Alert archive / Illinois / Mesoscale Discussions in 2012

Mesoscale Discussion 1987

September 25, 20124 states

The Storm Prediction Center issued this mesoscale discussion at Sep 25, 2012, 6:57 PM CDT for 4 states. It was in force for 93 min.

The area

The outline as issued.

The facts

Issued: Sep 25, 2012, 6:57 PM CDT (23:57 UTC)
Expired: Sep 25, 2012, 8:30 PM CDT
In force: 93 min
Issued by: the Storm Prediction Center

All 32 counties

Clinton County, IL, Edwards County, IL, Franklin County, IL, Gallatin County, IL, Hamilton County, IL, Jefferson County, IL, Marion County, IL, Monroe County, IL, Perry County, IL, Randolph County, IL, Richland County, IL, Saint Clair County, IL, Saline County, IL, Wabash County, IL, Washington County, IL, Wayne County, IL, White County, IL, Gibson County, IN, Pike County, IN, Posey County, IN, Vanderburgh County, IN, Warrick County, IN, Henderson County, KY, City of Saint Louis, MO, Crawford County, MO, Franklin County, MO, Jefferson County, MO, Saint Charles County, MO, Saint Louis County, MO, Sainte Genevieve County, MO, Warren County, MO, Washington County, MO

The radar

The St Louis radar (KLSX), 94 km from the middle of the area, began a volume at 23:59 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, 12.0 hours before the alert went out and 214 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: 221 J/kg
Mixed-layer CIN: -192 J/kg
Mixed-layer LCL: 560 m above ground
0-6 km bulk shear: 53 kt
0-1 km storm-relative helicity: 108 m²/s²
0-3 km storm-relative helicity: 134 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 3.7

Open this sounding in Storm Lab

The text

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

441 
ACUS11 KWNS 252357
SWOMCD
SPC MCD 252357 
INZ000-KYZ000-ILZ000-MOZ000-260130-

MESOSCALE DISCUSSION 1987
NWS STORM PREDICTION CENTER NORMAN OK
0657 PM CDT TUE SEP 25 2012

AREAS AFFECTED...ECNTRL MO...SRN IL...SRN IND

CONCERNING...SEVERE THUNDERSTORM WATCH 648...

VALID 252357Z - 260130Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 648
CONTINUES.

SUMMARY...A BAND OF STRONG/SEVERE THUNDERSTORMS WILL PROGRESS SLOWLY
ACROSS THE CURRENT WATCH.  LARGE HAIL AND ISOLATED STRONG WINDS ARE
THE PRIMARY SEVERE THREAT.

DISCUSSION...E-W BAND OF CONVECTION HAS SLOWLY EXPANDED IN AREAL
COVERAGE AS IT SAGS SLOWLY ESEWD ACROSS WW648.  THERE APPEARS TO BE
SUFFICIENT PRECIP EXPANSION ACROSS THE NCNTRL PORTIONS OF THE WW
SUCH THAT ONGOING ACTIVITY SHOULD GET SHUNTED SWD OVER THE NEXT FEW
HOURS.  LATEST RADAR DATA SUGGESTS LARGE HAIL IS THE PRIMARY SEVERE
THREAT AND NUMEROUS UPDRAFTS ARE LIKELY PRODUCING HAIL ON THE ORDER
OF 1-1.75 INCH.  ADDITIONALLY...GUSTY WINDS MAY ACCOMPANY THE
LEADING LINE SEGMENTS...ESPECIALLY THOSE THAT BECOME ORIENTED IN A
SW-NE ORIENTED FASHION.  GIVEN THE STEEP LAPSE RATE ENVIRONMENT THE
SEVERE THREAT WILL LIKELY CONTINUE WELL INTO THE EVENING HOURS.

..DARROW.. 09/25/2012

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

ATTN...WFO...IND...PAH...ILX...LSX...

LAT...LON   38919137 38668710 37658710 37919140 38919137

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 25, 12:51 AM CDT	Mesoscale Discussion	SPC	Bond, Calhoun, Clay, Clinton, Crawford, Edwards and 33 more	114 min
Sep 25, 12:59 PM CDT	Mesoscale Discussion	SPC	Bond, Calhoun, Clay, Clinton, Edwards, Effingham and 21 more	61 min
Sep 25, 5:05 PM CDT	Severe Thunderstorm Watch	SPC	Bond, Clinton, Edwards, Fayette, Franklin, Hamilton and 11 more	6 hr
Sep 25, 4:47 PM CDT	Mesoscale Discussion	SPC	Barry, Barton, Bates, Benton, Camden, Cedar and 16 more	88 min
Sep 25, 5:46 PM CDT	Severe Thunderstorm Watch	SPC	Barton, Benton, Camden, Cedar, Dade, Dallas and 12 more	4 hr

Nearby

Mesoscale Discussions in Illinois, 2012 Mesoscale Discussions in Missouri, 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.