FXUS65 KBOU 222151
AFDBOU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER CO
250 PM MST TUE DEC 22 2009
.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...SNOW IS EXPECTED TO START AT DIA AROUND 02Z THIS
EVENING. CEILINGS SHOULD GET BELOW 1000 FEET MSL BY 04Z THIS
EVENING AND STAY THAT WAY THROUGH WEDNESDAY. VISIBILITIES SHOULD
GET BELOW 2 MILES ABOUT 04Z TONIGHT AND STAY THAT WAY THROUGH
WEDNESDAY. PERIODS OF VISIBILITIES BELOW 1 MILE CAN BE EXPECTED
FROM 06Z TONIGHT THROUGH 18Z WEDNESDAY.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...WINTER STORM WARNING FOR THE
FAR EASTERN PLAINS TONIGHT THROUGH THURSDAY...ZONES 46..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>45..AND 47.
$$
RJK/CMG
