Alert archive / Illinois / Severe Thunderstorm Watches in 2012
Severe Thunderstorm Watch 243
The Storm Prediction Center issued this severe thunderstorm watch at May 4, 2012, 10:35 PM CDT for 30 counties in Illinois; 7 counties in Missouri. It was in force for 8 hr.
The area
The outline as issued.
The facts
- Issued
- May 4, 2012, 10:35 PM CDT (03:35 UTC)
- Expired
- May 5, 2012, 6:51 AM CDT
- In force
- 8 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 37 counties
Bond County, IL, Calhoun County, IL, Clinton County, IL, Edwards County, IL, Fayette County, IL, Franklin County, IL, Gallatin County, IL, Greene County, IL, Hamilton County, IL, Hardin County, IL, Jackson County, IL, Jefferson County, IL, Jersey County, IL, Johnson County, IL, Macoupin County, IL, Madison County, IL, Marion County, IL, Monroe County, IL, Montgomery County, IL, Perry County, IL, Pike County, IL, Pope County, IL, Randolph County, IL, Saint Clair County, IL, Saline County, IL, Wabash County, IL, Washington County, IL, Wayne County, IL, White County, IL, Williamson County, IL, City of Saint Louis, MO, Lincoln County, MO, Montgomery County, MO, Pike County, MO, Saint Charles County, MO, Saint Louis County, MO, Warren County, MO
The radar
The St Louis radar (KLSX), 60 km from the middle of the area, began a volume at 03:37 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
- 10%
- One or more EF2 to EF5 tornadoes
- 2%
- Ten or more severe wind reports
- 20%
- One or more gusts of 65 knots or more
- 20%
- Ten or more severe hail reports
- 30%
- One or more hailstones of 2 inches or more
- 20%
- Six or more combined severe hail and wind reports
- 60%
Warnings issued inside it
4 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 4, 11:18 PM CDT | Severe Thunderstorm Warning | PAH | Hamilton | 16 min |
| May 5, 12:04 AM CDT | Severe Thunderstorm Warning | PAH | Wayne | 19 min |
| May 5, 12:19 AM CDT | Severe Thunderstorm Warning | PAH | Wabash | 41 min |
| May 5, 4:12 AM CDT | Severe Thunderstorm Warning | PAH | Jefferson | 33 min |
Discussions around it
SPC mesoscale discussions over the same counties from four hours before the watch to its end.
The nearest sounding before it
Lincoln, IL (KILX), launched 00:00Z, 3.6 hours before the alert went out and 184 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
- 188 J/kg
- Mixed-layer CIN
- -108 J/kg
- Mixed-layer LCL
- 1330 m above ground
- 0-6 km bulk shear
- 21 kt
- 0-1 km storm-relative helicity
- -3 m²/s²
- 0-3 km storm-relative helicity
- 155 m²/s²
- Significant tornado parameter
- -0.0
- Supercell composite
- -0.1
The text
As transmitted, in the capitals the NWS used until 2016.
294
WWUS20 KWNS 050337
SEL3
SPC WW 050337
ILZ000-MOZ000-051000-
URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 243
NWS STORM PREDICTION CENTER NORMAN OK
1035 PM CDT FRI MAY 4 2012
THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
WEST CENTRAL INTO SOUTHERN ILLINOIS
EXTREME EAST CENTRAL MISSOURI
EFFECTIVE THIS FRIDAY NIGHT AND SATURDAY MORNING FROM 1035 PM
UNTIL 500 AM CDT.
HAIL TO 1.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.
THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 45
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 60 MILES NORTHWEST
OF SAINT LOUIS MISSOURI TO 35 MILES SOUTHEAST OF MOUNT VERNON
ILLINOIS. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU3).
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 240...WW 241...
DISCUSSION...ELEVATED CONVECTION WILL INCREASE IN COVERAGE/INTENSITY
THE NEXT FEW HOURS IN ASSOCIATION WITH WAA ON THE NOSE OF A 35 KT
SWLY LLJ. THE UPSTREAM FEED OF 2000-3000 J/KG MUCAPE AND STEEP
MIDLEVEL LAPSE RATES WILL SUPPORT A RISK FOR LARGE HAIL WITH THE
STRONGEST STORMS. OVERNIGHT...CONVECTION WILL CONTINUE TO SPREAD
ESEWD...WITH UPSCALE GROWTH INTO A CLUSTER/ISOLATED DAMAGING WINDS
POSSIBLE.
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 30025.
...THOMPSONSPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 4, 7:57 PM CDT | Mesoscale Discussion | SPC | Bond, Calhoun, Christian, Clay, Clinton, Crawford and 25 more | 63 min |
| May 4, 10:18 PM CDT | Mesoscale Discussion | SPC | Bond, Calhoun, Clinton, Franklin, Greene, Hamilton and 11 more | 87 min |
| May 5, 12:55 AM CDT | Mesoscale Discussion | SPC | Edwards, Gallatin, Hamilton, Hardin, Saline, Wabash and 1 more | 95 min |
| May 5, 5:06 AM CDT | Mesoscale Discussion | SPC | Gallatin, Hardin, White | 114 min |
Nearby
Severe Thunderstorm Watches in Illinois, 2012Severe Thunderstorm Watches in Missouri, 2012Every severe thunderstorm watch 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.