FXUS65 KBOU 230310 AAA
AFDBOU

AREA FORECAST DISCUSSION...UPDATE...
NATIONAL WEATHER SERVICE DENVER CO
805 PM MST TUE DEC 22 2009

.UPDATE...AS EXPECTED LATEST RUC/00Z NAM STILL SHOWING A SIGNIFICANT 
DRY MID LEVEL LAYER ACROSS THE FAR NERN PLAINS FOR MUCH OF TONIGHT. 
THIS SEEMS REASONABLE GIVEN 00Z SOUNDINGS AT LBF AND DDC AND SERLY 
STEERING FLOW. THERE MAY BE CONTINUED AREAS OF FOG/FREEZING DRIZZLE 
FOR THE NIGHT BUT NONE OF THE OBS ARE CURRENTLY SHOWING ANY DRIZZLE. 
HAVE DECIDED TO DELAY THE WINTER STORM WARNING UNTIL 12Z WHICH MAY 
STILL BE TOO EARLY. DON'T THINK THE FREEZING DRIZZLE WILL BE 
WIDESPREAD ENOUGH TO HAVE A SEPARATE ADVISORY AND CONFUSE THE ISSUE 
WITH THE LOOMING WINTER STORM WARNING. HATE TO KILL IT ALTOGETHER AS 
THE WINDS WILL BE PICKING UP WED AFTN/EVENING...BUT THE ACTUAL 
SNOWFALL WILL PROBABLY REMAIN IN ADVISORY CATEGORY.  WILL WORD THE 
WSW FOR THE MAIN SNOW IMPACT ON WEDNESDAY ON THE PLAINS AND A LESSER 
IMPACT TONIGHT FOR FOG/DRIZZLE. 

LIGHT SNOWFALL CONTINUES TO DEVELOP FURTHER WEST INTO THE FRONT 
RANGE AND ONGOING ADVISORIES SEEM ON TRACK. THE MOUNTAIN ADVISORIES 
BE BE A BIT OVERDONE BUT IT WILL STILL SNOW LIGHTLY. NO OTHER 
CHANGES PLANNED. 

.SHORT TERM...SATELLITE AND RADAR PICTURES INDICATE NO SNOW FALLING 
OVER THE FORECAST AREA YET.  IT IS FALLING IMMEDIATELY UPSTREAM 
HOWEVER.  IT APPEARS THE UPPER LEVEL CIRCULATION IS OVER THE 
SOUTHERN TIP OF NEVADA RIGHT NOW.  MODELS SHOW THAT CIRCULATION OVER 
WEST CENTRAL NEW MEXICO AT 12Z WEDNESDAY MORNING...THEN OVER THE 
TEXAS PANHANDLE AT 00Z TOMORROW LATE AFTERNOON.  THE UPPER TROUGH IS 
OVER THE FORECAST AREA THE ENTIRE TIME OF THESE FIRST TWO PERIODS 
...WITH WEAK FLOW ALOFT.  THE SYNOPTIC SCALE ENERGY IS PROGGED TO BE 
ALL UPWARD MOTION TONIGHT AND WEDNESDAY.  THE BOUNDARY LAYER FLOW IS 
PROGGED TO BE EASTERLY OVERNIGHT...THEN NORTH-NORTHEASTERLY ON 
WEDNESDAY.  WIND SPEEDS ARE NOT SIGNIFICANT DURING EITHER PERIOD.  
THE UPSLOPE GETS REAL DEEP AFTER 09Z TONIGHT.  CROSS SECTIONS SHOW 
DEEP MOISTURE FOR ALL THE FORECAST AREA TONIGHT AND WEDNESDAY.   THE 
QPF FIELDS FROM THE GFS AND NAM BOTH SHOW A FAIRLY DECENT AMOUNT OF 
PRECIPITATION OVERNIGHT AND WEDNESDAY.  THEY ARE BOTH PRETTY CLOSE 
IN AMOUNTS ON THEIR SNOWFALL ACCUMULATIONS.  WILL KEEP IN AND/OR GO 
WITH 100% POPS IN MOST ZONES FOR BOTH PERIODS.  WILL LET ALL THE 
HIGHLIGHTS RIDE AS IS.  FOR TEMPERATURES...WEDNESDAY'S HIGHS ARE 3-6 
C COLDER THAN THIS AFTERNOON'S.

.LONG TERM...STILL SOME LOOSE ENDS ABOUT THE DEPARTURE OF THE STORM 
AS MODELS VACILLATE ON THE DETAILS OF THE SYSTEM TO OUR EAST ON 
THURSDAY AND FRIDAY. WE WILL ONLY HAVE WEAK LIFT...AND MAYBE NOT AT 
ALL IN THE WEST PART OF THE AREA...AND ALSO DECREASING LOW LEVEL 
MOISTURE FROM THE WEST. BUT THE AMOUNT OF LIFT AND THE DEGREE OF 
DRYING IS STILL UNCERTAIN. STILL POTENTIAL FOR SOME INCREASE IN LIFT 
OVER THE NORTHEAST CORNER EARLY FRIDAY AS SOME WARM ADVECTION KICKS 
IN ON THE BACKSIDE OF THE LOW. QPF ON WEDNESDAY NIGHT SEEMS A BIT 
LOW AS THERE WILL STILL BE SOME WEAK LIFT AND UPSLOPE ON THE PALMER 
DIVIDE...WITH THE EXCEPTION OF AREAS NEAR THE CHEYENNE RIDGE. FOR 
THURSDAY AND FRIDAY THERE MAY STILL BE SOME LIGHT SNOW BUT THE MAIN 
STORY WILL BE THE WIND. GUSTS IN THE 30-45 MPH RANGE LOOK PROBABLE 
ON THE PLAINS THURSDAY...AND WHILE THE LOW LEVEL GRADIENT MAY START 
TO RELAX ON FRIDAY THE UPPER LEVEL WINDS WILL BE STRONGER SO THE 
SURFACE WIND MAY NOT BE MUCH LESS. WITH 700 MB WINDS NNW AT ABOUT 40 
KNOTS THE MOUNTAINS WILL HAVE PLENTY OF BLOWING SNOW AND VERY COLD 
WIND CHILLS ON FRIDAY. NEAR BLIZZARD CONDITIONS WILL LIKELY CONTINUE 
ON THE PLAINS AFTER THE SNOW ENDS...THOUGH THINGS SHOULD BE A BIT 
BETTER THURSDAY NIGHT AND FRIDAY. ENDING THE WINTER STORM WARNING 
THURSDAY AFTERNOON STILL A GOOD ESTIMATE...THOUGH WE MAY NEED TO 
DEAL WITH SOME BLOWING SNOW PROBLEMS AFTER THAT.

BETTER AGREEMENT NOW ON NORTHERLY FLOW SATURDAY THEN A RIDGE IN THE 
SOUTHERN STREAM SUNDAY. SOME WARMING OVER THE WEEKEND...PROBABLY 
MORE ALOFT THAN AT THE SURFACE...AND A DRY PERIOD. SOME COLD TEMPS 
ESPECIALLY IN THE MOUNTAIN VALLEYS AS THERE SHOULD BE A CLEAR 
NIGHT...AND THE COMBINATION OF COLD NIGHTS...SHORT DAYS...AND SNOW 
COVER WILL LIMIT SURFACE WARMING. WE MAY NEED A COLDER NIGHT OR TWO 
ON THE PLAINS AS WELL. ALSO BETTER AGREEMENT ON A SOUTHERN STREAM 
SYSTEM APPROACHING THOUGH CONSENSUS IS A LITTLE SLOWER THAN 
YESTERDAY WITH CYCLOGENESIS EAST OF THE SOUTHERN ROCKIES ABOUT 
TUESDAY. WILL KEEP LOW POPS IN THE MOUNTAINS MONDAY AND INTRODUCE 
THEM TO THE PLAINS TUESDAY.

&&

.AVIATION...UPDATE...WEAK DENVER CYCLONE ONGOING WITH MODEST SE 
WINDS CONTINUING AT KDEN. -SN HAS ALREADY BEGUN AT BJC/APA AND DEN 
WILL BE THE LAST TO START SNOWING DUE TO THE DOWNSLOPE SERLY WINDS. 
EVENTUALLY THIS WILL FILL INTO DEN BETWEEN 04-05Z. MORE WIDESPREAD 
SNOW EXPECTED STILL AFTER 06Z WHILE CEILINGS CONTINUE TO SLOWLY 
LOWER THRU THE EVENING.  

&&

.BOU WATCHES/WARNINGS/ADVISORIES...WINTER STORM WARNING FOR THE      
   FAR EASTERN PLAINS WEDNESDAY THROUGH THURSDAY...ZONES 48>51.       
  WINTER WEATHER ADVISORY FOR THE MOUNTAINS...FOOTHILLS...FRONT      
   RANGE URBAN CORRIDOR...AND REST OF THE EASTERN PLAINS             
   TONIGHT THROUGH WEDNESDAY NIGHT...ZONES 33>47.

$$

ENTREKIN/RJK/CMG