On Tuesday night, the local chapter of the National Weather Association/American Meteorological Society gathered for a meeting. NWS Meteorologist John Lewis gave a fantastic presentation about the current El Nino and how it has influenced our weather. We are expecting a transition into a La Nina as we go further into this spring and summer and that will of course have impacts on our weather that will be discussed later. He brought up a very interesting point, we have only had 29 nights at or below 32 degrees in Little Rock so far this meteorological winter (December 1 through February 17th). That's tied with 2011-2012 for the fewest since 2000. So where do we go from here?
I really like to look at the Arctic Oscillation Index (AO). It's usually a great tool to see coming cold within the next 2 weeks. It's not a long term tool like El Nino and La Nina outlooks. There has been a near perfect correlation this winter between the positive phase bringing mild temperatures and the negative phase bringing colder temperatures. The positive AO simply tells us the jet has retreated to the north not allowing the cold air to dive south, but the negative phase results in the transport of colder air to the south as blocking occurs and a more amplified pattern results. As you would expect, we're in that positive phase now. We were in most of December, then we went negative in January. It's during the negative phase that we must watch for moisture as arctic air gets introduced into our region of the country. Forecasting the moisture aspect is much more difficult until we can get within just a few short days of any event, but it's safe to say we need that AO in the negative for snow. HOWEVER, I do remember a very positive AO in the past and snow around here. It happened one December a few years ago with a cut-off low bringing light snow amounts of 1-2''. Also, if my memory is correct, we had a positive AO many times last winter 2014-2015, but several rounds of arctic air. That may have been due to another index known as the EPO (Eastern Pacific Oscillation). Using the AO this winter has proven to be a great tool. So what about the remainder portion of this month into March? Check out the maps and charts below.
One more important note I'm now calling the "John Lewis rule" since he told me this several years ago and it makes perfect sense. Watch when the AO makes a steep rise from negative to positive. That's when we are more likely to see heavy rain/severe weather events in the winter and spring.
|We are tied with 2011-2012 for the fewest nights 32 degrees or colder this meteorological winter.|