As Canadian and American mountain ranges go north-south, climate differences can be rather dramatic between locations at the same latitude, with occasional snowstorms down into the South. As a general principle, the inland (which makes up most of the North American continent) has larger temperature differences between summer and winter than the coast.
The United States uses US customary units for weather reports, including degrees Fahrenheit (°F), and inches of mercury for air pressure. Since 1970, Canada has officially used the metric scale (including degrees Celsius), but imperial units (including °F) are still in traditional use. Near the US-Canadian border, US and metric units are used in parallel. See Metric and Imperial equivalents for details about unit conversions.
Arctic Alaska and much of northern Canada are within the Arctic, like most of Greenland, and temperatures are normally below 10 °C during most of the year. The rest of Alaska and most of Canada have either boreal or sub-Arctic climates, with short summers and long, cold winters. The same applies for the highest parts of the Rocky Mountains in the United States. Southern Canada and most of the contiguous United States (except the south and southwest) have a temperate climate, where winters are relatively short, but can be intensely cold.
The southwestern and southern United States (as well as northern Mexico) have a subtropical climate, where sub-zero temperatures are unusual, but not unheard of. Higher altitudes in these regions (the Appalachians and the various plateaus and mountains of the southwest) will often be much colder. A particularly dramatic contrast by altitude is in Arizona. In the state's capital of Phoenix, freezing weather is rare; but Flagstaff, less than three hours' drive to the north but about 5,800 feet/1,750 m higher, gets regular winter snowfall and low temperatures below freezing for over 200 days per year. The tropics (Florida, Hawaii, the Caribbean and Central America) are warm year-round — except for higher altitudes which are not as warm but lack large temperature changes between the seasons. Southern California has a Mediterranean climate that is similar to tropical climates in its year-round warmth, though its precipitation pattern dramatically differs from tropical climates. Many Canadians and people from northern U.S. states take winter vacations to the beaches of Mexico. In Cancun, the average winter daily high temperature is 82 degrees and the average nightly low is 68 degrees. Winter days in southern Mexico are almost always sunny.
North America has colder winters than similar latitudes in Europe; on the US-Canada border (which mostly follows the 49th parallel) winter temperature is persistently minus 15 °C or colder; Paris and Vienna, which are nearly on the same latitude, are usually above zero. Churchill is roughly the same latitude as Stockholm, but can be 20 °C colder or more in winter.
The Great Lakes create a climate zone of their own; occasionally, the lands east of the lakes can see enormous amounts of snow.
The Pacific Coast has mild winters due to mountain ranges that keep the polar vortex to the east, while the Pacific brings rain during winter. However, high mountain ranges in the region are a different story, and can be cold and snowy in winter due to the impact of elevation on climate. The cities on the coast itself Vancouver, Seattle, Portland, San Francisco, Los Angeles and San Diego have comparatively mild winters to other cities of similar latitude further east; Vancouver typically only gets a light dusting of snow for a few days a year, while winter temperatures in the Los Angeles basin typically hover at a relatively comfortable 10–20°C (50–70°F), and snow has almost never been known to fall within the metropolitan area except at high elevations, mostly in the San Gabriel Mountains.
- See also: Winter driving
The United States and Canada are among the world's most car-dependent countries. Urban streets and major highways are usually plowed soon after snowfall; countryside roads are another story.
In the Sierra Nevada Mountains in California, there are several highways that go over the mountain passes, and many of the state routes close during the winter; some state maps show which months the state roads are typically open. The passes around Lake Tahoe have lower elevations than those to the south and therefore are less likely to be closed; as you go south, the passes get higher and the roads are likely to be closed for large portions of the year.
Many popular American tourist destinations, such as Yosemite, receive snow in winter.
North America has many resorts for downhill snowsports, especially in the Rocky Mountains. While ice hockey in North America is associated with winter, since the 1990s, the National Hockey League has expanded to the southern U.S.
In the warmer regions of California, along with Florida, outdoor activities such as hiking are not only possible in winter, but are also more appropriate for this time of year than in summer. In parts of California, especially low inland regions such as the East Bay and the Central Valley, low early morning temperatures that at coldest fall to 0 °C (32 °F) rise substantially during the course of a typical day to temperatures as high as 15 °C (59 °F).
Christmas is a major holiday in the United States and Canada, to the extent that Americans will simply refer to the period spanning American Thanksgiving in late November to New Year's Day as "the holidays". The definition of a "White Christmas" differs slightly in Canada and the United States, mainly due to different measuring systems in use; Canada defines White Christmas as 2 centimetres (0.79 in) of snow on the ground while the United States sets their threshold at 1 inch (2.5 cm). The chance of a White Christmas garners intense public and media speculation as Christmas approaches. A White Christmas is likely in most of Canada, with the exception of coastal British Columbia and southern Ontario, while in the United States, the Rocky Mountains, northern Plains, and interior Northeast present the best chances of White Christmases.
The need for precautions varies with location. Cities with regularly long and snowy winters (such as Winnipeg) tend to have better winter utilities than cities such as New York City, where snow and cold temperatures are less common.
Regions colored gold/brown on the map to the right, especially towards the southern end of the map, rarely receive extremely cold weather. However, in some regions where precipitation is low during the winter months, or even low year-round, cold temperatures can be reached without snow accumulation.