FXUS66 KOTX 142352 AAA
AFDOTX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SPOKANE WA
352 PM PST MON DEC 14 2009
.SYNOPSIS...
A SERIES OF STORM SYSTEMS WILL BRING SIGNIFICANT SNOW TO MUCH OF
THE INLAND NORTHWEST. THE FIRST SYSTEM WILL ARRIVE TONIGHT AND
LINGER INTO TUESDAY MORNING. THE SECOND SYSTEM WILL FOLLOW QUICKLY
ON ITS HEELS TUESDAY NIGHT INTO WEDNESDAY MORNING...WITH A THIRD
WEDNESDAY NIGHT. TEMPERATURES WILL WARM WITH EACH SYSTEM...TURNING
THE SNOW TO RAIN FROM THE SOUTH. THE MOST SIGNIFICANT SNOW OF THE
SEASON SO FAR IS LIKELY AROUND AND NORTH OF WENATCHEE...MOSES
LAKE...SPOKANE...AND COEUR D'ALENE.
&&
.DISCUSSION...
TONIGHT AND TUESDAY...THE WET SYSTEM THAT HAS BEEN ADVERTISED FOR
THE PAST FEW DAYS IS NOW MOVING INTO THE NORTHWEST COAST. THIS IS
A VERY COMPLICATED SYSTEM WITH A 2 PRONGED ATTACK.
FOR TONIGHT WARM OVER-RUNNING MOISTURE WILL MOVE INTO THE
FORECAST AREA THIS EVENING. ISENTROPIC LIFT WITH THIS WARM FRONT
IS VERY IMPRESSIVE...AND WILL OVERCOME ANY SHADOWING EFFECTS
CAUSED BY THE CASCADES. IN FACT SOUTH-SOUTHEAST FLOW WILL
ACTUALLY ENHANCE THE LIFT INTO THE EAST SLOPES OF THE CASCADES AND
NORTH INTO THE OKANOGAN VALLEY AND THE OKANOGAN HIGHLANDS. 12
MODELS GUIDANCE SHOWED ONLY MINOR VARIATIONS IN THE AMOUNT OF
PRECIPITATION WITH THIS SYSTEM. IN FACT PW'S INCREASE TO ALMOST
.60 TONIGHT WHICH IS 150 PERCENT OF NORMAL. IN ADDITION MIXING
RATIOS ARE AS MUCH AS 4G/KG WHICH IS VERY WET. THIS COMBINATION OF
MOISTURE AND STRONG LIFT WILL RESULT IN IMPRESSIVE PRECIPITATION
AMOUNTS.
VERTICAL PROFILES SHOW A SNOW RATIO OF RIGHT AROUND 17:1 NORTH OF
I-90 AND AROUND 15:1 SOUTH OF I-90 FOR OVERNIGHT. WITH THE QPF
AMOUNTS PUSHING 3 TENTHS OF AN INCH OR SO WE ARE EXPECTING SOME
HEAVY SNOW ACROSS THE REGION BY TUESDAY MORNING. WE DO GET A BRIEF
BREAK TUESDAY AFTERNOON BEFORE THE SECOND PART OF THE STORM COMES
THROUGH TUESDAY NIGHT AND WEDNESDAY.
HIGHLIGHTS HAVE BEEN UPGRADED THIS AFTERNOON FROM ADVISORIES TO
WARNINGS ACROSS A MAJORITY OF THE FORECAST AREA...DUE TO THE
AMOUNTS OF SNOW AND HOW LONG THIS STORM SYSTEM WILL LAST. SOME
ISSUES WARM AIR WILL HELP TO SCOUR OUT THE LOWER BASIN AROUND MID
DAY TUESDAY AND THERE MAY BE A FEW HOURS OF LIGHT FREEZING RAIN TO
CONTEND WITH IN THAT AREA. FOR THE PALOUSE AND THE SPOKANE AREA
WARM AIR WILL ALLOW SNOW LEVEL TO RISE BY LATE
AFTERNOON...ALLOWING SNOW TO CHANGE OVER TO A SNOW/RAIN MIX.
ALL THIS BEING SAID COMMUTING IN POPULATED AREAS TUESDAY INTO
WEDNESDAY WILL CAUSE NUMEROUS PROBLEMS. /TOBIN
TUESDAY NIGHT...THE INLAND NORTHWEST WILL BE BRACING ITSELF FOR
THE ARRIVAL OF ANOTHER WARM FRONT. A SURFACE LOW MOVES INTO THE
CENTRAL COAST OF BRITISH COLUMBIA...WHILE THE FLOW ALOFT REMAINS
OUT OF THE SOUTHWEST. THERE IS HIGH CONFIDENCE THAT PRECIPITATION
WILL MEASURE ACROSS THE REGION. THE QUESTION IS WHERE THE
RAIN/SNOW LINE WILL BE. SNOW LEVELS ARE FORECAST TO RISE AS A NOSE
OF WARMER AIR RIDES UP FROM THE FOOTHILLS OF THE BLUE MOUNTAINS...
THROUGH THE PALOUSE AND INTO THE SPOKANE/COEUR D'ALENE AREA.
MEANWHILE...COLD AIR AND LITTLE MIXING WILL KEEP SNOW LEVELS LOW
ACROSS THE WESTERN BASIN...OVER THE WATERVILLE PLATEAU AND THE
WENATCHEE AREA. AS THE NEXT SLUG OF MOISTURE MOVES OVER THE
CASCADES...ANTICIPATE THE BEST CHANCE OF SNOW TO SPREAD ACROSS THE
NORTHERN TIER ZONES...MAINLY ALONG AND NORTH OF HIGHWAY 2 WHERE AN
ADDITIONAL 2-4 INCHES ARE EXPECTED. WITH THE BREAK BETWEEN THIS
SYSTEM AND THE PREVIOUS SO SHORT...OPTED TO INCLUDE THIS ROUND OF
SNOW INTO THE CURRENT WINTER HIGHLIGHTS. IN ADDITION...WHERE THE
COLD AIR WILL BE STUBBORN TO ERODE...THERE IS A SMALL RISK OF
FREEZING RAIN IN THE EXTREME WESTERN COLUMBIA BASIN. TEMPERATURES
WILL CONTINUE TO WARM OVERNIGHT...SO OVERNIGHT LOWS WILL BE NOT
TOO FAR OFF FROM THE DAYTIME HIGHS ON TUESDAY.
WEDNESDAY AND WEDNESDAY NIGHT...AS THE FLOW ALOFT BECOMES MORE
WESTERLY...THE REMAINS OF THE FRONTAL BOUNDARY WILL BE SLOW TO
LEAVE THE SOUTHEAST ZONES...SUPPORTING HIGHER POPS ESPECIALLY IN
THE MORNING HOURS YET SNOW LEVELS WILL BE HIGH ENOUGH IN THIS
REGION TO SUPPORT VALLEY RAIN AND HIGH ELEVATION SNOW. LOW LEVEL
WINDS WILL REMAIN OUT OF THE SOUTHWEST WITH A COMBINATION OF WEAK
ISENTROPIC AND OROGRAPHIC LIFT TO BRING LIGHT PRECIPITATION
ACROSS THE NORTHERN AND PANHANDLE MOUNTAINS THROUGH THE AFTERNOON.
BY WEDNESDAY NIGHT...A WEAK SHORTWAVE IN THE FLOW RIDES THROUGH
BRITISH COLUMBIA WHICH WILL ENHANCE THE PRECIPITATION CHANCES
ACROSS THE NORTHEAST HALF OF THE FORECAST AREA. SO...ANTICIPATE
MORE SNOW FOR THE NORTHERN TIER ZONES INTO WEDNESDAY NIGHT
ALTHOUGH SNOW LEVELS WILL CONTINUE TO RISE LEAVING JUST A
RAIN/SNOW MIX FOR THE NORTHERN VALLEYS.
BY THURSDAY...SHORTWAVE RIDGING WILL BUILD INTO THE REGION WITH A
BRIEF BREAK IN THE WINTER WEATHER PATTERN. VALLEY DAYTIME
TEMPERATURES WILL CLIMB ABOVE FREEZING...ALTHOUGH ABUNDANT LOW
LEVEL WILL KEEP MOST AREAS OVERCAST. BACKING OF THE LOW LEVEL FLOW
BY AFTERNOON WILL SUPPORT LIGHT PRECIPITATION SPREADING ACROSS THE
CASCADES BY AFTERNOON AS ANOTHER WARM FRONT APPROACHES THE
FORECAST AREA. /RFOX.
THURSDAY NIGHT THROUGH MONDAY NIGHT...THE OVERALL CONFIDENCE IN
THE PATTERN THROUGH THE EXTENDED FORECAST AFTER ABOUT FRIDAY OR SO
IS RATHER LOW AT THIS POINT. THE MODELS HAVE GENERALLY FOCUSED ON
A SHORT WAVE RIDGE PEAKING ACROSS THE CWA LATE IN THE WEEK. THIS
IS FAIRLY WELL AGREED UPON AMONGST ALL OPERATIONAL MODELS AND
ENSEMBLES...HOWEVER ITS PROGRESSION AND UPSTREAM DEVELOPMENT SHOW
TWO DRASTICALLY DIFFERENT PATTERNS EVOLVING BY THE WEEKEND. THE
PATTERN PORTRAYED ON THE ECMWF SUGGESTS THE RIDGE LINGERS OVER THE
FORECAST AREA THROUGH THE WEEKEND...EVEN SLIGHTLY
RETROGRADING...BEFORE EVENTUALLY BEING USHERED TO THE EAST AROUND
MONDAY. THE GFS QUICKLY SHIFTS THE RIDGE EASTWARD WITH A HIGH
AMPLITUDE SHORT WAVE TROUGH ENTERING THE FORECAST AREA LATE
SATURDAY. GIVEN BETTER LONG WAVE AGREEMENT BETWEEN THE ECMWF AND
CANADIAN...THE SOLUTION OF THE ECMWF WAS ROUGHLY FOLLOWED THROUGH
THE BULK OF THE EXTENDED FORECAST PERIOD.
IN FOLLOWING ALONG THE ECMWF PATTERN...A DIRTY RIDGE SCENARIO
SEEMS LIKELY. BETWEEN THAT AND A COUPLE OF WAVES CENTERED AROUND
THURSDAY NIGHT AND SUNDAY RUNNING ALONG THE WESTERN FLANK OF THE
RIDGE...MID AND HIGH CLOUDS WILL BE COMMON. COUPLED WITH
THAT...THE HEAVY SNOWFALL AND RAIN THAT WILL FALL BETWEEN NOW AND
THEN ALONG WITH A RATHER STABLE PROFILE UNDER THE RIDGE...LOW
CLOUDS WILL LIKELY BE THE RULE AS WELL. AS A RESULT...UNDER THE
RIDGE...SKIES ARE LIKELY TO REMAIN CLOUDY EVEN WITHOUT MUCH IN THE
WAY OF PRECIPITATION CHANCES. BECAUSE OF THE ABUNDANT LOW
CLOUDS...DIURNAL TEMPERATURE RANGES WERE KEPT EXCEEDINGLY
SMALL...WITH LOWS NEAR FREEZING AND HIGHS ONLY IN THE MID 30S FOR
MOST VALLEY LOCATIONS THROUGH THE PERIOD. /FRIES
&&
.AVIATION...
SNOW WILL DEVELOP FROM SW TO NE STARTING AROUND 02Z THIS EVENING.
THIS SN WILL BECOME MODERATE TO HEAVY AT TIMES OVERNIGHT FOR MOST
LOCATIONS...WITH ONLY KLWS SEEING A MIXING OF RA WITH THE SN. SN
WILL GRADUALLY WIND DOWN FROM W TO E DURING THE LATE MORNING HOURS
TUESDAY...WITH -DZ/-FZDZ LINGERING THROUGH THE DAY. A SECOND STORM
ENTERS THE WESTERN SITES BY TUES AFTERNOON WITH -SN DEVELOPING YET
AGAIN AROUND KEAT AND KMWH. /FRIES
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 22 32 31 36 31 35 / 100 100 90 60 60 20
COEUR D'ALENE 22 33 32 37 30 36 / 90 100 90 60 70 20
PULLMAN 26 36 34 40 33 39 / 80 90 80 50 50 30
LEWISTON 31 42 38 44 35 43 / 60 80 70 60 40 30
COLVILLE 18 30 29 36 32 36 / 100 100 100 80 80 20
SANDPOINT 16 29 28 32 30 33 / 100 100 100 80 80 40
KELLOGG 21 33 31 38 32 36 / 90 100 100 80 80 60
MOSES LAKE 21 30 29 36 27 35 / 100 60 80 40 50 20
WENATCHEE 19 27 26 31 26 33 / 100 70 80 40 30 20
OMAK 14 26 25 31 26 33 / 100 50 100 60 60 20
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...WINTER WEATHER ADVISORY UNTIL 4 PM PST TUESDAY FOR IDAHO
PALOUSE.
WINTER STORM WARNING FROM 10 PM THIS EVENING TO 4 AM PST
WEDNESDAY FOR NORTHERN PANHANDLE.
WINTER STORM WARNING UNTIL 4 PM PST TUESDAY FOR COEUR D'ALENE
AREA.
WINTER STORM WARNING FROM 10 PM THIS EVENING TO 4 AM PST
WEDNESDAY FOR CENTRAL PANHANDLE MOUNTAINS.
WA...WINTER STORM WARNING UNTIL 10 PM PST TUESDAY FOR OKANOGAN
HIGHLANDS...OKANOGAN VALLEY.
WINTER WEATHER ADVISORY UNTIL 4 PM PST TUESDAY FOR NORTHEAST
BLUE MOUNTAINS.
WINTER WEATHER ADVISORY UNTIL 4 PM PST TUESDAY FOR WASHINGTON
PALOUSE.
WINTER STORM WARNING UNTIL 4 PM PST TUESDAY FOR MOSES LAKE
AREA...UPPER COLUMBIA BASIN.
WINTER STORM WARNING FROM 10 PM THIS EVENING TO 4 AM PST
WEDNESDAY FOR NORTHEAST MOUNTAINS.
WINTER STORM WARNING UNTIL 4 PM PST TUESDAY FOR SPOKANE AREA.
WINTER STORM WARNING UNTIL 10 PM PST TUESDAY FOR WATERVILLE
PLATEAU...WENATCHEE AREA.
WINTER STORM WARNING UNTIL 10 PM PST TUESDAY FOR EAST SLOPES
NORTHERN CASCADES.
&&
$$
