FXUS65 KGJT 050503 AAA
AFDGJT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1000 PM MST FRI DEC 4 2009

.9PM UPDATE...REGIONAL SOUNDINGS CAPTURE THE STRONG WARMING THAT HAS
OCCURRED ALOFT. THE GRAND JUNCTION SOUNDING SHOWS ABOUT 12C/22F OF
WARMING AT MTN TOP LEVEL. WARM ADVECTION CONTINUES TONIGHT INTO
SATURDAY MORNING AS THE UPPER FLOW TURNS TO SW. THE VALLEYS WILL
REMAIN TRAPPED IN THE INVERSIONS BUT THE WARM AIR ALOFT AND SOME
INVADING CLOUDS WILL KEEP OUR OVERNIGHT LOWS NOT QUITE AS COLD AS
LAST NIGHT. SOME MTN TEMPERATURES ARE WARMER THEN THE VALLEYS SUCH
AS 9PM READINGS AT GJT OF 15F WHILE AT MESA LAKES AT 10KFT IT IS
18F. GRAND JUNCTION'S RECORD LOW TONIGHT IS 7F. THOUGH WE HAVE BEEN
TO 10F ALREADY THIS EVENING...IT MAY BE DIFFICULT TO BREAK THE
RECORD.

NEW MODELS REMAIN IN GOOD AGREEMENT...WITH THE COLD FRONT PUSHING
INTO NE UTAH SATURDAY LATE AFTERNOON AND THEN ACROSS NW COLORADO
IN THE EVENING. SO THE BEST DYNAMICAL FORCING FAVORS THE EASTERN
UINTA TO THE ELKHEAD MTNS.

THERE IS SOME QUESTION ABOUT OROGRAPHIC SNOW ACCUMULATION IN THE
SOUTHERN MTNS. MOIST ISENTROPIC UPGLIDE ON THE 300K SURFACE (SUB
500MB) OCCURS OVER THE SOUTHERN MTNS SATURDAY NIGHT. THE JET NOSE IS
OVER THE SAN JUAN MTNS PRODUCING SOME DIVERGENCE ALOFT THERE IN THE
CENTRAL MTNS.  THE NAM INDICATES UP TO 6 INCH ACCUMULATIONS IN THE
WEST ELK MTNS/CRESTED BUTTE THROUGH SUNDAY EVENING WHERE SW-W FLOW
EFFICIENTLY PRODUCES SNOW. FORECAST SOUNDINGS FOR CRESTED BUTTE SHOW
A SATURATED UNSTABLE LAYER LAYER UP TO 15KFT WITH MTN TOP TEMPS
AROUND -15C. SO WILL ISSUE A SUNDAY ADVISORY FOR ZONE 12. ZONE 19...
THE SW SAN JUAN MTNS...WILL LIKELY SEE SOME 3-5 INCH ACCUMULATIONS
BUT WILL LOSE OROGRAPHIC SUPPORT AS THE FLOW TURNS TO W ON SUNDAY.

BEYOND THIS FIRST STORM...THE MODELS CONTINUE TO PRODUCE UP TO 3
FEET OF TOTAL SNOW IN THE MTNS BY TUESDAY...WITH THE NEW GFS
PRODUCING UP TO 5 FEET IN THE SAN JUAN MTNS BY NEXT WEEKEND. NO
MATTER THE DETAILS...IT WILL BE A STORMY WEEK.

&&

.SHORT TERM...TONIGHT THROUGH SUNDAY...
TEMPERATURES REMAIN COLD TODAY WITH THE JUST A FEW DEGREES OF
MODIFICATION OVER YESTERDAY'S HIGHS...MAINLY OVER THE NORTH.  SO
ANOTHER COLD NIGHT WILL BE IN-STORE TONIGHT. HOWEVER LOW TEMPS
TONIGHT ARE NOT EXPECTED TO DROP QUITE AS LOW AS LAST NIGHT'S.
SATELLITE IMAGES SHOW A FEW MORE CLOUDS UPSTREAM AS LOW PRESSURE
DEVELOPS OVER THE NORTHERN ROCKIES. EVEN THOUGH THE CLOUDS ARE
GENERALLY EXPECTED TO BE HIGH AND THIN...AND NOT TOO PLENTIFUL...
THEY WILL SUPPRESS RADIATIONAL COOLING A LITTLE. TEMPS WILL AGAIN
WARM A LITTLE ON SATURDAY...BUT WILL REMAIN WELL BELOW NORMAL.

FOR THE SYNOPTIC SCALE: A LARGE AND CONVOLUTED AREA OF LOW PRESSURE
WILL REMAIN POSITIONED OVER MOST OF CANADA THROUGH MIDWEEK.
ENERGY ROTATING AROUND THE BACKSIDE OF THIS LOW WILL BRING THE NEXT
WEATHER TO THE FORECAST AREA THROUGH EARLY NEXT WEEK.

FOR THE SHORT TERM PERIOD...THE NEXT FEATURE OF INTEREST IS THE ABOVE
MENTIONED LOW PRESSURE SYSTEM DEVELOPING OVER THE NORTHERN ROCKIES.
THIS SYSTEM WILL BECOME ELONGATED ACROSS THE PACIFIC NORTHWEST...WITH
THE FIRST IMPULSE EJECTING INTO THE NORTHERN GREAT BASIN AND ACROSS
THE FORECAST AREA SATURDAY NIGHT THROUGH SUNDAY. THIS SHORTWAVE WILL
FAVOR THE NORTHERN MOUNTAINS AND BRING ADVISORY AMOUNTS TO THE
MOUNTAINS OF NORTHEAST UTAH AND NORTHWEST COLORADO. AN ASSOCIATED
SURFACE FRONT WILL MOVE INTO NORTHEAST UTAH LATE SAT AFTERNOON...
AND THEN WEAKEN AND STALL ACROSS NORTHWEST COLORADO SAT EVENING.
FORECAST SOUNDINGS INDICATE A SATURATED AIR MASS BY 06Z SUN OVER
THOSE AREAS. THE COLD TEMPERATURE REGIME WILL MAXIMIZE DENDRITIC
GROWTH FOR HIGHLY EFFICIENT SNOW PRODUCTION...THAT WILL CONTINUE
THROUGH SUNDAY AS MOISTURE STAYS IN PLACE. ALSO ON SUNDAY THE UPPER
WEST TO EAST ORIENTED JET WILL STRETCH ACROSS THE NORTHERN HALF OF
THE FORECAST AREA. SO BY SUNDAY AFTERNOON 6-12 INCHES OF CHAMPAGNE
POWDER ARE EXPECTED TO BLANKET THE SLOPES IN THE ADVISORY AREAS.
LOCAL AMOUNTS WILL BE POSSIBLE. OTHER MOUNTAINS WILL ALSO SEE SOME
ACCUMULATIONS...BUT THEY SHOULD REMAIN BELOW ADVISORY CRITERIA. COLD
CONDITIONS WILL CONTINUE.

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...
FIRST SHRT WAVE WILL BE EXITING THE REGION SUNDAY NIGHT WHILE THE
NEXT SYSTEM...A STRONGER CLOSED LOW GATHERS STRENGTH AND DROPS SWRD
ALONG THE NRN CA COAST. AS WE LIE BETWEEN STORMS EXPECT ONLY
SCATTERED MTN SHOWERS...EXCEPT ACROSS THE PARK/GORE AND FLATTOPS
WHERE A MORE CONTINUOUS BUT LIGHT SNOWFALL WILL OCCUR. PCPN WILL
INCREASE AGAIN BY EARLY MONDAY FROM THE WEST AS THIS LOW TRACKS
EASTWARD TO AROUND LAKE TAHOE BY MON EVENING. IT APPEARS ALL THE
NECESSARY INGREDIENTS WILL BE PRESENT FOR SUBSTANTIAL AND WIDESPREAD
SNOWFALL OVER THE CWA. OROGRAPHIC FORCING COMBINED WITH JET LEVEL
DYNAMICS...OMEGA...FRONTOGENETICS AND FAVORABLE MICROPHYSICS SHOULD
ALL COMBINE TO BE AN EFFICIENT SNOW PRODUCER DESPITE ONLY MODEST
SPECIFIC HUMIDITY. SURFACE LOW ALSO FOLLOWS A FAVORABLE TRAJECTORY
TRACKING NEAR LAS VEGAS BY MONDAY EVENING.

CLOSED LOW BECOMES AN OPEN WAVE TUESDAY AS IT DROPS SWRD TO NEAR
THE 4 CORNERS...MEANWHILE SFC LOW JUMPS TO THE EAST SLOPE. PCPN WILL
CONTINUE WITH THE EMPHASIS SHIFTING MORE TO THE NORTH AS TROF
PASSAGE OCCURS AND THE FLOW ALOFT VEERS TO THE NW. SNOW DIMINISHES BY
WEDNESDAY EVEN OVER THE NRN MTNS IN DRY COLD NWLY FLOW...BUT NEXT
SYSTEM ALREADY APPROACHING FROM THE WEST WHICH STARTS AS AN
OVERRUNNING WAA EVENT...WITH TROF PASSAGE HOLDING OFF UNTIL AROUND
FRIDAY. THIS PROMISES TO BRING ANOTHER ROUND OF SIGNIFICANT SNOW.

&&

.AVIATION...

VFR CONDITIONS WILL PERSIST TONIGHT AND THROUGH SATURDAY. CLOUDS
WILL BEGIN TO INCREASE SATURDAY AFTERNOON AHEAD OF THE NEXT
WINTER-LIKE SYSTEM WHICH WILL MOVE OVER THE NORTH SATURDAY EVENING.
CIGS AND VSBYS WILL BEGIN TO LOWER OVER THE NORTH EARLY IN THE
EVENING WITH AREAS OF MVFR AND POSSIBLY IFR CONDITIONS DEVELOPING
OVER THE EASTERN UINTA...AND NORTHWEST COLORADO MOUNTAINS.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...SNOW ADVISORY SATURDAY EVENING THROUGH SUNDAY FOR ZONES
      4/10/13.
     SNOW ADVISORY SATURDAY MIDNIGHT THROUGH SUNDAY MIDNIGHT
      FOR ZONE 12.
UT...SNOW ADVISORY SATURDAY EVENING THROUGH SUNDAY FOR ZONE 23.

&&

$$

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