Alert archive / Illinois / Mesoscale Discussions in 2012

Mesoscale Discussion 1978

September 21, 201246 counties in Illinois; 9 counties in Indiana

The Storm Prediction Center issued this mesoscale discussion at Sep 21, 2012, 1:36 PM CDT for 46 counties in Illinois; 9 counties in Indiana. It was in force for 84 min.

The area

The outline as issued.

The facts

Issued: Sep 21, 2012, 1:36 PM CDT (18:36 UTC)
Expired: Sep 21, 2012, 3:00 PM CDT
In force: 84 min
Issued by: the Storm Prediction Center
Chance of a watch: 60%

All 55 counties

Bureau County, IL, Cass County, IL, Champaign County, IL, Christian County, IL, Clark County, IL, Clay County, IL, Coles County, IL, Crawford County, IL, Cumberland County, IL, DeWitt County, IL, Douglas County, IL, Edgar County, IL, Effingham County, IL, Fayette County, IL, Ford County, IL, Fulton County, IL, Henry County, IL, Iroquois County, IL, Jasper County, IL, Knox County, IL, LaSalle County, IL, Lawrence County, IL, Livingston County, IL, Logan County, IL, Macon County, IL, Marshall County, IL, Mason County, IL, McDonough County, IL, McLean County, IL, Menard County, IL, Mercer County, IL, Montgomery County, IL, Morgan County, IL, Moultrie County, IL, Peoria County, IL, Piatt County, IL, Putnam County, IL, Richland County, IL, Rock Island County, IL, Sangamon County, IL, Shelby County, IL, Stark County, IL, Tazewell County, IL, Vermilion County, IL, Warren County, IL, Woodford County, IL, Benton County, IN, Clay County, IN, Fountain County, IN, Greene County, IN, Parke County, IN, Sullivan County, IN, Vermillion County, IN, Vigo County, IN, Warren County, IN

The radar

The Lincoln radar (KILX), 39 km from the middle of the area, began a volume at 18:36 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 nearest sounding before it

Lincoln, IL (KILX), launched 12:00Z, 6.6 hours before the alert went out and 47 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: 2528 m above ground
0-6 km bulk shear: 63 kt
0-1 km storm-relative helicity: 120 m²/s²
0-3 km storm-relative helicity: 152 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.

133 
ACUS11 KWNS 211837
SWOMCD
SPC MCD 211836
INZ000-ILZ000-IAZ000-212000-

MESOSCALE DISCUSSION 1978
NWS STORM PREDICTION CENTER NORMAN OK
0136 PM CDT FRI SEP 21 2012

AREAS AFFECTED...CNTRL IL...WCNTRL IND

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 211836Z - 212000Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...AN ISOLATED SEVERE THREAT IS EXPECTED TO DEVELOP ACROSS
CNTRL IL INTO WRN IND THIS AFTERNOON. ISOLATED LARGE HAIL AND WIND
DAMAGE WILL INITIALLY BE THE MAIN THREAT. AN ISOLATED TORNADO THREAT
COULD ALSO DEVELOP LATER THIS AFTERNOON. WW ISSUANCE MAY BECOME
NECESSARY ACROSS THE REGION ONCE THE SCENARIO BEGINS TO UNFOLD.

DISCUSSION...THUNDERSTORMS ARE CURRENTLY INITIATING AND INCREASING
IN INTENSITY JUST TO THE EAST OF A DEEPENING SFC LOW CENTERED OVER
NE MO. THE STORMS ARE LOCATED ON THE NERN EDGE OF INSTABILITY AND ON
THE NOSE OF A MID-LEVEL JET MOVING INTO THE REGION FROM THE WEST
NORTHWEST. THE STRONG MID-LEVEL FLOW ASSOCIATED WITH THE JET IS
CREATING FAVORABLE SHEAR PROFILES FOR SEVERE STORMS IN SPITE OF THE
WEAK INSTABILITY IN PLACE. THE WSR-88D VWP AT SPRINGFIELD IL
CURRENTLY SHOWS ABOUT 65 KT OF 0-6 KM SHEAR WITH SUBSTANTIAL VEERING
WITH HEIGHT FROM 2 TO 3 KM. THIS COULD SUPPORT A SUPERCELL THREAT AS
LOW-LEVEL MOISTURE ADVECTS NWD INTO THE MCD AREA AND INSTABILITY
INCREASES. 500 MB TEMPS OF -15 C TO -19C WILL BE SUPPORTIVE OF
ISOLATED LARGE HAIL WITH THE MORE INTENSE CORES. IN
ADDITION...LOW-LEVEL LAPSE RATES HAVE STEEPENED SOME ACROSS ECNTRL
IL INTO WRN IND AS SHOWN ON MESOSANALYSIS WITH 0-3 KM LAPSE RATES
NOW AROUND 7.0 C/KM. THIS ALONG WITH THE STRONG WIND FIELDS AT
LOW-LEVELS MAY SUPPORT AN ISOLATED WIND DAMAGE AS CELLS MATURE LATE
THIS AFTERNOON. AN ISOLATED TORNADO THREAT COULD ALSO DEVELOP
ESPECIALLY IF THE CELLS CAN ROTATE AND PERSIST.

..BROYLES/MEAD.. 09/21/2012

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

ATTN...WFO...IWX...IND...PAH...LOT...ILX...LSX...DVN...

LAT...LON   40548702 41378876 41728987 41669052 41169094 40539089
            39348998 38558854 38778681 40548702

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 21, 4:59 PM CDT	Mesoscale Discussion	SPC	Bond, Clay, Clinton, Crawford, Cumberland, Edwards and 23 more	91 min
Sep 21, 6:30 PM CDT	Mesoscale Discussion	SPC	Clark, Clay, Coles, Crawford, Cumberland, Douglas and 10 more	3 hr

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.