Mesoscale Precipitation Discussion 0752
NWS Weather Prediction Center College Park MD
127 PM EDT Mon Sep 03 2018

Areas affected...Eastern IA, Northern IL, Southern WI

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

Valid 031726Z - 032326Z

Summary...Thunderstorms are increasing in coverage over saturated
ground.  Hourly totals to 2.5" with local amounts to 4" are
expected over the next several hours.

Discussion...Daytime heating combined with divergence aloft caused
by the right rear quadrant of a jet streak aloft is leading to
surface-based convection in and near northern IL, east of a weak
surface wave across southern IA.  Precipitable water values of
1.8-2.1" lie across the region per GPS values.  Inflow at 850 hPa
is west-southwest at 20 kts, with the flow fairly unidirectional
with height.  SPC mesoanalyses show 20-30 kts of effective bulk
shear across the area.

The guidance shows a slow uptick in convection across the region,
which is beginning to show up on recent radar imagery.  The
surface boundary in the area is forecast to lift slowly northward,
which would be problematic within the saturated area near the
WI/IL border.  Low-level inflow is expected to increase with time.
 Hourly rain totals to 2.5" are possible where storms organize,
merge, or train.  The mesoscale guidance shows a signal for local
amounts of 3-4", which would be problematic within such a
saturated area.  Left the category as possible due to uncertainty
in the coverage of the higher amounts.

Roth

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

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

LAT...LON   43228789 42358768 42118760 41798736 41828679
            41578682 41248741 40938858 41009079 41969122
            42899002