FXUS66 KOTX 242221
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
221 PM PST THU DEC 24 2009
.SYNOPSIS...
STRONG HIGH PRESSURE WILL GRADUALLY BUILD OVER THE PACIFIC NORTHWEST.
THIS RIDGE IS EXPECTED TO PERSIST THROUGH NEXT WEEK...RESULTING IN
LITTLE IF ANY CHANCE OF MEASURABLE PRECIPITATION. IT WILL ALSO
BRING INCREASING CHANCES FOR FOG AND LOW CLOUDS IN THE VALLEYS.
&&
.DISCUSSION...
CHRISTMAS EVE AND CHRISTMAS...FEW CHANGES HAVE BEEN MADE TO THE
FORECAST FOR TONIGHT AND TOMORROW. UPPER LEVEL HIGH PRESSURE WILL
AMPLIFY OVER THE INLAND NORTHWEST OVER THE NEXT 24 HOURS. THE
MODIFIED ARCTIC AIR MASS THAT SPILLED INTO EASTERN WASHINGTON
YESTERDAY WAS NOT DRY ENOUGH TO ELIMINATE ALL OF THE STRATUS IN
THE LOW ELEVATIONS. PATCHY LOW CLOUDS REMAIN AROUND LAKE
CHELAN...LEAVENWORTH...THE WATERVILLE PLATEAU...AND IN THE
SPOKANE/PULLMAN VICINITY. AN OVERALL INCREASE IN THE STRATUS IS
EXPECTED TONIGHT AS THE STRENGTH OF THE INVERSION INCREASES. THE
MOST FAVORABLE AREAS FOR INCREASING LOW CLOUDS TONIGHT WILL BE IN
THE LOWER BASIN AROUND THE TRI-CITIES AND POINTS SOUTH WHERE
DEWPOINTS ARE IN THE LOWER TO MID 20S. THE SNAKE RIVER VALLEY FROM
LEWISTON TO THE TRI-CITIES WILL HAVE A GOOD CHANCE OF FOG OR
STRATUS DEVELOPMENT AS WELL DUE TO THE ELEVATED DEWPOINTS THERE.
THE NAM...GFS...AND MM5 ARE IN GOOD AGREEMENT THAT EASTERLY
BOUNDARY LAYER FLOW WILL DEVELOP BY LATE EVENING WHICH USUALLY
MEANS FOG OR STRATUS ALONG THE EAST SLOPES...WENATCHEE AREA...AND
OVER THE WATERVILLE PLATEAU. ANY LOW CLOUDS THAT DEVELOP TONIGHT
WILL LIKELY BE TOUGH TO DISPERSE TOMORROW GIVEN THE WARMING IN THE
MID LEVELS. THE INVERSION WILL BECOME INCREASINGLY TOUGH TO MIX
OUT. /GKOCH
CHRISTMAS NIGHT THROUGH SUNDAY NIGHT...MODELS AGREE ON THE UPPER LEVEL
RIDGE REMAINING OVER THE AREA. MODELS INDICATE SOME ENERGY FROM
THE FRONT SIDE OF THE RIDGE RETROGRADING INTO THE INLAND NW
SATURDAY AND THEN LIFTING TO THE NORTH SUNDAY. MODELS HAVE
SLIGHTLY DIFFERENT TIMING AND STRENGTH OF THIS FEATURE. MODELS DO
AGREE THAT THE SURFACE AND BOUNDARY LAYER WILL REMAIN NEARLY
SATURATED...BUT ABOVE THAT WILL BE VERY VERY DRY. EXPECT FOG
FORMATION AND/OR STRATUS FOR MOST VALLEY LOCATIONS THROUGH SUNDAY
NIGHT. THE EXCEPTION TO THIS IS THE EASTERN PALOUSE/LEWISTON/CAMAS
PRAIRIE REGION WHERE SOUTHEAST FLOW WILL PREVENT FOG FORMATION.
GIVEN THE FOG/STRATUS SITUATION IN THE VALLEYS...AS THAT WEATHER
FEATURE MOVES ACROSS THE AREA IT MAKE MIX UP THE FOG/STRATUS
TEMPORARILY...OR EVEN BRING VERY BRIEF PERIOD OF FLURRIES TO THE
AREA. DID NOT ADD THE FLURRIES TO THE FCST ATTM GIVEN THE HIT AND
MISS NATURE OF THE FLURRIES. DID CONTINUE THE IDEA OF MOSTLY
CLOUDY TO CLOUDY CONDITIONS IN THE VALLEYS AND MOSTLY CLEAR TO
CLEAR SKIES IN THE MOUNTAINS. TEMPERATURES...MADE SOME CHANGES TO
THE TEMPS TO REFLECT THE CLEAR SKIES IN THE MTNS AND THE
FOG/STRATUS IN THE VALLEYS. HAVE WARMER DAYTIME TEMPS AND COOLER
NIGHTTIME TEMPS IN THE MOUNTAINS GIVEN THE CLEAR SKIES...DRY
CONDITIONS AND LOW DEWPOINTS. FOR THE VALLEYS HAVE A 10 DEGREE OR
LESS TEMPERATURE VARIATION FROM MAX TO MIN TEMPS GIVEN THE
FOG/STRATUS THAT WILL REMAIN ACROSS THE AREA. /NISBET
MONDAY THROUGH THURSDAY...THE CHANCE OF PRECIPITATION WILL INCREASE
DURING THE EXTENDED PERIOD AS THE REGION TRANSITIONS TO A MORE
PROGRESSIVE FLOW ALOFT. THE UPPER RIDGE AXIS WILL BE NUDGED TO THE
EAST BY A COUPLE OF SHORTWAVE TROUGHS...INCREASING THE CHANCE OF
PRECIPITATION WITH EACH PASSAGE. THE FIRST COLD FRONT WILL WEAKEN
CONSIDERABLY MONDAY NIGHT AS IT TRANSITS THE FORECAST AREA AND
LITTLE PRECIPITATION WILL RESULT...OTHER THAN A FEW MOUNTAIN SNOW
SHOWERS. THE MAIN EFFECT WILL BE TO WEAKEN THE SURFACE INVERSIONS
AND REDUCE THE LIKELIHOOD OF VALLEY FOG AND LOW STRATUS. THE SECOND
FRONT ARRIVING TUESDAY NIGHT AND WEDNESDAY WILL BE ACCOMPANIED BY
BETTER UPPER DYNAMICS AS THE SPLIT FLOW ALOFT BECOMES MORE
CONSOLIDATED. POPS HAVE BEEN INCREASED ACROSS THE FORECAST AREA BUT
STILL REMAIN A BIT BELOW CLIMO AS MODEL SOLUTIONS DIFFER IN THE
TIMING OF THE TROUGH PASSAGE. MODELS ARE IN BETTER AGREEMENT THAT A
STRONGER SYSTEM WILL AFFECT THE REGION BY THE END OF THE WORKWEEK SO
POPS HAVE BEEN TRENDED TO CLIMO FOR THURSDAY. SNOW LEVELS WILL
CONTINUE TO BE AT OR NEAR VALLEY FLOORS WITH DAYTIME TEMPERATURES
SLIGHTLY BELOW SEASONAL NORMALS. /KELCH
&&
.AVIATION...
PATCHES OF STRATUS WILL HAVE AN IMPACT ON AVIATION THURSDAY
AFTERNOON AND THURSDAY EVENING. LOW CLOUDS ARE NOT WIDESPREAD...
BUT WILL PRODUCE CEILINGS AROUND 3000 FEET IN THE WENATCHEE
AREA...AND CEILINGS AROUND 2000 FEET IN THE SPOKANE VICINITY. SOME
EROSION OF THESE LOW CLOUDS IS LIKELY BETWEEN 21Z-00Z. HIGH
PRESSURE WILL BUILD OVERNIGHT STRENGTHENING THE LOW LEVEL
INVERSION. REDEVELOPMENT OF LOW CLOUDS IS LIKELY BETWEEN 06Z-15Z
OVER THE MAJORITY OF THE LOW ELEVATIONS WITH CEILINGS BELOW 1500
FEET. /GKOCH
.AIR STAGNATION...
INVERSION LEVELS ON THE 12Z SPOKANE SOUNDING WAS
RELATIVELY WEAK AND ABOUT 1000-1500 FEET ABOVE THE SURFACE. AS THE
500MB RIDGE AXIS MOVES FROM THE WASHINGTON COAST THIS AFTERNOON
INLAND TONIGHT INTO CHRISTMAS DAY...SUBSIDENCE WILL CONTRIBUTE TO
SIGNIFICANT WARMING ALOFT. BY 12Z CHRISTMAS MORNING...WARMING OF
3-4C IS EXPECTED OVER THE MAJORITY OF CENTRAL AND EASTERN
WASHINGTON...AS WELL AS THE IDAHO PANHANDLE. WITH TEMPERATURES
FALLING INTO THE TEENS...INVERSION HEIGHTS WILL FALL BELOW 1000 FEET
OVER MOST OF THE SPOKANE FORECAST AREA CHRISTMAS MORNING. EASTERLY
FLOW IN THE BOUNDARY LAYER WILL FAVOR FOG AND STRATUS FORMATION
ALONG THE EAST SLOPES OF THE CASCADES...THE WENATCHEE AREA...AND
POSSIBLY OVER THE WATERVILLE PLATEAU. THE MODELS SUGGEST THAT THE
EASTERLY FLOW JUST BELOW THE INVERSION LAYER MAY INCREASE ABOVE
10KTS FRIDAY NIGHT THROUGH EARLY SUNDAY MORNING OVER THE
PALOUSE...UPPER BASIN...AND IN THE SPOKANE AREA. IF THIS
VERIFIES...THERE MAY BE ENOUGH DISPERSION TO PREVENT STAGNATION. IN
THIS EAST FLOW PATTERN...THE VALLEYS OF NORTHERN WASHINGTON
INCLUDING THE COLVILLE AREA...THE OKANOGAN VALLEY...AS WELL AS THE
METHOW...CHELAN...AND WENATCHEE AREA WOULD BE SHELTERED FROM MIXING.
AT THIS TIME THE AIR STAGNATION ADVISORY IS IN EFFECT FOR ALL
ELEVATIONS BELOW 3000 FEET IN EASTERN/CENTRAL WASHINGTON/NORTHERN
IDAHO THROUGH SATURDAY AFTERNOON. IF WIDESPREAD STRATUS DEVELOPS AS
EXPECTED...AND LOCKS OUR INVERSION IN PLACE...THE WEAK UPPER TROUGH
THIS WEEKEND MAY NOT BE STRONG ENOUGH TO PROVIDE ENOUGH MIXING TO
END AIR STAGNATION. IF THIS IS THE CASE...LOOK FOR THE ADVISORY TO
BE EXTENDED THROUGH EARLY NEXT WEEK. /GKOCH
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 14 26 19 27 19 26 / 0 0 0 0 0 0
COEUR D'ALENE 15 27 19 26 20 27 / 0 0 0 0 0 0
PULLMAN 19 30 20 31 20 29 / 0 0 0 0 0 0
LEWISTON 20 32 22 33 21 31 / 0 0 0 0 0 10
COLVILLE 15 27 19 25 20 26 / 0 0 0 0 0 10
SANDPOINT 14 25 17 25 17 26 / 0 0 0 0 0 0
KELLOGG 14 25 17 26 19 27 / 0 0 0 0 0 0
MOSES LAKE 15 29 18 28 17 28 / 0 0 0 0 0 10
WENATCHEE 20 26 21 28 20 28 / 0 0 0 0 0 10
OMAK 14 25 18 25 19 25 / 0 0 0 0 0 10
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...AIR STAGNATION ADVISORY UNTIL 4 PM PST SATURDAY FOR CENTRAL
PANHANDLE MOUNTAINS...COEUR D'ALENE AREA...IDAHO PALOUSE...
LEWIS AND SOUTHERN NEZ PERCE COUNTIES...LEWISTON AREA...
NORTHERN PANHANDLE.
WA...AIR STAGNATION ADVISORY UNTIL 4 PM PST SATURDAY FOR EAST SLOPES
NORTHERN CASCADES...LOWER GARFIELD AND ASOTIN COUNTIES...
MOSES LAKE AREA...NORTHEAST MOUNTAINS...OKANOGAN
HIGHLANDS...OKANOGAN VALLEY...SPOKANE AREA...UPPER COLUMBIA
BASIN...WASHINGTON PALOUSE...WATERVILLE PLATEAU...WENATCHEE
AREA.
&&
$$
