Wednesday, September 11, 2019

Mesoscale Discussion for McHenry Co., IL

<pre>ACUS11 KWNS 111748
SWOMCD

Mesoscale Discussion 1956
NWS Storm Prediction Center Norman OK
1248 PM CDT Wed Sep 11 2019

Areas affected...Portions of southern Wisconsin and southern Lower
Michigan

Concerning...Severe potential...Watch possible

Valid 111748Z - 111945Z

Probability of Watch Issuance...60 percent

SUMMARY...Convective coverage along a cold front in central
Wisconsin and central Lower Michigan will increase in the next two
hours. Damaging winds will the the primary threat with marginally
severe hail and an isolated tornado possible. A WW is possible in
the next hour or two.

DISCUSSION...Mid-level ascent continues to increase across southern
Wisconsin and southern Lower Michigan with the approach of a
shortwave trough. Despite cloud cover across Wisconsin, 1-minute
visible satellite imagery shows increasing agitated cumulus along
the cold front with convection also increasing in central Lower
Michigan where surface heating has been stronger. 1500-2000 J/kg
MLCAPE will exist this afternoon in areas that have remained
relatively cloud free. Stronger convection is likely to occur in
Wisconsin with the better upper-level support, though stronger
surface heating in Michigan may allow more isolated activity to
develop prior to the shortwave arriving. Given deep-layer shear
(effectively 30-40 kts) parallel to the boundary, congealing cold
pools and upscale growth is likely to occur quickly making damaging
winds the primary threat. Marginally severe hail may occur in
stronger cells, but modest mid-level lapse rates should keep
coverage of larger hail minimal. While the risk of a tornado will
remain low, a 30 kt 850 mb jet moving through the area will enlarge
low-level hodographs enough that an isolated tornado may occur early
in the convective cycle before upscale growth/storm interactions.
With time, the convection will reinforce the cold front and the
boundary will sag southward. Given the expected storm coverage and
potential for damaging wind gusts, a WW is possible within the next
hour or two.

..Wendt/Hart.. 09/11/2019

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...CLE...DTX...IWX...GRR...GRB...LOT...MKX...DVN...
ARX...

LAT...LON 43039028 43498999 44038699 43348387 42748262 41758326
41508379 41898659 42148875 42409000 43039028 </pre>


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