FXUS65 KGJT 092144
AFDGJT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
244 PM MST WED DEC 9 2009
.SHORT TERM...TONIGHT THROUGH FRIDAY
WEAK SHORTWAVE MOVING FROM NRN UT INTO NW CO EARLY THIS AFTERNOON...
WITH ANOTHER SHORTWAVE OVER SE ID THAT WILL SWEEP ACROSS NORTH-
CENTRAL CO TONIGHT. 2 PM WEB CAMS FROM STEAMBOAT SPGS SHOWED LOW
CLOUDS UP AGAINST THE MTNS...INDICATIVE OF LOW LEVEL MOIST AIR DUE TO
COLD AIR TRAPPED IN THE VALLEY AND EXTENSIVE CLOUD COVER. AS THE
SHORTWAVES COMES BY WITH AN OROGRAPHICALLY FAVORABLE WEST WIND...
EXPECT LIGHT SNOW AND GUSTY WINDS FOR THE NRN MTNS TONIGHT.
OROGRAPHIC SNOW MODEL PRODUCED 1-4 INCHES. MID-SLOPES MAY ACTUALLY BE
MOST FAVORED FOR SNOW DUE TO THE SHALLOWNESS OF THE MOIST LAYER.
VAIL WEB CAMS ALSO CLOUDY WITH POSSIBLY SNOW ON THE PEAKS. WILL
CONTINUE THE WINTER WEATHER ADVISORY FOR SNOW AND BLOWING SNOW FOR
THE PARK/GORE/FLATTOPS AND THE MTNS AROUND VAIL....ZONES 4 10 AND
13. WILL ADD MENTION OF DANGEROUS WIND CHILLS TONIGHT AS WELL.
CONTINUED THE BLOWING SNOW ADVISORY UNTIL 6 PM MST THIS EVENING FOR
THE SAN JUAN AND SAWATCH MTNS AS THE 140-150 KT UPPER JET CORE OVER
PULLS AWAY INTO THE PLAINS. WORDED STATEMENT TO FOCUS ON ELEVATIONS
OF 10,000 FT AND HIGHER AS THIS WAS WHERE AUTOMATED OBS SITES
INDICATED THE STRONGEST WINDS WERE LOCATED...WHICH INCLUDES THE HIGH
MTN PASSES.
VERY COLD TEMPERATURES AGAIN TONIGHT AND WILL GO BELOW GUIDANCE IN
MOST AREAS. PATCHY FREEZING FOG AND/OR LOW CLOUDS AGAIN ALONG RIVERS
AND LOW SPOTS.
AS WESTERLY FLOW BECOMES ESTABLISHED TONIGHT AND THU...WARM AIR
ADVECTION ALOFT COMMENCES...WHICH GENERALLY PERSISTS THROUGH FRI.
THIS WILL RESULT IN A SLOW WARM-UP FOR THE MTNS...BUT THE COLD AIR
WILL REMAIN TRAPPED IN VALLEYS WHERE STABLE CONDITIONS WILL DEVELOP
WITH POOR MIXING. HIGHER CLOUDS ON THE INCREASE THU AFTERNOON AHEAD
OF A VERY WEAK PACIFIC WAVE CROSSES THU NIGHT. THIS IS THE FIRST IN A
SERIES OF PAC WAVES AS THE SRN STREAM JET BEGINS TO WORK INLAND.
CLOUDS CONTINUE TO INCREASE FRI AS MOISTURE GRADUALLY INCREASES AHEAD
OF ANOTHER PAC WAVE.
.LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY...
DEEPER MOISTURE WILL ALREADY BE MOVING OVER THE FORECAST AREA AT THE
BEGINNING OF THE LONG TERM PERIOD. WARM ADVECTION WILL ACCOMPANY
THIS SURGE OF PACIFIC MOISTURE...WITH A SERIES OF EMBEDDED WAVES IN
THE WESTERLY FLOW. THESE IMPULSES ARE FAST-MOVING WITH NOT A LOT OF
TIME BETWEEN EACH ONE. THEREFORE WEATHER ON THE GROUND WILL LIKELY
BLEND TOGETHER WITH A GRADUAL UPSWING IN POPS FRI NIGHT INTO SAT...
AND WITH THE MOST ACTIVE PERIODS SAT NIGHT AND SUN. IN ADDITION TO AN
INCREASING CHANCE OF SNOW...THE 700 MB FLOW INCREASES SAT NIGHT AND
BECOMES MORE SOUTHWESTERLY AS THIS STRONGER WAVE APPROACHES.
THEREFORE WINDS WILL INCREASE OVERNIGHT...MAINLY OVER THE MOUNTAINS.
THEN BY SUNDAY AFTERNOON THE WINDS WILL DIMINISH AGAIN AS THE
SHORTWAVE MOVES OVERHEAD. ANOTHER WAVE IS FORECAST FOR MONDAY...BUT
THIS ONE LOOKS A LITTLE WEAKER.
THE FORECAST PACKAGE IN GOOD SHAPE WITH LIKELY POPS MOUNTAINS/CHANCE
VALLEYS...FOR THE STRONGEST WAVE SAT NIGHT AND SUN. HOWEVER THERE IS
STILL SOME MODEL UNCERTAINTY DUE TO THE PROGRESSIVE NATURE OF THE
FLOW. THE ECMWF IS NOT AS AMPLIFIED...AND THEREFORE IS FASTER. SO
SOME ADJUSTMENT FOR THE DETAILS IS EXPECTED WITH FUTURE FORECASTS.
AS THE MOIST WESTERLY FLOW MOVES OVER THE REGION...EXPECT SOME OF THE
VERY COLD TEMPERATURES TO MODIFY AS VALLEYS MIX OUT. HOWEVER SINCE
THE SNOW COVER IS RELATIVELY DEEP IN ALL BUT THE FAR SOUTHWEST
VALLEYS...HAVE CONTINUED TO KEEP TEMPS BELOW GUIDANCE.
&&
.AVIATION...
MVFR/IFR CONDITIONS EXPECTED OVER THE NRN CO MTNS FROM VAIL TO K3MW
INCLUDING VALLEY AIRPORT KSBS AND KHDN. GUSTY WEST WINDS OVER
MOUNTAIN TOPS LIKELY TO RESULT IN AREAS OF TURBULENCE OR MOUNTAIN
WAVES. ALLEY FOG FORMATION AND RESULTING IFR CONDITIONS ARE POSSIBLE
TONIGHT ESPECIALLY AT KASE...KEGE...KVEL...KGUC. VFR CONDITIONS
EXPECTED ELSEWHERE.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...WINTER WEATHER ADVISORY FOR SNOW/BLOWING SNOW THROUGH 6 AM
THURSDAY MORNING FOR THE NWRN CO MOUNTAINS (ZONES 4/10/13).
WINTER WEATHER ADVISORY FOR BLOWING SNOW THROUGH 6 PM TODAY
(ZONES 12/18/19).
UT...NONE.
&&
$$
SHORT TERM...JAD
LONG TERM....EH
AVIATION.....JAD
