Alert archive / Illinois / Mesoscale Discussions in 2021

Mesoscale Discussion 503

May 3, 202144 counties in Illinois; 11 counties in Missouri

The Storm Prediction Center issued this mesoscale discussion at May 3, 2021, 5:15 PM CDT for 44 counties in Illinois; 11 counties in Missouri. It was in force for 90 min.

The area

The outline as issued.

The facts

Issued: May 3, 2021, 5:15 PM CDT (22:15 UTC)
Expired: May 3, 2021, 6:45 PM CDT
In force: 90 min
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 131

All 55 counties

Bond County, IL, Brown County, IL, Calhoun County, IL, Cass County, IL, Champaign County, IL, Christian County, IL, Clinton County, IL, Coles County, IL, Cumberland County, IL, DeWitt County, IL, Douglas County, IL, Effingham County, IL, Fayette County, IL, Ford County, IL, Fulton County, IL, Greene County, IL, Jersey County, IL, Knox County, IL, Logan County, IL, Macon County, IL, Macoupin County, IL, Madison County, IL, Marion County, IL, Marshall County, IL, Mason County, IL, McDonough County, IL, McLean County, IL, Menard County, IL, Monroe County, IL, Montgomery County, IL, Morgan County, IL, Moultrie County, IL, Peoria County, IL, Piatt County, IL, Pike County, IL, Saint Clair County, IL, Sangamon County, IL, Schuyler County, IL, Scott County, IL, Shelby County, IL, Stark County, IL, Tazewell County, IL, Warren County, IL, Woodford County, IL, City of Saint Louis, MO, Franklin County, MO, Gasconade County, MO, Jefferson County, MO, Lincoln County, MO, Montgomery County, MO, Osage County, MO, Pike County, MO, Saint Charles County, MO, Saint Louis County, MO, Warren County, MO

The radar

The Lincoln radar (KILX), 43 km from the middle of the area, began a volume at 22:18 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.

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Severe Thunderstorm Watch 136May 3, 7:55 PM CDT

The nearest sounding before it

Lincoln, IL (KILX), launched 12:00Z, 10.3 hours before the alert went out and 81 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 460 m above ground
0-6 km bulk shear: 11 kt
0-1 km storm-relative helicity: 44 m²/s²
0-3 km storm-relative helicity: 56 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

518 
ACUS11 KWNS 032216
SWOMCD
SPC MCD 032215 
ILZ000-MOZ000-032345-

Mesoscale Discussion 0503
NWS Storm Prediction Center Norman OK
0515 PM CDT Mon May 03 2021

Areas affected...portions of eastern Missouri into central Illinois

Concerning...Severe Thunderstorm Watch 131...

Valid 032215Z - 032345Z

The severe weather threat for Severe Thunderstorm Watch 131
continues.

SUMMARY...The severe threat is expected to continue across Severe
Thunderstorm Watch 131 through the remainder of the afternoon. Large
hail and damaging winds are expected to be the primary threats, but
a tornado is also possible, particularly with any supercell
structures.

DISCUSSION...Organized linear segments and a discrete supercell have
matured across northern and central portions of Severe Thunderstorm
Watch 131 over the past couple of hours. A couple of severe
hail/damaging gust reports have recently been received with the more
discrete convection across west-central IL. Here, temperatures have
been able to warm into the mid to upper 70s, with mid 60s F
dewpoints contributing to MLCAPE values up to 1500 J/kg. While mid
to upper tropospheric flow is not particularly strong, modest
veering with height is contributing to 35+ kts of effective bulk
shear, supporting updraft organization. The severe threat is
expected to remain locally higher with the more discrete storms
across central IL, where instability is more robust relative to
points farther north. Low-level shear is weak across Severe
Thunderstorm Watch 131 overall, but given some directional shear in
the boundary layer, a tornado cannot be ruled out, particularly with
any supercell structures.

..Squitieri/Thompson.. 05/03/2021

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

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

LAT...LON   38498907 38229046 38379199 40449091 40999056 41168998
            41168913 41028879 40528785 39998774 39338810 38748861
            38498907

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 3, 2:08 PM CDT	Mesoscale Discussion	SPC	Adams, Bond, Brown, Calhoun, Cass, Champaign and 55 more	67 min
May 3, 2:47 PM CDT	Severe Thunderstorm Watch	SPC	Adams, Bond, Brown, Bureau, Calhoun, Cass and 43 more	6 hr
May 3, 4:51 PM CDT	Mesoscale Discussion	SPC	Monroe, Randolph, Saint Clair	84 min

Nearby

Mesoscale Discussions in Illinois, 2021 Mesoscale Discussions in Missouri, 2021 Every mesoscale discussion in 2021

Sources

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.