Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 120321
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
921 PM MDT FRI APR 11 2014

.UPDATE...(FOR TONIGHT AND SATURDAY)
ISSUED AT 921 PM MDT FRI APR 11 2014

CURRENT FORECAST ON TRACK. HIGH CLOUDS WILL BE ON THE INCREASE
OVERNIGHT AS HIGH LEVEL MOISTURE STREAMS IN FROM THE WEST-
SOUTHWEST OUT AHEAD OF THE NEXT UPPER TROUGH SETTING UP OVER THE
GREAT BASIN. TEMPERATURES OVERNIGHT SHOULD REMAIN ON THE MILD
SIDE WITH TYPICAL DRAINAGE WINDS. MADE FEW CHANGES AT THIS TIME.

&&

.AVIATION...DRAINAGE FLOW HAS ESTABLISHED ACROSS THE GREAT DENVER
METRO WITH HIGH CLOUDS ON THE INCREASE. NO PRECIP OVERNIGHT AND
NONE EXPECTED AT DENVER AREA TERMINALS THROUGH 2 PM MDT TOMORROW.
AFTER THAT...COULD SEE A FEW GUSTY MOSTLY DRY SHOWERS DRIFT EAST
OFF THE FOOTHILLS. THEY COULD GENERATE GUSTS TO AROUND 30 MPH.

AT THIS TIME NO CHANGES TO THE WINTER STORM WATCH IN EFFECT FROM
LATE SATURDAY NIGHT TO EARLY SUNDAY EVENING.

&&

.PREV DISCUSSION... /ISSUED 215 PM MDT FRI APR 11 2014/

SHORT TERM...(THIS AFTERNOON THROUGH SATURDAY)
ISSUED AT 215 P MDT FRI APR 11 2014

WEAK RIDGING ALOFT TO THE WEST OF COLORADO WITH A RESULTANT
DRY...NORTHWEST FLOW ALOFT CONTINUES THIS AFTERNOON.  THERE IS A
BAND OF HIGH LEVEL CLOUDS NOW MOVING INTO SOUTHWEST COLORADO AND
THIS WILL DRIFT INTO BOU CWA LATER THIS EVENING.

THE UPP ER LOW OFF THE CALIFORNIA COAST WILL WEAK AS IT MOVES
INLAND AND APPROACH THE 4 CORNERS REGION BY LATE SATURDAY
AFTERNOON. MEANWHILE STRONG COLD FRONT MAY APPROACH OUR NORTHERN
BORDER TOWARDS EVENING. WE WILL BE INBETWEEN SYSTEMS DURING THE
DAY SATURDAY BUT WILL SEE SOME INCREASE IN MOISTURE AND
INSTABILITY. THIS MAY LEAD TO ISOLATED SHOWERS AND EVEN A
THUNDERSTORM DURING SATURDAY AFTERNOON OVER MOUNTAINS AND
NORTHEAST PLAINS.  TEMPERATURES WILL ONLY BE SLIGHTLY COOLER ON
SATURDAY WITH MORE CLOUD COVER AND POSSIBLE SHOWERS.

LONG TERM...(SATURDAY NIGHT THROUGH THURSDAY)
ISSUED AT 215 PM MDT FRI APR 11 2014

FOCUS OF COURSE ON THE SNOW POTENTIAL FOR LATE SATURDAY NIGHT
THROUGH SUNDAY. AS HAS BEEN THE CASE WITH MOST OF THE STORMS THIS
WINTER/SPRING A BIT OF A COMPLEX MIX OF TWO APPROACHING TROUGHS
THAT REMAIN SEPARATE AND OVERALL A FAIRLY PROGRESSIVE STORM GIVING
THE THREAT OF A MODERATE TYPE STORM FOR THE AREA. THE SOUTHERN
SYSTEM IS A CLOSED LOW MOVING TOWARDS SOUTHERN CALIFORNIA BUT
WITHOUT A LOT OF MOISTURE. THE MORE VIGOROUS NORTHERN SYSTEM IS
CURRENTLY A SHORTWAVE LOCATED NEAR THE CENTRAL BRITISH COLUMBIA
COAST AND DIVING SOUTHEASTWARD ON THE EAST SIDE OF AN AMPLIFYING
UPPER LEVEL RIDGE THAT IS POKING NORTHWARD INTO ALASKA. THE TREND
IN THE GFS AND NAM MODELS HAS BEEN TO DIG THIS NORTHERN SYSTEM
FARTHER TO THE WEST WITH EACH RUN...SUPPORTING THE ECMWF SOLUTIONS
FROM EARLIER THIS WEEK...WHILE ALL THE MODELS HAVE KEPT THE
SOUTHERN SYSTEM SEPARATE AND HAVE THAT BECOMING AN OPEN WAVE AND
MOVING EASTWARD TO OUR SOUTH SATURDAY INTO SATURDAY NIGHT. THIS
SYSTEM COULD BRING SCATTERED SHOWERS AND EVEN A FEW THUNDERSTORMS
TO THE AREA. THE OTHER EFFECT OF THIS SOUTHERN WAVE IS TO DEVELOP
A SURFACE LOW NEAR THE OKLAHOMA PANHANDLE BY SATURDAY EVENING AND
THIS GETS NORTHEAST LOW LEVEL FLOW GOING ACROSS THE PLAINS...AHEAD
OF WHAT WILL BE A SECOND SURGE OF NORTH TO NORTHEAST FLOW
ASSOCIATED WITH THE NORTHERN WAVE. SO THE MAIN INFLUENCE IT SEEMS
OF THIS SOUTHERN FEATURE WOULD BE TO COOL THINGS DOWN AND MOISTEN
THEM UP AT LOWER LEVELS BEFORE THE MAIN SYSTEM COMES
SOUTHWARD...PERHAPS THEN ALLOWING FOR AN EARLIER START TO THE
PRECIPITATION THEN MIGHT HAVE OCCURRED AND AN EARLIER TRANSITION
TO SNOW.

THE LATEST ECMWF RUN FROM 12Z SUPPORTS THE GFS AND NAM WITH
DROPPING THE NORTHERN SYSTEMS TROUGH AXIS TOWARDS THE UT/CO
BORDER LATE SUNDAY. THIS TRACK SHOULD YIELD MORE SNOW FOR THE
MOUNTAINS THAN EARLIER RUNS HAD SUGGESTED AS THERE IS BETTER
UPWARD FORCING AS SEEN IN THE QG FIELDS AND AN UPPER LEVEL FRONT
IN THE MOUNTAINS ON SUNDAY ALTHOUGH OVERALL OROGRAPHIC LOWER LEVEL
FLOW WILL NOT BE THE BEST. BEST OROGRAPHIC FLOW WILL STILL BE
ALONG THE FRONT RANGE FOOTHILLS AND WEST TOWARDS THE CONTINENTAL
DIVIDE WITH NORTHEAST FLOW DEEPENING ABOVE 700 MB. THIS SYSTEM
LOOKS COLDER THAN THE ONE EARLIER THIS MONTH SO AT THIS POINT
THINK MOST OF THE PRECIPITATION WOULD BE IN THE FORM OF SNOW AT
LOWER ELEVATIONS EXCEPT WHATEVER FALLS SATURDAY NIGHT FARTHER EAST
ON THE PLAINS. THE DISTRIBUTION OF STORM TOTAL PRECIP VARIES
AMONGST THE GFS/NAM/ECMWF. THE ECMWF HAS AN AREA OF OVER AN INCH
ON THE PLAINS CENTERED NEAR THE NE/CO/WY TRIPLE POINT THAT IS FAR
LESS IN THE OTHER MODELS...INCLUDING OUR 00Z RUNS OF THE
EXPERIMENTAL FIM MODEL. THIS APPEARS TO BE ASSOCIATED WITH A
SMALLER SCALE MIDLEVEL CIRCULATION THAT COMES OUT OF THE MAIN
TROUGH LATE SATURDAY EVENING. THE GFS APPEARS TO HAVE THIS FEATURE
BUT EARLIER AND IS ALREADY EAST OF THE AREA BY 12Z SUNDAY SO
PRECIP WITH IT WOULD LIKELY BE RAIN.

GIVEN THE CONSISTENCY OF THE OVERALL SYSTEM COORDINATED WITH
SURROUNDING WFOS AND DECIDED TO HOIST A WINTER STORM WATCH FOR ALL
THE MOUNTAINS..FOOTHILL ZONES AND URBAN CORRIDOR. RIGHT NOW
FARTHER EAST PRECIP AMOUNTS IN THE FORM OF SNOW APPEAR TO BE TOO
LOW. THE STORM WILL LINGER INTO SUNDAY EVENING...ENDING FROM NORTH
TO SOUTH...AND THEN DRY WITH A WARMING TREND INTO MIDWEEK. THE
NEXT TROUGH WHICH WAS QUITE A WRAPPED UP SYSTEM IN THE GFS IS NOW
MUCH WEAKER IN AGREEMENT WITH THE LATEST ECMWF. ENSEMBLES FROM 00Z
WERE QUITE VARIABLE WITH THIS AND WOULD SAY VERDICT STILL OUT BUT
FOR NOW JUST HAVE SOME UNSETTLED LOWER LEVEL POPS LATER WED AND
THU.

AVIATION...(FOR THE TAFS THROUGH 00Z SATURDAY AFTERNOON)
ISSUED AT 215 PM MDT FRI APR 11 2014

STILL SOUTHEAST WINDS AT LOCAL TERMINALS BUT SEEING SOME SIGNS OF
WESTERLY WINDS DEVELOPING ACROSS BOULDER COUNTY. WILL DELAY THE
WEST WINDS A BIT OVE TERMINALS THIS AFTERNOON. WINDS WILL RETURN
TO DRAINAGE LATER THIS EVENING. THERE IS A SLIGHT CHANCE OF A
SHOWER OR THUNDERSTORM SATURDAY AFTERNOON. NOT ENOUGH TO INCLUDE
IN TAF FORECAST YET.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY
EVENING FOR COZ030>041.

&&

$$

SHORT TERM (UPDATE)...BAKER
LONG TERM....SZOKE
AVIATION (UPDATE)...BAKER


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