951
FXUS66 KOTX 021040
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
240 AM PST TUE DEC 2 2008
SYNOPSIS
A PACIFIC STORM SYSTEM WILL EXIT THE REGION THIS
MORNING. DRIER AIR FROM CANADA WILL MOVE INTO THE AREA WHICH WILL
INHIBIT FOG FORMATION AND ALLOW TEMPERATURES TO DROP BELOW
FREEZING TONIGHT. HIGH PRESSURE WILL KEEP THE AREA DRY THROUGH THE
END OF THE WORK WEEK. A WEAK PACIFIC FRONT WILL SLOWLY MOVE
THROUGH THE PACIFIC NORTHWEST OVER THE WEEKEND FOR MAINLY LIGHT
PRECIPITATION.
DISCUSSION
TODAY AND TONIGHT...WATER VAPOR IMAGERY SHOWS A WELL DEFINED
CIRCULATION MOVING ONSHORE NEAR ASTORIA AND TRACKING ACROSS THE
WA/OR BORDER. MODELS SHOW THIS 500MB CIRCULATION OPENING UP INTO
AN OPEN WAVE...WHICH IS REALLY JUST AN INDICATION THAT IT'S
FORECAST TO PICK UP SPEED AND ITS TRANSLATION SPEED WILL BE FASTER
THAN ITS WINDS ON THE NORTH SIDE OF THE WAVE. NORTHWESTERLY FLOW
DEVELOPS BEHIND THIS WAVE THIS AFTERNOON WHICH FAVORS CONTINUED
SHOWER ACTIVITY IN THE SOUTHEASTERN PART OF MY FORECAST
AREA...NAMELY THE PALOUSE...LEWISTON...AND THE CAMAS PRAIRIE.
THE BIG STORY HERE WILL BE THE REMOVAL OF OUR FOG. THE LOW LEVEL
FLOW WILL SWITCH TO NORTHERLY WHICH WILL ALLOW A WEAK CANADIAN
FRONT TO DROP INTO THE AREA. MECHANICAL MIXING FROM 10-15 MPH
NORTHERLY WINDS ALONG WITH DRIER AIR FROM THIS FRONT WILL NOT
ONLY GET RID OF OUR PERSISTENT DRIPPY FOG BUT SHOULD ACTUALLY
ALLOW SOME OF THE REGION TO SEE SOME AFTERNOON SUNSHINE FOR THE
FIRST TIME IN AWHILE. WHILE THE SHALLOW FRONT WILL SLIP DOWN ALL
THE WAY TO THE WA/OR BORDER...BOTH MODELS SHOW AN AREA OF LOW/MID
CLOUDS WILL PERSIST OVER THE SOUTHERN HALF OF EASTERN WASHINGTON.
THUS LOCATIONS SOUTH OF I-90 WILL GET RID OF THEIR FOG BUT MIGHT
ONLY GET A PEEK OF SUNSHINE IF THAT. BUT OVER NORTHEAST WASHINGTON
THERE COULD ACTUALLY BE A FEW HOURS OF AFTERNOON SUNSHINE.
THIS CLEARING AND DRIER AIR WILL ALSO ALLOW TEMPERATURES TO DROP
CONSIDERABLY TONIGHT. VALLEY LOCATIONS NORTH OF SPOKANE WILL DROP
INTO THE LOWER 20S WITH A FEW SPOTS INTO THE TEENS. TO THE SOUTH
AND WEST WHERE THE CLOUD COVER WILL BE MORE PREVALENT...TEMPERATURES
WILL ONLY DROP TO AROUND THE FREEZING MARK. BUT THE DRY AIR FROM
THE CANADIAN FRONT SHOULD BE ENOUGH TO KEEP FOG FROM REFORMING
OVERNIGHT...ALTHOUGH I WON'T RULE OUT SOME PATCHY FOG ALONG THE
LARGER RIVER VALLEYS. RJ
WEDNESDAY AND THURSDAY...THE MEAN UPPER LEVEL RIDGE HOLDS FIRM
OVER THE WESTERN U.S...INCLUDING THE PACIFIC NORTHWEST. THE
DEPARTING LOW SWINGS ACROSS THE CENTRAL ROCKIES AND SHIFTS THE
FLOW ALOFT TO THE NNW FOR WEDNESDAY. COLDER...DRIER STABLE
CONTINENTAL AIR WILL SPILL THROUGH THE NORTHERN VALLEYS AND HELP
SCOUR OUT ANY LEFT OVER LOW LEVEL MOISTURE IN THE FORM OF FOG AND
STRATUS. MEANWHILE...LOW LEVEL NORTHWEST LOW LEVEL FLOW WILL
ENHANCE UPSLOPE CLOUDS AND SNOW SHOWERS ACROSS THE NORTHEAST BLUE
MOUNTAINS AND THE CAMAS PRAIRIE. WILL KEEP QPF LIGHT WITH
INSTABILITY NOT AS FAVORABLE. THERE IS THE POTENTIAL FOR A COUPLE
OF INCHES OF NEW SNOW AT THE HIGHER ELEVATIONS BY THURSDAY
MORNING. THIS IS WHEN THE MODELS AGREE ON SHOWING A SHORTWAVE PASSING
THROUGH THE FLOW AND FINALLY VEERING THE LOW LEVEL FLOW TO THE
NORTHEAST- EAST. THE COLDER CONTINENTAL AIR WILL SPREAD SOUTH AND
PUT AN END THE PRECIPITATION. HIGH PRESSURE RETURNS WITH A RIDGE
ALOFT OFF THE COAST FOR THURSDAY AFTERNOON AND NIGHT. THIS WILL
CREATE LIGHT WINDS AND BUILD LOW LEVEL INVERSIONS. SOME PATCHY
FOG IS POSSIBLE NEAR THE LAKES AND RIVERS...ALTHOUGH EXPECT MAINLY
CLEAR SKIES AND CHILLY TEMPERATURES WITH SOME TEENS IN THE
OVERNIGHT HOURS.
BY FRIDAY...THE RIDGE AXIS ALOFT SHIFTS INLAND AND FLATTENS AS THE
UPPER LEVEL JET SINKS SLOWLY SOUTH ACROSS THE CANADIAN
PROVIDENCES. EXPECT A DIRTY RIDGE AS MOISTURE INCREASES IN THE
WESTERLY FLOW...AND ENHANCES ISENTROPIC LIFT IN THE MID TO UPPER
LAYERS OF THE ATMOSPHERE. CLOUD COVER WILL STEADILY INCREASE AND
LOWER THROUGH THE DAY ESPECIALLY ACROSS THE NORTHERN ZONES. WARM
AIR ADVECTION WILL PUSH UP 850MB TEMPS AND SNOW LEVELS...SO WHEN
THE LOW LEVELS FINALLY SATURATE AND PRECIPITATION FALLS...IT MAY
START OFF AS SNOW BRIEFLY BUT CHANGE OVER TO RAIN ACROSS MANY OF
THE VALLEY LOCATIONS BY EARLY SATURDAY MORNING.
SATURDAY THROUGH MONDAY...LITTLE CHANGE WAS MADE TO THE WEEKEND
FORECAST AND BEYOND. IT APPEARS TO BE AN ACTIVE PERIOD DESPITE
THE PREVAILING RIDGE ALOFT. THE FRONTAL BOUNDARY THAT STARTS THE
PRECIPITATION ACROSS THE NORTHERN ZONES BY EARLY SATURDAY
MORNING...WILL SLOWLY SHIFT SOUTH AND BRING A GOOD SHOT OF
PRECIPITATION THROUGH THE REGION SATURDAY NIGHT. BY SUNDAY...THE
WET WEATHER WILL CONTINUE IN THE SOUTHEAST ZONES AS A BROAD TROUGH
SWEEPS THROUGH THE REGION. A FLAT DIRTY RIDGE RETURNS FOR MONDAY
WITH MILDER AND WETTER CONDITIONS INTO TUESDAY. RFOX.
AVIATION
IFR CONDITIONS THIS MORNING WILL GRADUALLY IMPROVE BY 18Z AS A
PACIFIC STORM SYSTEM EXITS THE REGION AND NORTHWESTERLY WINDS MIX
OUT THE FOG AND LOW CLOUDS. KLWS AND KPUW WILL BE THE LAST SITES
TO IMPROVE...GOING TO MVFR/VFR CONDITIONS BY 00Z. SKIES TONIGHT WILL
CLEAR NORTH OF A LINE FOR KGEG TO KOMK WITH A VFR CIG TO THE SOUTH
OF THIS LINE. FOG IS NOT EXPECTED TO FORM OVERNIGHT. RJ
PRELIMINARY POINT TEMPS/POPS
SPOKANE 44 23 37 21 34 17 / 40 0 0 0 0 0
COEUR D'ALENE 44 23 39 22 37 19 / 50 10 10 0 10 10
PULLMAN 45 30 42 28 38 21 / 60 20 20 0 0 0
LEWISTON 51 35 46 30 40 26 / 40 20 30 10 10 0
COLVILLE 42 21 38 20 37 18 / 30 10 0 0 10 0
SANDPOINT 43 23 36 21 36 17 / 40 10 10 0 10 10
KELLOGG 40 25 36 23 34 22 / 80 20 10 10 10 10
MOSES LAKE 48 32 45 26 37 20 / 10 0 0 0 0 0
WENATCHEE 49 33 44 29 40 25 / 10 10 0 0 0 0
OMAK 43 27 39 23 37 20 / 10 10 0 0 10 0
OTX WATCHES/WARNINGS/ADVISORIES
ID...NONE.
WA...AIR STAGNATION ADVISORY UNTIL 3 PM PST THIS AFTERNOON FOR EAST
SLOPES NORTHERN CASCADES...WENATCHEE AREA.
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