Plenty goes into weather forecasts

Weather forecasts consist of quite a bit of information.

People want to know whether it will be wet or dry, sunny or cloudy, windy or calm, dry or muggy, and of course whether it will be warm or cold. Different aspects of the forecast get more or less attention from a meteorologist, depending on the weather situation.

When a heavy snowstorm is on the way, most folks are more concerned about snow amounts than temperatures. Since snow forecasting can be a difficult and complex process, it is likely that the temperature forecast will be given low priority. When snow is coming down hard, you probably won’t notice whether the high temperature is 23 degrees or 30 degrees.

In contrast, late summer months are often warm and dry, with little chance for precipitation of any kind, and little change in high temperatures from day to day. During these periods, especially if the summer has been particularly dry, a forecaster will pay extra attention to weather factors that may produce dry lightning or strong winds – keeping in mind the threat for dangerous fire weather.

It is during the transitional months such as spring and fall where more time has to be spent on temperature forecasting. Wild swings in temperatures can occur during these times of the year, and the public is usually counting on the meteorologists to help them figure out whether their vegetable garden is going to freeze over, whether to force the kids to bring their jackets to school, or if unseasonably warm weather will necessitate a trip to the golf course.

Just where do meteorologists come up with the temperature forecasts anyway? There are many methods for predicting temperatures, and each forecaster has his or her own favorites. One of the simplest methods is called “persistence” forecasting. The first thing I do when using this method is look at where temperatures ended up today. Starting with those numbers and using satellite images and computer models, I assess the big weather picture for the next day.

Assuming there are no major storms moving through, I can tweak today’s numbers for tomorrow by determining whether there will be more or less sun and/or wind. An increase in clouds would likely lead to lower afternoon temperatures, but warmer overnight readings – excluding other factors. In many cases, a day with more wind can result in warmer temps as turbulent air motions help to “mix out” the atmosphere.

Beyond persistence forecasting, computer models play a large part in providing guidance for temperature forecasting. Some computer models produce an array of forecast statistics (called MOS for model output statistics) which include temperatures among variables such as dew points, wind, and cloud cover. Each computer model has its own strengths and weaknesses for a particular time of year or geographic area.

This data, along with a few calculations, can help a meteorologist come up with more temperature possibilities. With many computer models, many methods, and different forecasters – you can see why the temperature forecast from one source may be slightly or even drastically different from another source.

One thing is for sure, however, temperatures are only going to be getting colder in the following months. Average highs now are only in the mid-50s, with average lows near the freezing mark.