SPC MD 1450



MD 1450 CONCERNING SEVERE POTENTIAL…SEVERE THUNDERSTORM WATCH LIKELY FOR PORTIONS OF NORTHERN/EASTERN IA…SOUTHERN WI…NORTHERN/CENTRAL IL…AND FAR NORTHEASTERN MO

MD 1450 Image


Mesoscale Discussion 1450
NWS Storm Prediction Center Norman OK
1042 AM CDT Mon Aug 10 2020

Areas affected...Portions of northern/eastern IA...southern
WI...northern/central IL...and far northeastern MO

Concerning...Severe potential...Severe Thunderstorm Watch likely 

Valid 101542Z - 101715Z

Probability of Watch Issuance...95 percent

SUMMARY...Widespread damaging winds, some potentially significant
(75+ mph), will become increasingly likely as a line of storms moves
quickly eastward this afternoon. A Severe Thunderstorm Watch will be
needed to address this threat, and an upgrade to Moderate Risk (for
significant severe/damaging winds) will be issued with the upcoming
1630Z update to the Day 1 Convective Outlook.

DISCUSSION...A compact MCS moving into central IA as of 1540Z has
recently produced numerous severe/damaging wind gusts. Recent radar
trends suggest this system has already become very well organized,
with the development of an 80-100+ kt rear-inflow jet only a couple
thousand feet off the surface per KDMX velocity data. The airmass
downstream of this MCS into eastern IA, southern WI, and
northern/central IL is already quite unstable, with MLCAPE of
2000-2500 J/kg present per 15Z mesoanalysis estimates. Additional
diurnal heating of this airmass is expected to yield very strong to
potentially extreme instability by this afternoon, with MLCAPE
potentially reaching the 3500-5500 J/kg range by peak heating.
Recent VWPs from the KDMX radar show sufficient mid-level flow
(around 30-35 kt) to support the continued intensity of the ongoing
MCS.

Additional storms have recently formed across parts of north-central
into northeastern IA along a weak cold front. Current expectations
are for the MCS in central IA to eventually merge with the new
development in north-central/northeastern IA. Result of this will
likely be a large, very well organized bow echo producing widespread
severe and damaging wind gusts across parts of eastern IA into
southern WI, and northern/central IL. The forecast combination of
very strong to extreme instability with adequate deep-layer shear
downstream of the ongoing MCS strongly suggests that a swath of
potentially significant severe wind gusts of 75+ mph is becoming
increasingly likely this afternoon across parts of these areas. A
new Severe Thunderstorm Watch will be needed downstream of the
current watch in central IA within the next hour or two. An upgrade
to Moderate Risk for numerous significant severe/damaging wind gusts
will be issued with the 1630Z update of the Day 1 Convective
Outlook.

..Gleason/Grams.. 08/10/2020

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

ATTN...WFO...LOT...ILX...MKX...DVN...ARX...

LAT...LON   40409210 42959200 42989298 43469189 43479023 43388772
            42658767 41638757 40528754 40128821 40179051 40409210 

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