Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 201119
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
419 AM MST SAT DEC 20 2014

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 410 AM MST SAT DEC 20 2014

HAND ANALYSIS TONIGHT INDICATES RIDGE STILL OVER THE REGION...BUT
THE RIDGE IS BREAKING DOWN THIS MORNING AHEAD OF THE NEXT
SUBSTANTIAL WEATHER SYSTEM. A FEW RETURNS ARE SHOWING UP ON RADAR
THIS MORNING...BUT UNLIKE YESTERDAY MORNING...THIS IS JUST LIKELY
MID LEVEL CLOUDS SHOWING UP MIXED IN WITH A FEW ELEVATED SHOWERS.
THE SHORT TERM MODELS (RAP AND HRRR) INDICATE SOME SCATTERED
SHOWERS DEVELOPING ON THE ROAN/TAVAPUTS THIS MORNING AND ACROSS
NORTHWEST COLORADO SO ADDED THOSE INTO THE POP GRIDS
TODAY...ESPECIALLY CONSIDERING BAGGS WY AND HEBER CITY UT ARE
RECEIVING LIGHT SNOW THIS MORNING. ATMOSPHERIC MOISTURE IS
DEFINITELY AVAILABLE WITH SPEC HUMIDITIES BACK UP TO 3G/KG THIS
MORNING...THOUGH MOISTURE IS ELEVATED WITH DWPT DEPRESSIONS LARGER
THIS MORNING THAN THE LAST FEW DAYS WITHOUT THE LOW/SFC LEVEL
MOISTURE.

70KT UPPER LEVEL JET SUPPORT MAKES ITS WAY INTO THE FORECAST AREA
FROM THE WEST WHICH WILL SLOWLY INCREASE WINDS AT HIGHER TERRAIN
ACROSS ELEVATED PARTS OF NE UT AND NW CO AND AID IN UPPER LEVEL
DIVERGENCE TODAY. EVEN STRONGER (100KT) JET STREAK BLAZES THROUGH
ON SUNDAY AS THE FIRST HEAVIER PRECIPITATION IS EXPECTED TO BEGIN
IN NORTHWEST AND NORTH CENTRAL COLORADO. LOW LEVEL MOISTURE WILL
INCREASE ACROSS NE UT AND NW CO TODAY...THEN ACROSS THE REST OF
THE FORECAST AREA ON SUNDAY IN WARM AIR ADVECTION. NOT EXPECTING
HIGH SNOW AMTS ACROSS THE EASTERN UINTAS AS WE ARE EXPECTING THIS
AREA TO BE SHADOWED DUE TO THE STRONG UPPER LEVEL WESTERLY
WINDS...THOUGH WILL NEED TO CONSIDER THE NEED FOR AN ADVISORY IF
CONDITIONS CHANGE.

THIS UPCOMING WINTER STORM WILL REALLY TAKE HOLD ON SUNDAY WHICH
WILL BE QUITE NOTICEABLE WITH NORTHWEST WINDS RAPIDLY INCREASING
SUNDAY MORNING OVER NE UT AND NW CO. SNOW ACROSS THE NORTH CENTRAL
AND CENTRAL MOUNTAINS OF WESTERN CO WILL INCREASE IN COVERAGE AND
INTENSITY ON SUNDAY AS WELL. BLOWING SNOW WILL DEFINITELY BECOME
AN ISSUE AT HIGHER TERRAIN AND DO EXPECT IT TO BE DIFFICULT TO
MEASURE SNOWFALL AMOUNTS FOR THIS STORM. SEE LONG TERM SECTION FOR
MORE DETAILS ON THIS STORM DEVELOPMENT.

.LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY)
ISSUED AT 410 AM MST SAT DEC 20 2014

...MAJOR WINTER STORM WILL CONTINUE TO BRING HEAVY SNOW AND
BLOWING SNOW TO THE MOUNTAINS OF WESTERN COLORADO THROUGH
MONDAY...

STRONG UPPER LEVEL JET WILL BE MOVING OVERHEAD SUNDAY NIGHT AND
MONDAY WITH H3 SPEEDS CLOCKING IN NEAR 140 KTS BY LATE MONDAY
AFTERNOON. THE FORECAST AREA WILL BE IN PRIME POSITION FOR
ENHANCED JET DYNAMICS FOR AT LEAST 18 HOURS BEGINNING SUNDAY
NIGHT AND THROUGH THE DAY ON MONDAY. PLENTY OF PACIFIC MOISTURE
WILL BE AVAILABLE AND WITH TEMPS IN FAVORABLE DENDRITIC GROWTH
ZONE OVERNIGHT SUNDAY THROUGH MONDAY...EXPECT HEAVY SNOWFALL WILL
NOT BE A PROBLEM WITH HIGH CONFIDENCE THAT MOST OF THE MOUNTAINS
IN WESTERN COLORADO WILL BE MEASURING SNOWFALL WITH A YARD STICK
BY THE TIME MONDAY EVENING ROLLS AROUND. WILL STILL BE CONTENDING
WITH A SHOT OF WAA ON SUNDAY WHICH MAY SLOW THINGS DOWN A
BIT...BUT COOLING ARRIVES SUNDAY NIGHT INTO THE DAY ON MONDAY AS
THE JET SHIFTS OVERHEAD.

A FEW AREAS MAY EXPERIENCE NEAR BLIZZARD CONDITIONS WITH GUSTS
EXCEEDING 45 MPH...ESPECIALLY ABOVE TIMBERLINE ACROSS THE PARK AND
GORE RANGES AND POSSIBLY AS FAR SOUTH AS VAIL PASS ON MONDAY.
SHARP GRADIENT TO THE HEAVY SNOW IS EXPECTED AND THE EXACT
POSITIONING OF THE JET WILL PLAY A BIG ROLE IN THE EVENTUAL
OUTCOME. OROGRAPHIC WIND FIELDS SHOWING SOME BEND TO A MORE
NORTHERLY COMPONENT ON MONDAY WHICH WOULD SLOW SNOW POTENTIAL
ACROSS THE NORTHERN MOUNTAINS...BUT SHIFT THINGS INTO THE CENTRAL
MOUNTAINS NEAR ASPEN...THUS THE EXPANSION OF HIGHLIGHTS TO
INCLUDE THE GRAND MESA AND ZONE 12 NEAR CRESTED BUTTE AND GOTHIC.

WITH CONFIDENCE HIGH AND HOLIDAY TRAVEL UNDERWAY...HAVE ISSUED
WARNINGS AND ADVISORIES FOR ALL OF THE MOUNTAINS IN WESTERN
COLORADO. HIGHER VALLEYS WILL ALSO BE GETTING INTO THE ACTION
SUNDAY AFTERNOON THROUGH MONDAY AND WILL EXPAND THE WATCH TO
INCLUDE CRAIG AND GUNNISON WHERE WE ARE GENERATING 6 PLUS INCHES
OF SNOW THROUGH THAT 24 HOUR PERIOD.

ADDITIONAL CONCERNS ACROSS NORTHEAST UTAH AND EXTREME NORTHWEST
COLORADO WILL BE WINDS WITH H7 SPEEDS CLOCKING IN AROUND 50-60KTS
BY LATE MONDAY AFTERNOON. FOOTPRINT OF THE STRONGEST WINDS ARE
CONFINED TO A NARROW REGION OF OUR FORECAST AREA...GENERALLY NORTH
OF THE EASTERN UINTA MOUNTAINS IN NORTHEAST UTAH INTO EXTREME
NORTHWEST COLORADO NORTH OF DINOSAUR NATIONAL MONUMENT. LATER
SHIFTS WILL NEED TO EVALUATE POTENTIAL FOR WIND OR WINTER
HIGHLIGHTS...BUT CONFIDENCE IN THE SNOW THROUGH THIS AREA WAS NOT
AS HIGH AND WE STILL HAVE TIME DO WORK OUT THE FINER DETAILS IN
THIS AREA.

THIS STORM WILL EXIT LATE MONDAY NIGHT AND TUESDAY WITH TRANSITORY
RIDGE SLIDING THROUGH TUESDAY NIGHT AND WEDNESDAY. THE POTENTIAL
STORM ON CHRISTMAS DAY IS ON SHAKEY GROUND AS THE LATEST GFS RUN
HAS BACKED OFF THE INTENSITY AND CONTINUES TO SHIFT BEST ENERGY
NORTH OF OUR FORECAST AREA. THE ECMWF HAS ALSO BACKED OFF
INTENSITY A BIT AND HAS STARTED TO SHIFT NORTH AS WELL. AFTER
COORDINATION WITH SURROUNDING OFFICES...WILL MAINTAIN HIGHER POPS
FOR NOW WITH FORECAST DIRECTED MORE TOWARD THE WETTER AND DEEPER
EC SOLUTION...WHICH HAS BEEN THE MOST CONSISTENT MODEL OVER THE
PAST FEW DAYS IN REGARDS TO THIS SYSTEM. BOTTOM LINE IS THAT
CONDITIONS WILL REMAIN UNSETTLED FOR MOST OF THE WEEK WITH
TEMPERATURES RUNNING CLOSE TO SEASONAL NORMS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 410 AM MST SAT DEC 20 2014

VFR CONDITIONS EXPECTED AT ALL SITES THROUGH 02Z THIS EVENING WITH
MID AND HIGH LEVEL CLOUDS STREAMING THROUGH THE REGION AHEAD OF A
DEEPER SURGE OF MOISTURE THAT WILL BE MOVING IN TONIGHT. AFTER
02Z...SCATTERED SHOWERS WILL BE DEVELOPING OVER THE HIGHER
MOUNTAINS ALONG AND NORTH OF INTERSTATE 70 WITH CIGS GRADUALLY
DROPPING THROUGHOUT THE NIGHT.

BY EARLY SUNDAY MORNING...WIDESPREAD MVFR CIGS WITH AREAS OF IFR
CIGS CAN BE EXPECTED ACROSS NORTHEAST UTAH AND MUCH OF NORTHWEST
COLORADO AND INTO THE CENTRAL MOUNTAINS IN WESTERN COLORADO.
KASE...KEGE...KHDN AND KSBS WILL ALL BE IMPACTED BY THE DROPPING
CIGS BY EARLY SUNDAY MORNING.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER WEATHER ADVISORY FROM 6 PM SUNDAY TO 6 PM MST MONDAY FOR
     COZ017>019.

     WINTER STORM WARNING FROM 6 AM SUNDAY TO MIDNIGHT MST MONDAY
     NIGHT FOR COZ010-012.

     WINTER STORM WATCH FROM SUNDAY AFTERNOON THROUGH MONDAY
     AFTERNOON FOR COZ002-008-014.

     WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT MST
     MONDAY NIGHT FOR COZ004-013.

     WINTER WEATHER ADVISORY FROM NOON SUNDAY TO 6 PM MST MONDAY FOR
     COZ003.

     WINTER STORM WARNING FROM NOON SUNDAY TO 6 PM MST MONDAY FOR
     COZ009.

     WINTER STORM WARNING FROM 6 AM SUNDAY TO 6 PM MST MONDAY FOR
     COZ005.

UT...NONE.
&&

$$

SHORT TERM...JAM
LONG TERM...JDC
AVIATION...JDC



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