December 3rd through the 8th is Winter Weather Awareness Week in Arkansas. The purpose of this week is to remind people what winter weather can bring, and how to deal with hazardous winter conditions. Now is the time to prepare for the upcoming winter season.
Monday’s topic is the outlook for the upcoming winter. Overall, winter around here has not exactly been cold in the last thirty years. Since the winter of 1987-88, winter temperatures were below average by at least a degree only six times. Readings were above average by a degree or more fourteen times. It was a Top 5 mild winter last year. Temperatures were over five degrees warmer than usual.
The only significant snowstorm occurred in early March /outside of climatological winter/. On the 11th, four to five inches of powder fell in parts of northeast Arkansas. The most snow accumulated at places such as Cave City /Sharp County/, Calico Rock /Izard County/, Mountain Home /Baxter County/ and Swifton /Jackson County/.
We are currently transitioning to a weak La Nina. This means water temperatures near the equator in the Pacific Ocean have cooled, and this will have some effect on the weather this winter. The textbook scenario features warmer/drier than usual conditions in portions of the southern United States, with colder/wetter than average weather in parts of the north. The Climate Prediction Center, which puts out the official winter forecast each year, is going with the textbook solution. So, in Arkansas, the forecast calls for a normal to dry season and temperatures in the plus category.
This textbook scenario becomes more likely as La Nina gets stronger. However, La Nina should remain fairly weak, so there is some doubt in the warm/dry forecast panning out locally. More specifically, a non-dominant La Nina opens the door to other variables that could have some say as to what unfolds the next few months. This happened in the winter of 2010/2011. La Nina was supposedly in charge, but the Arctic Oscillation /AO/ took over. The AO is all about pressure differences between the North Pole and the mid-latitudes /where we live/. The AO is negative when the pressure to the north increases, with lower than normal pressure closer to home. In winter, this causes cold air to spill into the United States more frequently. This led to cold temperatures and snow piling up in Arkansas. Whatever happens, we all know that the weather can be all over the place in this part of the world. It can feel like spring in January, and it can get really cold. That is an ordinary winter locally. Do not expect anything different this time around.
If more precipitation falls than expected, we will have to watch for three things. If we are in the midst of a warm period, be wary of severe thunderstorms, which are not unusual. If there is a lot of rain, then flooding can become a problem. Finally, given a well timed shot of subfreezing air, that is a recipe for a big snow or ice storm.
There is one other thing to remember. Severe storms seem to be the most numerous when La Nina is present. In 1999, a whopping 107 tornadoes were counted. An impressive 81 tornadoes were generated in 2008, with 75 tornadoes in 2011. These were the first, second, and fourth most active years on record /as far as numbers of tornadoes/, and were also La Nina years.
If it remains dry in Arkansas this winter, that could be devastating heading into the spring of next year. There is an ongoing drought in more than half of the state, and the drought is expected to persist or worsen. If the forecast verifies, vegetation will not have much ground water to work with and the wildfire danger will increase.