Alert archive / Illinois / Mesoscale Discussions in 2012

Mesoscale Discussion 850

May 20, 201238 counties in Illinois; 10 counties in Wisconsin

The Storm Prediction Center issued this mesoscale discussion at May 20, 2012, 1:17 PM CDT for 38 counties in Illinois; 10 counties in Wisconsin. It was in force for 118 min.

The area

The outline as issued.

The facts

Issued: May 20, 2012, 1:17 PM CDT (18:17 UTC)
Expired: May 20, 2012, 3:15 PM CDT
In force: 118 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 48 counties

Boone County, IL, Brown County, IL, Bureau County, IL, Carroll County, IL, Cass County, IL, DeKalb County, IL, DeWitt County, IL, DuPage County, IL, Fulton County, IL, Grundy County, IL, Henry County, IL, Kane County, IL, Kankakee County, IL, Kendall County, IL, Knox County, IL, Lake County, IL, LaSalle County, IL, Lee County, IL, Livingston County, IL, Logan County, IL, Marshall County, IL, Mason County, IL, McDonough County, IL, McHenry County, IL, McLean County, IL, Menard County, IL, Ogle County, IL, Peoria County, IL, Putnam County, IL, Schuyler County, IL, Stark County, IL, Stephenson County, IL, Tazewell County, IL, Warren County, IL, Whiteside County, IL, Will County, IL, Winnebago County, IL, Woodford County, IL, Columbia County, WI, Dane County, WI, Dodge County, WI, Green County, WI, Jefferson County, WI, Kenosha County, WI, Rock County, WI, Walworth County, WI, Washington County, WI, Waukesha County, WI

The radar

The Chicago radar (KLOT), 83 km from the middle of the area, began a volume at 18:16 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

Davenport, (KDVN), launched 12:00Z, 6.3 hours before the alert went out and 132 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: 693 J/kg
Mixed-layer CIN: -150 J/kg
Mixed-layer LCL: 1669 m above ground
0-6 km bulk shear: 19 kt
0-1 km storm-relative helicity: 39 m²/s²
0-3 km storm-relative helicity: 29 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.

326 
ACUS11 KWNS 201817
SWOMCD
SPC MCD 201817 
ILZ000-WIZ000-IAZ000-202015-

MESOSCALE DISCUSSION 0850
NWS STORM PREDICTION CENTER NORMAN OK
0117 PM CDT SUN MAY 20 2012

AREAS AFFECTED...SRN WI THROUGH NRN IL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 201817Z - 202015Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...STORMS ARE EXPECTED TO DEVELOP FROM SRN WI INTO PARTS OF
NWRN IL BY 20Z. STRONGER STORMS COULD PRODUCE LOCALLY STRONG TO
DAMAGING WIND GUSTS AND HAIL. WW MIGHT BE NEEDED ONCE THUNDERSTORM
INITIATION APPEARS IMMINENT.

DISCUSSION...THIS AFTERNOON A COLD FRONT EXTENDS FROM WRN WI...ERN
IA INTO NERN MO WITH WEAK PRE-FRONTAL CONVERGENCE BANDS INDICATED
AHEAD OF THE FRONT. WARM SECTOR HAS BECOME MODERATELY UNSTABLE
SUPPORTED BY A PLUME OF STEEPER /7-7.5 C/KM/ LAPSE RATES ABOVE UPPER
50S BOUNDARY LAYER DEWPOINTS. PRE-FRONTAL NEAR SFC WINDS HAVE VEERED
TO SSWLY TO THE SOUTH OF A NEWD EJECTING SHORTWAVE TROUGH LOCATED
OVER THE UPPER MS VALLEY. THIS IS CONTRIBUTING TO WEAKER CONVERGENCE
ALONG COLD FRONT. MOREOVER...DEEPER FORCING ASSOCIATED WITH EJECTING
SHORTWAVE TROUGH WILL REMAIN NORTH OF THIS REGION. THESE FACTORS
MAKE TIMING AND EXTENT OF THUNDERSTORM INITIATION IN THIS AREA
SOMEWHAT UNCERTAIN. HOWEVER...AS TEMPERATURES WARM INTO THE UPPER
80S...CONVECTIVE INHIBITION SHOULD WEAKEN ENOUGH FOR STORMS TO
DEVELOP WHERE DEEPER BAROCLINIC ZONE INTERACTS WITH THE UNSTABLE
WARM SECTOR. STRONGER FLOW ALOFT ATTENDING THE EJECTING IMPULSE WILL
REMAIN NORTH OF THIS REGION WITH DEEP SHEAR GENERALLY AOB 30 KT
SUPPORTIVE OF MULTICELLS. NEVERTHELESS...THE THERMODYNAMIC
ENVIRONMENT WITH MODERATE INSTABILITY...STEEP MID LEVEL LAPSE RATES
AND LARGE BOUNDARY LAYER TEMPERATURE-DEWPOINT SPREADS WILL PROMOTE A
THREAT OF ISOLATED DAMAGING WIND AND HAIL.

..DIAL/WEISS.. 05/20/2012

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

ATTN...WFO...LOT...ILX...MKX...LSX...DVN...

LAT...LON   43608819 42808789 41928772 41158759 40068903 39549085
            40469091 42669002 43678933 43608819

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 20, 1:33 PM CDT	Mesoscale Discussion	SPC	Alexander, Bond, Clinton, Franklin, Gallatin, Hamilton and 18 more	87 min
May 20, 3:50 PM CDT	Mesoscale Discussion	SPC	DeKalb, DuPage, Kane, McHenry	85 min
May 20, 10:52 AM CDT	Mesoscale Discussion	SPC	Adams, Clark, Florence, Forest, Jackson, Juneau and 18 more	113 min
May 20, 12:24 PM CDT	Severe Thunderstorm Watch	SPC	Adams, Brown, Calumet, Clark, Door, Florence and 24 more	7 hr
May 20, 2:57 PM CDT	Mesoscale Discussion	SPC	Adams, Brown, Calumet, Florence, Forest, Langlade and 12 more	2 hr

Nearby

Mesoscale Discussions in Illinois, 2012 Mesoscale Discussions in Wisconsin, 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.