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.