Spring has sprung, and everything around my house is blooming, which means lots of pollen! The warm weather has come on with abandon after a winter that had some fairly cold conditions, although nothing compared to what our friends in the central US and Texas experienced. In this article I will discuss why our winter did not turn out as expected, and what to expect for the growing season which is just starting.
Last winter was a La Nina winter, and statistically, when we have a winter like that, the subtropical jet stream gets pushed north into the Ohio River Valley, leaving a lot of the Southeast warmer, sunnier, and drier than usual. That is a good forecast for most La Nina winters, but this year we had a wild card that gave us a rare winter that did not match our statistical expectations (hey, even a great quarterback throws an interception from time to time!). In early January, the atmosphere about 10 miles above the North Pole rapidly increased its temperature by almost 100 degrees in just a few days, an event that we call a Sudden Stratospheric Warming (SSW). They are not predictable, so we can only react to them once they begin, and of course by then a lot of plans are already put in motion and it can be hard to pivot.
The SSW shoved the cold polar vortex that is usually around the North Pole off center, pushing the storm track back down south towards us and bringing the unexpected cooler, cloudier and wetter conditions that we experienced this winter, especially in southern Georgia. This event caused issues with the weather in the US for most of February, including the blast of cold air that caused so many problems in Texas, but it has gone away so we don’t expect the effects to continue into this growing season. In spite of the cold outbreak, here in Georgia we ended the winter just a little above the long-term average in temperature and slightly below the long-term average in precipitation due to conditions in December and January. We expect the summer to continue the long-term trend of warmer than normal temperatures, but there is no clear signal for precipitation after April (which so far looks like it could be drier than normal), so we will just have to watch and wait to see what happens.
We are at the end of a moderate La Nina, which is expected to go back to neutral conditions in the next few months. We often see drought in Georgia in the summer after a La Nina because the dry winter conditions don’t recharge the soil moisture completely. This can lead to rapidly developing drought in late spring or summer if we get a dry spell. Because of all the moisture around this year, I think drought is less likely to happen this year than it usually would after a La Nina winter. Of course, that does not mean it could not happen, just that it is less likely than usual. The big question this year will be the tropics. In neutral years, the Atlantic tropical season tends to produce more tropical systems than usual, so we could see another active season. But the paths of the storms are not likely to be the same as last year, so they could all hit Texas or else go up the East Coast, although some could hit us in the heart of the Southeast again too. Most likely there will be some storms, but not likely as many coming across our region as last year.
The long-range climate forecast shows that by fall we may go back into another La Nina. It is not rare to get a double-dip event, and usually the impacts the second year are more moderate than the first year. It’s too early to use that information for any planning, but it’s something to keep in mind as we go through this year’s growing season and look towards the next winter.