Alert archive / Illinois / Mesoscale Discussions in 2011

Mesoscale Discussion 2004

August 18, 20114 states

The Storm Prediction Center issued this mesoscale discussion at Aug 18, 2011, 2:40 PM CDT for 4 states. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Aug 18, 2011, 2:40 PM CDT (19:40 UTC)
Expired: Aug 18, 2011, 4:45 PM CDT
In force: 2 hr
Issued by: the Storm Prediction Center

All 59 counties

Alexander County, IL, Clay County, IL, Crawford County, IL, Edwards County, IL, Franklin County, IL, Gallatin County, IL, Hamilton County, IL, Hardin County, IL, Jackson County, IL, Jasper County, IL, Jefferson County, IL, Johnson County, IL, Lawrence County, IL, Massac County, IL, Perry County, IL, Pope County, IL, Pulaski County, IL, Richland County, IL, Saline County, IL, Union County, IL, Wabash County, IL, Wayne County, IL, White County, IL, Williamson County, IL, Daviess County, IN, Dubois County, IN, Gibson County, IN, Knox County, IN, Pike County, IN, Posey County, IN, Spencer County, IN, Vanderburgh County, IN, Warrick County, IN, Ballard County, KY, Caldwell County, KY, Carlisle County, KY, Crittenden County, KY, Daviess County, KY, Hancock County, KY, Henderson County, KY, Hopkins County, KY, Livingston County, KY, Lyon County, KY, Marshall County, KY, McCracken County, KY, McLean County, KY, Muhlenberg County, KY, Ohio County, KY, Trigg County, KY, Union County, KY, Webster County, KY, Bollinger County, MO, Cape Girardeau County, MO, Madison County, MO, Mississippi County, MO, Perry County, MO, Scott County, MO, Stoddard County, MO, Wayne County, MO

The radar

The Paducah radar (KPAH), 76 km from the middle of the area, began a volume at 19:41 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

Nashville Metro, TN (KBNA), launched 12:00Z, 7.7 hours before the alert went out and 237 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: 9 J/kg
Mixed-layer CIN: -250 J/kg
Mixed-layer LCL: 1809 m above ground
0-6 km bulk shear: 32 kt
0-1 km storm-relative helicity: 51 m²/s²
0-3 km storm-relative helicity: 46 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1

Open this sounding in Storm Lab

The text

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

498 
ACUS11 KWNS 181940
SWOMCD
SPC MCD 181940 
KYZ000-INZ000-ILZ000-MOZ000-182145-

MESOSCALE DISCUSSION 2004
NWS STORM PREDICTION CENTER NORMAN OK
0240 PM CDT THU AUG 18 2011

AREAS AFFECTED...SRN IL...SWRN IND...WRN KY...FAR SERN MO

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY 

VALID 181940Z - 182145Z

WHILE A FEW STORMS COULD CONTAIN GUSTY WINDS THIS AFTERNOON...AND AN
ISOLATED INSTANCE OR TWO OF DMGG WINDS CANNOT BE RULED OUT...THE SVR
THREAT IS EXPECTED TO REMAIN MINIMAL AND THE ISSUANCE OF A WW IS
UNLIKELY.

SFC MESOANALYSIS AT 19Z DEPICTS A WEAK FRONT DRAPED ACROSS PORTIONS
OF NRN IND/IL INTO W-CNTRL IL AND SRN MO...WITH AN ATTENDANT MESOLOW
OVER E-CNTRL MO. EAST OF THE MESOLOW...ISOLATED TO WIDELY SCATTERED
CONVECTION HAS EVOLVED FROM A DISORGANIZED BAND OF AGITATED CUMULUS
GROWTH...COINCIDENT WITH AN AXIS OF LOCALLY ENHANCED LOW-LEVEL
CONVERGENCE. HOWEVER...WITH FLOW BELOW 1 KM AGL AOB 10 KT PER
EVANSVILLE/PADUCAH VWP DATA AND SFC OBS...THE CONVERGENCE IS RATHER
WEAK. NEVERTHELESS...AMPLE INSOLATION HAS SUPPORTED TEMPERATURES
CLIMBING INTO THE UPPER 80S TO LOWER 90S AMIDST DEWPOINTS IN THE
LOWER/MIDDLE 70S...ALLOWING THE AIR MASS TO BECOME MODERATELY TO
VERY UNSTABLE. RUC FORECAST SOUNDINGS SUGGEST THAT ANY SUBSTANTIAL
TROPOSPHERIC FLOW IS RELEGATED TO THE UPPER LEVELS /E.G. NWLY WINDS
OF 50-60 KT BETWEEN 350 AND 200 MB/ SUPPORTING EFFECTIVE BULK SHEAR
MAGNITUDES OF GENERALLY 30-45 KT. THIS COULD SUPPORT OCCASIONALLY
ORGANIZED STORM STRUCTURES WITH GUSTY WINDS...AND AN ISOLATED
INSTANCE OR TWO OF DMGG WINDS CANNOT BE RULED OUT GIVEN DCAPE VALUES
AOA 1000 J/KG. HOWEVER NOTABLY WEAKER FLOW EXISTS IN THE LOW/MID
LEVELS...WHICH SHOULD BE A MITIGATING FACTOR FOR A MORE SUBSTANTIAL
SVR THREAT. FURTHERMORE...THE LACK OF MORE SALIENT FORCING
MECHANISMS FOR ASCENT SHOULD LIMIT THE OVERALL THREAT FOR MORE
ORGANIZED CONVECTION AND THE ATTENDANT SVR THREAT.

..COHEN.. 08/18/2011

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

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

LAT...LON   36808776 36668952 36939054 37519042 38278933 39068833
            39018725 38478665 37408660 36808776

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 18, 7:41 AM CDT	Mesoscale Discussion	SPC	Douglas, Howell, Oregon, Ozark, Ripley	3 hr
Aug 18, 2:51 PM CDT	Mesoscale Discussion	SPC	Atchison, Holt, Nodaway, Worth	84 min
Aug 18, 6:00 PM CDT	Mesoscale Discussion	SPC	Andrew, Atchison, Bates, Benton, Buchanan, Caldwell and 21 more	60 min
Aug 18, 6:18 PM CDT	Mesoscale Discussion	SPC	Atchison, Holt	27 min
Aug 18, 6:38 PM CDT	Tornado Watch	SPC	Andrew, Atchison, Daviess, DeKalb, Gentry, Harrison and 3 more	5 hr

Nearby

Mesoscale Discussions in Illinois, 2011 Mesoscale Discussions in Kentucky, 2011 Mesoscale Discussions in Indiana, 2011 Every mesoscale discussion in 2011

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.