Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 211629
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
929 AM MST WED JAN 21 2015

.UPDATE...
ISSUED AT 928 AM MST WED JAN 21 2015

FORECAST GETTING MORE DIFFICULT AT THE PRESENT TIME DUE TO TWO
FACTORS...VERY LOW SNOW DENSITY AND SHARP CUTOFF ON THE NORTHERN
FRINGE. AT THIS TIME...A SIGNIFICANT SNOW BAND WITH 1 INCH PER
HOUR RATES WAS SINKING SLOWLY SOUTH THROUGH DENVER METRO...WHILE
DRIER AIR AND CLEARING SKIES NOTED AROUND FORT COLLINS AND
GREELEY. AS LONG AS THIS DRIER AIR MOVES IN THEN AMOUNTS WOULD
HOLD UNDER ADVISORY CRITERIA FOR THE METRO AREA. HOWEVER...AT THE
SAME TIME AIRMASS IS DESTABILIZING AND UPSLOPE COMPONENT
INCREASES. THIS SHOULD BRING A CONVECTIVE COMPONENT TO
PRECIPITATION BUT ALSO HELP TO FOCUS HEAVIER SNOW IN/NEAR THE
FOOTHILLS. WILL MONITOR TRENDS OVER THE NEXT HOUR OR TWO. WEAK
UPPER LEVEL DEFORMATION ZONE IS SHIFTING SOUTH...BUT COULD STALL
AS UPPER LEVEL TROUGH DIGS THROUGH THE 4 CORNERS. VERY LOW SNOW
DENSITY INITIALLY ON THE ORDER OF 3-5 PERCENT OR 20-30 TO 1 SNOW
RATIOS WITH GOOD DENDRITIC GROWTH REGIME WILL LEAD TO A LARGER
ACCUMULATION OF FLUFFY SNOW AS WELL. FOR ABOVE MENTIONED
REASONS...HAVE BOOSTED SNOW AMOUNTS FROM THE SOUTHERN SUBURBS INTO
THE PALMER DIVIDE/SOUTHERN FOOTHILLS...WHILE POINTS TOWARD FORT
COLLINS MAY SEE ONLY A FEW PASSING SNOW SHOWERS LATER THIS
AFTERNOON.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 313 AM MST WED JAN 21 2015

OVERALL THE TIMING AND TRACK OF THESE NEXT TWO SYSTEM IS ON TRACK.
RADAR THIS MORNING ALREADY INDICATING SOME BANDED SNOW OVER THE
PALMER DIVIDE THIS MORNING. THE MDLS MERGE TWO SYSTEMS TODAY...ONE
SLIDING ACROSS ALONG THE SOUTHERN COLORADO BORDER WITH ANOTHER
DROPPING OUT OF NORTHWESTERN WYOMING. THE NAM/GFS MDLS SHOW
FAVORABLE WEAK TO MODERATE MID AND UPPER LEVEL QG ASCENT TODAY
AHEAD OF THESE TWO SYSTEMS. MDLS SOUNDINGS INDICATE FAVORABLE
LAPSE RATES AS WELL...SFC/700 AND 700/500...BOTH OF WHICH ARE
7-7.5C/KM IN THE AFTN. DEEPENING UPSLOPE AS WELL...NOT VERY STRONG
BUT FAIRLY DEEP...SFC/600 MB. WITH ALL THIS SAID...THE FOCUS FOR
THE BEST SNOWFALL WILL BE OVER LOCATIONS IN AND NEAR THE SOUTHERN
FRONT RANGE FOOTHILLS AND PALMER DIVIDE...MAINLY THE HIGHER
TERRAIN SOUTH OF INTERSTATE 70. WILL GO AHEAD AN ISSUE A WINTER
WEATHER ADVISORY FOR ZONES 34..36..37 AND 41 THROUGH 8 PM MDT THIS
EVENING. IT WILL BE A LITTLE TRICKIER FOR ZONES 45>47. SNOW TOTALS
GENERATED BY MOST OF THE MDLS RANGES FM 2 TO 4 INCHES. WL PARK
ZONES 46 AND 47 IN A WINTER WEATHER ADVISORY BUT LET THE DAY SHIFT
DECIDE ON THE INCLUSION OF ANY ADDITIONAL ZONES. FOR THE DENVER
AREA...1-3 INCHES LOOKS LIKE A GOOD START...HIGHEST OVER THE
SOUTHERN AND WESTERN SUBURBS. BEST POTENTIAL FOR ALL THE
AFOREMENTIONED INGREDIENTS PHASING WITH ONE ANOTHER WILL BE IN THE
18Z TO 00Z TIME FRAME. SNOW POTENTIAL IN THE ADVISORY AREA WL BE
IN THE 4 TO 8 INCH CATEGORY. FOR TONIGHT...INCREASING SUBSIDENCE
WILL SPREAD ACROSS THE REGION FROM NORTHWEST TO SOUTHEAST...WITH
MOST OF THE SNOWFALL WINDING DOWN BY 03Z. CLEARING SKIES OVERNIGHT
WL ADD UP TO VERY COLD MORNING LOWS IN THE SINGLE DIGITS.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 313 AM MST WED JAN 21 2015

UPPER LEVEL LOW WILL BE OVER THE SOUTHERN ROCKIES COME THURSDAY
MORNING. THERE MAY  BE A FEW LINGERING CLOUDS SOUTH OF I-70. ANY
PRECIPITATION WILL BE WELL SOUTH OF THE FORECAST AREA. A SURFACE
HIGH WILL BE OVER COLORADO ON THURSDAY AND BRING COOL AND DRY
CONDITIONS. A WEAK NORTHWEST FLOW ALOFT WILL PREVAIL BEHIND THE
EXITING SYSTEM THROUGH SATURDAY. THIS WILL KEEP TEMPERATURES NEAR
NORMAL WITH HIGHS IN THE UPPER 30S AND 40S ACROSS NORTHEAST
COLORADO.

NORTHWEST FLOW ALOFT WILL INCREASE AS TROUGH MOVE ACROSS THE
NORTHERN PLAINS SATURDAY NIGHT AND SUNDAY. WILL HAVE LOW POPS FOR
PARTS OF THE MOUNTAINS IN CASE THERE IS ENOUGH MOISTURE TO PRODUCE A
LITTLE LIGHT SNOW. THIS SYSTEM MAY ALSO BRING BREEZY CONDITIONS TO
PARTS OF THE AREA. WILL SEE SLIGHT WARMING SUNDAY AS AN UPPER LEVEL
RIDGE STARTS TO BUILD OVER THE GREAT BASIN AND ROCKIES.

FOR EARLY NEXT WEEK...THE RIDGE WILL INTENSIFY OVER THE ROCKIES
BRINGING DRY CONDITIONS AND ABOVE NORMAL TEMPERATURES. EXPECT HIGHS
TO REACH THE 50S AND LOWER 60S MONDAY AND TUESDAY.

&&

.AVIATION...(FOR THE TAFS THROUGH 18Z THURSDAY MORNING)
ISSUED AT 928 AM MST WED JAN 21 2015

IFR CONDITIONS WITH SNOW AND VSBYS DOWN TO 1/2SM OR LESS IN
HEAVIER SNOW SHOWERS. THOSE SHOWERS MAY BECOME QUITE VARIABLE
ESPECIALLY TOWARD KDEN AS DRIER AIR WORKS IN FROM THE NORTH BY
18Z. HEAVIER SNOW SHOWERS WILL FOCUS CLOSER TO THE FOOTHILLS LATER
THIS AFTERNOON AND EVENING...AND THEN DECREASE 03Z-06Z. BRIEF VFR
CONDITIONS POSSIBLE AT KDEN GIVEN SHOWERY NATURE AND SOME DRYING
NOTED FROM THE NORTH. TOTAL ACCUMULATIONS STILL EXPECTED TO BE 1-2
INCHES AT KDEN...WITH AMOUNTS CLOSER TO 5 INCHES POSSIBLE AT KAPA.
KBJC SHOULD SEE 2 TO POSSIBLY AS MUCH AS 4 INCHES.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 8 PM MST THIS EVENING FOR COZ034-
036-037-041-046-047.

&&

$$

UPDATE...BARJENBRUCH
SHORT TERM...COOPER
LONG TERM...MEIER
AVIATION...BARJENBRUCH



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