MESOSCALE PRECIPITATION DISCUSSION 0812
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
628 AM EDT SAT SEP 16 2017

AREAS AFFECTED...WEST-CENTRAL/NORTHERN IA...SOUTHEAST
MN...WEST-CENTRAL WI

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

VALID 161028Z - 161428Z

SUMMARY...SOME TRAINING SHOWERS AND THUNDERSTORMS OVER THE NEXT
FEW HOURS MAY RESULT IN SOME FLASH FLOODING.

DISCUSSION...THE LATEST NON-OPERATIONAL GOES-16 10.3 MICRON/IR
IMAGERY SHOWS AN AXIS OF COOLING CONVECTIVE TOPS FROM PARTS OF
WEST-CENTRAL IA NORTHEAST INTO SOUTHERN MN. THE RADAR IMAGERY
SHOWS THE CONVECTION TRAINING SOMEWHAT OVER AREAS ESPECIALLY
INVOLVING FAR NORTHERN IA AND SOUTHERN MN...AND ALREADY THERE HAVE
BEEN SOME DUAL-POL RADAR ESTIMATES OF 2 TO 3 INCHES...WITH
RAINFALL RATES OF 1.5 TO 2 INCHES/HR LOCALLY. A FEW OVERSHOOTING
TOPS HAVE BEEN NOTED AS WELL OVER THE LAST HOUR IN THE GOES-IR
IMAGERY WHICH ARE HELPING TO CONTRIBUTE TO THE HEAVIER RATES.

THE CONVECTION IS DEVELOPING IN RESPONSE TO A SHORTWAVE IMPULSE
LIFTING NORTHEAST THROUGH EASTERN NEB AND WESTERN IA WHICH IS
INTERACTING WITH A PLUME OF RELATIVELY AND UNSTABLE AIR POOLED OUT
AHEAD OF A SLOW-MOVING COLD FRONT. MLCAPE VALUES OF NEAR 1000 J/KG
ARE NOSED UP AHEAD OF THE FRONT...ALONG PWATS OF 1.5 TO 1.75
INCHES.

THE ACTIVITY SHOULD PERSIST THROUGH AT LEAST MID-MORNING AS THE
SHORTWAVE CONTINUES TO LIFT NORTHEAST ACROSS THE REGION. THE HIRES
MODEL CONSENSUS APPEARS TO BE GENERALLY UNDERDONE WITH THE LEVEL
OF CONVECTIVE ORGANIZATION AND INTENSITY...AND ACTUALLY SUGGESTS
WEAKENING OF THE CONVECTIVE CELLS TOWARD MID-MORNING.

BASED ON THE LATEST SATELLITE AND RADAR TRENDS...EXPECT THE
CONVECTION TO CONTINUE PRODUCING SOME HEAVY RAINFALL RATES...WITH
ADDITIONAL STORM TOTALS OF 3 TO 4 INCHES POSSIBLE THROUGH
MID-MORNING...AND PERHAPS SOME ISOLATED HEAVIER AMOUNTS WHERE
BETTER TRAINING OF CONVECTIVE CELLS OCCUR. THIS MAY RESULT IN SOME
FLASH FLOODING AS A RESULT.

ORRISON

ATTN...WFO...ARX...DMX...MPX...OAX...

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

LAT...LON   45359245 45169164 43919189 41839351 41259473
            41299536 41829545 42659457 43659383 44749312