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000
FXUS65 KGJT 030504
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1004 PM MST MON DEC 2 2013

.SHORT TERM...(TONIGHT THROUGH TUESDAY NIGHT)
ISSUED AT 428 PM MST MON DEC 2 2013

CHALLENGING FORECAST FOR THE NEXT COUPLE OF DAYS WITH A PROFOUND
CHANGE IN CONDITIONS EXPECTED BY MIDWEEK AS PREVIOUSLY ADVERTISED.

LOW CLOUDS FINALLY CLEARED OVER NORTHWEST COLORADO AND NORTHEAST
UTAH AHEAD OF THE APPROACHING WINTER STORM WHICH WILL IMPACT THE
AREA BEGINNING TONIGHT. MODELS INDICATED LIGHT SNOW FOR THE
NORTHERN COLORADO MOUNTAINS...THOUGH WEBCAMS SAY OTHERWISE.
MEANWHILE...LOWER VALLEYS OF EAST-CENTRAL AND SOUTHEAST UTAH AND
WESTERN COLORADO HAVE ALSO SEEN A CONSIDERABLE DECREASE IN STRATUS
THOUGH SOME LOCATIONS...INCLUDING GRAND JUNCTION AND DURANGO...
HAVE SEEN LOW CLOUDS STUBBORNLY PERSISTING.

EXPECT REMAINING LOW CLOUDS WILL EVENTUALLY DISSIPATE TONIGHT INTO
TUESDAY AS FLOW ALOFT INCREASES AHEAD OF THE APPROACHING WINTER
STORM. FAVORED THE EC/GFS SOLUTION TODAY OVER THE FASTER NAM
MODEL. ACCORDING TO MODELS...THE ARCTIC FRONT ASSOCIATED WITH THIS
STORM WILL MOVE TO NEAR THE NORTHERN UTAH/COLORADO BORDER BY 12Z
TUESDAY AHEAD OF THE UPPER LEVEL LOW CENTERED OVER WESTERN
MONTANA. MOISTURE MOVING AHEAD OF THE FRONT WILL BEGIN TO GENERATE
LIGHT SNOW OVER THE NORTHERN MOUNTAINS THIS EVENING. SNOW WILL
INCREASE OVER THE REMAINDER OF THE NORTHERN PORTION OF THE
FORECAST AREA TUESDAY AS THE FRONT DROPS TO NEAR THE I-70 CORRIDOR
DURING THE AFTERNOON. THE MOST INTENSE SNOWFALL IS EXPECTED ALONG
THE BAROCLINIC ZONE WHERE STRONG FRONTOGENETIC FORCING INDICATED.
THAT SAID...POSITION OF THE FRONT WILL BE CRUCIAL TO SNOWFALL
ACCUMULATIONS...ESPECIALLY IN THE VALLEYS. SUSPECT FRONT WILL BE
CLOSE ENOUGH TO THE UPPER I-70 CORRIDOR TO WARRANT WARNINGS FROM
RIFLE TO VAIL ALONG THE I-70 CORRIDOR. HOWEVER...APPEARS THE FRONT
WILL STALL NORTH OF THE GRAND VALLEY AND GRAND FLAT OF EASTERN
UTAH AND ANY PRECIPITATION IS LIKELY TO FALL AS RAIN TUESDAY.

THE FRONT REMAINS STATIONARY ACROSS THE CENTRAL MOUNTAINS TUESDAY
NIGHT WHILE ENERGY DIGGING DOWN THE WESTERN FLANK OF THE STORM
SWEEPS INTO THE NORTHERN GREAT BASIN. THIS WILL BEGIN TO MOVE THE
COLDER AIR ACROSS THE GRAND VALLEY AND INTO SOUTHEAST UTAH WITH
MODERATE TO HEAVY SNOW CONTINUING ALONG THIS BOUNDARY. APPEARS
THE FRONT WILL NOT REACH THE SOUTHERN MOST ZONES BY SUNRISE
WEDNESDAY SO...KEPT POPS LOW FOR THOSE AREAS.

CONFIDENCE SUFFICIENT TO UPGRADE WATCHES OVER THE LOWER ELEVATIONS
OF NORTHERN COLORADO...THE CENTRAL COLORADO MOUNTAINS AND THE
EASTERN I-70 CORRIDOR. LEFT WATCHES GOING FOR THE LOWER VALLEYS OF
THE I-70 CORRIDOR IN LIGHT OF UNCERTAINTY REGARDING TIMING CHANGE
OVER TO SNOW. IMPRESSIVE DYNAMIC LIFT ASSOCIATED WITH THE STRONG
JET AND SURFACE FRONTOGENETIC FORCING SEEMS CERTAIN TO BRING 1 TO
2 FEET OF SNOW TO THE MOUNTAINS WITH AS MUCH AS 3 FEET POSSIBLE
AND UP TO A FOOT IN SOME OF OUR VALLEYS BEFORE THE STORM ENDS.

TEMPERATURES SHOULD REMAIN MILD...RELATIVELY SPEAKING...TONIGHT.
ON TUESDAY...COOLER TEMPERATURES WILL TAKE HOLD OF THE NORTH
BEHIND THE FRONT WITH MILDER TEMPERATURES SOUTH OF THE I-70
CORRIDOR. BY TUESDAY NIGHT...ARCTIC AIR BECOMES MORE NOTICEABLE
WITH SINGLE DIGITS ACROSS THE NORTH.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 428 PM MST MON DEC 2 2013

BY WEDNESDAY MORNING...THE WINTER STORM WILL BE IN FULL FORCE INTENSITY
OVER WESTERN CO AND THE EASTERN FRINGES OF UT. THOUGH CONFIDENCE
ON THE TIMING OF THE COLD FRONT PASSAGE IS NOT HIGH...IT IS
EXPECTED TO PASS THROUGH EASTERN UT BY WEDNESDAY EVENING AND SOUTH
OF THE GRAND VALLEY BY WEDNESDAY NIGHT. DECIDED TO KEEP SOUTHERN
ZONES IN WINTER STORM WATCHES WHILE WE WAIT ANOTHER MODEL RUN TO
RESOLVE THE TIMING OF THIS FRONT AND WHERE IT STALLS. THE LOCATION
OF THE FRONTAL PASSAGE ULTIMATELY ANSWERS WHAT LOCATIONS WILL
RECEIVE THE HEAVIEST SNOW AND HOW MUCH PRECIPITATION WILL FALL AS
RAIN IN THE LOWER VALLEYS BEFORE SWITCHING OVER TO SNOW. LOCATIONS
ALONG AND BEHIND THE FRONT WILL BE IN A REGION OF VERY EFFICIENT
SNOW PRODUCTION. INTERESTINGLY...THE WX MODELS HAVE VERY BROAD
SNOWFALL ACCUMULATIONS UNLIKE WHAT WE USUALLY SEE WHERE THE
MOUNTAIN AREAS ARE FORECASTED A SUBSTANTIAL AMOUNT MORE THAN THE
VALLEYS. THIS IS CONCERNING FOR VALLEY FLOORS POTENTIALLY RECEIVING
A GOOD 5 TO 10 INCHES OF SNOW. VERY STRONG DIVERGENCE ALOFT WITH A
135 TO 145 KT JET WILL BE SITTING NEAR IF NOT OVERTOP I-70 ON TUES
NIGHT AND GRADUALLY SHIFT SOUTHEAST. BY WEDNESDAY EVENING...ALL
PRECIPITATION IN EASTERN UT AND WESTERN CO IS EXPECTED TO FALL AS
SNOW AND BEGIN TO TAPER OFF FROM NORTH TO SOUTH. MODELED TOTAL QPF
WATER EQUIVALENCY TUES EVENING THROUGH WED EVENING ARE AROUND 0.50
INCHES IN THE VALLEYS AND THE FOUR CORNERS AREA AND 1 TO 2 INCHES
IN MOUNTAIN AREAS AND ALONG THE STALL OF THE FRONTAL PASSAGE WHICH
COULD POTENTIALLY BE ALONG THE I-70 CORRIDOR OR JUST SOUTH OF IT.
AGAIN...THE BIGGEST FORECASTING CHALLENGE RIGHT NOW IS THE
POSITION OF THE FRONT WHEN IT STALLS AND HOW MUCH PRECIPITATION
WILL FALL AS RAIN IN THE VALLEYS BEFORE IT CHANGES OVER TO SNOW ON
TUESDAY NIGHT AND WEDNESDAY DUE TO THE POSITION OF THE COLD FRONT.
THE BULK OF THE SNOW IS EXPECTED TO MOVE EAST WEDNESDAY EVENING
BUT CONTINUE OVER THE CENTRAL MOUNTAINS UNTIL THURSDAY MORNING.

ON THE OVERALL LONGWAVE PATTERN...ALL MODELS ARE IN GOOD AGREEMENT ON
PLACING THE CENTER OF A LARGE AND VERY COLD H5 -42C UPPER LEVEL
LOW OVER SASKATCHEWAN ON WEDNESDAY. THIS SYSTEM ABSORBS THE TROUGH WHICH
IS EXPECTED TO PRODUCE COPIOUS AMOUNTS OF SNOW OVER THE GREAT
BASIN AND ALLOWS ADDITIONAL SUPPORT OF VERY COLD ARCTIC AIR OVER
THE REGION. THIS LOW GRADUALLY MOVES EAST AND AS IT
DOES...FORCES SEVERAL SHORTWAVES INTO OUR REGION THROUGH THE WEEKEND. THE
FIRST WILL BE THURSDAY AFTERNOON WHICH WILL PRODUCE A COUPLE
INCHES OF SNOW OVER THE WEST FACING SLOPES OF THE MOUNTAIN REGIONS...AND
THE SECOND TROUGH WILL MOVE THROUGH THE REGION WITH MORE MOISTURE
ASSOCIATED WITH IT.

THE NEXT WEEK AND A HALF ARE EXPECTED TO BE VERY UNSEASONABLY COLD
AND ACTIVE. TEMPERATURE RECOVERY WILL BE POOR WITH STRONG
INVERSIONS BECOMING ESTABLISHED DUE TO THE SNOWPACK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1004 PM MST MON DEC 2 2013

TONIGHT STILL IN THE PRE-STORM PERIOD...SO TIMING CHALLENGES WILL
CONTINUE. THE LOW STRATUS HAS CONTINUED TO DIMINISH IN SOME
LOCATIONS...AND IS NOT NEARLY AS WIDESPREAD AS EVEN THIS
AFTERNOON. EXPECT THIS TREND TO CONTINUE WITH THE SOUTHERN CO
VALLEYS HOLDING ONTO THE LOW CLOUDS THE LONGEST. SNOW SHOWERS
WILL CONTINUE TO DEVELOP OVER THE NORTHERN MOUNTAINS AND SPREAD TO
THE CENTRAL MOUNTAINS EARLY THIS MORNING...INCLUDING KASE AND
KEGE. SNOWFALL WILL BECOME MORE STEADY WITH LOWER CIGS/VSBY AFT
14Z. PRECIP AT OTHER SITES SHOULD HOLD OFF UNTIL AFT 18Z TUE. IN
GENERAL...WINDS ALOFT WILL BE INCREASING AND MID LEVEL CLOUDS
LOWERING...SO MTNS WILL BECOME OBSCURED AND MECHANICAL TURBULENCE
MORE PREVALENT OVER THE HIGHER TERRAIN.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...WINTER STORM WARNING FROM 9 AM TUESDAY TO 6 PM MST WEDNESDAY FOR
     COZ003-007-008.

     WINTER STORM WATCH FROM 9 AM MST TUESDAY THROUGH WEDNESDAY
     AFTERNOON FOR COZ006.

     WINTER STORM WATCH FROM TUESDAY EVENING THROUGH WEDNESDAY
     AFTERNOON FOR COZ011-014-020-022-023.

     WINTER STORM WARNING UNTIL 6 PM MST WEDNESDAY FOR COZ004-005-013.

     WINTER STORM WATCH FROM 6 AM MST TUESDAY THROUGH WEDNESDAY
     AFTERNOON FOR COZ017.

     WINTER STORM WARNING FROM 6 AM TUESDAY TO MIDNIGHT MST WEDNESDAY
     NIGHT FOR COZ009-010-012.

     WINTER STORM WATCH FROM 6 AM MST TUESDAY THROUGH WEDNESDAY
     EVENING FOR COZ018-019.

     WINTER STORM WARNING FROM 6 AM TUESDAY TO 6 PM MST WEDNESDAY FOR
     COZ001-002.

UT...WINTER STORM WARNING FROM 9 AM TUESDAY TO 6 PM MST WEDNESDAY FOR
     UTZ025.

     WINTER WEATHER ADVISORY FROM 9 AM TUESDAY TO 3 PM MST WEDNESDAY
     FOR UTZ024.

     WINTER STORM WATCH FROM 9 AM MST TUESDAY THROUGH WEDNESDAY
     AFTERNOON FOR UTZ027-029.

     WINTER STORM WARNING UNTIL 6 PM MST WEDNESDAY FOR UTZ023.

     WINTER STORM WATCH FROM 6 AM MST TUESDAY THROUGH WEDNESDAY
     AFTERNOON FOR UTZ028.

&&

$$

SHORT TERM...NL
LONG TERM...JAM
AVIATION...EH