Alert archive / Illinois / Severe Thunderstorm Watches in 2018
Severe Thunderstorm Watch 331
The Storm Prediction Center issued this severe thunderstorm watch at Aug 5, 2018, 7:58 PM CDT for 9 counties in Illinois; 4 counties in Wisconsin. It was in force for 83 min.
The area
The outline as issued.
The facts
- Issued
- Aug 5, 2018, 7:58 PM CDT (00:58 UTC)
- Expired
- Aug 5, 2018, 9:21 PM CDT
- In force
- 83 min
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
Counties Boone County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Kane County, IL, Lake County, IL, McHenry County, IL, Ogle County, IL, Winnebago County, IL, Kenosha County, WI, Racine County, WI, Rock County, WI, Walworth County, WI
The radar
The Chicago radar (KLOT), 87 km from the middle of the area, began a volume at 00:59 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.
What SPC expected
The probabilities SPC published with the watch, for the watch area over its life.
- Two or more tornadoes
- 5%
- One or more EF2 to EF5 tornadoes
- 2%
- Ten or more severe wind reports
- 20%
- One or more gusts of 65 knots or more
- 5%
- Ten or more severe hail reports
- 20%
- One or more hailstones of 2 inches or more
- 5%
- Six or more combined severe hail and wind reports
- 40%
Discussions around it
SPC mesoscale discussions over the same counties from four hours before the watch to its end.
The nearest sounding before it
Davenport, (KDVN), launched 00:00Z, 1.0 hours before the alert went out and 156 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.
- Mixed-layer CAPE
- 1536 J/kg
- Mixed-layer CIN
- -89 J/kg
- Mixed-layer LCL
- 1707 m above ground
- 0-6 km bulk shear
- 28 kt
- 0-1 km storm-relative helicity
- 160 m²/s²
- 0-3 km storm-relative helicity
- 198 m²/s²
- Significant tornado parameter
- 0.2
- Supercell composite
- 7.7
The text
As transmitted.
172 WWUS20 KWNS 060055 SEL1 SPC WW 060055 ILZ000-WIZ000-LMZ000-060600- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 331 NWS Storm Prediction Center Norman OK 800 PM CDT Sun Aug 5 2018 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Northeast Illinois Southeast Wisconsin Lake Michigan * Effective this Sunday night and Monday morning from 800 PM until 100 AM CDT. * Primary threats include... Isolated damaging wind gusts to 70 mph possible Isolated large hail events to 1.5 inches in diameter possible SUMMARY...A cluster of thunderstorms over northwest Illinois will persist for a few more hours, tracking across the watch area. The strongest storms may contain gusty/damaging winds and hail. The severe thunderstorm watch area is approximately along and 30 statute miles north and south of a line from 25 miles west southwest of Rockford IL to 75 miles east of Rockford IL. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU1). PRECAUTIONARY/PREPAREDNESS ACTIONS... REMEMBER...A Severe Thunderstorm Watch means conditions are favorable for severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings. Severe thunderstorms can and occasionally do produce tornadoes. && OTHER WATCH INFORMATION...CONTINUE...WW 330... AVIATION...A few severe thunderstorms with hail surface and aloft to 1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 27025. ...Hart
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 6, 3:16 PM CDT | Mesoscale Discussion | SPC | Alexander, Clay, Edwards, Franklin, Gallatin, Hamilton and 19 more | 2 hr |
| Aug 6, 5:21 PM CDT | Mesoscale Discussion | SPC | Champaign, DeWitt, Ford, Iroquois, Kankakee, Livingston and 5 more | 114 min |
Nearby
Severe Thunderstorm Watches in Illinois, 2018Severe Thunderstorm Watches in Wisconsin, 2018Every severe thunderstorm watch in 2018
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.