Alert archive / Missouri / Mesoscale Discussions in 2021

Mesoscale Discussion 548

May 6, 202113 counties in Illinois; 23 counties in Missouri

The Storm Prediction Center issued this mesoscale discussion at May 6, 2021, 9:52 AM CDT for 13 counties in Illinois; 23 counties in Missouri. It was in force for 83 min.

The area

The outline as issued.

The facts

Issued: May 6, 2021, 9:52 AM CDT (14:52 UTC)
Expired: May 6, 2021, 11:15 AM CDT
In force: 83 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

All 36 counties

Bond County, IL, Calhoun County, IL, Clinton County, IL, Greene County, IL, Jersey County, IL, Macoupin County, IL, Madison County, IL, Monroe County, IL, Montgomery County, IL, Perry County, IL, Randolph County, IL, Saint Clair County, IL, Washington County, IL, City of Saint Louis, MO, Crawford County, MO, Dent County, MO, Franklin County, MO, Gasconade County, MO, Iron County, MO, Jefferson County, MO, Lincoln County, MO, Madison County, MO, Maries County, MO, Montgomery County, MO, Osage County, MO, Perry County, MO, Phelps County, MO, Pulaski County, MO, Reynolds County, MO, Saint Charles County, MO, Saint Francois County, MO, Saint Louis County, MO, Sainte Genevieve County, MO, Warren County, MO, Washington County, MO, Wayne County, MO

The radar

The St Louis radar (KLSX), 47 km from the middle of the area, began a volume at 14:56 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 152May 6, 12:35 PM CDT

The nearest sounding before it

Lincoln, IL (KILX), launched 12:00Z, 2.9 hours before the alert went out and 286 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: 16 J/kg
Mixed-layer CIN: -111 J/kg
Mixed-layer LCL: 1453 m above ground
0-6 km bulk shear: 34 kt
0-1 km storm-relative helicity: 203 m²/s²
0-3 km storm-relative helicity: 211 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

069 
ACUS11 KWNS 061452
SWOMCD
SPC MCD 061452 
ILZ000-MOZ000-061615-

Mesoscale Discussion 0548
NWS Storm Prediction Center Norman OK
0952 AM CDT Thu May 06 2021

Areas affected...East-Central/Southeast MO....West-Central/Southwest
IL

Concerning...Severe potential...Watch unlikely 

Valid 061452Z - 061615Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated damaging wind gust and/or an instance of large
hail is possible over the next hour or two.

DISCUSSION...Recent surface analysis places a low over north-central
IL, with cold front extending southwestward from this low through
central and southwest MO. A subtle pre-frontal trough precedes the
cold front. Attempts at deeper convection have been noted over the
past half hour or so along both of these boundaries, although no
well developed updrafts have materialized thus far. This trend of
somewhat sporadic and short-lived deep updrafts will likely persist
for the next hour or two, fostered by modest buoyant attendant to
the cold mid-level temperatures and steep lapse rates. Limited
duration of the strong updrafts should temper the severe potential
enough to preclude watch issuance until farther southeast later this
afternoon. Even so, an isolated damaging wind gusts and/or instance
of large hail is possible for a few hours.

..Mosier/Grams.. 05/06/2021

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

ATTN...WFO...PAH...ILX...LSX...SGF...

LAT...LON   38449228 39549070 39278935 37998919 37099041 37529239
            38449228

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 6, 10:05 AM CDT	Mesoscale Discussion	SPC	Alexander, Franklin, Gallatin, Hamilton, Hardin, Jackson and 10 more	85 min
May 6, 12:02 PM CDT	Mesoscale Discussion	SPC	Alexander, Hardin, Jackson, Johnson, Massac, Pope and 4 more	118 min
May 6, 12:38 PM CDT	Severe Thunderstorm Watch	SPC	Alexander, Edwards, Franklin, Gallatin, Hamilton, Hardin and 13 more	5 hr
May 6, 1:10 PM CDT	Mesoscale Discussion	SPC	Champaign, Christian, Coles, Cumberland, DeWitt, Douglas and 10 more	2 hr
May 6, 2:45 PM CDT	Mesoscale Discussion	SPC	Dunklin, Mississippi, New Madrid, Pemiscot, Scott, Stoddard	90 min

Nearby

Mesoscale Discussions in Missouri, 2021 Mesoscale Discussions in Illinois, 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.