Over the past five years, I’ve written many articles for Grit about weather, from life-threatening storms to weather folklore. This time, I want to tell you where to get weather information and how to use it. All the sources I’ve cited are from the United States and Canadian governments’ official purveyors of such data, and all the information is free.
You can break down weather data into two groups: climate and weather. Climate deals with long-term weather conditions over a period of years. Weather refers to the current and future weather conditions, out to maybe a year at most.
Looking at the past climate, we can tell what the basic weather parameters have been. We can compute averages, highlight extremes, and determine trends of factors such as temperature and rainfall. Climate gives us an idea of what the weather has been like at a particular location and what that location’s weather could be like in the future, assuming no major climate changes. This type of information is useful for planning purposes. For example, if you want to grow things outside, you can use climate information to pick the right plants that grow and prosper in your particular climate.
The National Centers for Environmental Information (NCEI) has a wealth of climate information. You can get daily, monthly, and annual data for temperature and precipitation for the country, individual states, and even specific cities. This includes averages and recorded extremes. Although calculated at the NCEI, this information is often distributed locally by regional climate centers or by state climatologists. Similarly, in Canada, the Canadian Centre for Climate Services has produced useful data, most of which is available locally through the departments or ministries of agriculture in the various provinces.
Of great concern to anyone trying to grow any type of plant outdoors is the occurrence of frost or below-freezing temperatures. (“Frost” and “freeze” are often used interchangeably to indicate a temperature at or below 32 degrees Fahrenheit, or 0 degrees Celsius.) The growing season is defined as the time between the last frost in spring and the first frost in fall. Spring’s last frost date will often dictate planting schedules. On the NCEI website, you can see a map of the U.S. that shows the day of each region’s last spring frost. (See “Climate Resources,” right.)
Additionally, NCEI includes even more specific data for your location on its site. It offers frost occurrence tables by station, which give the probability of when the last and first 32-degree days will occur in spring and fall, respectively. You can also find tables that give the probabilities of growing season length. Calculated at the NCEI, these tables are typically available at local extension services. Similar products are generated in Canada in regions where they’re applicable, and, again, they’re usually available through provincial agricultural offices.
One of the statistics available from a location’s temperature data is the lowest temperature that occurs in winter. The survival of perennial plants often depends on this. The widely used U.S. Department of Agriculture (USDA) Plant Hardiness Zones are determined using this parameter. There are 13 Zones divided by 10-degree increments, and each Zone has two subdivisions. The Canadian version of the Plant Hardiness Zones incorporates even more temperature data and includes rainfall and snowfall statistics. It breaks the country down into nine Zones, each with two subcategories.
- NOAA National Centers for Environmental Information
- NCEI Regional Climate Center Program
- American Association of State Climatologists
- Canadian Centre for Climate Services
- NCEI Freeze Map
- USDA Hardiness Zones
- Plant Hardiness of Canada
What about finding your current weather conditions and forecast? Go to the official National Weather Service (NWS) website (see “Weather Resources,” right), and click on your location on the map. This will take you to your local NWS office. For Canada, go to the Government of Canada’s website, navigate to the weather information, and click on your province.
On these sites, you can review current weather conditions, such as temperature and winds, and you can also view the weather radar to check for any precipitation in your region. The latest satellite image is also available, which will show the location of clouds. For your area, you’ll see a weather forecast out to seven days. Given as 12-hour increments (day and night), the forecast includes sky condition, expected high temperature (day), expected low temperature (night), a probability of precipitation given as a percentage, and sometimes predicted rainfall amounts. Any severe weather forecast is highlighted. You’ll also find a section on past weather.
How accurate are these weather forecasts? Generally speaking, the “short-term forecast,” out to 36 hours, is highly accurate, more than 90 percent correct. Beyond seven days, the temperature forecasts are still fairly good. Precipitation occurrence is also forecast well. However, determining the timing of precipitation onset and ending can certainly be off by a few hours, and forecasting precise precipitation amounts is also difficult. Accurately forecasting even just the occurrence of precipitation becomes difficult by the fourth or fifth day.
Beyond seven-day forecasts, the NWS also releases a 6-to-10-day and an 8-to-14-day outlook. These are general forecasts for the U.S. depicting predicted temperature and precipitation as being above, below, or near normal amounts. Overall, these outlooks are reasonably accurate, temperature more so than precipitation. On this same site, you can also see monthly and seasonal outlooks all the way out to a year in advance. Canada’s seasonal forecasts are fairly general in terms of temperature and precipitation being above, below, or near normal amounts. Generally speaking, long-term forecasts probably push the science beyond what it’s capable of at this time.
- National Weather Service
- Government of Canada Weather Information
- NWS Outlooks Index
- Government of Canada Seasonal Forecasts
To get specific frost information before and after you plant, and to protect vulnerable plants, you can rely on your local NWS office to issue special notices. A freeze warning will be issued when air temperatures are expected to drop below freezing over a large area and for an extended period of time. A frost advisory will be issued when temperatures are generally in the mid-30s, but locally, surface temperatures below freezing are expected with frost occurrence.
How early in spring these forecasts are produced depends on local climatology: They’re released earlier in the South, and later in the North. This is true regardless of the actual recent weather. Warm, early spring temperatures that may promote plant development can lead to frost events before warnings are issued. In fall, the NWS also issues frost forecasts. The first occurrence of freezing temperatures officially ends the growing season, and no further warnings are issued. In Canada, where cold temperatures are even more of a threat, a frost advisory is issued locally anytime during the growing season when widespread frost or near-freezing temperatures are expected overnight.
Severe Weather Forecasts
A hazardous weather section — or, in Canada, a weather alert — highlights the potential for any dangerous weather conditions that may develop, allowing you to look at severe or dangerous weather elements prior to the official online forecast. Your local weather office will provide you with specific information if your area is threatened by a hurricane, severe thunderstorm, or other dangerous weather events. If you want to keep track of what’s going on in the U.S. outside your area, you can visit specific sites.
Whenever thunderstorms are mentioned in a local forecast, it implies a number of threats, including dangerous lightning, locally heavy rains, and possible strong winds. A forecast that includes the possibility of “severe” thunderstorms implies the threat of strong winds, large hail, or tornadoes. Heavy rain often accompanies thunderstorms, and, if needed, a flash flood advisory may be issued. Tornadoes are potentially so damaging that separate detailed information will be given in addition to the severe thunderstorm forecast.
Tropical cyclones pose a multitude of risks even to areas far removed from the coast. For tropical systems, go to the National Hurricane Center website or the Canadian Hurricane Centre website.
If you live in an area where wildfires occur (and this risk has been expanding for many areas in recent years), the NWS also deals with fire weather conditions. Red flag warnings imply a combination of dry and windy conditions, which could produce rapid advance of any wildfires that start. You can get the latest information on the NWS website, including current conditions and a forecast. In Canada, wind and heat warnings will be included and highlighted in the standard forecast.
In summer, some hazards are more insidious. Ultraviolet (UV) rays from the sun can cause painful burns and can even lead to cancer. To warn you of the risk, the NWS and Environment Canada both include a UV index value. Excess heat can also bring on a variety of health issues, the worst of which can be life-threatening. To help judge the heat risk, the NWS provides a heat index with forecasts in summer. The heat index combines the effects of the actual temperature and the humidity, which controls how fast your body can evaporate sweat and cool itself. Environment Canada uses the humidex scale.
In winter, warnings or advisories can be sent for winter storms, blizzards, snow, freezing rain or sleet, and extremely cold temperatures. When cold temperatures are accompanied by strong winds, wind chill warnings will be issued. The wind chill combines the direct effect of low temperatures and the cooling effect of wind.
Obtaining the weather information you need doesn’t have to be complicated or difficult. By collecting a list of trusted resources to check regularly, you can feel more informed about your local weather occurrences, and also feel more prepared for whatever elements occur in your area.
Tune in to Weather Radio
Long before home computers and the internet were developed, the National Weather Service would disseminate information via NOAA Weather Radio (www.Weather.gov/NWR). This is a nationwide network of radio stations that still continually broadcast weather information from the nearest NWS office. More than 1,000 transmitters cover all 50 states, adjacent coastal waters, Puerto Rico, the U.S. Virgin Islands, and U.S. Pacific Territories. You’ll need a radio receiver capable of receiving one of seven service bands in the 162-megahertz range. There are also special weather radios that have this capability, and also broadcast a warning signal if severe weather is imminent. Canadians with the proper receiver can tune in to Weatheradio Canada. For more information, you can Google “Government of Canada Weatheradio,” and click on the page’s first result.
Extreme Weather Resources
- National Weather Service Fire Weather
- Environment Canada Criteria For Public Weather Alerts
- Government of Canada Public Weather Alerts For Canada
- NOAA/NWS Storm Prediction Center
- National Hurricane Center and Central Pacific Hurricane Center
- Environment and Climate Change Canada Hurricane Forecasts and Facts
- NWS UV Safety
- NWS Heat Index
- Environment and Climate Change Canada Weather and Meteorology
- NWS Winter Weather Resources
- NWS Wind Chill Chart
For more than 30 years, Ed Brotak taught thousands of college students about weather, and he’s helped many of them pursue careers in meteorology. He lives in Asheville, North Carolina, with his wife.