Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 291730
AFDBOU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1130 AM MDT TUE JUL 29 2014

.UPDATE...
ISSUED AT 1117 AM MDT TUE JUL 29 2014

ONLY MINOR CHANGES TO THE FORECAST AT THIS TIME...MAINLY RAISING
POPS IN MOST PLACES. SHORTWAVE TIMING BECOMING MORE EVIDENT AND
THE MAIN EVENT WILL BE THE AREA OF LIFT NOW OVER THE NORTHWEST
QUARTER OF COLORADO MOVING EAST ACROSS THE MOUNTAINS THIS
AFTERNOON AND THEN MORE SLOWLY SOUTHEAST OVER THE PLAINS
OVERNIGHT. FOOTHILLS CONVECTION STARTING AHEAD OF THIS IN AN
AIRMASS THAT IS A LITTLE DRIER...PLAINS WILL LIKELY BE WEAKLY
CAPPED. NOT SURE IF THE EARLY CONVECTION WILL BE ABLE TO PROPAGATE
EASTWARD OR NOT...THE SYNOPTICALLY FORCED BLOB WILL BE A COUPLE OF
HOURS BEHIND IT REACHING DENVER IN THE MID AFTERNOON.

EXPECT THAT THE MAIN FLASH FLOOD THREAT WILL BE LOCALIZED
STATIONARY STORMS DUE TO BOUNDARY INTERACTIONS...BUT THERE IS SOME
POTENTIAL FOR A FOOTHILLS FOCUS WITH WEAK EASTERLY WINDS STARTING
TO DEVELOP AS EXPECTED. MESOSCALE MODELS ARE SHOWING ADDITIONAL
STORM DEVELOPMENT OVER THE FOOTHILLS BEHIND THE MAIN BLOB DURING
THE NIGHT...BUT IT IS RATHER RANDOM AND DISORGANIZED. I DO NOT
WANT TO DISCOUNT THE POSSIBILITY OF PROBLEMS IN THE FOOTHILLS
TONIGHT AS THE WIND PROFILE WILL BE GREAT FOR STATIONARY OR
TRAINING STORMS AND THE ENVIRONMENT WILL BE BETTER WITH A
SATURATED ENVIRONMENT. HOWEVER I AM NOT SEEING SIGNS OF AN
ORGANIZED LARGE SCALE EVENT AT THIS TIME. THINGS TO WATCH FOR AS
THE DAY GOES ON WOULD INCLUDE A BETTER LARGE MESOSCALE WIND FIELD
ASSOCIATED WITH THE SHORTWAVE...AND/OR ORGANIZED OUTFLOW FROM
CONVECTION IN NE COLORADO OR AREAS JUST NORTH OF US. THERE IS A
LITTLE BIT OF PRESSURE RISE IN THE EXISTING RAINBAND OVER WESTERN
WYOMING...IT WOULD NEED TO AMPLIFY TO PRODUCE STRONGER UPSLOPE
WHICH COULD HAPPEN.

&&

.SHORT TERM...(TODAY THROUGH TONIGHT )
ISSUED AT 403 AM MDT TUE JUL 29 2014

FCST THIS AFTN THRU TONIGHT IS RATHER COMPLICATED.  THERE IS A WELL
DEFINED UPPER LEVEL DISTURBANCE OVER SWRN UTAH WHICH IS MOVING NNE
WITH A SECONDARY DISTURBANCE POSSIBLY OVER NERN UTAH.  OVERALL THIS
FEATURE OVER NERN UTAH MAY BE THE ONE THAT IS SUPPOSED TO MOVE
SLOWLY AROUND THE UPPER LEVEL HIGH AND INTO NRN CO BY TONIGHT.
MEANWHILE AT THE SFC LOW PRES WILL BE OVER SERN CO AS SFC HIGH PRES
BUILDS INTO NRN CO THIS EVENING.

SHOULD SEE CONVECTION DEVELOP BY MIDDAY IN THE MTNS AND THEN IN AND
NR THE FOOTHILLS BY EARLY TO MID AFTN AND ACROSS THE ADJACENT PLAINS
BY LATE AFTN.  PRECIPITABLE WATER VALUES ARE FCST TO INCREASE TO
1.25 INCHES BY LATE THIS AFTN WITH VALUES POSSIBLY UP TO 1.5 INCHES
TONIGHT OVER NERN CO IF GFS IS CORRECT.  THUS ANY STORM WILL HAVE
THE POTENTIAL TO PRODUCE VERY HEAVY RAIN THIS AFTN THRU THE EARLY
EVENING HOURS.

FOR TONIGHT IF A WIDESPREAD HEAVY RAIN EVENT IS GOING TO DVLP WILL
HAVE TO GET WRM CORE RAIN PROCESSES TO TAKE OVER FM MID EVENING THRU
THE LATE NIGHT HOURS.  THERE IS SOME HINT THAT A WK 700 MB
CIRCULATION WILL OCCUR WITH THE DISTURBANCE MOVING ACROSS TONIGHT
AND WILL COMBINE WITH WK FNT MOVING INTO NERN CO TO ENHANCE ELY LOW
LVL FLOW IN AND NR THE HIGHER TERRAIN.  SO FAR THE NAM...ECMWF AND
THE SREF PLUMES ARE FOCUSING ON AREAS FM BOULDER COUNTY INTO LARIMER
COUNTY WHILE THE GFS HAS A WOUND UP 700 MB CIRCULATION CENTER OVER
THE ERN PLAINS WHICH FOCUSES THE HEAVIEST RAINS AWAY FM THE HIGHER
TERRAIN.  NATURALLY IF THE WRM RAIN PROCESSES GET GOING AFTER SUNSET
RAINFALL AMOUNTS OVER A 6 HOUR PERIOD CAN ADD UP QUICKLY AS WE SAW
LAST SEPTEMBER.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 403 AM MDT TUE JUL 29 2014

LOOKS LIKE WEDNESDAY IS GOING TO BE THE COOLEST DAY OF THE WEEK
AND MAYBE THE WETTEST. THE MOIST AIRMASS IS GOING TO REMAIN
ANCHORED OVER THE STATE WITH EASTERLY FLOW FROM THE SURFACE UP
TO ALMOST 600 MB. QUASI-GEOSTROPHIC DIAGNOSTICS FROM EACH OF THE
SYNOPTIC MODELS SHOW AT LEAST WEAK FORCING FOR ASCENT OVER THE
STATE THROUGH MONDAY AFTERNOON. THIS SHOULD ALLOW THE UPSLOPE FLOW
TO CONTINUE LIFTING THE AIRMASS...RELEASING THE INSTABILITY
THROUGH CONTINUED DEVELOPMENT OF RAIN SHOWERS. MODEL SOUNDINGS
FROM THE NAM SHOW A SATURATED AND MOIST ADIABATIC
AIRMASS...REMINISCENT OF THE SHAPE SEEN DURING WINTER STORMS.
PRECIPITABLE WATER VALUES ARE FORECAST TO BE AT OR ABOVE AN INCH
WITH AN ALMOST 8000 FOOT DEEP WARM LAYER. ALL OF THE INGREDIENTS
FOR HEAVY RAIN LOOK LIKE THEY WILL BE PRESENT. WILL CARRY THE
FLASH FLOOD WATCH THROUGH 6 PM WEDNESDAY EVENING.

THROUGH THE REST OF THE FORECAST PERIOD...TEMPERATURES WILL REMAIN
COOLER THAN SEASONAL NORMALS AS THE MONSOONAL FLOW KEEPS MOISTURE
OVER COLORADO. THE UPPER FLOW PATTERN WILL BE VERY COMPLICATED BUT
WEAK AS THE UPPER RIDGE REMAINS OVER THE SOUTHERN ROCKIES. WINDS
ALOFT WILL BE WEAK AND NORTHWESTERLY THROUGH SUNDAY AND THEN MAY
SWITCH TO SOUTHERLY ON MONDAY AS AN UPPER TROUGH PUSHES IN FROM
THE GREAT BASIN. MONSOONAL MOISTURE WILL CONTINUE ADVECTING OVER
THE SOUTHWESTERN U.S. WHILE A SURFACE RIDGE OVER THE CENTRAL
PLAINS SETS UP SOUTHERLY LOW LEVEL FLOW...LADEN WITH GULF
MOISTURE...ACROSS EASTERN COLORADO. DAYTIME HEATING WILL CAUSE
AIRMASS DESTABILIZATION EACH AFTERNOON...WITH SLOW MOVING
THUNDERSTORMS THE RESULT. BURN SCARS AND AREAS THAT GET RAINFALL
ON CONSECUTIVE DAYS WILL BE UNDER THE GUN FOR FLASH FLOODING
PROBLEMS.

&&

.AVIATION...(FOR THE TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 403 AM MDT TUE JUL 29 2014

MAIN AREA OF SHOWERS AND STORMS WILL MOVE INTO THE DENVER AREA
AROUND MID AFTERNOON...THOUGH THERE IS A CHANCE OF AN EARLIER
STORM OR WIND SHIFT. AFTER THAT EXPECT AREAS OF MVFR CONDITIONS
AND LOCALIZED IFR IN HEAVIER RAIN THROUGH THE NIGHT.

&&

.HYDROLOGY...
ISSUED AT 403 AM MDT TUE JUL 29 2014

THE THREAT FOR FLASH FLOODING WILL INCREASE THIS AFTERNOON
THROUGH TONIGHT. AT THIS TIME ITS STILL TOO EARLY TO TELL WHERE
THE HEAVIEST RAINS MAY FOCUS. OVERALL RAIN AMOUNTS WILL AVERAGE
FROM 1 TO 2 INCHES WITH 3 TO 4 INCHES IN A FEW LOCATIONS. IF THE
WARM RAIN PROCESSES KICK IN AFTER SUNSET AND CONTINUE OVERNIGHT
THEN A MORE WIDESPREAD HEAVY RAIN EVENT COULD OCCUR IN SOME AREAS
WITH EVEN HIGHER RAINFALL TOTALS. A FLASH FLOOD WATCH REMAINS IN
EFFECT FOR THE MOUNTAINS...FOOTHILLS AND MOST OF NORTHEAST
COLORADO THIS AFTERNOON THROUGH WEDNESDAY.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH WEDNESDAY AFTERNOON FOR COZ033>047-049.

&&

$$

UPDATE...GIMMESTAD
SHORT TERM...RPK
LONG TERM...DANKERS
AVIATION...GIMMESTAD
HYDROLOGY...RPK


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