Weather alerts in Montana, 2009
1,626 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
- 1,626
- Warnings
- 483
- Watches
- 129
- Advisories
- 370
- Busiest month
- July556 alerts
- Busiest day
- July 13, 200985 alerts
Over time
By month
Warning verification
How often warnings here had a storm report inside them, and how much warning the reports had.
2 of 21 tornado warnings covering Montana in 2009 had a tornado report inside them; 3 of 7 tornado reports fell inside a warning, on average 13 minutes after it went out.
Montana, 2009
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| Tornado warnings | 21 | 2 | 90% | 7 | 43% | 13 min |
| Severe thunderstorm warnings | 295 | 125 | 58% | 304 | 64% | 24 min |
| Flash flood warnings | 17 | 4 | 76% | 13 | 38% | 18 min |
Each office's whole area, 2009
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| NWS Missoula, MT: severe thunderstorm warnings | 30 | 13 | 57% | 35 | 80% | 22 min |
| NWS Missoula, MT: flash flood warnings | 3 | 1 | 67% | 8 | 13% | 48 min |
| NWS Great Falls, MT: tornado warnings | 3 | 0 | 100% | 0 | ||
| NWS Great Falls, MT: severe thunderstorm warnings | 87 | 30 | 66% | 68 | 53% | 21 min |
| NWS Great Falls, MT: flash flood warnings | 2 | 0 | 100% | 0 | ||
| NWS Billings, MT: severe thunderstorm warnings | 85 | 28 | 67% | 63 | 60% | 23 min |
| NWS Billings, MT: flash flood warnings | 8 | 3 | 63% | 8 | 50% | 11 min |
| NWS Glasgow, MT: tornado warnings | 18 | 2 | 89% | 7 | 43% | 13 min |
| NWS Glasgow, MT: severe thunderstorm warnings | 105 | 58 | 45% | 157 | 68% | 27 min |
| NWS Glasgow, MT: flash flood warnings | 4 | 0 | 100% | 0 |
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
1,626 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.
- Valley County178
- McCone County169
- Garfield County138
- Sweet Grass County133
- Stillwater County127
- Park County125
- Missoula County120
- Dawson County120
- Richland County117
- Phillips County116
- Roosevelt County114
- Flathead County113
- Carter County111
- Powell County109
- Granite County108
- Lake County105
- Wibaux County103
- Carbon County102
- Powder River County101
- Golden Valley County100
- Big Horn County97
- Fallon County97
- Sanders County94
- Ravalli County92
- Wheatland County92
- Rosebud County91
- Yellowstone County87
- Prairie County86
- Daniels County85
- Custer County84
- Sheridan County82
- Musselshell County80
- Deer Lodge County69
- Silver Bow County67
- Treasure County65
- Cascade County63
- Mineral County62
- Petroleum County62
- Gallatin County60
- Fergus County58
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.