Weather pattern overview through mid-March

Two strong features are likely to control the weather pattern over the next few weeks. First, we have a fairly strong negative phase of the Eastern Pacific Oscillation (EPO) in place (ridging over the Gulf of Alaska), which keeps sending strong surface high-pressure areas and cold air southward through the Plains. At the same time, we have been under a positive North Atlantic Oscillation (NAO) with the polar vortex stretching from Hudson Bay to near Greenland, which also helps reinforce the surges of cold going south into the Prairies and the northern United States.

By the end of this month and into the first days of March, the latest signals suggest that the EPO trends more positive, while the NAO remains mostly positive. The ridge that was over the Gulf of Alaska weakens but shifts into Western Canada, which, in turn, concentrates more of these colder surges farther east into eastern Canada and the eastern U.S. while western Canada and the western Lower 48 states turn warmer.

However, by the second week of March, there are indications that the EPO goes even more strongly into the negative camp with a ridge building over Alaska, which, in turn, dumps even more cold through the Prairies and into eastern Canada.

The ridge over Alaska then appears to break down by the third week of March, which may lead to less extremes and an introduction of Pacific air into North America.

I will note that the MJO is still projected to be in phase 4 late this month and then get to phase 5 in early March, which usually means (but not always) a warmer-than-normal pattern for the eastern half of North America. So this contradicts what the forecast pattern shows below. It will be interesting to see if the long-range ensemble model forecasts trend milder over the next week or so in response to the MJO.