MESOSCALE PRECIPITATION DISCUSSION 0681
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1231 AM EDT WED SEP 21 2016
 
...CORRECTED FOR WORDING IN LAST SENTENCE...

AREAS AFFECTED...SRN MN AND FAR NRN IA INTO SWRN WI 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 210401Z - 211000Z
 
SUMMARY...FLASH FLOODING APPEARS LIKELY OVER THE NEXT COUPLE OF
HOURS FROM SRN MN...FAR NRN IA INTO SWRN WI. RAINFALL RATES OF 1-2
IN/HR ARE EXPECTED...WITH THE THREAT LIKELY BECOMING CENTERED OVER
SERN MN LATER IN THE NIGHT.

DISCUSSION...RADAR IMAGERY AT 0345Z SHOWED ELEVATED THUNDERSTORMS
BECOMING MORE NUMEROUS ACROSS SRN MN...LOCATED IMMEDIATELY NORTH
OF A WEST-EAST ORIENTED SURFACE TROUGH LOCATED IN SRN MINNESOTA.
THE 00Z SOUNDING FROM MPX SHOWED 7.7 C/KM LAPSE RATES IN THE
700-500 MB LAYER AND RAP ANALYSIS SOUNDINGS OVER ONGOING
CONVECTION SOUTHWEST OF MPX SUGGESTED CELLS ARE LIKELY BASED NEAR
800 MB. THE STEEP LAPSE RATES ARE SUPPORTING ELEVATED INSTABILITY
OF 1000-3000 J/KG...BEING FED BY ADVECTION OF MOISTURE NEAR 850 MB
FROM THE SOUTHWEST ATOP A SLOW MOVING WARM FRONT. 

VAD WIND PLOTS SHOWED 850 MB FLOW OF 30-35 KTS FROM THE SOUTHWEST
FROM OAX TO DMX TO ARX...FEEDING 850 MB DEWPOINTS OF 13-16 C INTO
SRN MN. OBSERVED MEAN CELL MOTIONS HAVE BEEN OFF TO THE ENE AT
25-30 KTS AND RAP FORECASTS SHOW VEERING OF 850 MB FLOW THROUGH
06-07Z...BECOMING MORE ALIGNED WITH THE MEAN FLOW. GIVEN
DIFFLUENCE ALOFT...THESE INGREDIENTS SHOULD SUPPORT TRAINING
CONVECTION FROM WEST TO EAST. THERE IS THE POTENTIAL FOR A PORTION
OF THE ONGOING CLUSTER OF THUNDERSTORMS TO BECOME FORWARD
PROPAGATING TOWARD THE SOUTHEAST...FOLLOWING 1000-500 MB THICKNESS
DIFFLUENCE INTO SWRN WI. HRRR AND EXPERIMENTAL HRRR FORECASTS HAVE
BEEN CONSISTENT WITH THE WRN EDGE OF THE POTENTIAL OUTFLOW
BOUNDARY BEING OVERRUN BY WLY LOW LEVEL FLOW...SUPPORTING AN AXIS
OF REPEATING CELLS CENTERED NEAR SERN MN IN TH 08-10Z TIME FRAME.
GIVEN 3 HR FFG OF 2-3 INCHES...THESE VALUES APPEAR LIKELY TO BE
EXCEEDED RESULTING IN FLASH FLOODING.

OTTO

ATTN...WFO...ARX...DMX...FSD...MKX...MPX...

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

LAT...LON   44959369 44919256 44289086 43588996 42959017 
            42769112 42799219 42989328 43439429 43759517 
            44249547 44709471