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4.6 Severe Winter Weather

Winter storms may be categorized as ice storms, heavy snowfall, or blizzards. These storms vary in size and intensity and may affect a small part of the state or several states at once. Blizzards are common in Montana. A blizzard is a storm that has sustained winds or frequent gusts of 35 miles per hour or higher with snow and blowing snow reducing visibility to near zero. Blowing and rapid snowfall can overwhelm the plowing resources, making roadways impassable, and severely reduce visibility. Particularly heavy snows, early or late season snows, and ice events can damage infrastructure such as power lines, and block roads or damage structures with downed trees.

Table 54: NWS Warning Terminology Table

National Weather Service Warning Terminology
Winter Weather Advisory	Alert for ice, cold weather, or snow that can range from 2 - 6 inches.
Winter Storm Watch	Alert for severe winter weather with a high possibility in the next few days resulting in high accumulations of snow or ice.
Winter Storm Warning	Severe weather (ice, snow, cold) are about to begin or have already started.
Blizzard Warning	Snow condition resulting in high winds, snowdrifts, lack of visibility, and threatening conditions when traveling and to those exposed to the weather.
Ice Storm Warning	High accumulations of ice that will cause dangerous travel and problems to power infrastructure.
Heavy Snow Warning	Snow accumulation of 6 or more inches.

Cold temperatures into the negative numbers are also common throughout the winter months in Montana. The coldest places in Montana are in Valley, Sheridan and Roosevelt Counties where average daily low temperatures have ranged from -5.8°F to -2.0°F. The coldest temperature ever recorded in Valley County was -45°F at Glasgow on February 15, 1936. Extended cold periods, especially when coupled with strong winds, can create dangerous situations for those outdoors or those without heat, such as in the case of a utility disruption.

4.6.1 Severe Winter Weather Risk

The overall probability that severe winter weather will occur each year in Valley County is highly likely and its relative impact is moderate and thus the overall risk for Valley County is moderate. The risk for severe winter weather for each of the cities is the same because data was not available by individual city. In assessing severe winter storm 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. Each of the cities in Valley County are at moderate risk of winter storms. The table provided below provides the name of each of the cities in the county, the probability that winter storms 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 55: Severe Winter Weather Risk by City in Valley County

Winter Storms
City	Probability	Impact	Risk
Glasgow	Highly Likely	Moderate	Moderate
Fort Peck	Highly Likely	Moderate	Moderate
Nashua	Highly Likely	Moderate	Moderate
Opheim	Highly Likely	Moderate	Moderate
Valley County*	Highly Likely	Moderate	Moderate
Total	Highly Likely	Moderate	Moderate

4.6.2 Severe Winter Weather History in Valley County

Figure 18: Total Snowfall Glasgow 1894-2014

Winter storms occur each winter season in Valley County. The types of winter storm events that are reported for Valley County include blizzard, extreme cold/windchill, ice storms, winter storms, and heavy snowfall as provided by the National Oceanic Atmospheric Administration (NOAA). Some of the most notable winter storms in Valley County occurred in 2011. In 2011 alone, seven winter storms, ten days with extreme cold/ wind chill and three blizzards occurred in Valley County. This is an example of how harsh the winters in Valley County can be.

NOAA provided the history of winter storm events in Valley County. From 2009 to 2014, there have been numerous recorded events of winter storms in Valley County. A comprehensive list of the last 50 years of data can be found in Appendix B.
Of the winter storms, there has not been any severe winter weather in the last 50 years in Valley County which has been a declared disaster by FEMA.

4.6.3 Mitigation Actions in the Past Five Years

One mitigation action was to promote warning systems, which was accomplished by purchasing NOAA Weather Radios and enhancing weather radio coverage in Opheim. Upgrading the emergency advisory equipment at the radio station in Glasgow and achieving countywide Storm Ready designation from the National Weather Service has also been completed in the last five years.
An additional mitigation action listed in the previous mitigation plan was to improve the functionality of critical and special needs facilities and infrastructure during disasters by purchasing and installing generators, protecting electric infrastructure, and creating and enforcing ordinances that prevent the railroad from blocking emergency access routes. The county also wanted to improve the public’s ability to protect themselves during hazardous events by providing public education.
Due to thecertainty of future severe winter storms, preparing for and mitigating winter storms remains a critical focus of this iteration of the mitigation plan update. Beyond carrying the most pertinent actions like education, forecasting, and warnings outlined in the previous plan iterations, this iteration of the plan looks to increase capacity for sheltering.

4.6.4 Vulnerability for Valley County

The following information was provided by the 2013 Update to the State of Montana Multi-Hazard Mitigation Plan: Major problems with winter weather in Montana typically only occur during record snowfalls and extended periods of below zero temperatures. Initial consequences include threats to vulnerable populations from utility interruption, freezing pipes, and snow removal costs. Economic losses include commercial aviation delays/cancellations, medical flights unable to transport patients, and loss of revenue to hotels and restaurants when large events are canceled. Residual effects from severe winter weather include agricultural considerations and potential flooding concerns.
Most Montana residents are prepared for winter weather each year. Every community receives snow on an annual basis, so residents expect measurable snow several times each winter. Winter storms are generally slow in developing, often taking one to three days to mature. This does not in any way diminish their importance, nor their potential for causing loss of life and destruction. What it does mean is that the National Weather Service is often able to provide advance notice of winter storms, in some cases, lead times of one to two days. Winter weather typically affects the state from October to April each year but late storms can extend into June, causing extreme impacts to the agricultural industry.
The entire state is considered vulnerable to severe winter weather. Arctic cold fronts typically enter the state from the northeast and may cross the Continental Divide, affecting the entire state. Arctic fronts meeting wet maritime fronts often combine to cause heavy snowfall, which can occur in all parts of the state. The lowest temperatures are typically experienced in the northeast, whereas the heaviest snowfall most often occurs in the mountain regions.
Counties with the highest exposure to severe winter weather include Petroleum, Wibaux, Treasure, Prairie, and Carter; while the top cities/towns include: Pinesdale (Ravalli Co.), Browning (Glacier Co.), Wibaux (Wibaux Co.), Poplar (Roosevelt Co.) and Terry (Prairie Co.). Figure 19 presents percent exposure for the top counties and cities/towns.

Figure 19: Exposure of Severe Winter Weather in Montana

4.6.5 Severe Winter Weather and Climate Change

According to the National Climatic Assessment, summers are long and hot in the south; winters are long and often severe in the north. In the Northern Plains, warmer winters may lead to reduced heating demand while hotter summers will increase demand for air conditioning, with the summer increase in demand outweighing the winter decrease.
Changes to crop growth cycles due to warming winters and alterations in the timing and magnitude of rainfall events have already been observed in Montana and as these trends continue, they will require new agriculture and livestock management practices.

4.6.6 Relationship to Other Hazards

Winter storms have relationships to other hazards such as flooding and structural fires. Snowmelt from heavy snows can cause localized flooding which can cause dangerous conditions for residents and motorists. It can also destroy property and infrastructure such as roads. In addition, heavy winter snowstorms can cause power outages that may cause residents to use alternative heating methods, which can increase the risk of structural fires.

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