FXUS66 KOTX 232343
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
443 PM PST WED DEC 23 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.
&&
...STABLE HIGH PRESSURE TO BRING POTENTIAL FOR AIR STAGNATION...
.DISCUSSION...
TONIGHT THROUGH SATURDAY...THE MODELS ARE IN EXCELLENT AGREEMENT
THROUGH SATURDAY THAT A HIGH AMPLITUDE UPPER LEVEL RIDGE WILL
REMAIN ANCHORED OVER THE WESTERN UNITED STATES. STRONG HIGH
PRESSURE ALOFT WILL BRING THE DEVELOPMENT OF A DEEP LOW LEVEL
TEMPERATURE INVERSION. AT THE SAME TIME SUBSIDENCE WARMING
OCCURS ALOFT...THE INVERSION WILL BE REINFORCED BY STRONG
RADIATIONAL COOLING TONIGHT...AND ONCE AGAIN TOMORROW NIGHT. THE
TOUGHEST PART OF THE FORECAST WILL BE TIMING THE DEVELOPMENT OF
FOG AND STRATUS. AS OF 22Z...THE LAST REMNANTS OF OUR RESIDENT
STRATUS LINGERS OVER THE PALOUSE. DEWPOINTS HAVE PLUMMETED OVER
MUCH OF EASTERN WASHINGTON AND NORTHERN IDAHO TODAY COURTESY OF A
NORTH-SOUTH PRESSURE GRADIENT ACROSS THE NORTHERN VALLEYS OF
WASHINGTON. DEWPOINTS IN THE LOW TEENS ARE COMMON NORTH OF
INTERSTATE 90...BUT ADDITIONAL LOW LEVEL DRYING WILL BE HINDERED
BY A DECREASE IN THE NORTHERLY WINDS TONIGHT. GRADIENTS BETWEEN
PULLMAN AND YELLOW KNIFE IN SOUTHERN BC HAVE BEGUN TO WEAKEN THIS
AFTERNOON...AND THE WEAKENING TREND WILL CONTINUE THROUGH THE
NIGHT. WHAT LITTLE STRATUS REMAINS AROUND PULLMAN WILL LIKELY
DISSIPATE TONIGHT AS THE LIGHT NORTHWEST WIND (UPSLOPE) INTO THE
PALOUSE DECREASES.
THE NAM AND GFS HOLD ONTO A WEAK EAST OR NORTHEAST PRESSURE
GRADIENT AT THE SURFACE THROUGH SATURDAY. WITH THAT TYPE OF FLOW
PATTERN FOG AND STRATUS WILL LIKELY DEVELOP OVER THE OREGON BASIN
AND SOUTHERN WASHINGTON BASIN FIRST. THE SHELTERED VALLEYS OF THE
EAST SLOPES AND THE NORTHERN VALLEYS OF WASHINGTON WILL ALSO HAVE
A SHOT AT FOG DEVELOPMENT BEFORE THE NORTHERN BASIN AND PALOUSE.
ITS TOUGH TO TRUST THE BOUNDARY LAYER MOISTURE PROGS FROM THE
MODELS IN A DAY 2 OR DAY 3 FORECAST...ESPECIALLY GIVEN THE
COMPLEXITY OF WET GROUND FREEZING UP...SO THE PREVIOUS FORECAST
HASN'T BEEN CHANGED MUCH. STILL LOOKING FOR PATCHY FOG
DEVELOPMENT FRIDAY MORNING WITH EXPANSION OF THE FOG AND STRATUS
SATURDAY INTO SUNDAY.
PER COORDINATION WITH SURROUNDING OFFICES AND STATE AND LOCAL
AGENCIES AN AIR STAGNATION ADVISORY HAS BEEN ISSUED FOR THURSDAY
THROUGH SATURDAY. NORTHEAST FLOW BELOW THE INVERSION LAYER ON
THURSDAY AND FRIDAY MAY BE IN THE 5-10MPH RANGE AND MAY BE ENOUGH
TO PROVIDE A BIT OF MIXING OVER THE PALOUSE...BASIN AND SPOKANE
AREA...BUT THIS STABLE INVERSION IS LIKELY TO PERSIST WELL INTO
NEXT WEEK...SO IT WAS AGREED TO HOIST THE ADVISORY EARLY IN THE
EVENT. THERE IS A HIGH LIKELIHOOD THAT THE ADVISORY WILL BE
EXTENDED BEYOND SATURDAY AS MORE COORDINATION OCCURS THIS WEEKEND.
/GKOCH
SUNDAY THROUGH WEDNESDAY...MODELS IN THE LONGER RANGE FORECAST
CONTINUE TO BREAK DOWN THE RIDGE OVER THE WESTERN US WITH THE
REMNANTS ENDING UP IN WESTERN CANADA. EXPECT FREEZING
TEMPERATURES AT NIGHT AND MOST AREAS DURING THE DAY WITH THE
CONTINUED POTENTIAL FOR AREAS OF FOG AND FREEZING FOG AS A VERY
STABLE AIR MASS WILL BE IN PLACE. THERE WILL MORE SUN AND
WARM TEMPERATURES IN THE MOUNTAINS AS THE STRATUS DECK IS EXPECTED
TO ONLY TOP 3000 FEET AT MAXIMUM. THE RIDGE BREAKDOWN COOLS 850
TEMPS TO NEAR JUST BELOW FREEZING.
ON MONDAY A SLOW TRANSITION TO A MORE WESTERLY FLOW COMPONENT ALOFT
WILL CONTINUE. HOWEVER...STORM TRACK JET ENERGY WILL STILL BE
SPLIT OFF THE PACIFIC NORTH AND SOUTH WITH THE PAC NW IN BETWEEN FOR A
MAINLY DRY FORECAST MONDAY. BY TUESDAY THE ECMWF AND THE GFS TO A
DEGREE HAVE THE POTENTIAL FOR WEAK PACIFIC TROUGH ENERGY AND MOISTURE IN
WEST FLOW ALOFT TO ONCE AGAIN IMPACT THE AREA. THEREFORE THE TREND
WILL BE TOWARD INCREASING POPS TUESDAY AND WEDNESDAY INTRODUCING A
CHANCE OF A SNOW/RAIN MIX. RIGHT NOW THE POTENTIAL FOR ANY
SIGNIFICANT STORM ACTIVITY IS LOW. TEMPERATURES LOOK TO BE NEAR
NORMAL FOR THIS PERIOD WITH LOWS IN THE TEENS AND 20S AND HIGHS
UPPER 20S TO MID 30S.
&&
.AVIATION...
DRY AIR IN THE LOW LEVELS WILL CONTINUE TO ERODE THE LOW CLOUDS OVER
SOUTHEAST WASHINGTON AND ADJACENT PORTIONS OF THE CENTRAL AND
SOUTHERN IDAHO PANHANDLE THIS THROUGH 03Z TONIGHT. HOWEVER LOOK FOR
LOW CLOUDS TO POTENTIALLY REDEVLOP IN THE PULLMAN AND LEWISTON AREAS
FROM 06Z-12Z. GENERALLY...THE AIRMASS OVER EASTERN WASHINGTON AND
NORTHERN IDAHO WILL LIKELY BE TOO DRY FOR THE FORMATION OF FOG
TONIGHT...BUT SOME LOCALIZED STRATUS MAY REDEVELOP LATE TONIGHT AND
EARLY THURSDAY MORNING AT LEWISTON...SPOKANE...AND WENATCHEE
ESPECIALLY NEAR WATER BODIES. /TCARTER
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 12 26 14 26 17 29 / 0 0 0 0 0 0
COEUR D'ALENE 15 26 15 27 16 28 / 0 0 0 0 0 0
PULLMAN 18 26 17 30 19 29 / 0 0 0 0 0 0
LEWISTON 22 31 19 29 19 32 / 0 0 0 0 0 0
COLVILLE 9 24 12 27 15 29 / 0 0 0 0 0 10
SANDPOINT 13 23 13 25 13 28 / 0 0 0 0 0 0
KELLOGG 12 23 13 25 12 27 / 0 0 0 0 0 0
MOSES LAKE 13 28 13 27 13 29 / 0 0 0 0 0 0
WENATCHEE 19 28 19 26 18 29 / 0 0 0 0 0 10
OMAK 10 26 10 25 15 28 / 0 0 0 0 0 10
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...AIR STAGNATION ADVISORY FROM 4 AM THURSDAY TO 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 FROM 4 AM THURSDAY TO 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.
&&
$$
