Weather alerts in South Dakota, 2009
1,339 weather alerts in 2009, from the National Weather Service and the Storm Prediction Center. An alert counts here when it covered any part of the state, so the counties below add up to more than the state.
Weather alerts by county
Each county as a circle sized by its count in 2009. Tap one for its archive.
- Alerts
- 1,339
- Warnings
- 786
- Watches
- 114
- Advisories
- 239
- Busiest month
- June345 alerts
- Busiest day
- July 9, 200975 alerts
Over time
By month
Warning verification
How often warnings here had a storm report inside them, and how much warning the reports had.
28 of 91 tornado warnings covering South Dakota in 2009 had a tornado report inside them; 32 of 38 tornado reports fell inside a warning, on average 19 minutes after it went out.
South Dakota, 2009
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| Tornado warnings | 91 | 28 | 69% | 38 | 84% | 19 min |
| Severe thunderstorm warnings | 521 | 342 | 34% | 689 | 75% | 22 min |
| Flash flood warnings | 44 | 22 | 50% | 39 | 77% | 56 min |
Each office's whole area, 2009
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| NWS Rapid City, SD: tornado warnings | 27 | 6 | 78% | 10 | 90% | 19 min |
| NWS Rapid City, SD: severe thunderstorm warnings | 262 | 172 | 34% | 345 | 79% | 27 min |
| NWS Rapid City, SD: flash flood warnings | 10 | 4 | 60% | 4 | 75% | 59 min |
| NWS Aberdeen, SD: tornado warnings | 24 | 7 | 71% | 10 | 80% | 19 min |
| NWS Aberdeen, SD: severe thunderstorm warnings | 147 | 86 | 41% | 173 | 71% | 19 min |
| NWS Aberdeen, SD: flash flood warnings | 18 | 8 | 56% | 25 | 72% | 60 min |
| NWS Sioux Falls, SD: tornado warnings | 49 | 16 | 67% | 23 | 78% | 21 min |
| NWS Sioux Falls, SD: severe thunderstorm warnings | 232 | 172 | 26% | 374 | 81% | 19 min |
| NWS Sioux Falls, SD: flash flood warnings | 25 | 18 | 28% | 34 | 88% | 49 min |
An office's figures cover every county it serves, including across state lines.
Verified by the Iowa Environmental Mesonet's Cow, which matches each storm-based warning with the local storm reports inside its polygon while it was in force, within 15 km of its edge: a tornado warning counts as verified on a tornado report, a severe thunderstorm warning on hail of 1 inch or more, a gust of 58 mph or more, or wind damage, a flash flood warning on a flash flood report. The false alarm ratio is the share of warnings with no such report; "inside a warning" is the probability of detection, the share of reports that fell inside one; lead time runs from the warning's issue to each report inside it, counting zero for a report that came first. A warning with no report is not proof nothing happened: reports come from spotters, the public and damage surveys, and are thin where few people live.
The alerts
1,339 alerts are too many to list on one page. Narrow it to a product above, to a month in the chart, or to a county.
By product
Every kind of product issued here, grouped by hazard. Each opens the same place narrowed to that product.
By county
Every county with at least one alert. A county page lists each alert that covered it.
- Meade County220
- Pennington County213
- Custer County161
- Lawrence County154
- Perkins County154
- Butte County153
- Mellette County146
- Jackson County145
- Todd County140
- Union County137
- Brown County136
- Dewey County135
- Tripp County132
- Haakon County129
- Stanley County129
- Corson County128
- Harding County127
- Hand County125
- Ziebach County125
- Sully County125
- Edmunds County124
- Hughes County123
- Bennett County121
- Aurora County120
- Charles Mix County120
- Turner County120
- Jones County119
- Codington County118
- Hyde County118
- Lincoln County118
- McPherson County117
- Hutchinson County117
- Clay County117
- Spink County116
- Jerauld County116
- Faulk County116
- Sanborn County116
- Lyman County116
- Beadle County115
- Davison County114
26 more counties
- Walworth County113
- Hanson County112
- Day County111
- Potter County111
- Douglas County111
- Hamlin County110
- Yankton County110
- Gregory County109
- McCook County109
- Campbell County108
- Miner County107
- Buffalo County106
- Grant County104
- Brookings County104
- Brule County104
- Clark County103
- Minnehaha County102
- Kingsbury County101
- Bon Homme County100
- Deuel County98
- Roberts County97
- Lake County96
- Fall River County96
- Marshall County95
- Moody County93
- Oglala Lakota County76
The busiest days
Days with the most alerts issued, by UTC date.
Nearby
Alerts in force nowTornadoes on recordThe radar archive20082010
Sources
National Weather Service watches, warnings, advisories and statements from the Iowa Environmental Mesonet's VTEC archive, which reconstructs tornado, severe thunderstorm, flash flood and marine warnings back to 1986 from the NWS text archive. Storm Prediction Center watches and mesoscale discussions from SPC's archive through the Mesonet. County centers from the US Census Bureau. Warning verification from the Mesonet's Cow. Rebuilt daily.