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4.11 Tornado

Tornadoes are defined as violentlyrotating columns of air extending from thunderstorms to the ground, with wind speeds between 40-300 mph.Tornadoes can and do occur in all months of the year; however, the most tornadoes usually occur during severe thunderstorms in the warm months.They develop under three scenarios: (1) along a squall line; (2) in connection with thunderstorm squall lines during hot, humid weather; and (3) in the outer portion of a tropical cyclone. Funnel clouds are rotating columns of air not in contact with the ground; however, the column of air can reach the ground very quickly and become a tornado.

4.11.1 Annual Tornadoes

The following figure outlines the average tornadoes per month in the northern to central plains by state. For the state of Montana, the average number of tornadoes peaks in the months of June and July with an average of 4 tornadoes per month in each of these two summer months.

Figure 22: Average Annual Number of Tornadoes per State in Northern to Central Plains

4.11.2 Tornado Risk

The overall probability that tornadoes will occur each year in Valley County is likely, its relative impact is moderate, and thus the overall risk for Valley County is low. The risk for tornadoes for each of the cities is different and was determined based upon the specific data collected and outlined in the history section of this hazard profile. In assessing tornado data for the 2015 update, data from 2009 to 2014 was used to determine the risk for each of the cities and the county as a whole. Most notable are the cities of Glasgow, Opheim and the unincorporated areas of Valley County. The table below provides the name of each of the cities in the county, the probability that tornadoes will have an impact on that jurisdiction, the impact potential, as well as the overall risk calculated by the determine probability and impact ratings.

Table 64: Tornado Risk by City in Valley County

Tornado Storms
City	Probability	Impact	Risk
Glasgow	Likely	Moderate	Low
Fort Peck	Possible	Low	Little to No
Nashua	Possible	Low	Little to No
Opheim	Likely	Low	Little to No
Valley County*	Likely	Moderate	Low
Total	Likely	Moderate	Low

*Valley County information takes into account unincorporated areas of the county.

4.11.3 Tornado History in Valley County

Tornadoes in Montana peak in the months of June and July. The typical time of day for tornadoes in Montana ranges between 4:00 P.M. and 7:00 P.M. Most of these are tornadoes have wind speeds under 125 miles per hour. The history of tornado events in Valley County was provided by National Oceanic Atmospheric Administration (NOAA). From 2009 to 2015, there have been 4 recorded events of atornado in Valley County. A comprehensive list of the last 50 years of data can be found in Appendix B.
The most recent tornado in Valley County took place on June 29, 2011. This tornado affected the city of Glasgow. The tornado was an EF0 and was 0.01 miles long and 1 yard wide. There was no reported fatalities, injuries, property damage or crop damage. The narrative for this storm provided by the National Centers for Environmental Information indicated a tornado briefly touched down in open country. Very brief dust cloud at the surface was observed with no damage. The funnel cloud and very weak landspout were observed by numerous National Weather Service (NWS) Glasgow employees. No wall cloud was present at the time of the event, but one did form after the funnel dissipated.
The following image shows the tornado track for the tornadoes which, have occurred in the county from 1964 to 2014. There have been 38 reported tornadoes in Valley County during this timeframe, with no fatalities and no injuries. The numbers on the map correspond to the Fujita Scale number for each tornado that is a scale from 0-5, with 0 being the least severe and 5 being the most severe.

Figure 23: Tornado Track for Valley County

Source: Tornado History Project for Valley County, MT

4.11.4 Mitigation Actions in the Past Five Years

Mitigation actions for severe summer weather from the 2008 Valley County Pre-Disaster Mitigation Plan stated they would build tornado safe rooms in the communities of Nashua and Opheim as well as construct the safe rooms with a multi-hazard vision.
There were also other mitigation actions which are related to tornadoes. One mitigation action was to promote the use of multi-hazard mitigation measures and this was to be accomplished by purchasing NOAA weather Radios and enhancing weather radio coverage in Opheim. Updating the siren systems in Glasgow, Fort Peck, Richland, Opheim, Nashua, and Hinsdale was also included. As well as upgrading the emergency advisory equipment at the radio station in Glasgow and achieving countywide StormReady designation from the National Weather Service.
An additional mitigation action was to improve the functionality of critical and special needs facilities and infrastructure during disasters. This was to be accomplished by purchasing and installing generators, protecting electric infrastructure and creating and enforcing ordinances that prevent the railroad from blocking emergency access routes. Additionally, the county wanted to improve the public’s ability to protect themselves during hazardous events by providing public education. Thus, as Valley County continues to be at risk for tornados and as many of the past projects were not fully completed, tornadoes continue to be a focus in this iteration of the Valley County Mitigation Plan.

4.11.5 Vulnerability in Valley County

Generally, June and July are the months with the highest probability of severe thunderstorms and tornados in Valley County. Some tornados have however, been recorded as early as May and as late as September.  High wind events can occur during any time of year.
Schools, hospitals, fire departments, police departments and other critical facilities are also at increased vulnerability because if they would become damaged during a tornado. The county would be required to rely on other facilities within the county or surrounding counties depending upon the amount of damage. Manufactured homecommunities and other areas with limited sheltering options are also at an increased risk.

4.11.6 Tornado and Climate Change

According to the National Center for Atmospheric Research, the main climate change connection to tornadoes is via the basic instability of the low-level air that creates the convection and thunderstorms in the first place. Warmer and moister conditions are the keys for unstable air and the oceans are warmer because of climate change. Some studies however state that trends in severe storms, including the intensity and frequency of tornadoes, hail, and damaging thunderstorm winds, are uncertain. Since the impact of more frequent or intense storms can be larger than the impact of average temperature, climate scientists are actively researching the connections between climate change and severe storms (National Climate Assessment Development Advisory Committee, 2013).

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