(KERO) — A detailed weather forecast can only go out for about a week, and even then, details get fuzzy towards day 7. In forecasting the further out you go, the less you know. There are ways to forecast for months or even years ahead of time, but we’re limited in what we can predict that far out.
There are several things we can look at to make a long-range forecast. Probably the most basic is seasonal climate variability. We know that our summers are hot and our winters are cool, so while we might not be able to make a detailed forecast for the holidays at this point, we can be almost certain that the Fourth of July is going to be warmer than Christmas.
Another thing we can look at is astronomical patterns. We can identify patterns in things like the tilt of the Earth’s axis and the shape of its orbit. These things change over thousands of years though, so they’re more suited to predicting changes in climate.
We can also look at things like global weather patterns and ocean circulations that change over the course of months to years. This is the most common and important source of data for making long-range forecasts. Ocean temperature patterns like El Nino or La Nina are easily identifiable and have a big effect on our weather.
El Nino and La Nina make a great example of how long-range forecasting works. This past winter we were in La Nina, which refers to cooler than normal water temperatures in the Eastern Pacific. This cool water interacts with the atmosphere and sends the jet stream well north of California, meaning we don’t get as many storms. Forecasters at the Climate Prediction Center recognized this pattern and issued an outlook that the said for the three-month period from December to February Bakersfield was more likely to be drier than average. To their credit they were right. After a very rainy December, we got almost no rain for January and February and ended up below average for the three-month period. So while we can’t provide a day-to-day forecast for months out, we can identify important trends in the weather.