Weather alerts in Louisiana, 2009
2,503 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
- 2,503
- Warnings
- 1,576
- Watches
- 167
- Advisories
- 566
- Busiest month
- October400 alerts
- Busiest day
- December 24, 2009106 alerts
Over time
By month
Warning verification
How often warnings here had a storm report inside them, and how much warning the reports had.
43 of 183 tornado warnings covering Louisiana in 2009 had a tornado report inside them; 73 of 128 tornado reports fell inside a warning, on average 18 minutes after it went out.
Louisiana, 2009
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| Tornado warnings | 183 | 43 | 77% | 128 | 57% | 18 min |
| Severe thunderstorm warnings | 563 | 207 | 63% | 467 | 74% | 24 min |
| Flash flood warnings | 167 | 96 | 43% | 232 | 87% | 83 min |
Each office's whole area, 2009
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| NWS Jackson, MS: tornado warnings | 126 | 21 | 83% | 41 | 73% | 18 min |
| NWS Jackson, MS: severe thunderstorm warnings | 600 | 264 | 56% | 647 | 83% | 26 min |
| NWS Jackson, MS: flash flood warnings | 191 | 100 | 48% | 198 | 93% | 107 min |
| NWS Shreveport, LA: tornado warnings | 131 | 51 | 61% | 134 | 60% | 18 min |
| NWS Shreveport, LA: severe thunderstorm warnings | 390 | 173 | 56% | 463 | 76% | 24 min |
| NWS Shreveport, LA: flash flood warnings | 126 | 102 | 19% | 356 | 92% | 110 min |
| NWS Lake Charles, LA: tornado warnings | 59 | 12 | 80% | 56 | 63% | 15 min |
| NWS Lake Charles, LA: severe thunderstorm warnings | 213 | 66 | 69% | 184 | 69% | 23 min |
| NWS Lake Charles, LA: flash flood warnings | 50 | 26 | 48% | 56 | 80% | 87 min |
| NWS New Orleans, LA: tornado warnings | 73 | 8 | 89% | 20 | 30% | 19 min |
| NWS New Orleans, LA: severe thunderstorm warnings | 191 | 39 | 80% | 102 | 56% | 22 min |
| NWS New Orleans, LA: flash flood warnings | 59 | 24 | 59% | 66 | 85% | 88 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
2,503 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.
- Bossier Parish250
- Caddo Parish238
- Webster Parish226
- Bienville Parish223
- East Carroll Parish217
- Union Parish210
- Madison Parish203
- Morehouse Parish198
- Lincoln Parish197
- Natchitoches Parish197
- Claiborne Parish196
- Red River Parish196
- West Carroll Parish191
- De Soto Parish188
- Richland Parish182
- Ouachita Parish174
- Tensas Parish173
- Franklin Parish173
- Winn Parish171
- Jackson Parish168
- Concordia Parish166
- Beauregard Parish163
- Sabine Parish163
- Washington Parish159
- Rapides Parish158
- Saint Landry Parish156
- Allen Parish154
- Catahoula Parish154
- Grant Parish153
- Vernon Parish150
- Evangeline Parish146
- Saint Martin Parish144
- Caldwell Parish143
- Calcasieu Parish142
- Saint Bernard Parish141
- Avoyelles Parish140
- Lafayette Parish139
- Saint John the Baptist Parish139
- East Baton Rouge Parish137
- LaSalle Parish136
24 more counties
- Saint Tammany Parish131
- East Feliciana Parish126
- Saint Helena Parish126
- Saint James Parish122
- Pointe Coupee Parish121
- West Feliciana Parish120
- West Baton Rouge Parish116
- Assumption Parish112
- Iberville Parish112
- Tangipahoa Parish111
- Livingston Parish107
- Jefferson Parish100
- Jefferson Davis Parish99
- Saint Charles Parish94
- Lafourche Parish92
- Acadia Parish83
- Ascension Parish81
- Orleans Parish81
- Plaquemines Parish81
- Cameron Parish72
- Vermilion Parish70
- Terrebonne Parish66
- St. Mary Parish60
- Iberia Parish54
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.