Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 211045
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
345 AM MST FRI NOV 21 2014

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 345 AM MST FRI NOV 21 2014

THE NEXT PACIFIC TROUGH WILL CONTINUE TO DIVE TO THE SOUTHEAST
TODAY...WITH THE LOW CENTER MAKING IT TO THE AZ/MEXICO BORDER BY
EARLY THIS EVENING. MOST OF THE ENERGY/MOISTURE ASSOCIATED WITH THIS
RELATIVELY WEAK SYSTEM WILL REMAIN TO OUR SOUTH. HOWEVER WE CAN
EXPECT AN INCREASE IN CLOUDS...AND POSSIBLY A FEW MOUNTAIN SHOWERS
OVER THE SOUTHERN THIRD OF THE FORECAST AREA. TEMPERATURES WILL
REMAIN NEAR NORMAL AGAIN TODAY...WITH OVERNIGHT LOWS A COUPLE
DEGREES WARMER THAN THIS MORNING/S READINGS.

THEN ON SATURDAY...A MORE INTERESTING PATTERN WILL BEGIN TO UNFOLD
AS A STRONG...MOIST AND UNSETTLED PACIFIC FLOW SPREADS OVER THE
INTERMOUNTAIN REGION. THE FIRST SHORTWAVE TROUGH AND AN ASSOCIATED
COLD FRONT WILL APPROACH OUR NORTHWEST CORNER DURING THE AFTERNOON.
PRECIPITATION WILL BEGIN OVER THE EASTERN UINTA MOUNTAINS DURING THE
MORNING...THEN WILL SPREAD EAST-SOUTHEAST THROUGH THE AFTERNOON. BY
MID-AFTERNOON SNOW IS EXPECTED TO BECOME WIDESPREAD ACROSS THE
CENTRAL AND NORTHERN MOUNTAINS...AND HIGHER NORTHERN VALLEYS. WINDS
WILL INCREASE THROUGH THE DAY IN THE PREFRONTAL ENVIRONMENT AND AS
THE GRADIENT TIGHTENS AHEAD OF THE APPROACHING TROUGH. THE STRONGEST
WINDS WILL BE OVER THE MOUNTAINS AND NORTH. SATURDAY AFTERNOON
REPRESENTS THE ONSET OF A RATHER PROLONGED WET AND UNSETTLED
PERIOD. FOR MORE DETAILS ABOUT THE BRUNT OF THE STORM IN LATER
PERIODS READ THE LONG TERM DISCUSSION BELOW.

HIGH TEMPERATURES ON SATURDAY WILL BE JUST A TAD COOLER DUE TO
THE AFTERNOON SHOWERS AND EXTENSIVE CLOUD COVER.

FOR THIS FORECAST...WE HAVE UPGRADED THE WINTER STORM WATCH TO A
WINTER STORM WARNING FOR THE CENTRAL AND NORTHERN COLORADO
MOUNTAINS...AND HAVE EXTENDED THE TIMING TO LAST THROUGH MONDAY
AFTERNOON. FOR THE MIDDLE YAMPA RIVER BASIN...THE WATCH HAS BEEN
UPGRADED TO AN ADVISORY WHICH WILL END SUNDAY MORNING.

.LONG TERM...(SATURDAY NIGHT THROUGH THURSDAY)
ISSUED AT 345 AM MST FRI NOV 21 2014

EXPECT SNOW INTENSITY WILL INCREASE WITH PASSAGE OF THE COLD FRONT
FROM NORTH TO SOUTH ACROSS THE FORECAST AREA SATURDAY NIGHT. JET
LEVEL DIVERGENCE ASSOCIATED WITH THE 110 KT JET NOSING INTO THE
FOUR CORNERS AREA IN CONJUNCTION WITH THE LOW LEVEL LIFT PROVIDED
BY THE FRONTAL BOUNDARY IS MECHANISM EXPECTED TO ENHANCE SNOW
ACCUMULATIONS. PASSAGE OF THE FRONT WILL BRING SNOW TO LOWEST
VALLEY BOTTOMS BY SUNRISE SUNDAY MORNING. MEANWHILE...STRONG
POST-FRONTAL WINDS WILL CONTINUE TO BUFFET THE REGION RESULTING
IN AREAS OF BLOWING SNOW AND LOW VISIBILITY.

THEREAFTER...MODELS WERE IN PRETTY GOOD AGREEMENT WITH MOIST AND
UNSTABLE NORTHWEST FLOW REGIME PERSISTING THROUGH MONDAY
AFTERNOON. LAPSE RATES WILL STEEPEN DURING THIS PERIOD AS COLDER
MID-LEVEL AIR MOVES OVERHEAD. MEANWHILE...GOOD OROGRAPHIC LIFT
PROVIDED BY STRONG 7H FLOW AND SOME JET LEVEL DIVERGENCE WILL
CONTINUE TO GENERATE WIDESPREAD SNOWFALL...AND BLOWING SNOW...OVER
THE NORTHERN AND CENTRAL MOUNTAINS. BY THE TIME THIS PROTRACTED
EVENT WINDS DOWN MONDAY NIGHT THESE MOUNTAIN AREAS SHOULD HAVE
OVER A FOOT OF SNOW ON AVERAGE WITH HIGHER AMOUNTS ON FAVORED
PEAKS AND RIDGES. WHAT/S LESS CERTAIN ARE SNOW ACCUMULATIONS FOR
THE HIGHER CENTRAL VALLEYS AND THE NORTHWEST SAN JUAN MOUNTAINS
WHERE SNOW PROBABLY LESS PERSISTENT. ADDITIONAL HILITES MAY BE
NEEDED FOR THESE AREAS WHICH ARE MORE LIKELY TO EXPERIENCE
ADVISORY LEVEL SNOWFALL. TEMPERATURES BEHIND THE FRONT WILL BE
CONSIDERABLY COOLER DROPPING TO LEVELS FROM 15 TO 20 DEGREES BELOW
NORMAL. FORTUNATELY...CLOUDS AND DIABATIC HEATING ASSOCIATED WITH
FORMATION OF SNOW WILL MODERATE OVERNIGHT TEMPERATURES TO SOME
DEGREE...THOUGH LOWS WILL STILL BE BELOW NORMAL.

MODELS INDICATED SNOW WILL DECREASE SIGNIFICANTLY MONDAY NIGHT
INTO TUESDAY AS THE SOUTHEASTWARD FLOWING POLAR JET FINALLY PUSHES
EAST OF THE CONTINENTAL DIVIDE AND LAPSE RATES EASE. ADDITIONAL
SNOWFALL POSSIBLE OVER THE NORTHERN MOUNTAINS TUESDAY INTO TUESDAY
NIGHT AS ANOTHER WEAK DISTURBANCE BRUSHES THE AREA. WHERE MODELS
WERE ONCE CARVING OUT ANOTHER TROUGH OVER THE WEST FOR MIDWEEK...
LATEST GFS AND ECMWF NOW FAVOR A FLAT RIDGE OVER THE WEST WITH DRY
AND MILDER CONDITIONS EXPECTED WEDNESDAY AND THURSDAY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 345 AM MST FRI NOV 21 2014

VFR CONDITIONS WILL CONTINUE DESPITE MID AND HIGH CLOUDS MOVING
OVER THE AREA DURING THE NEXT 24 HOURS.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...WINTER STORM WARNING FROM 3 PM SATURDAY TO 6 PM MST MONDAY FOR
     COZ004-005-009-010-012-013.

     WINTER WEATHER ADVISORY FROM 3 PM SATURDAY TO 6 AM MST SUNDAY
     FOR COZ002.

UT...NONE.

&&

$$

SHORT TERM...EH
LONG TERM...NL
AVIATION...NL



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