Weather Service Report


867 
FXUS65 KGJT 290445
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
945 PM MST SUN DEC 28 2014

.UPDATE...
ISSUED AT 943 PM MST SUN DEC 28 2014

ISSUED A WINTER WEATHER ADVISORY FOR THE I-70 CORRIDOR FROM DEBEQUE 
TO AVON (CO ZONES 7 AND 8) FOR TONIGHT AND MONDAY. BAND OF SNOW 
ACROSS NW CO IN WESTERLY FLOW WILL CONTINUE TO SINK SLOWLY 
SOUTHWARD INTO WEST-CENTRAL CO OVERNIGHT. THIS EVENING'S NAM AND GFS 
MODELS CONTINUED TO SHOW A LOW LEVEL CIRCULATION/CONVERGENT AREA 
DEVELOPING OVER GARFIELD/PITKIN/ EAGLE COUNTIES ON MONDAY..AND 
BELIEVE THIS WILL SUPPORT PERIODS OF SNOW FOR ZONES 7 AND 8 WITH 
ACCUMULATIONS ROUGHLY 2-5 INCHES. THE GRAND VALLEY COULD ALSO
SEE SOME LIGHT ACCUMULATIONS BUT APPEARS TO BE JUST OUT OF THE BEST 
CONVERGENCE.

AVIATION SECTION ALSO UPDATED.

&&

.SHORT TERM...(TONIGHT THROUGH MONDAY NIGHT)
ISSUED AT 257 PM MST SUN DEC 28 2014

MODELS IN RELATIVELY GOOD AGREEMENT IN THE SHORT TERM WITH
INCREASING LOWER LEVEL MOISTURE FROM THE NW ACROSS THE NORTHERN
TWO-THIRDS OR SO OF OUR CWA TONIGHT...AS THE SOUTHWESTERN LOBE OF
A VERY ELONGATED NE-SW TROUGH DROPS FURTHER DOWN INTO THE CENTRAL
INTERMOUNTAIN AREA. ENOUGH DYNAMIC LIFT...QG FORCING...AND GOOD
DENDRITIC GROWTH ZONE TEMPERATURES AT H7-H6 TO SUPPORT THE
SNOWFALL HIGHLIGHTS FOR ALL OUR NORTHERN AND CENTRAL MOUNTAIN
ZONES...AS WELL AS THE HIGHER NORTHWEST COLORADO VALLEYS.

H7-H6 WINDS ALSO SHOULD CONTINUE TO PROVIDE GOOD OROGRAPHIC LIFT
TO MANY NORTHERN AND CENTRAL MOUNTAINS...UNTIL EARLY MONDAY
MORNING WHEN AN EXPECTED CIRCULATION IN THE FLOW SHOULD RESULT IN
EASTERLY WINDS IN OUR NORTHERN MOUNTAINS. THE SAME FEATURE SHOULD
RESULT IN THE H7-H6 FLOW BECOMING SOUTH TO SOUTHWEST IN WEST-
CENTRAL CO.

ALTHOUGH THE DYNAMIC LIFT OVER OUR CWA IS GREATLY REDUCED BY
MONDAY EVENING...THE AIRMASS IS LIKELY TO REMAIN QUITE MOIST
ACROSS THE NORTHERN AND CENTRAL PORTIONS OF OUR CWA THROUGH MONDAY
NIGHT UNDER OR NEAR A COL ZONE. THERE MAY BE ENOUGH LINGERING
SNOWFALL MONDAY NIGHT...PERHAPS MORE THAN PRESENTLY IN THE
GRIDS...THAT SOME MOUNTAIN HIGHLIGHTS MAY NEED TO BE EXTENDED.
HOWEVER...THERE REMAINS ENOUGH UNCERTAINTY AT THIS TIME REGARDING
ADDITIONAL SNOWFALL AMOUNTS THAT THIS DECISION MAY HAVE TO WAIT
UNTIL TOMORROW WHEN CONFIDENCE INCREASES ONE WAY OR THE OTHER.

LITTLE CHANGE IN SURFACE TEMPERATURES DURING THE SHORT TERM
PERIOD... THOUGH IT LOOKS LIKE THE UPPER GUNNISON RIVER VALLEY
WILL REMAIN SIGNIFICANTLY COLDER THAN PREVIOUSLY FORECAST FOR
TONIGHT AND MONDAY...AND ADJUSTED TEMPERATURES DOWN SIGNIFICANTLY 
FOR THAT ZONE.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 257 PM MST SUN DEC 28 2014

BY TUESDAY MORNING...A VERY STRONG 140KT JET STREAK WILL BE SLUNG
ACROSS SOUTHEAST UTAH AND SOUTHERN COLORADO. THE JET WILL INCH NORTH
A BIT DURING THE DAY AS A CLOSED LOW PINCHES OFF OF THE LARGE
TROUGH OVER THE AREA. A CONVERGENCE ZONE LOOKS TO SET UP ON
THURSDAY ACROSS EASTCENTRAL UTAH AND WESTCENTRAL COLORADO...WHICH
COULD SET UP A LOT OF SNOWFALL WHERE THE CONVERGENCE ZONE STALLS.
RIGHT NOW THE EC TARGETS THE BOOKCLIFFS...UNCOMPAHGRE...AND GRAND
VALLEY ON TUESDAY AFTERNOON...BUT THE GFS IS EARLIER WITH THE AREA
OF CONVERGENCE.

THE CLOSED LOW IS PROGGED TO DEVELOP OVER SOCAL ON TUESDAY NIGHT
AND LESSEN THE MOISTURE TAP ACROSS THE FORECAST AREA...THOUGH A
DEFORMATION ZONE WILL HELP KEEP SHOWERS GOING ACROSS THE REGION.
THE SECTION OF THE TROUGH AFFECTING OUR AREA THE NEXT COUPLE OF
DAYS WILL SCOOT EAST WHILE THE NEWLY CLOSED LOW PICKS UP MOISTURE
FROM THE PACIFIC. THIS LOW PRESSURE IS EXPECTED TO APPROACH
EASTERN UTAH SOMETIME ON THURSDAY MORNING WITH SPECIFIC HUMIDITIES
REACHING ABOUT 3 G/KG...THOUGH THE GFS AND EC SOLNS DIFFER WITH
THE TRACK AND AMT OF MOISTURE WITH THIS SYSTEM. COULD POTENTIALLY
BE A GOOD SNOWMAKER FOR THE SAN JUANS BUT IT COULD ALSO SKIM BY
THE VERY SOUTHERN SAN JUANS AND ONLY PRODUCE A COUPLE OF INCHES OF
SNOW OR GO TOO FAR SOUTH ALTOGETHER. THE OTHER ITEM TO MENTION
WITH THIS LOW PRESSURE DEVELOPING IS THAT WARMER AIR WILL BE
OVERRUNNING COOLER AIR SO WILL NEED TO KEEP AN EYE ON PRECIP TYPE
ACROSS SOUTHERN AREAS.

MAX TEMPERATURES ACROSS THE FORECAST AREA WILL REMAIN AROUND
NORMAL AND MIN TEMPERATURES SLIGHTLY BELOW NORMAL UNTIL THURSDAY
WHEN A NOTICEABLE WARM UP IS EXPECTED DURING THE DAYTIME HOURS.
NORTHERN AREAS OF THE FORECAST AREA ARE EXPECTED TO BE UNAFFECTED
BY THE PASSING CLOSED LOW MIDWEEK...AND WILL REMAIN IN SEASONABLY
NORMAL TEMPERATURES AND DRY CONDITIONS UNTIL AT LEAST SUNDAY.
THERE IS THE POSSIBILITY OF ANOTHER DISTURBANCE REACHING THE
FORECAST AREA FROM THE NORTH SOMETIME ON SUNDAY...BUT MAJOR MODEL
DIFFERENCES KEEP CONFIDENCE LOW ON THAT SOLN.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 943 PM MST SUN DEC 28 2014

AN EAST-WEST BAND OF HEAVIER SNOW OVER THE TAVAPUTS TO FLATTOPS WILL 
CONTINUE TO SINK SLOWLY SOUTHWARD OVERNIGHT. EXPECT PERIODS OF
MVFR OR IFR CIGS/VSBY IN SNOW UNDER THIS BAND. WESTERLY WINDS WERE
AROUND 35KT AT 12K FEET AT KGJT CURRENTLY. PILOTS MAY ENCOUNTER
SOME WIND SHEAR RISING OUT OF PROTECTED MOUNTAIN VALLEYS SUCH AS
AT KASE. SNOW WILL REMAIN WIDESPREAD NORTH OF THE SAN JUAN
MOUNTAINS ON MONDAY BUT DECREASING BY LATE AFTERNOON.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER WEATHER ADVISORY UNTIL 6 PM MST MONDAY FOR COZ003-007>010-
     012.

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

     WINTER WEATHER ADVISORY UNTIL NOON MST MONDAY FOR COZ002-005.

UT...WINTER WEATHER ADVISORY UNTIL 6 PM MST MONDAY FOR UTZ023-025.

&&

$$

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

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