Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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000
FXUS65 KBOU 140437
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
937 PM MST SAT DEC 13 2014

.UPDATE...
ISSUED AT 930 PM MST SAT DEC 13 2014

LATEST MODEL RUNS SEEM TO BE CATCHING UP TO THE SLOWER TIMING OF
THIS SYSTEM. IT APPEARS WIDESPREAD SNOW WILL NOT BEGIN UNTIL AROUND
MIDNIGHT IN THE MOUNTAINS OF NORTH CENTRAL COLORADO. ONCE IT BEGINS
SNOW SHOULD BECOME MODERATE TO HEAVY. FOR THE DENVER AREA...SNOW
WILL BEGIN MID TO LATE MORNING...AROUND 9AM TO 11AM. THERE IS SOME
DRIER AIR WITH THIS SYSTEM...SO SNOWFALL AMOUNTS FROM DENVER
NORTH COULD BE LIGHT.

FOR THE EASTERN PLAINS...EXPECT SNOW TO BEGIN AFTER NOON. AS THE LOW
LIFTS FROM NORTHEAST NEW MEXICO TO WESTERN KANSAS WIDESPREAD WILL
DEVELOP ON THE BACKSIDE OF THE LOW. WILL ISSUE A WINTER STORM WATCH
FOR THE NORTHEAST CORNER OF COLORADO WHERE 4 TO 8 INCHES OF SNOW
WILL BE POSSIBLE. BECAUSE OF THE SLOWER MOVEMENT OF THIS
STORM...WOULD NOT BE SURPRISED FOR SNOW TO LAST LONGER THEN THE
MODELS ARE SHOWING WHICH WOULD INCREASE SNOWFALL AMOUNTS OVER THE
PLAINS. THE 00Z MODELS ARE SHOWING THE WESTERN EXTEND OF THE HEAVIER
SNOW BAND MAKING IT TO EASTERN ADAMS/ARAPAHOE COUNTIES AND JUST EAST
OF DENVER AIRPORT WHERE UP TO 4 INCHES WILL BE POSSIBLE IF THE BAND
DEVELOPS THIS FAR WEST.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 340 AM MST SAT DEC 13 2014

HIGH CLOUDS CONTINUE TO STREAM IN AHEAD OF THE APPROACHING WINTER
STORM. REGARDLESS OF THE CLOUDS...GULF MOISTURE SURGING INTO THE
EASTERN COLORADO PLAINS TOWARDS THE SURFACE TROUGH HAS BEEN ABLE
TO BRING VISIBILITIES DOWN TO A QUARTER MILE IN FOG OVER LINCOLN
COUNTY. EXPECT THIS FOG TO HANG AROUND THROUGH MID-MORNING BEFORE
LIFTING AND MOVING EAST. COOLER AIR WILL BEGIN SPREADING OVER THE
AREA TO BRING MAX TEMPERATURES ABOUT 5 TO 10 DEGREES COOLER OVER
YESTERDAY. MOISTURE WILL BE INCREASING OVER THE MOUNTAINS WITH A
SLIGHT CHANCE OF SNOW LATE THIS AFTERNOON...BUT THEN BECOMING
WIDESPREAD THIS EVENING AND OVERNIGHT AS UPWARD QG VERTICAL
VELOCITIES INCREASE...ESPECIALLY AFTER MIDNIGHT AND MOUNTAIN TOP
FLOW BEGINS TO TURN TO THE FAVORED NORTHWEST DIRECTION. THERE IS A
SMALL AMOUNT OF CAPE BEING SHOWN IN THE MODELS....CURRENTLY OVER
FAR SOUTHEASTERN UT WHERE A COUPLE THUNDERSTORMS ARE OCCURRING.
SOME OF THIS CAPE IS MODELED TO MOVED UP OVER OUR MOUNTAINS LATE
THIS AFTERNOON AND EVENING...SO THERE IS A SMALL CHANCE WE COULD
SEE SOME CONVECTIVE ACTIVITY...BUT DID NOT ADD IT INTO THE
FORECAST AS I BELIEVE THIS SHOULD STAY A LOT FURTHER SOUTH. EXPECT
UP TO A COUPLE INCHES OF SNOW TO FALL OVER THE HIGH TERRAIN
OVERNIGHT. ON THE PLAINS...THE SURFACE TROUGH WILL DEEPEN AND
BECOME A LOW EAST OF THE PALMER DIVIDE BY THIS EVENING. GENERALLY
LIGHT WINDS ARE EXPECTED WITH ONLY HIGH CLOUD COVER. HIGH SURFACE
PRESSURE WILL BEGIN SURGING SOUTH OUT OF MONTANA AND WYOMING THIS
TONIGHT TO PUSH IN A COLD FRONT AFTER MIDNIGHT INTO THE STATE.
THIS WILL HELP TURN LOW LEVEL WINDS UPSLOPE...COMBINING WITH THE
PERIOD OF UPWARD QG VERTICAL VELOCITY ALOFT AND INCREASING
MOISTURE TO SPREAD RAIN AND SNOW OVER THE FOOTHILLS AND PLAINS
TOWARDS SUNRISE. AT THE SAME TIME...FOG WILL HAVE CREPT BACK IN
OVER THE FAR NORTHEASTERN CORNER OF THE STATE FOR REDUCED
VISIBILITIES AGAIN...MAINLY OVER SEDGWICK AND PHILLIPS COUNTIES.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 340 AM MST SAT DEC 13 2014

FORECAST CHALLENGES SURROUND THE CLOSED LOW DEVELOPMENT AND
STORM TRACK SUNDAY AND SUNDAY NIGHT.

THERE IS STILL A LOT OF UNCERTAINTY WITH REGARD TO EVENTUAL
MOVEMENT AND DEVELOPMENT OF UPPER LEVEL TROUGH. WATER VAPOR
IMAGERY SHOWS A LARGE AND SOMEWHAT ELONGATED TROUGH MOVING SLOWLY
EAST INTO THE GREAT BASIN AND DESERT SOUTHWEST. THERE IS ANOTHER
WEAK WAVE MOVING INTO THE BASE OF THE TROUGH THIS MORNING...AND
THIS IS ALREADY BECOMING EVIDENT ON THE Q-G ANALYSIS WITH THE
ENERGY SPLITTING INTO TWO PIECES. THIS SECONDARY PIECE WHICH
STRENGTHENS MAY BE THE KEY PLAYER IN DEVELOPMENT OF THE UPPER
LEVEL CLOSED LOW...AS WELL AS THE INFLUX OF GULF MOISTURE INTO THE
SYSTEM.

MOST OF THE 00Z MODEL RUNS INCLUDING THE OPERATIONAL GFS AND GEM
HAVE SHIFTED THE UPPER LOW TRACK ANYWHERE FROM 60-120 MILES NORTH
OF THE TRACK JUST 24 HOURS AGO. MEANWHILE...THE ECMWF HAS REMAINED
MOST STABLE TRACKING THE UPPER LOW FROM NEAR THE FOUR CORNERS AREA
INTO NORTHEAST NEW MEXICO BY LATE SUNDAY MORNING...AND THEN
EAST/NORTHEAST INTO SOUTH CENTRAL KANSAS BY SUNDAY NIGHT. THIS
SOLUTION WAS GENERALLY FAVORED BUT OVERALL A BLEND OF MODELS WAS
STILL UTILIZED IN THE FORECAST GIVEN THE MULTITUDE OF SCENARIOS
INCLUDING A MUCH SNOWIER CANADIAN...AT LEAST FOR THE FRONT RANGE.
SOME OF THE MESOSCALE MODELS ALSO SEEMED HEAVY HANDED...BUT
CONSIDERING THEIR LACK OF THE BIG PICTURE ISSUES TENDED TO SHY
AWAY FROM THOSE PARTICULAR SNOW FORECASTS FOR THE MOST PART.

THAT SAID...THERE IS A THREAT OF HEAVIER SNOWFALL SHAPING UP FOR
THE NORTHEASTERN CORNER OF THE STATE...MAINLY FROM AKRON AND
STERLING EASTWARD TOWARD THE NEBRASKA/KANSAS BORDER AREA.
INGREDIENTS THAT WOULD FAVOR HEAVIER SNOW HERE INCLUDE STRONGER
Q-G LIFT THROUGH SUNDAY EVENING...BETTER INFLUX OF GULF
MOISTURE...AND TROWAL LOCATION. THIS LOCATION WILL HAVE TO BE
MONITORED CLOSELY FOR POTENTIAL HEAVY SNOWFALL AND POSSIBLE WATCH.
MEANWHILE...PALMER DIVIDE COULD HAVE A THREAT OF SOMEWHAT HEAVIER
SNOWFALL AS WELL WITH STRONG AND DEEP NORTHERLY FLOW IN PLACE ON
SUNDAY.

ALONG THE FRONT RANGE I-25 CORRIDOR...LOOKS LIKE AN AREA OF SNOW
WILL BECOME ORGANIZED SUNDAY MORNING AND SPREAD SLOWLY EAST.
HOWEVER...THREAT OF HEAVIER SNOWFALL WOULD LIKELY BE LIMITED BY A
RATHER QUICK TRANSITION FROM UPSLOPE NORTH/NORTHEAST FLOW TO
SLIGHTLY DOWNSLOPE NORTH/NORTHWEST FLOW OFF THE FOOTHILLS SOMETIME
IN THE AFTERNOON. TEMPERATURES WILL ALSO BE MARGINAL OUTSIDE OF
THE ELEVATED TERRAIN SO EXPECT SOME MELTING DURING THE DAYLIGHT
HOURS. ONLY CHANCE THE FRONT RANGE METRO AREAS COULD SEE HEAVIER
SNOWFALL WOULD LIKELY HINGE ON A SLOWER EASTWARD PROPAGATION AND
THUS ABILITY TO TAP INTO GULF MOISTURE AND SLING IT BACK TOWARD
THE FRONT RANGE. HOWEVER...AT THIS TIME THE MAIN THREAT WOULD BE
OVER THE NORTHEAST CORNER OF THE STATE AS MENTIONED ABOVE.

SNOW WILL DECREASE RATHER QUICKLY ALONG THE FRONT RANGE URBAN
CORRIDOR BY SUNDAY EVENING...BUT COULD PERSIST IN WRAPAROUND OVER
THE NORTHEAST CORNER THROUGH SUNDAY NIGHT. MOUNTAIN AREAS WILL
ALSO LIKELY SEE A FEW SNOW SHOWERS CONTINUE IN MORE FAVORABLE
OROGRAPHIC FLOW. MOISTURE IS SHALLOW THOUGH...SO MAINLY THINKING
ADVISORY CRITERIA FOR THE HIGH COUNTRY STARTING LATE TONIGHT
THROUGH SUNDAY AND SUNDAY NIGHT.

AFTER THIS SYSTEM...LOOKS LIKE WE WILL BE SETTLING INTO NEAR
NORMAL TEMPERATURES THROUGH MOST OF THE UPCOMING WEEK. THERE ARE A
FEW WAVES TO CONTEND WITH...ONE POSSIBLY LATE WEDNESDAY INTO
THURSDAY WITH ANOTHER TOWARD THE WEEKEND. EACH OF THOSE WOULD
BRING A CHANCE OF SNOW TO THE FORECAST AREA.

&&

.AVIATION...(FOR THE TAFS THROUGH 06Z SUNDAY EVENING)
ISSUED AT 930 PM MST SAT DEC 13 2014

I-25 URBAN CORRIDOR AND FRONT RANGE MOUNTAINS UNDER A WIDE SLOT
OF DRY AIR IN ADVANCE OF A SLOWLY ADVANCING CLOUD AND PRECIP BAND
STRETCHING FROM SOUTHWEST WYOMING TO WEST CENTRAL NEW MEXICO. AT
THEIR PRESENT SPEED SHOULD SEE FRONT EDGE OF PRECIP AND LOW
CLOUDS ENTERING THE WESTERN DENVER METRO AREA BY 15Z OR 16Z
TOMORROW MORNING. UNTIL THEN EXPECT VFR CONDITIONS AND WEST-
SOUTHWEST WINDS OF 6-13 KTS AT DENVER AREA TERMINAL. AFTER
12Z...LOOK FOR WINDS TO BECOME NORTHWESTERLY AT 8-16KT JUST PRIOR
TO THE PASSAGE OF A COLD FRONT. THIS FRONT IS FORECAST TO MOVE
SOUTH THROUGH THE METRO AREA AROUND MID-MORNING WITH GUSTY NORTH-
NORTHWEST WINDS OF 20-25KTS. CIGS QUICKLY LOWER WITH ILS CIGS AND
VSBYS BY 17Z OR SO IN COMBINATION WITH SNOW OR A RAIN/SNOW MIX.
DURING THE AFTERNOON PRECIP SHOULD GO ALL SNOW WITH LIGHT
ACCUMULATION BY EVENING. CONDITIONS SHOULD QUICKLY IMPROVE THROUGH
SUNDAY EVENING AS THIS STORM SYSTEM MOVES AWAY FROM THE FRONT
RANGE.

BOU WATCHES/WARNINGS/ADVISORIES...WINTER STORM WATCH FROM SUNDAY
AFTERNOON THROUGH LATE SUNDAY NIGHT FOR COZ048>051.

WINTER WEATHER ADVISORY UNTIL 6 PM MST SUNDAY FOR COZ033-034.

WINTER WEATHER ADVISORY UNTIL 6 PM MST SUNDAY FOR COZ031.

&&

$$

UPDATE...MEIER
SHORT TERM...KRIEDERMAN
LONG TERM...BARJENBRUCH
AVIATION...BAKER



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