FXUS65 KBOU 051118
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
415 AM MST SAT DEC 5 2009

.SHORT TERM...UPPER TROUGH OVER THE NORTHERN ROCKIES WILL SAG INTO 
COLORADO BY TONIGHT. WEAK LIFT WILL SPREAD ACROSS OUR AREA 
TODAY...BUT THE LOW LEVEL AIR WILL REMAIN QUITE DRY. SURFACE 
PRESSURE FALLS WILL CREATE A LOW OVER SOUTHEASTERN COLORADO AND PULL 
A WEAK BOUNDARY SOUTHWARD FROM WYOMING WITH BETTER LOW LEVEL 
MOISTURE BEHIND IT. SOME HIGH CLOUDS ALREADY MAINLY OVER THE SOUTH 
PART OF THE AREA...BUT ANY MORE INCREASE WILL LIKELY WAIT UNTIL LATE 
TODAY. TEMPERATURES ARE ALREADY MILD ALONG THE FOOTHILLS AND SHALLOW 
INVERSIONS SHOULD MIX OUT IN MOST PLACES THIS MORNING...BUT THEN 
COLD ADVECTION WILL BE INCREASING AND TEMPERATURES SHOULD FALL THIS 
AFTERNOON ESPECIALLY IN THE NORTHERN PART OF THE AREA. 

FOR TONIGHT...STILL JUST A GRADUAL INCREASE IN LIFT BUT WE WILL 
LIKELY BE CLOUDING UP AND TRYING TO SNOW. THEN MUCH STRONGER FORCING 
ARRIVES BEFORE MORNING. WHILE LOW LEVEL FORCING IS LIMITED...THERE 
IS GOOD LIFT IN MOIST AND NOT TOO STABLE AIR ABOVE THE COLD DOME...
SO WE SHOULD GET DECENT VERTICAL MOTION. ONLY NEGATIVE I SEE IS THE 
LIMITED MOISTURE DUE TO THE COLD TEMPERATURES. GIVEN THAT THE SNOW 
MAY NOT START IN EARNEST UNTIL AFTER MIDNIGHT...I LIMITED AMOUNTS TO 
AN INCH OR TWO WITH A BIT MORE IN THE FRONT RANGE MOUNTAINS. 
TEMPERATURES MAY ALSO BOTTOM OUT THIS EVENING IN SOME PLACES AND 
THEN RECOVER AS THE ENVIRONMENT MOISTENS.

.LONG TERM...MODELS KEEP A MEAN TROUGH OVER A GOOD PORTION OF NORTH 
AMERICA WELL INTO THE EXTENDED PERIOD...WITH OUR FORECAST AREA IN 
COLD AIR.  AT 12Z SUNDAY MORNING...MODELS SHOW TWO UPPER CLOSED 
LOWS...ONE OVER THE CENTRAL OREGON COAST...THE OTHER OVER NORTHERN 
UTAH.  THE TWO LOWS CONGEAL INTO ONE OVER NORTHERN CALIFORNIA/EAST 
CENTRAL OREGON BY 12Z MONDAY MORNING.  BY TUESDAY MORNING AT 
12Z...THERE IS AN OPEN TROUGH DIGGING DOWN INTO THE GREAT BASIN TO 
FOUR CORNERS AREA.   THE FLOW ALOFT IS BRISK SOUTHWESTERLY SUNDAY 
MORNING...MORE ZONAL BY AFTERNOON AND BEYOND.  BY 03Z-06Z SUNDAY 
NIGHT A DECENT DUE WESTERLY JET MAXIMUM MIGRATES NORTHWARD ACROSS 
THE FORECAST AREA.  BY MONDAY 18Z...THE FLOW BECOMES SOUTHWESTERLY 
AGAIN WITH ANOTHER JET MAXIMUM ACROSS THE FORECAST AREA THROUGH 06Z 
MONDAY NIGHT.  THE BOUNDARY LAYER FLOW IS ALL EAST-NORTHEASTERLY 
UPSLOPE...NEARLY TO THE DIVIDE...SUNDAY THROUGH MONDAY MORNING.  IT 
BECOMES MORE SOUTHEASTERLY ON THE PLAINS MONDAY IN THE DAY... 
TRANSITIONING TO MORE STANDARD UPSLOPE BY TUESDAY AS A SURFACE 
CYCLONE DEVELOPS OVER SOUTHEASTERN COLORADO.  FOR SYNOPTIC SCALE 
ENERGY...THERE IS STRONG UPWARD MOTION PROGGED SUNDAY MORNING...THEN 
DOWNWARD MOTION IN THE AFTERNOON.  BY SUNDAY NIGHT LATE...WEAK 
UPWARD MOTION RETURNS TO THE FORECAST AREA INTO MONDAY...BEFORE 
BECOMING STRONG UPWARD AGAIN MONDAY NIGHT AND TUESDAY MORNING.   FOR 
MOISTURE...IT IS DEEP FOR ALL THE THE FORECAST AREA ALL DAY SUNDAY.  
SUNDAY NIGHT...BOTH MODELS HAVE SOME DRYING ABOVE 700 MB OVER THE 
PLAINS...BUT BELOW THAT IT STAYS SATURATED.  THE MOUNTAINS KEEP 
PRETTY DEEP MOISTURE SUNDAY NIGHT.  THE MOISTURE STAYS VERY DEEP 
OVER THE MOUNTAINS ON MONDAY INTO TUESDAY.  MOISTURE GETS PRETTY 
DEEP AGAIN OVER THE PLAINS BY MONDAY AFTERNOON CONTINUING MONDAY 
NIGHT.  THE GFS QPF FIELDS KEEP MEASURABLE SNOWFALL OVER ALL THE 
FORECAST AREA SUNDAY WELL INTO THE EXTENDED PERIOD...EXCEPT FOR THE 
FAR EASTERN PLAINS ZONES SUNDAY NIGHT ONLY.  THE NAM IS BIT TONED 
DOWN FROM THAT...HAVING NO QPF SUNDAY NIGHT AND MONDAY OVER THE FAR 
EAST.  THE NAM'S TOTAL AMOUNTS OF LIQUID ARE A BIT LESS THEN THE 
GFS' OVERALL.  I REALLY SEE NOTHING OBVIOUS TO PREVENT IT FROM 
SNOWING MUCH OF THE TIME SUNDAY THROUGH AT LEAST TUESDAY.   THERE IS 
MOISTURE...COLD AIR ADVECTION ...UPWARD VERTICAL VELOCITY... 
UPSLOPE...AND A JET OVER THE FORECAST AREA MUCH OF THE TIME.  THERE 
IS NOT A BUNCH OF AVAILABLE MOISTURE ACCORDING TO PRECIPITABLE WATER 
VALUES ON THE FORECAST SOUNDINGS...BUT YOU DON'T NEED MUCH WATER 
WITH THIS COLD OF AN AIRMASS IN PLACE.  WILL UP POPS A BIT SUNDAY 
...TAPPER THINGS OF BIT SUNDAY INTO MONDAY...THEN INCREASE POPS 
AGAIN BY MONDAY AFTERNOON INTO TUESDAY.  NO HIGHLIGHTS RIGHT NOW... 
NOT SURE IF AMOUNTS WARRANT IT JUST YET...AND IT MAY BE A BIT EARLY 
FOR AN ADVISORY.  FOR TEMPERATURES...SUNDAY'S HIGHS ARE 5-7 C 
COLDER THAN TODAY'S.  MONDAY'S HIGHS WARM UP 2-4 C FROM SUNDAY'S.  
FOR THE LATER DAYS...TUESDAY THROUGH FRIDAY...MODELS HAVE AN UPPER 
TROUGH MAKE IT ACROSS THE FORECAST AREA TUESDAY...WITH VERY STRONG 
WEST-NORTHWESTERLY FLOW ALOFT TUESDAY NIGHT THROUGH WEDNESDAY 
NIGHT.  BY THURSDAY THROUGH FRIDAY...THE FLOW ALOFT IS DUE WESTERLY 
AND DECREASING SIGNIFICANTLY.  MOISTURE IS PRETTY GOOD IN THE 
MOUNTAINS THROUGHOUT.  WILL MAINLY KEEP "CHANCES" GOING FOR SNOW 
THERE.   TEMPERATURES LOOK THE COLDEST YET THIS WINTER FOR TUESDAY'S 
HIGHS.  WEDNESDAY IS QUITE BELOW NORMAL TOO.  THURSDAY AND FRIDAY 
MODERATE SOMEWHAT...BUT READINGS ARE STILL BELOW SEASONAL NORMALS.  

&&

.AVIATION...EXPECTING LOWER CLOUDS TO DEVELOP IN THE LATE AFTERNOON 
OR EARLY EVENING HOURS WITH SNOW BEGINNING IN THE LATE EVENING. IFR 
CONDITIONS ARE LIKELY AFTER MIDNIGHT...AND WILL LIKELY CONTINUE 
THROUGH SUNDAY.

&&

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

$$
GIMMESTAD/RJK