FXUS65 KGJT 252131
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
231 PM MST FRI DEC 25 2009

.SHORT TERM...TONIGHT THROUGH SUNDAY

AFTERNOON SATELLITE IMAGERY SHOWED A DEEP UPPER LEVEL LOW CENTERED
OVER EASTERN KANSAS WITH A LONG NARROW RIDGE POSITIONED ALONG THE
WEST COAST...RESULTING IN A STRONG NORTHERLY FLOW OVER THE FORECAST
AREA. MID TO HIGH LEVEL CLOUDS WERE WRAPPING AROUND THE STORM SYSTEM
TOWARD NORTHERN COLORADO WHILE A SHORTWAVE DISTURBANCE HEADED
SOUTHWARD ACROSS WESTERN WYOMING. THE COMBINATION OF THE NORTHERLY
WINDS...MOISTURE IN THE LOW AND MID LEVELS OF THE ATMOSPHERE...AND
OROGRAPHIC FORCING WAS RESULTING IN WIDESPREAD SNOWS OVER THE
NORTHERN AND CENTRAL MOUNTAINS OF COLORADO.

TONIGHT AND SATURDAY...THE UPPER LEVEL LOW OVER THE CENTRAL U.S. WILL
SLOWLY TRACK EASTWARD KEEPING THE FORECAST AREA IN A NORTHERLY
FLOW. BUFKIT TEMPERATURE PROFILES FOR THE CENTRAL AND NORTHERN
MOUNTAINS CONTINUE TO SHOW AIR TEMPS IN THE FAVORABLE SNOW GROWTH
REGION TROUGH SATURDAY MORNING RESULTING IN CONTINUED SNOW AND
BLOWING SNOW IN THESE AREAS.  THE REST OF THE FORECAST AREA
SHOULD BE MAINLY DRY...BUT ABUNDANT MOISTURE WILL RESULT IN
CLOUDINESS WITH SOUTHWESTERN COLORADO AND SOUTHEASTERN UTAH SEEING
THE MOST SUN.

ON SATURDAY NIGHT AND SUNDAY...A DEFORMATION ZONE BETWEEN THE EXITING
PLAINS STORM AND A STORM SYSTEM ENTERING THE PACIFIC NORTHWEST WILL
SLOWLY BUILD TOWARDS THE AREA. DURING THIS TIME THE NORTHERLY FLOW
WILL WEAKEN AND PRECIPITATION WILL TAPER OFF OVER THE NORTHERN AND
CENTRAL MOUNTAINS LEAVING A MIXTURE OF CLOUDS AND SUN OVER MUCH OF
THE REGION ON SUNDAY.

TEMPERATURES WILL CONTINUE TO BE BELOW NORMAL THROUGH THE SHORT TERM.
THE AMOUNT AND DURATION OF CLOUD COVERAGE WILL HAVE A LARGE IMPACT...
ESPECIALLY ON NIGHT TIME TEMPS...SO TRIED TO ADJUST TEMPS
ACCORDINGLY.

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...

MODEL DIFFERENCES MUDDLING THE MIDRANGE FORECAST FOR THE COMING WEEK.
EARLY IN THE WEEK...DISCREPANCIES BETWEEN THE EC AND GFS/NAM WERE OF
LITTLE CONSEQUENCE AS NONE DEPICTED ANYTHING BUT THE LIGHTEST QPF IN
A BROAD DEFORMATION REGION OVER THE FORECAST AREA. BY TUESDAY HOWEVER
...GFS FAVORED MORE ENERGY AND MOISTURE ACROSS THE NORTHERN PART OF
THE CWFA IN WEST-NORTHWEST FLOW. IN CONTRAST...EC HAD BEGUN TO CLOSE
OFF AN UPPER-LEVEL LOW OVER THE WESTERN GREAT BASIN WHILE CHANNELING
MORE ENERGY INTO THE SOUTHERN STREAM. AS A RESULT...EC FAVORED
SHOWERS OVER THE SOUTHERN HALF OF THE CWFA WHILE GFS FAVORED THE
NORTH. GIVEN MODEL DISCREPANCIES...CONTINUED TO STRADDLE THESE
SOLUTIONS WITH LOW CHANCES...MAINLY OVER THE MOUNTAINS ACROSS THE
ENTIRE CWFA THROUGH TUESDAY.

MODEL DIFFERENCES CONTINUED THROUGH WEDNESDAY AND WEDNESDAY NIGHT
WITH GFS FAVORING A MOIST AND ACTIVE NORTHWEST FLOW WHILE EC MAINLY
DRY. GIVEN DIFFERENCES MADE FEW CHANGES TO THE GOING FORECAST AT
MIDWEEK.

BY THE LATTER PART OF THE WEEK...MODELS FOUND SOME MEASURE OF
AGREEMENT...DEPICTING A PERIOD OF MAINLY OROGRAPHIC SNOW FOR THE
NORTHERN AND CENTRAL MOUNTAINS UNDER A MOIST NORTHWEST FLOW.

IN THE ABSENCE OF A STRONG DYNAMIC STORM THROUGH THE PERIOD...EXPECT
TEMPERATURES WILL MODERATE MORE SLOWLY THAN GUIDANCE WOULD SUGGEST.
THEREFORE...GENERALLY UNDERCUT GUIDANCE THROUGH THE COMING WEEK
FAVORING A CONTINUATION OF COLDER THAN NORMAL READINGS. THIS IS
LIKELY TO BE ESPECIALLY TRUE FOR VALLEYS WHERE STRONG INVERSIONS
WILL LIMIT DAYTIME HEATING.

&&

.AVIATION...

AREAS OF SNOW SHOWERS WILL PERSIST OVER THE COLORADO NORTHERN AND
CENTRAL MOUNTAINS TONIGHT THROUGH MIDDAY SATURDAY CAUSING AREAS OF
MVFR CIGS AND VSBYS...PARTICULARLY IN THE HIGH PASSES AND AT ASE.
ELSEWHERE...VFR CONDITIONS ARE EXPECTED.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...WINTER WEATHER ADVISORY UNTIL 6 AM MST SATURDAY FOR
       COZ004-010-013.
UT...NONE.

$$

SHORT TERM...BAL
LONG TERM....NL
AVIATION.....BAL

$$