Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 240510
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1010 PM MST TUE DEC 23 2014

.UPDATE...
ISSUED AT 1010 PM MST TUE DEC 23 2014

A COLD WEDNESDAY MORNING IS IN STORE. AT 9PM REGIONAL TEMPERATURES
ARE 8 TO 22 DEGREES COOLER THAN MONDAY NIGHT. HAVE UPDATED FOR
COLDER MIN TEMPERATURES AND ADDED PATCHY MORNING FOG ALONG
WATERWAYS.

ATTENTION TURNS TO THE CHRISTMAS STORM. MODELS REMAIN IN GOOD
AGREEMENT. THE SLIGHTLY SLOWER GFS LOOKS LIKE BETTER TIMING WITH
SHOWERS SPREADING INTO NE UTAH BEFORE SUNRISE THEN ACROSS THE
REGION THROUGH THE AFTERNOON. THE CLOSING OF THE UPPER LOW  OVER
THIS REGION WILL PRODUCE A PROLONGED EVENT. ALSO MESOSCALE
FEATURES UNDER THE SLOW MOVING LOW WILL DEFINE THE BEST SNOW
ACCUMULATIONS...STILL TIMED TO OCCUR THURSDAY NIGHT. THE 00Z NAM
SHOWS A TIGHT NEAR SURFACE CONVERGENT OVER THE FLATTOPS IN THE
LATE AFTERNOON DROPPING TO THE GRAND MESA THROUGH THE EVENING
DROPPING INTO THE NW SAN JUANS FRIDAY MORNING. THE 00Z GFS IS NOT
FAR OFF THOUGH FAVORING THE CASTLE PEAK RIDGE BETWEEN ASPEN AND
CRESTED BUTTE OVERNIGHT. THIS DETAIL IS IMPORTANT AS IT MAY DEFINE
WHERE WARNINGS WILL BE NEEDED. WE WILL LOOK AT THIS IN DETAIL
OVERNIGHT.

&&

.SHORT TERM...(TONIGHT THROUGH WEDNESDAY NIGHT)
ISSUED AT 251 PM MST TUE DEC 23 2014

STRATOCUMULUS CLOUDS WERE HOLDING ON ACROSS MUCH OF WESTERN CO
THIS AFTERNOON IN COLD NORTHERLY FLOW WITH GUSTY WINDS AND STILL A
FEW AREAS OF LIGHT SNOW OVER THE CO MTNS. THE UPPER JET WILL
CONTINUE TO WEAKEN AS IT SLIDES EAST OF OUR AREA THIS EVENING...
WITH CLEARING SKIES AND COLD TEMPS TONIGHT.

A PACIFIC RIDGE WAS BUILDING INTO THE WEST TODAY. IT WILL SLIDE OVER
OUR AREA ON WEDNESDAY FOR DRY AND STABLE CONDITIONS WITH LESS WIND.
TEMPS WILL BEGIN WARMING ALOFT BUT MORNING SURFACE INVERSIONS
WILL LIKELY RETARD WARMING IN VALLEYS...ESPECIALLY WHERE THERE IS
FRESH SNOW COVER.

A FAST-MOVING SHORTWAVE TROUGH RACING ACROSS THE NERN PACIFIC
OCEAN TODAY IS EXPECTED TO REACH THE WA/OR/NRN CA COAST LATE
WEDNESDAY AFTERNOON...THEN DROP INTO THE GREAT BASIN WEDNESDAY
NIGHT AND PUSHING A COLD FRONT INTO UT. CLOUDS WILL INCREASE
WEDNESDAY NIGHT IN STRENGTHENING SOUTHWEST FLOW ALOFT...WITH A
CHANCE OF SNOW OVER THE ERN UT/WRN CO MTNS AND NRN VALLEYS BY
CHRISTMAS MORN.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 251 PM MST TUE DEC 23 2014

THE NEXT STORM SYSTEM IS STILL ON TRACK AS A SIGNIFICANT LOW
PRESSURE TROUGH IS PROGGED TO DROP OUT OF THE NORTHWEST AND
APPROACH OUR FORECAST AREA BY EARLY CHRISTMAS MORNING.
PRECIPITATION WILL SPREAD INTO THE FORECAST AREA AS AN ASSOCIATED
AND LEADING COLD FRONT PASSES OVER THE AREA FROM NORTHWEST-TO-
SOUTHEAST EARLY IN THE DAY. ALONG WITH THE FRONT AND AHEAD OF THE
UPPER LEVEL TROUGH...JET STREAM ENERGY WILL SWEEP OVER THE FOUR
CORNERS...BEFORE THE JET SINKS SOUTHWARD TOWARDS THE U.S./MEXICO
BORDER BY MIDDAY. BY THEN INSTABILITY AND DYNAMICS WILL INCREASE
AS THE UPPER TROUGH TAKES OVER. THE TROUGH AXIS REACHES THE UT/CO
BORDER DURING THE EVENING...WITH ENERGY DROPPING SOUTHWARD TO THE
4-CORNERS AND SWINGING AROUND THE 4-CORNERS AND NORTHWEST NM ON
FRI/FRI NIGHT. MODELS ARE GENERALLY IN VERY GOOD AGREEMENT...
HOWEVER THERE ARE STILL SOME DIFFERENCES IN THE DETAILS. FOR
EXAMPLE...MODELS SHOW A LOW CLOSING OFF OVER UT CHRISTMAS
AFTERNOON THEN MOVING OVER THE 4-CORNERS LATE THURSDAY NIGHT TO
AROUND DAYBREAK FRIDAY. THE NAM AND GFS STAY MORE PROGRESSIVE
MOVING THE TROUGH EAST OF THE AREA BY MIDDAY...WITH ANOTHER SURGE
DROPPING INTO PLACE OVER THE FORECAST AREA ON SAT. THE ECMWF KEEPS
THE MAIN TROUGH MORE COHESIVE...HOLDING IT BACK OVER THE 4-CORNERS
THROUGH MIDNIGHT FRIDAY NIGHT.

BUT EVEN WITH THE DIFFERENCES...MODELS AGREE THAT THIS SYSTEM
WILL BRING THE NEXT ROUND OF SNOW TO THE HIGH COUNTRY...AND A
WHITE CHRISTMAS TO MANY OF THE VALLEYS AS WELL. THE LOWER VALLEYS
WILL SEE A CHANCE OF RAIN OR MIXED PRECIPITATION EARLY IN THE DAY
BEFORE IT CHANGES OVER TO ALL SNOW BY DUSK. SO SNOW MAY HAVE A
HARD TIME ACCUMULATING IN THOSE LOWER VALLEYS DURING THE DAYLIGHT
HOURS. HAVE GONE AHEAD AND ADDED THE WESTERN SAN JUAN MOUNTAINS TO
THE WINTER WEATHER WATCH THAT IS IN EFFECT FROM CHRISTMAS MORNING
THROUGH FRIDAY EVENING. OTHER AREAS MAY NEED HIGHLIGHTS AS
WELL...BUT WILL WAIT UNTIL THE DETAILS ARE A LITTLE BETTER
RESOLVED.

MODELS INDICATE ANOTHER SHORTWAVE WILL DROP IN OUT OF THE
NORTHWEST. HOWEVER THE TIMING IS UNCERTAIN. AS MENTIONED ABOVE THE
GFS BRINGS THIS SECOND SHORTWAVE ACROSS THE AREA ON
SATURDAY...QUICKLY FOLLOWING OUR CHRISTMAS DAY-FRIDAY STORM. THE
ECMWF IS SLOWER...AND BRINGS THE NEXT SHORTWAVE ACROSS THE AREA ON
SUNDAY/SUNDAY NIGHT. A NORTHWEST FLOW FOLLOWS WITH EMBEDDED WEAK
WAVES KEEPING THE AREA ON THE UNSETTLED SIDE THROUGH THE REMAINDER
OF THE PERIOD.

BELOW NORMAL TEMPERATURES WILL DOMINATE...REBOUNDING SLIGHTLY BY
NEXT TUESDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY EVENING)
ISSUED AT 1010 AM MST TUE DEC 23 2014

VFR CONDITIONS TO DOMINATE WITH THE EXCEPTION OF PATCHY FOG FROM
09Z-18Z IN VALLEY BOTTOMS. KEGE HAS THE BEST THOUGH SLIGHT CHANCEOF
MORNING ICE FOG IMPACTING OPERATIONS...BUT ALSO POSSIBLY KVEL KCAG
KHDN KSBS KASE KGUC. HIGH CLOUD CEILINGS LOWER THROUGH WEDNESDAY
BUT SHOWERS BEGIN AFTER THIS TIME FRAME...CLOSER TO CHRISTMAS
MORNING AND MAINLY OVER NE UTAH.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER STORM WATCH FROM THURSDAY MORNING THROUGH FRIDAY EVENING
     FOR COZ003-004-009-010-012-013-018-019.

UT...WINTER STORM WATCH FROM THURSDAY MORNING THROUGH FRIDAY EVENING
     FOR UTZ023.

&&

$$

UPDATE...JOE
SHORT TERM...JAD
LONG TERM...EH
AVIATION...JOE


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