FXUS66 KOTX 251152
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
347 AM PST FRI DEC 25 2009
.SYNOPSIS...
STRONG HIGH PRESSURE WILL CONTINUE TO BUILD OVER THE PACIFIC
NORTHWEST. THIS RIDGE WILL 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...ESPECIALLY BY EARLY NEXT WEEK.
&&
.DISCUSSION...
TODAY AND TONIGHT...STRONG UPPER LEVEL RIDGE AXIS WILL ONCE AGAIN BE
THE DOMINANT FEATURE OVER THE INLAND NW. AS OF 10Z...PER THE LATEST
WATER VAPOR IMAGERY...THE RIDGE APPEARED TO BE CENTERED ON THE
COAST. THE SHORT-RANGE MODELS ARE CONSISTENT IN BRINGING THE RIDGE
AXIS INTO THE CASCADES BY LATE THIS AFTERNOON AND THEN PINCH IT OFF
AS A CLOSED HIGH OVER SOUTHEAST BC OVERNIGHT. AS THE RIDGE STEADILY
SLIDES INTO THE CWA DURING THE NEXT 24 HOURS...WE EXPECT TO SEE
GRADUAL DRYING THROUGH THE RELATIVELY MOIST BOUNDARY LAYER. THIS IS
DUE TO THE TRANSITION OF THE LOW-LEVEL WINDS TO MORE OF A
NORTHEASTERLY ORIENTATION. THESE NORTHEASTERLY WINDS WILL INCREASE
AS THE 1037MB CURRENTLY OVER SOUTHEAST BC DROPS SLOWLY SOUTHEAST
ALONG THE CONTINENTAL DIVIDE THROUGH TONIGHT. MEANWHILE...THE
PRESENCE OF THE UPPER LEVEL RIDGE WILL LEAD TOWARD INCREASED
SUBSIDENCE AND GENERALLY DRY OUT THE MID/UPPER LEVELS OF THE
ATMOSPHERE. THE COMBINATION OF DRYING AND SUBSIDENCE SUGGESTS THE
STRATUS FIELDS WE ARE CURRENTLY SEEING OVER THE IDAHO PANHANDLE AND
LOWER COLUMBIA BASIN WILL BECOME LESS PREVALENT THROUGH THE PERIOD.
MEANWHILE THE SAME EASTERLY LOW-LEVEL FLOW WILL KEEP THE LOW CLOUDS
PILED UP NEAR THE CASCADES. LOOKING AT THE SOUNDING DATA FROM ACROSS
THE REGION...WE CANNOT ENTIRELY RULE OUT THE CHANCES FOR SHALLOW
RADIATION FOG FORMING AWAY FROM THE CASCADE STRATUS DECK...HOWEVER
THE CHANCES DO NOT LOOK GREAT. THIS IS ESPECIALLY TRUE THROUGH THE
PURCELL TRENCH AND INTO THE EASTERN COLUMBIA BASIN AND PALOUSE.
THESE LOCATIONS WILL SEE THE STRONGEST NORTHEAST-EAST LOW LEVEL FLOW
AND THE MOISTURE PROFILES DEPICT AN UNFAVORABLE DECREASING MIXING
RATIO WITH HEIGHT. THE BEST CHANCES OF FOG WILL LIKELY BE RESERVED
FOR PROTECTED LOCATIONS IN THE NORTHERN VALLEYS.
TEMPERATURES WILL LIKELY SHOW LITTLE VARIATION FROM YESTERDAY...
HOWEVER THE INCOMING RIDGE LEAD TO SOME MODERATE WARMING OVER THE
MOUNTAINS AS 850 MB TEMPS CLIMB SOME 3-6C VS YESTERDAY. FX
SATURDAY THROUGH SUNDAY NIGHT...MODELS ARE IN GOOD AGREEMENT WITH
AN UPPER HIGH CLOSING OFF OVER ALBERTA...RESULTING IN A DRY
EASTERLY FLOW OVER THE AREA. AT THE SFC...THE NAM SHOWS THE
EASTERLY PRESSURE GRADIENT TIGHTENING ON SATURDAY WITH NE WINDS
INCREASING TO 5 TO 15 MPH FOR COEUR D'ALENE...SPOKANE...PULLMAN...AND
THE COLUMBIA BASIN. THESE WINDS WILL LIMIT FOG FORMATION TO THE
SHELTERED VALLEYS OF NE WASHINGTON NEAR WATER SOURCES. THE
EASTERLY UPSLOPE FLOW NEAR THE CASCADES WILL AID IN STRATUS
PERSISTING FOR PLACES LIKE WENATCHEE AND THE WATERVILLE PLATEAU.
STRATUS IS ALSO EXPECTED TO REMAIN POOLED UP OVER THE LOWER
COLUMBIA BASIN SO MOSTLY CLOUDY SKIES ARE EXPECTED NEAR AND SOUTH
OF MOSES LAKE. ELSEWHERE MOSTLY SUNNY SKIES ARE EXPECTED BUT WITH
STILL LOW MIXING HEIGHTS AND COLD AIR TRAPPED BENEATH A TEMPERATURE
INVERSION VALLEY HIGHS WILL ONLY REACH THE MID 20S TO LOWER 30S. A
NEAR REPEAT IS EXPECTED ON SUNDAY ALTHOUGH BY SUNDAY NIGHT
PRESSURE GRADIENTS BEGIN TO RELAX SO MORE WIDESPREAD FOG AND
STRATUS IS POSSIBLE.
MONDAY THROUGH THURSDAY...OVERALL MODEL AGREEMENT DECREASES NEXT
WEEK SO NO CHANGES WERE MADE TO THE FORECAST. THE NEW 00Z ECMWF
MODEL SPLITS THE TUE NGT/WED SYSTEM LEAVING EASTERN WASHINGTON AND
NORTH IDAHO DRY FOLLOWED BY HIGH PRESSURE BUILDING IN THROUGH
FRIDAY. THIS WOULD RESULT IN DRY CONDITIONS ALL THE WAY THROUGH
THE NEW YEAR. HOWEVER THE 00Z GFS SHOWED MORE CONSOLIDATED FLOW
WITH AN UNSETTLED PATTERN DEVELOPING. CLIMO POPS LOOK GOOD FOR MID
TO LATE WEEK DUE TO UNCERTAINTY IN THE FORECAST. JW
&&
.AVIATION...
MVFR CIGS FROM LOW CLOUDS WILL CONTINUE TO IMPACT KEAT THROUGH MOST
OF THE PD...WITH A CHANCE OF CIGS LOWERING TO IFR CONDITIONS LATE
TONIGHT IN RESPONSE TO INCOMING UPR LVL RIDGE AXIS. OTHER PROBLEM
SPOTS THIS MORNING...WILL BE NEAR KCOE AND KMWH AS STRATUS FIELDS
NEAR THOSE AIRPORTS EXPANDS. SOME OF THIS LOW CLOUDINESS COULD
IMPACT KSFF AND KGEG AFT 14Z...BUT HARD TO ASCERTAIN THE TRENDS OF
THESE LOW CLOUDS AS THEY ARE BEING CONCEALED BY MID LEVEL CLOUDS AT
THIS TIME. ALL TAFS SITES ASIDE FROM KEAT WILL SEE DECREAING CLOUD
TREND THROUGH THE DAY AS MUCH DRIER AIR MOVES INTO THE REGION FROM
THE NORTHEAST. VFR CONDITIONS ARE THEN EXPECTED AT ALL SITES
OVERNIGHT...HOWEVER THERE IS A SLIGHT CHANCE OF BCFG LATE. FX
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 26 14 28 17 26 18 / 0 0 0 0 0 0
COEUR D'ALENE 27 15 29 19 27 20 / 0 0 0 0 0 0
PULLMAN 30 19 31 20 29 20 / 0 0 0 0 0 0
LEWISTON 34 22 33 22 31 22 / 0 0 0 0 0 0
COLVILLE 28 17 25 15 26 18 / 0 0 0 0 0 0
SANDPOINT 27 14 28 18 26 18 / 0 0 0 0 0 0
KELLOGG 26 17 26 14 27 20 / 0 0 0 0 0 0
MOSES LAKE 30 17 28 18 28 18 / 0 0 0 0 0 0
WENATCHEE 28 19 26 21 28 20 / 0 0 0 0 0 0
OMAK 25 15 25 13 25 15 / 0 0 0 0 0 0
&&
.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.
&&
$$
