Blizzard in Oregon, December 12 to 13, 2001

NORTHEAST OREGON/SOUTHEAST WASHINGTON FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PENDLETON OR
830 PM PST WED DEC 12 2001

CORRECTED TYPO FOR WRONG DAY (FRIDAY SHOULD BE THURSDAY LINE 13-18)

SATELLITE AND RADAR LOOPS SHOW THE BACK EDGE OF THE MAIN AREA OF
PRECIPITATION MOVING THROUGH THE LOWER COLUMBIA BASIN AND THE BLUE
MOUNTAIN FOOTHILLS.  WINDS HAVE ALSO INCREASED FROM THE SOUTH ALONG
THE BLUE MOUNTAIN FOOTHILLS...INDICATING THE INCREASED PRESSURE
GRADIENT AS THE WARM FRONT MOVES THROUGH THE AREA.  SNOW LEVELS ARE
STILL AROUND 3500-4000 FEET IN THE BLUE MOUNTAINS AND AROUND
1000-1500 ALONG THE EAST SLOPES OF THE SOUTHERN WASHINGTON
CASCADES.  SINCE IT IS STILL SNOWING IN THE BLUE MOUNTAINS AND WILL
CONTINUE TO DO SO FOR THE NEXT FEW HOURS AT LEAST...WILL LEAVE THE
CURRENT SNOW ADVISORY IN PLACE.  THE WARM FRONT SHOULD MOVE THROUGH
ALL OF THE FORECAST AREA BY 06-08Z TONIGHT WITH A BREAK IN THE
PRECIPITATION WHILE THE CWA IS IN THE WARM SECTOR THROUGH EARLY
MORNING THURSDAY.  THERE WILL BE A WEAK COLD FRONT THAT WILL MOVE
THROUGH THE FORECAST AREA BY LATE THURSDAY MORNING...BUT THE AIR
BEHIND IT IS NOT THAT COLD.  THEN A STRONGER WEATHER SYSTEM WITH AN
EVEN STRONGER WARM FRONT WITH ABUNDANT MOISTURE AND SIGNIFICANT WARM
ADVECTION ALOFT (CREATING GOOD OVER-RUNNING PRECIPITATION) WILL MOVE
INTO THE REGION THURSDAY NIGHT.  THIS NEXT SYSTEM HAS THE POTENTIAL
TO BRING SIGNIFICANT PRECIPITATION AMOUNTS TO THE FORECAST AREA...
ESPECIALLY IN FAVORABLE UP SLOPE AREAS AND OVER THE MOUNTAINS.
HOWEVER 850 MB TEMPERATURES AND 1000-850 MB THICKNESSES AND THE GOOD
SOUTHERLY FLOW AHEAD OF THE SYSTEM WILL CAUSE MAINLY RAIN TO
OCCUR...EVEN AT MOST PASS LEVELS.  AS SUCH WILL NOT NEED ANY WATCHES
FOR HEAVY SNOW AT THIS TIME.  A STRONG COLD FRONT WILL THEN MOVE
THROUGH THE REGION FRIDAY AFTERNOON BRINGING SNOW LEVELS BACK DOWN
TO BETWEEN 1000 AND 2000 FEET.  SNOW SHOWERS WILL OCCUR MAINLY IN
NORTHWEST UP SLOPE AREAS BEHIND THE COLD FRONT FRIDAY AFTERNOON AND
EVENING.  THEN DRYING CONDITIONS WILL TAKE PLACE WITH CLEARING SKIES
LATER FRIDAY NIGHT AND EARLY SATURDAY AS WEAK HIGH PRESSURE BUILDS
OVER THE AREA.  WILL MAKE ONLY MINOR ADJUSTMENTS TO THE EVENING
FORECAST TO LOWER POPS WHERE THE RAIN/SNOW HAS ENDED ALREADY.  RSC.

EXTENDED...A WARM FRONT FROM THE NEXT SYSTEM WILL MOVE INTO THE
REGION BY LATE SATURDAY BRINGING PRECIPITATION BACK TO THE FORECAST
AREA DURING THE DAY. THE COLD FRONT WITH THIS SYSTEM WILL TAKE ITS
TIME MOVING THROUGH THE PACIFIC NORTHWEST UNTIL LATE SUNDAY NIGHT
AND MONDAY. THEN ANTI-CYCLONIC TO ZONAL FLOW WILL BRING COOLER AIR
AND A CHANCE OF RAIN AND SNOW SHOWERS EACH DAY MONDAY THROUGH
WEDNESDAY. MEAD/RSC.

PDT 8686  ALW 8686  PSC 7483  YKM 6482

.KPDT...WSR-88D...VCP32/CSR21...OPERATIONAL.

.KPDT...SNOW ADVISORY IN EFFECT TONIGHT FOR WAZ30 AND ORZ46.