Mesoscale Precipitation Discussion 0303
NWS Weather Prediction Center College Park MD
659 PM EDT Mon Jun 06 2022

Areas affected...northern IL into northern IN, southern MI and
northwestern OH

Concerning...Heavy rainfall...Flash flooding possible

Valid 5:58PM CDT - 11:30PM CDT...

Summary...Cell mergers and brief training will pose a flash flood
threat across northern IL into northern IN, southern MI and
northwestern OH. Rainfall rates will locally exceed 2 in/hr with
totals in the 2-4 inch range expected on a localized basis through
04Z.

Discussion...Water vapor imagery showed the presence of a
vorticity max over northeastern IA at 2230Z, tracking toward the
east. Visible satellite and radar reflectivity showed an arc of
convergence out ahead of this feature extending through eastern IA
into northern MO, with a forward propagating line of thunderstorms
moving into northern MO and western IL. East of the vort/low level
convergence axis, numerous thunderstorms have developed with
periods of training and localized radar-derived rainfall rates
over 2 in/hr across portions of northern IL. Satellite/radar
imagery also showed thunderstorms developing along a west-east
oriented convergence axis extending from northeastern IL into
northern IN. This region is located within a region with uncapped
MLCAPE ranging between 1000-2000 J/kg and 1.5 to 1.6 inch
precipitable water values per the 22Z SPC mesoanalysis.

Mean westerly to southwesterly flow in the lower-middle levels of
the troposphere will be supportive of brief training, especially
where relatively stronger 850 mb winds develop ahead of the
approaching vorticity max, meeting or exceeding the deeper-layer
mean flow. Continued development and increasing coverage of
thunderstorms can be expected from northern IL into northern IN
over the next 1-3 hours, with cell mergers and periods of training
supporting hourly rainfall totals of 1-2 inches in an hour, but
locally over 2 inches in an hour where training maximizes.
Convective development into southern Lower MI and northwestern OH
is expected in the 02-04Z time frame as instability increases with
the transport of higher low level moisture into the region. Flash
flood guidance varies across the region but is as low as 1.5
inches in 3 hours in a few locations. Some additional areas of
flash flooding will possible over the next 6 hours.