Graphic for MPD #0709

MESOSCALE PRECIPITATION DISCUSSION 0709
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1210 AM EDT MON AUG 21 2017

AREAS AFFECTED...NORTHEASTERN NEBRASKA...WESTERN AND CENTRAL IOWA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 210410Z - 211010Z

SUMMARY...CONVECTION IS EXPECTED TO INCREASE IN COVERAGE OVER THE
NEXT FEW HOURS AND MAY BEGIN TO BACK-BUILD/TRAIN...RESULTING IN
LOCALLY HEAVY ACCUMULATIONS.  FLASH FLOODING IS POSSIBLE.

DISCUSSION...A LOW LEVEL JET STRENGTHENING TO 30-40 KTS WILL
SUPPORT A DEEPENING MOISTURE POOL NEAR THE INTERSECTION OF A
SLOW-MOVING FRONTAL BOUNDARY THAT EXTENDS FROM THE UPPER GREAT
LAKES BACK INTO THE MID MO VALLEY AND AN OUTFLOW BOUNDARY
ASSOCIATED WITH THE PREVIOUS NIGHT'S CONVECTION THAT STRETCHES
FROM NORTHERN MO BACK INTO EASTERN NEB.  LATEST SPC MESOANALYSIS
SHOWS PWS OF 1.4 TO 1.6 ACROSS MUCH OF THE HIGHLIGHTED AREA...WITH
THE 03 UTC RAP SHOWING A FURTHER INCREASE TO AROUND 1.75 INCHES AS
THE LOW LEVEL FLOW INCREASES.  WITH THE LOSS OF DAYTIME
HEATING...CONVECTIVE INHIBITION HAS INCREASED ACROSS THE
REGION...HOWEVER MUCAPE VALUES REMAIN AROUND 2000-3000 J/KG ALONG
THE NEB/IA BORDER.  CONVECTION IS EXPECTED TO DEVELOP INITIALLY
ACROSS NORTHEASTERN NEB INTO NORTHWESTERN IA BEFORE PROPAGATING
FURTHER TO THE SOUTHEAST ALONG AN AXIS OF INCREASING INSTABILITY. 
HOWEVER...SUSTAINED 30-40 KT SOUTHWESTERLY LOW LEVEL INFLOW INTO
THE BOUNDARIES TO THE WEST INTERACTING WITH FAVORABLE MID/UPPER
LEVEL FORCING MAY SUPPORT BACK-BUILDING/ TRAINING CONVECTION FOR
SEVERAL HOURS.

SEVERAL OF THE 12 UTC HI-RES RUNS SHOW AN AXIS OF MODERATE TO
HEAVY ACCUMULATIONS EXTENDING FROM THE NORTHERN NEB/IA BORDER INTO
SOUTH-CENTRAL IA.  LATEST RUNS OF BOTH THE OPERATIONAL AND
EXPERIMENTAL HRRR SHOW LOCALLY HEAVY AMOUNTS ON THE ORDER TO 2-3
INCHES FOR THE 6-HR PERIOD ENDING AT 10 UTC.  

PEREIRA

ATTN...WFO...DMX...FSD...OAX...

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

LAT...LON   42739461 41789264 40959294 40959448 41649588
            42069789 42729737


Last Updated: 1210 AM EDT MON AUG 21 2017