Weather For Dummies. John D. Cox

Flavors of Forecasts

      Depending on where you live and what you do, the weather forecast you wake up to in the morning probably lets you know what basic conditions to expect of the day. Sometimes it delivers important information about your safety or comfort, and every day millions of people rely on it without giving it much thought.

      In the newspaper, on the radio, on television, and on the Internet or smartphone app, the basic weather forecast is usually routine, simple, and to the point. It directs itself to the questions that most people want answers to as they start their day. How warm or how cold is it going to be? Will it rain or snow? Is a storm on the way? Will the wind blow? Before this day is over, will I need an umbrella or a light jacket or a heavy coat?

      The National Weather Service and other agencies and private companies also prepare daily a number of specialized forecasts. They provide important weather information about the day, or the next few days, to a variety of special audiences around the country. Private forecasting companies supply specially tailored forecasts for hundreds of special users such as utility companies, construction companies, hotels, ski resorts, and motion picture studios.

      Here are some of the more common special forecasts.

      Agricultural forecasts

      A farmer wants to know everything you want to know about tomorrow’s weather, but the farmer also has to keep an eye out for a few other special things. Much depends on the average seasonal conditions, or climate, of the region, and, of course, on the kinds of crops in the field.

      All farmers are on the lookout for frost, because of the damage it causes to crops. In areas with large citrus orchards and vineyards, where freezing temperatures are rare, growers use large outdoor fans and heating devices to keep their trees and vines from freezing. These fans cause the coldest air, which is nearest the ground, to circulate with warmer air above it.

      

Another key indicator for many farmers is the combination of sunshine, heat, humidity, and wind conditions that let them know how much evaporation of moisture from their fields to expect. This evapotranspiration rate is closely watched by farmers who irrigate their fields.

      The U.S. Department of Agriculture and many private companies provide farmers with weather forecasts tailored especially to their local needs around the country.

      Aviation forecasts

      Forecasters provide specific nowcast guidance for Federal Aviation Administration air traffic controllers to use in advising pilots for flight planning and flight operations. (If you’re unfamiliar with nowcasts, see the section “Take what is happening now …” earlier in this chapter.)

      Also, many of the automatic and manually operated weather stations are located near the touchdown zones of airport runways. The readings from their instruments are automatically broadcast to pilots. (See Chapter 16 for more on these and other tools of the trade.)

      Using communication satellites, the National Weather Service now beams a new radio broadcast system called the World Area Forecast System to pilots of commercial airliners around the globe. This tool gives them the best information available about such things as upper-level winds and temperatures, which is crucial to aviators (and their passengers!).

      Marine forecasts

      No group is more dependent on weather conditions for their safety and well-being than mariners — professional sailors, recreational boaters, and commercial and sports fishermen.

      Monitoring coastal and offshore conditions, the National Weather Service forecast offices in coastal areas around the United States and in the Great Lakes region issue a variety of specialized forecasts and warnings for professional mariners and recreational boaters.

      Marine forecasts let boaters know what kinds of winds to expect, whether the sea will be calm, and, if not, the height and direction of rolling swells. Small craft warnings for strong winds or fog conditions and other hazard advisories are issued in areas along the seacoasts and the shores of large lakes.

      River forecasts

      National Weather Service forecasters work closely with hydrologists, who are water experts. A weather forecaster estimates how much rainfall is likely from a particular storm, and the hydrologist figures out how much that precipitation will cause certain rivers and streams to rise.

Forecasters also keep operators of federal and state dams informed as major storm systems approach large river systems. Sometimes a dam is good for saving water when there is too little, and sometimes a dam is good for saving a downstream city where there is too much. If they know a big storm is on the way, dam operators sometimes release more water from their spillways to make more room in their reservoirs to hold floodwaters.

      Regional River Forecast Centers are spread around 13 locations in the United States. These centers are where National Weather Service forecasters prepare river and flood forecasts and warnings for approximately 3,000 communities around the country.

      Fire forecasts

      A corps of specially-trained weather specialists keep their eyes on the skies above national forests and other regions of their nation where wildfires are a major threat. These specialists are experts on the effect that weather has on the risk of a fire starting. They keep an eye on the dryness of the soil and vegetation, on temperatures, and on winds and humidity.

      They also have special knowledge about local conditions, such as the mountains and canyons, and how they affect winds, which are crucial to how fast and how far a fire burns. During some large fires in the western United States, a fire weather specialist is sometimes dispatched to the scene to keep firefighters informed of changing conditions. Chapter 13 has more detail about fire weather and the impact of our changing climate on wildfires.

Keywords to the Wise

      You hear these words all the time on your local forecast: highs and lows and temperatures and pressures and wind chills and humidities and chances of showers and wind speeds and directions. But just how slight or how likely is a chance of showers? What exactly are you being told?

      Precipitation

      When forecasters see rain or snow on the way, they have some decisions to make about how to describe the precipitation they expect. They need to think about how likely it is, how long it will last, and how intense it will be. What is the probability, or chance, that it will rain? Will it rain “’til the cows come home” or only briefly? When it rains, will it “come down like cats and dogs” or merely sprinkle?

Sometimes when people hear the word rain in a forecast, that’s the only word that catches their attention. They make the mistake of assuming that it is absolutely certain that rain will fall on their head sometime during the day. And if it doesn’t, well, “Wrong again, the weatherperson said it would rain.” More likely, the forecaster used a few key words that didn’t make the same impression as “rain in the forecast.”

      The National Weather Service has issued guidelines for expressing the likelihood of precipitation in hopes that certain word usages would become standard among forecasters. It hasn’t worked out very well.

      For one thing, the terms the agency uses are easy to misunderstand. It leans heavily on using something