Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 280226
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
726 PM MST SAT DEC 27 2014

.UPDATE...
ISSUED AT 723 PM MST SAT DEC 27 2014

TEMPERATURES ACROSS THE FORECAST AREA CONTINUE TO DROP QUICKLY
TONIGHT WITH SEVERAL LOCATIONS ALREADY APPROACHING FORECAST LOWS
FOR THE OVERNIGHT PERIOD. CLOUD COVER IS INCREASING WHICH WILL
HELP SLOW THE COOL DOWN...ALTHOUGH INITIAL WAVE OF CLOUDS
THINNING WITH SEVERAL BREAKS OBSERVED ON SATELLITE. AS A
RESULT...HAVE LOWERED MIN TEMPS BY 2 TO 5 DEGREES ACROSS MOST OF
THE FORECAST AREA...WHICH TAKES SOME OF THE LOWER SNOW COVERED
VALLEYS INTO THE SINGLE DIGITS. REMAINDER OF THE FORECAST REMAINS
ON TRACK.

&&

.SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)
ISSUED AT 334 PM MST SAT DEC 27 2014

FINALLY A QUIET WEATHER DAY ACROSS EASTERN UTAH AND WESTERN
COLORADO...BUT THINGS WON/T BE QUIET FOR LONG. HIGH CLOUDS WILL
BEGIN TO INCREASE THIS EVENING FROM NORTH TO SOUTH AS THE NEXT
WEATHER SYSTEM HEADS TOWARD THE REGION. EXPECTING PROTECTED VALLEY
TOWNS IN THE GUNNISON BASIN AND SAN JUANS TO REACH THE TEENS
BELOW ZERO TONIGHT UNTIL ENOUGH CLOUD COVER REACHES THEM TO BREAK
THE TEMPERATURE INVERSIONS WHICH SET UP. A 100KT ULJ IS
ASSOCIATED WITH THESE INCOMING CLOUDS AND IS EXPECTED TO CREATE
GOOD UPPER LEVEL DIVERGENCE IN THE DENDRITIC GROWTH REGION WITH H7
TEMPS BETWEEN -18C AND -10C OVER THE NEXT COUPLE OF DAYS. THE
TROUGH ASSOCIATED WITH THE INCOMING ULJ IS QUITE BROAD BUT WILL
SET UP ENERGY AND SUFFICIENT MOISTURE (THOUGH SMALL AMTS COMPARED
TO THE LAST COUPLE OF STORMS) TO BRING LIGHT BUT STEADY SNOWFALL
ACROSS NORTHERN COLORADO BY SUNDAY MORNING. HOW FAR SOUTH THE JET
DROPS TO WILL DETERMINE THE AREA MOST SIGNIFICANTLY IMPACTED. WITH
SUCH COOL AIR ACROSS THE NORTHERN PART OF THE FORECAST
AREA AND HIGH SWE RATIOS EXPECTED...DECIDED TO GO AHEAD AND
UPGRADE WATCHES. KEPT EASTERN UINTAS IN AN ADVISORY WITH
EXPECTATIONS OF MODERATE SNOW IN THE MOUNTAINS BEGINNING TO REALLY
ACCUMULATE MONDAY EVENING INTO TUESDAY AS WINDS TURN NORTHEASTERLY.
UPGRADED ZONE 4 AND 13 TO WARNINGS CONSIDERING THESE AREAS WILL BE
WORKING WITH EFFICIENT SNOW PRODUCTION AND OROGRAPHICS ON THEIR
SIDE. SEE LONG TERM SECTION FOR MORE DETAILS ON THIS SYSTEM.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 334 PM MST SAT DEC 27 2014

A COLD DISTURBANCE WILL CONTINUE TO MOVE INTO THE NORTH AS A
TROUGH DROPS OUT OF THE NORTH INTO THE GREAT BASIN. THIS TROUGH
WILL EVENTUALLY CUT OFF A LOW OVER THE DESERT SOUTHWEST TUE-WED.
BUT IN THE MEAN TIME...THE WEST-EAST ORIENTED UPPER JET WILL
STRETCH ACROSS THE CENTER OF OUR FORECAST AREA ON MONDAY. NORTH OF
THE JET VERY COLD AIR WILL DROP INTO THE NORTHERN ZONES...WITH
-34C/500MB AND -16C/700MB AT 00Z TUE. THESE TEMPERATURES WILL
RESULT IN EFFICIENT SNOW PRODUCTION AS THE LOWER LEVELS OF THE AIR
MASS REMAIN SATURATED THROUGH THE FAVORED DENDRITIC GROWTH
REGION. IN ADDITION...SOUTHWEST FLOW AT 700MB AHEAD OF THE
SOUTHERN BRANCH LOW WILL REACH INTO THE SOUTHERN PORTION OF THE
FORECAST AREA...AND WILL RESULT IN A CONVERGENT ZONE UNDER THE
JET. MODELS SHOW THE HEAVIEST SNOW UNDER THIS BAND. THERE
CONTINUES TO BE SOME DIFFERENCES IN JUST WHERE THE BAND WILL SET
UP...BUT IT LOOKS LIKE IT MAY DROP INTO THE I-70 CORRIDOR DURING
THE AFTERNOON. THEREFORE I UPPED POPS OVER THE SOUTHER PORTION OF
THE FORECAST AREA ON MON...AND PROLONGED THEM IN THE CENTRAL
MOUNTAINS MON NIGHT. ON THE FLIP SIDE...AN EASTERLY FLOW WILL
DEVELOP NORTH OF THIS BAND OVER THE NORTHERN ZONES LATE
MON...WHICH CAN BE QUITE COUNTER-PRODUCTIVE FOR SNOW FOR NORTHWEST
CO.

THE AREA WILL REMAIN UNDER A DEFORMATION ZONE OF SORTS BETWEEN THE
SOUTHERN BRANCH LOW AND THE MORE PROGRESSIVE NORTHERN BRANCH TUE
AND WED. THIS WILL KEEP A CHANCE OF MOUNTAIN SNOW THROUGH
WEDNESDAY. THE LOW THEN WILL BEGIN TO IMPACT THE AREA WED NIGHT-
THU AS IT MOVES EAST. WHILE MODELS SHOW EXCELLENT AGREEMENT IN THE
TIMING...THE TRACK IS A LITTLE MORE PROBLEMATIC. THE MORE
NORTHERLY ECMWF SUGGESTS A BETTER HIT FOR OUR AREA...WITH THE GFS
TAKING MOST OF THE ACTION ACROSS NEW MEXICO.

LATE IN THE WEEK...MODELS KEEP THE STORM TRACK TO OUR NORTH AS
ENERGY ROTATES AROUND A BROAD HUDSON BAY LOW.

TEMPERATURES WILL GENERALLY BE BELOW NORMAL. AT TIMES SNOW COVERED
VALLEYS WILL BE STRONGLY INVERTED...WARMING ONLY WHEN
DISTURBANCES AFFECT THE AREA.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 443 PM MST SAT DEC 27 2014

VFR CONDITIONS EXPECTED TO CONTINUE OVERNIGHT AND THROUGH MUCH OF
THE DAY ON SUNDAY. THE EXCEPTION WILL BE NEAR KVEL WHERE AREAS OF
LOW CLOUDS AND FOG MAY DIP CIGS INTO MVFR CONDITIONS BETWEEN 06Z
AND 16Z. MID LEVEL CLOUDS DECKS WILL BE DROPPING THROUGHOUT THE
DAY ON SUNDAY AS ANOTHER STORM SYSTEM MOVES IN FROM THE WEST.
EXPECT SCATTERED SHOWERS TO DEVELOP ACROSS THE NORTHERN VALLEYS
AND MOUNTAINS BY 18Z SUNDAY...SPREADING INTO THE CENTRAL VALLEYS
AND MOUNTAINS BY 00Z MONDAY.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY AFTERNOON
     FOR COZ009-010-012.

     WINTER STORM WARNING FROM 6 AM SUNDAY TO 6 PM MST MONDAY FOR
     COZ004-013.

UT...WINTER WEATHER ADVISORY FROM 6 PM SUNDAY TO 6 PM MST MONDAY FOR
     UTZ023.

&&

$$

UPDATE...JDC
SHORT TERM...JAM
LONG TERM...EH
AVIATION...JDC



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