Alert archive / Illinois / Mesoscale Discussions in 2012

Mesoscale Discussion 943

May 28, 201221 counties in Illinois; Des Moines County, Lee County, Scott County, Iowa

The Storm Prediction Center issued this mesoscale discussion at May 28, 2012, 4:59 PM CDT for 21 counties in Illinois; Des Moines County, Lee County, Scott County, Iowa. It was in force for 91 min.

The area

The outline as issued.

The facts

Issued: May 28, 2012, 4:59 PM CDT (21:59 UTC)
Expired: May 28, 2012, 6:30 PM CDT
In force: 91 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 24 counties

Des Moines County, IA, Lee County, IA, Scott County, IA, Boone County, IL, Bureau County, IL, Carroll County, IL, DeKalb County, IL, Henderson County, IL, Henry County, IL, Kane County, IL, Knox County, IL, LaSalle County, IL, Lee County, IL, Marshall County, IL, Mercer County, IL, Ogle County, IL, Peoria County, IL, Putnam County, IL, Rock Island County, IL, Stark County, IL, Stephenson County, IL, Warren County, IL, Whiteside County, IL, Winnebago County, IL

The radar

The Quad Cities radar (KDVN), 36 km from the middle of the area, began a volume at 22:02 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 311May 28, 6:05 PM CDT

The nearest sounding before it

Davenport, (KDVN), launched 12:00Z, 10.0 hours before the alert went out and 30 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: 29 J/kg
Mixed-layer CIN: -143 J/kg
Mixed-layer LCL: 1746 m above ground
0-6 km bulk shear: 42 kt
0-1 km storm-relative helicity: 127 m²/s²
0-3 km storm-relative helicity: 109 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.

793 
ACUS11 KWNS 282200
SWOMCD
SPC MCD 282159
ILZ000-IAZ000-MOZ000-282330-

MESOSCALE DISCUSSION 0943
NWS STORM PREDICTION CENTER NORMAN OK
0459 PM CDT MON MAY 28 2012

AREAS AFFECTED...EXTREME ERN IA THROUGH NRN IL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 282159Z - 282330Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...STORMS DEVELOPING FROM ERN IA INTO NRN IL WILL POSE A
THREAT FOR ISOLATED DAMAGING WIND AND LARGE HAIL THIS EVENING. WW
ISSUANCE WILL ULTIMATELY DEPEND ON CONVECTIVE TRENDS...AND IF STORMS
CONTINUE TO INCREASE IN COVERAGE AND INTENSITY...A SEVERE TSTM WATCH
MAY BE NEEDED.

DISCUSSION...RECENT TRENDS HAVE BEEN FOR STORMS TO INCREASE IN
COVERAGE WITHIN ZONE OF FRONTAL CONVERGENCE FROM ERN IA...EXTREME
NWRN IL AND CNTRL WI. DOWNSTREAM THE WARM SECTOR IS MODERATELY
UNSTABLE OVER NRN IL WITH 2000-2500 J/KG MLCAPE AND 7.5 C/KM 700-500
MB LAPSE RATES. LOW LEVEL WINDS HAVE VEERED AHEAD OF THE FRONT WHICH
IS SERVING TO LIMIT CONVERGENCE TO SOME DEGREE. ALOFT A WEAK IMPULSE
WAS INDICATED ON THE RAPID REFRESH ANALYSIS LIFTING NEWD THROUGH IA.
NEVERTHELESS...BOUNDARY LAYER TEMPERATURES HAVE CLIMBED TO AROUND 90
CONTRIBUTING TO A RELATIVELY WEAK CAP...AND STORMS MAY CONTINUE
DEVELOPING AS THE FRONT ADVANCES INTO NRN IL. WHILE SHEAR IN THE
WARM SECTOR IS WEAK...STRONGER FLOW ALOFT HAS OVERTAKEN THE FRONTAL
ZONE RESULTING IN 35-40 KT UNIDIRECTIONAL EFFECTIVE DEEP LAYER
SHEAR. BOTH MULTICELL LINE SEGMENTS AND POSSIBLY SOME SUPERCELL
MODES MAY OCCUR.

..DIAL/HART.. 05/28/2012

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

ATTN...WFO...LOT...ILX...DVN...

LAT...LON   41509100 42408990 42278799 40858926 40519187 41509100

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 28, 12:00 PM CDT	Mesoscale Discussion	SPC	Jo Daviess, Stephenson	60 min
May 28, 6:02 PM CDT	Severe Thunderstorm Watch	SPC	Boone, Bureau, Cook, DeKalb, DuPage, Grundy and 10 more	3 hr
May 27, 9:51 PM CDT	Mesoscale Discussion	SPC	Buena Vista, Cherokee, Clay, Dickinson, Emmet, Ida and 5 more	84 min
May 28, 12:54 PM CDT	Severe Thunderstorm Watch	SPC	Clayton	7 hr

Nearby

Mesoscale Discussions in Illinois, 2012 Mesoscale Discussions in Iowa, 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.