FXUS66 KOTX 152354 AAA
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
354 PM PST TUE DEC 15 2009
.SYNOPSIS...
THE NEXT ROUND OF A WINTRY MIX OF PRECIPITATION WILL CONTINUE
ACROSS THE FORECAST AREA TONIGHT AND WEDNESDAY. WARMER AIR IS
MOVING INTO THE REGION RESULTING IN SNOW...RAIN AND LOCAL FREEZING
RAIN THIS EVENING. PORTIONS OF CENTRAL AND NORTHEAST WASHINGTON...
AS WELL AS THE NORTHERN IDAHO PANHANDLE WILL RECEIVE ADDITIONAL
HEAVY ACCUMULATIONS OF SNOW TONIGHT AND WEDNESDAY. MILDER
CONDITIONS ARE EXPECTED TO CONTINUE THROUGH THE END OF THE WEEK.
&&
.DISCUSSION...
,..A WINTER WEATHER SYSTEM WILL BRING MORE SNOW...RAIN AND LOCAL
FREEZING RAIN TO THE AREA TONIGHT...
TONIGHT...A DEEP LOW CONTINUES TO MOVE TOWARDS THE COAST WITH A
MULTITUDE OF DISTURBANCES AROUND THE FLOW PER SATELLITE IMAGERY.
THIS WILL KEEP THE PACIFIC NORTHWEST IN A MOIST SOUTHWEST FLOW FOR
THE NEXT 24 HOURS OR SO. THE NEXT WAVE IS NOW MOVING INTO THE
REGION AND WILL RESULT IN ANOTHER VERY GOOD SHOT OF PRECIPITATION
TO THE REGION. A VERY NICE MOISTURE TAP IS POINTED AT THE INLAND
NORTHWEST WITH PW'S AROUND .50 WHICH IS ABOUT 160 PERCENT OF
NORMAL. THIS FLOW IS ALSO BRINGING UP QUITE A BIT OF WARM AIR. THE
WARM AIR IS ERODING SOME OF THE COLD AIR THAT HAS BEEN IN PLACE
FOR THE PAST 10 DAYS OR SO. THUS SNOW LEVELS ARE ON THE RISE. THE
EXCEPTION IS IN AREAS THAT ARE TYPICALLY HARD TO MIX OUT...FOR
EXAMPLE THE EAST SLOPES OF THE CASCADES...THE UPPER COLUMBIA BASIN
AND THE NORTHERN VALLEYS. HIGHLIGHTS FOR THE BLUE
MOUNTAINS...SHOSHONE COUNTY AND THE PALOUSE HAVE BEEN CANCELLED AS
TEMPERATURES HAVE RISEN ABOVE FREEZING AND IN A FEW AREAS WELL
ABOVE FREEZING. FOR SHOSHONE COUNTY EXPECT MORE SNOW AT THE HIGHER
ELEVATIONS...BUT NOT MUCH BELOW ABOUT 4000 FEET. IN THE COLDER
AREAS PREVIOUSLY MENTIONED THAT WERE TOUGHER TO MIX OUT HIGHLIGHTS
WERE KEPT IN PLACE FOR ADDITIONAL ACCUMULATIONS OF SNOW. AREA OF
CONCERN WILL BE THE BASIN WHERE A PERIOD OF FREEZING RAIN IS NOT
OUT OF THE QUESTIONS...BUT SHOULD BE LOCALIZED AND NOT LAST LONG.
THE OTHER CHALLENGING AREA WILL BE THE SPOKANE-COEUR D'ALENE
AREAS. A SURFACE LOW IS SITTING BETWEEN SPOKANE AND PULLMAN.
SOUTHERLY FLOW HAS BEEN BATTLING NORTHEAST FLOW ALL DAY. EARLIER
THIS AFTERNOON SOUTHEAST WINDS ALLOWED TEMPERATURES AT SPOKANE
AIRPORT TO JUMP 7 DEGREES...IN THE PAST HOUR LIGHT NORTHEAST WINDS
HAVE DROPPED TEMPS BACK BELOW FREEZING. THERE IS NO CLEAR CUT
SIGNAL THAT ANY OF THE SURFACE GRADIENTS WILL TOTALLY WIN OUT
UNTIL LATER THIS EVENING WHEN THE SOUTHERLY FLOW WILL FINALLY
BECOME DOMINANT. AS SUCH THE WARNING FOR SNOW AND FREEZING DRIZZLE
WILL BE EXTENDED THROUGH 06Z. IN THE MOUNTAINS SNOW LEVELS WILL
REMAIN LOW THROUGH THE NIGHT AND EXPECT ADDITIONAL ACCUMULATIONS
OF SNOW THROUGH THE NIGHT. MINIMUM TEMPERATURES WILL BE ON THE
INCREASE WITH OVER NIGHT LOWS 5-10 DEGREES ABOVE NORMAL. /TOBIN
WEDNESDAY THROUGH SATURDAY...AFTER TONIGHT'S STORM PASSAGE THE
WEATHER WILL REMAIN WET AND UNSETTLED THROUGH THE REMAINDER OF THE
SHORT TERM PERIODS WITH TWO MORE DISTURBANCES MIGRATING THROUGH
THE FORECAST AREA. THE NEXT SYSTEM IS VISIBLE ON SATELLITE
CURRENTLY AS A SPIRALING AREA OF CELLULAR CLOUDS NEAR 140W OFF
THE COAST OF OREGON. THE NAM MODEL...GFS AND ECMWF MODELS ARE IN
REASONABLE AGREEMENT WITH THE TIMING OF THIS FEATURE AND ARE
PLAUSIBLE AGAINST SATELLITE EXTRAPOLATION. THIS WAVE WILL PASS
THROUGH ON THE HEELS OF TONIGHT'S SYSTEM AS A COLD OCCLUDED FRONT
DURING THE DAY WEDNESDAY. IF THERE IS GOING TO BE ANY DETECTABLE
BREAK BETWEEN SYSTEMS...IT WILL MANIFEST ITSELF AS A BRIEF DRY BUT
CLOUDY AND DAMP PERIOD WEDNESDAY MORNING WITH A DETERIORATION BACK
INTO MOUNTAIN SNOW AND VALLEY RAIN OR SNOW BY AFTERNOON AND
LASTING THROUGH MOST OF THE NIGHT. THE STRONG WARM FRONT PASSAGE
TONIGHT WILL FORCE SNOW LEVELS UP WELL OFF THE BASIN FLOOR OVER
THE EASTERN HALF OF THE FORECAST AREA. THE FREEZING LEVEL WILL
STAY ELEVATED THROUGH FRIDAY OVER THE EASTERN BASIN DESPITE BEING
WORN DOWN BY WEDNESDAY'S SYSTEM. THUS CONFIDENCE IS HIGH THAT
FURTHER PRECIPITATION IN THE SPOKANE-CD'A REGION AND POINTS
SOUTH...AS WELL AS THE VALLEYS OF SHOSHONE COUNTY WILL BE RAIN.
THE NORTHERN VALLEYS ESPECIALLY NEAR THE CANADIAN BORDER...AND THE
CASCADES LEE VALLEYS FROM OMAK TO WENATCHEE WILL NOT BE AS
EFFICIENTLY SCRUBBED AS THE EASTERN ZONES...AND THUS A MIX OF
VARIOUS WINTER METEORS IS POSSIBLE WEDNESDAY AND INTO THURSDAY
INCLUDING SNOW...RAIN...ICE PELLETS AND POSSIBLE FREEZING RAIN.
A MORE NOTICEABLE BRIEF BREAK IS POSSIBLE OVER MOST OF THE
FORECAST AREA ON THURSDAY AS A WEAK SHORT WAVE RIDGE AND MODERATE
SURFACE HIGH PRESSURE BUILDS OVER THE REGION. THIS WILL BE MAINLY
A DRY BUT VERY DIRTY RIDGE...WITH A CONTINUING CHANCE OF STRAY
RAIN OR SNOW SHOWERS THROUGH THE DAY. BY THURSDAY NIGHT THE NEXT
PACIFIC STORM SYSTEM...CURRENTLY VISIBLE ON SATELLITE FAR OUT OVER
THE PACIFIC BOUT MIDWAY BETWEEN THE US AND ASIA...WILL FLING WHAT
APPEARS TO BE A WARM OCCLUDED FRONT THROUGH THE REGION FOR ANOTHER
ROUND OF ISENTROPICALLY DRIVEN VALLEY RAIN AND MOUNTAIN SNOW
THURSDAY NIGHT AND FRIDAY.
ALL OF THESE SYSTEMS ARE FUELED BY AT LEAST MODERATELY DEEP
PACIFIC MOISTURE FETCHES...WHICH SHOULD ENSURE A CONTINUED MOIST
AIR MASS QUICK TO PRECIPITATE OVER THE REGION GIVEN ANY FRONTAL
FOCUS AND DYNAMIC DISTURBANCE. THUS CONFIDENCE IS HIGH FOR A
CONTINUED WET AND UNSETTLED FORECAST FOR THE NEXT 72 HOURS. /FUGAZZI
FRIDAY NIGHT THROUGH TUESDAY...OVERALL CONFIDENCE IS MODERATE
THROUGH SATURDAY NIGHT THEN DECREASES THEREAFTER AS A COMPLEX
PATTERN DEVELOPS. A WEAK SHORT WAVE WILL TRACK ACROSS THE AREA FRI
NGT/SAT BRINGING A CHANCE FOR LIGHT RAIN AND SNOW. A SHORT WAVE
RIDGE THEN MOVES IN FOR A DRY PERIOD SATURDAY NIGHT AND POSSIBLY
SUNDAY AS WELL. FOR MONDAY AND TUESDAY...THE GFS AND ECMWF TAKE A
CLOSED LOW EAST OFF THE COAST WHILE A BLOCKING HIGH PRESSURE RIDGE
DEVELOPS TO THE NORTH OF THIS LOW. THIS RESULTS IN THE POSSIBLE
INTRUSION OF COOLER AIR AS A NORTHERLY FLOW DEVELOPS OVER BRITISH
COLUMBIA WHILE A SOUTHWEST FLOW IS PREVALENT AHEAD OF THE CLOSED
LOW AS IT SLOWLY MOVES EAST TOWARDS THE AREA. THE END RESULT IS
TRICKY AS A COMBINATION OF COOLER AIR DROPPING DOWN FROM CANADA
AND INCREASED MOISTURE AND LIFT AHEAD OF THE CLOSED LOW COMBINE
OVER THE INLAND NW. THE ECMWF KEEPS THE SOUTHWEST FLOW MORE
PREVALENT RESULTING IN A COMBINATION OF RAIN AND SNOW OVER THE
AREA WHILE GFS 1000-850MB THICKNESSES SUGGEST SNOW LEVELS TO THE
VALLEY FLOORS WITH PROLONGED PRECIP MONDAY AND TUESDAY AS THE
MOISTURE AND COLD AIR MERGE OVER THE AREA. CANADIAN AND UKMET
EXTENSION SUPPORT MORE OF AN ECMWF SOLUTION SO TEMPERATURES ARE
FORECAST TO BE SLIGHTLY ABOVE NORMAL WITH CLIMO POPS BUT WITH LOW
CONFIDENCE. JW
&&
.AVIATION...
RAIN...SNOW...FREEZING RAIN AND FREEZING DRIZZLE WILL ALL BE
ENCOUNTERED ACROSS THE FORECAST AREA THIS EVENING...BEFORE TURNING
OVER TO LOW ELEVATION RAIN AND MOUNTAIN SNOW ON WEDNESDAY. AS
PRECIPITATION COMES TO END WEDNESDAY MORNING WARM AIR OVER SNOW WILL
RESULT IN WIDESPREAD STRATUS AND FOG FORMATION. EXPECT WIDESPREAD
LOW CEILINGS AND VISIBILITIES WITH CONDITIONS REMAINING IFR OR
LOWER. THE EXCEPTION WILL BE KLWS..KPUW WHERE CONDITIONS WILL BOUNCE
FROM VFR/MVFR TO IFR AT TIMES. FROM THE COLUMBIA BASIN THROUGH THE
SPOKANE AREA EXPECT CIGS BELOW OVC012 FEET AND VSY BELOW 2 MILES
THROUGH THE FORECAST PERIOD. /TOBIN
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 30 36 33 37 34 37 / 100 60 60 20 20 40
COEUR D'ALENE 30 37 33 39 35 37 / 100 70 60 30 20 40
PULLMAN 33 40 35 38 34 39 / 90 70 60 20 20 20
LEWISTON 37 44 36 42 37 42 / 70 60 40 20 10 20
COLVILLE 26 36 32 35 32 36 / 100 70 60 30 50 50
SANDPOINT 25 32 28 33 29 33 / 100 80 70 40 30 40
KELLOGG 29 38 34 36 32 35 / 100 90 80 60 20 30
MOSES LAKE 28 36 29 37 33 38 / 80 30 40 20 40 40
WENATCHEE 25 32 32 36 29 36 / 90 30 40 30 50 40
OMAK 24 30 30 38 32 36 / 100 50 50 30 60 60
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...WINTER STORM WARNING UNTIL 4 AM PST WEDNESDAY FOR NORTHERN
PANHANDLE.
WINTER STORM WARNING UNTIL 10 PM PST THIS EVENING FOR COEUR
D'ALENE AREA.
WA...WINTER STORM WARNING UNTIL 4 AM PST WEDNESDAY FOR NORTHEAST
MOUNTAINS.
WINTER WEATHER ADVISORY UNTIL 4 AM PST WEDNESDAY FOR OKANOGAN
HIGHLANDS...OKANOGAN VALLEY...WENATCHEE AREA.
WINTER STORM WARNING UNTIL 10 PM PST THIS EVENING FOR SPOKANE
AREA.
WINTER STORM WARNING UNTIL 10 PM PST THIS EVENING FOR EAST
SLOPES NORTHERN CASCADES.
WINTER WEATHER ADVISORY UNTIL 4 AM PST WEDNESDAY FOR MOSES LAKE
AREA...UPPER COLUMBIA BASIN...WATERVILLE PLATEAU.
&&
$$
