Thursday, September 12, 2019

Mesoscale Discussion for McHenry Co., IL

<pre>ACUS11 KWNS 121828
SWOMCD

Mesoscale Discussion 1966
NWS Storm Prediction Center Norman OK
0127 PM CDT Thu Sep 12 2019

Areas affected...portions of northern IL

Concerning...Severe potential...Watch possible

Valid 121827Z - 122000Z

Probability of Watch Issuance...40 percent

SUMMARY...Isolated thunderstorms could produce strong gusts and
possible a tornado across northern IL this afternoon. Trends will be
monitored and a watch may be needed.

DISCUSSION...Isolated thunderstorms are ongoing just west of RFD in
the vicinity of the warm front, which extends west to east across
northern IL. Strong heating south of the front has resulted in
temperatures in the mid 80s, with cooler temperatures in the low 70s
just north of the boundary. With dewpoints in the low 70s south of
the warm front, this is resulting in a corridor of weak to moderate
instability near the front. Vertical shear profiles supportive of of
supercells structure with the surface boundary further augmenting
low level SRH and tornado potential. Any storm that can organize and
interact with the warm front will access the most favorable
environment and tornado potential. Most recently, a cell over Ogle
County IL has shown supercell characteristics, but appears to be
slightly to the cool side of the boundary and now is interacting
with other cells lifting northeast. How this interference impacts
these isolated cells remains to be seen, but at least an isolated
tornado threat could continued eastward for a few hours this
afternoon. Trends will be monitored and a watch may be needed this
afternoon.

..Leitman/Hart.. 09/12/2019

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

ATTN...WFO...LOT...DVN...

LAT...LON 42458906 42278806 42048762 41728750 41488774 41398832
41368958 41598995 41838999 42208991 42398972 42458906 </pre>


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