Tornado and Hail in Montana, July 29, 2011

Spotter reported hen egg-sized hail stones covering the ground.

Public estimated golf ball-sized hail stones.

Spotter estimated quarter-sized hail stones.

Public estimated tennis ball-sized hail stones.

Hail covered the ground, and lasted for 15 minutes.

Public report relayed through Sheridan County Dispatch office.

Observer reported quarter-sized hail stones along with 40 to 50 mph winds and measured 0.71 inches of rain.

Richland County dispatch received 4 public calls reporting the tornado near Lambert. The majority of the damage in the Lambert to Savage area was straight line wind damage, not tornadic. The tornado caused little damage.

Spotter reported ping pong ball-sized hail stones and estimated 60 mph wind gusts and half an inch of rain.

Some light damage consisting of tree branches down and fence damage was noted south of Lambert. More significant damage was found about 9 miles southeast of Lambert on Rd. 115. At this location, numerous trees were uprooted or snapped, and there was damage to homes and vehicles. Residents reported hail up to 2.5 inches breaking windows in homes.

Major to minor crop damage was seen over a large area from 9 southeast of Lambert to Savage. An irrigation system was destroyed just north of Savage. There was some damage to structures in and near the town of Savage, with the most significant structural damage surveyed occurring on a ranch 6 miles west-northwest of Savage. At this location, an attached garage was destroyed with the garage door torn off and a wall blown out. The garage door and wall, which were blown 200 feet down wind of the house. Also, this ranch had a grain bin torn off its foundation and blown a half mile down wind, where it was found in a mining pit.

About 4 miles of power poles were blown down or snapped along Rd. 107 west of Lambert. Poles on the south side of the road were blown down, while those on the north side were not, even though those on the south side were thicker poles. The poles that were blown down were a little taller than those that did not get blown down, and had cross members near the top.

In the town of Savage, numerous trees were uprooted or snapped. The cemetery at Savage had the most trees blown down.

Crop damage occurred as far south as County Road 107, with hail also being reported. However, significant structural and tree damage was reported by the public (not surveyed) further south, without hail also being reported. A dairy 2.4 miles west-southwest of Savage had considerable damage, including the roof. All of the debris from the dairy was blown down wind towards the south.

The perception of the residents of Savage was that they experienced a tornado. This is a reasonable perception as the residents first received a tornado warning form the NWS, then lost power, and then experienced powerful damaging winds. However, all of the damage surveyed flowed primarily in one direction, towards the south. Also, the damage extended over a wide area exceeding 4 miles in width, and tornadoes are much more localized. In fact, this wide area of damage is more significant than that produced by most tornadoes.

As all of the observed damage implied flow from the north, it was concluded that the damage was caused by a strong macroburst. A macroburst is defined as a strong downdraft from a thunderstorm affecting a path of greater than 2.5 miles. A macroburst forms when hail and rain aloft fall and entrain air, forming a downdraft. As large hail has a high fall speed, strong downdrafts can develop in storms with a lot of large hail (which this storm had). When the downdraft impacts the ground, the flow spreads out horizontally, creating strong straight line winds which radiate out from the center of the downdraft along a gust front. The rotation of the storm can add to the downdraft effect, creating a large area of uniform wind direction. Radar indications did not show large hail approximately south of County Road 107, which agrees with surveyed crop damage and public reports. However, significant damage still occurred for at least several miles south of Rd. 107. It is not unusual for gust fronts to travel considerable distances away from the storms which produce them, which evidently happened in this case.

The maximum wind speeds with this event are estimated from the resulting damage. Uprooted and snapped hardwood trees, building damage, and broken power poles are all consistent with winds above 95 mph over a wide area, with winds up to about 110 mph for the most significant damage.

The survey team did not find any damage from a tornado at any location, though one was conclusively observed and photographed. This is not surprising as the time the tornado was observed, when combined with radar indications of a possible tornado, place the tornado in an empty area just southwest of Fox Lake near Lambert. A tornado in this location would not have left behind any damage for the survey team to catalog.

Lots of tree damage and power lines down. A facility lost part of its roof. An official NWS Damage Survey estimated the highest winds in this storm at 110 mph.

Spotter reported golf ball-sized hail stones and estimated 60 mph wind gusts.

Spotter reported a 35-foot tall tree was blown over which also downed some power lines.