Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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000
FXUS65 KBOU 222200
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
300 PM MST MON DEC 22 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 300 PM MST MON DEC 22 2014

A 150 PLUS KNOT JET OVER THE GREAT BASIN AND FOUR CORNERS IS HELPING
TO PRODUCE SNOW BANDS ACROSS COLORADO. STILL WIDESPREAD SNOW ONGOING
IN THE MOUNTAINS DUE TO OROGRAPHIC LIFT AND THE JET. FAVORED
LOCATIONS ARE STILL SEEING MODERATE TO OCCASIONALLY HEAVY SNOW.
PROTECTED LOCATIONS ARE JUST SEEING LIGHT SNOW AT TIMES. EXPECT
WIDESPREAD SNOW TO CONTINUE THROUGH THE EVENING AND THEN DECREASE
OVERNIGHT. WILL KEEP THE WARNINGS AND ADVISORIES GOING THROUGH
MIDNIGHT.

THESE SNOW BANDS HAVE MOVED ONTO THE FRONT RANGE. A FEW AREAS WILL
SEE A BRIEF PERIOD OF HEAVY SNOW. IN GENERAL...ACCUMULATION WILL BE
LESS THAN AN INCH THROUGH THE EVENING...THOUGH ISOLATED LOCATIONS
COULD SEE A LITTLE MORE THAN AN INCH ON GRASSY SURFACES.

NEXT CONCERN IS STRONG WINDS OVER THE EASTERN PLAINS. MODELS SHOWING
AREAS FROM SIDNEY TO LIMON MIXING 50 PLUS KNOT WINDS DOWN TO THE
SURFACE. SOME QUESTION AS TO HOW FAR WEST THE STRONG WINDS WILL
MAKE...SO LEFT A HIGH WATCH FOR THE WEST PART FOR THESE AREAS AND
UPGRADE THE REST OF THE EASTERN PLAINS TO A HIGH WIND WARNING. MOST
MODELS SHOWING SNOW SHOWERS FORMING LATE TONIGHT AND TUESDAY MORNING
OVER THE PLAINS. IF ENOUGH SNOW FALLS...BLOWING SNOW COULD PRODUCE
VISIBILITY TO NEAR ZERO. WENT WITH LIKELY POPS FOR THIS...THOUGH
STILL UNSURE IF ENOUGH SNOW WILL FALL TO PRODUCE WHITE OUT
CONDITIONS. MENTIONED THE POTENTIAL FOR WHITE OUT CONDITIONS IN THE
HIGH WIND WARNING.

THE WINDS WILL DECREASE DURING THE AFTERNOON HOURS AS WINDS ALOFT
AND THE PRESSURE GRADIENT SLACKENS. HIGH TEMPERATURES WILL BE
SLIGHTLY COOLER TUESDAY. THERE WILL BE ENOUGH MOISTURE AND
OROGRAPHIC LIFT OVER THE MOUNTAINS FOR POCKETS OF LIGHT SNOW. ANY
ADDITIONAL ACCUMULATION ON TUESDAY SHOULD BE LIGHT AND LESS THAN 3
INCHES.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 300 PM MST MON DEC 22 2014

HIGH AMPLITUDE RIDGE/TROUGH WAVE TRAIN MIGRATING ACROSS
THE CONUS HAS NERN COLORADO UNDER STRONG NORTHERLY FLOW ALOFT
TUESDAY NIGHT IN ADVANCE OF AN UPPER RIDGE BUILDING OVER THE
INTERMOUNTAIN REGION. MODEL CROSS SECTIONS AND SOUNDINGS INDICATE A
SWIFT DECOUPLING OF THE STRONG FLOW ALOFT FROM THE BNDRY LAYER
RESULTING IN A EQUALLY FAST REDUCTION IN WIND SPEEDS ON THE PLAINS.
AS WINDS DECREASE SO WILL SFC-500MB SPECIFIC HUMIDITIES AS DRIER AIR
ADVECTS DOWN FROM WYOMING...RESULTING IN CLEARING FROM NORTH TO
SOUTH OVERNIGHT. OVERNIGHT TEMPS FORECASTED TO BE 3-4C LOWER THAN
THOSE THE NIGHT BEFORE.

WEDNESDAY...WESTERN UPPER RIDGE SHIFTS EAST OVER THE ROCKY MTN
REGION DURING THE DAY RESULTING IN A 4-5C WARMUP ACROSS THE FCST
AREA. WINDS ALSO LIGHT AND SKIES MOSTLY CLEAR.

WEDNESDAY NIGHT AND CHRISTMAS DAY...MODELS SHOW THE UPPER RIDGE
FLATTENING AS IT TRACKS SOUTHEAST AWAY FROM COLORADO. UPSTREAM
HEIGHT FALLS IN RESPONSE TO STRONG COOLING ALOFT OVER THE PACIFIC
NORTHWEST AND STRONG JET DRIVING DOWN ACROSS NORTHERN CALIFORNIA.
MODELS SHOW THE RESULTANT UPPER TROUGH SWINGING EASTWARD OVER THE
NORTHERN AND CENTRAL GREAT BASIN WEDNESDAY NIGHT WITH THE ECMWF
INDICATING LOWER HEIGHTS AND A MORE SOUTHERLY TRACK TO THIS TROUGH.
FOR CHRISTMAS DAY...LAST COUPLE MODEL RUNS HAVE COME INTO BETTER
AGREEMENT WITH THIS SYSTEM. THE GFS...ECMWF AND NAM SHOW THE 500 MB
TROUGH AXIS OVER CENTRAL UTAH AT 18Z/THURSDAY AND A DRY AND
RELATIVELY WARM SWLY MEAN LAYER FLOW OVER EASTERN COLORADO. THIS
SAME FLOW ADVECTS A DECENT AMOUNT OF MOISTURE OVER WRN COLORADO AND
UP WEST FACING MTN SLOPES DURING THE DAY RESULTING IN SCATTERED TO
NUMEROUS RAIN AND SNOW SHOWERS BY AFTERNOON AS IT LOOKS NOW.
MEANWHILE MODELS ALSO INDICATE GUSTY WEST-SOUTHWEST WINDS ON THE
PLAINS AND PALMER DIVIDE RESULTING IN ANOTHER DAY OF DRY AND MILD
CONDITIONS UNDER CLEAR/PARTLY CLOUDY SKIES.

THURSDAY NIGHT...MODELS SHOW THE UPPER TROUGH PASSING OVERHEAD AND
WITH ITS PASSAGE A COLD FRONT DRIVES SOUTH OUT OF SERN WYOMING.
INCREASING LOW-LEVEL MOISTURE COUPLED WITH MID-LEVEL LIFT AND
INSTABILITY POINTS TO A RAPID DEVELOPMENT OF CLOUDS...GUSTY
NORTHERLY WINDS AND AN INCREASE IN SNOW CHANCES ACROSS THE PLAINS
AND FRONT RANGE DURING THE EVENING HOURS. AT THIS TIME...WILL GO
WITH HIGH SCATTERED POPS ON THE PLAINS AND PALMER DIVIDE THURSDAY
NIGHT WITH LIGHT SNOW ACCUMULATION SCATTERED ABOUT. IN THE HIGH
COUNTRY...LIGHT TO MODERATE SNOWFALL CONTINUES WITH ONGOING COLD
ADVECTION. WINDS DO NOT APPEAR TO BE A BIG CONCERN IN THE HIGH
COUNTRY WITH THIS STORM SYSTEM. LATER SHIFTS MAY FIND IT NECESSARY
TO ISSUE A WINTER WEATHER ADVISORY FOR THE HIGH ELEVATIONS.

ON FRIDAY...MEDIUM RANGE MODELS SHOW THE UPPER TROUGH WITH ITS COLD
AIR AND MOISTURE STILL INFLUENCING THE REGION. FRIDAY WILL MOST
LIKELY BE THE COLDEST DAY OF THE WEEK WITH CONSIDERABLE CLOUD COVER
AND COLD NORTHERLY WINDS AROUND. SHOULD SEE LIGHT SNOWFALL IN THE
HIGH COUNTRY LINGERING THROUGH EARLY AFTERNOON AS IT LOOKS NOW...
AND A FEW LIGHT MORNING SNOW SHOWERS ON THE PLAINS. MODELS SHOW THIS
TROUGH AND ITS WEATHER SHIFTING EAST OF THE FCST AREA FRIDAY
AFTERNOON AND EVENING WITH GRADUAL CLEARING OVERNIGHT.

FOR THE WEEKEND...FLAT UPPER RIDGE SUPPOSEDLY MOVES ACROSS THE
REGION RETURNING TEMPERATURES TO NEAR AVERAGE AND PROVIDING DRY
CONDITIONS ON SATURDAY. FOR SUNDAY...MODELS HINT AT ANOTHER SYSTEM
SWINGING DOWN FROM THE PAC NORTHWEST WITH THE GFS FASTER THAN THE
ECMWF. AT MOST...COULD SEE SNOW SHOWERS RETURNING THE HIGH
COUNTRY... WITH DRY DOWNSLOPE EAST OF THE MTNS.

&&

.AVIATION...(FOR THE TAFS THROUGH 00Z TUESDAY LATE AFTERNOON)
ISSUED AT 300 PM MST MON DEC 22 2014

SNOW BANDS WILL LINGER UNTIL AROUND 00Z AT KDEN...AND UP TO 02Z AT
KBJC AND KAPA. THE MODERATE TO HEAVY SNOW WILL BE SHORT LIVED WITH
SNOWFALL AMOUNTS UP TO AN INCH. CEILINGS MAY BRIEFLY FALL BELOW 2000
FEET WITH A QUARTER MILE VISIBILITY.

NORTHERLY WINDS MAY DECREASE BETWEEN 00-06Z...BUT WILL THEN INCREASE
OVERNIGHT WITH GUSTS TO 40 KNOTS POSSIBLE AT KDEN FROM 08Z TO 18Z.
WINDS WILL SLOWLY DECREASE TUESDAY AFTERNOON. THERE WILL BE A SLIGHT
CHANCE FOR SNOW AT KDEN AFTER 08Z...THOUGH THE BEST CHANCE WILL
REMAIN OVER THE EASTERN PLAINS.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 2 AM TO 1 PM MST TUESDAY FOR COZ042-044-
046>051.

WINTER STORM WARNING UNTIL MIDNIGHT MST TONIGHT FOR COZ031>034.

WINTER WEATHER ADVISORY UNTIL MIDNIGHT MST TONIGHT FOR COZ030.

HIGH WIND WATCH FROM 2 AM MST TUESDAY THROUGH TUESDAY AFTERNOON
FOR COZ038-041-043-045.

&&

$$

SHORT TERM...MEIER
LONG TERM...BAKER
AVIATION...MEIER



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