FXUS65 KBOU 011053
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
350 AM MST TUE DEC 01 2009

.SHORT TERM...REASONING FROM THE PREVIOUS DISCUSSION IS STILL 
VALID.  A NICE PRESSURE SURGE DEVELOPED OVER MONTANA LAST EVENING 
AND IS NOW BEGINNING ITS SOUTHEASTWARD MARCH.  STATIONS IN NORTHERN 
WYOMING HAVE NOT SHOWN ANY WIND SHIFTS YET...BUT THESE SHOULD SHOW 
UP IN THE NEXT COUPLE HOURS.  COLD FRONT SHOULD STILL GET INTO 
NORTHEAST COLORADO SOMETIME IN THE EARLY TO MID-AFTERNOON WITH LIGHT 
TO MODERATE POST-FRONTAL NORTHERLY WINDS CONTINUING THROUGH THE 
EVENING.  WITH THE AIRMASS STARTING OUT QUITE DRY...IT WILL TAKE 
AWHILE FOR CLOUDS TO DEVELOP BEHIND THE FRONT.  SNOW IS STILL 
EXPECTED TO BEGIN IN EARNEST AFTER THE SUN GOES DOWN.  TEMPERATURES 
BEHIND THE FRONT ARE FORECAST TO TUMBLE INTO THE TEENS BY WEDNESDAY 
MORNING...SO THE SNOW THAT FALLS SHOULD BE DRY AND POWDERY RATHER 
THAN WET AND SLOPPY.  MODEL SOUNDINGS SHOW THAT BY 06Z THERE WILL BE 
A STRONG FRONTAL INVERSION ON TOP OF THE INCOMING AIRMASS THAT WILL 
PERSIST THROUGH 12Z.  THIS WILL HELP LIMIT THE SNOW CRYSTAL 
DEVELOPMENT REGION TO THE LOWEST 5000 FEET.  THIS ALSO POINTS TO 
ONLY LIGHT ACCUMULATION RATES.  GIVEN THESE FACTORS AND MODEL QPF 
FIELDS SHOWING LIQUID AMOUNTS ONLY AROUND .10 INCHES MAKES IT SEEM 
LIKELY THAT ACCUMULATIONS THROUGH WEDNESDAY MORNING SHOULD BE LESS 
THAN 2 INCHES ON THE PLAINS AND MAYBE 3-4 INCHES IN THE FOOTHILLS.  
NO HIGHLIGHTS WILL BE NEEDED FOR THIS EPISODE.  WITH ALL THE COLD 
AIR ADVERTISED FOR THE LATTER HALF OF THE WEEK...ONE WOULD DO WELL 
TO MAKE THE MOST OF THE SEASONAL TEMPERATURES WE WILL HAVE THIS 
AFTERNOON.  

.LONG TERM...COLDER AIR WILL CONTINUE TO ADVECT INTO THE AREA ON WED 
BEHIND COLD FRONT.  MEANWHILE AN  UPPER LEVEL TROUGH WILL SWING 
ACROSS THE AREA AS WELL.  BOTH NAM AND GFS SHOW FAVORABLE UPSLOPE 
FLOW AONG THE FRONT RANGE THRU WED AFTN WITH BOTH SHOWING SOME MINOR 
QG ASCENT AND QG VERTICAL VELOCITIES AS WELL.  WILL BUMP POPS UP TO 
LIKELY IN THE FOOTHILLS AND URBAN CORRIDOR THRU MIDDAY.  SNOW 
AMOUNTS WILL BE LIGHT WITH AN ADDITIONAL INCH OR TWO POSSIBLE.  IN 
THE MTNS OROGRAPHICS WILL BE RATHER WEAK HOWEVER WITH FAVORABLE 
LAPSE RATES WILL MENTION SCT -SHSN THRU WED NIGHT.  HIGHS ON WED 
WILL BE MUCH COLDER WITH READINGS ONLY IN THE 20S ACROSS MOST OF THE 
PLAINS.  FOR TUE NIGHT WEAK UPSLOPE FLOW WILL PERSIST IN AND NR THE 
FOOTHILLS SO COULD STILL SEE SOME VERY LIGHT SNOW OVERNIGHT SO WILL 
MENTION SOME LOW POPS.  LOWS WED NIGHT MAY DROP INTO THE SINGLE 
DIGITS OVER NERN CO.  FOR THU NW FLOW ALOFT WILL REMAIN OVER THE 
AREA AS ANOTHER WEAK DISTURBANCE MOVS ACROSS THE AREA.  ANOTHER 
MINOR SURGE OF SLIGHTLY COLDER AIR MAY MOVE INTO NERN CO WHICH WILL 
KEEP WEAK UPSLOPE FLOW IN PLACE.  LAPSE RATES WILL IMPROVE ON THU 
WITH SOME MINOR QG VERTICAL VELOCITIES SO COULD SEE SOME LIGHT SNOW 
ONCE AGAIN IN AND NR THE FOOTHILLS.  IN THE MTNS OROGRAPHICS WILL 
REMAIN WEAK HOWEVER LINGERING MOISTURE AND DECENT LAPSE RATES SHOULD 
PRODUCE SOME -SHSN.  HIGHS ON THU WILL REMAIN COLD WITH READINGS 
ONCE AGAIN STAYING IN THE 20S OVER NERN CO.                

BY FRI THE FLOW ALOFT WILL BECOME MORE NNW WITH MOISTURE GRADUALLY 
DECREASING SO PCPN CHANCES WILL BE LOW.  TEMPS MAY BEGIN TO MODERATE 
SOME AS DOWNSLOPE LOW LEVEL FLOW BEGINS TO DVLP IN THE FOOTHILLS.  
FOR NOW WILL KEEP TEMPS IN THE LOWER TO MID 30S OVER THE PLAINS.  BY 
THE WEEKEND THE LONGER RANGE MODELS SHOW VARYING SOLUTIONS.  THE GFS 
SHOWS A MORE DEFINED UPPER LEVEL TROUGH DEVELOPING OVER THE NRN AND 
CNTRL ROCKIES BY SUN WITH ANOTHER SURGE OF COLDER AIR MOVING INTO 
NRN CO SAT AFTN OR NIGHT WITH A GOOD CHC OF PCPN SAT NIGHT INTO 
SUN.  MEANWHILE THE ECMWF HAS AN ALONGATED TROUGH FROM OFF THE 
PACIFIC NW INTO THE NRN ROCKIES WITH ZONAL FLOW ALOFT OVER NRN CO.  
HOWEVER IT DOES SHOW ANOTHER COLD FRONT MOVING INTO NRN CO ON SUN 
WITH SOME LIGHT PCPN POSSIBLE.  AT THIS TIME SEE NO REASON TO ALTER 
FCST FOR SAT/SUN DUE TO MODELS SHOWING VARYING SOLUTIONS.       

&&

.AVIATION...THE COLD FRONT SHOULD PASS THROUGH DENVER BETWEEN 18Z 
AND 21Z FOLLOWED BY NORTH TO NORTHEAST WINDS GUSTING TO AROUND 20 
KNOTS.  CLOUD DEVELOPMENT WILL BE SLOW BEHIND THE FRONT.  INSTRUMENT 
APPROACHES MAY BE NEEDED IN THE LATE AFTERNOON...BUT MORE LIKELY 
WILL WAIT UNTIL EVENING.  LIGHT SNOW IS LIKELY OVERNIGHT WITH 
ACCUMULATIONS LESS THAN TWO INCHES BY WEDNESDAY MORNING.  ADDITIONAL 
LIGHT SNOW WILL FALL THROUGH MIDDAY WEDNESDAY AND THEN TAPER OFF.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...NONE. 

$$

KDRBY/RPK