MESOSCALE PRECIPITATION DISCUSSION 0487
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1119 PM EDT THU JUL 19 2018

AREAS AFFECTED...NEAR WI/IL BORDER

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

VALID 200318Z - 200758Z

SUMMARY...A BROAD AREA OF SHOWERS AND THUNDERSTORMS IS MOVING EAST
NEAR THE IL/WI BORDER.  HOURLY RAIN TOTALS TO 2" WITH LOCAL
AMOUNTS TO 4" ARE POSSIBLE.

DISCUSSION...A VARIETY OF SWIRLS/SHORTWAVES ARE SEEN SATELLITE
IMAGERY.  THE MORE EASTERN CIRCULATION HAS INDUCED A MESOSCALE
WAVE OF LOW PRESSURE IN NORTHERN IL AND INVERTED TROUGH/TROWAL
FEATURE WHICH APPEAR TO BE HELPING TO FOCUS A BROADENING AREA OF
CONVECTION AND MAINTAINING INSTABILITY ACROSS NORTHEAST IL.  A FEW
AREAS OF HEAVY RAINFALL HAVE BEEN NOTED ON RECENT RADAR IMAGERY
NEAR THE IL/WI BORDER, WHICH HAVE BEEN SUBSTANTIATED WITH GROUND
TRUTH SHOWING LOCAL AMOUNTS IN THE 1-2.5" RANGE.  PRECIPITABLE
WATER VALUES ARE 1.5-1.75" PER GPS DATA.  INFLOW AT 850 HPA IS OUT
OF THE SOUTHWEST AT 30-35 KTS PER VAD WIND PROFILES.  EFFECTIVE
BULK SHEAR OF 25-35 KTS EXISTS HERE, WHICH IS LEADING TO SOME
ORGANIZATION.  MU CAPE VALUES ARE IN THE 500-1500 J/KG RANGE
ACROSS THE AREA. 

THE 12Z AND 18Z MESOSCALE GUIDANCE WAS WAY TOO SLOW/WESTERLY WITH
THIS ACTIVITY, BUT THERE ARE SIGNS OF IMPROVEMENT IN THE 00Z
GUIDANCE.  A SOUTHEAST-ADJUSTED 00Z NAM CONEST APPEARS TO BEST
REFLECT THE CURRENT CONVECTIVE PATTERN AT 03Z.  THE NEW GUIDANCE
SHOWS THE CONVECTION MOVING EASTWARD WITH THE MESOSCALE WAVE
THROUGH 08Z BEFORE MOVING INTO LAKE MICHIGAN AS A CONVECTIVE ARC. 
LOCAL AMOUNTS OF 3-4" ARE FORECAST BY THE NEWER GUIDANCE, WHICH
APPEARS REALISTIC.  THE AVAILABLE MOISTURE AND INSTABILITY
SUPPORTS HOURLY RAIN RATES TO 2".  THIS COULD PROVE PROBLEMATIC IN
URBAN AREAS SUCH AS MILWAUKEE AND CHICAGO.

ROTH

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

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

LAT...LON   43398781 43108776 42998775 42778768 42438770
            42028758 41628762 41508913 41539029 42029019
            43059059 43249016 43208932 43228859 43288812