AREA FORECAST DISCUSSION

 
 FXUS66 KOTX 220615
 AFDOTX
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE SPOKANE WA
 1015 PM PST SAT NOV 21 2009
 
 .SYNOPSIS...
 A STRONGER AND COLDER STORM SYSTEM WILL BRING MODERATE TO HEAVY
 SNOWFALL OVER MUCH OF THE REGION TONIGHT AND SUNDAY. A SERIES OF
 STORM SYSTEMS WILL CONTINUE TO PASS THROUGH THE INLAND NORTHWEST
 EVERY 24 TO 36 HOURS THROUGH AT LEAST THE MIDDLE OF NEXT WEEK.
 
 &&
 
 .DISCUSSION...
 
 ...MODERATE TO HEAVY SNOWFALL OVER MOST OF THE AREA TONIGHT AND SUNDAY...
 
 WATER VAPOR SATELLITE SHOWS A STRENGTHING LOW APPROACHING THE
 SOUTHERN WASHINGTON AND NORTHERN OREGON COAST. SFC ANALYSIS AT 05Z
 SHOWED THE SFC LOW TO BE LOCATED BETWEEN HOQUIAM AND ASTORIA JUST
 OFF THE COAST WITH SFC PRESSURE FALLING BY THE HOUR...WITH A
 CENTRAL PRESSURE ESTIMATED TO BE NEAR 991MB. THIS FITS WELL WITH
 THE GFS ALTHOUGH MAY BE SLIGHTLY FURTHER SOUTH. THERE IS GOOD
 AGREEMENT BETWEEN THE GFS AND NAM IN DUMBBELLING THIS LOW NORTHEAST
 TONIGHT AROUND ANOTHER SFC LOW NEAR THE QUEEN CHARLOTTE ISLANDS.
 SATELLITE TRENDS IN THE LAST HOUR INDICATE THE TURNING TOWARDS THE
 NORTHEAST IS JUST BEGINNING SO THE GFS IDEA MATCHES WELL WITH THE
 SATELLITE. THE LOW WILL WEAKEN AS IT CROSSES THE CASCADES BUT IT
 WILL SEND A COLD OCCLUSION OVER THE AREA BRINGING A BURST OF HEAVY
 PRECIPITATION FOR 3-6 HRS WITH PRECIPITATION PERSISTING OVER NORTH
 IDAHO FOR A LONGER PERIOD DUE TO STRONG LOW LEVEL UPSLOPE FLOW.
 
 TIMING OF THE HEAVY PRECIP BAND LOOKS TO CROSS THE CASCADES
 AROUND MIDNIGHT...TRACKING INTO THE OKANOGAN VALLEY AND COLUMBIA
 BASIN OVERNIGHT INTO EARLY SUNDAY MORNING...AND THEN ACROSS
 EASTERN WASHINGTON IN THE EARLY TO MID MORNING HOURS ON
 SUNDAY...AND THEN FINALLY INTO N IDAHO MID TO LATE MORNING. THE
 GFS AND NAM BRING ABOUT A QUARTER INCH OF LIQUID PRECIP WITH THIS
 COLD OCCLUSION. SNOW LEVELS WILL BE TRICKY TONIGHT INTO SUNDAY
 MORNING. AS OF 10 PM LIGHT RAIN WAS FALLING IN OMAK...WITH PRECIP
 TYPE OF RAIN ALSO SUPPORTED IN WENATCHEE. HOWEVER WITH THE HEAVIER
 PRECIP RATES EXPECTED...MODELS QUICKLY COOL THE LOWER PART OF THE
 ATMOSPHERE WITH 1000-850MB THICKNESSES FALLING TO 1300-1305DM
 WHICH IS LOW ENOUGH FOR SNOW FOR MOST LOCATIONS. THUS RAIN AT OMAK
 SHOULD CHANGE OVER TO SNOW OVERNIGHT SO ADVISORY WAS UPDATED TO
 INCLUDE THE LOWER PART OF THE VALLEY. WENATCHEE CURRENTLY IT A
 LITTLE WARMER SO SUB ADVISORY ACCUMULATIONS ARE MORE LIKELY MAINLY
 ON GRASSY SURFACES. THE ONE AREA WHERE A RAIN AND SNOW MIX IS
 MORE PROBABLE IS ELEVATIONS BELOW 2000 FEET SOUTH OF A LINE FROM
 MOSES LAKE TO LEWISTON AS SLIGHTLY WARMER LOW LEVEL AIR RESIDES.
 AS THE PRECIP SWINGS INTO NE WA/N IDAHO SUNDAY MORNING...ALL AREAS
 SHOULD SEE A BURST OF HEAVY SNOW AS CURRENT WET BULB ZERO
 TEMPERATURES ARE 32F OR BELOW. WITH THE BRIEF PERIOD OF HEAVY SNOW
 EXPECTED MOST LOCATIONS ARE UNDER A WINTER WEATHER ADVISORY.
 HOWEVER UPSLOPE FLOW WILL KEEP SNOW PERSISTING FOR THE IDAHO
 PALOUSE...COEUR D`ALENE AREA...AND CENTRAL PANHANDLE MOUNTAINS ON
 SUNDAY SO WINTER STORM WARNINGS ARE IN EFFECT. PRESSURE GRADIENTS
 ALSO TIGHTEN SUNDAY MORNING WITH WINDY CONDITIONS DEVELOPING ON
 THE PALOUSE...IN THE BLUE MTNS...AND CENTRAL PANHANDLE
 MOUNTAINS...SO AREAS OF BLOWING SNOW ARE EXPECTED ESPECIALLY FOR
 ELEVATIONS ABOVE 3000 FEET. JW
 
 &&
 
 .AVIATION...
 CONDITIONS WILL RAPIDLY DETERIORATE AT THE TAF SITES AS A STRONG
 SYSTEM MOVES THROUGH THE AREA. VISIBILITIES AND CEILINGS WILL CRASH
 FROM WEST TO EAST WITH A BURST OF MAINLY SN AND +SN MOVING THROUGH
 THE AREA. TIMING OF WORST CONDITIONS WILL BE BTWN 09Z-19Z AT THE
 TAF SITES WITH THE EARLIER ONSET FOR LOCATIONS NEAR THE CASCADES
 AND A LATER ONSET OVER N IDAHO. BLSN IS ALSO EXPECTED AT KPUW BTWN
 12-18Z.  JW
 
 
 &&
 
 .PRELIMINARY POINT TEMPS/POPS...
 SPOKANE        31  37  25  38  30  40 /  50 100  10  20  40  20 
 COEUR D`ALENE  30  38  27  39  30  40 /  20 100  20  20  50  20 
 PULLMAN        31  37  27  40  29  44 /  70  90  10  10  30  20 
 LEWISTON       35  42  31  47  32  49 /  50  80  20  10  20  20 
 COLVILLE       32  40  27  39  29  40 /  60 100  10  50  60  10 
 SANDPOINT      30  37  27  34  27  36 /  40  90  20  50  60  40 
 KELLOGG        29  33  28  33  29  37 /  20 100  70  20  50  30 
 MOSES LAKE     31  44  24  43  26  45 / 100  50   0  30  30   0 
 WENATCHEE      32  43  29  43  32  45 / 100  50   0  30  40   0 
 OMAK           31  43  22  41  29  45 / 100  90   0  70  80   0 
 
 &&
 
 .OTX WATCHES/WARNINGS/ADVISORIES...
 ID...WINTER WEATHER ADVISORY FROM 4 AM TO 10 PM PST SUNDAY FOR 
      NORTHERN PANHANDLE.
 
      WINTER STORM WARNING FROM 4 AM TO 10 PM PST SUNDAY FOR IDAHO 
      PALOUSE.
 
      WINTER STORM WARNING FROM 4 AM TO 10 PM PST SUNDAY FOR COEUR 
      D`ALENE AREA.
 
      WINTER STORM WARNING FROM 4 AM SUNDAY TO 1 AM PST MONDAY FOR 
      CENTRAL PANHANDLE MOUNTAINS.
 
 WA...WINTER WEATHER ADVISORY FROM 4 AM TO 4 PM PST SUNDAY FOR 
      NORTHEAST MOUNTAINS...SPOKANE AREA.
 
      WINTER WEATHER ADVISORY UNTIL 10 AM PST SUNDAY FOR EAST SLOPES 
      NORTHERN CASCADES.
 
      WINTER WEATHER ADVISORY UNTIL NOON PST SUNDAY FOR OKANOGAN 
      HIGHLANDS...OKANOGAN VALLEY.
 
      WINTER WEATHER ADVISORY UNTIL NOON PST SUNDAY FOR UPPER COLUMBIA 
      BASIN...WATERVILLE PLATEAU.
 
      WINTER WEATHER ADVISORY FROM 4 AM TO 10 PM PST SUNDAY FOR 
      NORTHEAST BLUE MOUNTAINS.
 
      WINTER WEATHER ADVISORY FROM 4 AM TO 4 PM PST SUNDAY FOR 
      WASHINGTON PALOUSE.
 
 &&
 
 $$