Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 242352
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
452 PM MST WED DEC 24 2014

.SHORT TERM...(TONIGHT THROUGH THURSDAY NIGHT)
ISSUED AT 359 PM MST WED DEC 24 2014

TRICKY FORECAST COMING UP FOR CHRISTMAS AND FRIDAY WITH GENERAL
GIST REMAINING THE SAME...MORE SNOW. IT`S THE AMOUNTS THAT MAKE
IT DIFFICULT. TO START...UPPER LEVEL SUPPORT IS REALLY WEAK AND
DIFFUSE WITH A 70KT STREAK MOVING OVERHEAD WHICH WILL PRODUCE SOME
LIFT BUT NOTHING LIKE WE SAW WITH THE PREVIOUS STORM. MOISTURE IS
ALSO STREAMING DOWN FROM THE PACNW AND WILL GET WRUNG OUT AS IT
MAKES THE TREK SOUTHWEST INDICATED BY SPECIFIC HUMIDITIES OF 3
G/KG OR SO. BIG PICTURE WISE...AN APPROACHING TROUGH WILL BRING
PRECIP TO THE AREA EARLY CHRISTMAS MORNING BEFORE CLOSING OFF A
LOW OVER CENTRAL UT AND SLOWING DOWN SOMEWHAT. AS THIS
OCCURS...SNOW WILL BE FALLING IN THE MTNS AND SOME RAIN/SNOW IN
THE VALLEYS. THIS WILL BE THE WARM PART OF THE STORM DUE TO SW
FLOW. AT THIS POINT...H7 STREAMLINES THEN SHOW SOME CONVERGENCE
OVER THE GRAND VALLEY SLOWLY SHIFTING TO THE SAN JUANS FOLLOWING
THE AREA OF LOW PRESSURE. FLOW WILL THEN SHIFT AND START COMING
FROM THE NORTH WHICH `SHOULD` ALLOW TEMPS TO DROP BELOW FREEZING
SO SOME ACCUMULATIONS POSSIBLE FOR THE GRAND VALLEY...1 TO 2
INCHES LOOK GOOD FOR NOW...AND SOME HEAVIER SNOW SOUTH.

MODEL SNOW AMOUNTS ALL OVER THE PLACE WITH THE EC SHOWING ONLY 2
TO 4 INCHES FOR ENTIRE FORECAST AREA...WAY UNDERDONE...GFS GOING 5
TO 12 INCHES AND NAM A LITTLE HIGHER THAN THAT. MODEL
UNCERTAINTY...UNFORTUNATELY...REMAINS HIGH WITH ANY CHANGES TO LOW
TRACK...STRENGTH...AND SFC TEMPS CAUSING NOTICEABLE CHANGES TO
FORECAST ESPECIALLY IN THE VALLEYS. ALL THAT BEING SAID...ALL
WATCHES ARE NOW ADVISORIES WITH GENERALLY 8 TO 10 INCHES FOR MTNS
WITH SOME LOCALES SEEING A FOOT OR MORE AND 3 TO 6 FOR THE
VALLEYS. IF YOU ARE TRAVELING THIS HOLIDAY SEASON...EXPECT
HAZARDOUS DRIVING CONDITIONS ESPECIALLY OVER MOUNTAIN PASSES. GIVE
YOURSELF EXTRA TIME TO GET TO YOUR DESTINATION AND MAKE SURE YOU
HAVE A JOYOUS HOLIDAY SEASON!

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 359 PM MST WED DEC 24 2014

THE 12Z MODELS HAVE REACHED CONSENSUS ON THE LOCATION OF THE H7
LOW PRESSURE SYSTEM FOR FRIDAY...WHICH IS PROGGED TO BE OVER THE
FOUR CORNERS EARLY FRIDAY MORNING AND THEN TRACK EAST ACROSS
SOUTHERN COLORADO THROUGHOUT THE DAY. THAT BEING SAID...THE
VORTICITY MAXIMA IS EXPECTED TO REMAIN SOUTH OF THE FORECAST AREA
IN AZ AND NM SO NO AREA OF EASTERN UTAH OR WESTERN COLORADO WILL
BE PARTICULARLY PRONE TO HEAVY SNOW...YET THE POSSIBILITY OF
SCATTERED SNOW SHOWERS WILL EXIST NEARLY EVERYWHERE. THE CHANCE OF
SNOW WILL DECREASE FROM WEST TO EAST THROUGHOUT THE DAY FRIDAY
WITH ONLY A FEW LINGERING SHOWERS IN NORTHWEST FLOW BY SATURDAY
MORNING. SNOW RATIOS ARE EXPECTED TO BE SOMEWHERE BETWEEN 15 TO 1
AND 18 TO 1 WITH GOOD COLD AIR ADVECTION MOVING IN.

THE WEATHER WON/T STAY DRY FOR LONG AS ANOTHER TROUGH WILL SWING
DOWN INTO THE GREAT BASIN FROM THE PAC NW AND REACH NORTHERN
COLORADO BY SUNDAY MORNING. THE GFS AND EC DIVERGE SOMEWHAT WITH
THIS SYSTEM...BUT THERE IS REASONABLE CONFIDENCE THAT THE BULK OF
THE PRECIPITATION ON SUNDAY WILL STAY NORTH OF THE I-70 CORRIDOR.
HOWEVER...ON MONDAY WHEN THE UPPER LEVEL LOW ASSOCIATED WITH THIS
TROUGH SWINGS THROUGH...THE AREA OF PRECIPITATION IS FORECAST TO
SWING SOUTHWARD INTO SE UTAH AND SW COLORADO. WILL HAVE TO FIGURE
OUT DETAILS ON THIS NEXT SYSTEM OVER THE NEXT FEW DAYS...AS SOLNS
AGREE TO AN ACTIVE PATTERN BUT A CHANGE IN THE LOW CENTER/S
POSITIONING WILL MAKE ALL THE DIFFERENCE IN SNOWFALL AMOUNTS. THE
GOOD NEWS IS...AT THIS POINT WE CAN FAIRLY CONFIDENTLY SAY THAT
ALL PRECIPITATION WILL FALL AS SNOW.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 452 PM MST WED DEC 24 2014

CLOUDS WILL BE LOWERING LATE THIS EVENING WITH LIGHT SNOW
DEVELOPING OVER THE MOUNTAINS AFTER MIDNIGHT OBSCURING THE PEAKS
BY SUNRISE. SNOW WILL SPREAD ACROSS EASTERN UTAH AND INTO THE
WESTERN COLORADO VALLEYS BEFORE 18Z RESULTING IN PERIODS OF IFR
CIGS AND VSBY THROUGHOUT THE REMAINDER OF CHRISTMAS DAY. ALL
MOUNTAINS WILL BE OBSCURED IN CLOUD AND SNOW FROM LATE MORNING
THROUGH THE AFTERNOON.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...WINTER WEATHER ADVISORY FROM 3 AM THURSDAY TO 6 PM MST FRIDAY
     FOR COZ001-002.

     WINTER WEATHER ADVISORY FROM 6 AM THURSDAY TO MIDNIGHT MST
     FRIDAY NIGHT FOR COZ003-004-008>010-012-013-017>019.

UT...WINTER WEATHER ADVISORY FROM 3 AM THURSDAY TO 6 PM MST FRIDAY
     FOR UTZ023-025.

&&

$$

SHORT TERM...TGR
LONG TERM...JAM
AVIATION...NL


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