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000
FXUS65 KGJT 292226
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
326 PM MST FRI NOV 29 2013

.SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)
ISSUED AT 325 PM MST FRI NOV 29 2013

THE BIGGEST CHALLENGE IN THE SHORT TERM WILL BE PREDICTING WHEN
AND WHERE THE FOG RETURNS TONIGHT.

THE CLOSED LOW JUST OFF OF THE COAST OF SOUTHERN CA IS IN THE
PROCESS OF WEAKENING IN PLACE. A BROAD AND WEAK DEFORMATION ZONE
CONTINUES TO HANG OVERHEAD OF THE REGION SIGNIFYING FRONTOLYSIS
ASSOCIATED WTH THE WEAKENING LOW. CONDITIONS ARE NOT EXPECTED TO
CHANGE MUCH IN THE NEAR TERM UNTIL SATURDAY EVENING WHEN A WEAK
TROUGH SWINGS DOWN INTO NW CO. CLOUDS AND A NORTHWESTERLY WIND WILL
BEGIN TO INCREASE SAT NIGHT...PARTICULARLY OVER NW CO.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 325 PM MST FRI NOV 29 2013

THE GRADIENT TIGHTENS ON SUN AS THE SOUTHERN CUT OFF LOW RETREATS
SOUTHWESTWARD TO A POSITION WELL WEST OF THE BAJA PENINSULA...AND
A SHORTWAVE IN THE NORTH-WESTERLIES DROPS INTO THE CENTRAL PLAINS.
OUR AREA WILL SEE SOME COLD ADVECTION AT 700 MB THROUGH SUN UNDER
A STRENGTHENING NORTHWEST FLOW...MAINLY OVER THE NORTHERN EDGE.
THEREFORE THE FIRST FORECAST QUESTION THAT ARISES...IS WHETHER
THIS WILL BE ENOUGH COOLING ABOVE THE SURFACE LAYER TO DISRUPT THE
STRONG INVERSIONS...AND THUS INHIBIT THE VALLEY FOG THAT HAS
PLAGUED MUCH OF THE LOWER ELEVATIONS THIS PAST WEEK. WILL GO AHEAD
AND KEEP MENTION OF SOME PATCHY FOG IN THE FAR SOUTHWEST/WEST
VALLEYS ON SUN...BUT REDUCE COVERAGE ESPECIALLY ACROSS THE WESTERN
CO VALLEYS.

AS THE ABOVE MENTIONED NORTHWEST FLOW GETS ESTABLISHED...
OROGRAPHIC SNOW WILL DEVELOP ON SUN OVER THE NORTHERN MOUNTAINS...
ESPECIALLY THE PARK AND ELKHEAD RANGES...AND LESS SO THE FLATTOPS
AND GORE MTNS...AND TO THE ASPEN AREA. THIS SNOW WILL CONTINUE
THROUGH MON. BY LATE MON THE GRADIENT WILL RELAX A LITTLE AS A
SHORTWAVE RIDGE PASS OVERHEAD FOR A DECREASE IN SNOW. ALL TOLD A
FEW INCHES AT BEST MAY ACCUMULATE ACROSS THE FAVORED NORTHWEST
SLOPES. THIS IS ALL AHEAD OF A MORE UNSETTLED PERIOD THAT BEGINS
TO SET UP LATE TUE AND WILL POSSIBLY LAST THROUGH THE END OF THE
WORK WEEK.

THE MIDRANGE MODELS SHOW A STRONG AND COLD LOW PRESSURE SYSTEM
DROPPING INTO THE PACIFIC NORTHWEST ON MON. THERE IS STILL SOME
UNCERTAINTY IN THE TRACK AND TIMING AS THIS INITIAL LOW MOVES
EAST. MODELS DO KEEP ITS TRACK TO OUR NORTH. BUT THEY ALSO SHOW AN
ASSOCIATED COLD FRONT IN THE LOWER LEVELS...AND AN UPPER LEVEL JET
CORE MOVING OVER THE NORTHWEST CORNER OF THE FORECAST AREA AS
EARLY AS TUE AFTERNOON. THE FRONT THEN PROCEEDS TO THE
SOUTH/SOUTHEAST OVERNIGHT AND ON WED FOR MUCH COLDER TEMPERATURES
AT THE SURFACE. THE ONLY EXCEPTION MAY BE THOSE VALLEYS THAT HAVE
BEEN LOCKED UNDER STRONG INVERSIONS...THEY MAY ACTUALLY SEE
AFTERNOON HIGHS RISE A FEW DEGREES COMPARED TO TUE. PRECIPITATION
WILL BEGIN TO SPREAD IN FROM THE NORTH AS THE FRONT APPROACHES
LATE TUE...THEN INCREASE TUE NIGHT AS THE FRONT PASSES AND THE
UPPER JET SPREADS ACROSS THE FORECAST AREA. PRECIPITATION WILL
BECOME LIKELY BY WED...ESPECIALLY MOUNTAINS. ONLY A FEW OF THE
LOWEST VALLEYS WILL SEE RAIN OR MIXED PHASE ON WED BEHIND THE
FRONT.

THEN OVER THE NEXT COUPLE OF DAYS...ADDITIONAL REINFORCING
SHORTWAVES WILL CARVE OUT A LONG WAVE TROUGH OVER THE WESTERN
CONUS. THERE CONTINUES TO BE DISCREPANCIES IN HOW THIS LARGE SCALE
AND COMPLICATED PATTERN WILL UNFOLD...BUT IT DOES LOOK LIKE THE
REGION WILL SEE SIGNIFICANT SNOWFALL THROUGH THE END OF THE WEEK.
THE COLD NATURE OF THIS STORM SYSTEM...TEMPS BELOW -30C/500 MB
AND -12C/700 BY FRI...WILL BRING SNOW INTO THE LOWEST VALLEYS.
AND...AT TIMES STRONG SOUTHWEST WINDS MAY RESULT IN BLOWING AND
DRIFTING SNOW.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 325 PM MST FRI NOV 29 2013

LOW CEILING DECK CONTINUES TO HANG IN THE VALLEYS...PARTICULARLY
IN EASTERN UTAH. EXPECTING CEILING TO LOWER AGAIN TONIGHT AFTER
SUNSET SINCE THE SYNOPTIC WEATHER CONDITIONS WILL NOT BE CHANGING OVER
THE NEXT 24 HRS. LIFR CONDITIONS ARE POSSIBLE NEAR DAYBREAK AT
VALLEY AIRPORTS BUT EXPECTING MOST TO STAY AT MVFR THROUGH 19Z OR
SO. VFR EXPECTED OUTSIDE OF THE VALLEY STRATUS.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...NONE.

UT...NONE.

&&

$$

SHORT TERM...JAM
LONG TERM...EH
AVIATION...JAM