FXUS65 KGJT 090059
AFDGJT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
559 PM MST TUE DEC 8 2009
.UPDATE...FAVORABLE WINDFLOW BEHIND LAST STORM SYSTEM IS CAUSING
DECENT OROGRAPHIC LIFT OVER GRAND/BATTLEMENT MESAS. CURRENT
REPORTS INDICATE 3 TO 4 INCHES OF NEW SNOW SINCE THIS AFTN WITH
SNOWFALL REACHING RATES OF 1 INCH PER HOUR. IN RESPONSE...ISSUED WINTER WX
ADVISORY THRU 6AM THURSDAY FOR ANOTHER 4 TO 8 INCHES OVER THE
MESAS. PREVIOUS DISCUSSION LOOKS ON TRACK.
&&
.PREV DISCUSSION... /ISSUED 305 PM MST TUE DEC 8 2009/
SHORT TERM...CONVECTIVE BANDS HAVE DEVELOPED OVER ERN UTAH AND
EXTEND INTO THE WESTERN SLOPE. THESE BANDS ACCOUNT FOR MOST OF THE
SNOW SHOWERS THIS AFTERNOON...BUT THE BRUNT OF THE STORM WITH
SIGNIFICANT ACCUMULATIONS HAVE MOVED EAST OF THE DIVIDE. BRISK WINDS
STILL EXIST...MOSTLY ACROSS THE SRN VALLEYS AND OVER THE SRN
CONTINENTAL DIVIDE BUT NOT NEARLY AS EXTENSIVE AS THE OBSERVATIONS
SHOWED THIS MORNING. WITH WIDESPREAD SIGNIFICANT SNOW AND SUBSIDING
WINDS...WILL CANCEL ALL WARNINGS MID AFTERNOON.
THIS DOES NOT MEAN THAT WINTER WEATHER HAS ENDED...THERE ARE TWO
AREAS OF CONCERN. FIRST IS THE NWRN COLORADO MOUNTAINS...IN
PARTICULAR THE ELKHEAD MOUNTAINS AND PARK RANGE AND TO A LESSER
EXTENT THE FLAT TOP MOUNTAINS AND GORE RANGE. SHEAR AXIS WILL STREAM
ACROSS THE COLORADO AND WYOMING BORDER TONIGHT INTO WEDNESDAY
MORNING...FOLLOWED BY THE PASSAGE OF THE POLAR TROUGH EARLY WEDNESDAY
NIGHT. NORTHWEST GRADIENT FLOW WILL BEGIN TO LIFT NORTHWARD ON
THURSDAY WITH OROGRAPHIC SNOWS TAPERING OFF. MOISTURE IS LIMITED IN
THE MODIFIED ARCTIC AIR MASS REGIME...BUT THE HIGH RELATIVE HUMIDITY
IN THE DENDRITIC ICE CRYSTAL GROWTH REGIME COULD LEAVE THE
ELKHEADS/PARK RANGE IN STEADY LIGHT SNOW THAT COULD PRODUCE LOTS OF
FLUFF. THIS COULD EXTEND AS FAR SOUTH AS VAIL PASS AND THE FLAT
TOPS. THEREFORE WILL ISSUE A WINTER WEATHER ADVISORY FOR SNOW AND
BLOWING SNOW THROUGH WEDNESDAY NIGHT FOR THIS REGIME. FOR THE SAN
JUAN/ELK AND SAWATCH MOUNTAINS...BLOWING SNOW IS A CONCERN AS A
STRONG JET WILL BE POSITIONED OVER THE SRN MOUNTAINS THROUGH
WEDNESDAY. THE AIR MASS STABILIZES SO SOME OF THIS JET ENERGY WILL
NOT TRANSLATE TO THE SURFACE...BUT GRADIENT FOR IS GOOD ENOUGH FOR
GUSTY WINDS OVER THE PASSES AND EXPOSED AREAS. WITH THE RECENTLY
HEAVY SNOW...SOME OF THIS WILL BE EASY TO BLOW AROUND AND DRIFT AND
FEEL THAT A WINTER WEATHER ADVISORY FOR BLOWING SNOW IS APPROPRIATE
FOR THE EXPOSED MOUNTAINS AND PASSES. SOME SNOW SHOWERS CAN BE
EXPECTED FOR THE SRN MOUNTAINS...BUT WIDESPREAD SIGNIFICANT SNOW
ACCUMULATIONS ARE NO LONGER EXPECTED DURING THE NEXT 24 HOURS.
FOR THE REMAINDER OF THE FORECAST AREA...TURNING COLDER FOR MUCH OF
THE AREA WITH MOSTLY CLEAR CONDITIONS EXPECTED OVER MOST OF ERN
UTAH AND PARTS OF SOUTHWEST COLORADO. THE VALLEYS OF NW AND WEST
CENTRAL COLORADO COULD SEE A FEW FLURRIES AS ENERGY ALOFT
TRANSLATES ACROSS THE REGION...BUT THE MAIN MESSAGE WILL BE COLD
TEMPERATURE WITH SUB ZERO READINGS AT NIGHT. PATCHY FREEZING FOG
WILL BE POSSIBLE TONIGHT...BUT A BETTER CHANCE OF PATCHY FREEZING FOG
EXISTS THURSDAY MORNING AS MORNING INVERSIONS WILL BE STRONGER.
LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...
UNSETTLED WEATHER IN GENERAL EXPECTED DURING THIS PERIOD. THE FLOW
ALOFT TURNS WESTERLY THU NIGHT AND FRIDAY AS A SERIES OF PACIFIC
DISTURBANCES UNDERCUT A BLOCKING ERN PACIFIC RIDGE AND MOVE INLAND.
TEMPERATURES WILL MODERATE SOME BUT STILL AVERAGE BELOW NORMAL FOR
THE MOST PART. WITH EXTENSIVE SNOW COVER GENERALLY WEST BELOW
MOS TEMP GUIDANCE FOR THE VALLEYS.
TIMING THE DISTURBANCES IS STILL A BIT TRICKY IN THE FAST WESTERLY
FLOW...BUT LOOKS LIKE THE MORE SIGNIFICANT WAVES PASS FRIDAY
NIGHT/SAT...AND THEN ANOTHER SUNDAY/SUN NIGHT. THIS IS A LITTLE
DIFFERENT FROM THE PREV RUNS THAT FOCUSED MORE ON SAT NIGHT. WITH
UNCERTAINTY IN TIMING DID NOT CHANGE MUCH IN THE PRECIP GRIDS
TO AVOID YO-YOING...BUT DID BUMP UP POPS SOME FRI NIGHT AND SUNDAY.
THE FIRST WAVE LOOKS TO FAVOR SE UT AND SW CO AND MAY BE MAINLY A
MTN STORM...WHILE THE SECOND WAVE SUNDAY CARRIES MORE MOISTURE AND
SHOULD AFFECT VALLEYS AND MTNS ALIKE. WINTER HIGHLIGHTS MAY ONCE
AGAIN BE NEEDED AT SOME POINT THIS WEEKEND.
PRECIP CHANCES EXPECTED TO GRADUALLY DECREASE MON AND TUE AS MODELS
IN AGREEMENT ON BUILDING A RIDGE OVER THE WEST BY NEXT WEDNESDAY.
AVIATION...
CONDITIONS WILL CONTINUE TO IMPROVE FROM THE WEST THIS EVENING.
HOWEVER AREAS OF MVFR AND IFR CONDITIONS WILL PERSIST UNTIL LATE THIS
EVENING OVER SOME OF THE WESTERN VALLEYS IN SNOW AND LOW CIGS. IN
ADDITION VALLEYS MAY SEE SOME PATCHY FOG LATE TONIGHT AND EARLY
WEDNESDAY MORNING. OTHERWISE VFR CONDITIONS ARE EXPECTED OVER MOST
VALLEY AREAS BY EARLY WEDNESDAY. SNOW AND BLOWING SNOW WILL CONTINUE
OVER THE HIGHER MOUNTAINS THIS EVENING THROUGH WEDNESDAY...ESPECIALLY
NEAR THE CONTINENTAL DIVIDE...RESULTING CONTINUED MVFR AND IFR
CONDITIONS.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 PM MST WEDNESDAY FOR COZ012-018-
019.
WINTER WEATHER ADVISORY UNTIL 6 AM MST THURSDAY FOR COZ004-009-
010-013.
&&
$$
UPDATE.......TGR
SHORT TERM...PF
LONG TERM....JAD
AVIATION.....ELH
