SPC MD 638


MD 0638 Image

Mesoscale Discussion 0638
NWS Storm Prediction Center Norman OK
1209 PM CDT Thu May 16 2019

Areas affected...Parts of northern and central Illinois and Indiana

Concerning...Severe potential...Watch possible 

Valid 161709Z - 161815Z

Probability of Watch Issuance...40 percent

SUMMARY...Vigorous thunderstorm development is currently being
maintained near a southward advancing cold pool, to the southwest of
the Chicago area.  It is not certain how long this will persist this
afternoon, but there is at least some potential for further
intensification and organization which could require a severe
weather watch.

DISCUSSION...Warm and capping elevated mixed-layer air is in the
process of advecting across the mid/lower Missouri Valley, toward
portions of the Upper Midwest, around the northern periphery of
amplified ridging within the mid-latitude westerlies.  Along the
leading edge of this air mass, a zone of enhanced lower/mid
tropospheric warm advection is maintaining vigorous thunderstorm
development, which may be also increasingly forced by lift above an
associated surface cold pool.  This appears to be occurring in the
presence of modest (30+ kt) west-northwesterly deep layer mean flow.

The influence of a 30-40 kt west-southwesterly 850 mb speed maximum
nosing east of the Mississippi River may contribute to more of a
southward propagation near and west of the Illinois/Indiana state
border area through 18-20Z.  While this track will be increasingly
into weak mid-level height rises, mid/upper ridging and weaker flow
aloft, the boundary layer ahead of the southwestern flank of the
outflow continues to gradually moisten across much of central
Illinois.  Additional boundary layer warming and moistening may
contribute to weakening inhibition for boundary layer parcels with
CAPE increasing in excess of 2000 J/kg.

Thus, while it remains unclear if synoptic forcing for ascent will
maintain ongoing convection this afternoon, it appears at least
possible that mesoscale processes will, with subsequent further
intensification and organization possible.  This probably would be
accompanied by increasing potential for strong winds at least
approaching severe limits along a strengthening gust front.

..Kerr/Grams.. 05/16/2019

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


LAT...LON   41738809 41408742 40008694 39228759 39398916 40308975
            41068968 41308869 41738809 

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