Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 182046
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
146 PM MST THU DEC 18 2014

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 1231 PM MST THU DEC 18 2014

A WEAK UPPER LEVEL TROUGH WILL MAKES ITS WAY ACROSS NORTHERN CO
TONIGHT. NOT MUCH LIFT WITH THIS SYSTEM...BUT ENOUGH MOISTURE
COUPLED WITH WEAK FORCING ALOFT TO PRODUCE AREAS OF LIGHT SNOW IN
THE MOUNTAINS WITH LITTLE IF ANY ADDITIONAL ACCUMULATION. SPATIAL
CROSS-SECTIONS AND MDL QPF INDICATE DECREASING MOISTURE OVER THE
MOUNTAINS LATE TONIGHT AND FRIDAY MORNING WITH ANY LINGERING SNOW
DIMINISHING BY THAT TIME. ACROSS THE NERN PLAINS...WEAK PRESSURE
GRADIENT WILL ALLOW FOR LIGHT AND VARIABLE WINDS TONIGHT. BOUNDARY
LAYER RELATIVE HUMIDITIES WILL BE LOWER WHICH SHOULD NEGATE THE
DEVELOPMENT OF FOG...ALTHOUGH SOME PATCHY COVERAGE COULD OCCUR IN
LOW LYING AREAS. ON FRIDAY...A RIDGE OF HIGH PRESSURE WILL MOVE
INTO FROM THE WEST WITH A DRIER NORTHWESTERLY FLOW ALOFT OVER
COLORADO. TEMPERATURES WILL MODIFY SOMEWHAT OVER THE NORTHEAST
PLAINS BUT MIXING WILL BE LIMITED.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 1231 PM MST THU DEC 18 2014

...MOIST AND COLD IN THE LONG TERM WILL LEAD TO A GOOD POTENTIAL
FOR SNOW...

FRIDAY NIGHT INTO SATURDAY WILL SEE THE UPPER LEVEL
TROUGH MOVE EAST WITH NORTHWEST FLOW CONTINUING OVER COLORADO.
MODEL CROSS SECTIONS SHOW LOW LEVEL MOISTURE STICKING AROUND IN
THE HIGH COUNTRY SO WILL MAINTAIN SOME LIGHT POPS. LEE TROUGHING
WILL KEEP PRECIP OUT OF THE PLAINS WITH THE ONSET OF ANOTHER WEAK
UPPER LEVEL TROUGH THAT WILL CONTINUE LIGHT SNOW SHOWERS OVER THE
MOUNTAINS ON SATURDAY.

ON SUNDAY THE NORTHWESTERLY FLOW ALOFT WILL INCREASE. MOISTURE
OVER THE MOUNTAINS WILL INCREASE AS WELL WITH AN UPPER LEVEL JET
DROPPING OUT OF THE NORTH. BETTER CHANCES FOR MOUNTAIN SNOW SUNDAY
MORNING INTO THE AFTERNOON MOVING ONTO THE PLAINS BY SUNDAY
EVENING INTO MONDAY. TEMPERATURES ON SUNDAY WILL INCREASE INTO THE
50S PRIOR TO THE COOL AIR MOVING IN.

FOR SUNDAY EVENING INTO MONDAY THE MOIST NORTHWEST FLOW COMBINED
WITH THE UPPER LEVEL JET AND DECENT LAPSE RATES FROM 7-8 C/KM WILL
PROVIDE FOR A DECENT SNOW MAKER FOR THE NORTHERN MOUNTAINS. THE
ONLY ISSUE FOR SUNDAY NIGHT INTO MONDAY MORNING ARE THE TEMPERATURES.
MODELS ARE INDICATING THAT NORTHERN MOUNTAINS TO START WILL BE ON
THE WARMER SIDE OF THE JET WITH TEMPS IN THE 20S AT MOUNTAIN TOP.
THIS HAS STILL PROVEN TO PRODUCE DECENT AMOUNTS OF SNOW IN THE
PAST BUT COULD ALSO MEAN A MORE SLUSHY WET SNOW THAT WOULD NOT
ACCUMULATE AS MUCH OVERNIGHT. FOR MONDAY HOWEVER TEMPERATURES AT
700 MB COOL CONSIDERABLY INCREASING POTENTIAL FOR INCREASED SNOW
FALL. CURRENT MODELS ARE INDICATING 2 TO 3 INCHES OF WATER FOR THE
ENTIRETY OF THE STORM SUNDAY INTO TUESDAY...WHICH COULD EQUATE TO
POSSIBLE WATCH CRITERIA STARTING SUNDAY SO WILL BE KEEPING A CLOSE
EYE ON MODEL DEVELOPMENT. WINDS WILL INCREASE OVER THE MOUNTAINS
WITH THE PLACEMENT OF THE UPPER LEVEL JET. MODEL CROSS SECTIONS
ARE CURRENTLY INDICATING COMPONENT ALONG OF 60 TO 70 MPH AT
MOUNTAIN TOP MONDAY MORNING. THIS COMBINED WITH THE SNOWFALL OVER
THE MOUNTAINS COULD CREATE BLOWING SNOW AND REDUCED VISIBILITIES
FOR HOLIDAY AND WEEKEND TRAVELERS.

ON MONDAY THE MOIST NW FLOW COMBINED WITH THE JET AND LAPSE RATES
WILL BRING SOME LIGHT SNOW ACTIVITY TO THE NE PLAINS. THE EC HAS
THE BEST CHANCE EARLY MONDAY MORNING AND CONTINUES THROUGH THE DAY
WHILE THE GFS LAGS AND STARTS PRECIP IN THE AFTERNOON. KEPT THE
POPS IN THE 30 RANGE OVER THE PLAINS AS THE MODELS AND PLACEMENT
OF THE JET EVOLVE.

ON TUESDAY THE STRONG N TO NW FLOW ALOFT WILL CONTINUE AS THE JET
MOVES OFF TO THE EAST. CROSS SECTIONS SHOWING MOISTURE DECREASING
OVER THE PLAINS AS SURFACE HIGH PRESSURE BUILDS INTO CENTRAL
COLORADO FROM THE EAST. EC SHOWING SOME LIGHT SNOW IN THE
MOUNTAINS DUE MAINLY TO LINGERING MOISTURE IN THE MOUNTAINS AND
LAPSE RATES SITTING IN THE 8-9 C/KM RANGE. WILL KEEP POPS IN THE
HIGH COUNTRY FOR TUESDAY INTO WEDNESDAY. TEMPERATURES WILL DROP ON
TUESDAY AFTER THE COOLER AIR MOVES IN MONDAY WITH HIGHS OVER THE
PLAINS IN THE LOWER 40S.

FOR TUESDAY NIGHT INTO WEDNESDAY THE STRONG AND MOIST NW FLOW
ALOFT WILL CONTINUE. MOISTURE WILL INCREASE IN THE MOUNTAINS AND
PLAINS WEDNESDAY AFTERNOON WITH DECENT LAPSE RATES SO OROGRAPHIC
SNOW WILL CONTINUE TO ACCUMULATE OVER THE NORTHERN MOUNTAINS. WITH
THE JET DIPPING SOUTH AND INCREASED MOISTURE AHEAD OF THE NEXT
TROUGH KEPT POPS OVER THE PLAINS FOR WEDNESDAY WITH LIGHT
ACCUMULATION EXPECTED. TEMPERATURES WILL BE COOLER THAN NORMAL
WITH HIGHS OVER THE FRONT RANGE IN THE UPPER 30S.

THE BIG STORY HOWEVER IS WILL IT SNOW ON CHRISTMAS...

CURRENT MODEL RUNS ARE CONTINUING TO INDICATE A VERY GOOD CHANCE
OF ACCUMULATING SNOW ON THURSDAY AND INTO FRIDAY. AN UPPER LEVEL
TROUGH WILL DROP OUT OF THE NORTHWEST BRINGING LOTS OF MOISTURE
AND COLD AIR. CURRENT QG FORECASTS ARE VERY PROMISING WITH THE EC
INDICATING -35 MB/HR OVER NERN COLORADO. DECIDED TO GO WITH
CHANCE POPS WITH DECENT LIKELIHOOD OF SEEING SOME SNOW BUT WILL
WAIT ON MENTIONING SNOW AMOUNTS UNTIL LATER MODEL RUNS.

&&

.AVIATION...(FOR THE TAFS THROUGH 00Z FRIDAY LATE AFTERNOON)
ISSUED AT 1231 PM MST THU DEC 18 2014

WEAK SFC PRESSURE GRADIENTS WILL ALLOW FOR LIGHT DIURNAL WINDS
OVER THE NEXT 24 HOURS. SOME MID AND UPPER LEVEL CIGS THROUGH THIS
EVENING THEN DECREASING. NO CIG/VSBY RESTRICTIONS EXPECTED. LOWER
LEVELS ARE PROGGED TO BE A BIT DRIER OVERNIGHT SO DO NOT
ANTICIPATEPATCHY FOG LATE TNGT/FRIDAY MORNING. IF ANY DOES
DEVELOP IT WILL BE EAST OF THE AIRPORTS.

&&

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

$$

SHORT TERM...COOPER
LONG TERM...BOWEN
AVIATION...COOPER



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