FXUS65 KBOU 071152
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
440 AM MST MON DEC 7 2009

.SHORT TERM...NOT MUCH OF A BREAK BETWEEN SYSTEMS AFTER ALL. GENTLE 
WARM ADVECTION IN SOUTHWEST FLOW AHEAD OF THE NEXT SYSTEM IS ALREADY 
CREATING WIDESPREAD LIGHT SNOW ACROSS WESTERN COLORADO...AND THIS 
LIFT WILL SPREAD ACROSS NORTHEASTERN COLORADO DURING THE DAY TODAY. 
THE FORCING IS WEAK BUT IT WILL NOT TAKE MUCH TO KEEP LIGHT SNOW 
GOING. IN OTHER SITUATIONS WE COULD JUST CALL THIS FLURRIES...BUT 
GIVEN THE LOW SNOW DENSITY THERE WILL BE SOME ACCUMULATION JUST A 
FEW HUNDREDTHS OF AN INCH OF WATER WILL BE AN INCH OF SNOW. FORCING 
GRADUALLY INCREASES THIS EVENING...THEN THE STRONGEST LIFT 
ASSOCIATED WITH THE NEXT TROUGH IS OVER DENVER BY 12Z. THIS SYSTEM 
LOOKS SIMILAR OR A BIT STRONGER THAN THE LAST BOTH AS FAR AS THE 
LIFT AND THE TRACK. WIND FIELDS ARE A BIT STRONGER...GIVING SOME 
OROGRAPHIC SNOW IN THE MOUNTAINS THAT WAS LACKING. EAST TO SOUTHEAST 
WINDS AND THE TRACK OF THE SYSTEM BOTH FAVOR AREAS NORTH OF 
DENVER...ESPECIALLY LARIMER COUNTY AGAIN. FOR NOW RAISED POPS AND 
SNOW AMOUNTS. ISSUING A WINTER WEATHER ADVISORY FOR THE HIGH 
MOUNTAINS...NOT QUITE TIME FOR A DENVER ADVISORY YET BUT LIKELY 
NEEDED FOR LATER TONIGHT AND TUESDAY.

.LONG TERM...MODELS HAVE ONE PIECE OF ENERGY MOVE ACROSS THE 
FORECAST AREA INSIDE THE MEAN TROUGH ON TUESDAY.  AFTER A TROUGH 
AXIS MOVES ACROSS TUESDAY AFTERNOON...STRONG WEST-NORTHWESTERLY FLOW 
ALOFT IS PROGGED FOR US...WITH A DECENT JET MAX TO OUR SOUTH.  THIS 
CONTINUES TUESDAY NIGHT AND WEDNESDAY.  BY WEDNESDAY AFTERNOON 
...CONTINUING WEDNESDAY NIGHT...THE GFS HAS A 130 KNOT WEST- 
NORTHWESTERLY JET MAX OVER THE FORECAST AREA...THE NAM HAS IT A BIT 
SOUTH OF US.  THERE IS SUBSTANTIAL UPWARD MOTION PROGGED OVER THE 
FORECAST AREA TUESDAY MORNING...THEN IT EXITS WEST TO EAST THROUGH 
THE AFTERNOON...WITH DOWNWARD MOTION IN PLACE TUESDAY NIGHT.  ON 
WEDNESDAY...MAINLY WEAK DOWNWARD MOTION IS PROGGED FOR THE FORECAST 
AREA.  MODELS HAVE A DECENT SURFACE CYCLONE OVER THE SOUTHEAST 
CORNER OF COLORADO AT 18Z TUESDAY WITH THE BOUNDARY LAYER FLOW 
PROGGED TO BE NORTHERLY UPSLOPE FOR THE PLAINS AND FOOTHILLS THROUGH 
THE DAY.  AFTER THAT...IT LOOKS LIKE NORMAL DIURNAL WIND TRENDS 
SHOULD DOMINATE.  MOISTURE IS DEEP OVER ALL THE FORECAST AREA ON 
TUESDAY.  THE NAM STARTS DECREASING IT OVER THE PLAINS LATE IN THE 
DAY...THE GFS DOESN'T DO THAT UNTIL TUESDAY IN THE EVENING.  THE 
MOUNTAINS  STAY IN PRETTY DEEP MOISTURE ON BOTH MODELS THROUGH 
WEDNESDAY.  THE PLAINS ARE FAIRLY DRY ACCORDING TO THE NAM FOR MUCH 
OF TUESDAY NIGHT AND WEDNESDAY.  THE GFS DRIES THE PLAINS OUT TO A 
LESSER DEGREE LATE TUESDAY NIGHT AND WEDNESDAY...BUT BRINGS A LOT OF 
MID AND UPPER LEVEL MOISTURE OVER LATE WEDNESDAY AFTERNOON AND 
EVENING.  THE QPF FIELDS SHOW ALL AREAS HAVING MEASURABLE SNOWFALL 
TUESDAY...THE GFS HAS MORE.  EITHER OF THEM SHOWS SIGNIFICANT 
AMOUNTS. THE PLAINS ARE DRY BY TUESDAY EVENING...WITH BOTH MODELS 
CONTINUING MEASURABLE SNOW IN THE MOUNTAINS THROUGH WEDNESDAY 
EVENING.  CONCERNING POPS...OUR MOUNTAINS HAVE NOT BEEN DOING GREAT 
WITH SNOW THESE LAST COUPLE DAYS.  I FEEL SOME OF THAT HAS TO DO 
WITH THE LACK OF OROGRAPHIC ENHANCEMENT.  BY TUESDAY MORNING 
15Z...MOUNTAIN TOP WIND PROGGS HAVE WEST-NORTHWESTERLIES AT 15 TO 25 
KNOTS.  THIS CONTINUES ALONG WITH DEEP MOISTURE THROUGH TUESDAY 
NIGHT.  COLD AIR ADVECTION IS ALSO PROGGED.  SNOW MODEL FINALLY 
SHOWS SOME DECENT SNOWFALL FOR OUR HIGH MOUNTAINS.  WILL CONTINUE 
SHORT-TERM FORECASTER'S ADVISORY THROUGH 12Z WEDNESDAY.  FOR THE 
PLAINS...THE MOISTURE IS THERE AND SO IS THE THE UPSLOPE.  WILL UP 
POPS SOMEWHAT...AS WELL AS SNOWFALL AMOUNTS ON TUESDAY...BUT NO 
HIGHLIGHTS.  FOR TEMPERATURES...TUESDAY'S HIGHS COOL OFF SOME 1-4 C 
FROM TOADY'S.  WEDNESDAY'S ARE ONLY 1-3 C WARMER THAN TUESDAY'S.  
FOR THE LATER DAYS...THURSDAY THROUGH SUNDAY...THE MEAN TROUGH 
STARTS PULLING AWAY TO THE EAST AND NORTHEAST OF THE FORECAST AREA 
ON THURSDAY AND THURSDAY NIGHT...WITH STRONG ZONAL FLOW ALOFT SLOWLY 
DECREASING.  BY FRIDAY...WEAKER WEST-NORTHWESTERLY FLOW ALOFT IS 
PROGGED FOR THE FORECAST AREA WITH UPPER RIDGING TO OUT WEST.  ON 
FRIDAY NIGHT AND SATURDAY A FLAT UPPER RIDGE MOVES OVER THE FORECAST 
AREA.  SATURDAY NIGHT AND SUNDAY SEE A RETURN TO STRONG 
WEST-NORTHWESTERLY FLOW ALOFT...AT LEAST ACCORDING TO THE GFS.  
TEMPERATURES STAY BELOW NORMAL THURSDAY AND FRIDAY...AND WARM TO 
NEAR NORMAL SATURDAY AND SUNDAY.  WILL KEEP SOME POPS GOING IN THE 
MOUNTAINS MUCH OF THE TIME...THE PLAINS WILL BE DRY.

&&

.AVIATION...OCCASIONAL VERY LIGHT SNOW WILL CONTINUE TODAY. CEILINGS 
EXPECTED TO LIFT A LITTLE BUT INSTRUMENT APPROACHES WILL LIKELY BE 
NEEDED ALL DAY. INCREASING SNOW OVERNIGHT WITH LOWERING 
CONDITIONS...IFR EXPECTED AND PERIODS OF IFR LIKELY LATER TONIGHT 
INTO TUESDAY MORNING. UP TO AN INCH OF SNOW TODAY...2 TO 4 TONIGHT 
AND ACCUMULATIONS WILL CONTINUE ON TUESDAY.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...WINTER WEATHER ADVISORY FOR SNOW  
      AND BLOWING SNOW FROM 19Z TODAY THROUGH WEDNESDAY MORNING AT   
      12Z FOR ZONES...31/33/34.

$$
GIMMESTAD/RJK