Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 192131
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
231 PM MST FRI DEC 19 2014

.SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)
ISSUED AT 229 PM MST FRI DEC 19 2014

A WEAK DISTURBANCE AND LOW-LEVEL INSTABILITY GENERATED AREAS OF
LIGHT SNOW THIS MORNING ACROSS WEST-CENTRAL AND NORTHWEST COLORADO.
WE RECEIVED 0.5 INCH OF SNOW HERE AT THE GJT WEATHER OFFICE...THE
FIRST MEASURABLE SNOW AT THE OFFICE SO FAR THIS SEASON.

MOST OF THE AREA WILL REMAIN DRY TONIGHT THROUGH SATURDAY AFTERNOON.
WARM ADVECTIVE HIGH CLOUDS WERE MOVING IN THIS AFTERNOON AHEAD OF A
WEAK WAVE THAT WILL CROSS TONIGHT. ANOTHER PACIFIC TROUGH AND ITS
ASSOCIATED SURFACE COLD FRONT WAS PUSHING ACROSS THROUGH THE PAC NW
AND WESTERN GREAT BASIN THIS AFTERNOON. Q-G DIAGNOSTICS SHOWED THIS
WAVE WEAKENING CONSIDERABLY BY THE TIME IT CROSSES WRN CO SAT
MORNING FOR SCATTERED LIGHT SNOW ACROSS THE NRN MOUNTAINS SAT. MAY
SEE A FEW FLAKES AROUND MEEKER...CRAIG TO STEAMBOAT SPGS AS THE
WESTERLY FLOW ENCOUNTERS THE HIGHER TERRAIN. THESE WAVES WILL NOT BE
STRONG ENOUGH TO FLUSH OUT THE EASTERN UINTA BASIN WHERE LOW CLOUDS
WILL HANG ON.

A STRONG AND MOIST PACIFIC JET PUNCHES INTO WA/OR WITH 310K AND 315K
ISENTROPIC FIELDS SHOWING THE INITIAL MOISTURE PUSH REACHING NE
UT/NW CO SAT NIGHT IN WARM ADVECTION/ISENTROPIC UPGLIDE. MADE ONLY
MINOR CHANGES TO THE CURRENT POP GRIDS WHICH HAVE SNOW BECOMING
WIDESPREAD ACROSS THE NRN MOUNTAINS AFTER MIDNIGHT SAT NIGHT AND
SPREADING INTO THE CENTRAL MTNS BY 12Z SUNDAY. LIKELY TO SEE SOME
LIGHT SNOW IN THE CRAIG/MEEKER/STEAMBOAT AREAS BY 12Z SUNDAY AS
WELL. IN CONTRAST...ONLY A CHANCE OF LIGHT SNOW FOR THE EASTERN
UINTA MTNS SAT NIGHT IN THE SHADOW OF THE HIGHER MTNS TO THEIR
WEST.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 229 PM MST FRI DEC 19 2014

TWO STORMS ARE STILL TIMED TO IMPACT THE REGION SUNDAY THOUGH
MONDAY AND THEN AGAIN CHRISTMAS DAY. DETAILS FOR THE WEEKEND
STORM ARE BETTER RESOLVED FAVORING THE NORTH...ESPECIALLY THE NW
CO MTNS...WITH SIGNIFICANT SNOWFALL. CURRENT HIGHLIGHTS ARE IN
GOOD SHAPE THOUGH SURROUNDING MTN ZONES LOOK LIKE THEY MAY REACH
ADVISORY SNOW AMOUNTS.

SUNDAY IN MILD NW FLOW...MOISTURE DEEPENS OVER THE FORECAST AREA.
700MB SPECIFIC HUMIDITIES CLIMB TO 4 G/KG OVER THE NORTH. SNOW
LEVELS WILL BE A CHALLENGE EXPECTED TO RISE TO AROUND 7KFT IN THE
AFTERNOON. OROGRAPHICS IS THE MAIN FORCING MECHANISM. DENDRITIC
CRYSTAL GROWTH REGION IS NEAR SATURATION BUT IS HIGH AT AROUND
15-17KFT MSL. SO HAVE KEPT THE HIGH POPS FOR SUNDAY BUT LOWERED
SNOW ACCUMULATIONS SOMEWHAT.

SUNDAY NIGHT-MONDAY JET SUPPORT NOSES IN FROM THE NW WITH COLD
ADVECTION LOWERING 700MB TEMPS FROM -6 TO -10. DENDRITIC LAYER
LOWERS TO AROUND 11KFT MSL. THE GFS IS PRODUCING OVER A FOOT OF
SNOW OVER THE PARK GORE FLAT TOP RANGES THROUGH THESE PERIODS.
MONDAY NIGHT...NW COLORADO SNOWFALL IS EXPECTED TO DIMINISH BUT
NOT NECESSARILY END. WINTER HIGHLIGHTS COULD BE POTENTIALLY BE
EXTENDED INTO THIS PERIOD FOR THE NW CO MTNS.

HIGHLY AMPLIFIED WEST COAST RIDGE AMPLIFIES INLAND TUESDAY INTO
WEDNESDAY.

BY THURSDAY THE NEXT NORTHERN PACIFIC WAVE WORKS INTO THE GREAT
BASIN. THE EC IS DEEPER AND COLDER WITH THIS SYSTEM WHILE THE GFS
KEEPS MOST OF ITS ENERGY IN THE NORTHERN ROCKIES. CONFIDENCE IS
HIGH FOR THE NORTHERN ZONES TO RECEIVE SOME SNOWFALL INTO
FRIDAY...WHILE CONFIDENCE LOWERS SOMEWHAT INTO THE CENTRAL AND
SOUTHERN ZONES. SNOW LEVELS START OUT HIGH ON CHRISTMAS DAY THEN
LOWER OVERNIGHT. HIGHLIGHTS ARE EXPECTED.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 958 AM MST FRI DEC 19 2014

AREAS OF LIGHT SNOW WILL PERSIST OVER THE NRN CO MTNS INTO MID-
AFTERNOON BUT DIMINISH ELSEWHERE AS A WEAK DISTURBANCE EXITS TO THE
EAST. LOW CLOUDS CURRENTLY ENTRENCHED IN MANY VALLEYS MAY BE
STUBBORN TO LEAVE...THOUGH DO EXPECT VFR CONDITIONS TO DEVELOP AT
THE TAF SITES...AND MOST AIRFIELDS... BY 21Z IF NOT SOONER THIS
AFTERNOON. A COUPLE OF WEAKENING UPPER DISTURBANCES WILL IMPACT
THE AREA...ONE TONIGHT AND ANOTHER ON SATURDAY FOR THE POTENTIAL
OF MVFR CIGS AT TIMES OVER AT LEAST THE NORTHERN MTNS.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER STORM WATCH FROM SUNDAY AFTERNOON THROUGH MONDAY
     AFTERNOON FOR COZ008.

     WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH MONDAY
     AFTERNOON FOR COZ004-013.

     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY AFTERNOON
     FOR COZ005-010.

UT...NONE.
&&

$$

SHORT TERM...JAD
LONG TERM...JOE
AVIATION...JAD


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