"Where are you, winter? Why can't I find you?"
So far, the winter of 2017 has been the fifth warmest on record in our area. This includes high temperatures at or above 60° on 21 of the last 72 days. In the Tri-Cities, we've seen half the average amount of snowfall. (Some higher elevations have seen more than the 4" seen in the Tri-Cities this winter.)
The question we often get is "Why has this winter been so warm?" We can answer that by referencing something called the 'North Atlantic Oscillation' (NAO). This refers to the pressure difference between the Icelandic Low and the Azores High (shown below).
When that pressure difference between the two systems is less, the NAO is in a negative phase. That lesser pressure difference relaxes the winds and allows cold air to sink down into Canada and into the eastern US.
A positive-phased NAO is the opposite, where the pressure difference between the high and low above is greater. That means the winds are stronger, and they lock up the colder air in the northern latitudes.
When looking at the NAO phases since December, you see that roller coaster between positive and negative. However, there's been more of (and a longer-lasting) positive phase. This is why we've seen those warm spells, a brief cold snap, and then another prolonged warm spell.
We expect a warm-up this weekend, followed by slightly cooler weather next week. Part of that is due to a weaker, positive-phased NAO. The rest of February is forecast to be above average, temperature-wise.
Might we still see a cold snap/chance of snow here or there? Absolutely, but most of the month looks like it will feature above average temperatures.