Alert archive / Illinois / Mesoscale Discussions in 2012

Mesoscale Discussion 1561

July 24, 201216 counties in Illinois; Dubuque County, Jackson County, Iowa; Green County, Lafayette County, Rock County, Wisconsin

The Storm Prediction Center issued this mesoscale discussion at Jul 24, 2012, 3:32 AM CDT for 16 counties in Illinois; Dubuque County, Jackson County, Iowa; Green County, Lafayette County, Rock County, Wisconsin. It was in force for 58 min.

The area

The outline as issued.

The facts

Issued: Jul 24, 2012, 3:32 AM CDT (08:32 UTC)
Expired: Jul 24, 2012, 4:30 AM CDT
In force: 58 min
Issued by: the Storm Prediction Center
Chance of a watch: 40%

All 21 counties

Dubuque County, IA, Jackson County, IA, Boone County, IL, Bureau County, IL, Carroll County, IL, DeKalb County, IL, DuPage County, IL, Grundy County, IL, Jo Daviess County, IL, Kane County, IL, Kendall County, IL, LaSalle County, IL, Lee County, IL, McHenry County, IL, Ogle County, IL, Stephenson County, IL, Whiteside County, IL, Winnebago County, IL, Green County, WI, Lafayette County, WI, Rock County, WI

The radar

The Milwaukee radar (KMKX), 114 km from the middle of the area, began a volume at 08:32 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 506Jul 24, 4:50 AM CDT

The nearest sounding before it

Davenport, (KDVN), launched 00:00Z, 8.5 hours before the alert went out and 109 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: 1702 J/kg
Mixed-layer CIN: -39 J/kg
Mixed-layer LCL: 2470 m above ground
0-6 km bulk shear: 27 kt
0-1 km storm-relative helicity: 38 m²/s²
0-3 km storm-relative helicity: 108 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 3.2

Open this sounding in Storm Lab

The text

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

391 
ACUS11 KWNS 240832
SWOMCD
SPC MCD 240832 
ILZ000-WIZ000-IAZ000-240930-

MESOSCALE DISCUSSION 1561
NWS STORM PREDICTION CENTER NORMAN OK
0332 AM CDT TUE JUL 24 2012

AREAS AFFECTED...SWRN-SRN WI/NRN IL AND EXTREME NERN IA

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 240832Z - 240930Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...A LINE OF TSTMS MOVING SEWD AT 40-44 KT WILL REACH FAR
NWRN-NRN IL AROUND 10Z...AND IF THIS ACTIVITY REMAINS IN TACT...IT
WILL REACH THE CHICAGO METRO AREA BETWEEN 11-12Z.  MARGINALLY SEVERE
WIND GUSTS WILL BE POSSIBLE IN THE SHORT TERM...WITH THIS ACTIVITY
BEING MONITORED FOR ANY FURTHER UPSCALE GROWTH AND GREATER SEVERE
THREAT.

DISCUSSION...AT 0810Z...REGIONAL RADAR IMAGERY SHOWED A SEWD MOVING
LINE OF TSTMS EXTENDING FROM SAUK COUNTY TO CRAWFORD COUNTY WI. 
THIS ACTIVITY WAS LOCATED ALONG AND JUST NE OF A STALLED SURFACE
BOUNDARY AND WITHIN THE ERN EXTENT OF STEEP MIDLEVEL LAPSE RATES
CONTRIBUTING TO A WNW-ESE CORRIDOR OF MODERATE INSTABILITY EXTENDING
FROM NRN IA TO FAR SRN WI AND NRN IL.  AREA VWPS INDICATED 40 KT
NWLY MIDLEVEL WINDS...WITH SWLY LOW LEVEL WINDS INCREASING SOME INTO
NRN IA /AT 25-30 KT/.  GIVEN THE NWLY MEAN FLOW AND EFFECTIVE BULK
SHEAR AROUND 40 KT WITH VECTORS PARALLEL TO THE SURFACE
BOUNDARY...STORM MODE SHOULD REMAIN LINEAR.  THIS LINE OF STORMS
WILL PROGRESS SEWD WITH RAP FORECAST SOUNDINGS SUGGESTING A LAYER OF
DRY AIR IN THE LOW LEVELS THAT COULD SUPPORT AN ENHANCEMENT IN
DOWNDRAFT MOMENTUM DUE TO EVAPORATIVE COOLING.  THIS COMBINED WITH
THE FORWARD SPEED OF 40 KT WILL BE SUFFICIENT FOR AT LEAST
MARGINALLY SEVERE WIND GUSTS AS HAVE BEEN RECENTLY OBSERVED IN FAR
NERN IA AND SWRN WI WITH GUSTS RANGING FROM 47-52 KT.

..PETERS/THOMPSON.. 07/24/2012

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

ATTN...WFO...LOT...MKX...DVN...ARX...

LAT...LON   43158975 42148781 41208816 41198913 41779024 42509094
            43158975

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 23, 11:13 PM CDT	Mesoscale Discussion	SPC	Stephenson	92 min
Jul 24, 4:47 AM CDT	Severe Thunderstorm Watch	SPC	Boone, Cook, DeKalb, DuPage, Kane, Kankakee and 7 more	4 hr
Jul 24, 6:35 AM CDT	Mesoscale Discussion	SPC	Cook, DeKalb, DuPage, Grundy, Kane, Kankakee and 4 more	55 min
Jul 24, 3:25 PM CDT	Mesoscale Discussion	SPC	Clay, Clinton, Crawford, Edwards, Effingham, Fayette and 20 more	95 min

Nearby

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