Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 181547
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
847 AM MST THU DEC 18 2014

.UPDATE...
ISSUED AT 840 AM MST THU DEC 18 2014

NO SIGNIFICANT CHANGES AT THIS TIME. SOME PATCHY FOG HAS DEVELOPED
NEAR DIA BUT EXPECT THIS TO IMPROVE THROUGH THE MORNING. SOME SLGT
ADJUSTMENTS TO POPS IN THE FOOTHILLS...GENERALLY SLGT
CHC...THROUGH THE DAY.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 400 AM MST THU DEC 18 2014

A VERY WEAK LOW AMPLITUDE UPPER TROUGH WILL BE MOVING OVER THE
STATE TODAY WITH WEAK WESTERLY WINDS ALOFT AND VERY LITTLE FORCING
FOR ASCENT. MOISTURE LEVELS OVER THE MOUNTAINS WILL BE SUFFICIENT
FOR THE WEAK WEST WINDS TO PRODUCE PERIODS OF LIGHT OROGRAPHIC
SNOWFALL. DO NOT EXPECT TO SEE ANY ACCUMULATIONS GREATER THAN ONE
OF TWO INCHES. AREAS OF FOR AND LOW CLOUDS HAVE BEEN DRIFTING OVER
THE NORTHEAST CORNER OF THE STATE EARLIER THIS MORNING...BUT
VISIBILITIES AT METAR STATIONS HAVE RECENTLY BEEN IMPROVING. WILL
HANG ON TO THE MENTION OF AREAS OF FOG THROUGH ABOUT MID MORNING.
WILL ALSO HANG ON TO PARTLY AND MOSTLY CLOUDY SKY COVER ACROSS THE
FORECAST AREA DUE TO THE MID-LEVEL MOISTURE THAT WILL BE ADVECTING
ACROSS THE REGION. TEMPERATURES SHOULD BE AROUND NORMAL FOR THIS
TIME OF YEAR IN THE ABSENCE OF ANY STRONG DOWNSLOPING WARMING OR
STRONG SUNSHINE. THE UPPER TROUGH WILL REMAIN OVER THE FORECAST
AREA THROUGH MIDNIGHT TONIGHT...SO THERE IS LITTLE NEED TO REDUCE
POPS OVER THE MOUNTAINS UNTIL THEN.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 400 AM MST THU DEC 18 2014

A WK UPPER LEVEL TROUGH WILL MOVE EAST OF THE AREA EARLY ON FRI AS A
FLAT UPPER LVL RIDGE DEVELOPS BY AFTN.  OVERALL CROSS-SECTIONS ONLY
SHOW SOME MOISTURE NR MTN TOP SO WILL ONLY MENTION A SLIGHT CHC OF
SHSN OVER THE HIGHER PEAKS WITH DRY CONDITIONS ELSEWHERE.  850-700
MB TEMPS DO NOT CHANGE MUCH ON FRI SO WILL KEEP HIGHS IN THE LOWER
TO MID 40S OVER THE URBAN CORRIDOR BUT KEEP HIGHS IN THE 30S OVER
THE PLAINS WHERE SNOW COVER WILL STILL EXIST.

ON SAT ANOTHER WK UPPER LEVEL TROUGH MAY AFFECT THE AREA BRINGING A
CHC OF -SHSN TO THE MTNS WITH DRY CONDITIONS ELSEWHERE.  850-700 MB
TEMPS RISE A FEW DEGREES SO WILL HAVE HIGHS IN THE LOWER TO MID 40S
OVER NERN CO ALTHOUGH READINGS AROUND DENVER COULD REACH THE UPPER
40S.

BY SUN THE FLOW ALOFT WILL BECOME MORE NWLY AND INTENSIFY.  MOISTURE
WILL GRADUALLY INCREASE IN THE MTNS THRU THE DAY SO SHOULD A BETTER
CHC OF SNOW ESPECIALLY BY AFTN.  OVER NERN CO IT WILL REMAIN DRY
ALTHOUGH MAY SEE AN INCREASE IN MID AND HIGH LVL CLOUD COVER.  850-
700 MB TEMPS RISE ANOTHER 3 DEGREES OR SO WHICH MAY ALLOW FOR HIGHS
TO REACH THE LOWER 50S AROUND DENVER WITH 40S ACROSS THE PLAINS.

FOR SUN NIGHT INTO MON STG MOIST NWLY FLOW ALOFT WILL BE OVER THE
AREA WITH INCREASING INSTABILITY ACROSS THE AREA AS LAPSE RATES RISE
INTO THE 7-8 C/KM RANGE.  WITH FAVORABLE OROGRAPHICS IN PLACE ALONG
WITH PLACEMENT OF UPPER LVL JET MAY SEE A HEAVY SNOW EVENT IN THE
MTNS AND PORTIONS OF HIGHER VALLEYS.  OVER NERN CO APPEARS A BORA
TYPE FNT WILL MOVE ACROSS THE AREA LATE SUN NIGHT INTO MON MORNING.
DESPITE NWLY FLOW IN THE LOWER LEVELS PLACEMENT OF UPPER LEVEL JET
AND DECENT LAPSE RATES COULD LEAD TO SOME SHOWER ACTIVITY OVER NERN
CO.  THE ECMWF HAS THE BEST CHC OF PCPN LATE SUN NIGHT INTO MON
MORNING WHILE THE GFS HAS THE BEST CHC MON AFTN INTO MON EVENING.
IN ADDITION THE GFS ATTEMPTS TO TURN THE WINDS MORE NNE MON AFTN
INTO MON EVENING WHICH WOULD INCREASE THE CHC OF PCPN FM DENVER
SOUTH ACROSS THE PALMER DIVIDE.  MEANWHILE TEMP PROFILES FM THE
ECMWF WOULD FAVOR PCPN MOSTLY AS SNOW WHILE THE GFS KEEPS READINGS
WARMER WITH PCPN FALLING AS RAIN MON AFTN BEFORE CHANGING TO SNOW
MON EVENING.  THIS FAR OUT HARD TO SAY HOW THINGS WILL EVOLVE SO
WILL KEEP POPS IN THE 20-30 PERCENT RANGE FOR NOW SINCE TIMING OF
PCPN IS STILL UNCERTAIN.

FOR TUE STG NWLY FLOW ALOFT WILL CONTINUE OVER THE AREA.  CROSS-
SECTIONS SHOW SOME DECREASE IN MOISTURE DEPTH IN THE MTNS HOWEVER
LAPSE RATES REMAIN IN THE 7-8 C/KM RANGE.  THUS WILL STILL SEE
PERIODS OF OROGRAPHIC DRIVEN SNOW.  OVER NERN CO THE ECMWF SHOWS A
WK SURGE OF COOLER AIR MON NIGHT INTO TUE MORNING ALONG THE FRONT
RANGE WHICH COMBINES WITH DECENT LAPSE RATES TO PRODUCE SNOW ALONG
THE URBAN CORRIDOR WHICH IS ENHANCED BY PLACEMENT OF UPPER LEVEL
JET.  THE GFS SORT OF SHOWS A SIMILAR SET UP BUT DOES NOT HAVE AS
MUCH PCPN.  FOR NOW WILL JUST MENTION A SLIGHT CHC OF SNOW FOR THE
LATE MON NIGHT INTO TUE MORNING TIME PERIOD.  AS FOR HIGHS WILL KEEP
HIGHS IN THE 35 TO 40 DEGREE RANGE OVER THE PLAINS.

FOR TUE NIGHT INTO WED THE FLOW ALOFT WILL CONTINUE MAINLY NWLY.
CROSS-SECTIONS SHOW MOISTURE DEPTH INCREASING IN THE MTNS WITH
FAVORABLE LAPSE RATES SO SHOULD CONTINUE TO SEE PERIODS OF
OROGRAPHIC SNOW WHICH MAY BE ENHANCED BY PLACEMENT OF UPPER LEVEL
JET. OVER NERN CO BOTH THE ECMWF AND GFS SHOW ANOTHER SURE OF
COOLER AIR MOVING INTO THE AREA TUE NIGHT INTO EARLY WED. ONCE
AGAIN WITH PLACEMENT OF UPPER LEVEL JET AND FAVORABLE LAPSE RATES
COULD SEE ANOTHER CHC OF SNOW DURING THIS TIME PERIOD. THUS WILL
INCLUDE SOME LOW POPS. HIGHS ON WED SHOULD STAY IN THE 30S OVER
NERN CO BASED ON LATEST 850-700 MB TEMPS.

LOOKING AHEAD TOWARDS CHRISTMAS EVE INTO CHRISTMAS DAY LATEST ECMWF
AND GFS INDICATE A GOOD CHC OF SNOW AS AN UPPER LEVEL TROUGH MOVES
SE INTO THE RGN ALONG WITH ANOTHER SHOT OF COLDER AIR.  OF COURSE
THIS IS STILL A WEEK AWAY SO WE SHALL SEE HOW THINGS PLAY OUT.

&&

.AVIATION...(FOR THE TAFS THROUGH 18Z FRIDAY MORNING)
ISSUED AT 840 AM MST THU DEC 18 2014

PATCHY FOG AT DIA SHOULD GRADUALLY IMPROVE AS TEMPERATURES
GRADUALLY RECOVER THIS MORNING. HAVE GONE WITH TEMPO MVFR VSBYS
THROUGH 17Z...THEN NO VSBY RESTRICTIONS. SURFACE PRESSURE
GRADIENTS WILL BE QUITE WEAK ACROSS NORTHEAST COLORADO THROUGH
TONIGHT...SO LIGHT WINDS ARE EXPECTED TO CONTINUE.

RAP INDICATES SOME LIGHT EASTERLY WINDS IN THE AFTERNOON AND
EVENING...BUT SPEEDS SHOULD REMAIN IN THE 4-8 KNOT RANGE. NOTHING
MORE THAN MID AND HIGH LEVEL CLOUDS ARE EXPECTED THROUGH THE NEXT
24 HOURS AS THE WEAK UPPER LEVEL DISTURBANCE MEANDERS OVERHEAD.

&&

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

$$

UPDATE...COOPER
SHORT TERM...DANKERS
LONG TERM...RPK
AVIATION...COOPER



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