FXUS66 KOTX 082221
AFDOTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WA
221 PM PST TUE DEC 8 2009
.SYNOPSIS...
A FRIGID ARCTIC AIR MASS WILL RESIDE OVER THE INLAND NORTHWEST AT
LEAST THROUGH THE END OF THE WEEK. TEMPERATURES TODAY WILL BE ABOUT
20 TO 25 DEGREES BELOW NORMAL...BUT WILL SLOWLY MODERATE THROUGH THE
WEEK AS THE NORTHERLY FLOW WEAKENS. THE WEATHER WILL GENERALLY BE
DRY...HOWEVER A WEAK DISTURBANCE COULD PRODUCE SOME LIGHT SNOW OVER
EXTREME NORTHEAST WASHINGTON AND THE IDAHO PANHANDLE LATE TONIGHT
AND WEDNESDAY. THE NORTHERLY FLOW WILL TURN INCREASINGLY ONSHORE BY
THE WEEKEND RESULTING A CHANCE OF SNOW FOR MOST LOCATIONS.
&&
.DISCUSSION...
TONIGHT AND TOMORROW...A HIGH AMPLITUDE UPPER LEVEL RIDGE REMAINS
OVER THE WEST COAST...AND ARCTIC AIR IS LOCKED OVER THE INTERIOR
NORTHWEST. SOME AIR MASS MODIFICATION HAS OCCURRED TODAY...BUT THE
LOW DECEMBER SUN ANGLE HAS DONE LITTLE TO TEMPER THE BITTER COLD.
EVEN THOUGH HIGH TEMPERATURES ARE AT OR BELOW YESTERDAYS
READINGS...THE BIGGEST INDICATION THAT THE AIR MASS HAS MODIFIED
IS THE UPWARD TREND IN SURFACE DEWPOINTS OVER THE LAST 24 HOURS.
MOST LOW ELEVATION STATIONS IN EASTERN WASHINGTON AND NORTHERN
IDAHO ARE REPORTING DEWPOINT INCREASES OF 4-8F.
OVERNIGHT LOWS WILL CONTINUE TO BE A GOOD 20 DEGREES BELOW
AVERAGE...BUT EARLY MORNING TEMPERATURES TOMORROW SHOULD BE A FEW
DEGREES WARMER THAN THEY WERE THIS MORNING. A WEAK UPPER LEVEL
DISTURBANCE IS EVIDENT OVER NORTHERN BRITISH COLUMBIA ON THE
AFTERNOON WATER VAPOR IMAGERY. A FEW REPORTING STATIONS NORTH OF
THE JASPER ARE REPORTING LIGHT SNOW...AND CLOUDINESS ASSOCIATED
WITH THIS DISTURBANCE WILL SPREAD OVER NORTHEAST WASHINGTON AND
NORTHERN IDAHO. THE MOST NOTABLE INCREASE IN CLOUD COVER WILL BE
AFTER MIDNIGHT IN THE COLVILLE...SANDPOINT...AND SPOKANE
AREAS. THESE SPOTS WILL LIKELY EXPERIENCE A QUICK DROP IN
TEMPERATURES THIS EVENING...THEN HAVE STEADY OR RISING
TEMPERATURES TOWARD DAYBREAK. THE CLOUDS WILL HAVE LESS EFFECT
OVER CENTRAL AND SOUTHEAST WASHINGTON...WHERE MOSTLY CLEAR SKIES
WILL PERSIST LATER THROUGH THE NIGHT. MOS GUIDANCE AND RAW MODEL
TEMPERATURE DATA HAS REALLY STRUGGLED IN THE OMAK...WENATCHEE...
AND WATERVILLE AREAS THE LAST FEW DAYS. THE COLD BIAS MAY BE
CAUSED BY THE MODEL INITIALIZATION OF SNOW IN THESE SPOTS. THE NAM
INITIALIZATION OF SNOW DEPTH HAS AS MUCH AS 2 INCHES OF SNOW ON
THE GROUND IN OMAK...WENATCHEE...AND WATERVILLE...WHICH IS AN
OVERESTIMATE FOR THIS REGION AS A WHOLE. OUR FORECAST TOOK LAST
NIGHTS LOWS AND ADDED A COUPLE DEGREES ACCOUNTING FOR THE
AFOREMENTIONED AIR MASS MODIFICATION.
THE BRITISH COLUMBIA DISTURBANCE WILL BE RELATIVELY MOISTURE
STARVED BY THE TIME IT REACHES THE IDAHO PANHANDLE TOMORROW
MORNING. ONLY LIGHT SNOW OR FLURRIES ARE EXPECTED OVER THE
PANHANDLE AND ALONG THE WASHINGTON BORDER TOMORROW AND TOMORROW
NIGHT. /GKOCH
THURSDAY THROUGH FRIDAY NIGHT...MODELS ARE IN GOOD AGREEMENT
DURING THIS PERIOD WITH A BLOCKING RIDGE OF HIGH PRESSURE
WEAKENING...BUT PERSISTING IN THE EASTERN PACIFIC RESULTING IN A
COLD AND GENERALLY DRY NORTHWEST FLOW. A COUPLE OF WEAK WAVES WILL
PASS THROUGH DURING THE PERIOD BRINGING A CHANCE FOR LIGHT SNOW
SHOWERS OR FLURRIES MAINLY OVER NORTH IDAHO AND NEAR THE CANADIAN
BORDER. WITH THE ABSENCE OF ANY STRONG MIXING MECHANISM TO SCOUR
OUT THE COLD AIR IN PLACE...VALLEY TEMPERATURES WILL ONLY SHOW A
SLIGHT MODERATION DURING THE PERIOD. JW
SATURDAY THROUGH TUESDAY...THE MODEL CONSENSUS IS GRADUALLY
FIRMING UP FOR THE WEEKEND AND EARLY NEXT WEEK...WITH A BIAS
TOWARD A MORE SOUTHERN SOLUTION FOR THE SYSTEM SATURDAY NIGHT AND
SUNDAY YIELDING THE BEST SNOW CHANCES FOR NOW GENERALLY SOUTH OF
PULLMAN WITH SNOW ALSO POSSIBLE ALONG AN ARCTIC BOUNDARY TO ITS
NORTH THROUGH THE NORTHEASTERN PORTIONS OF THE AREA. THE MORE
SOUTHERN SOLUTION GENERALLY HAS SUPPORT FROM THE 12Z GFS...AFTER 4
SUCCESSIVE RUNS WITH A MORE NORTHERN SOLUTION...IN ADDITION TO THE
ECMWF AND CANADIAN. THE ECMWF AND CANADIAN HAVE PERSISTENTLY
FORECAST OVERWHELMINGLY COLDER THAN THE GFS THROUGHOUT THE
EXTENDED FORECAST...AND EVEN WITH SOME RUN TO RUN ISSUES...THE
COLDER IDEA GENERALLY SEEMS TO BE THE BEST TO FOLLOW UNTIL AT
LEAST THE MIDDLE OF NEXT WEEK.
THE 12Z GFS TURNING TOWARD THE PREVIOUS ECMWF SOLUTIONS HAS
ALLOWED FOR SOME POP REDUCTIONS THROUGH THE WEEKEND...PARTICULARLY
ACROSS THE NORTHERN AND WESTERN FLANKS OF THE CWA. HOWEVER...WITH
THE ARCTIC BOUNDARY HANGING AROUND THE NORTHEASTERN PORTION OF THE
CWA...AND THE SYSTEM MOVING ALONG THE SOUTHEAST...MOST OF THE REST
OF THE AREA REMAINS IN CHANCE OR HIGH CHANCE CATEGORY POPS FROM
SATURDAY THROUGH SUNDAY OR SO. THE ONE THING THAT WAS MADE A BIT
MORE CLEAR IS THAT THE BOUNDARY LAYER WILL STAY COLD ENOUGH TO
SUPPORT SNOW ACROSS ALL PORTIONS OF THE AREA THROUGH AT LEAST
MONDAY AS A SOUTHERN TRACK WOULD PULL COLD AIR DOWN...AND AN
ARCTIC BOUNDARY DRAPING THE AREA WOULD REINFORCE THIS. HOWEVER...A
PATTERN SHIFT AFTER MONDAY IS LOOKING INCREASINGLY LIKELY.
BY THE TIME MONDAY NIGHT AND TUESDAY APPROACH...SOUTHWESTERLY FLOW
AT ALL LEVELS BECOMES WELL ESTABLISHED ON THE GFS AND ECMWF. AS
THIS OCCURS...THE RIDGE AXIS BEHIND THE WEEKEND SYSTEM SHIFTS
EASTWARD...AND EVEN LOW LEVEL FLOW STARTS TO TURN TO THE
SOUTHWEST...EXCEPT IMMEDIATELY EAST OF THE CASCADES WHERE THE
PRESSURE GRADIENTS ARE LIKELY TO KEEP IT EASTERLY FOR A TIME. THIS
WILL LOCK COLD AIR INTO THE VALLEYS OF THE EAST SLOPES FOR A TIME
THROUGH MID-WEEK NEXT WEEK AS STRONG ISENTROPIC ASCENT IN ADVANCE
OF A SUB-TROPICAL LOOKING WARM FRONT ADVANCES OVER THE ENTIRE AREA
AROUND TUESDAY. QPF ON THE MODELS IS IMPRESSIVE AHEAD OF A
DEVELOPING WARM FRONT. THE COLUMN AHEAD OF THE WARM FRONT
GENERALLY SHOULD SUPPORT SNOW FOR MOST PLACES...HOWEVER AS IT
SWINGS THROUGH BY MID-WEEK...850 MB TEMPERATURES ON THE MODELS
JUMP FROM NEAR -5C TO ABOUT +3C. THIS WILL END THE CHANCE OF
VALLEY SNOWS...HOWEVER AS THE WARM FRONT LIFTS NORTHWARD...IT
SEEMS THE LIFT GOES WITH IT...SO COPIOUS RAINFALL SEEMS RATHER
UNLIKELY AT THIS TIME. /FRIES
&&
.AVIATION...
THERE WILL BE A GRADUAL INCREASE IN CLOUDS...MAINLY AFTER 09Z.
THE CLOUD DECK MAY BECOME LOW ENOUGH TO OBSCURE THE MOUNTAINS OVER
THE IDAHO PANHANDLE AND PORTIONS OF FAR NORTHEAST WASHINGTON. SOME
VERY LIGHT SNOW MAY ALSO FALL IN THESE PREVIOUSLY MENTIONED AREAS
BETWEEN 10Z AND 18Z. NO SIGNIFICANT IMPACT ON THE MAIN TERMINALS
ARE EXPECTED. /GKOCH
&&
.PRELIMINARY POINT TEMPS/POPS...
SPOKANE 4 15 5 19 10 21 / 0 10 0 0 0 0
COEUR D'ALENE 3 16 7 20 12 22 / 0 10 0 0 0 0
PULLMAN 0 15 6 19 10 21 / 0 0 0 0 0 0
LEWISTON 4 19 9 24 12 26 / 0 0 0 0 0 0
COLVILLE 7 17 8 21 10 23 / 10 10 0 0 0 0
SANDPOINT 3 17 8 17 9 19 / 10 20 10 10 0 10
KELLOGG -3 12 3 18 8 20 / 10 20 20 10 10 10
MOSES LAKE 1 20 2 22 7 23 / 0 0 0 0 0 0
WENATCHEE 5 18 9 22 12 24 / 0 0 0 0 0 0
OMAK 6 20 6 21 6 23 / 0 0 0 0 0 0
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...NONE.
WA...NONE.
&&
$$
