Now that we know how meteorologists think about seasons (see my prior post), let’s look at how they predict them. Every month the Climate Prediction Center, part of the National Oceanic and Atmospheric Administration, issues updated three-month outlooks for temperature and precipitation. The current one runs from February through April. You can find the forecast on their website, and you’ll see the results of a complex process presented in a map form.
The temperature map (see below) for the next three months shows that North Carolina has equal chances of having above average, about average (normal), or below average temperature and precipitation. Our chances for each are 33.3%. You might think that it means this forecast is useless, but that’s not quite the case. What it does mean is that there is nothing in all of the components that the forecasters take into consideration that points to an unusual season for us.
If, for example, we had a better chance for above average temperatures (more than a 33.3% chance), we would see the letter A and a rust colored, highlighted area surrounding it over the region expected to be warmer than normal during the three month period the way it is on the map below. The probabilities for precipitation work the same way.
The components that go into making these long range predictions are limited to a handful of computer models and global scale weather features such as El Nino/La Nina and sea surface temperatures. The results are compared to the 30 year “normal” values and trends over the past 10 years for temperatures and 15 years for precipitation. Once the forecaster considers everything, he or she decides on the probabilities for the temperature and precipitation to be above normal, average, or below normal.
These outlooks are more of a guide than a concrete forecast. They can be useful for people whose livelihoods depend on the weather like farmers, natural resource managers, nursery owners, outdoor event planners, etc. Because the predictions are for a very broad area, they are not necessarily accurate for a specific point on the map. There are many conditions unique to locations that can affect the weather that could make the outlook much less useful. However, if you are looking for a general idea of what the spring will hold for a region, the Climate Prediction Center’s Three-Month Outlook is a good place to start.