Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 230519
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1019 PM MST MON DEC 22 2014

.UPDATE...
ISSUED AT 1015 PM MST MON DEC 22 2014

THE JET STREAM IS ORIENTED NW-SE ALONG THE ROCKIES THIS EVENING.
WITH THE PUSH OF THE WEST COAST RIDGE THE NORTHERN PORTION OF THE
JET SHIFTS EAST AND OUR LOCAL WINDS BECOME NE OVERNIGHT. BEFORE
THE RIDGE TAKES CONTROL...THE LAST DISTURBANCE DROPS DOWN THE UT-
CO BORDER TONIGHT. THE -32C COLD CORE ROLLS DOWN THE CONTINENTAL
DIVIDE WITH LITTLE COLD ADVECTION IN EASTERN UTAH. THE RESULTING
W-E PRESSURE GRADIENT ACTUALLY INCREASES THE 700MB WINDS THROUGH
THE NIGHT TO NE 35-40KTS. THIS HAS TWO EFFECTS. IT WILL KEEP
OVERNIGHT LOW TEMPS FROM BOTTOMING OUT... AND SNOW SHOWERS WILL
CONTINUE OVER NORTH-FACING SLOPES INTO TUESDAY. THE NAM AND RAP
PRODUCE ANOTHER 1-4 INCHES ON NORTH SLOPES THROUGH TUESDAY BUT
THE UNCOMPAHGRE GORGE MAY SEE ANOTHER 6 INCHES IN IDEAL COLD
ADVECTION NORTH FLOW. WE MAY NEED TO EXTEND THE NW SAN JUAN MTN
WARNING UNTIL SUNRISE.

OTHERWISE THE WESTERN RIDGE BUILDS INTO THE NORTHERN ROCKIES FOR
COLD OVERNIGHT LOWS TUESDAY NIGHT. AS THE RIDGE BUILDS OVERHEAD ON
WEDNESDAY THE FLOW ALOFT BACKS FROM NORTH TO WEST. MOISTURE AND
CLOUDS INCREASE FROM THE WEST ON WEDNESDAY.

UPDATE ISSUED AT 808 PM MST MON DEC 22 2014

WINDS HAVE DROPPED OVER SOUTHWEST COLORADO FOLLOWING SUNSET THIS
EVENING. GUSTY NORTHWEST WINDS PERSIST...HOWEVER DO NOT EXPECT
THEM TO EXCEED 45 MPH. THEREFORE...ALLOWED THE WIND ADVISORY TO
EXPIRE.

UPDATE ISSUED AT 608 PM MST MON DEC 22 2014

SNOW HAD LARGELY DIMINISHED OVER THE UPPER COLORADO RIVER BASIN
AND ACROSS THE GRAND MESA EARLY THIS EVENING. EXPECT THERE WILL BE
ADDITIONAL SNOW SHOWERS...THOUGH MORE SCATTERED IN NATURE.
THEREFORE...ALLOWED WINTER STORM WARNINGS EXPIRE FOR THOSE AREAS.
ELSEWHERE IN THE MOUNTAINS...SNOW AND WIND WERE MORE PERSISTENT
SO WILL CONTINUE WSW/S AND BLIZZARD WARNINGS THROUGH MIDNIGHT.
STRONG WINDS CONTINUED ACROSS SOUTHWEST COLORADO SO WILL KEEP
ADVISORIES GOING THERE AS WELL.

&&

.SHORT TERM...(TONIGHT THROUGH TUESDAY NIGHT)
ISSUED AT 341 PM MST MON DEC 22 2014

SATELLITE WATER VAPOR LOOP SHOWING DARKENING OVER ERN UT/WRN CO
INDICATIVE OF THE UPPER JET CORE MOVING OVERHEAD. PRECIPITATION
HAS TAKEN ON A MORE BANDED APPEARANCE ON GJX RADAR UNDERNEATH THE
JET. THE COLDER AIR IN WY HAS NOT REALLY MADE INROADS INTO WRN CO
AT THE SURFACE BUT MODELS SHOWED IT OCCURRING ALOFT. PRECIPITATION
HAS ALSO BECOME MORE SHOWERY FROM THE RESULTANT CONVECTIVE
INSTABILITY. COMBINED WITH STRONG VERTICAL WIND SHEAR BECAUSE OF
THE UPPER JET...A FEW SHORT-LIVED THUNDERSTORMS HAVE ALSO
OCCURRED. A BRIEF PERIOD OF HAIL WAS OBSERVED AT THE GJT WEATHER
OFFICE FROM ONE OF THE STRONGER CELLS.

NORTHWEST FLOW WAS IN THE PROCESS OF BECOMING NORTH LATE THIS
AFTERNOON AND WILL CONTINUE THAT TREND THIS EVENING AS THE JET
SETS UP OVER THE AREA. BANDED NATURE OF THE PRECIP WILL RESULT IN
MORE VARIABLE SNOW AMOUNTS LATE TODAY WITH SOME AREAS IN
PERSISTENT SNOW AND OTHERS PERHAPS SEEING LITTLE OR NONE.
CANCELED THE WINTER STORM WARNING FOR THE STEAMBOAT SPGS VALLEY
WITH THIS SHIFT IN WINDS...THOUGH SNOW SHOWERS STILL THIS
AFTERNOON WILL BRING SOME LOCAL ACCUMULATIONS. TEMPTED TO DO THE
SAME WITH THE GUNNISON ZONE 14 EXCEPT THAT A CDOT WEBCAM STILL
SHOWED SNOW AND POOR ROAD CONDITIONS OVER CERRO SUMMIT.
OTHERWISE...KEPT THE MOUNTAIN WINTER HIGHLIGHTS AND THE CORTEZ-
PAGOSA WIND ADVISORY INTACT FOR THE TIME BEING. DRIER AIR WAS
ADVECTING IN ONE THE NORTHERLY FLOW...SO THINK THE TREND OF
DECREASING SNOW OVERNIGHT IS STILL GOOD.

THE 12Z MODELS SHOW A 120KT TO 130KT UPPER JET STILL OVER WRN CO
TUE MORNING FOR STILL SOME WIND OVER THE HIGHER PEAKS AND
SCATTERED SNOW MAINLY ON THE NORTH FACING SLOPES OF THE WRN CO
MTNS. THE JET GRADUALLY WEAKENS AS IT SLIDES EAST OF OUR FORECAST
AREA BY TUESDAY EVENING WITH SKIES CLEARING FROM THE WEST. ERN UT
SHOULD HAVE MOSTLY SUNNY SKIES ALL DAY ON TUE. THE CLEARING SKIES
WILL BRING COLDER TEMPERATURES FOR TUE NIGHT.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 341 PM MST MON DEC 22 2014

THE RIDGE AXIS WILL PASS OVERHEAD ON WEDNESDAY FOR A QUIET
WEATHER DAY. THE NEXT LOW PRESSURE TROUGH WILL THEN DROP INTO THE
GREAT BASIN CHRISTMAS EVE AND THEN MOVE OVER THE AREA ON CHRISTMAS
DAY. MODELS ARE IN PRETTY GOOD AGREEMENT IN THE HANDLING OF THIS
STORM...WITH THE ECMWF CONSISTENTLY A LITTLE STRONGER. WHILE THIS
SYSTEM COMES OUT OF THE NORTHWEST...IT SHOULD BE COLDER THAN OUR
PRESENT STORM. HOWEVER IT STILL LOOKS LIKE SNOW LEVELS WILL BE A
CONCERN FOR RAIN OR A RAIN/SNOW MIX IN THE LOWER VALLEYS. SO FOR
NOW A WHITE CHRISTMAS FOR THESE VALLEYS REMAINS IFFY. HOWEVER IT
IS LIKELY THE MOUNTAINS AND HIGHER CENTRAL AND NORTHERN VALLEYS
WILL SEE FRESH ACCUMULATIONS WITH A CHANCE OF SNOW FOR THE MIDDLE
VALLEYS. THE SNOW LEVELS WILL CONTINUE TO BE CHALLENGING.

MODEL SOLUTIONS FOR LATE THIS WEEK THEN QUICKLY DIVERGE AS THE EC
SHOWS A COLD SECONDARY SHOT DROPPING IN AND REINFORCING THE LONGER
WAVE TROUGH OVER OUR FORECAST AREA ON FRIDAY. IF THIS
VERIFIES...THIS COLDER AIR AND THE LINGERING MOISTURE COULD RESULT
IN A BETTER CHANCE OF VALLEY SNOWFALL THU NIGHT INTO FRI. THE GFS
ON THE OTHER HAND SHOWS THE MAIN TROUGH SHIFTING EAST AND
ACTIVITY QUICKLY WINDING DOWN BY LATE THU NIGHT AND FRI. FOR NOW
HAVE KEPT THE BEST POPS ON CHRISTMAS AFTERNOON/EVENING...WITH A
DOWNWARD TREND THROUGH FRI. HOWEVER THE FORECAST WILL HAVE TO BE
WATCHED TO SEE HOW THIS PLAYS OUT.

THE PATTERN REMAINS UNSETTLED INTO EARLY NEXT WEEK. MODELS INDICATE
ANOTHER STORM SYSTEM WILL MOVE OVER THE REGION DURING THE WEEKEND.
HOWEVER TIMING/STRENGTH IS STILL UNCERTAIN DUE TO DIFFERENCES IN
MODEL SOLUTIONS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1015 PM MST MON DEC 22 2014

WIND SHEAR WILL CONTINUE NEAR MTN TOP LEVEL INTO TUESDAY.
CLOUDS AND SHOWERS WILL CONTINUE FAVORING OVER NORTH FACING
SLOPES PRODUCING MOUNTAIN OBSCURATIONS. AIRPORTS WILL SEE VFR
CONDITIONS WITH OCNL CIGS BLO 030 VSBY BLOW 2SM IN SHSN THROUGH
00Z. THEN VFR CONDITIONS WILL DOMINATE.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER STORM WARNING UNTIL MIDNIGHT MST TONIGHT FOR COZ004-010-
     012>014-018.

     BLIZZARD WARNING UNTIL MIDNIGHT MST TONIGHT FOR COZ003-017>019.

UT...BLIZZARD WARNING UNTIL MIDNIGHT MST TONIGHT FOR UTZ023.

&&

$$

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


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