FXUS65 KGJT 232311
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
400 PM MST WED DEC 23 2009

.SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT...
THE FLOW...WHICH BEGAN AS EAST OR NORTHEAST EARLY TODAY...HAS
CONTINUED TO TRANSITION TO NORTHERLY AS THE SOUTHERN LOW MAKES ITS
WAY ACROSS NEW MEXICO. AS A RESULT...SNOW HAS INCREASED OVER THE
NORTH FACING SLOPES...AND DIMINISHED OVER THE SOUTH FACING ONES. AND
THE FOCUS HAS SWITCHED TO THE THE NORTHERN MOUNTAINS. ALSO AS THE LOW
SHIFTED EAST...THE WESTERN ZONES SAW SNOW DIMINISH OR END EARLY
TODAY. AND THAT TREND HAS CONTINUED.

FOR TONIGHT...COLD ADVECTION WILL INTENSIFY AS THE NEXT IMPULSE
APPROACHES FROM THE NORTH. THIS WILL KEEP SNOWFALL ON-GOING OVER
THOSE FAVORED AREAS THROUGH THE NIGHT. THE PRESENT HILITES COVER THE
PERIOD WELL WITH AN ADDITIONAL 2 TO 4 INCHES OF SNOWFALL EXPECTED BY
MORNING. MOST ENERGY WILL STAY ALONG OR EAST OF THE CONTINENTAL
DIVIDE...KEEPING THE WESTERN ZONES DRY.

AGAIN EXPECT FOG TO FORM IN THE LOWER VALLEYS OVERNIGHT AS INVERSIONS
AGAIN FORM. WE DID SEE WARMER TEMPS TODAY AT KGJT AND KCNY THAN IN
MANY A DAY. BUT THIS HAS JUST INCREASED THE SNOW MELT ADDING TO
AVAILABLE MOISTURE FOR TONIGHT. BUT DO NOT EXPECT THE FOG TO BE AS
THICK AS WHAT WE SAW THIS MORNING.

BY THURSDAY...ACTIVITY WILL WIND DOWN SOMEWHAT AS DRIER AIR MOVES
OVER THE REGION. BUT ENOUGH INSTABILITY/MOISTURE WILL REMAIN TRAPPED
NEAR THE SURFACE UPSTREAM OF THOSE FAVORED NORTHERN SLOPES TO PRODUCE
SCATTERED SNOW SHOWERS THROUGH THE DAY. THE TROUGH AXIS ASSOCIATED
WITH THIS SECOND WAVE WILL PASS LATE THURSDAY NIGHT. HAVE UPPED POPS
THROUGH THE NIGHT AS A RESULT. LESS ACTIVITY IS EXPECTED ELSEWHERE.
THE WEST/CENTRAL/SOUTH VALLEYS WILL STAY DRY SINCE THE CENTER OF THE
LOW ONLY BRUSHES NORTHEAST COLORADO.

THE COOLING ALOFT ON THURSDAY NIGHT MAY ACT TO WEAKEN THE VALLEY
INVERSIONS. WHILE SOME FOG WILL PROBABLY STILL FORM IN PLACES...
EXPECT IT WILL BE MORE LIMITED. SO HAVE LEFT IT OUT OF THE FORECAST
FOR NOW.

.LONG TERM...CHRISTMAS DAY THROUGH WEDNESDAY...

INTERESTING UNUSUAL WEATHER PATTERN EVOLVES FOR THE END OF DECEMBER.
HIGHLY AMPLIFIED AND SLOWLY PROGRESSIVE PATTERN CONTINUES. THESE
PERIODS BEGIN WITH A DEEP LOW OVER NEBRASKA-IOWA AND ANOTHER DEEP LOW
IN THE GULF OF ALASKA...AND A SHORTWAVE SQUEEZED RIDGE ALONG THE
WEST COAST.

FRIDAY-SATURDAY...RESULTING NW FLOW REINFORCES THE COLD AIR IN
PLACE OVER THE FORECAST AREA...ESPECIALLY THE NE PORTION. ALL MODELS
ROTATE A SIGNIFICANT DISTURBANCE THROUGH THE AREA BY EARLY
SATURDAY. POTENTIAL FOR SNOW ACROSS THE NORTH LOOKS BETTER WITH
TODAY/S MODEL RUNS. FORECAST SOUNDINGS OVER THE ELKHEAD/PARK/FLATTOPS
RANGES SHOWS THE PROFILE WARMING ALOFT TO BECOME ISOTHERMAL WITHIN
THE DENDRITIC CRYSTAL GROWTH REGION TO A DEPTH OF NEARLY 550MB FRIDAY
EVENING. THIS WILL LIKELY PRODUCE VERY EFFICIENT CHAMPAGNE POWDER
PRODUCTION FOR THE NORTHERN MTNS. QUICK DRYING SEEN BY SATURDAY
MORNING ON THE BACK SIDE OF THE DISTURBANCE. OTHERWISE INVERSIONS
REMAIN TRAPPED OVER MANY VALLEYS KEEPING TEMPERATURES WELL BELOW
NORMAL.

SUNDAY-WEDNESDAY...RIDGE GETS PINCHED AS PACIFIC TROUGH PROGRESSES
AND TURNS THE UPPER FLOW TO SW ON SUNDAY. THE MORE SPLIT EC IS
FAVORED FOR THESE PERIODS. MOISTURE AND MILDER TEMPS ALOFT BEGIN TO
ADVECT IN FROM THE SOUTHWEST. THIS WILL BEGIN A TREND TOWARDS
MILDER TEMPERATURES AND A CHANCE OF SHOWERS FAVORING THE SOUTH.

&&

.AVIATION...
LOW CLOUDS AND OCCASIONAL SNOW SHOWERS WILL CONTINUE TO IMPACT
WESTERN COLORADO THROUGH TONIGHT...MAINLY NORTHERN AND CENTRAL
MOUNTAINS...WHILE VFR CONDITIONS SHOULD PERSIST ACROSS EASTERN
UTAH. HOWEVER...AREAS OF VALLEY FOG...HAZE...LOW CLOUDS WILL PERSIST
OR DEVELOP TONIGHT POTENTIALLY IMPACTING MANY AIRPORTS IN WESTERN CO
AND EASTERN UT WITH MVFR AND LOCAL IFR CONDITIONS. IMPROVING
CONDITIONS ARE EXPECTED BY MID MORNING THURSDAY AS FOG DISSIPATES AND
MOUNTAIN SNOWFALL DIMINISHES.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...WINTER WEATHER ADVISORY UNTIL 6 AM MST THURSDAY FOR ZONES
      003-004-010-012-013-017-018.
     WINTER STORM WARNING UNTIL 6 AM MST THURSDAY FOR ZONE 009.
UT...NONE.

$$

SHORT TERM...EH
LONG TERM....JOE
AVIATION.....JP

$$