Mesoscale Excessive Precipitation Discussion – includes northern portion of Chicago area until 6PM CDT…
Mesoscale Precipitation Discussion 0349 NWS Weather Prediction Center College Park MD 200 PM EDT Mon Jun 13 2022 Areas affected…Eastern Wisconsin…Northern Illinois…Southern Michigan Concerning…Heavy rainfall…Flash flooding possible Valid 1PM CDT to 6PM CDT SUMMARY…Ongoing complex of thunderstorms to bring torrential rainfall rates to parts of the Lower Great Lakes this afternoon. Areas of flash flooding are possible. DISCUSSION…17Z surface analysis continued to show a surface warm front inching north through the Midwest with increasingly unstable atmospheric profiles within the warm sector. Dew points are reaching the low 80s in parts of southern Illinois and 850mb moisture flux is increasing along and north of the front. The ongoing complex of thunderstorms associated with an MCV tracking into central Wisconsin will continue on an ESE trajectory this afternoon with convection forming along the strengthening MUCAPE gradient. MUCAPE will vary significantly by location, but range generally between 2,000-4,000 J/kg. PWs are also on the rise with values approaching 2.0″ later this afternoon. RAP mesoanalysis and short term forecasts suggest effective bulk vertical wind shear will increase to 50-60 knots and effective SRH values from 100-200 m2/s2 this afternoon. These values are very favorable for keeping ongoing convection organized.As low level inflow intersects the front,additional strengthening of the convection is possible,along with the potential for intensifying convection on the southwest flank of the complex.Some areas,notably north of Milwaukee,in southwest Michigan, and northern Indiana have dealt with measurable rainfall over the last week. Soils are closer to normal saturation-wise, but they still have picked up 200-400% of normal rainfall over the last week. Given rainfall rates with the previous convective cluster in Minnesota had already produced >2″/hr rates, and the atmosphere contains similar favorable parameters, the expectation is for max hourly rainfall rates to range be tween 2-3″/hr. Areas most susceptible to flash flooding are the areas that contain more sensitive soils from rainfall over the past week, as well as urbanized centers and poor drainage locations. FFGs in these areas are as low as 1-1.5″/hr, which does include areas between Milwaukee and Green Bay.
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