It’s been an unusually cold winter so far, and that is expected to continue for the next couple of weeks. The national weather service office has released data that places the mean average temperature for January at twenty-three-point-one degrees, as recorded at its Bloomington station. This average was over six degrees below the long-term average for the month, and Bloomington had less than average precipitation. However, as the local station does not differentiate between rain and snow forms of precipitation, snow probably dominated as temperatures were lower than average, and as it stayed on the ground for longer than usual. Dave Tusek, at the Indianapolis office of the weather service, explains that this cold weather has been here since the Fall.
“We started that pattern really back in November time frame. It kind of reached a crescendo during the month of January in which the polar vortex, or the coldest air in the northern hemisphere, ended up over on our side of the hemisphere. So we were below normal for, I believe, the month of November, below normal for December, and here again below normal for the month of January, so more or less a continuation, just an amplification and deepening of that trough as we went on through the winter months,” said Tusek.
Tusek mentioned the polar vortex, which has been responsible for this year’s cold pattern. This has brought the coldest temperatures in the northern hemisphere down to the region, between the Great Lakes and the Ohio River. While we did experience some brief breaks of unseasonably warm weather, the extremely low positioning of the arctic vortex over the U.S. midwest has persisted for the last several months.
“That’s not uncommon to see kind of an up and down ride, if you will, in regard to your temperatures from day to day,” said Tusek. “And that was simply tied to a likely weather system that moved across the southern Great Lakes and drew warm air up from the south. But that was also, if you continue looking at the daily records, we eventually dropped back to highs around freezing and lows in the teens or a little below normal. So it’s not unusual to see this pattern persist, but to that extent in time, that’s not all that common.”
He explains that the arctic vortex has been pulled far south by the jet stream. This upper atmospheric, fast moving stream of air follows a wave pattern across the northern hemisphere. Weather systems tend to be trapped on either side of the stream. Unfortunately for us, the wave sitting over the continental U.S. had dipped unusually far to the south, and it has not moved east as it usually does. This trough has drawn cold air from the arctic to the south. By contrast, the unusually high ridge of this wave is sitting to the far north over the western part of North America, bringing that region unseasonably warm temperatures with much less than normal precipitation. The historic drought happening in California is a manifestation of this pattern. Unusually, this wave is moving a little to the west, which will bring some intermittent periods of warmer, wetter weather. Tusek provides us with weather predictions for February:
“For the month of February, expect to see our conditions more or less near normal. As we look at this larger-scale pattern that I referenced before, it’s undergoing a de-amplification. So that means instead of having really sharp ridges and troughs with extremes underneath the ridge in the way of warm and dry and in the trough cold and wet, it’s becoming what we refer to as a more zonal pattern, and with that, that means that our air will be arriving more often from the Pacific Ocean with each weather system that comes in, as opposed to coming in with arctic air. Now, that’s not to say the arctic air won’t follow on its heels because that is going to continue to happen. We certainly have some cold ahead of us here in the coming week or so, but that is expected to transition.”
So, Hoosiers will continue to experience colder and wetter weather during February, broken up by more frequent and longer episodes of warm and dry conditions, as daylight increases and the sun moves north.