Alert archive / Iowa / Severe Thunderstorm Watches in 2018
Severe Thunderstorm Watch 42
The Storm Prediction Center issued this severe thunderstorm watch at Apr 13, 2018, 3:22 PM CDT for 19 counties in Iowa. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- Apr 13, 2018, 3:22 PM CDT (20:22 UTC)
- Expired
- Apr 13, 2018, 9:00 PM CDT
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 2 in
- Strongest gust expected
- 50 kt
Counties Audubon County, IA, Black Hawk County, IA, Boone County, IA, Calhoun County, IA, Carroll County, IA, Dallas County, IA, Greene County, IA, Grundy County, IA, Guthrie County, IA, Hamilton County, IA, Hardin County, IA, Jasper County, IA, Marshall County, IA, Polk County, IA, Poweshiek County, IA, Sac County, IA, Story County, IA, Tama County, IA, Webster County, IA
The radar
The Des Moines radar (KDMX), 45 km from the middle of the area, began a volume at 20:25 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
- 60%
- One or more hailstones of 2 inches or more
- 40%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
10 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 13, 4:18 PM CDT | Severe Thunderstorm Warning | DMX | Audubon, Cass | 57 min |
| Apr 13, 5:36 PM CDT | Severe Thunderstorm Warning | DMX | Carroll, Greene | 39 min |
| Apr 13, 6:02 PM CDT | Severe Thunderstorm Warning | DMX | Calhoun, Greene, Webster | 43 min |
| Apr 13, 6:39 PM CDT | Severe Thunderstorm Warning | DMX | Hamilton, Webster, Wright | 51 min |
| Apr 13, 6:52 PM CDT | Severe Thunderstorm Warning | DMX | Boone, Dallas, Greene | 38 min |
| Apr 13, 6:57 PM CDT | Severe Thunderstorm Warning | DMX | Hamilton, Webster, Wright | 63 min |
| Apr 13, 7:23 PM CDT | Severe Thunderstorm Warning | DMX | Boone, Hamilton, Hardin, Marshall, Story | 52 min |
| Apr 13, 7:52 PM CDT | Severe Thunderstorm Warning | DMX | Franklin, Hamilton, Hardin, Marshall, Story, Wright | 39 min |
| Apr 13, 8:19 PM CDT | Severe Thunderstorm Warning | DMX | Butler, Cerro Gordo, Franklin, Grundy | 41 min |
| Apr 13, 8:43 PM CDT | Severe Thunderstorm Warning | DMX | Dallas, Polk | 36 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, 8.4 hours before the alert went out and 214 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
- 230 J/kg
- Mixed-layer CIN
- -547 J/kg
- Mixed-layer LCL
- 838 m above ground
- 0-6 km bulk shear
- 59 kt
- 0-1 km storm-relative helicity
- 342 m²/s²
- 0-3 km storm-relative helicity
- 346 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- -0.2
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 13, 8:44 AM CDT | Mesoscale Discussion | SPC | Allamakee, Dickinson, Emmet, Howard, Lyon, Mitchell and 4 more | 3 hr |
| Apr 13, 2:06 PM CDT | Mesoscale Discussion | SPC | Adair, Adams, Cass, Clarke, Decatur, Fremont and 8 more | 2 hr |
| Apr 13, 2:19 PM CDT | Tornado Watch | SPC | Adair, Adams, Appanoose, Cass, Clarke, Davis and 17 more | 7 hr |
| Apr 13, 5:31 PM CDT | Mesoscale Discussion | SPC | Audubon, Carroll, Cass, Fremont, Greene, Guthrie and 5 more | 29 min |
Nearby
Severe Thunderstorm Watches in Iowa, 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.