Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 151520
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
920 AM MDT MON SEP 15 2014

.UPDATE...
ISSUED AT 859 AM MDT MON SEP 15 2014

CURRENT OBSERVATIONS AND TRENDS SUGGEST THAT THE LOW STRATUS
ACROSS THE NORTHEASTERN COLORADO PLAINS IS UNLIKELY TO MOVE WEST
INTO THE FRONT RANGE CORRIDOR. THERE IS SOME WESTWARD MOVEMENT OF
THE STRATUS, BUT THE WEST EDGE IS ERODING AT ALMOST THE SAME PACE.
THE DISSIPATION OF STRATUS WILL BECOME MORE DOMINANT BY MIDDAY.
THEREFORE ADJUSTED THE CLOUD COVER A LITTLE TO REDUCE COVERAGE A
FEW HOURS SOONER ALONG WESTERN AND NORTHERN SIDES OF LOW CLOUD
SHIELD. ALSO INCREASED MAX TEMPS THIS AFTERNOON BY A DEGREE OR TWO
ALONG THE FRONT RANGE. DEVELOPMENT OF DENVER CYCLONE PATTERN IN THE
SURFACE WINDS STILL LOOKS GOOD. DID NOT CHANGE THE POPS OR QPF.
STILL EXPECT ONLY ISOLATED IN THE MOUNTAINS DUE TO LIMTED SURFACE
HEATING EAST OF THE MOUNTAINS.

UPDATE ISSUED AT 646 AM MDT MON SEP 15 2014

STRATUS DECK HAS ACTUALLY ERODED SLIGHTLY BACK TO THE EAST WITH A
SLIGHT NORTH/NORTHWEST COMPONENT JUST OFF THE DECK SEEN IN THE
KFTG VAD WIND PROFILER. STILL WAITING FOR A TURN TO MORE EASTERLY
BUT STRATUS WILL ALSO BE TRYING TO ERODE FROM THE WESTERN EDGE
WITH DAYTIME HEATING. WILL ADJUST SKY COVER ACCORDINGLY...BUT
STILL POTENTIAL FOR THE STRATUS DECK TO FILL BACK IN ALONG THE
I-25 CORRIDOR BEFORE FURTHER EROSION THIS AFTERNOON.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 333 AM MDT MON SEP 15 2014

MAIN CONCERN TODAY IS EXTENT OF STRATUS AND EFFECT ON HIGH
TEMPERATURES. CURRENT 11-3.9 MICRON IMAGERY SHOWS AN EXPANDING
STRATUS DECK EARLY THIS MORNING ACROSS NORTHEAST COLORADO.
HOWEVER...THERE WAS A NARROW NOSE OF DRIER NORTH/NORTHWEST FLOW
CLOSER TO THE FRONT RANGE WHICH WAS LIMITING DEVELOPMENT IN THE
BOULDER TO FORT COLLINS CORRIDOR. WHILE THE SURFACE FLOW COULD
REMAIN LIGHT/VARIABLE IN THIS AREA...THE FLOW JUST ABOVE THE
SURFACE SHOULD BE TURNING MORE EASTERLY THROUGH DAYBREAK ALLOWING
MORE STRATUS TO DEVELOP. FARTHER EAST...AIRMASS WAS MORE MOIST
WITH AREAS OF FOG AND PERHAPS SOME DRIZZLE DEVELOPING EARLY THIS
MORNING. TEMPERATURES WILL BE MUCH COOLER THAN YESTERDAY...BUT
CERTAINLY HARD TO PIN POINT ESPECIALLY WITH CURRENT GAPS IN
STRATUS DECK. THIS COULD ALLOW EROSION FROM THE EDGES LATER THIS
MORNING INTO THE AFTERNOON...BUT AT THE SAME TIME AN INCREASING
EASTERLY COMPONENT IN DENVER CYCLONE REGIME WOULD REINFORCE
DEVELOPMENT FROM DENVER NORTHWARD. WILL OPT FOR A CONSERVATIVE
FORECAST WITH HIGH TEMPS IN THE MID/UPPER 60S MOST AREAS...BUT A
FEW SPOTS COULD REACH LOWER TO MID 70S WITH ENOUGH SUNSHINE. AT
THIS TIME THE WARMER TEMPS WOULD MOST LIKELY OCCUR IN THE PALMER
DIVIDE AREA IF LATE DAY FLOW TURNS DOWNSLOPE SOUTHEASTERLY THERE.

ANY AFTERNOON CONVECTION SHOULD REMAIN CONFINED TO THE HIGH
COUNTRY WHERE ENOUGH DAYTIME HEATING WILL OCCUR TO BREAK CAP. MOST
CONVECTION SHOULD FIRE ON THE BOUNDARY ACROSS THE FRONT RANGE
MOUNTAINS BETWEEN HIGHER MOISTURE AIR ON THE EAST AND DRIER BUT
MORE UNSTABLE AIRMASS TO THE WEST. SOME WESTERLY COMPONENT SHOULD
PUSH A FEW SHOWERS/STORMS INTO THE FOOTHILLS BUT THEN DISSIPATE AS
THEY MOVE INTO THE CONSIDERABLY MORE STABLE AIRMASS OF THE
PLAINS.

FOR TONIGHT...SKIES EXPECTED TO GRADUALLY CLEAR WITH THE EXCEPTION
OF THE EASTERN PLAINS. THERE...RETURN FLOW MOISTURE WILL LIKELY
RESULT IN REDEVELOPMENT OF STRATUS AND SOME FOG.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 333 AM MDT MON SEP 15 2014

AN UPPER LEVEL RIDGE WILL BE OVER THE SWRN US ON TUE AND THEN WILL
EXPAND NORTHEAST INTO COLORADO ON WED.  SOME LIMITED MID LVL
MOISTURE MAY AFFECT THE MTNS BOTH DAYS WHICH COULD LEAD TO SOME
ISOLD AFTN STORMS OVER THE HIGHER TERRAIN OTHERWISE IT LOOKS DRY
BOTH DAYS.  TEMPERATURES WILL REBOUND INTO THE LOWER TO MID 80S OVER
NERN CO ON TUE AS DOWNSLOPE WNW LOW LVL WINDS DVLP.  ON WED BOTH THE
NAM AN ECMWF SHOW A WEAK SURGE AFFECTING THE FAR NERN PLAINS WHILE A
LEE TROUGH IS ALONG THE FRONT RANGE.  THUS MAY SEE SOME VARIANCE IN
AFTN HIGHS WITH READINGS IN THE MID TO UPPER 80S ALONG THE FRONT
RANGE WHILE OVER THE FAR NERN CORNER HIGHS MAY ONLY REACH THE LOWER
80S.  MEANWHILE DECENT CAPE WILL OCCUR OVER THE FAR NERN CORNER
WHERE LOW LVL MOISTURE POOLS BEHIND THE WEAK BNDRY.  SOUNDINGS SHOW
AIRMASS WILL BE CAPPED SO WILL NOT MENTION ANY STORMS FOR NOW.

BY THU THE UPPER LEVEL RIDGE WILL MOVE SLIGHTLY EASTWARD WITH THE
FLOW ALOFT BECOMING MORE SWLY.  AT THIS TIME THERE STILL IS NOT MUCH
TROPICAL MOISTURE EMBEDDED IN THE FLOW SO WILL ONLY KEEP IN SOME
ISOLD STORMS IN THE MTNS.  AFTN HIGHS WILL ONCE AGAIN BE SEVERAL
DEGREES ABV NORMAL WITH READINGS IN THE 85 TO 90 DEGREE RANGE OVER
NERN CO.  FOR FRI BOTH THE ECMWF AND GFS EJECT THE REMNANTS OF ODILE
ENE ACROSS THE SRN ROCKIES INTO SERN CO.  IF IT TAKES THIS TRACK
THEN TROPICAL MOISTURE FM ODILE WILL STAY MAINLY SOUTH OF THE
AREA. MEANWHILE A WEAK UPPER LEVEL TROUGH MAY STILL AFFECT NRN CO
AS A COOL FNT MOVES ACROSS IN THE AFTN OR EVENING HOURS. AT THIS
TIME IT LOOKS LIKE THE BEST CHC OF PCPN WILL BE IN THE MTNS WITH A
SLIGHT CHC OVER THE PLAINS. AS FOR HIGHS READINGS WILL DEPEND ON
TIMING OF FNTL PASSAGE. IF FNT COMES IN DURING THE LATE AFTN OR
EVENING HOURS THEN HIGHS MAY RISE BACK INTO THE 80S ONCE AGAIN
OVER NERN CO.

ON SAT NRN CO WILL BE IN WK NWLY FLOW ALOFT AS SFC HIGH PRES BUILDS
INTO NERN CO.  FOR NOW THE BEST MOISTURE IS FCST TO BE IN THE MTNS
WITH A DRIER AIRMASS OVER NERN CO.  THUS WILL KEEP A CHC OF STORMS
IN THE MTNS BUT KEEP NERN CO MAINLY DRY EXCEPT NR THE FOOTHILLS.
HIGHS ON SAT SHOULD DROP BACK INTO THE 70S OVER NERN CO.  FOR SUN A
WEAK UPPER LEVEL LOW WILL BE OVER THE GREAT BASIN WHICH MAY ALLOW
FOR SOME TROPICAL MOISTURE TO ADVECT INTO THE MTNS SO WILL KEEP IN A
A CHC OF TSTMS.  OVER NERN CO THE LOW LEVEL FLOW WILL BE SELY WHICH
MAY ALLOW FOR SOME RETURN OF LOW LVL MOISTURE SO WILL KEEP IN A
SLIGHT CHC OF SHOWERS/TSTMS WITH HIGHS IN THE LOWER TO MID 70S.

&&

.AVIATION...(FOR THE TAFS THROUGH 18Z TUESDAY MORNING)
ISSUED AT 859 AM MDT MON SEP 15 2014

LESS CONCERNED ABOUT WIDESPREAD LOW STRATUS BACKING INTO THE
FRONT RANGE BUT KEPT THE POSSIBILITY OF A FEW BRIEF PERIODS OF
BROKEN STRATUS THIS MORNING OUT NEAR DIA. KEPT THE PROGRESSION OF
WIND DIRECTION AROUND TO NORTHEAST AND THEN TO SOUTHEAST BUT HAVE
THE SOUTHEAST WIND DIRECTION KICKING IN THIS AFTERNOON ABOUT AN
HOUR EARLIER THAN PREVIOUS DISCUSSION. THIS IS IN RESPONSE TO
STRONG PRESSURE FALLS OVER NORTHEASTERN COLORADO AND EASTERN
WYOMING. WILL PROBABLY SET UP A DENVER CYCLONE CIRCULATION WITH
SOUTHEAST WINDS AT DIA BUT LIGHT NORTH WINDS AT BJC THIS
AFTERNOON.

&&

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

$$

UPDATE...GIMMESTAD/KELSCH
SHORT TERM...BARJENBRUCH
LONG TERM...RPK
AVIATION...GIMMESTAD/KELSCH


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