Dickinson County Emergency Management

An average winter in northwest Iowa brings 36" of snow.

Winter Storms the Deceptive Killers

Winter Weather Safety

Click here to skip to the BeSafe information for Winter Weather

How do winter storms form?
Just like any other storm at other times of the year, just the right combination of ingredients is necessary for a winter storm to develop.

Three basic ingredients are necessary to make a winter storm.

Cold air – below freezing temperatures in the clouds and near the ground are necessary to make snow and/or ice.
Lift – something to raise the moist air to form the clouds and cause precipitation. An example of lift is warm air colliding with cold air and being forced to rise over the cold dome. The boundary between the warm and cold air masses is called a front. Another example of lift is air flowing up a mountainside.
Moisture – to form clouds and precipitation. Air blowing across a body of water, such as a large lake or the ocean, is an excellent source of moisture.

Snow – Most precipitation that forms in wintertime clouds starts out as snow because the top layer of the storm is usually cold enough to create snowflakes. Snowflakes are just collections of ice crystals that cling to each other as they fall toward the ground. Precipitation continues to fall as snow when the temperature remains at or below 0 degrees Celsius from the cloud base to the ground.

Precipitation falls as SNOW when air temperature remains below freezing throughout the atmosphere

Snow Flurries – Light snow falling for short durations. No accumulation or light dusting is all that is expected.
Snow Showers – Snow falling at varying intensities for brief periods of time. Some accumulation is possible.
Snow Squalls – Brief, intense snow showers accompanied by strong, gusty winds. Accumulation may be significant. Snow squalls are best known in the Great Lakes Region.
Blowing Snow – Wind-driven snow that reduces visibility and causes significant drifting. Blowing snow may be snow that is falling and/or loose snow on the ground picked up by the wind.
Blizzard – Winds over 35mph with snow and blowing snow, reducing visibility to 1/4 mile or less for at least 3 hours.

Sleet occurs when snowflakes only partially melt when they fall through a shallow layer of warm air. These slushy drops refreeze as they next fall through a deep layer of freezing air above the surface, and eventually reach the ground as frozen rain drops that bounce on impact.

Sleet forms when snow falls through a shallow layer of warm air and partially melts, then refreezes near the ground.

Freezing Rain occurs when snowflakes descend into a warmer layer of air and melt completely. When these liquid water drops fall through another thin layer of freezing air just above the surface, they don't have enough time to refreeze before reaching the ground. Because they are "supercooled," they instantly refreeze upon contact with anything that that is at or below O degrees C, creating a glaze of ice on the ground, trees, power lines, or other objects. A significant accumulation of freezing rain lasting several hours or more is called an ice storm.

Freezing rain is formed when snow falls through a deep layer of warm air, completely melting. It then becomes "supercooled" in cold air and freezes on contact.

Wind Chill
Even without snow and ice, winter can bring hazardous temperatures and dangerous wind chills to Iowa. The wind chill chart below depicts a scientifically derived length of time before frostbite occurs based upon temperature and wind speed on a human.

National Weather Service Wind Chill Chart

Winter Weather Safety

Prepare a Winter Storm Plan

Have extra blankets on hand.
Ensure that each member of your household has a warm coat, gloves or mittens, hat, and water-resistant boots.

Assemble a Disaster Supplies Kit Containing

First aid kit and essential medications.
Battery-powered NOAA Weather radio, flashlight, and extra batteries.
Canned food and can opener.
Bottled water (at least one gallon of water per person per day to last at least 3 days).
Extra warm clothing, including boots, mittens, and a hat.
Assemble a Disaster Supplies Kit for your car, too.
Have your car winterized before winter storm season.

Stay Tuned for Storm Warnings...

Listen to NOAA Weather Radio and your local radio and TV stations for updated storm information.

Know What Winter Storm WATCHES and WARNINGS Mean

A winter storm WATCH means a winter storm is possible in your area.
A winter storm WARNING means a winter storm is headed for your area.
A blizzard WARNING means strong winds, blinding wind-driven snow, and dangerous wind chill are expected. Seek shelter immediately!

When a Winter Storm WATCH is Issued...

Listen to NOAA Weather Radio, local radio, and TV stations, or cable TV such as The Weather Channel for further updates.
Be alert to changing weather conditions.
Avoid unnecessary travel.

When a Winter Storm WARNING is Issued...

Stay indoors during the storm.
If you must go outside, several layers of lightweight clothing will keep you warmer than a single heavy coat. Gloves (or mittens) and a hat will prevent loss of body heat. Cover your mouth to protect your lungs.
Understand the hazards of wind chill, which combines the cooling effect of wind and cold temperatures on exposed skin.
As the wind increases, heat is carried away from a person's body at an accelerated rated, driving down the body temperature.
Walk carefully on snowy, icy, sidewalks.
After the storm, if you shovel snow, be extremely careful. It is physically strenuous work, so take frequent breaks. Avoid overexertion.
Avoid traveling by car in a storm, but if you must...
- Carry a Disaster Supplies Kit in the trunk.
- Keep your car's gas tank full for emergency use and to keep the fuel line from freezing.
- Let someone know your destination, your route, and when you expect to arrive. If your car gets stuck along the way, help can be sent along your predetermined route.

If You Do Get Stuck...

Stay with your car. Do not try to walk to safety.
Tie a brightly colored cloth (preferably red) to the antenna for rescuers to see.
Start the car and use the heater for about 10 minutes every hour. Keep the exhaust pipe clear so fumes won't back up in the car.
Leave the overhead light on when the engine is running so that you can be seen.
As you sit, keep moving your arms and legs to keep blood circulating and to stay warm.
Keep one window away from the blowing wind slightly open to let in air.

What to Do After a Winter Storm

Continue listening to local radio or television stations or a NOAA Weather Radio for updated information and instructions. Access may be limited to some parts of the community, or roads may be blocked.
Help a neighbor who may require special assistance--infants, elderly people, and people with disabilities. Elderly people and people with disabilities may require additional assistance. People who care for them or who have large families may need additional assistance in emergency situations.
Avoid driving and other travel until conditions have improved. Roads may be blocked by snow or emergency vehicles.
Avoid overexertion. Heart attacks from shoveling heavy snow are a leading cause of deaths during winter.
Follow forecasts and be prepared when venturing outside. Major winter storms are often followed by even colder conditions.

Source: Red Cross

Sources: NSSL, NWS