FXUS65 KBOU 061113
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
357 AM MST SUN DEC 6 2009

.SHORT TERM...FORECAST LOOKING ON TRACK AS TROUGH ELONGATED 
EAST-WEST SLIDES EAST ACROSS COLORADO TODAY. STRONG LIFT WILL MOVE 
FROM NORTHWESTERN COLORADO ACROSS THE NORTHEAST BY THIS 
AFTERNOON...BRINGING A PERIOD OF ENHANCED SNOWFALL AS IT PASSES. 
PRECIPIATION AMOUNTS LIMITED BY THE COLD TEMPERATURES...THOUGH IT 
WILL ALSO BE PRETTY FLUFFY ESPECIALLY DURING THE PERIOD OF HEAVIER 
SNOW. PREVIOUS FORECAST SNOW AMOUNTS LOOK PRETTY GOOD WITH THE 
HEAVIEST SNOW OVER AND JUST EAST OF THE FRONT RANGE BEGINNING IN A 
FEW HOURS AND GOING THROUGH ABOUT NOON. THE FORCING ALOFT WILL SHIFT 
EASTWARD BY THE END OF THE DAY...BUT WEAK BOUNDARY COOLING THROUGH A 
DEEP LAYER SHOULD CONTINUE TO PRODUCE AT LEAST FLURRIES INTO THIS 
EVENING AROUND DENVER. 

TONIGHT HAS SEVERAL UNKNOWNS. DRYING AND SUBSIDENCE ALOFT COULD 
ALLOW CLEARING OF THE LOW CLOUDS AS WELL. OVER THE PLAINS WE COULD 
GO TO A CLEAR SKY WITH ICE CRYSTALS OR FROST...OR THE COOLING COULD 
MAINTAIN THE LOW CLOUDS. DID NOT CHANGE THE IDEA OF LOW LEVEL CLOUDS 
AND SURFACE MOISTURE LIMITING THE COOLING...ESPECIALLY SINCE THERE 
IS LITTLE WIND AT LOW LEVELS TO REMOVE THE MOISTURE. WE WILL 
PROBABLY GET A SOUTHERLY COMPONENT TO THE LIGHT WIND OFF THE PALMER 
DIVIDE...SO THAT AREA WOULD BE MOST LIKELY TO CLEAR AND HAVE 
TEMPERATURES TANK. ALSO SOME QUESTION ABOUT CLEARING IN THE 
MOUNTAINS. MODELS ARE SHOWING SOME WARM ADVECTION ALOFT SETTING IN 
AGAIN...SO IF THERE IS CLEARING IT COULD BE SHORT LIVED. THIS IS 
ALSO WHY POPS REMAIN OVER THE MOUNTAINS AS THE WEAK LIFT COULD 
PRODUCE SOME VERY LIGHT SNOW.

.LONG TERM...THE LARGE MEAN TROUGH OVER MUCH OF NORTH AMERICA IS 
PROGGED TO STICK AROUND WELL INTO THE EXTENDED PERIOD.  MODELS HAVE 
STRONG WESTERLY FLOW ALOFT OVER THE FORECAST AREA MONDAY MORNING AT 
12Z.  THE FLOW STAYS QUITE STRONG AND BECOMES SOUTHWESTERLY THROUGH 
THE DAY MONDAY.  IT'S STILL SOUTHWESTERLY MONDAY NIGHT/TUESDAY 
MORNING BUT IT DECREASES IN SPEED AS THE UPPER TROUGH AXIS 
APPROACHES.  THE TROUGH AXIS PUSHES OVER TUESDAY AFTERNOON...WITH 
STRONG WEST-NORTHWESTERLY FLOW BEHIND IT.  STRONG ZONAL FLOW ALOFT 
IS PROGGED TUESDAY NIGHT.  THERE IS WEAK UPWARD MOTION PROGGED 
MONDAY FOR THE FORECAST AREA...AND IT GRADUALLY INCREASES MONDAY 
NIGHT...WITH PRETTY STRONG UPWARD MOTION PROGGED TUESDAY MORNING 
FROM 12Z TO 18Z.  BY LATER TUESDAY AFTERNOON AND EVENING DOWNWARD 
MOTION MOVES IN.  THE BOUNDARY LAYER FLOW IS SOUTHEASTERLY ON MONDAY 
AND MUCH OF MONDAY NIGHT...BECOMING NORTH-NORTHEASTERLY TUESDAY AND 
TUESDAY EVENING.  FOR MOISTURE...MODELS CONTINUING SHOWING VERY DEEP 
MOISTURE IN THE MOUNTAINS MONDAY THROUGH TUESDAY...AND STILL PRETTY 
DEEP TUESDAY NIGHT. THE PLAINS HAVE SOME LOW LEVEL MOISTURE ON 
MONDAY...A BIT OF DRIER AIR AT THE MID LEVELS...THEN MOIST ALOFT.  
THE MOISTURE GETS DEEP BY MID AFTERNOON MONDAY OVER THE PLAINS AND 
STAYS THAT WAY THROUGH TUESDAY EVENING...BEFORE SOME MID LEVEL 
DRYING IS PROGGED ONCE AGAIN.  THE QPF FIELDS HAVE A BIT OF 
MEASURABLE SNOWFALL OVER THE WESTERN HALF OF THE FORECAST AREA 
MONDAY...THEN OVER ALL THE FORECAST AREA MONDAY NIGHT THROUGH 
TUESDAY EVENING.  SOME REMAINS OVER THE MOUNTAINS THE REST OF 
TUESDAY NIGHT.  EITHER MODEL SHOWS SUBSTANTIAL AMOUNTS...BUT THERE 
IS SOME.   CONCERNING POPS...MODELS HAVE SLIGHT WARM-AIR ADVECTION 
ON MONDAY.  NEUTRAL MONDAY NIGHT...THEN COLD-AIR ADVECTION ON 
TUESDAY.  THE GFS'S COLD ADVECTION IS STRONGER THAN THE NAM'S ON 
TUESDAY.  IN THE MOUNTAINS...THE RIDGE TOP FLOW IS SOUTHWESTERLY 
MONDAY AND MONDAY NIGHT...AND IT'S PRETTY WEAK TO BOOT.  WILL GO 
WITH "LIKELY"S THROUGH MUCH OF MONDAY NIGHT.  FOR THE REST OF MONDAY 
NIGHT AND TUESDAY...THERE IS SOME COOLER AIR COMING IN...THE BEST 
UPWARD MOTION...AND SLIGHTLY BETTER MOUNTAIN TOP FLOW.  WILL UP THE 
POPS TO 80%S.  TOTAL AMOUNTS DON'T LOOK GREAT...BUT IT WILL SNOW.  
NO HIGHLIGHTS YET...MAYBE AN ADVISORY LATTER.  FOR THE PLAINS...THE 
MOISTURE IS NOT GREAT WITH THE DOWNSLOPING ABOVE 800MB-750MB...AND 
THE BIT OF WARMING.  WILL GO WITH "SLIGHT CHANCE" ALL DAY 
MONDAY...THEN UP THINGS A BIT IN THE EVENING.  BY EARLY TUESDAY 
MORNING WILL GO WITH "LIKELY'S FOR THE PLAINS.  AMOUNTS DO NOT LOOK 
GREAT RIGHT NOW...BUT IT WILL SNOW.  FOR TEMPERATURES...MONDAY'S 
HIGHS ARE EXPECTED TO WARM 1.0-2.5 C FROM TODAY'S HIGHS.  TUESDAY'S 
HIGHS COOL OFF 2-5 C FROM MONDAY'S...MORE SO ON THE GFS.  FOR THE 
LATER DAYS...WEDNESDAY THROUGH SATURDAY...MODELS HAVE THE LARGE MEAN 
TROUGH MOVING ACROSS THE FORECAST AREA WEDNESDAY...WITH STRONG 
NORTHWESTERLY FLOW ALOFT WEDNESDAY NIGHT.  STRONG ZONAL FLOW EARLY 
THURSDAY DECREASES SOMEWHAT THE REST OF THE DAY THROUGH FRIDAY.  FOR 
FRIDAY NIGHT AND SATURDAY...STRONG WEST-NORTHWESTERLY FLOW ALOFT 
RETURNS TO THE FORECAST AREA.  THE PLAINS ARE DRY THROUGH THE 
PERIOD...WITH BELOW NORMAL TEMPERATURES.  PERHAPS GETTING CLOSE TO 
NORMALS SATURDAY.  THE MOUNTAINS DRY OUT QUITE A BIT BY WEDNESDAY 
NIGHT...BUT MOISTEN UP AGAIN BY FRIDAY NIGHT AND SATURDAY.  WILL 
KEEP SOME POPS GOING IN THE MOUNTAINS THROUGHOUT.

&&

.AVIATION...SNOW WILL CONTINUE INTO THIS AFTERNOON IN THE DENVER 
AREA...THEN DIMINISH. IFR CONDITIONS ARE EXPECTED WITH PERIODS OF 
LIFR POSSIBLE MOST OF THE DAY. VISIBILITIES WILL IMPROVE THIS 
EVENING BUT MVFR CEILINGS ARE STILL EXPECTED. 

&&

.BOU WATCHES/WARNINGS/ADVISORIES...WINTER WEATHER ADVISORY THROUGH 
      8 PM MOUNTAINS...FOOTHILLS...AND ADJACENT PLAINS...ZONES 31..
      33>36..38>41 AND 43.

$$

GIMMESTAD/KOOPMEINERS