPSLOPE PCPN TO QUICKLY
CHANGE OVER TO SNOW AND POTENTIAL FOR LIGHT ACCUMULATIONS. I WOULD
NOT COMPLETELY COUNT OUT LOW-END ADVISORY AMTS FOR THE CENTRAL
PANHANDLE MTNS (PARTICULARLY IN THE DEARY AREA)...CAMAS
PRAIRIE...AND NORTHERN BLUE MTNS WHERE W/NW LOW- LEVEL FLOW TENDS
TO ENHANCE POST-FRONTAL PCPN.

SATURDAY THROUGH SUNDAY NIGHT...THE TROUGH AXIS WILL TRACK
THROUGH THE INLAND NW WITH HIGH PRESSURE QUICKLY BUILDING ON ITS
HEELS. THE COOLING ALOFT COMBINED WITH RESIDUAL BL MOISTURE AND
SFC HEATING ON SATURDAY WILL LIKELY RESULT IN CONDITIONAL
INSTABILITY TO PROMOTE WIDESPREAD CUMULUS FIELDS BY MIDDAY
SATURDAY. HOWEVER...EXPECT THE BULK OF THE SHOWER ACTIVITY TO
REMAIN CONFINED TO THE ID PANHANDLE OR JUST SLIGHTLY OVER THE
BORDER IN EXTREME EASTERN WA. THE SHORTWAVE RIDGING BUILDING ON
ITS HEELS WILL CAP SHWR ACTIVITY OVER THE CASCADES AND WESTERN
BASIN THROUGH THE DAY. BY THE TIME THE WARMING ALOFT REACHES
IDAHO...IT WILL BE SUNSET AND INSTABILITY WILL NATURALLY BE ON THE
DECREASE. HIGH PRESSURE WILL DOMINATE SUNDAY BRINGING DRY
CONDITIONS AND TEMPERATURES NEAR TO SLIGHTLY ABOVE NORMAL. /SB

FOR MONDAY THROUGH THURSDAY...A HIGH AMPLITUDE UPPER LEVEL TROUGH
WILL INITIALLY BE TO OUR WEST OVER THE EASTERN PACIFIC...WHICH
WILL RESULT IN DEEP SOUTHWEST FLOW ACROSS THE INLAND NORTHWEST.
ABOVE NORMAL TEMPERATURES AND SPRINGLIKE WEATHER WILL OCCUR ON
MONDAY AND TUESDAY REGION WIDE. HOWEVER...THE MODELS ARE IN FAIRLY
GOOD AGREEMENT THAT THE AFOREMENTIONED SHORTWAVE TROUGH WILL SWING
THROUGH THE REGION SOME TIME LATE TUESDAY INTO EARLY WEDNESDAY. AS
A RESULT...TEMPERATURES WERE ADJUSTED DOWN FOR WEDNESDAY AND
THURSDAY AND POPS WERE INCREASED FOR TUESDAY NIGHT AND WEDNESDAY.
THERE IS SOME CONCERN THAT THIS TROUGH WILL SPLIT AND WEAKEN...GIVEN
HOW SIMILAR THE UPPER LEVEL PATTERN EARLY NEXT WEEK WILL BE TO THE
MEAN UPPER LEVEL PATTERN OF THE PAST THREE MONTHS. HOWEVER...THE
FACT BOTH MODELS SEEM TO BE TRENDING TOWARDS THE MORE COMPACT
UPPER LEVEL TROUGH AND PROGRESSIVE PATTERN BRINGS AT LEAST A
LITTLE INCREASE IN CONFIDENCE. /NEUMAN

&&

.AVIATION...
A MOIST PACIFIC STORM SYSTEM WILL SPREAD MAINLY VALLEY RAIN AND
MOUNTAIN SNOW ACROSS THE REGION FROM WEST TO EAST TODAY. INITIALLY
PRECIPITATION AT KEAT WILL BE SNOW THIS MORNING WITH MVFR CEILINGS
AND VIS...CHANGEING TO RAIN AFTER 18Z. SOME LIGHT EARLY MORNING SNOW
IS ALSO POSSIBLE AT KMWH...WITH INTERMITTANT MVFR CEILING RAIN
SHOWERS AFTER 18Z. ACROSS THE EASTERN TAF SITES VFR CEILINGS WILL
THICKEN AND LOWER THIS MORNING WITH AN ONSET OF RAIN IN THE
AFTERNOON HOURS. ONCE PRECIPITATION BEGINS AT ANY PARTICULAR TAF
SITE...MVFR CEILINGS WILL BE COMMON WITH WIDESPREAD PRECIPITATION
CONTINUING THROUGH TONIGHT AND MERGING CLOUD LAYERS TO 20 KFT.
MOUNTAINS SURROUNDING THE BASIN WILL BE UNIVERSALLY OBSCURED THROUGH
12Z THURSDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 42 37 53 33 47 30 / 60 60 40 80 20 10
COEUR D'ALENE 43 36 53 32 45 29 / 50 60 30 80 30 10
PULLMAN 46 34 58 32 46 29 / 10 30 40 80 30 10
LEWISTON 54 38 61 36 51 33 / 0 20 10 70 20 0
COLVILLE 42 34 48 33 48 28 / 90 100 80 70 20 10
SANDPOINT 42 34 50 32 44 28 / 60 80 40 80 30 10
KELLOGG 46 36 54 32 42 28 / 10 30 10 80 50 10
MOSES LAKE 46 36 58 33 53 29 / 50 50 90 40 10 0
WENATCHEE 43 34 49 33 51 32 / 60 50 80 20 10 0
OMAK 38 34 47 30 48 29 / 80 90 90 20 10 0

&&

.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...WINTER WEATHER ADVISORY UNTIL 10 AM PST FRIDAY EAST SLOPES
NORTHERN CASCADES...OKANOGAN HIGHLANDS.

WINTER WEATHER ADVISORY UNTIL 4 PM PST THIS AFTERNOON ABOVE 1500
FEET FOR THE OKANOGAN VALLEY.

&&

$$







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