Friday, March 29 2013
The tornado season and naturally, the storm chasing season, has been very slow to start. In fact for all intents and purposes we have yet to see a true beginning to the season. Usually by late March storm chasers have already had their first half decent chase day of the season, or are anxiously looking forward to a severe weather setup in the near future. Not this year.
Instead, winter decided to show up in March and hasn’t given up yet! Since the middle of March, high latitude blocking associated with the negative phase of the Arctic Oscillation has been at historically low levels. Looking back over the past 40 years, only a few other years had Arctic Oscillation values during the month of March at such low levels!
Below is a hemispheric plot of 500mb height anomalies from March 15 to March 27 of this year. As you can see, strong height anomalies are located from over the north pole to Greenland, associated with the Arctic Oscillation as well as the North Atlantic Oscillation. Also notice the below normal height anomalies over the eastern half of the U.S. This has been instrumental in keeping temperatures cold and has sure made it difficult for severe weather to occur across the plains states.
On top of the slow start to the tornado season, we have what’s becoming a widespread and quite severe drought across nearly the entire Great Plains region. Below you can see the latest U.S. drought monitor as of March 26, 2013. A severe drought covers almost the entire plains regions, but some areas of the central and southern plains are in extreme drought conditions. Some are even at exceptional levels – the worst level of drought we have on the scale. And the outlook isn’t great. In fact it’s not good at all, it’s actually bad news for the long term future of the tornado season this year.
The expectations are for a continued drought over the southern and central plains. The only areas that show signs of possible improvements are across the northern plains. The one good thing I can say is it’s late March and there’s still time for some of these trends to turn around. April can a lot of times bring much needed improvements before the peak of the season really kicks into high gear. So let’s hope that happens..but I’m not holding my breath.
Even with these totally negative trends, there will be tornadoes. There always are, even in the worst seasons. It’s simply a matter of going storm chasing when those severe weather setups unfold, because the atmosphere is doing it’s best (or worst!) to keep severe weather and tornadoes from occurring!
Though from what I’m seeing right now I’d bet on the bulk of the tornadoes this season occurring before the back half of May. I also think when we do come out of this never ending winter pattern that the chase season will start fast, like someone suddenly turned on a light and it’s go time. What I’m saying is the transition from this winter like pattern to spring will be dramatic, and that could involve severe weather if the right conditions come together. But I also don’t think it will last all that long before the drought and other factors like ENSO and other Pacific signals fight back as mother nature wakes up again…or goes back to sleep, depending on your point of view.
Until next time…hopefully sooner than later…