Arctic, North Atlantic systems drive big weather swings

Winter
Caption
Winter

While winter is more than a month away, it appears the season has shown up a little bit early. Over the past week, we’ve experienced winter-like weather with temperatures more typical to December or January, and an accumulating snow that forced many school districts to use their first calamity days of the year.

As we discussed in last week’s article, snow this time of year is not out of the questions, but it’s a bit unusual to have the amount of snow we experienced so early.

At this point in November, the typical daytime high for southwest Ohio should be around 50 degrees. We’ll get a taste of the 50s and perhaps even the 60s over the next couple of days, but it will be short-lived. This back and forth from cold to warm and back to cold again is not surprising based on the overall weather pattern.

About a month ago, I told you this upcoming winter would be filled with big swings in temperatures. This is due to the lack of an El Nino or La Nina to be the main driver of our winter weather pattern. That means other global patterns, such as the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) would have a bigger impact on our temperatures and precipitation.

How does the NAO affect winter?

The North Atlantic Oscillation is the difference in pressure between two points located in the eastern Atlantic. When the oscillation is in its positive phase, a Subtropical High located near the Azores and a Subpolar Low located near Greenland is strong. That tends to allow for a warmer pattern in our region. In a negative phase, the pressure gradient between these two points is weaker, and colder air can surge south from Canada.

How does the AO affect winter?

The Arctic Oscillation is a global weather pattern that is characterized by winds that circulate counterclockwise around the Arctic. When the AO is in its positive phase, the winds are stronger and act to confine the colder air in the polar regions. When the AO becomes negative, the winds are weaker and the colder arctic air can slip southward and increase storminess in our region.

Now that you have a little better of an understanding of these two global patterns, I can now tell you both have been in a negative phase recently. That explains why we’ve seen colder than normal temperatures and even a bit of snow.

Our computer models do a pretty good job of predicting how the phase of these oscillations will shift for the next two weeks. The long-range pattern shows a gradual shift back to neutral by early December. That would indicate a weather pattern that could have some shifts back and forth, but perhaps not as extreme as we approach the end of November.

The National Weather Service Climate Prediction Center has hinted at that same thought process. The temperatures and precipitation outlook for the end of the month shows a more “near-normal” chance to see typical late-November weather compared to the below normal and wet pattern we’ve seen lately.

I guess we will have to wait and see how these forecasts stack up. You can stay updated on our daily forecast on whio.com and on News Center 7 every day.