Alert archive / Iowa / Severe Thunderstorm Watches in 2012
Severe Thunderstorm Watch 255
The Storm Prediction Center issued this severe thunderstorm watch at May 6, 2012, 7:17 AM CDT for 22 counties in Iowa. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- May 6, 2012, 7:17 AM CDT (12:17 UTC)
- Expired
- May 6, 2012, 1:00 PM CDT
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 22 counties
Adair County, IA, Adams County, IA, Appanoose County, IA, Clarke County, IA, Dallas County, IA, Davis County, IA, Decatur County, IA, Guthrie County, IA, Jasper County, IA, Lucas County, IA, Madison County, IA, Mahaska County, IA, Marion County, IA, Monroe County, IA, Polk County, IA, Poweshiek County, IA, Ringgold County, IA, Taylor County, IA, Union County, IA, Wapello County, IA, Warren County, IA, Wayne County, IA
The radar
The Des Moines radar (KDMX), 37 km from the middle of the area, began a volume at 12:19 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
- 40%
- One or more gusts of 65 knots or more
- 10%
- Ten or more severe hail reports
- 30%
- One or more hailstones of 2 inches or more
- 10%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
5 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 6, 7:29 AM CDT | Severe Thunderstorm Warning | DMX | Adair, Dallas, Guthrie, Madison | 31 min |
| May 6, 7:59 AM CDT | Severe Thunderstorm Warning | DMX | Dallas, Polk | 46 min |
| May 6, 8:27 AM CDT | Severe Thunderstorm Warning | DMX | Jasper, Marion, Polk, Warren | 48 min |
| May 6, 9:03 AM CDT | Severe Thunderstorm Warning | DMX | Jasper, Marion | 42 min |
| May 6, 9:12 AM CDT | Severe Thunderstorm Warning | DMX | Jasper, Marion | 48 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
Omaha, NE (KOAX), launched 12:00Z, 0.3 hours before the alert went out and 225 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 880 m above ground
- 0-6 km bulk shear
- 52 kt
- 0-1 km storm-relative helicity
- -415 m²/s²
- 0-3 km storm-relative helicity
- -233 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted, in the capitals the NWS used until 2016.
575
WWUS20 KWNS 061220
SEL5
SPC WW 061220
IAZ000-061800-
URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 255
NWS STORM PREDICTION CENTER NORMAN OK
720 AM CDT SUN MAY 6 2012
THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
SOUTHERN IOWA
EFFECTIVE THIS SUNDAY MORNING AND AFTERNOON FROM 720 AM UNTIL 100
PM 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 60
STATUTE MILES EAST AND WEST OF A LINE FROM 30 MILES NORTH
NORTHEAST OF DES MOINES IOWA TO 25 MILES EAST OF LAMONI IOWA.
FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU5).
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.
DISCUSSION...OVERNIGHT TSTM N-S BAND OVER THE LWR MO VLY...WITH
SPORADIC STRONGER STORMS...RECENTLY HAS BECOME SOMEWHAT BETTER
ORGANIZED ACROSS SW IA...MOST LIKELY IN RESPONSE TO ACTIVITY HAVING
REACHED ZONE OF GREATER LOW LVL MOISTURE /PW AOA 1.25 INCHES/.
ORIENTATION OF THE SQLN LINE RELATIVE TO SELY SFC FLOW...AND ONSET
OF SFC HEATING...SUGGEST POSSIBILITY FOR A CONTINUED INCREASE IN
STORM STRENGTH/SUSTENANCE THROUGH LATER THIS MORNING...WITH AN
ATTENDANT INCREASED RISK FOR DMGG WIND/SVR HAIL DESPITE MODEST DEEP
SHEAR.
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 27030.
...CORFIDISPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| 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, 8:40 AM CDT | Mesoscale Discussion | SPC | Cedar, Clinton, Des Moines, Henry, Iowa, Jefferson and 9 more | 65 min |
| May 6, 9:29 AM CDT | Severe Thunderstorm Watch | SPC | Benton, Cedar, Clinton, Des Moines, Henry, Iowa and 12 more | 4 hr |
| May 6, 1:42 PM CDT | Severe Thunderstorm Watch | SPC | Des Moines, Henry, Lee, Louisa, Van Buren | 7 hr |
| May 6, 3:56 PM CDT | Mesoscale Discussion | SPC | Lee | 64 min |
Nearby
Severe Thunderstorm Watches in Iowa, 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.