FXUS65 KGJT 062241
AFDGJT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
341 PM MST SUN DEC 6 2009

...A MAJOR WINTER STORM WILL IMPACT EASTERN UTAH AND WESTERN COLORADO
MONDAY THROUGH TUESDAY...

.SHORT TERM...TONIGHT THROUGH TUESDAY...

THE TAIL END OF THE SHORTWAVE WHICH BROUGHT SNOW TO THE NORTHERN AND
CENTRAL PORTIONS OF THE CWFA WILL PASS EAST OF THE DIVIDE LATE THIS
EVENING. AS A RESULT...EXPECT SNOWFALL WILL CONTINUE OVER THE
NORTHERN AND CENTRAL MOUNTAINS THROUGH MIDNIGHT AND WW.A WILL BE
ALLOWED TO CONTINUE. DURING THE LATTER PART OF THE NIGHT...WINDS
BACK TO THE SOUTHWEST RESULTING IN A WEAK OVERRUNNING REGIME. THIS
WILL PRODUCE AREAS OF LIGHT SNOW THROUGH MORNING...THOUGH ADDITIONAL
ACCUMULATIONS WILL BE LIGHT.

A MAJOR WINTER STORM BEGINS MONDAY AS SOUTHWEST 7H FLOW INCREASES
WITH SPEEDS OF UP TO 45 KNOTS NOSING INTO THE FOUR CORNERS AREA.
RESULTANT OVERRUNNING OF COLD AIR TRAPPED IN THE SOUTHERN VALLEYS
POINTING TO SIGNIFICANT ACCUMULATIONS...ESPECIALLY OVER THE FOUR
CORNERS AREA. 7H TEMPS COLDER THAN PREVIOUS RUNS SO CONFIDENT
PRECIPITATION WILL BE OF THE FROZEN VARIETY FOR ALL BUT THE LOWEST
ELEVATIONS. MOUNTAIN SNOW OVER THE MOUNTAINS OF SOUTHEAST UTAH AND
THE SOUTHWEST AND SOUTH-CENTRAL MOUNTAINS OF COLORADO WITH OROGRAPHIC
LIFT AIDING SNOW PRODUCTION. WINDS WILL INCREASE OVER THOSE ARES
DURING THE DAY RESULTING IN BLIZZARD CONDITIONS LATER IN THE DAY.
THE BROAD ISENTROPIC UPGLIDE ENHANCED BY JET DIVERGENCE WILL GENERATE
PRECIPITATION OVER THE ENTIRE CWFA...THOUGH ACCUMULATIONS WILL BE
LIGHTER OVER THE REMAINING VALLEYS OF EASTERN UTAH AND WESTERN
COLORADO AS WELL AS THE NORTHERN MOUNTAINS. REMAINED ON THE FENCE
WITH RESPECT TO THE GUNNISON VALLEY SO CONTINUED THE WATCH.

THE STORM ACHIEVES ITS GREATEST STRENGTH MONDAY NIGHT INTO TUESDAY
MORNING AS A 150 KT JET DRIVES THE MID-LEVEL TROF INTO THE WESTERN
GREAT BASIN DURING THE NIGHT. AS THIS OCCURS...THE NORTHERN BRANCH OF
THE JET EXITS TO THE EAST PLACING THE CENTER OF THE CWFA UNDER THE
COMBINED DIVERGENCE ASSOCIATED WITH THE LEFT EXIT AND RIGHT ENTRANCE
REGIONS OF THE APPROACHING SOUTHERN AND EXITING NORTHERN JET. THIS
AIDS THE DEEPENING OF THE ENTIRE SYSTEM AND SOUTHWEST FLOW INCREASES
OVER THE FOUR CORNERS REGION. BY 12Z SYSTEM HAS SPUN UP INTO A
CLASSIC CYCLONE WHICH IS FAIRLY RARE FOR THIS REGION. UPGLIDE
BECOMES FURTHER ENHANCED WHILE LAPSE RATES SIMULTANEOUSLY STEEPEN
AIDING IN SNOW PRODUCTION. 7H WINDS INCREASE DURING THIS PERIOD
WHICH WILL RESULT IN WHITE-OUT CONDITIONS AT TIMES FOR THE SOUTHERN
AND SOUTH-CENTRAL MOUNTAINS.

LATEST GUIDANCE MOVES THE SURFACE CYCLONE ACROSS SOUTHEAST UTAH AND
SOUTH-CENTRAL COLORADO. THIS THREATENS TO GENERATE A HEAVY SNOW BAND
ACROSS AREAS ALONG THE I-70 CORRIDOR FROM EASTERN UTAH INTO THE
GRAND VALLEY AND MAY RESULT IN ACCUMULATIONS OF UP TO ONE FOOT.
CONFIDENCE OF THE STORMS TRACK NOT SUFFICIENT TO HOIST WARNING BUT
HAVE POSTED A WATCH FOR ALL OF THE VALLEYS OF EASTERN UTAH AND
WESTERN COLORADO AS THE DYNAMICS ASSOCIATED WITH THIS STORM ARE
REMARKABLE.

STORM FINALLY BEGINS TO WIND DOWN THURSDAY AFTERNOON AS THE STORM
PUSHES EAST OF THE DIVIDE. HOWEVER...WRAP-AROUND MOISTURE COMBINED
WITH STEEP LAPSE RATES AND OROGRAPHIC LIFT WILL CONTINUE TO
GENERATE SIGNIFICANT SNOWFALL ACROSS THE MOUNTAINS.

TEMPERATURES WILL REMAIN MUCH COLDER THAN NORMAL...THOUGH OVERNIGHT
LOWS NOT QUITE AS COLD AS RECENTLY DUE TO CLOUDS AND DIABATIC
WARMING ASSOCIATED WITH PRECIPITATION PROCESSES.

.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...

A MOIST WEST-NORTHWEST FLOW WILL BE OVER THE REGION TUES NIGHT AND
WED IN THE WAKE OUR BIG STORM. EMBEDDED WEAK VORT MAXES COMBINED
WITH STEEP LAPSE RATES AND 15-20 KT WINDS AIDING OROGRAPHIC ASCENT
WILL KEEP SNOW GOING MOST ELEVATED LOCATIONS...BUT RATE OF FALL WILL
BE NOTICEABLY LIGHTER. THE FLOW BACKS A LITTLE MORE TOWARD THE WEST
WEDNESDAY AND EMPHASIS TURNS TO THE W AND SW MTN SLOPES.
ACCUMULATIONS ARE EXPECTED TO BE LIGHT AND GENERALLY 1-3 INCHES OR
LESS.

MOSTLY DRY CONDITIONS ARE EXPECTED WEDNESDAY NIGHT THROUGH FRIDAY
EXCEPT FOR A FEW SCATTERED SHOWERS FROM TIME TO TIME OVER THE MTNS
AS JET ENERGY AND FORCING ARE EITHER NORTH OR SOUTH OF THE CWA.
TEMPS WILL MODERATE SLOWLY GIVEN EXPECTED SNOW ACCUMULATIONS FROM
THIS WEEKS EARLIER STORM.

NEXT SHORT WAVE WEAKENS AS IT PULLS AWAY FROM PARENT CLOSED LOW OFF
THE PAC NW. HOWEVER BY SATURDAY NIGHT LEFT EXIT REGION OF JET NOSING
INTO THE 4 CORNERS FAVORS SOME PCPN OVER THE SRN FOOTHILLS AND SAN
JUANS. ALTHO MDLS SHOWING SOME DIFFERENCES SO CONFIDENCE NOT MORE
INSPIRING THAN SCATTERED SHOWERS FOR THE TIME BEING.

&&

.AVIATION...
MOSTLY VFR CONDITIONS ARE EXPECTED THROUGH MIDNIGHT...THEN AS THE
NEXT WEATHER SYSTEM APPROACHES CONDITIONS WILL DETERIORATE TO MVFR BY
EARLY MONDAY MORNING. CLOUDS WILL LOWER AND THICKEN THROUGH THE DAY
MONDAY. EXPECT AREAS OF IFR/LIFR CIGS AND VSBYS AS SNOW SPREADS OVER
THE REGION MONDAY AFTERNOON.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...WINTER STORM WARNING FROM 6 AM MONDAY TO 6 PM MST TUESDAY FOR
       COZ003-004-010-013-021>023.
     WINTER STORM WATCH FROM MONDAY MORNING THROUGH TUESDAY
       AFTERNOON FOR COZ001-002-006>008-011-014-020.
     WINTER WEATHER ADVISORY UNTIL 6 PM MST THIS EVENING FOR COZ002-
       005.
     WINTER WEATHER ADVISORY FROM 6 AM MONDAY TO 6 PM MST TUESDAY
       FOR COZ005.
     BLIZZARD WARNING FROM 6 AM MONDAY TO 6 PM MST TUESDAY FOR
       COZ009-012-017>019.
     WINTER WEATHER ADVISORY UNTIL MIDNIGHT MST TONIGHT FOR COZ004-
       010-012-013.
UT...WINTER STORM WARNING FROM 6 AM MONDAY TO 6 PM MST TUESDAY FOR
       UTZ025.
     WINTER STORM WATCH FROM MONDAY MORNING THROUGH TUESDAY
       AFTERNOON FOR UTZ022-024-027-029.
     WINTER WEATHER ADVISORY UNTIL 6 PM MST THIS EVENING FOR UTZ023.
     WINTER WEATHER ADVISORY FROM 6 AM MONDAY TO 6 PM MST TUESDAY
       FOR UTZ023.
     BLIZZARD WARNING FROM 6 AM MONDAY TO 6 PM MST TUESDAY FOR
       UTZ028.

&&

$$

SHORT TERM...NL
LONG TERM....MC
AVIATION.....MC