AWUS01 KWNH 160102
FFGMPD
OHZ000-MIZ000-INZ000-WIZ000-ILZ000-160600-

Mesoscale Precipitation Discussion 0624
NWS Weather Prediction Center College Park MD
902 PM EDT Mon Jul 15 2024

Areas affected...Southern WI...Northern IL...Northwest
IND...Southwest Lower MI...

Concerning...Heavy rainfall...Flash flooding likely

Valid 160100Z - 160600Z

SUMMARY...Considerable flash flooding possible along warm
advective portion of the maturing MCS.  Training heavy rainfall
capped off with very intense sub-hourly totals of 1.5-2"/30min.
Given recent rainfall broad area of likely flash flooding
conditions expected through early overnight period.

DISCUSSION...Regional RADAR depicts a maturing QLCS that is quite
broad in width crossing out of E IA into far southern WI, N & NW
IL.  00z surface analysis denotes warm front continues to lift
north and is near/just north of I-90 in N IL before sagging south
a bit across NW IND aligning with reduced convergent line of cu
seen in fading visible imagery... this seems to demarcate very
high surface Tds in the upper 70s and lower 80s from lower 70s and
even 60s in north of a secondary boundary across southern Lower
MI.  South of the warm front highly unstable air with 5000+ J/kg
of MLCAPE.  Strengthening LLJ continues to be slightly confluent
just along/ahead of the main squall line now reaching over 2"
total PWats through depth advecting on 25-30kts per VWP sites
across N IL. This is ascending over the boundary and breaking out
elevated convection downstream of the main line across the
southern row of counties in WI with overshooting tops now starting
to cool below -65C indicating strengthening updrafts and moisture
flux capable of 2-2.5"/hr rates.

The intersection of the squall line and warm front in proximity to
Freeport to Rockford, will continue to experience very strong to
extreme moisture flux convergence and will support instantaneous
rates over 4"/hr though ample downdraft CAPE and deep layer
steering has been progressing to reduce duration to about 30-45
minutes given the broader than normal width of the squall itself. 
This will result in 1.5-2" in 30minute period.  As such, as the
trailing intersection trains across the southern counties of
WI/far northern counties of WI.  Spots of 2-3" maybe locally
higher may be laid down prior to the arrival of the additional 2"
in such short-duration.  As such, local 4"+ totals may be
possible.

This alone would result in likely flash flooding along the axis of
training; however, recent heavy rainfall over the last few days
with prior MCS passages, have saturated the area with 0-40cm
ratios over 75%, so infiltration may be difficult especially at
those rates.  As such, grounds may act as hydrophobic resulting in
a majority of the rainfall as runoff; combined with increasing
urban coverage into SE WI/NE IL, only adds to the potential
concern for considerable, life-threatening flash flooding
possible.

As the line crosses Lake Michigan, the warm front is starting to 
advect higher theta-E air into NW IND, but is a bit slow to reach
SW MI. So while there will be sufficient downstream isentropical
convergence for isolated convection, it should be an order of
magnitude/coverage lower than in WI/IL...though that is still
likely to result in stronger pre-cursory elevated cells from
strong isentropic ascent/convergence.  Rates of 2"/hr and spots of
2-3" are likely and given recent wetter ground conditions flash
flooding is likely across SW Lower MI and far NW IND.

Gallina

ATTN...WFO...DVN...GRR...IWX...LOT...MKX...

ATTN...RFC...NCRFC...OHRFC...NWC...

LAT...LON   43048901 42878666 42848620 42688535 42248455 
            41878439 41378468 41158526 41248692 41358785 
            41728926 42178984 42748975 
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