Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 281718
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1018 AM MST SUN DEC 28 2014

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 334 AM MST SUN DEC 28 2014

THE NEXT STORM TO AFFECT OUR AREA WAS DROPPING SOUTHEAST ACROSS
WA/OR/ID EARLY THIS MORNING. REGIONAL RADARS SHOWED MOST OF THE
PRECIPITATION WAS AHEAD OF THIS SHORTWAVE THROUGH IN WARM ADVECTION
ON THE NOSE OF THE UPPER JET. LIGHT SNOW WAS OBSERVED IN SE ID/SW
WY. LIGHT SNOW WILL DEVELOP ACROSS THE NRN CO MTNS THIS MORNING AND
INTO THE CENTRAL MTNS THIS AFTERNOON AS THE UPPER JET SETTLES OVER
SE UT AND SW CO BY THIS EVENING.  AVAILABLE MOISTURE REMAINS A
LIMITING FACTOR WITH THIS INITIAL STORM THOUGH...WITH MODELS
INDICATING ONLY 0.15 TO 0.20 INCH PRECIPITABLE WATER AND 700 MB
SPECIFIC HUMIDITY 1.5-2.0 G/KG.

ADDITIONAL SHORTWAVE ENERGY WILL CONTINUE TO CARVE OUT A LARGE
TROUGH OVER THE PACIFIC NORTHWEST/NORTHERN ROCKIES TONIGHT AND
MONDAY. BEST SNOWFALL IS EXPECTED TONIGHT INTO MONDAY MORNING WHEN Q-
G DIAGNOSTICS SHOW DEEP-LAYER VERTICAL VELOCITY MAXIMA MOVING ACROSS
THE NORTH HALF OF OUR FORECAST AREA. FAVORABLE WESTERLY OROGRAPHIC
FLOW PLUS TEMPS FAVORABLE FOR DENDRITIC SNOW GROWTH SHOULD ALSO
CONTRIBUTE TO WIDESPREAD SNOW IN THE CENTRAL MTNS TONIGHT.
THUS...HAVE UPGRADED THE WINTER STORM WATCH TO A WINTER WEATHER
ADVISORY FOR THE CENTRAL MTNS FOR 6-12 INCHES OF SNOW THROUGH
MONDAY...BUT STARTED IT EARLIER WITH THE EXPECTED ONSET OF LIGHT
SNOW  THIS AFTERNOON. NO CHANGES TO THE WINTER HIGHLIGHTS FOR THE
NORTHERN MTNS. WILL NEED TO KEEP AN EYE ON THE NORTHWEST CO LOWER
ELEVATIONS INCLUDING CRAIG/MEEKER/STEAMBOAT FOR POSSIBLE ADVISORY
THERE. BETTER SNOW PROSPECTS SHOULD COME INTO PLAY FOR THE ERN UINTA
MTNS TONIGHT AS FLOW TURNS MORE TO THE NORTH IN COLD ADVECTION. THE
SAN JUANS SHOULD SEE A LITTLE SNOW BUT WILL LIKELY MISS OUT ON THE
HEAVIER AMTS WHICH STAY TO THEIR NORTH.

NORTH TO NORTHEAST FLOW IS EXPECTED ACROSS NE UT/NW CO MONDAY
MORNING AS A COLD FRONT PUSHES IN. MODELS INDICATE A WEAK 700 MB
LOW/CONVERGENT AREA DEVELOPS ACROSS NW OR WEST-CENTRAL CO. NOT
CONFIDENT OF ITS LOCATION...SO DID NOT REALLY JUMP ON THIS FEATURE
FOR HEAVIER SNOW AMTS AT THIS TIME...BUT IT COULD PERHAPS AFFECT
THE I-70 CORRIDOR MONDAY.

.LONG TERM...(MONDAY NIGHT THROUGH SATURDAY)
ISSUED AT 334 AM MST SUN DEC 28 2014

MODELS WERE PRETTY SIMILAR IN DEEPENING THE LATITUDINALLY
ORIENTED LOW PRESSURE TROUGH OVER THE WEST MONDAY NIGHT. GFS AND
ECMWF BOTH INDICATED GOOD CONVERGENCE ALONG A LINE BENEATH THE
STRONG JET WHICH SHOULD CONTINUE TO GENERATE SCATTERED SNOW
SHOWERS ACROSS EAST-CENTRAL UTAH AND WEST-CENTRAL COLORADO THROUGH
WEDNESDAY AFTERNOON.

THE DEEPENING TROUGH EVOLVES INTO A CLOSED LOW OVER SOUTHERN
CALIFORNIA TUESDAY NIGHT RESULTING IN A BROAD AREA OF STRETCHING
DEFORMATION ACROSS THE SOUTHERN HALF OF THE CWFA. CONSEQUENTLY...
EXPECT SHOWER CHANCES TO CONTINUE...MAINLY SOUTH OF THE I-70
CORRIDOR THROUGH WEDNESDAY NIGHT.

EXPECT CHANCES TO INCREASE THURSDAY AS THE LOW CENTER SHIFTS
EASTWARD OVER NORTHERN ARIZONA BRINGING A SURGE OF MOISTURE INTO
THE SOUTHERN MOUNTAINS THROUGH FRIDAY MORNING. THE ECMWF SPREADS
MOISTURE INTO THE NORTHERN MOUNTAINS BENEATH A COL CENTERED
BETWEEN THE NORTHERN STREAM AND THE SOUTHERN LOW. THE LOW PASSES
ONTO THE SOUTHERN PLAINS FRIDAY NIGHT CAUSING FLOW TO SHIFT TO THE
NORTHWEST. BOTH GFS AND ECMWF THEN BEGIN TO GENERATE OROGRAPHIC
SNOW ACROSS COLORADO`S NORTHERN MOUNTAINS SATURDAY.

COLD TEMPERATURES WILL LINGER THROUGH THE EARLY PART OF THE
WEEK...THEN GRADUALLY MODERATE LATE AS FLOW ALOFT BECOMES
SOUTHWESTERLY. STRONG INVERSIONS WILL PREVENT MUCH WARMING FOR
SOME VALLEYS WHERE SNOW REMAINS ON THE GROUND.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1002 AM MST SUN DEC 28 2014

CLOUDS AND SNOWFALL WILL GRADUALLY INCREASE AND LOWER FROM THE
NORTHWEST THE REST OF TODAY AND TONIGHT...AND THEN PERSIST MONDAY AS
THE NEXT STORM SYSTEM MOVES INTO THE REGION...WITH AREAS OF MVFR
AND IFR CIGS AND VISIBILITIES. MOUNTAINS SHOULD CONTINUE TO HAVE
SNOW SHOWERS AND LOWER CLOUDS WITH OBSCURATIONS THROUGH TODAY EVEN
AHEAD OF THE MAIN PUSH OF SNOWFALL.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER WEATHER ADVISORY UNTIL 6 PM MST MONDAY FOR COZ009-010-012.

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

UT...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM MST
     MONDAY FOR UTZ023.

&&

$$

SHORT TERM...JAD
LONG TERM...NL
AVIATION...JRP



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