FXUS65 KGJT 161145
AFDGJT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
445 AM MST MON FEB 16 2009
.SHORT TERM...TODAY THROUGH TUESDAY NIGHT...
A CHALLENGING FORECAST AHEAD AS THE VORTEX JUST OFF THE NRN CA COAST
FINALLY OPENS UP AND SHEARS INLAND IN PIECES.
A WEAK WAVE LIFTS NE ACROSS UT AND NW CO TODAY IN SSW FLOW AND
WARM ADVECTION. SURFACE AIR STILL RATHER DRY...SO EXPECT MOSTLY JUST
CLOUDS WITH A CHANCE OF LIGHT SHOWERS OVER THE HIGHER TERRAIN AS THE
ATMOSPHERE MOISTENS FROM THE TOP DOWN. FLOW ALOFT WILL BE
STRENGTHENING FOR BREEZY CONDITIONS OVER THE HIGHER TERRAIN THIS
AFTERNOON.
A STRONGER WAVE EJECTS ACROSS THE GREAT BASIN TONIGHT AS THE WEST
COAST LOW OPENS UP. THIS FIRST WAVE CROSSES ERN UT/WRN CO LATE
TONIGHT AND TUE MORNING...ACCOMPANIED BY A WEAKENING COLD FRONT.
MOIST SW OROGRAPHIC FLOW AND UPWARD FORCING ASSOCIATED WITH THE
APPROACHING SHORTWAVE AND LEFT EXIT REGION OF THE JET WILL ALLOW
WIDESPREAD MTN SNOW TO DEVELOP TONIGHT INTO TUE MORNING...WITH SOME
RAIN/SNOW IN THE VALLEYS. FIRST FAVORED WILL BE THE MOUNTAINS OF ERN
UT EARLY TONIGHT...WITH THE SAN JUANS AND SOUTHERN FLANKS OF THE
CENTRAL CO MTNS GETTING GOING AFTER MIDNIGHT. SSW WINDS OF 20-40 KTS
AT 700 MB /10K FT/ WILL CREATE AREAS OF BLOWING SNOW OVER THE HIGHER
ELEVATIONS. DEEP POTENTIAL INSTABILITY THEN FOLLOWS TUE AFTERNOON.
WILL LIKELY SEE THE PRECIP CHANGE TO MORE CONVECTIVE SHOWER ACTIVITY
TUE AFTERNOON UNDER AN E-W ELONGATED COLD POOL ALOFT...AND HAVE ADDED
A SLIGHT CHANCE OF THUNDERSTORMS TO ROUGHLY THE NRN TWO-THIRDS OF
THE AREA TUE AFTN WHERE THE LIFTED INDEX IS NEAR ZERO AND SOME CAPE
EXISTS. FLOW ALOFT BECOMES WESTERLY TUE AFTERNOON/NIGHT.
HIGHLIGHTS AND CONCERNS...WILL UPGRADE THE SOUTHWESTERN SAN JUAN MTNS
TO A WINTER STORM WARNING BASED ON THE STRONG SW OROGRAPHIC FORCING
AND JET DYNAMICS ALOFT...BUT DELAY THE START UNTIL MIDNIGHT TONIGHT.
WILL KEEP THE NORTHWEST SAN JUANS AND CENTRAL AND NRN CO MTNS AS A
WINTER STORM WATCH AS I AM ON THE FENCE WITH ADVISORY VS. WARNING
SNOW AMTS FOR ALL BUT THE NORTHERNMOST MTNS HERE. COLD ADVECTION
TAPERS OFF RATHER SUBSTANTIALLY BEHIND THE WEAKENING FRONT EARLY
TUE AS THE SYSTEM COMES THROUGH IN PIECES AND FORCING TAPERS OFF.
CONVECTIVE INPUT COULD OFFSET THIS SOMEWHAT BUT ALSO RESULT IN A
WIDER THAN NORMAL SPREAD IN SNOW AMTS. ALSO CONCERNED THAT DURATION
MAY BE LONGER THAN ORIGINALLY THOUGHT. THEREFORE...DECIDED TO GIVE
THE DAY SHIFT ONE MORE LOOK.  FINALLY...ADDED THE EASTERN UINTA
MTNS AS A WINTER WEATHER ADVISORY BEGINNING THIS EVENING AND GOING
UNTIL MIDNIGHT TUE NIGHT. NICE E-W BARRIER SHOULD BENEFIT FROM THE
STRONG SW OROGRAPHIC FLOW...BUT ONCE THE FLOW BECOMES WESTERLY AND
MORE DOWNSLOPE OFF THE HIGHER PEAKS TO THEIR WEST LATE TUE...PRECIP
SHOULD DECREASE. DAY SHIFT CAN ALSO LOOK AT THE LA SAL/ABAJO/
UNCOMPAHGRE/TAVAPUTS FOR THE NEED OF ANY HIGHLIGHTS. THANKS FOR THE
COORDINATION PUB/BOU/SLC.
.LONG TERM...WEDNESDAY THROUGH SUNDAY...
AIR MASS REMAINS UNSETTLED WITH A NWLY COMPONENT THAT FAVORS
OROGRAPHIC SNOW FROM THE NRN MOUNTAINS TO THE NWRN SAN JUANS.  THE
ELKHEAD MOUNTAIN AND PARK RANGE WILL RECEIVE THE BEST SNOW WHICH MAY
PERSIST INTO WEDNESDAY EVENING.  BY WEDNESDAY NIGHT...THE NW FLOW
BECOMES ANTICYCLONIC AND SNOW SHOWERS WILL WANE...ALTHOUGH A FEW
FLURRIES MAY LINGER ALONG THE NRN DIVIDE.  ANOTHER FAST MOVING BUT
WEAK DISTURBANCE SKIRTS THE NRN DIVIDE ON THURSDAY AND LOW POPS ARE
REASONABLE.  FOR THE REMAINDER OF THE FORECAST AREA...EXPECT DRIER
WEATHER AND MORE SUNSHINE FROM RISING HEIGHTS AS A RIDGE BUILDS OVER
THE GREAT BASIN.
INTO THE WEEKEND...SLOW BUT STEADY WARMING TREND FRIDAY AND SATURDAY
AS THE GREAT BASIN RIDGE SHIFTS TOWARD WRN COLORADO.  BY
SUNDAY...CLOUDS WILL BE INCREASING FROM THE WEST AS THE RIDGE WILL
MOVES EAST AND OUT OF OUR FORECAST AREA.  ANOTHER STRONG ERN
PACIFIC VORTEX FORMS SOMEWHERE ALONG THE PACIFIC COAST FROM
WASHINGTON STATE TO NRN CALIFORNIA...AND SENDING MID/HIGH CLOUDS IN
OUR DIRECTION.
&&
.AVIATION...
VFR CONDITIONS TODAY AND CONTINUES THIS EVENING THROUGH 06Z.  AFTER
06Z...CIGS OVER THE MOUNTAINS WILL LOWER WITH SNOW INCREASING OVER
THE PASSES.  IN NORTHEAST UTAH...CIGS WILL LOWER WITH A CHANCE OF
SNOW AFTER 08Z AS A FRONT APPROACHES FROM THE WEST.  SNOW...MIXED
WITH RAIN AT TIMES BELOW 5000 FEET...WILL BE WIDESPREAD AFTER 12Z
CAUSING AREAS OF MVFR AND IFR.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
.CO...WINTER STORM WARNING FOR THE SOUTHWEST SAN JUAN MOUNTAINS
        FROM MIDNIGHT TONIGHT UNTIL 6 AM WED...ZONE 19
      WINTER STORM WATCH FROM MIDNIGHT TONIGHT THROUGH TUESDAY NIGHT
        FOR THE NORTHWEST SAN JUAN MOUNTAINS...ZONES 18.
      WINTER STORM WATCH FROM MIDNIGHT TONIGHT THROUGH WED MORNING
        FOR THE CENTRAL AND NORTHERN MOUNTAINS...ZONES 4/9/10/12/13.
.UT...WINTER WEATHER ADVISORY FOR THE EASTERN UINTA MOUNTAINS FROM
        6 PM TODAY UNTIL MIDNIGHT TUE NIGHT...ZONE 23.
$$
SHORT TERM.....JAD
LONG TERM......AS
AVIATION.......TL