Alert archive / Montana / Severe Thunderstorm Watches in 2011
Severe Thunderstorm Watch 818
The Storm Prediction Center issued this severe thunderstorm watch at Aug 29, 2011, 2:34 PM MDT for 10 counties in Montana; 4 counties in Wyoming. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 29, 2011, 2:34 PM MDT (20:34 UTC)
- Expired
- Aug 29, 2011, 8:24 PM MDT
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
Counties Big Horn County, MT, Carter County, MT, Custer County, MT, Garfield County, MT, Musselshell County, MT, Petroleum County, MT, Powder River County, MT, Rosebud County, MT, Treasure County, MT, Yellowstone County, MT, Campbell County, WY, Crook County, WY, Sheridan County, WY, Weston County, WY
The radar
The Billings radar (KBLX), 148 km from the middle of the area, began a volume at 20:36 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
- 20%
- One or more EF2 to EF5 tornadoes
- 5%
- Ten or more severe wind reports
- 30%
- One or more gusts of 65 knots or more
- 30%
- Ten or more severe hail reports
- 30%
- One or more hailstones of 2 inches or more
- 20%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
6 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 29, 2:44 PM MDT | Severe Thunderstorm Warning | BYZ | Big Horn, Yellowstone | 61 min |
| Aug 29, 3:41 PM MDT | Severe Thunderstorm Warning | BYZ | Musselshell, Rosebud, Yellowstone | 51 min |
| Aug 29, 3:46 PM MDT | Severe Thunderstorm Warning | BYZ | Big Horn, Treasure, Yellowstone | 28 min |
| Aug 29, 5:47 PM MDT | Severe Thunderstorm Warning | BYZ | Sheridan | 28 min |
| Aug 29, 5:49 PM MDT | Severe Thunderstorm Warning | UNR | Campbell | 56 min |
| Aug 29, 6:31 PM MDT | Severe Thunderstorm Warning | UNR | Campbell, Crook, Weston | 59 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
Great_falls, MT (KTFX), launched 12:00Z, 8.6 hours before the alert went out and 335 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
- 3295 m above ground
- 0-6 km bulk shear
- 17 kt
- 0-1 km storm-relative helicity
- 10 m²/s²
- 0-3 km storm-relative helicity
- -13 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 29, 1:52 PM MDT | Mesoscale Discussion | SPC | Big Horn, Carbon, Fergus, Golden Valley, Musselshell, Petroleum and 3 more | 83 min |
| Aug 29, 5:09 PM MDT | Mesoscale Discussion | SPC | Custer, Powder River, Rosebud | 96 min |
| Aug 29, 1:05 PM MDT | Mesoscale Discussion | SPC | Goshen, Laramie, Niobrara, Platte | 85 min |
Nearby
Severe Thunderstorm Watches in Montana, 2011Severe Thunderstorm Watches in Wyoming, 2011Every severe thunderstorm watch in 2011
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.