MESOSCALE PRECIPITATION DISCUSSION 0239
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1223 PM EDT THU SEP 12 2013
 
AREAS AFFECTED...CENTRAL AND NORTHERN CO/SOUTHEASTERN WY... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 121622Z - 122052Z
 
SUMMARY...PERSISTENT UPSLOPE FLOW COUPLED WITH RECORD ATMOSPHERIC
MOISTURE CONTENT HAS LED TO NUMEROUS FLASH FLOODS IN THE BOULDER
CO AREA. LITTLE CHANGE TO THESE PARAMETERS WILL MAINTAIN THE
THREAT FOR FLASH FLOODING IN THE ENCOMPASSED AREA...BUT IN
PARTICULAR WITHIN THE REGION WHICH ALREADY HAS SEEN 4 TO 7 INCHES
OF RAIN.

DISCUSSION...THE 12Z RAOB FROM DNR DEPICTED A MOIST ADIABATIC
SOUNDING FROM THE SURFACE UP TO 500 MB. MUCH OF THIS REGION OF
SATURATION WAS LOCATED BELOW THE FREEZING LEVEL LEADING TO AN
EXPANSIVE WARM CLOUD LAYER. THIS LOW-TOPPED CONVECTION CONTINUES
TO FEED OFF THE MINIMAL...BUT SUFFICIENT TALL/SKINNY CAPE PROFILE
WHICH HAS GENERALLY BEEN IN PLACE THE PAST SEVERAL HOURS. THE KFTG
RADAR HAS SHOWN VERY LITTLE CHANGE IN THE LOW-LEVEL UPSLOPE FLOW
PER THE VAD WIND PROFILE. THE 14Z RAP/13Z HRRR ACTUALLY SHOWS THE
BOUNDARY LAYER TO 700-MB WINDS WILL BE ON THE INCREASE WHILE
MAINTAINING THE SOUTHEAST TO EASTERLY DIRECTION. THIS IS FORECAST
TO AID IN LOCALLY ENHANCING THE PWAT VALUES WHICH WERE ALREADY AT
A SEPTEMBER RECORD MAXIMUM OF 1.33 INCHES AS OF 12Z. FURTHER...THE
TRANSPORT OF SURFACE MOISTURE IS EVIDENT AS THE BOUNDARY OF 60F
AND ABOVE DEWPOINTS HAVE WORKED THEIR WAY WELL INTO EASTERN CO.

THE UPPER LEVEL PATTERN OVER THE REGION IS NOT EXPECTED TO CHANGE
MUCH IN THE UPCOMING HOURS AS A VERY DIFFULENT 250-MB FLOW IS
DEPICTED BY ALL RECENT GUIDANCE. THE EXPECTED HIGHLY EFFICIENT
WARM RAIN PROCESSES WILL CONTINUE WITH ADDITIONAL HEAVY RAINFALL
OVER AREAS WHICH ARE CURRENTLY FLOODING. THIS EVENT ALREADY HAS A
HISTORY OF SEVERE DAMAGE TO INFRASTRUCTURE WHICH INCLUDES A COUPLE
FATALITIES. THE FLASH FLOOD THREAT WILL REMAIN LIKELY WITH THE
POSSIBILITY OF FUTURE MESOSCALE DISCUSSIONS IF CONDITIONS DO NOT
CHANGE DRASTICALLY.


RUBIN-OSTER

ATTN...WFO...PUB...BOU...CYS...

ATTN...RFC...ABRFC...CBRFC...MBRFC...

LAT...LON   38160557 39310555 40100577 41530625 42210554 41660463
            40070392 39310393 38790451 37870481 38160557