FXUS66 KOTX 041202
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
400 AM PST FRI DEC 4 2009
.SYNOPSIS...
THE DRY AND COOL WEATHER ACROSS THE INLAND NORTHWEST WILL GIVE
WAY TO A SERIES OF CANADIAN COLD FRONTS TODAY AND THROUGH THE
WEEKEND. A WEAK FRONT WILL BRUSH THE REGION TODAY...WHILE A
SECOND FRONT ARRIVES LATE SATURDAY INTO SUNDAY. EACH SYSTEM WILL
BRING A SHOT OF COLD AIR WITH A CHANCE OF LIGHT SNOW AND GUSTY
NORTH WINDS. EXPECT MUCH COOLER TEMPERATURES WITH GENERALLY DRY
CONDITIONS THROUGH THE MIDDLE OF NEXT WEEK.
&&
.DISCUSSION...
TODAY AND TONIGHT...THE WATER VAPOR LOOP SHOWS THE UPPER LEVEL
FRONT HAS MOVED THROUGH THE REGION WITH VERY DRY AIR BEHIND THE
FRONT...MEANWHILE THE RIDGE IN THE PACIFIC WILL CONTINUE TO
AMPLIFY THIS MORNING. TAKING A LOOK AT THE SURFACE IT APPEARS THE
SURFACE FRONT IS STILL MOVING THROUGH BRITISH COLUMBIA AND IS ON
TRACK TO MOVE THROUGH MY FORECAST AREA LATE THIS MORNING. UNTIL
THEN CLEARING SKIES AND LIGHT WINDS HAS INCREASED THE STRATUS
DEVELOPMENT THROUGH THE OKANOGAN VALLEY AND BASIN AND IS SLOWLY
PUSHING EASTWARD BEHIND THE CLEARING SKIES. EXPECT PATCHY FOG
DEVELOPMENT AS WELL AND WENT AHEAD AND INCREASED SKY CONDITIONS
AS WELL.
THE 00Z MODELS ARE SIMILAR IN SHOWING THE SURFACE FRONT WEAKENING
QUITE A BIT AS IT SLOWLY MOVES THROUGH THE FORECAST AREA THIS
MORNING THERE WILL BE SOME LIFT PROVIDED BY THE FRONTAL PASSAGE
AND ENHANCED BY THE LEFT ENTRANCE REGION OF THE JET. AT ISSUE IS
HOW DRY THE ATMOSPHERE IS WITH PW'S ONLY .15 TO .20. WITH THIS IN
MIND EXPECT ONLY ISOLATED TO SCATTERED PRECIPITATION WITH THE
FRONT ITSELF. SNOW LEVELS WILL REMAIN AT THE SURFACE THROUGH THE
WEEKEND AND BEYOND AND ALL PRECIPITATION WILL BE AS SNOW. BEHIND THE
FRONT THE ATMOSPHERE WILL DESTABILIZE ENOUGH TO SUPPORT SHOWERS.
LOOKING AT SATELLITE PRODUCTS UPSTREAM IN BC THERE IS A SURGE OF
LOW TO MID LEVEL MOISTURE MOVING SOUTH. SURFACE OBSERVATIONS ARE
PICKING UP SOME SNOW IN PLACES. EXPECT WITH THE SOUTH-SOUTHEAST
MOVEMENT OF THE TROUGH THE BEST CHANCES OF ACCUMULATING SNOW WILL
BE ACROSS THE OROGRAPHICALLY ENHANCED PANHANDLE MOUNTAINS THIS
AFTERNOON AND EARLY EVENING. CHANCES FOR PRECIPITATION WERE HANDLED
WELL IN PREVIOUS FORECASTS AND ONLY MINOR ADJUSTMENTS WERE MADE.
TEMPERATURES WILL BE IN THE MID 20S TO MID 30S AND ON THE COOL
SIDE OF NORMAL.
LATE THIS AFTERNOON AND THROUGH THE NIGHT THE PRESSURE GRADIENT WILL
INCREASE FORM THE NORTH BEHIND THE FRONT. COMBINED WITH NORTHERLY
850H WINDS OF 20-25KTS EXPECT INCREASING WINDS THROUGH THE
NORTH-SOUTH VALLEYS...OKANOGAN VALLEY AND DOWN THE KETTLE RIVER.
NORTH WINDS 10-20 MPH WITH GUSTS 25-30 MPH ARE EXPECTED. THE WINDS
SHOULD KEEP THE SURFACE MIXED AND TEMPERATURES...WHILE STILL ON THE
COOL SIDE...WILL BE SEVERAL DEGREES WARMER THEN THIS MORNING.
NORTH-NORTHWEST FLOW WILL KEEP THE BEST CHANCES OF SNOW SHOWERS
ACROSS THE PANHANDLE MOUNTAINS. /TOBIN
...VERY COLD TEMPERATURES...BREEZY WINDS...AND NEAR ZERO
WINDCHILLS EXPECTED OVER THE WEEKEND INTO NEXT WEEK...
SATURDAY THROUGH WEDNESDAY...THE BIG CHILL LOOKS TO BE WELL ON
TRACK AS EVENING WATER VAPOR SHOWING A RIDGE OF HIGH PRESSURE
RAPIDLY AMPLIFYING POLEWARD INTO CENTRAL ALASKA. OUR SECONDARY
SHORTWAVE FEATURE...WHICH WILL BE RESPONSIBLE FOR DRAGGING THE
COLDEST AIR INTO THE INLAND NW SATURDAY NT...IS NOW ROUNDING
THE TOP OF THE RIDGE AND DRIFTING INTO EXTREME NORTHEASTERN ALASKA.
MODELS APPEAR TO HAVE INITIALIZED WELL AND SHOW VERY LITTLE SPREAD
AMONGST ONE ANOTHER THROUGHOUT THE NEXT 72HRS. THIS MORNING'S
SHORTWAVE IS SETTING THE STAGE FOR THE INITIAL COLD TROUGH OVER THE
REGION...BUT IT WILL BE THIS SECOND WAVE WHICH TAKE MORE OF AN
OFFSHORE ROUTE AND DRAG AN ARCTIC FRONT ACROSS THE REGION. 09Z
METARS UNDER THIS SHORTWAVE...IN EASTERN AK/NW CANADA ARE WELL
SUPPORTIVE OF THE COLD TO COME WITH TEMPERATURES GENERALLY RANGING
FROM THE SINGLE DIGITS TO BELOW ZERO. OVERALL...LITTLE CHANGES WERE
MADE TO THE PREVIOUS FORECAST REGARDING THE WINDS AND TEMPERATURES.
LOOK FOR HIGH TEMPERATURES IN THE TEENS WITH LOWS IN THE SINGLE
DIGITS TO BELOW ZERO. SEE WEATHER STORY 2 FOR A QUICK LOOK AT
TEMPERATURES IN SELECTED CIITES. WINDS WILL BE BREEZY ACROSS THE
ENTIRE REGION WITH THE STRONGEST WINDS EXPECTED ACROSS THE LOWER
COLUMBIA BASIN AND FUNNELING DOWN THE PURCELL TRENCH WHERE WE CAN
EXPECT SUSTAINED WINDS OF 15-25 MPH WITH GUSTS 30-45 MPH STARTING
SATURDAY NIGHT...CONTINUING THROUGH SUNDAY NIGHT.
THE BIGGEST CHANGES TO THE FORECAST WERE WITH POPS AND QPF AMTS
WHICH WERE ADJUSTED SLIGHTLY HIGHER OVER THE EAST SLOPES... OKANOGAN
VALLEY...OKANOGAN HIGHLANDS...AND WATERVILLE PLATEAU WHERE A SMALL
WINDOW OF DEEP OMEGA WILL EXIST FROM THE SFC TO 500MB ASSOCIATED
WITH LIFT ALONG THE LEADING EDGE OF THE ARCTIC BOUNDARY AND INCR
800-600MB DEFORMATION ALONG THE NORTHERN PERIPHERY OF A BROAD AREA
OF LOW PRESSURE SETTING UP TO OUR SOUTH. INITIAL THOUGHTS WERE THAT
THE AIRMASS WOULD BE TOO DRY TO SUPPORT ANY MEASURABLE
PRECIPITATION...HOWEVER EVEN WITH PWAT VALUES NEAR 0.12"...THE
FRIGID AIRMASS BECOMES RELATIVE TO THE LOW WATER CONTENT AND
SATURATION IS MET JUST AS IT WOULD WITH TEMPERATURES IN THE 50'S AND
HAVING HALF AN INCH OF PWAT. THE NAM IS AMONGST THE WETTEST
SOLUTIONS WITH AS MUCH AS 0.22" IN THE NORTHERN CASCADES AND GFS/EC
TRENDING WITH UP TO 0.15". THE FORECAST WILL FOLLOW THE LATTER WITH
LESSER AMTS IN THE VALLEYS. USING A 25-30:1 SLR...THIS COULD SQUEEZE
OUT UP TO A FEW INCHES OF EXTREMELY FLUFFY SNOW UNDER THE HEAVIEST
PRECIP BANDS BUT WITH COLD TEMPERATURES ALREADY IN PLACE PRIOR THE
PRECIP ONSET...TEMPERATURES CONTINUING TO FALL THROUGHOUT THE
DAY...AND SNOW BEING VERY DRY IN NATURE...EXPECT VERY LITTLE IMPACTS
TO TRAVEL WITH ANY SNOWFALL LIKELY TO DRIFT OR BLOW OFF ANY ROADWAYS
BY PASSING CARS OR THE BREEZY ENVIRONMENTAL WINDS.
THE COLD TEMPERATURES WILL BE HERE THROUGH MUCH OF THE WEEK BUT
THERE IS STILL SOME UNCERTAINTY TO WHAT DEGREE OF MODIFICATION
CAN BE EXPECTED BY THE END OF THE WEEK. I LIKE THE IDEA OF KEEPING
POPS LOW AND TEMPERATURES BELOW GUIDANCE AS MODEL TRENDS CONTINUE
TO POINT TOWARD DELAYING THE ONSET OF PRECIPITATION UNTIL
SUNDAY/MONDAY. /SB
&&
.AVIATION...
COMPLEX FOG AND LOW STRATUS EVENT UNFOLDING. LOW STRATUS IS
CURRENTLY BUILDING ACROSS MUCH OF EASTERN WA...AND IS CURRENTLY
SPREADING NORTHEASTWARD OVER KGEG. THE NAM AND RUC BOTH BRING THE
STRATUS OVER KSFF SHORTLY...WITH IT NEARING KCOE AS IT DISSIPATES
LATER THIS MORNING. HOWEVER...LOW LEVEL E-NE FLOW WILL MAKE IT
DIFFICULT FOR THE STRATUS TO OVERSPREAD KSFF AND ESPECIALLY KCOE SO
CONFIDENCE IS LOW ON HOW IT WILL UNFOLD AT KSFF AND KCOE. KPUW IS
ALSO CURRENTLY SITTING JUST EAST OF THE STRATUS...WITH THE CURRENT
LOW LEVEL DOWNSLOPING/EASTERLY WINDS KEEPING IT AT BAY. THE PRESSURE
GRADIENT AND LOW LEVEL WIND FIELDS SEEM CONDUCIVE FOR THE SFC
EASTERLIES TO END SHORTLY PER THE NAM AND RUC MODELS...WHICH MEANS
IT SEEMS LIKELY THAT FOG AND LOW STRATUS WILL OVERTAKE KPUW SHORTLY
AS WELL. KMWH AND KEAT ARE BOTH FIRMLY ENTRENCHED IN MVFR STRATUS.
850MB AND 900MB WINDS PER THE NAM AND RUC INCREASE THIS AM TO 20+KTS
OUT OF THE NW...WHICH SHOULD BEGIN TO CLEAR THE STRATUS OUT OF KEAT
AND THEN AN HOUR OR TWO LATER AT KMWH. IF THE INCREASE IN WESTERLY
FLOW DOES NOT KICK OUT THE STRATUS...EXPECT THE FRONT AND ATTENDANT
DRIER AIR DIVING SOUTH OUT OF BRITISH COLUMBIA TO CLEAR OUT THE
WESTERN BASIN EARLY THIS AFTERNOON. EXPECT TAF AMENDMENTS AT MOST
SITES. /NEUMAN
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 29 20 30 14 19 6 / 10 10 20 10 10 0
COEUR D'ALENE 31 20 30 14 18 5 / 10 10 20 10 10 0
PULLMAN 33 19 30 15 20 8 / 10 10 20 10 0 0
LEWISTON 37 23 35 19 26 13 / 10 10 20 10 0 0
COLVILLE 33 25 33 17 23 6 / 10 10 10 40 10 0
SANDPOINT 29 22 29 12 14 2 / 10 30 20 20 10 0
KELLOGG 31 20 29 10 15 3 / 20 40 40 10 10 10
MOSES LAKE 31 21 34 18 25 8 / 10 10 10 20 10 0
WENATCHEE 34 25 35 18 26 10 / 10 10 10 60 10 10
OMAK 33 22 34 18 25 7 / 10 10 10 70 0 0
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...NONE.
&&
$$
