Mesoscale Discussion 1455

Issued

Aug 9, 2021, 8:33 PM CDT (01:33 UTC)

Expired

Aug 9, 2021, 10:00 PM CDT

In force

87 min

Issued by

the Storm Prediction Center

Concerning

Tornado watch 417

Counties Bureau County, IL, Knox County, IL, LaSalle County, IL, Livingston County, IL, Marshall County, IL, Peoria County, IL, Putnam County, IL, Stark County, IL, Tazewell County, IL, Woodford County, IL

The Lincoln radar (KILX), 103 km from the middle of the area, began a volume at 01:35 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

675 
ACUS11 KWNS 100133
SWOMCD
SPC MCD 100133 
ILZ000-100300-

Mesoscale Discussion 1455
NWS Storm Prediction Center Norman OK
0833 PM CDT Mon Aug 09 2021

Areas affected...Parts of north central Illinois

Concerning...Tornado Watch 417...

Valid 100133Z - 100300Z

The severe weather threat for Tornado Watch 417 continues.

SUMMARY...The risk for tornadoes has diminished considerably. 
Continuing severe weather potential remains more unclear, but there
still appears at least some potential for intensifying thunderstorm
development and the formation of a cluster of storms to the north of
Peoria into the 9-11 PM CDT time frame.  This could eventually pose
increasing potential for strong wind gusts, but it remains unclear
whether a new severe weather watch will be needed.

DISCUSSION...A lower/mid-level low over eastern Wisconsin is
forecast to continue to slowly migrate northeastward this evening,
into a more stable environment across the Great Lakes region. 
However, on the southwestern flank of the mid-level troughing,
low-level warm advection will persist through this evening across
north central Illinois, where the boundary-layer remains very moist
and characterized by large CAPE in excess of 3000-4000 J/kg.

Strong thunderstorm development is ongoing along a low-level
confluence zone north of Peoria, with perhaps some continuing
increase in coverage underway.  This appears to be occurring in the
presence of at least modest deep-layer shear, beneath 30 kt
northwesterly flow around 500 mb.  This is contributing to a
southward propagation of activity, and moderate southerly inflow of
the potentially strongly buoyant low-level air.  At the same time,
however, warmer and more strongly capping elevated mixed layer air
is in the process of advecting eastward into the region, and could
suppress convective development.

So, subsequent convective developments remain uncertain, and
probably hinge of the strength of the surface cold pool ongoing
storms are able to generate in the next hour or two.  If a
developing cold pool is able to maintain convective development,
there appears potential for an upscale growing, southward
propagating cluster that could pose increasing potential for strong
surface gusts.

..Kerr.. 08/10/2021

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

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

LAT...LON   41209038 41478950 41478898 41368844 40738836 40448963
            40659037 41209038

Mesoscale Discussions in Illinois, 2021Every mesoscale discussion in 2021

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.