Heavy Snow in Washington, December 14 to 15, 2004

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WASHINGTON
230 PM PST TUE DEC 14 2004

.SYNOPSIS...A LOW PRESSURE SYSTEM OVER CENTRAL WASHINGTON THIS
AFTERNOON WILL CREATE RAIN AND MOUNTAIN SNOW SHOWERS OVER EASTERN
WASHINGTON AND THE IDAHO PANHANDLE INTO THE EARLY EVENING. SHOWERS
WILL LINGER THROUGH THE NIGHT OVER THE PANHANDLE MOUNTAINS. AN
UPPER LEVEL RIDGE BUILDS IN TOMORROW...SHUTTING OFF PRECIPITATION BUT
CREATING PERIODS OF VALLEY FOG AND LOW CLOUDS THROUGH THE WEEK.

&&

.DISCUSSION...POST FRONTAL TROUGH THIS AFTERNOON OVER CENTRAL
WASHINGTON DRIVING A BAND OF RAIN AND MOUNTAIN SNOW SHOWERS THAT
EXTENDS FROM NORTHERN STEVENS SOUTHWARD THROUGH WHITMAN COUNTY.
TROUGH WILL CONTINUE TO DRIVE EASTWARD PLACING THE BRUNT OF SHOWER
ACTIVITY OVER THE PANHANDLE BY THIS EVENING. LEFT LINGERING SHOWERS
OVER EASTERN WA FOR EARLY EVENING AS THE SUPPORTING UPPER LEVEL
VORTICITY MAXIMUM MOVES THROUGH AND TAPS INTO THE RESIDUAL POTENTIAL
INSTABILITY IN THE LOWER LEVELS. ASIDE FROM LINGERING
OROGRAPHIC SHOWERS OVER THE CREST...BLUES...AND PANHANDLE...
PRECIPITATION SHOULD SHUT-OFF TONIGHT AS THE UPPER LEVEL RIDGE
BUILDS IN. RAIN MOISTENED LOW-LEVELS...LIGHT SURFACE GRADIENT AND
NOCTURNAL COOLING WILL ALLOW FOR THE FORMATION OF VALLEY FOG AND
STRATUS OVERNIGHT...SLOWLY BURNING OFF TOMORROW.  FROM
WEDNESDAY THROUGH FRIDAY THE UPPER LEVEL RIDGE SHOULD UMBRELLA
THE REGION WITH THE POLAR FRONT JET AND STORM TRACK REMAINING
NORTH OVER CANADA. HOWEVER, MODELS TO DEPICT A COUPLE OF WEAK...
UNIMPRESSIVE...WAVES PUNCHING THROUGH THE RIDGE SO ADDED SLIGHT
CHANCE OF MOUNTAIN SHOWERS THURSDAY NIGHT AND FRIDAY.
OTHERWISE A FAIRLY STAGNANT...NOCTURNALLY DRIVEN
VALLEY FOG AND STRATUS REGIME SHOULD PREVAIL.  HIGH AND LOW
TEMPERATURES SHOULD TREND ABOVE THE SEASONAL NORM THROUGH THE
PERIOD. /JVW

FRIDAY NIGHT THRU TUESDAY...PER LATEST GFS MOSTLY A DRY FORECAST FOR
THE BULK OF POPULATION BASE FOR EASTERN WASHINGTON AND NORTHERN
IDAHO. LATEST RUN..HOWEVER...FROM SUNDAY NIGHT INTO TUESDAY...HAS
AN INTERESTING SOLUTION WHICH DRAGS A FAIRLY DECENT LOOKING COLD
FRONT THRU EASTERN WASHINGTON AND NORTHER IDAHO. NUDGED THE FORECAST
SLIGHTLY IN THIS DIRECTION WITH SLIGHT CHANCE POPS OVER NORTHEAST
MOUNTAINS AND IDAHO PANHANDLE...WITH TEN PERCENT POPS ASSOCIATED WITH
NO WEATHER PHENOMENA FOR REMAINDER OF EXTREME EASTERN WASHINGTON AND
NORTHERN IDAHO WITH ITS PASSAGE. IF MORE MODEL RUNS COME IN WITH
SIMILAR SOLUTIONS THESE POPS MAY GET BUMPED UP...BUT WITH THIS RUN
BEING THE FIRST AM COMFORTABLE WITH THESE LOW POPS AT THE MOMENT.
SOME OTHER LINGERING SLIGHT CHANCE POPS FOR THE EXTREME NORTH IN THE
EARLIER PORTION OF THE EXTENDED FORECAST EXIST AS WELL AS AXIS OF
BLOCKING RIDGE ALOFT GETS MOVED ABOUT IN THE MODEL RUNS...MORE
SPECIFICALLY THE AXIS GETS MOVED FARTHER WEST DUE TO DIGGING OF
CYCLONES INTO THE LONGWAVE RIDGE PATTERN NEAR 150W. THIS SHIFTS THE
FLOW ALOFT OVER EASTERN WASHINGTON AND NORTHERN IDAHO TO MORE
NORTHWEST ALONG THE FARTHER EDGES OF THE HIGH...RATHER THAN CLOSER TO
THE MORE LIKELY UNDISTURBED ATMOSPHERE UNDER AN CLOSER TO THE RIDGE
AXIS. NOISY SNOW LEVELS CONTINUE IN THIS PERIOD AS THERE ARE EXPECTED
TO BE MULTIPLE ZERO DEGREE ISOTHERM CROSSINGS WITH HEIGHT UNDER THE
RIDGE. UNREMARKABLE FORECAST TEMPERATURES OTHER THAN THAT THEY ARE
WARMER THAN AVERAGE DUE TO THE INFLUENCE OF THE HIGHLY AMPLIFIED
BLOCKING RIDGE ALOFT. CLIMATE PREDICTION CENTER FORECAST OF CONTINUED
WEAK WARM EPISODE EL NINO...WITH RESULTING WARMER AND DRIER
CONDITIONS OVER ERN WA AND NRN IDAHO...APPEARS TO BE VERIFYING QUITE
WELL GIVEN CURRENT CONDITIONS AND ABOVE FORECAST SCENARIO.

&&

.PRELIMINARY POINT TEMPS/POPS...

SPOKANE        033 039 027 037 027 037/ 30 05 00 05 05 05
COEUR DALENE  033 040 026 037 028 037/ 50 05 00 05 05 05
PULLMAN        034 043 026 038 027 038/ 30 05 00 05 05 05
LEWISTON       039 045 032 044 031 044/ 20 05 00 00 05 00
COLVILLE       029 037 027 035 027 035/ 20 00 10 00 05 10
SANDPOINT      031 038 026 036 025 036/ 50 05 05 05 05 10
WALLACE        033 038 024 037 024 037/ 70 10 00 05 00 10
MOSES LAKE     032 044 027 040 027 040/ 10 00 00 00 05 10
WENATCHEE      032 040 028 040 026 040/ 05 00 00 00 05 10
OMAK           029 037 029 040 025 040/ 05 00 00 00 05 10
&&

.OTX WATCHES/WARNINGS/ADVISORIES...
.WA...NONE.
.ID...NONE.