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000
FXUS65 KGJT 061156
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
456 AM MST FRI DEC 6 2013

.SHORT TERM...(TODAY THROUGH SATURDAY)
ISSUED AT 456 AM MST FRI DEC 6 2013

SOME PATCHY FOG AGAIN DEVELOPED LATE LAST NIGHT IN LOCALIZED
VALLEY AREAS. WHILE IT DOES NOT SEEM TO BE VERY EXTENSIVE...DENSE
FOG WAS AGAIN SEEN IN SPOTS ALONG THE I-70 CORRIDOR. THEREFORE
WILL KEEP THE PRESENT DENSE FOG ADVISORY IN EFFECT UNTIL MID
MORNING.

ONE WEAK WAVE WILL MOVE EAST BY THIS AFTERNOON...AS THE NEXT MORE
SIGNIFICANT TROUGH TAKES SHAPE OVER THE PACIFIC NORTHWEST. TODAY
WILL REMAIN COLD...WITH GENERALLY QUIET WEATHER AHEAD OF THIS NEXT
DISTURBANCE. SOME LOW TO MID LEVEL CLOUDS HAVE DEVELOPED OVER THE
AREA DUE TO LINGERING MOISTURE IN PLACE AND SOME ADDITIONAL
MOISTURE MOVING IN ON THE WESTERLY FLOW. THIS IS MOST PLENTIFUL
OVER THE NORTH. I CANNOT RULE OUT SOME LIGHT SNOWFALL OVER HIGHER
NORTHERN MOUNTAINS. ANOTHER COLD NIGHT FOLLOWS WITH SOME
MODIFICATION AS CLOUDS BEGIN TO SPREAD IN AS THE NEXT TROUGH
APPROACHES.

THE BASE OF THIS TROUGH WILL MOVE FROM WASHINGTON TO OREGON FRI
NIGHT THEN INTO ID/NV BY SAT AFTERNOON. A SOUTHWEST FLOW WILL
DEVELOP OVER OUR FORECAST AREA BY EARLY SAT MORNING AND WILL BRING
A MODEST AMOUNT OF MOISTURE. THROUGH SAT THE SITUATION WILL BE
DOMINATED BY WARM ADVECTION...ISENTROPIC UPGLIDE AND OROGRAPHICS.
EXPECT THAT SNOW WILL DEVELOP AS THE WARM AND RELATIVELY MOIST AIR
OVERRUNS THE VERY COLD LAYER NEAR THE SURFACE. THE GFS AND ECMWF
BOTH SHOW GOOD ISENTROPIC UPGLIDE CENTERED OVER WEST CENTRAL CO
EARLY SAT. THEREFORE UPPED POPS IN THE GRAND VALLEY THROUGH THE
MORNING. ALSO MOISTURE DEEPENS QUICKEST OVER THE NORTH...SO EXPECT
SNOW TO RAMP UP THERE THROUGH THE MORNING. THE SOUTH LAGS BEHIND A
LITTLE...BUT THAT IS THE AREA WHERE THE OROGRAPHICS ARE BEST. THE
UPPER JET REMAINS TO OUR SOUTH...AND NOSES INTO WEST-
CENTRAL/SOUTHWEST NM BY LATE AFTERNOON. THEREFORE OUR SOUTHERN
EDGE WILL SEE THE STRONGEST WINDS...AND SOME UPPER DIVERGENCE DUE
TO THE PROXIMITY TO THE LEFT EXIT REGION OF THE JET. EXPECT
TEMPERATURES TO WARM ON SAT AS THE AIR MASS BECOMES MORE
UNSETTLED. HOWEVER TEMPERATURES REMAIN A LITTLE TRICKY AS SOME
VALLEYS MAY NOT MIX OUT UNTIL LATER IN THE STORM/S CYCLE...WAITING
FOR THE COLD FRONT TO PASS. MORE DETAILS FOLLOW IN THE LONG TERM
DISCUSSION AS THIS STORM IS EXPECTED TO CONTINUE THROUGH THE
WEEKEND.

.LONG TERM...(SATURDAY NIGHT THROUGH THURSDAY)
ISSUED AT 456 AM MST FRI DEC 6 2013

GFS AND ECMWF WERE IN GOOD AGREEMENT WITH THE LATTER PHASES OF THE
STORM DISCUSSED PREVIOUSLY IN THE SHORT TERM SECTION WHILE THE
NAM WAS AGAIN THE OUTLIER. BOTH MODELS SHOWED THE COLD FRONT
ASSOCIATED WITH THE STORM MOVING EASTWARD ACROSS THE REGION
SATURDAY NIGHT AS THE MID-LEVEL TROUGH AXIS MOVES TO THE GREEN
RIVER BY 12Z SUNDAY. BEST UPWARD FORCING INDICATED DURING THIS
PHASE OF THE STORM WITH LOW LEVEL CONVERGENCE ALONG THE FRONT...
DECENT NEGATIVE DIVERGENCE OF Q AT MID-LEVELS...AND DIVERGENCE
ASSOCIATED WITH THE 135 KNOT JET MOVING THROUGH THE BASE OF THE
TROUGH. IN ADDITION...LAPSE RATES FAIRLY STEEP AND DENDRITIC
GROWTH REGION SATURATED WHICH WOULD SEEMINGLY FAVOR HEAVY SNOW
AMOUNTS. HOWEVER...MOISTURE SEEMED TO REMAIN THE LIMITING FACTOR
AND THEREFORE MODELS ONLY GENERATE MODERATE ACCUMULATIONS DURING
THIS PERIOD.

THE SHORTWAVE TROUGH PUSHES ACROSS THE FORECAST AREA SUNDAY
THOUGH THE LONGWAVE TROUGH WILL LINGER OVER THE AREA. REMNANT
MOISTURE AND OROGRAPHIC LIFT PROVIDED BY WESTERLY FLOW IN THE WAKE
OF THIS WEEKEND/S STORM WILL KEEP SOME LIGHT SNOW GOING OVER THE
DIVIDE MOUNTAINS SUNDAY AFTERNOON. A WEAKER SHORTWAVE DROPS OUT OF
THE NORTH ON TH BACKSIDE OF THE LONGWAVE TROUGH WHICH WAS SLOWLY
PULLING AWAY FROM THE AREA SUNDAY NIGHT. MOISTURE EXTREMELY
LIMITED BY THIS TIME SO ADDITIONAL ACCUMULATIONS WILL BE LIGHT.

RAW SNOW OUTPUT AND INPUT FROM HPC-WWD CONTINUED TO SHOW ADVISORY
LEVEL SNOW FOR MUCH OF THE FORECAST AREA THIS WEEKEND. HOWEVER...
CONSIDERATION MUST BE GIVEN SNOW RATIOS WHICH COULD BE ELEVATED IN
THE COLD AIR WHICH COULD BRING HIGHER SNOW ACCUMULATIONS. GIVEN
WATCH GOES FROM THIRD PERIOD AND BEYOND AND SNOW AMOUNTS SOMEWHAT
QUESTIONABLE...WILL LEAVE THE WATCH GOING FOR THE TIME BEING.

THOUGH DIFFERENCES BETWEEN THE GFS AND ECMWF APPEAR TOWARD THE
MIDDLE OF THE COMING WEEK...BOTH INDICATED DRY CONDITIONS WILL
PREVAIL THROUGH THURSDAY.

IRONICALLY...THE COLD FRONTAL PASSAGE SATURDAY NIGHT SHOULD
DISRUPT VALLEY INVERSIONS AND LOWS WILL ACTUALLY BE LESS COLD.
HOWEVER...REINFORCING SHOT OF COLD AIR WILL SUSTAIN TEMPERATURES
MUCH BELOW NORMAL INTO THE COMING WEEK.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 456 AM MST FRI DEC 6 2013

SCT-BKN LOW-MID CLOUDS WILL PERSIST OVER THE AREA THROUGH THE NEXT
24 HOURS. PATCHY VALLEY FOG WILL LINGER IN A FEW SPOTS ALONG THE
COLORADO RIVER THIS MORNING...WITH FOG RETURNING ALONG THE
COLORADO...AND OTHER VALLEYS AGAIN AFTER MIDNIGHT. THIS MAY IMPACT
AREA TAF SITES INCLUDING KCNY...KDRO...KGJT...KRIL...KVEL...AND
KEGE. OTHER VALLEY AIRPORTS ACROSS EASTERN UTAH AND WESTERN
COLORADO MAY ALSO BE IMPACTED. VFR CONDITIONS ARE EXPECTED AT ALL
LOCATIONS FROM 18Z FRIDAY TO 02Z SATURDAY.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...WINTER STORM WATCH FROM SATURDAY AFTERNOON THROUGH LATE SUNDAY
     NIGHT FOR COZ006>012-014-017>023.

     WINTER STORM WATCH FROM SATURDAY MORNING THROUGH LATE SUNDAY
     NIGHT FOR COZ001>005-013.

     DENSE FOG ADVISORY UNTIL 9 AM MST THIS MORNING FOR COZ006>008.

UT...WINTER STORM WATCH FROM SATURDAY MORNING THROUGH SUNDAY MORNING
     FOR UTZ023>025.

     WINTER STORM WATCH FROM SATURDAY AFTERNOON THROUGH LATE SATURDAY
     NIGHT FOR UTZ022-027>029.

&&

$$

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