SPC MD 1687


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Mesoscale Discussion 1687
NWS Storm Prediction Center Norman OK
0517 PM CST Sat Dec 01 2018

Areas affected...Central Illinois

Concerning...Tornado Watch 434...

Valid 012317Z - 020045Z

The severe weather threat for Tornado Watch 434 continues.

SUMMARY...The risk for severe storms, including supercells with
potential for tornadoes, may continue around the Peoria and
Springfield IL areas through 6-7 PM CST, before diminishing.  The
need for an additional watch is not anticipated.

DISCUSSION...Supporting mid-level forcing for ascent (as inferred
from water vapor imagery) continues to gradually pivot northeastward
through northern/central Illinois.  The southern periphery of this
forcing appears likely to remain roughly along/north of the I-70
corridor, and provide the southern limit to ongoing and subsequent
thunderstorm initiation.  

The warm front, ahead of the mid-level forcing, appears likely to
remain the northern limit to any appreciable further severe weather
potential.  It appears that this boundary will continue to slowly
advance north of the I-74 corridor.  However, the onset of warm
sector boundary layer cooling by the 01-02Z time frame is expected
to provide the main impetus for diminishing convective trends.

Until then, for another hour or two, the environment around the
Springfield/Peoria areas appears to remain conducive to discrete
supercells accompanied by a continuing risk for tornadoes, in
addition to severe hail and localized strong surface gusts.

..Kerr.. 12/01/2018

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


LAT...LON   38979027 39719028 40459046 40939032 41268956 40778811
            39648872 39068921 38898945 38579017 38979027 

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