National Weather Service

Strong winter storms are common in Nevada and eastern California from October through May. The primary hazardous winter weather threat is frozen precipitation, usually in the form of snow. Major winter storms can drop several feet of snow in a short period of time, especially over the mountains, causing widely used travel routes to close and strand travelers. The worst conditions are when strong winds accompany heavy snow, creating “whiteout” conditions that bring extremely dangerous conditions for anyone venturing outdoors. In addition to heavy snow, winter storms can also bring freezing rain, sleet, flooding and bitterly cold temperatures.

Winter weather hazards in Nevada and eastern California result in thousands of motor vehicle accidents each year. Sadly, many of these accidents can be avoided if travelers would use common sense by slowing down and putting their headlights on. Typically, the greatest number of weather related vehicle accidents occur during the first seasonal snowfall of the year as motorists get re-acclimate to winter driving conditions.

If you are driving and a snowstorm forces you to pull off the road or if you become stranded in deep snow, stay in your car and wait for help. Run your car's engine for short periods of time to keep warm. Remember to keep the exhaust pipe clear of snow to prevent deadly carbon monoxide fumes from entering the car. Signal rescuers with your interior light at night or a bright cloth on your car during the day. Store emergency supplies in your car such as blankets, an extra change of dry clothes, a flashlight, high-energy snacks and clay cat litter for traction.

During cold weather outbreaks, prolonged exposure to the cold temperatures and over-exertion can be life threatening. Cold weather alone can put an extra strain on the heart and lead to hypothermia. Heavy exertion, like shoveling snow, pushing a car or walking in deep snow, increases the chance for a heart attack or stroke.

Make preparations before the storm arrives by making sure you have enough food and water to survive several days. When a winter storm hits, use common sense and don’t venture out in the storm unless it’s absolutely necessary. If you have to go out, dress warmly with multiple layers of clothes, especially over your hands, feet, and face. Be sure to have the following items available:

- Flashlight and extra batteries
- Battery Powered NOAA Weather Radio or AM/FM portable radio
- Extra food and water
- Extra medication and baby supplies
- First-Aid Kit
- Heating fuel
- Emergency heating source
- Fire extinguisher and smoke detector
- Carbon Monoxide Detector (300 people die in the U.S. each year due to Carbon Monoxide Poising)

Cold weather also spells extra hardship for pets and livestock who can suffer from frostbite, exposure, and dehydration. In fact, most animal deaths in winter storms result from dehydration due to the freezing of water sources.

Finally be sure to check on elderly or disabled friends, family, or neighbors to ensure they are prepared for winter storms or are moved to a safe location before it hits.

Winter Weather Hazards:

Rain and snow can form under many different conditions. Whether it is the passage of a front or a low pressure system moving across the area, rain and snow can become heavy at times reducing visibilities, and making roads slippery and dangerous. The amount and intensity of rain and snow can vary greatly over just 5 to 10 miles. Heavy or steady rain during warmer weather, combined with a solid snow pack, can increase snow melt suddenly and, in turn, cause flooding of land and rivers. Winter flooding is possible anytime during the season when warmer storms move through and drop heavy amounts of rainfall. However, flooding is most common toward the end of the season when the temperatures are warming toward spring, and when warmer storm systems may drop heavy amounts of rain onto a thick snow pack.

Heavy snow is also a major concern in both the high and low elevations of California and Nevada. Snow can fall and produce little to no accumulation if the snow is light and ground is warm, or it can accumulate to over a foot of snow. One to several feet of snow is common during a storm in the higher elevations of the Sierra Nevada through the winter. Heavy snow can paralyze a city or region, stranding commuters, closing airports, stopping the flow of supplies, and disrupting emergency and medical services. Significant snow accumulations can cause roofs to collapse, and knock down trees and power lines. Heavy snow can also lead to avalanches in the mountains.

A car buried in 2 feet of heavy snow at the National Weather Service office in Reno, NV on January 7, 2005.

Freezing rain or drizzle can be another major winter weather concern. In western Nevada we do not see many freezing rain events, but they do occur, and are certainly possible any time during the winter season. Freezing rain forms when there is a shallow sub-freezing layer of air at the surface, and a layer of warmer air (above freezing) just above the cold layer. However, since the cold layer of air at the surface is so shallow, the raindrops that are falling through the cold layer do not have a chance to freeze, a phenomena called supercooling (or forming "supercooled raindrops"). The supercooled raindrops are raindrops that are colder than 0C and freeze on contact when they strike the ground.

Freezing rain forms when rain falls through a warm layer of air above the surface, and becomes supercooled as it falls through a sub-freezing shallow layer of air right at the surface.

Therefore, the precipitation essentially falls as rain, but freezes on contact with the surface, such as the ground, trees, power lines, motor vehicles, streets, highways, etc. Small accumulations of ice can cause driving and walking difficulties while heavy accumulations produce extremely dangerous and damaging situations primarily by pulling down trees and power lines.

Sleet is another form of wintry precipitation. Sleet forms when the sub-freezing layer at the surface is deeper than during freezing rain events, and the warmer layer above is much shallower. In this cold layer, the precipitation falling as rain higher in the atmosphere has a chance to change over to frozen precipitation. Sleet (commonly referred to as ice pellets) usually bounce after hitting the ground or other hard surfaces. Heavy sleet is a relatively rare event, and is defined as an accumulation of ice pellets covering the ground to a depth of one half inch or more.

Dense fog is common through the winter months in both the high Sierra valleys and the lower valleys of Nevada. Fog forms when the temperature at the surface reaches it’s saturation point, the dewpoint. Fog is often hazardous especially when the fog is widespread and visibility is reduced to one quarter mile or less, making travel difficult or impossible. Freezing fog can also develop during the winter when fog forms during times when temperatures at the surface fall below freezing. This can cause roads and surfaces to become icy and increase travel hazards dramatically.

Looking over a layer of dense fog covering the valley as seen from atop Virgina Peak in western Nevada.

Looking over the valley from Virginia Peak in Nevada, over a thick, dense layer of fog.

Cold temperatures in the winter can be a concern by themselves. Exposure to the cold can cause frostbite or hypothermia, and become life-threatening. The wind chill is a good indication of how cold the air will feel on the human skin. Wind chill is not the actual temperature, but rather how wind and cold feel on exposed skin. As the wind increases, heat leaves the body at an accelerated rate, rapidly lowering the body temperature. Animals are also affected by wind chill, but other things such as cars and plants are not. The elderly and infants are most susceptible to the frigid temperatures. Extreme cold may cause pipes to freeze and burst in homes that are poorly insulated or without heat.

Winter Storms:

Winter Weather Hazards: