Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 191701
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1001 AM MST FRI DEC 19 2014

AVIATION SECTION UPDATED

.UPDATE...
ISSUED AT 742 AM MST FRI DEC 19 2014

A WEAK DISTURBANCE SEEN IN SATELLITE WATER VAPOR WAS CROSSING WRN
CO EARLY THIS MORNING GENERATING AREAS OF LIGHT SNOW IN A NEUTRAL
TO WEAKLY UNSTABLE ENVIRONMENT ALOFT PER THIS MORNINGS SOUNDING.
SNOW WILL GENERALLY BE JUST A DUSTING BUT ENOUGH TO BRING SOME
WHITENESS AT LEAST TEMPORARILY. AREAS OF FOG ALSO PRESENT THIS
MORNING. EXPECT THE MAJORITY OF THIS LIGHT SNOW TO END BY MIDDAY.
HAVE UPDATED GRIDDED FORECAST TO REFLECT CURRENT AND EXPECTED
CONDITIONS THIS MORNING.

&&

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 420 AM MST FRI DEC 19 2014

STILL HANGING ONTO A FEW ISOLATED SNOW SHOWERS ACROSS THE
BOOKCLIFFS AT MEEKER...SUNLIGHT...AND ASPEN THIS MORNING. FOG HAS
INTERMITTENTLY BEEN REDUCED TO A HALF MILE AT TIMES AT CRAIG THIS
MORNING BUT MOST LOCATIONS ARE STAYING OUT OF THE SOUP. WEAK
TRANSITORY RIDGING WILL BUILD INTO THE REGION TODAY...BUT BY THIS
EVENING MID TO HIGH LEVEL CLOUDS WILL BEGIN MOVING IN FROM THE
WEST. A FEW ISOLATED SHOWERS ARE POSSIBLE ON SATURDAY MORNING AHEAD
OF THE MAIN MOISTURE OVER NE UTAH AND NW COLORADO MOUNTAINS...BUT
THE MORE INTERESTING WEATHER IS IN THE FOLLOWING LONG TERM
SECTION.

.LONG TERM...(SATURDAY NIGHT THROUGH THURSDAY)
ISSUED AT 420 AM MST FRI DEC 19 2014

MOIST NORTHWEST FLOW WILL BE SETTLING IN OVER THE FORECAST AREA
SATURDAY NIGHT WITH A SLOW SOUTHWARD PROGRESSION INTO OUR CENTRAL
MOUNTAINS BY EARLY SUNDAY MORNING. STRONG UPPER LEVEL JET SLOPES
INTO THE AREA...PROVIDING DYNAMIC SUPPORT. MODELS REMAIN VERY
AGGRESSIVE WITH QPF VALUES WITH SNOWFALL ACCUMULATIONS EXCEEDING
A FOOT OVER A LARGE PORTION OF OUR NORTHERN AND CENTRAL MOUNTAINS
FROM VAIL NORTH TO THE WYOMING STATE LINE. FAVORED WEST AND
NORTHWEST SLOPES COULD EXCEED 2 FEET BY LATE MONDAY AS 30-40 KTS
H7 FLOW PROVIDES FAVORABLE OROGRAPHIC FLOW AND WORKS TO SQUEEZE
OUT ALL AVAILABLE MOISTURE ALONG AND WEST OF THE CONTINENTAL
DIVIDE. INITIAL SURGE FAVORS THE NORTHERN AND CENTRAL MOUNTAINS
BUT THE JET IS EXPECTED TO SAG SOUTH A BIT MORE THAN FORECAST AND
DRIVE MOISTURE SOUTHWARD INTO THE SAN JUANS BY SUNDAY
NIGHT...ALTHOUGH POTENTIAL SNOWFALL AMOUNTS WILL BE ABOUT HALF OF
WHAT WE CAN EXPECT OVER THE NORTH.

WITH HOLIDAY TRAVEL PICKING UP THIS WEEKEND...WE WENT AHEAD AND
ISSUED A WINTER STORM WATCH FOR THE NORTHERN AND CENTRAL MOUNTAINS
IN WESTERN COLORADO LATE IN THE 4TH AND 5TH PERIODS OF THE
FORECAST. WILL NEED TO WATCH SHOT OF WAA ON SUNDAY WHICH MAY SLOW
POTENTIAL SNOWFALL A BIT...BUT SERIES OF FAST MOVING PACIFIC WAVES
WILL EVENTUALLY SEND IN A LITTLE COOLER AIR ALOFT AND KEEP
SNOWFALL EFFICIENCY HIGH THROUGH EARLY MONDAY. NEW NAM IS A LITTLE
FAST...ADVERTISING A BREAK LATE MONDAY AND MONDAY NIGHT WITH THE
GFS A LITTLE SLOWER SHOWING SOME DRAG TO THE MOISTURE AND APPEARS
TO BE MORE REASONABLE BASED ON PREVIOUS EVENTS OF SIMILAR NATURE.

FLAT RIDGING SLIDES THROUGH TUESDAY AND WEDNESDAY AHEAD OF YET
ANOTHER POTENTIAL SYSTEM THAT IS EXPECTED TO ARRIVE BY CHRISTMAS
MORNING. THE GFS AND ECMWF CONTINUE TO JUMP AROUND FROM RUN TO RUN
WITH THE NEW ECMWF BACK TO SHOWING A CLOSED LOW MOVING OVER THE
FORECAST AREA ON CHRISTMAS. GFS HINTING AT MORE OF A SPLITTING
SYSTEM SENDING ENERGY NORTH AND SOUTH...WITH THE SOUTHERN SYSTEM
ROLLING ACROSS OUR FORECAST AREA. EITHER SCENARIO WOULD BRING
PRECIPITATION TO MUCH OF EASTERN UTAH AND WESTERN COLORADO...BUT
WITH SOME UNCERTAINTY STILL EVIDENT...WILL RUN WITH BLENDED POP
SOLUTIONS...WHICH OFFER SLIGHT CHANCE TO CHANCE POPS FOR NOW.
TEMPS COOL DOWN BEHIND THE CHRISTMAS SYSTEM.

&&

.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.
&&

$$

UPDATE...JAD
SHORT TERM...JAM
LONG TERM...JDC
AVIATION...JAD


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