Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 171512
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
912 AM MDT SUN MAY 17 2015

.UPDATE...
ISSUED AT 857 AM MDT SUN MAY 17 2015

WATER VAPOR IMAGERY SHOWING WEAK UPPER WAVE ROTATING THROUGH
NORTHEAST COLORADO THIS MORNING. WEAK SUBSIDENCE BEHIND THIS
FEATURE AS SNOWFALL HAS DECREASED OVER HIGHER MOUNTAINS. HOWEVER
STILL ENOUGH MOISTURE AND OROGRAPHIC FLOW TO KEEP SNOW SHOWERS
GOING OVER HIGHER MOUNTAINS BUT THERE WILL BE SOME DIMINISHMENT AS
THE AFTERNOON WEARS ON AS MOUNTAIN TOP FLOW WEAKENS AND SHIFTS
MORE WEST AND SOUTHWEST. AIRMASS WILL ONLY BE SLIGHTLY UNSTABLE
THIS AFTERNOON DUE TO CLOUD COVER IN MOUNTAINS WHILE LOWER
ELEVATIONS HAVE RELATIVELY DRY LOW LEVELS. GUSTY NORTHWEST WINDS
HAVE ALREADY MIXED DOWN OVER THE PLAINS.  ONLY MINOR CHANGES TO
FORECAST PACKAGE.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 330 AM MDT SUN MAY 17 2015

THE STRONG TROUGH THAT LIFTED NORTHEAST OUT OF SOUTHEAST COLORADO
AND STRENGTHENED INTO A CLOSED LOW WILL BE OVER THE NORTHERN PLAINS
TODAY. A WEAKER WAVE EMBEDDED IN THE WEST-NORTHWEST FLOW ALOFT WILL
MOVE ACROSS WYOMING AND FAR NORTHERN COLORADO THIS MORNING. THIS
SYSTEM IS BRINGING SNOW TO THE MOUNTAINS. WILL HAVE HIGH POPS EARLY
THIS MORNING FOR THIS WITH AN ADDITIONAL 2 INCHES OF SNOW POSSIBLE.
WEB CAMERAS SHOWING MINOR SNOW ACCUMULATION ON THE ROADS OVER THE
HIGHER PASSES. DO NOT PLAN ON ISSUING ANY WINTER WEATHER HIGHLIGHTS
FOR THIS SYSTEM. ADDED LOW POPS THIS MORNING TO FAR NORTHERN
COLORADO FOR THIS WAVE.

IT WILL BE COME SLIGHTLY UNSTABLE THIS AFTERNOON. CAPES WILL BE LESS
THAN 500 J/KG AND MOISTURE WILL BE LIMITED WITH DEW POINTS IN THE
30S. EXPECT ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS FOR THIS
AFTERNOON AND EARLY EVENING. ANY PRECIPITATION IS EXPECTED TO BE
LIGHT AND SHORT LIVED. DUE TO THE DRY LOW LEVELS...GUSTY OUTFLOW
WINDS WILL BE POSSIBLE FROM THE CONVECTION.

FOR LATER TONIGHT...SURFACE HIGH PRESSURE WILL MOVE INTO THE
NORTHERN ROCKIES. THIS WILL PRODUCE A SURGE FROM THE NORTH AND BRING
COOLER AIR. MOISTURE WILL ALSO INCREASE BEHIND IT. EXPECT LOW CLOUDS
TO DEVELOP AFTER MIDNIGHT. COULD BE ENOUGH MOISTURE TO PRODUCE
DRIZZLE AROUND SUNRISE. THE INCREASE IN MOISTURE AND CLOUD COVER
WILL RESULT IN LOWS IN THE UPPER 30S AND LOWER 40S.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 330 AM MDT SUN MAY 17 2015

SWLY FLOW ALOFT WILL BE OVER THE AREA ON MON AS ANOTHER UPPER LEVEL
TROUGH DEVELOPS OVER THE WRN US.  MEANWHILE COOL SFC HIGH PRES WILL
CONTINUE TO BUILD ACROSS NERN CO.  THERE IS A WK DISTURBANCE
EMBEDDED IN THE SWLY FLOW WHICH COULD LEAD TO A CHC OF SHOWERS IN
THE MTNS MON MORNING WITH A SLIGHT CHC IN AND NR THE FOOTHILLS.  BY
AFTN THE LOW LVL FLOW WILL BE ELY ACROSS NERN CO WITH A STABLE
AIRMASS OVER THE PLAINS. BEST CHC OF SHOWER/TSTM DEVELOPMENT BY
AFTN WILL FOCUS OVER THE HIGHER TERRAIN WITH SOME OF THIS ACTIVITY
AFFECTING THE URBAN CORRIDOR BY LATE AFTN/EARLY EVENING. HIGHS ON
MON WILL BE MAINLY IN THE UPPER 50S TO LOWER 60S ACROSS NERN CO.

FOR MON NIGHT INTO TUE THE UPPER LEVEL TROUGH OVER THE WRN US WILL
BEGIN TO MOVE EASTWARD INTO THE GREAT BASIN WITH INCREASING SELY LOW
LVL FLOW EAST OF THE MTNS. MEANWHILE QG ASCENT WILL INCREASE ON
TUE AHEAD OF THE SYSTEM WITH DIFFLUENT FLOW ALOFT. THIS WILL ALLOW
FOR WIDESPREAD SHOWERS AND A FEW TSTMS BY TUE. WITH INCREASING
PRECIPITABLE WATER VALUES AND MOIST ADIABATIC SOUNDINGS WILL
LIKELY SEE SOME HEAVY RAIN WITH AVERAGE RAINFALL FROM 1 TO 1.5
INCHES OVER THE PLAINS WITH LOCALLY HIGHER AMOUNTS CERTAINLY
POSSIBLE. IN THE MTNS THERE WILL BE SOME POTENTIAL FOR HEAVY SNOW
ABOVE 10000 FT ESPECIALLY ON EAST FACING SLOPES. AS FOR HIGHS ON
TUE READINGS MAY STRUGGLE TO GET MUCH ABOVE 50 OVER NERN CO.

BY TUE NIGHT THE MAIN UPPER LEVEL TROUGH WILL MOVE ACROSS THE AREA
WITH MID LVL DESCENT SPREADING ACROSS THE AREA ALONG WITH SOME DRIER
AIR. PCPN SHOULD GRADUALLY DECREASE FM SW TO NE ACROSS THE CWA.  ON
WED A FLAT UPPER LEVEL RIDGE WILL BE OVER THE AREA.  THE ECMWF AND
GFS DIFFER ON THE SFC PTRN ACROSS NERN CO AS THE ECMWF HAS ANOTHER
SHOT OF COOLER AIR MOVING IN ON WED WHILE THE THE GFS DOES NOT.
THIS LEADS TO TEMP DIFFERENCES OF AROUND 10 DEGREES FOR AFTN HIGHS
AS THE ECMWF KEEPS READINGS IN THE LOWER TO MID 50S WHILE THE GFS
HAS HIGHS IN THE LOWER TO MID 60S.  IF THE AIRMASS IS COOLER LIKE
THE ECMWF SHOWS THEN THE CHC FOR AFTN CONVECTION OVER NERN CO WOULD
BE RATHER LIMITED AND CONFINED TO THE HIGHER TERRAIN AS A STABLE
AIRMASS WOULD BE IN PLACE OVER THE PLAINS. FOR NOW WILL NOT CHANGE
MUCH FM PREVIOUS FCST.

ON THU THE FLOW ALOFT WILL BECOME MORE SWLY AS ANOTHER TROUGH DVLPS
OVER THE WRN US.  AT THE SFC LOW PRES WILL BE OVER WRN CO AS SFC
HIGH PRES RESIDES OVER THE CNTRL US.  THIS SHOULD LEAD TO INCREASING
SELY LOW LVL FLOW EAST OF THE MTNS.  THERE IS STILL SOME
DISAGREEMENT AS TO HOW MUCH WARMING WILL OCCUR OVER NERN CO AS THE
ECMWF HAS HIGHS ONLY IN THE MID 50S TO LOWER 60S WHILE THE GFS HAS
READINGS IN THE MID 60S TO LOWER 70S.  IF TEMPS ARE COOLER LIKE THE
ECMWF SHOW THEN THE CHANCE FOR CONVECTION OVER THE PLAINS WILL BE
RATHER LOW VS THE GFS WHICH HAS FAR MORE INSTABILITY DUE TO WARMER
TEMPS.  FOR NOW WILL LEAVE IN LOW POPS.  IN THE MTNS THERE WILL BE
BETTER INSTABILITY SO WILL KEEP IN SCT POPS.

FOR FRI THE GFS MOVES THE UPPER LEVEL TROUGH INTO THE GREAT BASIN
WHILE THE ECMWF KEEPS THE MAIN TROUGH FURTHER TO THE SW.  AT THE SFC
LOW PRES WILL DVLP FM CNTRL WY INTO CNTRL CO WITH SELY LOW LVL FLOW
EAST OF THE MTNS.  THIS SHOULD ALLOW FOR DEEPER LOW LVL MOISTURE AND
HIGHER INSTABILITY TO DVLP OVER NERN CO WITH A BETTER CHC OF TSTMS
AS WK DISTURBANCES MOVE ACROSS IN SWLY FLOW ALOFT.  THE MTNS SHOULD
ALSO SEE A CHC OF SHOWERS AND STORMS AS WELL. BY SAT THE MAIN UPPER
LEVEL TROUGH IS FCST TO MOVE ACROSS COLORADO WHICH WOULD LEAD TO
ANOTHER GOOD CHC OF SHOWERS AND TSTMS WITH SOME SNOW IN THE MTNS.
TEMPS BOTH FRI AND SAT WILL LIKELY STAY BLO SEASONAL NORMALS.

&&

.AVIATION...(FOR THE TAFS THROUGH 18Z MONDAY MORNING)
ISSUED AT 857 AM MDT SUN MAY 17 2015

SURFACE WINDS WILL SHIFT MORE NORTHERLY BY LATER THIS MORNING AS
WEAK BOUNDARY CAN BE SEEN MOVING SOUTH OVER WELD COUNTY. DON`T SEE
MUCH SUPPORT FOR THUNDERSTORMS AT KDEN THIS AFTERNOON AS IT
APPEARS MOST SHOWERS WILL REMAIN ANCHORED ON HIGHER TERRAIN WITH
MINIMAL MOISTURE AND INSTABILITY. WILL REMOVE THE VCTS FROM KDEN
AT LEAST. WINDS WILL BECOME MORE NORTHEAST TONIGHT AS SURFACE HIGH
PRESSURE BUILDS SOUTHWARD FROM WYOMING. THIS WILL LEAD TO STRATUS
DEVELOPING LATER TONIGHT ALONG WITH LIGHT SHOWERS/DRIZZLE.

&&

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

$$

UPDATE...ENTREKIN
SHORT TERM...MEIER
LONG TERM...RPK
AVIATION...ENTREKIN



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