Heavy Snow in Colorado, December 10 to 11, 2001

WESTERN COLORADO & EASTERN UTAH AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
232 PM MST MON DEC 10 2001

BROAD CIRRUS SHIELD ASSOCIATED WITH APPROACHING STORM ESTABLISHED
OVER THE CWFA EARLY TODAY AND HAS HINDERED TEMPERATURE RECOVERY SO
FAR. SYNOPTIC PATTERN FEATURES CLOSED LOW OVER WESTERN AZ EARLY
THIS AFTERNOON WITH SOUTHERLY FLOW OVER THE REGION.

SNOW MOVES BACK INTO THE REGION TONIGHT AS THE CLOSED LOW IS FORECAST
TO MOVE NORTHEASTWARD ACROSS FOUR CORNERS THEN EJECT TO THE NORTHEAST
LATER TONIGHT. MODELS LARGELY SIMILAR...THOUGH INTENSITY CONTINUES
TO BE AN ISSUE. AVN IS MOST CONSISTENT...BUT EVEN THIS MODEL HAS
BACKED OFF SOMEWHAT ON WINDS AND LIFT ASSOCIATED WITH THIS EVENT.
APPEARS BEST LIFT COMES FOR THE SOUTHWEST ZONES THIS EVENING...
THOUGH SUSPECT THAT MOISTURE MAY BE LIMITED INITIALLY...WHICH WILL
CUT INTO SNOW OUTPUT. CONSEQUENTLY...HAVE GONE WITH A SNOW ADVISORY
FOR THE WESTERN SAN JUAN MOUNTAINS AND THE GRAND MESA AND WEST ELK
AND SAWATCH RANGES FOR TONIGHT AND TUESDAY. FLOW INITIALLY IS QUITE
GOOD EARLY FROM THE SOUTHWEST AT 25 KTS BUT WEAKENS TO 15 KTS AND
SHIFTS MORE WESTERLY LATE. ALSO...UNLIKE YESTERDAYS 12Z RUN...AVN
LAPSE RATES NOT AS STEEP. GIVEN BREVITY OF EVENT OVER SOUTHWEST...
CANCELLED WATCH FOR THE LOWER ELEVATIONS OF THE FOUR CORNERS. SNOW
WILL SPREAD INTO THE NORTHERN MOUNTAINS LATER TONIGHT...SO INITIAL
ACCUMULATIONS LIGHT UP NORTH.

ONCE INITIAL WAVE IS THROUGH...EVENT BECOMES LARGELY OROGRAPHIC IN
NATURE WITH NORTHERN MOUNTAINS GETTING INTO THE ACTION. WESTERLY
FLOW ONLY ON THE ORDER OF 15 TO 20 KTS...SO ACCUMULATIONS NOT ALL
THAT IMPRESSIVE. TONIGHT AND TUESDAY TOTALS ON THE ORDER OF 4 TO 8
INCHES WHICH MAY BE A BIT OPTIMISTIC...THEREFORE HAVE HELD OFF
ON ANY HIGHLIGHTS NORTH...BUT INVITE LATER SHIFTS TO REEVALUATE.

DIGGING JET ALONG THE WEST COAST HOLDS BROAD TROF IN PLACE OVER THE
REGION INTO WEDNESDAY. SO UNSETTLED WEATHER WILL STAY US...THOUGH
FLOW REMAINS FAIRLY LIGHT SO ADDITIONAL ACCUMULATIONS NOT ALL THAT
GREAT. TROF PUSHES EASTWARD WEDNESDAY AND WEDNESDAY NIGHT...SO WILL
INTRODUCE SOME CLEARING TO WESTERN ZONES...BUT WILL MAINTAIN SNOW
CHANCE FOR MOST MOUNTAIN LOCATIONS.

TEMPERATURES ALSO A CHALLENGE. AVN MUCH COLDER THAN NGM MOS FOR
TUESDAY. THIS APPEARS A TAD OVERDONE...ESPECIALLY NORTH. MODEL
INDICATES BACK DOOR COLD FRONT PUSHING ACROSS LATE TONIGHT SO WILL GO
COOLER...BUT NOT QUITE TO AVN MOS GUIDANCE. NL

EXTENDED (THU-MON)...AT THE START OF THE PERIOD THE LONGWAVE TROUGH
AXIS WILL BE OVER THE WESTERN PLAINS WITH NORTHWEST FLOW OVER EASTERN
UTAH AND WESTERN COLORADO.  THROUGH THE PERIOD THE TROUGH MOVES
EAST AND WEAKENS. THEN BY THE WEEKEND A BROAD TROUGH REFORMS OVER
WESTERN NORTH AMERICA AS SHORTWAVES DIG OVER WESTERN CANADA.  HATE TO
FLIP-FLOP ON FORECAST FOR THU...BUT SITUATION AGAIN LOOKS ON THE DRY
SIDE. A WEAK SHORTWAVE EMBEDDED IN THE NORTHWEST FLOW WILL CLIP THE
AREA...BUT DO NOT BELIEVE IT WILL BE STRONG ENOUGH TO BRING
PRECIPITATION TO MOST VALLEYS. WILL KEEP MENTION OVER THE MOUNTAINS
AND NORTH BUT GO PARTLY CLOUDY ELSEWHERE. A BETTER SHOT WILL PUSH-IN
ON FRI AS THE FLOW BECOMES MORE WESTERLY...FOLLOWED BY ANOTHER
STRONGER SHORTWAVE ON SAT.  MODEL INCONSISTENCIES CONTINUE FOR LATER
PERIODS...BUT IT LOOKS LIKE COLD AND DRY NORTHWEST FLOW WILL SET IN
FOR SUN. TEMPERATURES SHOULD MODERATE A BIT FOR MON AS THERMAL LOW
MOVES EAST...BUT WILL LUMP WITH SUN AT THIS TIME. HEFFERNAN

.GJT...SNOW ADVISORY TONIGHT AND TUE FOR COLORADO ZONES 9/12/18/19.