Heavy Snow in Washington, February 6, 2002

EASTERN WASHINGTON AND NORTH IDAHO AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SPOKANE WASHINGTON
230 AM PST WED FEB 6 2002

COMPLEX SITUATION SETTING UP NEXT AS A DEEP CLOSED LOW TRACKS TOWARDS
BC WITH A SHORTWAVE ROTATING AROUND THE SOUTHERN PERIPHERY NEAR 40N
140W POSSIBLY INDUCING CYCLOGENESIS OFF THE OREGON COAST AND TRACKING
INTO NW WASHINGTON TONIGHT. COLD AIR ALOFT ASSOCIATED WITH THE DEEP
TROUGH AXIS TO PASS THROUGH THE REGION THURSDAY NIGHT. ALL IN
ALL...ITS A SITUATION THAT COULD OFFER HEAVY MOUNTAIN SNOWS ONCE
AGAIN WITH THE ADDED TWIST OF SOME PRECIPITATION TYPE UNCERTAINTY IN
THE LOWER VALLEYS. WINTER STORM WATCH WILL BE REQUIRED FOR THE
MOUNTAINS OF NE WASHINGTON THROUGH CENTRAL IDAHO PANHANDLE.

.SHORT RANGE...WARM ADVECTION PATTERN UNDERWAY FROM THE CASCADES WEST
THIS MORNING WITH A WEAKENING...STRETCHED VORT LOBE TRACKING NORTH
INTO BC. CANT RULE OUT PASSING AREAS OF LIGHT SNOW THIS MORNING NEAR
THE CREST...HOWEVER A MORE SIGNIFICANT SHORTWAVE THAT APPEARS TO BE
SLIGHTLY SOUTH FROM THE AVN POSITION WILL ROTATE NORTHEAST PROVIDING
MUCH BETTER UPPER DYNAMICS. THE CHALLENGE IS WHETHER THE AVN SOLUTION
(AS DEPICTED FOR SEVERAL RUNS) OF A CLOSED SURFACE LOW PASSING WEST
OF THE CASCADES IS CORRECT. 06Z ETA RUN SHOWS A BIT MORE INFLECTION
IN THE SURFACE PRESSURE PATTERN...IMPLYING A STRONGER SURFACE WAVE
THAN ITS PRECEDING RUNS. THIS SCENARIO MAY ALLOW MORE GREATER UPSLOPE
COMPONENT INTO THE EAST CASCADE VALLEYS...AND HAVE BOOSTED POPS INTO
THE LIKELY CATEGORY THIS AFTERNOON INTO THE EARLY PART OF TONIGHT. AT
THIS TIME WILL KEEP SNOW AMOUNTS IN THE NORTHERN EAST SLOPES BELOW
ADVISORY CRITERIA. FURTHER THE EAST STRENGTHENING SOUTHWEST 850 MB
WILL THRIVE ON THE WARM ADVECTION PATTERN AND STRONG LIFT FOCUSING
POSSIBLE WARNING CRITERIA SNOW AMOUNTS IN THE NORTHEAST QUARTER OF
THE CWA. OKANOGAN HIGHLANDS WILL BE LIMITED BY LARGER WESTERLY 700 MB
WIND COMPONENT WHICH CONTINUES TO BE SEEN ON LATEST MODEL RUNS.
FURTHER SOUTH INTO THE SPOKANE/COE AREA THE WET BULB PROFILE WILL BE
HUGGING THE FREEZING MARK...AND THERE COULD BE SOME RAIN IN THE MIX
IN THE LOWER ELEVATIONS. THAT AND THE WETTER SNOW WILL LIMIT
ACCUMULATIONS. EVEN FURTHER SOUTH THE SOUTHWEST WINDS WILL KEEP
PRECIPITATION SPOTTY INTO LEWISTON WITH BLUE MOUNTAIN SHADOWING. IN
THE NEAR TERM...WILL MENTION BREEZY WINDS ONCE AGAIN FOR THE LEWISTON
AREA AS GRADIENT REMAINS TIGHT. ALSO BUMPED UP MAX TEMPERATURES
CLOSER TO YESTERDAYS MILD READINGS.

A PAUSE IN THE ACTION OCCURS FOR CENTRAL AND WESTERN LOCATIONS BEFORE
THE MAIN TROUGH AXIS BRINGS IN COLDER AIR ALOFT. BY THURSDAY EVENING
LAPSE RATES BECOMING VERY STEEP (EXCEEDING 8 C PER KM) ALLOWING FOR
HIGH LIKELIHOOD OF CONVECTIVE SNOWS IN THE EAST. AVN GOES FURTHER TO
SHOW STRONGER SURFACE DEVELOPMENT ACROSS SOUTHERN IDAHO ALLOWING 700
MB FLOW TO TURN MORE TO THE NORTHWEST. THIS POINTS TO BETTER CHANCE
OF SNOW ACROSS THE CAMAS PRAIRIE. MEANWHILE FOCUS OF SNOWS WILL BE
FURTHER SOUTH PINNING THE CENTRAL PANHANDLE MOUNTAINS.

THANKS MSO AND PDT FOR YOUR GREAT COORDINATION THIS MORNING.  JR

.EXTENDED...MOIST SOUTHWEST FLOW REMAINS OVER THE CWA WITH IMBEDDED
SHORTWAVES THROUGH THE FIRST TWO OR THREE DAYS OF THE PERIOD. RIDGING
TAKING PLACE LATE IN THE PERIOD FOR DECREASING SHOWERS ESPECIALLY FOR
THE EAST SLOPES AND THE BASIN. WILL KEEP CHANCE MENTION OF SNOW IN
THE MOUNTAINS AND OROGRAPHIC FAVORED VALLEYS OF SOUTHEAST. NEAR
NORMAL TEMPERATURES AT FIRST THEN COOLING MONDAY AND TUESDAY AS THE
FLOW SHIFTS TO NW. GDB

...THE INFORMATION IN THIS PRODUCT CONCERNING WARNINGS AND FORECASTS
IS VALID ONLY AT THE TIME OF ISSUANCE. THE LATEST WARNING AND
FORECAST INFORMATION WILL BE FOUND IN THE APPROPRIATE PRODUCTS...

GEG 036/032/037/029/038 38564
COE 036/030/036/028/038 39575
PUW 037/032/038/030/037 38565
LWS 046/038/047/035/045 26565
CQV 036/030/036/028/038 49666
SPT 035/030/035/028/035 3+676
WWP 034/029/034/027/034 3+887
EAT 035/030/039/029/040 66353
MWH 038/032/042/030/041 47353

.OTX...WINTER STORM WATCH ID ZONE 01 AND WA ZONE 37 TONIGHT THROUGH
THURSDAY.
    ...WINTER STORM WATCH ID ZONE 04 TONIGHT THROUGH FRIDAY.