If I had a weather vane for every time that I heard someone say “Forecasters can’t get tomorrow’s forecast right, and they’re trying to forecast the weather for next three months?” about a long-range forecast, then I’d be the most vane person in the world. (For a preview of the upcoming winter, please see Snowy, Cold Winter on the Way?)
Different Types of Forecasts
If we were using the same forecasting tools to generate long-range forecasts as short-range forecasts, then I’d agree with the statement, but the difference between short range and long range forecasting is dramatic. Short-range forecasts are based on current observations, satellite images, and computer forecast models (that generate forecast information for anywhere from the next 12 hours to the next two-plus weeks). Long-range forecasts are based on various teleconnections (details below), ocean water temperature changes, and different types of computer models.
In other words, it’s possible that short-range forecasts can be wrong while long-range forecasts can be correct.
While we may not understand ocean water temperature changes (including our friends El Nino and La Nina) and long-range computer models, we have a general idea of what those are. Teleconnections, however, is most likely a foreign term.
In its most basic sense, a teleconnection is making a forecast for one region based on a current observation elsewhere in world, a sort of “If this happens here, then this will happen there” in a couple of weeks or a couple of months. This is based on knowledge of world-wide weather patterns and how they interact, and teleconnections can surprisingly useful for forecasting the overall pattern for the coming weeks or months–giving guidance on what areas will be stormy or what areas will be hotter than normal, etc. This information may or may not result in a clear, coherent forecast (Summer 2009 Forecast?).
The details of these general ideas will then have to be forecast on an individual basis later, but there is some science to long-range forecasting. For more information on a few of the commonly used teleconnections, visite the Climate Prediction Center page on teleconnections.