Alert archive / Illinois / Mesoscale Discussions in 2012

Mesoscale Discussion 684

May 3, 20127 counties in Illinois; Lake County, Indiana

The Storm Prediction Center issued this mesoscale discussion at May 3, 2012, 6:22 PM CDT for 7 counties in Illinois; Lake County, Indiana. It was in force for 23 min.

The area

The outline as issued.

The facts

Issued: May 3, 2012, 6:22 PM CDT (23:22 UTC)
Expired: May 3, 2012, 6:45 PM CDT
In force: 23 min
Issued by: the Storm Prediction Center

Counties Cook County, IL, DeKalb County, IL, DuPage County, IL, Kane County, IL, Kendall County, IL, Lake County, IL, Will County, IL, Lake County, IN

The radar

The Chicago radar (KLOT), 61 km from the middle of the area, began a volume at 23:23 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 233May 3, 6:45 PM CDT

The nearest sounding before it

Lincoln, IL (KILX), launched 12:00Z, 11.4 hours before the alert went out and 223 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: 1717 J/kg
Mixed-layer CIN: -76 J/kg
Mixed-layer LCL: 775 m above ground
0-6 km bulk shear: 25 kt
0-1 km storm-relative helicity: 122 m²/s²
0-3 km storm-relative helicity: 49 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

547 
ACUS11 KWNS 032323
SWOMCD
SPC MCD 032322
MIZ000-INZ000-ILZ000-032345-

MESOSCALE DISCUSSION 0684
NWS STORM PREDICTION CENTER NORMAN OK
0622 PM CDT THU MAY 03 2012

AREAS AFFECTED...NERN IL /INCLUDING CHICAGO METRO AREA/...FAR NWRN
IND AND SRN LAKE MICHIGAN

CONCERNING...SEVERE THUNDERSTORM WATCH 230...

VALID 032322Z - 032345Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 230
CONTINUES.

SUMMARY...A NEW WW WILL BE COORDINATED SOON TO REPLACE PARTS OF
EXISTING WW 230...AND INCLUDE PARTS OF FAR NWRN IND.

TSTMS ARE INCREASING IN COVERAGE AND INTENSITY ALONG A LOW LEVEL
CONVERGENCE ZONE FROM SRN LAKE MICHIGAN SWWD THROUGH NERN TO CENTRAL
IL.  A THREAT FOR SEVERE STORMS ARE EXPECTED TO PERSIST THROUGH THE
EVENING.

DISCUSSION...AT 2310Z...REGIONAL RADAR IMAGERY SHOWED AN INCREASING
TREND IN STORM INTENSITIES ALONG A LOW LEVEL CONVERGENCE ZONE
EXTENDING FROM SRN LAKE MI SWWD THROUGH NERN INTO CENTRAL IL.  GIVEN
A MODERATELY-STRONGLY UNSTABLE AIR MASS RESIDING OVER WRN/CENTRAL TO
NERN IL TO NWRN IND AND EFFECTIVE BULK SHEAR OF 30-35 KT...A THREAT
FOR SEVERE STORMS IS EXPECTED TO PERSIST BEYOND THE 00Z EXPIRATION
TIME OF THE WW 230.  MODELS TEND TO AGREE WITH THE SCENARIO SHOWING
STORMS DEVELOPING AND PERSISTING THROUGH THE EVENING ALONG THIS ZONE
OF LOW LEVEL CONVERGENCE...WHILE A SWLY LLJ AT 30-35 KT FEEDS THE
MODERATE-STRONG INSTABILITY INTO THIS REGION.

..PETERS.. 05/03/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...GRR...LOT...

LAT...LON   42498624 41538723 41228799 41318826 41548869 41878931
            42438824 42508695 42608663 42498624

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 3, 1:07 PM CDT	Severe Thunderstorm Watch	SPC	Boone, Cook, DeKalb, DuPage, Kane, Kendall and 5 more	6 hr
May 3, 2:53 PM CDT	Mesoscale Discussion	SPC	Boone, Cook, DeKalb, DuPage, Kane, Lake and 3 more	67 min
May 3, 3:53 PM CDT	Mesoscale Discussion	SPC	Brown, Bureau, Cass, DeWitt, Fulton, Greene and 22 more	37 min
May 3, 4:20 PM CDT	Tornado Watch	SPC	Bureau, Cass, Champaign, DeWitt, Ford, Fulton and 26 more	8 hr
May 3, 6:41 PM CDT	Severe Thunderstorm Watch	SPC	Boone, Cook, DeKalb, DuPage, Ford, Grundy and 12 more	5 hr
May 3, 6:42 PM CDT	Mesoscale Discussion	SPC	Adams, Brown, Cass, DeWitt, Fulton, Greene and 17 more	63 min

Nearby

Mesoscale Discussions in Illinois, 2012 Mesoscale Discussions in Indiana, 2012 Every mesoscale discussion in 2012

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.