Weather Whys; Long Range Outlook

This is weather-wise. Periodically, the National Weather Service issues something called a long-range outlook, which is a forecast covering the entire United States for the coming 30 or 90 days. It's a very general forecast, which tells only if an area is expected to be warmer or cooler than normal, and if precipitation will be greater or less than normal. To understand the significance of those forecasts, it's necessary to know what normal really means. In the context of the forecasts, normal is the climatic average over some period of years or even decades. The forecasts are made at the National Meteorological Center near Washington, D.C., and they're based on current patterns of pressure and temperature in the atmosphere. One major atmospheric feature that's closely monitored for those forecasts is the meandering of jet streams. Since the path of jet streams generally changes very slowly, meteorologists can sometimes use them to predict the general tendency of the weather for an extended period of time.

Now the idea of an extended forecast can be misleading since the forecasts only give tendencies for a given period of time, and even if the overall tendency for a month is to be hot and dry, that doesn't mean there won't be cool days or even a rainy spell. A forecast of hot really says that if you average all the temperatures for the month, the average is likely to come out higher than normal. And a forecast of dry really says the total precipitation should be below normal. Like any forecast, the long-range outlooks are far from perfect. Often, the jet streams move faster or slower than expected, and that makes the forecasters job more difficult. But at least the forecasts provide some idea of what kind of weather lies ahead. This is weather wise. Our writer is Christine Harper, our executive producer is Karen Hope, and I'm Drew Barlow.