MESOSCALE PRECIPITATION DISCUSSION 0127
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
126 AM EDT THU APR 20 2017

AREAS AFFECTED...PORTIONS OF CENTRAL AND SOUTHERN WI

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

VALID 200525Z - 200830Z

SUMMARY...ELEVATED CONVECTION OVER AREAS WITH LOWER FLASH FLOOD
GUIDANCE VALUES COULD RESULT IN FLASH FLOODING ACROSS PORTIONS OF
CENTRAL AND SOUTHERN WI THROUGH THE EARLY MORNING HOURS.

DISCUSSION...REGIONAL RADARS INDICATED A LINE OF ELEVATED
CONVECTION EXTENDING FROM  FAR EASTERN IA INTO CENTRAL WI. THE
CONVECTION WAS BEING MAINTAINED BY AN AXIS OF 500-1000 J/KG MUCAPE
EXTENDING OVER THE SAME AREA.  A 40 TO 50 KNOT LOW LEVEL SOUTHWEST
FLOW CONTINUES TO FUNNEL A 1.25 INCH PRECIPITABLE PLUME JUST AHEAD
OF THE CONVECTION...WHICH REMAINS ORGANIZED DUE TO DECENT
DIFFLUENCE IN THE PRESENCE OF AN 80 KNOT JET STREAK OVER NORTHERN
WI.

WHILE THE CONVECTION HAS BEEN PROGRESSIVE...THE KARX RADAR HAS
SHOWN HOURLY RAINFALL RATES NEAR AN INCH OVER EASTERN IA AND FAR
SOUTHWEST WI. MESONET OBSERVATIONS HAVE SHOW 1.00 TO 1.50 INCH
RAINFALL AMOUNTS IN THREE HOURS ASSOCIATED WITH THE CONVECTION
OVER FAR SOUTHEAST NM AND FAR SOUTHWEST WI.

HIGH RESOLUTION GUIDANCE SUGGESTS THAT SIMILAR RAINFALL AMOUNTS
ARE POSSIBLE OVER THE REMAINDER OF CENTRAL AND SOUTHERN WI THROUGH
0830Z...AS THE LATEST RAP SHOWED 500-1000 J/KG OF MUCAPE REMAINING
AVAILABLE TO THE ELEVATED CONVECTION THROUGH THAT TIME. IT SHOULD
BE NOTED THAT ALMOST ALL OF THE AVAILABLE HIGH RESOLUTION GUIDANCE
(INCLUDING THE LATEST HRRR/EXPERIMENTAL HRRR) ARE A COUPLE OF
HOURS TOO SLOW ACROSS WI.

FLASH FLOOD GUIDANCE VALUES ACROSS PORTIONS OF SOUTHEAST WI ARE AS
LOW AS 1.00 TO 1.50 INCHES IN THREE HOURS...AND GIVEN THESE
AMOUNTS HAVE ALREADY OCCURRED WITH THE ELEVATED CONVECTION...A
FLASH FLOOD THREAT IS EXPECTED TO REMAIN IN PLACE THROUGH 0830Z.
AFTER THAT TIME...WEAKENING INSTABILITY AND MOVEMENT OF THE
CONVECTION OUT OF WI SHOULD MITIGATE ANY REMAINING FLASH FLOOD
THREAT.

HAYES

ATTN...WFO...ARX...GRB...MKX...

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

LAT...LON   44608800 44118758 42618804 42609057 43159122
            43909089 44578901