Contrary to what you may have heard, Wisconsin weather ain’t all that bad. Sure, temperatures varying from 105°F to -30°F degrees spice things up a bit and, come late February, most people are psychotically ready for the snow to go, but overall it isn’t terrible.
Wisconsin is near the path of the jet stream, and it lacks any declivity large enough to impede precipitation or climatic patterns. Its northerly latitude produces seasonal shifts in the zenith angle, which result in drastic temperature fluctuations. It’s not unusual for farmers near Lake Geneva to be plowing while ice fishers near the Apostle Islands are still drilling holes in the ice.
The state’s mean temperature is 43°F, though this is not a terribly useful statistic. You’ll find 100°F in the shade come August, 40°F or more below with wind chill in winter, and everything in between.
The average precipitation amount is 38.6 inches annually. Northern counties experience more snowfall than southern ones, and anyplace near the Great Lakes can see some sort of precipitation when the rest of the state is dry. Snow cover ranges from 140 days per annum in the north to 85 days in the south. Snowfall ranges from 30 inches in the extreme south to 120 inches or more in Bayfield County and the Lake Superior cap.
Wisconsin has two contiguous sea-size bodies of water, which give rise to their own littoral microclimates. Get used to hearing “cooler near the lake” in summer and “warmer near the lake” in winter. This moderating influence is particularly helpful for the orchards and gardens in Door County  on Lake Michigan and Bayfield County on Lake Superior. On the other hand, it also means more precipitation: One freaky day in 2009, Milwaukee’s south side had 14.8 inches of snow, while 30 miles to the west it was sunny all day!
Generally, not much here in Wisconsin can kill you—no hurricanes, freeway snipers, or grizzlies. But the state does endure the eye-popping experience of tornadoes, generally averaging six serious twisters and many more near-misses or unsubstantiated touchdowns each year.
Tornado season begins in March and peaks during late May, June—especially—and July. A secondary spike occurs during September and extends occasionally into mid-October. Many of the midsummer tornadoes are smaller and less intense than the ones in April-June or in September.
A tornado watch means conditions are favorable for the development of a tornado. A tornado warning means one has been sighted in the vicinity. In either case, emergency sirens are active almost everywhere in Wisconsin. Get yourself an emergency weather radio and keep it with you.
Seek shelter in a basement and get in the southwest corner (they often, but not always, move from the southwest), under a table if possible. Avoid windows at all costs. If there is no basement, find an interior room, such as a bathroom, with no windows. Avoid rooms with outside walls on the south or west side of a building. If you are driving, position yourself at right angles to the tornado’s apparent path. If overtaken, you’ve got a dilemma: experts howlingly disagree about whether to stay in the car with your seatbelt on or get out and lie flat in a ditch.
Lightning still kills about 200–300 people per year nationwide, more than tornadoes and hurricanes combined. Wisconsin averages two serious thunderstorms per year, with a midsummer average of two relatively modest ones each week. Don’t let this lull you into complacency in autumn, however; this author scribbled edition number one of this guide during ferocious thunderstorms on Halloween, replete with marble-size hail, flash floods, and tornadic activity.
Thunderstorms are often deadlier than tornadoes, particularly when you’re driving or when isolated in open areas. Lightning is serious stuff—remember, if you’re close enough to hear thunder, you’re close enough to get fried. The cardinal rule when lightning is present: Do the opposite of what gut instincts tell you. Avoid anything outside—especially trees. If you cannot get indoors, squat on the balls of your feet, hugging your knees in a balled position, reducing your contact with the ground and your apparent size. If indoors, stay away from anything that has a channel to the outside: telephones, TVs, radios, even plumbing.
Technically, four inches of snow per 24-hour period qualifies as heavy snowfall (but to that paltry amount a Wisconsinite would just sniff in derision).
Six inches in 8–12 hours will cause serious transportation disruptions and definitely close airports for a while. Snow generally begins to stick in mid- to late October in northern Wisconsin, and early December in southern Wisconsin, though snow has fallen as early as September and as late as May on rare occasions.
Odds are, if you’re in Wisconsin in the winter you’re going to be driving in the stuff. Still, even the hardiest winter drivers need to practice prudence. If you’re a novice at winter driving, don’t learn it on the road, especially on a crowded highway at dawn or dusk.
Rule One: It's important to slow down. Be cautious on bridges, even when the rest of the pavement is OK; bridges are always slippery. In controlled skids on ice and snow, take your foot off the accelerator and steer into the direction of the skid. Follow all owner’s manual advice if your car is equipped with an Anti-Lock Braking System (ABS). Most cars come equipped with all-season radials, so snow tires aren’t usually necessary. Tire chains are illegal in Wisconsin.
During nighttime snowstorms, keep your lights on low beam. If you get stuck, check your owner’s manual for the advisability of “rocking” the car; be sure to keep the front wheels cleared and pointed straight ahead. Do not race the engine; you’ll just spin your wheels into icy ruts. Winterize your vehicle. Most important, carry an emergency kit including anything you may need to spend the night in a snowbank (I can’t tell you how many people have learned this the hard way in a blizzard that’s trapped them on an interstate for ten hours).
And please, if you see someone hung up in a snowbank, stop and help push him or her out.
The Department of Transportation’s website (dot.state.wi.us) updates winter driving conditions from November to late March four times daily. You can also call the state’s toll-free roads hotline at 511 on your mobile phone (Iowa and Minnesota also participate in the program, Illinois and Michigan hopefully soon)—it’s a brilliant service.
The most dangerous part of winter in Wisconsin is the wind-chill factor—the biting effect of wind, which makes cold colder and more lethal. For example, when the temperature is 30°F, with a wind of 40 mph the temperature is actually -6°F; if the temperature were 0°F, 40 mph winds would make it -54°F—the point at which it’s no longer a joke how cold a Wisconsin winter is.
When the wind chill takes temperatures low enough, exposed skin is in immediate danger. Lots of Badgers still remember one serious case of frostbite (probably frostnip) that they swear they can still feel today when the weather changes. The most serious cases of frostbite—you’ve seen photos of mountain climbers with black ears and digits—can require amputation.
Worse, without proper clothing, you’re at risk for hypothermia.