FXUS65 KGJT 071155 CCA
AFDGJT
AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
454 AM MST MON DEC 7 2009
..A MAJOR WINTER STORM WILL IMPACT EASTERN UTAH AND WESTERN COLORADO
TODAY THROUGH TUESDAY...
.SHORT TERM...TODAY THROUGH TUESDAY NIGHT...
A WARM FRONT SWEPT OVER THE REGION FROM SOUTHWEST TO NORTHEAST LAST
NIGHT MOISTENING THE LOWER LEVELS AND STARTING SNOWFALL FOR MOST
VALLEY LOCATIONS AND CONTINUING LIGHT SNOWFALL IN THE NORTHERN
MOUNTAINS.
TODAY: WARM ADVECTION CONTINUES FOR A WEAK OVERRUNNING EVENT. THIS
WILL START GENERALLY LIGHT ACCUMULATIONS IN MOST VALLEYS. LATENT HEAT
OF EVAPORATION WILL KEEP TEMPERATURES SOMEWHAT STEADY THROUGH THE DAY
WITH A MIX OF RAIN EXPECTED THIS AFTERNOON ONLY IN THE LOWEST
ELEVATIONS. THE SOUTHERN MOUNTAINS WILL GET HAMMERED WITH THE STRONG
WINDS AND HEAVY OROGRAPHIC SNOWFALL...WITH LESS SNOW ACCUMULATION
EXPECTED ACROSS THE CENTRAL AND NORTHERN MOUNTAINS. BUT THERE IS
STILL JET DYNAMICAL LIFT ACROSS THE REGION TODAY TO SUPPORT SNOWFALL.
SOUTHWEST 7OOMB WINDS INCREASE TO 45 KNOTS OVER THE SOUTHERN ZONES
PRODUCING OCCASIONAL WHITE-OUT CONDITIONS IN THE SOUTHERN MOUNTAINS.
THE STORM STRENGTHENS TONIGHT AS STRONG LIFT/UPPER LEVEL DIFLUENCE
IS GENERATED BETWEEN JET STREAKS. A RESULTANT RAPIDLY DEEPENING
SURFACE COLD FRONT PUSHES W-E ACROSS THE NORTHERN AND CENTRAL ZONES
AFTER MIDNIGHT AND THEN QUICKLY EAST OF THE DIVIDE BY TUESDAY LATE
MORNING. VERY IMPRESSIVE AND DANGEROUS SNOWFALL IS LIKELY ALONG THIS
BOUNDARY. BOTH THE 00Z GFS AND EC BRING THIS FRONTAL FORCING AS FAR
SOUTH AS THE I-70 CORRIDOR. MEANWHILE MOIST SW FLOW CONTINUES TO POUR
OVER THE SOUTHERN ZONES INTO TUESDAY.
FLY IN THE OINTMENT FOR FRONTAL SNOWFALL AMOUNT IS THE THE LACK OF
LONGEVITY...BUT OROGRAPHIC NW FLOW ON TUESDAY WILL CONTINUE TO
GENERATE SOME SNOW ACCUMULATIONS. POTENTIAL SNOW ACCUMULATION
PROBLEM FOR THE SOUTHERN ZONES IS HIGHER THAN EXPECTED RAIN-SNOW
LINE THAT WILL BEAR WATCHING. THE SW SAN JUAN MOUNTAINS STILL LOOK TO
ACCUMULATE THE MOST STORM TOTAL SNOW OF 2-3 FEET...POSSIBLY UP TO 5
FEET. SNOWFALL WILL DIMINISH QUICKLY FROM W-E TUESDAY NIGHT AND
TEMPERATURES WILL PLUMMET ESPECIALLY ACROSS THE NORTHERN HALF OF THE
FORECAST AREA.
.LONG TERM...WEDNESDAY THROUGH SUNDAY...
THE MAJOR WINTER STORM WILL BE EXITING THE FORECAST AREA LEAVING
MOIST WEST TO NORTHWEST FLOW ALOFT IN ITS WAKE. THIS WILL KEEP SNOW
SHOWERS GOING ALONG THE DIVIDE...MAINLY NORTH OF INTERSTATE 70...
ALTHOUGH AMOUNTS ARE EXPECTED TO REMAIN LIGHT AS STRONGER DYNAMIC
FORCING WILL BE LACKING. HOWEVER...LAPSE RATES REMAIN FAIRLY STEEP
AND OROGRAPHIC FLOW IS NOT ALL THAT BAD...SO THERE WILL CONTINUE TO
BE SOME ACCUMULATING SNOWS...JUST NOT HIGHLIGHT WORTHY ATTM.
BY THURSDAY AND FRIDAY...MODELS DIVERGE A BIT WITH THE ECMWF
FAVORING A DRY PERIOD WITH SHRTWV RIDGING BUILD IN...VERSUS THE
GFS WHICH KEEPS SOME ENERGY MOVING THROUGH THE SOUTHERN JET...
CLIPPING OUR SOUTHERNMOST ZONES. WE ARE LEANING TOWARD THE WETTER
GFS SOLUTION ATTM AND WILL KEEP LOW POPS IN THE FORECAST FOR OUR
SOUTHERN MOUNTAINS AND ADJACENT VALLEYS THROUGH THE END OF THE
WEEK. NEXT STRONGER STORM IS POISED TO ARRIVE BY LATE IN THE
WEEKEND...WITH LIGHT PRECIP BREAKING OUT SAT NIGHT AND SUNDAY IN WAA
PATTERN AS SOUTHWEST FLOW BECOMES ESTABLISHED AHEAD OF A LONG WAVE
TROUGH PUSHING INTO THE WESTERN U.S. TEMPS ARE EXPECTED TO RUN NEAR
SEASONAL NORMALS THROUGH THIS PERIOD.
&&
.AVIATION...
WIDESPREAD MVFR CONDITIONS WILL BLANKET EASTERN UTAH AND
WESTERN COLORADO THROUGH TUESDAY AS A MAJOR WINTER STORM PASSES
THROUGH THE ROCKIES. IN ADDITION...OCCASIONAL IFR/LIFR CIGS
AND VSBYS CAN BE EXPECTED...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.
&&
$$
SHORT TERM...99
LONG TERM....JDC
AVIATION.....JDC/JOE
