FXUS66 KOTX 241212
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
404 AM 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...
TODAY AND TONIGHT...WATER VAPOR LOOPS ARE SHOWING A BUILDING UPPER
LEVEL RIDGE JUST OFF THE COAST THIS MORNING. ALL SHORT RANGE MODELS
TAKE THIS RIDGE AXIS INTO THE CASCADES OVERNIGHT...RESULTING IN
INCREASING SYNOPTIC SCALE SUBSIDENCE AND GENERALLY FAIR CONDITIONS.
AS IS USUALLY THE CASE WITH STRONG RIDGES THIS TIME OF YEAR...THE
FORECAST PROBLEM WILL BE STRATUS AND FOG FORMATION. THE INITIAL
FORMATION OF THIS STRATUS AND OR FOG IS USUALLY PROBLEMATIC FOR THE
SHORT-RANGE MODELS AND THIS MORNING IS NO EXCEPTION. THE ONLY PLACE
THE SHORT-RANGE MODELS ARE CONSISTENT IN PLACING THE LOW CLOUDS AND
FOG THIS MORNING IS OVER THE SE CORNER OF THE CWA NEAR LEWISTON AND
PULLMAN AS WELL AS NEAR THE CASCADES. HOWEVER THE FOG PRODUCT IS
ALSO SHOWING A GROWING AREA OF LOW CLOUDS AND FOG EXTENDING FROM THE
WEST PLAINS AND INTO THE EASTERN COLUMBIA BASIN. THERE WAS ANOTHER
EXTENSIVE AREA OF LOW CLOUDS NORTH OF SANDPOINT. SUSPECT THAT IF
ANYTHING...THE FOG AND STRATUS WILL VARY LITTLE TODAY GIVEN THE
STRENGTHENING RIDGE AXIS. THE MAIN CHANGES...IF THEY OCCUR WILL BE
OVER THE PALOUSE AND INTO THE SOUTHERN COLUMBIA BASIN AS THE
EASTERLY WINDS ARE SUPPOSED TO INCREASE THROUGH THE AFTERNOON.
HOWEVER THE MODELS...PARTICULARLY THE NAM ARE OVERPLAYING THE
CROSS-CONTINENTAL DIVIDE PRESSURE GRADIENT. WHEREVER THE LOW CLOUDS
AND FOG FORM...THIS WILL HAVE AN IMPACT ON LOWER THE DIURNAL
TEMPERATURE SWINGS THIS AFTERNOON AND INTO TONIGHT.
FOR TONIGHT...THE MODELS HAVE BEEN CONSISTENT ON STEADILY INCREASING
THE EAST TO NORTHEAST BOUNDARY WINDS EXTENDING FROM THE NORTHERN
TIP OF IDAHO THROUGH THE EASTERN COLUMBIA BASIN. IF THIS WERE TO
OCCUR...MUCH OF THE STRATUS AND FOG WOULD ERODE OVER THE EASTERN
HALF OF THE CWA. THE ONLY AREAS WHICH WOULD BE IMMUNE TO THIS
INCREASED MIXING WOULD BE OVER THE NORTHERN VALLEYS...WHERE FOG
AND STRATUS WILL GENERALLY BE MORE WIDESPREAD THAN EARLY THIS
MORNING. THE OTHER AREAS WHICH WOULD SEE INCREASED COVERAGE WILL
BE NEAR THE CASCADES AND OKANOGAN VALLEYS AS SHALLOW MOISTURE
BEGINS TO ADVECT INTO THAT AREA. AGAIN CONFIDENCE IS FAR FROM HIGH
WITH THIS FORECAST GIVEN POOR INITIALIZATION OF THE CURRENT SKY
CONDITIONS AND PRESSURE GRADIENTS. FX
CHRISTMAS DAY THROUGH SATURDAY...VERY FEW FORECAST CHANGES MADE TO
THE FORECAST. MODELS IN GOOD AGREEMENT WITH RIDGE AXIS MOVING
DIRECTLY OVER EASTERN WASHINGTON AND OREGON ON CHRISTMAS DAY AND
SATURDAY. THIS WILL RESULT IN A STAGNANT PATTERN WITH STRENGTHENING
TEMPERATURE INVERSIONS LEADING TO AN INCREASE IN FREEZING FOG AND
STRATUS IN THE VALLEYS. FOR THE MOUNTAINS...CLEAR SKIES WILL OCCUR
ABOVE THE STRATUS.
SATURDAY NIGHT THROUGH WEDNESDAY...MODELS AGREE THAT RIDGE AXIS
WILL MOVE NORTH AND EAST OF THE AREA FOR THE EARLY PART OF NEXT
WEEK. HOWEVER STRONG SPLIT FLOW OFF THE COAST WILL GREATLY WEAKEN
PACIFIC SYSTEMS THAT ATTEMPT TO MOVE INTO THE AREA. THIS WILL
RESULT IN CONTINUED STRATUS AND POSSIBLE FREEZING FOG IN THE
VALLEYS. THUS THE AIR STAGNATION ADVISORY THAT CURRENTLY RUNS
THROUGH 4 PM SATURDAY MAY NEED TO BE EXTENDED. TOWARDS THE MIDDLE
OF THE WEEK THE GFS/CANADIAN/ECMWF BEGIN TO CONSOLIDATE THE FLOW
IN THE EASTERN PACIFIC WHICH MAY ALLOW FOR A MORE UNSETTLED
PATTERN TO DEVELOP. CONFIDENCE IS NOT HIGH WITH THIS DEVELOPING
GIVEN THE STRONG SPLIT FLOW EARLY IN THE WEEK SO PRECIPITATION
CHANCES REMAIN LOW ON WEDNESDAY AT THIS TIME. JW
&&
.AVIATION...
A MYRIAD OF FLIGHT CONDITIONS ARE EXPECTED THROUGH 12Z FRI OVER E WA
AND N ID AS UPPER LEVEL RIDGE STREGTHENS OVER THE AREA. AS OF
12Z...PATCHES OF IFR/MVFR CIGS WERE LOCATED IN AND AROUND ALL TAF
SITES SAVE KMWH. THE COVERAGE WAS RATHER SPOTTY...XCP NEAR KLWS AND
THIS IS THE ONLY SITE WHERE MVFR/IFR CIGS WILL LIKELY PERSIST
THROUGH AT LEAST 20Z. THE OTHER SITES...NAMELY KPUW...KGEG...AND
KEAT WERE ON THE OUTTER FRINGES OF THESE LOW CLOUDS. MODEL GUIDANCE
NOT HELPING THAT MUCH WITH CURRENT COVERAGE...HOWEVER WE WOULD
EXPECT TO SEE SOME EXPANSION THROUGH THE MORNING...WHICH WILL IMPACT
THE AFOREMENTIONED SITES AT TIMES THROUGH THE MORNING. DIURNAL
TRENDS WOULD SUGGEST THESE CLOUDS WILL ERODE SOMEWHAT THIS AFTN AND
INTO THE EVE. FOR TONIGHT...AFT 06Z...WE WOULD EXPECT TO SEE MORE
WDSPRD MVFR/IFR CIGS AS LOW LVL MOISTURE INCREASES BENEATH GROWING
NEAR SURFACE INVERSIONS. CONFIDENCE IS LOW WHERE EXACTLY THIS WILL
OCCUR THOUGH. FX
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 26 14 26 17 29 21 / 0 0 0 0 0 0
COEUR D'ALENE 26 15 27 16 28 20 / 0 0 0 0 0 10
PULLMAN 29 19 30 21 29 22 / 0 0 0 0 0 0
LEWISTON 32 20 32 23 32 23 / 0 0 0 0 0 0
COLVILLE 28 15 27 15 29 20 / 0 0 0 0 10 10
SANDPOINT 25 14 25 13 28 18 / 0 0 0 0 0 0
KELLOGG 25 14 25 12 27 19 / 0 0 0 0 0 0
MOSES LAKE 30 16 29 16 29 21 / 0 0 0 0 0 10
WENATCHEE 32 20 26 20 29 22 / 0 0 0 0 10 10
OMAK 26 14 25 15 28 19 / 0 0 0 0 10 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.
&&
$$
