Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 110941
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
341 AM MDT THU SEP 11 2014

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 338 AM MDT THU SEP 11 2014

MAIN CONCERNS ARE THREAT OF SNOW TONIGHT AND MUCH COLDER
TEMPERATURES.

FIRST SURGE OF COOLER AIR AND WIDESPREAD STRATUS HAD ALREADY
SPREAD ACROSS MUCH OF NORTHEAST COLORADO EARLY THIS MORNING. WHILE
THE PRESSURE SURGE ASSOCIATED WITH THIS HAS WEAKENED A BIT...THE
INCREASE IN BAROCLINICITY ALONG ANY DIFFERENTIAL HEATING BETWEEN
THE SUNSHINE IN SOUTHEAST COLORADO AND THE CLOUD COVER IN
NORTHEAST COLORADO WILL LIKELY KEEP A WELL ORGANIZED SURFACE
CYCLONE JUST SOUTH OF THE DENVER AREA TODAY. THIS WOULD ONLY HELP
REINFORCE THE LOW LEVEL COOLING ON THE NORTHER SIDE OF THE CYCLONE
AND KEEP MOST OF THE FORECAST AREA CLOUDY AND MUCH COOLER. HAVE
THEREFORE LOWERED HIGH TEMPERATURES SEVERAL DEGREES FOR TODAY.

THERE IS A GRADUAL INCREASE IN THE DEPTH AND MAGNITUDE OF Q-G
LIFT THROUGH THE DAY AS UNSEASONABLY COLD UPPER TROUGH PUSHES
SOUTHEAST ACROSS THE NORTHERN ROCKIES. WHILE AREAS OF FOG AND
LIGHT DRIZZLE CAN BE EXPECTED THIS MORNING...SHOWER CHANCES WILL
INCREASE SIGNIFICANTLY LATE THIS AFTERNOON THROUGH THE EVENING.
THIS OCCURS AS LARGE SCALE Q-G LIFT INTERACTS WITH DEEPENING
UPSLOPE AS ANOTHER REINFORCING SHOT OF MUCH DEEPER COLD AIR PUSHES
ACROSS NORTHEAST COLORADO LATE THIS AFTERNOON AND EVENING.
TEMPERATURE PROFILES ALL SUPPORT RAIN CHANGING OVER TO SNOW BY
LATE EVENING INTO THE EARLY MORNING HOURS ACROSS THE FORECAST
AREA. MOST MODEL DATA SUPPORTS GENERALLY LIGHT SNOWFALL AND THERE
SHOULD BE CONSIDERABLE MELTING AS WELL WITH SURFACE WET BULB TEMPS
HOLDING JUST ABOVE FREEZING...SIMILAR TO UPSTREAM OBS.
HOWEVER...WILD CARD IS POTENTIAL CONVECTION AS CROSS SECTIONS SHOW
A LAYER OF POTENTIAL INSTABILITY ABOVE THE FRONTAL INVERSION. THIS
WOULD SUPPORT A FEW LOCALLY HEAVY BANDS...AND IF RAIN CHANGES OVER
TO SNOW QUICKER WHICH IS POSSIBLE IN CONVECTIVE SITUATIONS...THEN
A COUPLE PLACES ESPECIALLY JUST EAST OF DENVER COULD BE LOOKING AT
A QUICK 2-3 INCHES OF SNOW. THIS COULD WARRANT AN ADVISORY BUT
HARD TO PIN POINT A LOCATION AT THIS TIME SO WILL CONTINUE TO
MONITOR POTENTIAL THROUGH THE COURSE OF THE DAY.

PRECIPITATION INTENSITY IS EXPECTED TO DECREASE LATE TONIGHT AS
BEST LIFT PUSHES SOUTH AND UPSLOPE COMPONENT BEGINS TO WEAKEN.
LOW TEMPERATURES WILL GET CLOSE TO FREEZING BUT WIDESPREAD
FREEZING TEMPS NOT ANTICIPATED ON THE PLAINS DUE TO CLOUDS/WET
BULB TEMPS. MOST MOUNTAIN LOCATIONS SHOULD DROP BELOW FREEZING.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 338 AM MDT THU SEP 11 2014

STRONG UPSLOPE FLOW WILL CONTINUE FRIDAY MORNING AS THE SURFACE
HIGH MIGRATES FROM THE NEBRASKA PANHANDLE SOUTH INTO KANSAS.
MOISTURE WILL BEGIN THINNING FROM THE TOP DOWN WHICH MAY STOP
THE SNOW OR RAIN/SNOW MIX AND TURN IT MORE INTO A DRIZZLE EVENT.
HOWEVER MODELS HAVE BEEN SLOWING THIS...SO FOR NOW WILL KEEP THE
PRECIPITATION IN RAIN/SNOW FORM. EXPECTING LOW CLOUDS OVER THE
FOOTHILLS AND PLAINS THROUGH THE MORNING AND MOST OF THE
DAYTIME...KEEPING TEMPERATURES IN THE 40S AND LOW 50S OVER THE
PLAINS...WHERE AREAS ABOVE IN THE HIGHER TERRAIN WILL CLEAR OUT
AND WARM INTO THE 60S. SEEMS AS THOUGH THE LOW CLOUDS WILL HANG ON
LATEST OVER THE SOUTHERN FOOTHILLS AND PALMER DIVIDE AREA BEFORE
TOTALLY DISSIPATING FRIDAY EVENING. AS DRIER NORTHWESTERLY FLOW
ALOFT MOVES IN...A SURFACE TROUGH WILL BEGIN FORMING OVER THE
FRONT RANGE URBAN CORRIDOR AND EASTERN PLAINS. THIS WILL BRING IN
WARMER AIR WITH SLIGHT DOWNSLOPING WINDS FROM THE FOOTHILLS.
CLEARING SKIES WILL ALLOW RADIATIONAL COOLING AND SOME AREAS MAY
SEE SOME PATCHY FOG...WITH MODELS POINTING AT THE PALMER DIVIDE
AND CYCLONING INTO WELD COUNTY AND INTO THE URBAN
CORRIDOR...HELPING TO MODERATE MINIMUM TEMPERATURES.

AN UPPER RIDGE WILL BEGIN BUILDING OVER THE SOUTHWEST STATES AND
SOUTHERN GREAT BASIN THIS WEEKEND. SATURDAY WILL BEGIN THE WARM
UP WHILE STAYING DRY WHILE SUNDAY WILL CONTINUE TO WARM TO NEAR OR
ABOVE AVERAGE READINGS...BUT WITH A SLIGHT CHANCE OF SHOWERS OVER
THE MOUNTAINS. MODELS ARE PICKING UP ON AN UPPER TROUGH PASSING
OVER THE NORTHERN GREAT PLAINS AND PUSHING A COLD FRONT DOWN INTO
NORTHEASTERN COLORADO MONDAY WITH SHOWERS AND THUNDERSTORMS
POSSIBLE AHEAD OF IT...AND TEMPERATURES TO COOL SLIGHTLY FOR
MONDAY. TUESDAY AND WEDNESDAY WILL RETURN TO WARMING TEMPERATURES
AND ISOLATED MOUNTAIN SHOWERS AS THE RIDGE BUILDS BACK NORTH
AGAIN.

&&

.AVIATION...(FOR THE TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 338 AM MDT THU SEP 11 2014

LARGE AND COLD SURFACE HIGH PRESSURE OVER THE NORTHERN PLAINS
COMBINED WITH SURFACE CYCLONE JUST SOUTH OF DENVER SHOULD KEEP
IFR STRATUS ALONG WITH AREAS OF DRIZZLE/FOG IN THE FRONT RANGE
AIRPORTS THROUGH TONIGHT. FOG MAY BE THICK WITH VISIBILITIES
OCCASIONALLY DIPPING TO AROUND 1/4SM THROUGH 14Z...THEN CLOUDS/FOG
SHOULD LIFT SLIGHTLY TO PERHAPS MVFR CONDITIONS FOR MOST OF THE
LATE MORNING THROUGH AFTERNOON HOURS. RAIN SHOWERS WILL DEVELOP
22Z-02Z WITH IFR CONDITIONS THEN LIKELY THROUGH THE NIGHT. TEMPS
EXPECTED TO TURN COLD ENOUGH FOR RAIN MIXING WITH SNOW 04Z-06Z AND
CHANGING OVER TO ALL SNOW BY 07Z-09Z. SOME ACCUMULATION UP TO 1
INCH POSSIBLE IN GRASSY/ELEVATED SURFACES BUT NONE ON VERY WARM
PAVEMENT.

&&

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

$$

SHORT TERM...BARJENBRUCH
LONG TERM...KRIEDERMAN
AVIATION...BARJENBRUCH



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