FXUS65 KGJT 060434
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
934 PM MST SAT DEC 5 2009

.915PM UPDATE...NEW MODEL IS COMING IN AND IT JUST RAISES QUESTIONS.

FIRST THE CURRENT ADVISORIES OUT FOR THE NORTHERN MTNS AND WEST
ELKS: COLD FRONT IS THRU VEL AND IS SHOWING NICE VENTILATION. THIS
FRONT SHIFTS ACROSS THE NORTH TONIGHT AND THE WEST ELKS ARE STILL
IN STORE FOR SOME OROGRAPHIC SNOWFALL. BUT SNOWFALL AMOUNTS LOOK
LESS AT THIS TIME...MORE LIKE 3-6 INCH RANGE.

MONDAY-TUESDAY STORM: THE 00Z NAM IS CONSIDERABLY SLOWER THAN OTHER
SOLUTIONS. WARM ADVECTION SW FLOW ON MONDAY BRINGS RAIN-SNOW LINE
ISSUES. 700 TEMPS CLIMB TO -5C FOR THE SOUTHERN VALLEYS WHICH WOULD
YIELD SNOW LEVELS AROUND 7000 FT +/- 500 FT WHICH LEAVES CORTEZ IN
RAIN BUT DURANGO ON THE CUSP. GIVEN THE CURRENT PROGGED 700 WINDS
OF 45KTS THINK ZONE 9/GRAND MESA WILL GO TO A BLIZZARD WARNING WITH
THE SOUTHERN MTNS. BUT TIMING FOR THE NORTHERN MTNS ZONES 4/10/13 ARE
A CONCERN. IT LOOKS THEY WILL BLOW WITH LITTLE SNOW ON MONDAY...
THEN ACCUMULATE TUE-WED. SO LIKELY WILL LEAVE THEM IN A WATCH
TONIGHT.

ADDING TO THIS COMPLEXITY IS VERY DIFFERENT TIMING SOLUTIONS SEEN
IN THE NAM AND GFS. THE GFS DYNAMICS WILL PRODUCE GOOD SNOWFALL FOR
THE I-70 CORRIDOR INCLUDING GRAND JUNCTION. THE NAM WILL ONLY
PRODUCE SNOW IN AN OVERRUNNING SITUATION. PROBLEM WITH THAT IS WE
ARE ALREADY ERODING THE VALLEY COLD AIR. GRAND JUNCTION HAS CLIMBED
TO 21F AND DURANGO UP TO A BALMY 30. AND THE WARM ADVECTION SW FLOW
ON MONDAY WILL EFFECTIVELY SCOUR OUT OUR COLD AIR.

SO WE WILL BE LOOKING AT THESE ISSUES OVERNIGHT FOR THE MORNING
FORECAST.

.SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT...
NAM AND GFS FINALLY IN PRETTY GOOD AGREEMENT WITH SNOW AMOUNTS...AND
INHERITED PACKAGE LOOKS SOUND...AND WE ARE IN PRETTY GOOD SHAPE FOR
THIS FIRST STORM SYSTEM.

UPPER LOW WILL BE LOCATED NEAR SRN ID THIS EVENING WITH ITS
ASSOCIATED COLD FRONT OVER NE UTAH EXTENDING EASTWARD ALONG THE
CO/WY BORDER. AFOREMENTIONED LOW DROPS SWRD INTO NW UTAH BY SUNDAY
MORNING. GOOD FORCING SEEN WITH THIS SYSTEM OVER THE NRN MTNS AND
HAVE DECIDED TO ADD UPPER AND CNTRL YAMPA BASIN (CRAIG/STEAMBOAT
AREAS) TO ADVISORY.

UPPER LOW APPEARS TO KIND OF WASHOUT SUNDAY AS IT ABSORBED BY
DUMB-BELLING UPSTREAM LOW OFF NRN CA COAST. THIS ALSO BACKS THE FLOW
TO WEST WITH PCPN CONTINUING OVER THE MTNS...BUT BECOMES MORE
LIMITED OVER THE SRN MTNS WHERE OROGRAPHIC POTENTIAL WANES. IN THE
MEANTIME FRONT ALONG THE ROAN/TAVAPUTS PLATEAU STARTS TO RETREAT
NWRD AS WAA AND SOUTHWESTERLY FLOW BECOMES REESTABLISHED. MOUNTAIN
SNOWFALL IS PROGGED TO BE ON THE ORDER OF 4-8 INCHES...BUT WITH
FRONTAL DYNAMICS AND SFC CONVERGENCE UP TO A FOOT IS POSSIBLE
FAVORING THE ELKHEAD MOUNTAINS. THE CRAIG AREA MAY SEE ACCUMULATIONS
OF 3-5 INCHES.

SNOW WILL DECREASE IN INTENSITY AND RATES OF ACCUMULATION WILL
DROP SUNDAY NIGHT PRECEDING THE NEXT STORM SYSTEM AS STABILITY
INCREASES IN WAA PATTERN AND Q-G FORCING SUBSIDES. HOWEVER
SCATTERED SNOW SHOWERS WILL CONTINUE OVER THE MTNS IN DIFFLUENT
PATTERN...ESPECIALLY WEST AND SOUTHWEST FACING SLOPES.

.LONG TERM...MONDAY THROUGH SATURDAY...

NEXT SIGNIFICANT STORM ON TRACK FOR THE MON-TUE TIME FRAME. HOWEVER
THE 12Z MODEL RUNS NOW INDICATE ANOTHER SHOT COMING THROUGH ON WED.
THIS IMPULSE WOULD MAINLY IMPACT THE NORTHERN ZONES AND EXTEND SNOW
THROUGH TUE NIGHT AND INTO WED. HAVE UPPED POPS FOR THOSE PERIODS...
BUT SO FAR HAVE NOT GONE TOO HEAVY AS I EXPECT THESE DETAILS TO
CONTINUE TO EVOLVE. ALSO OTHER TIMING DIFFERENCES SHOWED UP LATER IN
THE WEEK. SO CONTINUED THE BROAD-BRUSHED...CHANCE/SLIGHT CHANCE POPS
FOR THE LATER PERIODS DUE TO THE UNCERTAINTY.

NOW FOR THE MAIN STORY...AN OVER-RUNNING SITUATION DEVELOPS ON
MONDAY AS A MOIST SOUTHWEST FLOW STRENGTHENS OVER THE AREA ON TOP
OF THE COLD AIR THAT HAS BEEN REINFORCED BY THIS WEEKEND'S STORM.
THE SOUTHERN MOUNTAINS ARE INITIALLY FAVORED WITH 700 MB WINDS
INCREASING TO 50+ KTS OVER THE 4-CORNERS. THIS SOUTHWEST FLOW
DEVELOPS AHEAD OF THE NEXT TROUGH THAT IS PROGGED TO DEEPEN OVER THE
WESTERN CONUS. THE UPPER JET DIGS INTO THE DESERT SOUTHWEST ON
MONDAY...THEN TRANSLATES OVER THE 4-CORNERS ON TUESDAY. THEREFORE
VERY STRONG WINDS WITH HEAVY SNOW WILL TAKE AIM OVER THE SOUTHERN
MOUNTAINS.

A FRONTAL BOUNDARY DROPS INTO THE NORTH ON TUESDAY...THEN STALLS
NORTH OF THE TAVAPUTS/FLATTOPS RANGES AS THE FRONT'S EASTERN PORTION
DROPS SOUTHWARD ALONG THE EAST SIDE OF THE DIVIDE. THIS BRINGS
WESTERLY WINDS TO THE AREA WITH SNOWFALL PICKING UP OVER THE NORTH
AND CENTRAL PORTIONS. EXPECT WIDESPREAD SNOW OVER THE ENTIRE AREA...
WITH VALLEYS POSSIBLY RECEIVING SIGNIFICANT SNOW AS WELL.

THEREFORE HAVE UPGRADED THE BLIZZARD WATCH TO A BLIZZARD WARNING WITH
THIS PACKAGE. BUT OTHERWISE HAVE LEFT THE WINTER STORM WATCHES AS
THEY STAND TO AVOID UNNECESSARY CONFUSION. ALSO EXPECT THE
TIMING/DURATION UNCERTAINTIES TO BECOME CLEARER WITH FUTURE RUNS...SO
WILL WAIT A DAY FOR THE DETAILS TO WORK THEMSELVES OUT BEFORE
ADDING HILITES FOR OTHER VALLEY AREAS.

&&

.AVIATION...

VFR CONDITIONS WILL PERSIST ACROSS THE REGION INTO THIS EVENING.
THEN CONDITIONS WILL BEGIN TO DETERIORATE LATE THIS EVENING AS A COLD
FRONT SPILLS OVER NORTHEAST UTAH AND NORTHWEST COLORADO. SCATTERED
SNOW SHOWERS WILL DEVELOP ALONG THE LEADING EDGE OF THE FRONT
CREATING POCKETS OF MVFR CIGS AND VSBY ESPECIALLY NORTH OF GJT-ASE
LINE. SNOW WILL BECOME WIDESPREAD NORTH OF A K4BL-KDRO-KALS LINE
AFTER MIDNIGHT AS THE STORM INTENSIFIES RESULTING IN LARGE SWATHS OF
MVFR CONDITIONS WITH AREAS OF IFR/LIFR CIGS AND VSBY.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...WINTER STORM WATCH FROM MONDAY MORNING THROUGH TUESDAY
       AFTERNOON FOR COZ003-004-009-010-012-013-021>023.
     BLIZZARD WARNING FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON
       FOR COZ017>019.
     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM MST
       SUNDAY FOR COZ002-004-005-010-013.
     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO MIDNIGHT MST
       SUNDAY NIGHT FOR COZ012.
UT...WINTER STORM WATCH FROM MONDAY MORNING THROUGH TUESDAY
       AFTERNOON FOR UTZ025.
     BLIZZARD WARNING FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON
       FOR UTZ028.
     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM MST
       SUNDAY FOR UTZ023.

&&

$$

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