FXUS66 KOTX 072317
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
315 PM PST MON DEC 7 2009
.SYNOPSIS...
TEMPERATURES TONIGHT WILL BE THE COLDEST OF THE WINTER SEASON THUS
FAR. RECORDS MAY BE THREATENED IN WENATCHEE...MOSES LAKE...AND
OMAK. MUCH BELOW AVERAGE TEMPERATURES WILL CONTINUE THROUGH THE
END OF THE WEEK. THE NEXT CHANCE FOR SNOW IS EXPECTED THIS WEEKEND.
&&
.DISCUSSION...
TONIGHT...THE 22Z SURFACE ANALYSIS SHOWS STRONG ARCTIC HIGH
PRESSURE EXTENDING FROM THE CENTRAL CANADIAN PRAIRIES INTO EASTERN
WASHINGTON. THE PRESSURE GRADIENT ACROSS EASTERN WASHINGTON AND
NORTHERN IDAHO HAS WEAKENED CONSIDERABLY OVER THE LAST 24 HOURS.
THE GRADIENT FROM GLACIER PARK TO PORTLAND SUNDAY AFTERNOON WAS
ABOUT 16MB...AND THIS AFTERNOON IT HAS DROPPED TO 5MB. THIS TREND
WILL CONTINUE THIS EVENING...AND SURFACE WINDS SHOULD BE LIGHT
SHORTLY AFTER SUN SET. THE VERY DRY DEWPOINTS AND LIGHT WINDS OVER
THE MAJORITY OF EASTERN WASHINGTON WILL ALLOW FOR EFFICIENT
RADIATIONAL COOLING TONIGHT. A THIN VEIL OF HIGH CLOUDS DROPPING
OUT OF SOUTHERN BRITISH COLUMBIA MAY RETARD THE TEMPERATURE FREE
FALL OVER THE OKANOGAN VALLEY...THE EAST SLOPES...AND WENATCHEE
AREA. VISIBLE IMAGERY SUGGESTS THAT THESE CLOUDS ARE FAIRLY
TRANSPARENT...AND THEY MAY DISSIPATE AS THEY DESCEND INTO DRIER
AIR OVERNIGHT. I FAVORED THE COLDER MOS GUIDANCE FROM THE NAM FOR
MOST LOCATIONS TONIGHT...AND RECORDS MAY BE THREATENED AT
OMAK...WENATCHEE...MOSES LAKE...AND WATERVILLE. /GKOCH
TUESDAY...SURFACE HIGH PRESSURE WILL BE PLANTED OVER THE INLAND
NORTHWEST ON TUESDAY. WITH VERY LITTLE WIND IN THE BOUNDARY
LAYER...MECHANICAL MIXING WILL BE ALMOST NIL TOMORROW. EVEN WITH
FILTERED SUNSHINE TOMORROW...AND WARMER 850MB TEMPERATURES...HIGHS
WILL BE COLDER THAN TODAY./GKOCH
WEDNESDAY THROUGH FRIDAY...NORTHERLY FLOW ON THE EAST SIDE OF THE
BLOCKING RIDGE OFF THE COAST ALLOWS MINOR NUISANCE SHORTWAVES WITH
VERY LIMITED MOISTURE TO DROP DOWN FROM THE NORTH ALLOWING CONTINUED
MENTION OF SNOW FLURRIES OR VERY LIGHT SNOW...PRIMARILY IN THE IDAHO
PANHANDLE FOR THE MOST PART UP INTO FRIDAY. RIDGE NARROWS AND GETS
UNDERCUT WITH SHORTWAVE DISTURBANCES PASSING THROUGH ITS MIDSECTION
BUT THEY ARE STILL WELL TOO FAR TO THE SOUTH TO HAVE ANY INFLUENCE
AS FAR AS WEATHER FOR EASTERN WASHINGTON AND NORTHERN IDAHO GOES
INTO FRIDAY...HOWEVER A GRADUAL WARMING TREND SHOULD RESULT AS THE
SHORTWAVE RIDGING ASSOCIATED WITH THOSE DISTURBANCES PASSING TO THE
SOUTH AID IN PUSHING BACK ON THE COLD AIR OVER THE AREA. /PELATTI
FRIDAY NIGHT THROUGH MONDAY...THE MODELS SEEM TO HAVE COME INTO
DECENT AGREEMENT AT A GRADUAL TRANSITION OUT OF THE DRY ARCTIC
PATTERN THAT WILL HAVE ENCOMPASSED THE AREA FOR ABOUT A WEEK BY
THE START OF THE EXTENDED PERIOD. BY FRIDAY NIGHT...LARGE SCALE
FLOW WILL GENERALLY BE TRANSITIONING TO A MORE WEST-NORTHWESTERLY
PATTERN OVER THE FORECAST AREA...WITH A WEAK RIDGING ARCING UP THE
WEST COAST AND A COUPLE OF OFF SHORE SYSTEMS DRIVING PACIFIC
MOISTURE TOWARD THE APEX OF THE RIDGE.
THE 12Z GUIDANCE GENERALLY FAVORS WARM ADVECTION THROUGH THE
ENTIRE COLUMN COMMENCING BY SATURDAY MORNING AND SPREADING FROM
SOUTHWEST TO NORTHEAST ACROSS THE AREA. MODEL SPECIFICS ARE VERY
DIFFICULT TO PIN DOWN AT THIS POINT...HOWEVER DECENT AGREEMENT
AMONGST THE 12Z GFS...ECMWF...CANADIAN...AND 18Z DGEX EXISTS IN
ORDER TO RELATIVELY CONFIDENTLY STATE THAT A BAND OF MODERATE TO
HEAVY PRECIPITATION IS LIKELY SOMETIME BETWEEN SATURDAY AND SUNDAY
IN AN EAST-WEST ORIENTED AXIS SOMEWHERE BETWEEN SPOKANE AND
NORTHERN OREGON. IT SEEMS LESS LIKELY AT THIS TIME THAT THE
NORTHERN THIRD OF WASHINGTON WILL SEE MODERATE OR HEAVY
PRECIPITATION. THE 12Z GFS AND 18Z DGEX FOCUSED THE STRONGEST
OMEGAS VIA A LONG DURATION ISENTROPIC ASCENT EVENT AND STALLED
WARM FRONT DIRECTLY OVER THE SPOKANE-COEUR D'ALENE CORRIDOR FROM
SATURDAY THROUGH SUNDAY MORNING. THE RESULT OF THIS SOLUTION WAS
ABOUT 1.25 INCHES OF LIQUID EQUIVALENT...WHICH USING LOW END
RATIOS YIELDS WELL OVER A FOOT OF SNOW. HOWEVER...THE ECMWF
FAVORED PLACES A BIT FARTHER SOUTH AND ABOUT 12 HOURS LATER THAN
THE GFS. THE 12Z CANADIAN FOCUSED THINGS ACROSS NORTHERN
OREGON...WHILE KEEPING MUCH DEEPER AND COLDER ARCTIC AIR
ENTRENCHED OVER THE CWA THROUGHOUT THE WEEKEND THAT WOULD LIKELY
KEEP MOST OF THE CWA BELOW ZERO THROUGHOUT THE WEEKEND. DUE TO
THE GFS AND ECMWF FAVORING A FARTHER NORTH POSITIONING...THE
CANADIAN THERMAL PROFILES WERE DISMISSED AS TOO COLD...WITH A
COMPROMISE OF THE GFS AND ECMWF FAVORED. THIS YIELDED PROFILES
SUCH THAT BASICALLY EVERYWHERE ALONG AND NORTH OF I-90 WOULD
REMAIN BELOW FREEZING THROUGHOUT THE ENTIRE EVENT. FARTHER
SOUTH...WARM ADVECTION AND A MEANDERING WARM FRONTAL BOUNDARY
MAKES THE BOUNDARY LAYER MARGINAL FOR ACCUMULATING SNOW.
HOWEVER...THE FORECAST WILL CONTINUE TO FEATURE ALL SNOW FOR
ALMOST ALL LOCATIONS ACROSS THE AREA THROUGH THE WEEKEND AS WARM
AIR ALOFT IS UNLIKELY TO SURGE ABOVE FREEZING IN LOCATIONS WHERE
THE BOUNDARY LAYER WOULD BE COLD ENOUGH TO SUPPORT FREEZING RAIN
OR SLEET. AS A RESULT AND WITH THE STRONG QPF OF THE GFS AND DGEX
ALONG THE FRONTAL BOUNDARY...MODERATE SNOW WAS CARRIED IN THE
GRIDS FROM SATURDAY THROUGH SUNDAY. MODEL TRENDS WILL NEED TO BE
MONITORED CLOSELY...AS QPF OF THE MAGNITUDE PRESENT IN THE MODELS
WOULD WARRANT WINTER STORM WATCHES BY A COUPLE OF DAYS FROM NOW
FOR THE WEEKEND.
AFTER THE WEEKEND'S SYSTEM MOVES EAST...LARGE SCALE WESTERLY FLOW
LOOKS TO BE THE MAIN INFLUENCE. AS A RESULT...TEMPERATURES SHOULD
MODERATE TO NEAR NORMAL BY MONDAY. /FRIES
&&
.AVIATION...
ARCTIC HIGH PRESSURE WILL BRING VFR CONDITIONS REGION WIDE THROUGH
00Z WEDNESDAY. IN ADDITION...EXPECT LIGHT AND VARIABLE WINDS WITH
ONLY A FEW PASSING HIGH CIRRUS OVERNIGHT AND INTO TOMORROW. /NEUMAN
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE -4 13 4 15 7 19 / 0 0 10 0 0 0
COEUR D'ALENE -2 15 3 14 7 19 / 0 0 10 0 0 0
PULLMAN -3 13 4 16 9 20 / 0 0 10 0 0 0
LEWISTON 2 17 8 22 11 26 / 0 0 10 0 0 0
COLVILLE -2 19 8 16 9 23 / 0 0 20 0 0 0
SANDPOINT -2 15 3 12 5 16 / 0 0 20 10 10 0
KELLOGG -4 15 3 11 5 19 / 0 0 20 10 10 10
MOSES LAKE -4 15 3 20 8 22 / 0 0 10 0 0 0
WENATCHEE 1 16 3 23 9 25 / 0 0 0 0 0 0
OMAK 0 18 4 21 7 23 / 0 0 10 0 0 0
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...NONE.
&&
$$
