MESOSCALE PRECIPITATION DISCUSSION 0364
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
634 PM EDT TUE JUN 26 2018

AREAS AFFECTED...PORTIONS OF SOUTHERN WI/NORTHERN IL

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

VALID 262234Z - 270334Z

SUMMARY...THUNDERSTORMS ARE SLOWLY INCREASING IN COVERAGE NEAR THE
IL/WI BORDER.  HOURLY RAIN TOTALS TO 1.75" WITH LOCAL AMOUNTS OF
4" ARE POSSIBLE THROUGH 04Z.

DISCUSSION...THUNDERSTORMS ARE SHOWING A TENDENCY TOWARDS
CONSOLIDATING NEAR THE WI/IL BORDER AHEAD OF A DEEP LAYER LOW NEAR
ITS ASSOCIATED STATIONARY FRONT.  PRECIPITABLE WATER VALUES ARE
1.4-1.7" PER GPS VALUES.  INFLOW AT 850 HPA IS CONVERGENT OUT OF
THE SOUTHWEST AT 20-30 KTS PER VAD WIND PROFILES.  ML CAPE VALUES
HAVE BEEN SLOWLY RISING DUE TO INSOLATION GETTING THROUGH THIN
HIGH CLOUDS FROM ACTIVITY DOWN SOUTH, WITH 1000-2000 J/KG EXISTS
HERE, ALONG WITH EFFECTIVE BULK SHEAR OF 25-30 KTS.  SINCE THIS IS
A DEEP LAYER CYCLONE, THE FLOW IS CYCLONIC AND UNIDIRECTIONAL WITH
HEIGHT.

THE GUIDANCE SUPPORTS SOME ADDITIONAL RAMP UP OF CONVECTION OVER
THE NEXT 3-6 HOURS, WHICH SHOULD ATTEMPT TO TAKE ON A CURVE BAND
STRUCTURE AND SHOW SOME TRAINING.  INSTABILITY SHOULD PEAK DURING
THE NEXT COUPLE HOURS BEFORE CLOUDS ATTEMPT TO THICKEN FROM THE
SOUTH AND THE SUN SETS.  THE 18Z HREF PROBABILITIES OF 1"+ AN HOUR
SUGGEST SOME FADING AFTER 01Z, WHILE THE 12Z SSEO NEIGHBORHOOD
PROBABILITIES OF EXCEEDING THE RELATIVELY LOW THREE HOURLY FLASH
FLOOD GUIDANCE VALUES SUGGEST A DECENT SIZED AREA OF 50%+ CHANCE
OF EXCEEDANCE THROUGH 03Z BEFORE FADING THEREAFTER.  OF SOME
CONCERN IS THE SURFACE BASED CONVECTION WHICH COULD ELEVATE
SOMEWHAT NORTHWARD/APPEAR STATIONARY AROUND THE TIME CIN SETS IN
IN THE 02-04Z TIME FRAME.  THE GUIDANCE SHOWS A CONSISTENT SIGNAL
FOR LOCAL AMOUNTS IN THE 3-4" RANGE BETWEEN MILWAUKEE AND CHICAGO,
WHICH COULD PROVE PROBLEMATIC GIVEN RAINFALL OF 200-400% OF NORMAL
DURING THE PAST COUPLE WEEKS AND THE URBANIZATION IN THOSE AREAS. 

ROTH

ATTN...WFO...ARX...DVN...ILX...LOT...MKX...

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

LAT...LON   43078903 43068798 42748767 42258760 41848740
            41698719 41178756 40868828 41069004 41669068
            42489046 42938966