Alert archive / Iowa / Severe Thunderstorm Watches in 2012
Severe Thunderstorm Watch 256
The Storm Prediction Center issued this severe thunderstorm watch at May 6, 2012, 9:29 AM CDT for 17 counties in Illinois; 18 counties in Iowa; Clark County, Scotland County, Missouri. It was in force for 4 hr.
The area
The outline as issued.
The facts
- Issued
- May 6, 2012, 9:29 AM CDT (14:29 UTC)
- Expired
- May 6, 2012, 1:49 PM CDT
- In force
- 4 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 2 in
- Strongest gust expected
- 60 kt
All 37 counties
Benton County, IA, Cedar County, IA, Clinton County, IA, Des Moines County, IA, Henry County, IA, Iowa County, IA, Jackson County, IA, Jefferson County, IA, Johnson County, IA, Jones County, IA, Keokuk County, IA, Lee County, IA, Linn County, IA, Louisa County, IA, Muscatine County, IA, Scott County, IA, Van Buren County, IA, Washington County, IA, Bureau County, IL, Carroll County, IL, Fulton County, IL, Hancock County, IL, Henderson County, IL, Henry County, IL, Knox County, IL, Marshall County, IL, McDonough County, IL, Mercer County, IL, Peoria County, IL, Putnam County, IL, Rock Island County, IL, Schuyler County, IL, Stark County, IL, Warren County, IL, Whiteside County, IL, Clark County, MO, Scotland County, MO
The radar
The Quad Cities radar (KDVN), 46 km from the middle of the area, began a volume at 14:32 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.
What SPC expected
The probabilities SPC published with the watch, for the watch area over its life.
- Two or more tornadoes
- 20%
- One or more EF2 to EF5 tornadoes
- 5%
- Ten or more severe wind reports
- 30%
- One or more gusts of 65 knots or more
- 30%
- 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
- 70%
Warnings issued inside it
2 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 6, 1:37 PM CDT | Severe Thunderstorm Warning | DVN | Bureau | 38 min |
| May 6, 1:42 PM CDT | Severe Thunderstorm Warning | DVN | Bureau, Henry | 63 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
Davenport, (KDVN), launched 12:00Z, 2.5 hours before the alert went out and 52 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
- 2361 J/kg
- Mixed-layer CIN
- -82 J/kg
- Mixed-layer LCL
- 571 m above ground
- 0-6 km bulk shear
- 31 kt
- 0-1 km storm-relative helicity
- 181 m²/s²
- 0-3 km storm-relative helicity
- 188 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 9.6
The text
As transmitted, in the capitals the NWS used until 2016.
548
WWUS20 KWNS 061428
SEL6
SPC WW 061428
IAZ000-ILZ000-MOZ000-062200-
URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 256
NWS STORM PREDICTION CENTER NORMAN OK
930 AM CDT SUN MAY 6 2012
THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
EASTERN IOWA
NORTHWEST ILLINOIS
FAR NORTHEAST MISSOURI
EFFECTIVE THIS SUNDAY MORNING AND AFTERNOON FROM 930 AM UNTIL 500
PM CDT.
HAIL TO 2 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 75
STATUTE MILES EAST AND WEST OF A LINE FROM 55 MILES EAST
NORTHEAST OF CEDAR RAPIDS IOWA TO 35 MILES SOUTH SOUTHEAST OF
BURLINGTON IOWA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6).
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 255...
DISCUSSION...WHILE BOWING MCS OVER S-CNTRL IA APPEARS TO HAVE
TEMPORARILY WEAKENED...DOWNSTREAM AIR MASS ACROSS THE WATCH AREA IS
ALREADY VERY UNSTABLE WITH 12Z SOUNDINGS SHOWING MUCAPE VALUES OF
4000-5000 J/KG. CONTINUED BOUNDARY LAYER HEATING ALONG STATIONARY
FRONT FROM SERN IA INTO CNTRL IL SHOULD ALLOW STORMS TO BECOME
PROGRESSIVELY SURFACE-BASED WITH AN INCREASED THREAT FOR DAMAGING
WINDS AND HAIL.
AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 27030.
...MEADSPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 6, 8:40 AM CDT | Mesoscale Discussion | SPC | Bureau, Fulton, Hancock, Henderson, Henry, Knox and 12 more | 65 min |
| May 6, 1:22 PM CDT | Mesoscale Discussion | SPC | Adams, Brown, Cass, Fulton, Grundy, Hancock and 20 more | 53 min |
| May 6, 1:42 PM CDT | Severe Thunderstorm Watch | SPC | Adams, Brown, Bureau, Cass, Champaign, Cook and 35 more | 7 hr |
| May 6, 3:56 PM CDT | Mesoscale Discussion | SPC | Adams, Brown, Cass, Champaign, DeWitt, Ford and 32 more | 64 min |
| May 6, 5:07 PM CDT | Mesoscale Discussion | SPC | Clark, Edgar, Iroquois, Vermilion | 53 min |
| May 5, 10:03 PM CDT | Severe Thunderstorm Watch | SPC | Buena Vista, Cherokee, Clay, Dickinson, Ida, Lyon and 6 more | 7 hr |
| May 5, 11:31 PM CDT | Mesoscale Discussion | SPC | Lyon | 89 min |
| May 6, 2:12 AM CDT | Mesoscale Discussion | SPC | Buena Vista, Butler, Cerro Gordo, Cherokee, Clay, Dickinson and 17 more | 63 min |
| May 6, 4:55 AM CDT | Mesoscale Discussion | SPC | Adair, Adams, Audubon, Cass, Fremont, Guthrie and 8 more | 2 hr |
| May 6, 7:17 AM CDT | Severe Thunderstorm Watch | SPC | Adair, Adams, Appanoose, Clarke, Dallas, Davis and 16 more | 6 hr |
| May 6, 2:40 PM CDT | Mesoscale Discussion | SPC | Platte | 95 min |
| May 6, 3:49 PM CDT | Severe Thunderstorm Watch | SPC | Andrew, Bates, Buchanan, Cass, Clay, Clinton and 10 more | 7 hr |
Nearby
Severe Thunderstorm Watches in Iowa, 2012Severe 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.