MESOSCALE PRECIPITATION DISCUSSION 0235
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1158 PM EDT WED SEP 11 2013
 
AREAS AFFECTED...CENTRAL AND NORTHERN CO...SE WY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 120340Z - 120840Z
 
SUMMARY...UNIQUE FLASH FLOOD THREAT WAS EVOLVING ALONG THE
COLORADO FRONT RANGE. ENVIRONMENT FAVORING HEAVY RAIN RATES WITH
LITTLE OR NO LIGHTNING...EXPECTED TO PERSIST OVERNIGHT. FLASH
FLOOD PRONE AREAS ALONG THE ROCKIES FRONT RANGE ARE AT RISK FOR
SIGNIFICANT FLASH FLOODING.

DISCUSSION...AT 03Z WE NOTE RECENT FLASH FLOOD WARNINGS AND
OBSERVED RAIN RATES AS HIGH AS 1 INCH IN A HALF HOUR FROM PUEBLO
TO BOULDER. DNR RAOB INDICATED DEEPLY SATURATED LOW LEVELS WITH
WEAK BUT SUFFICIENT CAPE TO SUPPORT DEEP MOIST CONVECTION.
FREEZING LEVEL WAS RATHER HIGH...AT OVER 10000 FT AGL...AND RADAR
REVEALED CLOUD TOPS PEAKING NEAR 25000 FT AGL. PER THE
SOUNDING...MUCH OF THE CLOUD BEARING LAYER WAS WARMER THAN
-12C...WITH VERY WARM AND SATURATED LOW LEVELS. THIS YIELDS A
LIKELY WARM RAIN PROCESS WHICH MATCHES THE ABSENCE OF LIGHTNING
AND INTENSITY OF THE OBSERVED RAIN RATES. AND THE SATURATED LOW
LEVELS WERE LEAVING LITTLE ROOM FOR COLD POOL PRODUCTION.
THIS...COMBINED WITH LIGHT MID LEVEL STEERING WINDS...WILL YIELD
SLOW CELL MOVEMENT TO THE NORTH AND WEST.

ALREADY ONE MCV APPEARED TO HAVE FORMED BETWEEN DENVER AND
BOULDER...AND THIS CIRCULATION WAS FOCUSING A BAND OF TRAINING
ECHOES FROM EAST TO WEST. KFTG DUAL POL RAIN ESTIMATES APPEARED
REASONABLE...WITH THREE HOUR AMOUNTS APPROACHING 2.5 INCHES IN
THIS BAND. THE CONCERN IS THAT THIS REGION WILL REMAIN BENEATH
DIFFLUENT UPPER LEVELS THAT WILL MAINTAIN WEAK INSTABILITY TO
OFFSET THE STABILIZING INFLUENCE OF THE CONVECTION... ALLOWING FOR
A RELATIVELY LONG DURATION PERIOD OF THIS TYPE OF ORGANIZED HEAVY
RAINFALL. HIGH RESOLUTION MODELS BEAR THIS OUT...WITH THE WRF
ARW...NSSL WRF...NAM CONEST...AND THE MEAN OF THE EXPERIMENTAL
SREF RUNS PREDICTING POCKETS OF 3-4 INCH RAINFALL AMIDST AN EAST
TO WEST SWATH OF HEAVY RAIN OVER NORTHEAST COLORADO TONIGHT. OTHER
MORE ISOLATED CELLS WILL BE POSSIBLE FARTHER SOUTH...AND THE MAIN
BAND MAY TEND TO LIFT NORTHWARD...AFFECTING SOUTHEAST WYOMING.

WITH INITIAL ACTIVITY SHOWING TENDENCY TO BECOME BETTER ORGANIZED
AS IT FEEDS INTO THE ZONE OF CONVERGENT 850 MB WINDS ALONG THE
FRONT RANGE...SOME OF THE HEAVIEST RAIN MAY AFFECT TERRAIN THAT IS
VERY PRONE TO FLASH FLOODING. LACK OF LIGHTNING WILL MAKE THIS A
DECEPTIVE RAINFALL...PERHAPS MASKING THE DANGERS OF FLASH FLOODING.

BURKE

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

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

LAT...LON   41880541 41800613 41380639 39720612 38510602 38010578
            37700526 38010447 38550379 39240250 40410287 41020408
            41550471 41880541