FXUS65 KGJT 080429 AAA
AFDGJT
AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
929 PM MST MON DEC 7 2009
.9PM UPDATE...LET IT SNOW! THIS EVENING...MOIST OVERRUNNING CONTINUES
IN WARM ADVECTION SW FLOW. OUR LOCAL 00Z BALLOON RELEASE SHOWS
ONLY A SHALLOW SURFACE INVERSION UP TO ABOUT 800MB. WINDS REMAIN
LIGHT NEAR POWDERHORN ON THE GRAND MESA INDICATING THOUGH THIS
INVERSION IS SHALLOW IT SEEMS TO BE HUGGING THE TERRAIN EFFECTIVELY.
THE GRADIENT WIND STRENGTH IS EVIDENT IN THE HIGHER SAN JUAN MTNS
WHERE EAGLE TOWER AT 12,900FT IS GUSTING TO 68 MPH AND KENDALL/PUTNEY
ARE GUSTING IN THE MID 40S. SNOWFALL ACCUMULATIONS WILL GENERALLY
REMAIN LIGHT THROUGH MIDNIGHT IN THIS OVERRUNNING REGIME.
SNOW REPORTS ARE AVAILABLE ON OUR WEBPAGE UNDER TOP NEWS OF THE DAY.
AFTER MIDNIGHT ALL HECK WILL BREAK LOOSE AS THE UPPER TROUGH
APPROACHES. JET INTERACTION CREATES STRONG DIVERGENCE IN THE UPPER
ATMOSPHERE AND A STRONG SURFACE CONVERGENT BOMB FORMS OVER EASTERN
UT/WESTERN CO BEFORE SUNRISE. THE MODELS REMAIN CONSISTENTLY
DIFFERENT ON THE PLACEMENT OF THIS FEATURE: THE FURTHER N NAM PLACING
IT ON A LINE FROM GREEN RIVER TO MEEKER...THE GFS FROM CANYONLANDS-
GRAND JUNCTION-RIFLE. THE GFS HAS BEEN THE FAVORED MODEL...AND IF
ITS PLACEMENT VERIFIES WE ARE LOOKING AT AROUND 8 INCHES OF NEW SNOW
ALONG THE I-70 CORRIDOR BETWEEN RIFLE-GRAND JUNCTION. IF THE NAM
VERIFIES...WE STILL SEE SOME 3-4 INCHES OF NEW SNOW HERE IN THE GRAND
VALLEY...AND I-70 IN EASTERN UTAH WILL GET MORE. EITHER WAY TRAVEL
TONIGHT AND TUESDAY IS HIGHLY DISCOURAGED WITH DANGEROUS CONDITIONS
EXPECTED.
TUESDAY...WINDS WILL BEGIN TO MIX DOWN TO THE SURFACE LATE TONIGHT
AND CONTINUE AS THE UPPER TROUGH PASSES AROUND 15Z. STRONG COLD
ADVECTION THROUGH THE DAY WILL REALLY INCREASE SNOWFALL OVER NW-
FACING SLOPES AND ACROSS THE NORTH IN GENERAL. MTN TOP (700MB)
TEMPS DROP FROM -8C TONIGHT TO -20C BY SUNSET.
TUESDAY EVENING...SHOWERS WILL END FROM W-E THROUGH THE AFTERNOON AND
EVENING. TEMPERATURES WILL PLUMMET UNDER PARTIALLY CLEARING SKIES.
&&
..A MAJOR WINTER STORM WILL IMPACT EASTERN UTAH AND WESTERN COLORADO
TONIGHT THROUGH TUESDAY...
.SHORT TERM...TONIGHT THROUGH WEDNESDAY...
UPPER LOW SHIFTS EASTWARD INTO THE GRT BASIN TONIGHT WHILE STRONG
AND DEEPENING SFC LOW APPROACHES THE 4 CORNERS BY EARLY TUESDAY
MORNING. GOOD BAROCLINIC BOUNDARY ACROSS THE NW PLATEAU AT TIME
WITH SINGLE DIGITS TEMPS IN CAG...EEO AND HDN...THIS COULD BE
SECONDARY FOCUS AREA TONIGHT AS STRONG WARM ADVECTION AND ISENTROPIC
UPGLIDE OCCUR. CURRENT WINTER HIGHLIGHTS LOOK GOOD WITH MOST AREAS
ALREADY IN SNOW ACCUMULATION MODE. LAPSE RATES TONIGHT ALSO VERY
UNSTABLE ABOVE H7 ENSURING GOOD RESPONSE...EVEN ON THE DOWNSTREAM
SIDE OF TERRAIN.
GFS A LITTLE MORE CONSISTENT WITH THE HANDLING OF THIS STORM AND
LATEST RUN SHOWS SFC LOW A LITTLE STRONGER THAN THE NAM AND 500MB
TROF PASSAGE A LITTLE EARLIER. TROF PASSAGE EXPECTED BY NOON BUT
COLD FRONT LAGS BEHIND AND ON A LINE FROM CNY TO SBS.
THE FLOW ALOFT BACKS TO THE WEST-SOUTHWEST TUESDAY NIGHT AFTER
FRONTAL PASSAGE WITH THE FOCUS OF SNOW BECOMING MORE ORIENTED OVER
THE NRN AND CNTRL MTNS ALONG THE CONTINENTAL DIVIDE. A DECENT
SHORTWAVE WITH SOME JET SUPPORT WILL ALSO APPROACH THE CWA FROM THE
NORTH WED AFTERNOON ENHANCING SNOW FALL OVER THE AFOREMENTIONED
AREAS. HOWEVER VERY DRY NATURE OF ATMS WILL LIMIT ADDITIONAL SNOW
AMOUNTS EVEN IF SNOW DENSITY IS VERY LOW.
.LONG TERM...WEDNESDAY NIGHT THROUGH MONDAY...
AREAS OF SNOW TO PERSIST WED NIGHT IN MOIST NW FLOW OROGRAPHICS
BEHIND THE LAST OF THE TRAILING DISTURBANCES. BEST CHANCE WILL BE
IN THE NORTHERN AND CENTRAL CO MTNS.
UNSETTLED CONDITIONS EXPECTED FOR THE REMAINDER OF THE WEEK AS
PERIODIC DISTURBANCES MOVE BY...WHICH ARE DIFFICULT TO TIME AT THE
MOMENT. NW FLOW PERSISTS THROUGH THU NIGHT BEHIND THE CURRENT
WINTER STORM AND DOWNSTREAM FROM A BLOCKING RIDGE IN THE NE PACIFIC.
JET ENERGY UNDERCUTTING THE RIDGE PUSHES ACROSS THE CA COAST FRI AND
TO OUR AREA THIS WEEKEND...RESULTING IN WINDS ALOFT BECOMING
WESTERLY. 12Z ECMWF BRINGS A MORE PRONOUNCED SHORTWAVE TROUGH ACROSS
ERN UT/WRN CO MONDAY...WHILE THE 12Z GFS IS MUCH FLATTER. TEMPS
RECOVER THE LAST HALF THE WEEK TO LEVELS CLOSER TO NORMAL FOR THIS
TIME YEAR.
&&
.AVIATION...
IN RESPONSE TO A MAJOR WINTER STORM WHICH WILL PASS THROUGH THE
ROCKIES...WIDESPREAD IFR/LIFR CIGS AND VSBYS CONDITIONS WILL BLANKET
EASTERN UTAH AND WESTERN COLORADO TONIGHT THROUGH TUESDAY ESPECIALLY
AROUND HIGH VALLEY AIRPORTS SUCH AS KEGE...KASE...KHDN AND KTEX.
STRONG SOUTHWEST WINDS GUSTING OVER 50 MPH WILL ALSO OCCUR THROUGH
06Z TONIGHT. THEN WIDESPREAD IFR TO LIFR CONDITIONS IN +SHSN ARE
EXPECTED BETWEEN 06Z-15Z ALONG AND NORTH OF THE I-70 CORRIDOR. EXPECT
IMPROVING CONDITIONS FROM WEST TO EAST LATE TUESDAY AFTERNOON AND
EVENING.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER STORM WARNING UNTIL 6 PM MST TUESDAY FOR COZ003-004-
006>008-010-011-013-014-020>023.
WINTER STORM WARNING UNTIL 6 PM MST TUESDAY FOR COZ001-002-005.
BLIZZARD WARNING UNTIL 6 PM MST TUESDAY FOR COZ009-012-017>019.
UT...WINTER STORM WARNING UNTIL 6 PM MST TUESDAY FOR UTZ022-025-027-
029.
WINTER STORM WARNING UNTIL 6 PM MST TUESDAY FOR UTZ023-024.
BLIZZARD WARNING UNTIL 6 PM MST TUESDAY FOR UTZ028.
&&
$$
UPDATE.......JOE
SHORT TERM...MC
LONG TERM....JAD
AVIATION.....MC
