Weather

Pittsburgh to see above-average temperatures through mid-January

PITTSBURGH — Looking at long-range forecast data, temperatures should be above average through the middle of January in our area. The average temperature is calculated using the low and high temperature of the day. Average lows are in the low 20s and average highs are in the mid-30s this time of year in Pittsburgh. The Climate Prediction Center also favors above-average temperatures for our area through mid-January.

However, looking at climate patterns and the forecast for those, you wouldn’t guess we’d see above-average temperatures. I often analyze the Arctic Oscillation and the North Atlantic Oscillation in the winter season to see how our weather will trend. The AO is a circulation pattern over the mid and high latitudes of the Northern Hemisphere. When the AO is negative, our part of the country is more likely to see periods of frigid weather.

The NAO is a fluctuation in the differences in sea level pressure between the Icelandic Low and Azores High. When the NAO is negative, it can also lead to outbreaks of cold across our region.

The model forecasts for both the AO and NAO are negative, which suggests below-average temperatures but that doesn’t match with our forecast. There’s a reason!

Looking at the jet streams, the Pacific jet, a jet stream that flows west to east across the Pacific, has been helping lead to storm tracks that favor above-average temperatures for Pittsburgh. In fact, the jet is favoring what’s typical during a La Niña pattern. During La Niña, the Pacific jet builds north, closer to Alaska in the winter, which leads to wetter-than-average conditions across the Pacific Northwest and Midwest and warmer-than-average conditions across western PA.

If the Pacific jet stays where it’s at, we should continue to see above-average temperatures despite what the climate patterns suggest.