MESOSCALE PRECIPITATION DISCUSSION 0319
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
131 AM EDT TUE AUG 26 2014
 
AREAS AFFECTED...SOUTHEAST NE...CENTRAL AND SOUTHERN IA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 260530Z - 261130Z
 
SUMMARY...EXPANDING BANDS OF BACK-BUILDING AND TRAINING CONVECTION
WITH VERY HEAVY RAINFALL ARE EXPECTED OVERNIGHT AND INTO THE EARLY
MORNING HOURS.

DISCUSSION...THE LATEST RADAR IMAGERY SHOWS A RAPIDLY EXPANDING
AXIS OF INTENSE ELEVATED CONVECTION OVER PORTIONS OF SERN NEB AND
DEVELOPING NEAR THE NE/IA BORDER. CLOUD TOPS ARE RAPIDLY EXPANDING
IN THIS AREA AND THE CONVECTION IS DEVELOPING WITHIN A VERY STRONG
INSTABILITY GRADIENT THAT EXTENDS NORTH OF A STATIONARY FRONT.
THERE IS EVIDENCE IN WV SAT IMAGERY OF A WEAK SHORTWAVE EJECTING
OUT OF NERN CO AND THIS ENERGY IS INTERACTING WITH THE
AFOREMENTIONED FRONT AND STRONG INSTABILITY GRADIENT. MUCH OF THE
CONVECTION APPEARS SO FAR TO BE ALIGNING ITSELF WITH THE BEST
850MB TO 800 MB CONVERGENCE.

THE 00Z NAM-CONEST AND 00Z NSSL-WRF INDICATE A FORMIDABLE W/E OR
WSW/ENE AXIS OF STRONG CONVECTION SETTING UP THROUGH 06Z AND TWD
THE PREDAWN HOURS INVOLVING SERN NEB AND CNTRL AND SWRN IA.
ADDITIONALLY...THE EXPERIMENTAL NEARCAST PRODUCT INDICATES AN AXIS
OF DIFFERENTIAL THETA-E THAT SUPPORTS AN INSTABILITY AXIS ACROSS
SERN NEB AND THROUGH A LARGE PART OF CNTRL AND SRN IA. THIS IS
ALREADY WITHIN THE INSTABILITY GRADIENT AS SEEN BY THE LATEST RAP
ANALYSIS...BUT THE NEARCAST PRODUCT INDICATES THIS PERSISTING
THROUGH 12Z. THEREFORE...CONFIDENCE IS RATHER HIGH THAT CONVECTION
WILL CONTINUE TO ORGANIZE AND EXPAND IN A GENERAL WSW/ENE FASHION
OVERNIGHT AND ADVANCE INTO OR DEVELOP ACROSS CNTRL/SWRN IA IN
PARTICULAR.

PWATS NEAR 1.75 INCHES WILL FAVOR RAINFALL RATES UP TO 2
INCHES/HR...AND WITH TRAINING CONVECTION APPEARING LIKELY ALONG
WITH BACK-BUILDING CELLS...STORM TOTALS MAY LOCALLY EXCEED 5
INCHES. THEREFORE...THE THREAT FOR FLASH FLOODING IS ELEVATED.

ORRISON

ATTN...WFO...DVN...DMX...OAX...GID...

ATTN...RFC...MBRFC...NCRFC...

LAT...LON   41839646 42219495 42389321 42339217 42089155 41579134
            41139165 40849230 40759333 40739472 40539622 40209771
            40229855 40589895 41159821 41839646