FXUS66 KOTX 221212
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
412 AM PST TUE DEC 22 2009
.SYNOPSIS...
A COLD FRONT WILL MOVE THROUGH THE PACIFIC NORTHWEST THIS MORNING BRINGING
ANOTHER ROUND OF RAIN AND HIGH MOUNTAIN SNOW TO THE REGION. THE
FRONT WILL ALSO BRING AN END TO THE FOG AND LOW CLOUDS THAT HAVE
PLAGUED CENTRAL WASHINGTON FOR THE LAST SEVERAL DAYS. AN UPPER
LEVEL DISTURBANCE WILL BRING THE CHANCE FOR SOME LIGHT SNOW TO THE
IDAHO PANHANDLE TUESDAY NIGHT INTO WEDNESDAY MORNING. COLD...BUT
DRY WEATHER IS EXPECTED FOR CHRISTMAS EVE THROUGH THE WEEKEND
FOLLOWING CHRISTMAS.
&&
.DISCUSSION...
TODAY AND TONIGHT...WE'LL BE TRACKING THE EVOLUTION OF TWO KEY
FEATURES OF INTEREST TODAY. THE FIRST IS THE THETA-E RIDGE AXIS
AND MOIST AIRSTREAM STRETCHING FROM ERN OREGON N INTO SERN
SW...AND THE SECOND IS THE VORT MAX UPSTREAM CURRENTLY OVER WRN
WA THAT WILL DRIFT SE INTO CNTRL OREGON TODAY. ERN WA HAS BEEN
UNDER A NARROW CORRIDOR STUCK BETWEEN THE STRATIFORM PCPN BAND
ASSOCIATED WITH THE AFOREMENTIONED MOIST PLUME AND THE CONVECTIVE
PCPN TIED TO THE WRN WA VORT MAX. AS THIS VORT MAX SHIFTS S
TODAY...THE ORIENTATION OF THE THETA-E RIDGE AXIS COMBINED WITH
FRONTOGENETIC FORCING WILL PRODUCE A BAND OF PCPN THAT WILL
STRETCH NW-TO-SE FROM CNTRL WA TO NE OREGON THAT WILL DRIFT S
TODAY. WE'RE ALSO EXPECTING THE LOW-LEVEL FLOW TO VEER TO A MORE
NW DIRECTION...BECOMING MORE FAVORABLE FOR OROGRAPHIC ASCENT INTO
THE PALOUSE...CNTRL ID PANHANDLE AND THE CAMAS PRAIRIE AREA TODAY.
CAA HAS LOWERED SNOW LEVELS TO THE VALLEY FLOORS IN THESE ZONES
ALREADY...AND ANY SUBSEQUENT PCPN FALLING TODAY WILL REMAIN AS
SNOW. WE'VE ISSUED ADVSYS TO COVER THIS SNOW THREAT...THE HEAVIEST
ACCUMULATIONS CONFINED TO SE WA AND N ID CLOSEST TO THE MOIST
PLUME AND TROWAL AXIS. THE PALOUSE AND NRN BLUE MTNS WILL ALSO BE
UNDER AN INCREASED SNOW THREAT BASED ON THE LATEST MOSAIC RADAR
TRENDS...WITH LATER FCST UPDATES TO INCREASE SNOW ACCUMULATIONS
POSSIBLE. STAY TUNED. BZ
WEDNESDAY THROUGH CHRISTMAS DAY...AN UPPER LEVEL WAVE WILL EXIT
FROM IDAHO INTO MONTANA ON WEDNESDAY WITH A FEW LINGERING SNOW
SHOWERS OVER THE CENTRAL PANHANDLE MOUNTAINS AND CAMAS PRAIRIE. ON
THE BACK SIDE OF THIS WAVE NORTHWEST FLOW WILL AID IN USHERING IN
A COLD CANADIAN AIR MASS WITH 850MB TEMPS ON WEDNESDAY FALLING TO
AROUND -12C NEAR THE CANADIAN BORDER AND OVER NORTH IDAHO...AND -8
TO -10C OVER SOUTHERN WASHINGTON. DRIER AIR WILL ALSO MOVE INTO
THE AREA WHICH WILL RESULT IN MOSTLY CLEAR TO PARTLY CLOUDY SKIES
WITH ONLY OCCASIONAL MID AND HIGH CLOUDS EXPECTED. WITH FRESH SNOW
COVER ON THE CAMAS PRAIRIE FROM TODAY/S SNOWFALL AND THE COLD/DRY
AIR MASS MOVING IN...TEMPERATURES AT WINCHESTER WILL LIKELY
RAPIDLY FALL AND WERE LOWERED SEVERAL DEGREES FOR WED NGT AND
AGAIN THURS NIGHT. ON CHRISTMAS DAY UPPER LEVEL HIGH PRESSURE WILL
NOSE EAST TOWARDS THE AREA BRINGING A WARMING TREND TO THE
MOUNTAINS. IN THE VALLEYS THE SHORT LATE DECEMBER DAYS...AND VERY
STRONG TEMPERATURE INVERSIONS DEVELOPING WILL LEAD TO CONTINUED
COLD TEMPERATURES WITH HIGHS MAINLY IN THE MID 20S. OVERALL FOG
COVERAGE ON FRIDAY WAS SCALED BACK DUE TO THE NAM AND GFS SHOWING
UNSATURATED BOUNDARY LAYER AND ONLY VERY SHALLOW NEAR SATURATED
LAYER AT THE SFC. THIS IS DUE TO THE ADVECTION OF DRY AIR ON
WEDNESDAY INTO THE AREA AND THUS FOG ON CHRISTMAS WILL LIKELY BE
LIMITED TO NEAR WATER SOURCES.
SATURDAY THROUGH MONDAY...THERE IS GENERAL AGREEMENT IN THE MODELS
OF THE RIDGE AXIS MOVING EAST AND WEAKENING OVER THE WEEKEND.
ALTHOUGH THE SPLIT FLOW OFF THE COAST WILL CONSIDERABLY WEAKEN ANY
SYSTEMS THAT APPROACH THE AREA WITH DRY CONDITIONS LIKELY TO
CONTINUE. WITHOUT ANY NOTEWORTHY SYSTEMS TO SCOUR OUT THE COLD AIR
AND INVERSIONS...FOG AND STRATUS THAT DEVELOPS FRI NGT/SATURDAY
WILL LIKELY BE STAYING FOR AWHILE. POTENTIAL EXISTS FOR AN AIR
STAGNATION PERIOD FRIDAY THROUGH MONDAY. JW
&&
.AVIATION...
A MID-LEVEL DISTURBANCE DROPPING THROUGH THE AREA TODAY WILL
PRODUCE SNOW ACROSS A LARGE PART OF THE REGION THIS MORNING...DECREASING
TO ISOLATED SNOW SHOWERS BY MIDDAY. THE HEAVIEST SNOWS WILL BE FROM
KLWS TO KPUW...AND AS FAR N AS KGEG/KSFF/KCOE THROUGH 18Z...WITH
IFR VSBYS AND CEILINGS LIKELY. KPUW WILL SEE THE LOWEST CEILINGS
AND VSBYS.
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 33 21 27 14 24 13 / 50 20 10 0 0 0
COEUR D'ALENE 35 25 28 14 25 15 / 60 40 10 0 0 0
PULLMAN 34 24 28 12 25 14 / 60 30 30 0 0 0
LEWISTON 40 26 35 19 29 18 / 60 20 20 0 0 0
COLVILLE 36 19 26 11 24 11 / 30 20 0 0 0 0
SANDPOINT 35 24 28 13 23 13 / 50 60 20 0 0 0
KELLOGG 33 23 26 11 25 13 / 90 60 40 10 0 0
MOSES LAKE 37 20 31 16 27 12 / 20 0 0 0 0 0
WENATCHEE 37 22 29 19 28 16 / 20 0 0 0 0 0
OMAK 35 18 23 12 25 10 / 40 0 0 0 0 0
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR CENTRAL
PANHANDLE MOUNTAINS...LEWIS AND SOUTHERN NEZ PERCE
COUNTIES...LEWISTON AREA.
WA...NONE.
&&
$$
