FXUS65 KGJT 222250
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
350 PM MST TUE DEC 22 2009

.SHORT TERM...TONIGHT THROUGH THURSDAY...
MOIST SOUTHERLY FLOW CONTINUES OVER THE FORECAST AREA THIS AFTERNOON
WITH WIDESPREAD SNOW FALLING OVER THE SOUTHERN HALF OF THE REGION.
THE SNOW CONTINUES TO WORK NORTH AND EAST OF THE REGION AS A DEEP
UPPER LEVEL LOW OVER ARIZONA CONTINUES TO SLIDE SLOWLY SOUTHEAST
INTO NORTHERN ARIZONA. THE MOIST DIFLUENT FLOW RIDING OVER THE COLD
VALLEYS WILL CONTINUE TO BRING HEAVY SNOWFALL TO THE LOWER VALLEYS
OF SOUTHEAST UTAH AND EVENTUALLY ARRIVING OVER SOUTHWEST COLORADO.
SNOWFALL AMOUNTS HAVE BEEN IMPRESSIVE THUS FAR WITH OVER 8 INCHES
AT SEVERAL LOCATIONS ACROSS SOUTHEAST UTAH. ACTIVITY LOOKS TO PEAK
OVER OUR SOUTHERN ZONES BETWEEN 06Z AND 12Z TONIGHT WITH SFC LOW
SLIDING OVERHEAD AND INTO SOUTHWEST COLORADO. BROAD NORTHERLY
FLOW THEN SETS UP EARLY WEDNESDAY WITH EMPHASIS OF HEAVIER
SNOWFALL SHIFTING TO THE NORTHERN AND CENTRAL ZONES. HOWEVER...
THERE WILL BE A LULL IN ACTIVITY AS THE SYSTEM AWAITS THE ARRIVAL
OF A COLDER PUSH OF AIR FROM THE NORTH...WITH A STRONG COLD FRONT
MOVING INTO THE PICTURE BY LATE WEDNESDAY AFTERNOON. GOOD CAA AND H7
FLOW SHIFTING TO A MORE FAVORABLE NORTHWEST COMPONENT WILL SQUEEZE
OUT THE REMAINING MOISTURE OVER OUR AREA WEDNESDAY NIGHT...WITH THE
NORTHERN AND CENTRAL MOUNTAINS FAVORED. AMOUNTS WILL BE IN THE
ADVISORY RANGE AND HAVE ALREADY ISSUED THOSE FOR TONIGHT THROUGH
WEDNESDAY NIGHT.

INTERESTING NIGHT IN STORE FOR MANY OF THE VALLEYS TONIGHT AS TEMPS
WILL INITIALLY FALL...BUT EXPECT THEM TO BOTTOM OUT EARLY THIS
EVENING AND THEN ACTUALLY RISE OR BECOME STEADY WITH THE PASSAGE OF
A WEAK PACIFIC FRONT THIS EVENING. THIS WILL HELP TO SCOUR OUT
THE STRONG INVERSIONS...PROMISING A WARMER DAY ON WEDNESDAY.
HOWEVER...THIS IS SHORT-LIVED AS THE ABOVE MENTION COLDER FRONT
ARRIVES WEDNESDAY NIGHT...DRIVING MANY OF THE VALLEYS BACK DOWN
INTO THE SINGLE DIGITS AND TEENS FOR OVERNIGHT LOWS. AS HIGH
PRESSURE BUILDS BACK IN THURSDAY...INVERSIONS WILL AGAIN BE
DEVELOPING BY WEEKS END.

.LONG TERM...CHRISTMAS EVE THROUGH TUESDAY...
AT THE BEGINNING OF THE PERIOD...MODELS ARE NOW A LITTLE FARTHER EAST
WITH THE SECONDARY SHOT THAT WILL REINFORCE THE CLOSED LOW LOCATED
OVER THE CENTRAL CONUS. THEREFORE MOST ENERGY/MOISTURE WILL STAY EAST
OF THE DIVIDE. HOWEVER WESTERN COLORADO REMAINS ON THE CYCLONIC SIDE
OF THE NORTH-SOUTH ORIENTED UPPER JET...SITTING ALONG THE CO/UT
BORDER INTO THE WEEKEND. THIS WILL ALLOW A FEW OROGRAPHIC SHOWERS TO
CONTINUE IN THE NORTHWEST FLOW ALONG THE FAVORED NORTHERN DIVIDE
AREA. THE JET WEAKENS WITH TIME AND EVENTUALLY SHIFTS EAST AS THE
TIGHTLY WOUND 500 MB LOW MOVES OVER THE GREAT LAKES. IN THE MEAN
TIME...AN ELONGATED RIDGE OF HIGH PRESSURE STRETCHED NORTH-SOUTH
ALONG THE ENTIRE WEST COAST EARLY IN THE PERIOD...WILL SHIFT OVER THE
GREAT BASIN AND STRETCH INTO SOUTHWEST CANADA DURING THE WEEKEND.
BY EARLY IN THE NEXT WORK WEEK...THE RIDGE WILL BREAK DOWN AS ENERGY
UNDERCUTS IT AND LOW PRESSURE DROPS INTO THE DESERT SOUTHWEST AND
THEN MOVES ACROSS NEW MEXICO.

AS FOR SENSIBLE WEATHER...THE LONG TERM PERIOD WILL BE PREDOMINANTLY
DRY. A FEW LIGHT SHOWERS WILL BE POSSIBLE THROUGH FRIDAY ALONG THE
CONTINENTAL DIVIDE...MAINLY NORTH. THEN LATE IN THE PERIOD...A LITTLE
MOISTURE/ENERGY ASSOCIATED WITH THE SOUTHERN LOW MAY REACH THE INTO
SOUTHERN MOUNTAINS...BUT SO FAR THIS LOOKS MINIMAL. EXPECT THE
FORECAST IN THE LATER DAYS TO EVOLVE WITH FUTURE FORECASTS.

CONDITIONS WILL AGAIN BE COLD. VALLEY INVERSIONS WILL STRENGTHEN
EARLY IN THE PERIOD...AND PERSIST THROUGH NEXT TUESDAY WITH NO GOOD
MIXING TO SCOUR OUT THE COLD AIR. AT THE HIGHER ELEVATIONS...700 MB
TEMPS REMAIN ON THE COLD SIDE WHILE THE NORTHWEST FLOW CONTINUES...
MODERATING A LITTLE ON MONDAY AND TUESDAY AS THE SOUTHERN LOW MOVES
EAST.

&&

.AVIATION...
WIDESPREAD SNOW WILL CONTINUE TO IMPACT EASTERN UTAH AND WESTERN
COLORADO THROUGH WEDNESDAY. EXPECT MVFR CIGS AND VSBYS WITH
AREAS OF OF IFR AND LIFR CONDS...ESPECIALLY OVER SOUTHEAST
UTAH AND SOUTHWEST COLORADO. CONDITIONS WILL SLOWLY IMPROVE FROM WEST
TO EAST LATE WEDNESDAY NIGHT.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...WINTER WEATHER ADVISORY UNTIL 6 PM MST WEDNESDAY FOR COZ020.
     WINTER STORM WARNING UNTIL 6 PM MST WEDNESDAY FOR
      COZ019-021>023.
     WINTER WEATHER ADVISORY UNTIL 6 AM MST THURSDAY FOR
      COZ003-004-009-010-012-013-017-018.
UT...WINTER WEATHER ADVISORY UNTIL 6 PM MST WEDNESDAY FOR
      UTZ023-025-027-029.
     WINTER STORM WARNING UNTIL 6 PM MST WEDNESDAY FOR UTZ022-028.

$$

SHORT TERM...JDC
LONG TERM....EH
AVIATION.....JDC

$$