FXUS65 KGJT 051058 AAA
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
358 AM MST SAT DEC 5 2009

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT...

RECORD LOW TEMPERATURE OF 3F SET AT GRAND JUNCTION
AGAIN THIS MORNING. WARM ADVECTION CLOUDS ARE SPREADING IN THIS
MORNING FROM A WEAK VORT MAX IN SW UTAH.

NEW MODELS REMAIN IN GOOD AGREEMENT...WITH THE COLD FRONT PUSHING
INTO NE UTAH LATE THIS AFTERNOON AND THEN ACROSS NW COLORADO IN THE
EVENING. THE BEST DYNAMICAL FORCING FAVORS THE EASTERN UINTA TO
THE ELKHEAD MTNS. THE CRAIG AREA MAY REACH ADVISORY CRITERIA OF 3
INCHES. THE CURRENT GRIDS STRADDLE THIS VALUE BUT WILL LET THE DAY
SHIFT EVALUATE. MOUNTAIN SNOWFALL IS NOW PROGGED TO BE MORE ON THE
ORDER OF 4-8 INCHES...BUT WITH FRONTAL DYNAMICS AND SFC
CONVERGENCE UP TO A FOOT IS POSSIBLE FAVORING THE ELKHEAD
MOUNTAINS.

OROGRAPHIC SNOWS ARE LIKELY ACROSS THE SOUTHERN MTNS. MOIST
ISENTROPIC UPGLIDE ON THE 300K SURFACE (SUB 500MB) OCCURS OVER THE
SOUTHERN MTNS SATURDAY NIGHT. THE JET NOSE IS NEAR THE FOUR
CORNERS PRODUCING SOME DIVERGENCE ALOFT IN THE CENTRAL MTNS. BOTH
NAM AND GFS FORECAST SOUNDINGS FOR CRESTED BUTTE SHOW A SATURATED
UNSTABLE LAYER UP TO 15KFT WITH MTN TOP TEMPERATURES AROUND -15C
THROUGH SUNDAY EVENING. THE WEST ELKS CAN EFFICIENTLY PRODUCE SNOW
IN SW-W FLOW. SO ISSUED A SUNDAY ADVISORY FOR ZONE 12. ZONE 19...
THE SW SAN JUAN MTNS...WILL LIKELY SEE SOME 3-5 INCH ACCUMULATIONS
BUT WILL LOSE BEST OROGRAPHIC SUPPORT AS THE FLOW TURNS TO W ON
SUNDAY.

SUNDAY NIGHT...SNOWFALL IS EXPECTED TO TAPER OFF AS THE UPPER FLOW
SHIFTS BACK TO WARM ADVECTIVE SW. SW-FACING SLOPES MAY NOT SEE
MUCH BREAK IN SNOWFALL. WINDS WILL AGAIN BECOME GUSTY ON NORTH
FACING SLOPES.

&&

.LONG TERM...MONDAY THROUGH FRIDAY...

MODELS REMAINED IN GOOD AGREEMENT WITH THE WINTER STORM POISED TO
BEGIN IMPACTING THE AREA ON MONDAY. EC AND NAM WERE CLOSER WITH
RESPECT TO TIMING WHILE GFS FASTER BY ABOUT 6 HOURS. REGARDLESS...
GIVEN RUN-TO-RUN AND MODEL-TO-MODEL CONSISTENCY...CONFIDENT THAT
SIGNIFICANT WINTER STORM IS ON THE WAY. WATCH WILL BE ISSUED WITH
THIS PACKAGE WITH DETAILS BELOW IN THE WATCH/WARNING/ADVISORY
SECTION.

EVENT BEGINS WITH MOIST AIR OVERRUNNING REMNANTS OF THE COLD FRONT
LEFT BEHIND BY THIS WEEKEND'S STORM. MODELS INDICATED SNOWFALL WILL
BE ENHANCED BY DIVERGENCE ASSOCIATED WITH RIGHT ENTRANCE REGION OF
EXITING JET OVER THE CO/WY BORDER AND THE LEFT EXIT REGION OF THE JET
ROUNDING THE BASE OF THE A DEEPENING CLOSED CIRCULATION OVER THE
WESTERN U.S. OROGRAPHICS ALSO PLAYS A STRONG ROLE MONDAY AFTERNOON
AND MONDAY NIGHT AS 7H WINDS INCREASE TO 35 TO 40KTS OVER THE
SOUTHERN MOUNTAINS. THIS VERY WELL COULD BRING BLIZZARD CONDITIONS
TO THE SAN JUAN MOUNTAINS...THE LA SAL AND ABAJO MOUNTAINS AS WELL
AS THE UNCOMPAHGRE PLATEAU. STRONG SOUTHERLY FLOW ALSO FAVORS HEAVY
SNOW EVENT FOR THE FOOTHILL AREAS OF THE SAN JUANS.

THE SYSTEM OVER THE WEST OPENS AND BEGINS TO SWING INTO THE GREAT
BASIN MONDAY NIGHT. A STRONG SURFACE CYCLONE TRANSLATES INTO CENTRAL
UTAH DURING THIS PERIOD AND SNOWFALL INTENSIFIES OVER THE NORTH
WHILE CONTINUING UNABATED ACROSS THE SOUTH. STRONG DYNAMICAL
FORCING WILL CONTINUE TO GENERATE WIDESPREAD SNOW TUESDAY AS THE
SURFACE CYCLONE SWEEPS ACROSS THE CENTER OF THE CWFA PASSING EAST OF
THE DIVIDE DURING THE AFTERNOON. MODELS SHOWED SNOWFALL DECREASING
TUESDAY NIGHT IN A DRIER NORTHWEST FLOW...THOUGH MODELS MAY BE TOO
FAST WITH SCATTERED SHOWERS LIKELY LINGERING INTO WEDNESDAY.

REINFORCING SHOT OF COLD AIR WITH THIS NEXT SYSTEM WILL KEEP
TEMPERATURES WELL BELOW NORMAL FOR THIS TIME OF YEAR THROUGH THE
EARLY PART OF THE WEEK.

NEXT SYSTEM ALREADY APPROACHING FROM THE WEST WHICH STARTS AS AN
OVERRUNNING WAA EVENT THURSDAY...WITH TROF PASSAGE HOLDING OFF UNTIL
SOMETIME FRIDAY. THIS PROMISES TO BRING ANOTHER ROUND OF SIGNIFICANT
SNOWFALL TO THE REGION.

&&

.AVIATION...

VFR CONDITIONS WILL PERSIST ACROSS THE REGION TODAY AHEAD OF STORM
DROPPING INTO THE AREA FROM THE NORTHWEST. CONDITIONS WILL BEGIN TO
DETERIORATE 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.
SNOW WILL BECOME WIDESPREAD NORTH OF A K4BL-KDRO-KALS LINE LATER
TONIGHT 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 WATCH FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON
       FOR COZ017>019.
     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM MST
       SUNDAY FOR COZ004-010-013.
     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 WATCH FROM MONDAY MORNING THROUGH TUESDAY AFTERNOON
       FOR UTZ028.
     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM MST
       SUNDAY FOR UTZ023.

&&

$$

SHORT TERM...JOE
LONG TERM....NL/MC
AVIATION.....NL