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000
FXUS65 KGJT 302328
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
428 PM MST SAT NOV 30 2013

.SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)
ISSUED AT 427 PM MST SAT NOV 30 2013

INVERSIONS WHICH FORMED IN THE WAKE OF LAST WEEK/S STORM REMAINED
IN PLACE TODAY. AS A RESULT...LOW CLOUDS AND FOG CONTINUED TO
IMPACT VALLEYS BELOW 6500 FEET ASL AND ADJACENT MOUNTAINS TO
BETWEEN 8000 AND 8500 FEET. DAYTIME WARMING ENHANCED BY CLEAR
SKIES ON THE EDGE OF THE STRATUS FIELD WILL CONTINUE TO ERODE THE
STRATUS THROUGH THE AFTERNOON...BUT EXPECT CLOUDS WILL AGAIN
SPREAD UPVALLEY WITH FOG REFORMING IN RESPONSE TO COOLING
TEMPERATURES OVERNIGHT.

SOME QUESTION AS TO WHETHER THE APPROACHING SHORTWAVE TROUGH IN
THE NORTHWESTERLIES WILL ALLOW FOR MIXING OF LOWER LEVELS LATE
TONIGHT. WAA AHEAD OF THIS FEATURE SUGGESTS OTHERWISE AND SURFACE
PRESSURE GRADIENT WEAK AT BEST. CONSEQUENTLY...WILL LEAVE LOW
CLOUDS AND CONTINUE WITH FORECAST FOR FOG. FOR THE NORTHERN
MOUNTAINS...LIFT AND MOISTURE ASSOCIATED WITH THE SHORTWAVE MAY
BEGIN TO GENERATE SOME LIGHT SNOW AFTER MIDNIGHT.

SNOW WILL INCREASE OVER THE ELKHEAD AND PARK RANGES EARLY SUNDAY
AS THE SHORTWAVE SWEEPS OVER THE AREA. THERE WILL BE A BRIEF
PERIOD OF DYNAMIC LIFT WITH THE WAVES PASSAGE SUNDAY MORNING.
THEREAFTER...FROM SUNDAY AFTERNOON THROUGH SUNDAY NIGHT...
OROGRAPHIC LIFT WILL BECOME THE DOMINANT MECHANISM FOR SNOW AS
STRONG WEST TO WEST-NORTHWEST WINDS FROM 20 TO 30 MPH BUFFET THE
AREA. THE 12Z/SAT BUFR SOUNDING FOR KHDN INDICATED THAT A
SATURATED DENDRITIC GROWTH REGION WILL ENHANCE SNOWFALL SUNDAY
MORNING...BUT QUICKLY DRIES AND RISES WITH TROUGH PASSAGE BY
MIDDAY AS TEMPERATURE ADVECTION SHIFTS FROM WEAKLY COLD AIR
ADVECTIVE...TO NEUTRAL SUNDAY AFTERNOON...THEN BECOMES WARM AIR
ADVECTIVE SUNDAY EVENING. THOUGH WAA WILL LIMIT ACCUMULATIONS
BELIEVE ELKHEADS AND SOME OF THE PARK RANGE COULD SEE AMOUNTS
CLOSER TO NAM GUIDANCE OF 3 TO 6 INCHES SUNDAY AND SUNDAY NIGHT...
BUT MAINLY OVER HIGHER EXPOSED PEAKS.

IT/S DOUBTFUL THAT THIS ACTIVITY WILL HAVE MUCH AFFECT ON THE
VALLEY INVERSIONS DISCUSSED PREVIOUSLY AND THEREFORE WILL
CONTINUE TO FORECAST LOW CLOUDS AND FOG FOR THOSE AREAS.
MEANWHILE...THE SOUTHERN MOUNTAINS MAY SEE SOME MID AND HIGH
CLOUDS BUT ARE UNLIKELY TO GET SNOWFALL.

AS FOR TEMPERATURES...SEE NO REASON TO STRAY FROM PERSISTENCE
FORECAST THROUGH THE NEXT THREE PERIODS. THE ONLY EXCEPTION IS
ACROSS THE NORTH WHERE INCREASED LOW AND MID CLOUDS SHOULD BRING
SLIGHTLY WARMER LOWS SUNDAY NIGHT.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 427 PM MST SAT NOV 30 2013

OROGRAPHIC SNOWFALL ALONG THE NORTHERN DIVIDE WILL TAPER OFF ON
MONDAY AS THE FLOW TRANSITIONS FROM NORTHWEST EARLY IN THE DAY TO
WESTERLY BY EVENING. THIS SHIFT IN THE FLOW IS THE RESULT OF THE
NEXT STORM SYSTEM DROPPING INTO THE PACIFIC NORTHWEST THROUGHOUT
THE DAY. AS THIS HAPPENS THE GRADIENT WILL TIGHTEN...MAINLY OVER
THE NORTH. OTHER THAN BREEZES OVER THE HIGHER TERRAIN AND
NORTH...AND A FEW LINGERING SNOW SHOWERS OVER THE NORTHERN
DIVIDE...MONDAY WILL GENERALLY BE A QUIET DAY.

THEN THE BIG CHANGE IN CONDITIONS WILL BEGIN TO TAKE PLACE ON
TUESDAY AS THE NORTHWEST UPPER LOW PRESSURE SYSTEM AND ITS
ASSOCIATED SURFACE COLD FRONT APPROACH FROM THE NORTHWEST. THIS
MUCH ADVERTISED STORM SYSTEM IS STILL ON TRACK TO BRING
SIGNIFICANT WEATHER TO THE FORECAST AREA BEGINNING LATE TUE
THROUGH WED...WITH COLD TEMPERATURES AND THE POTENTIAL FOR
CONTINUED UNSETTLED CONDITIONS THROUGH THE END OF THE LONG TERM
PERIOD.

THE FLOW BECOMES SOUTHWEST MON NIGHT INTO TUE AND STRENGTHENS AS
THE UPPER LOW TRACKS INTO ID. IN ADDITION...THE STRONG SURFACE
COLD FRONT WILL REACH OUR NORTH/NORTHWEST EDGE LATE IN THE
AFTERNOON TO THE EVENING...THEN PROCEED SOUTH/SOUTHEAST OVERNIGHT.
IN THE PRE-FRONTAL ENVIRONMENT SOUTHWEST WINDS WILL BECOME STRONG
ACROSS THE MOUNTAINS EARLY IN THE DAY...THEN WILL MIX INTO THE
VALLEYS BY THE AFTERNOON. THE GFS IS QUITE A BIT FASTER THAN THE
NAM12 AND ECMWF WITH THE TIMING OF THIS FRONT. IT BRINGS THE FRONT
INTO NORTHWEST CO/NORTHEAST UT IN THE MORNING...WHERE IT STALLS
NORTH OF THE TAVAPUTS/FLATTOPS THROUGH THE AFTERNOON/EVENING.
WHILE I MOSTLY DISCOUNTED THE GFS TIMING DUE TO LACK OF AGREEMENT
AND CONTINUITY...IF IT WERE TO VERIFY IT COULD RESULT IN
SIGNIFICANT SNOW OVER THE NORTH THROUGH TUE. GENERALLY FOLLOWING
THE NAM AND ECMWF...POPS GRADUALLY TREND UPWARDS THROUGH TUE OVER
THE NORTH...THEN INCREASE AND SPREAD SOUTH OVERNIGHT. WHILE THE
UPPER LOW CENTER IS PROGGED REMAIN TO OUR NORTH...AT LEAST A
COUPLE OF SHORTWAVES WILL SWING AROUND ITS BASE AND ACROSS OUR
FORECAST AREA. WED PROMISES TO BE THE MOST ACTIVE DAY AS THE FIRST
SHORTWAVE AND AN ASSOCIATED 120KT JET PASS OVERHEAD BRINGING GOOD
DYNAMICS AND UPPER SUPPORT TO A SATURATED AIR MASS. PRECIPITATION
WILL MOSTLY BE SNOW IN THE WAKE OF THE STRONG SURFACE FRONT AND BY
WED EVENING ALL AREAS WILL SEE SNOW IN THE COLD ADVECTION BEHIND
THE SHORTWAVE/COLD FRONT.

ANOTHER SHORTWAVE WILL SWING AROUND THE LOW THU/THU NIGHT BRINGING
EVEN COLDER AIR OVER THE REGION...-32C/500MB AND -20C/700MB. THIS
COLD AIRMASS WILL JUST NOT BE ABLE TO HOLD MUCH MOISTURE...AND
MODELS INDICATE A MARKED DOWNTURN IN POPS. HOWEVER MODELS OFTEN
DRY THINGS OUT TOO FAST. THEREFORE KEPT AT LEAST
CHANCE/MOUNTAINS...SLIGHT CHANCE/VALLEYS THROUGH THE DAY ON THU.
THEN POPS DIMINISH THROUGH FRI AND SAT. HOWEVER COLD CONDITIONS
AND GENERAL TROUGHINESS WILL PERSIST OVER THE REGION THROUGH THE
END OF THE WEEK. SO UNSETTLED CONDITIONS ARE POSSIBLE THROUGH SAT.
FRI AND SAT MORNINGS ARE PROMISING TO BE THE COLDEST SO FAR THIS
SEASON WITH TEMPS AT MANY LOCATIONS DROPPING INTO THE SINGLE
DIGITS OR BELOW ZERO...WITH LOWER TEENS ELSEWHERE.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 427 PM MST SAT NOV 30 2013

THOUGH THERE WAS SOME EROSION OF LOW STRATUS DURING THE
AFTERNOON...THE STAGNANT...INVERTED AIRMASS IS UNLIKELY TO BE
ALTERED BY THE PERSISTENT WEAK WESTERLY FLOW ALOFT. THEREFORE...
STRATUS AND LIGHT FOG WILL CONTINUE THIS EVENING...EXPANDING
EASTWARD OVERNIGHT TO A KDWX-KCAG-KEGE-KMTJ-KAIB-KCEZ LINE BY
SUNRISE SUNDAY MORNING. FALLING TEMPERATURES WILL CAUSE FOG TO
SPREAD AND BECOME MORE DENSE OVERNIGHT AND SUNDAY MORNING. THE
ONLY EXCEPTION TO THIS RULE WILL BE ACROSS THE NORTH...WHERE AN
UPPER LEVEL DISTURBANCE MAY WEAKEN INVERSIONS CAUSING CLOUDS TO
LIFT WHILE FOG DECREASES IN COVERAGE AND INTENSITY. MVFR CIGS WILL
LINGER IN THE LOWER VALLEYS BEFORE EXPANDING EAST WHILE PATCHY FOG
DEVELOPS. FOG WILL SPREAD...BECOMING LOCALLY DENSE LATE TONIGHT
AND INTO SUNDAY MORNING RESULTING IN AREAS OF IFR VSBY AND CIGS.
AREAS EAST OF THE LINE DESCRIBED ABOVE WILL HAVE VFR CONDITIONS
THROUGHOUT THE NEXT 24 HOURS. THE ONLY EXCEPTION BEING THE
NORTHERN COLORADO MOUNTAINS WHERE THE DISTURBANCE MENTIONED
PREVIOUSLY WILL BRING NUMEROUS SNOW SHOWERS RESULTING IN
OBSCURATION OF THE ELKHEAD AND PARK RANGES ON SUNDAY.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...NONE.

UT...NONE.

&&

$$

SHORT TERM...NL
LONG TERM...EH
AVIATION...NL