Weekend Nor’easter increasingly likely, but impacts still uncertain

Forecast models have come into better agreement, over the past day or so, in regards to the eventual atmospheric pattern evolution over the next several days. The evolution of the pattern has been a topic of major discussion over the past several days, with hints of the potential for a Nor’Easter several days ago. After a few blip model runs which showed the storm system, operational and ensemble guidance was a mess — with each suite showing separate evolution’s and resultant solutions in regards to the track and intensity of a developing surface low off the East Coast.

On Wednesday, however, global model guidance came into much better agreement on the evolution of a few major features, all of which will play a major role in the development of a powerful Nor’Easter from Sunday into Monday. The majority of global model guidance, including ensembles, agree on this. The question moving forward will be, as it always is, in the details and nuances of the setup. Those will decide whether or our area receives a glancing blow, or significant impacts and potentially a late-season winter storm.

There are a few major players on the field with this storm system, all of which are handled slightly differently on global model and ensemble guidance over the next few days:

A Western USA Ridge

Forecast models (pictured, the GFS) show a west coast ridge axis and mid level disturbance over the Ohio Valley. This disturbance eventually becomes a strong Nor'Easter.

Forecast models (pictured, the GFS) show a west coast ridge axis and mid level disturbance over the Ohio Valley. This disturbance eventually becomes a strong Nor’Easter.

For the first two weeks of March, lower than normal heights and troughing had dominated the West Coast of the United States. This helped to pump a ridge into the Eastern United States, leading to above normal temperatures in our area. However, a changing pattern has led to the development of a large ridge on the West Coast. This ridge extends northward into British Columbia this week.

This ridge — its placement, and intensity, will become a focal point in the development of the incoming storm system. It essentially serves as a “highway” for the incoming energy which eventually develops into our storm system. Each forecast model handles it a bit differently. A weaker, more progressive ridge should generally aid in a more progressive coastal storm. A more stout, stronger ridge should generally lead to a more amplified solution along the East Coast. While this method isn’t perfect, it certainly will help us understand the pattern moving forward as we monitor each forecast models handling of this ridge.

A Central Canadian blocking ridge

We speak often about the importance of blocking, whether it be in the higher latitudes or closer to our area over Canada or the North Atlantic. Blocking slows down the atmospheric pattern, and allows for more amplified solutions in the atmosphere to occur. In this case, forecast models are in good agreement that a block will develop over Central Canada during the end of this week. This block will have a major impact on our storm system as it develops.

Forecast models agree that a Central Canadian block will develop, aiding in the eventual development of a Nor'Easter this weekend.

Forecast models agree that a Central Canadian block will develop, aiding in the eventual development of a Nor’Easter this weekend.

Essentially, the block itself works with the ridge on the West Coast to “force” the incoming energy southward, along the east axis of the ridge. This allows the energy to amplify southeastward. The block itself eventually progresses east/southeastward and de-amplifies, but it continues to be important as it moves toward Eastern Canada.

Forecast models differ on exactly how the block behaves at this point. Those who keep it stronger allow it to slow down the pattern over Canada and the Northwest Atlantic. This allows the storm system developing off the East Coast to develop closer to the coast. Models that keep this feature farther east and weaker allow the storm to develop later.

Nuances, details, phasing, and a summary

Models agree that a northern stream disturbance will phase in with our lead energy eventually. This allows for rapid deepening of a Nor’Easter late this weekend into this early next week. The nuances and details in exactly how this phase occurs, when it occurs, and where it occurs, will have significant impacts on the weather that our area experiences. Generally, a faster and more organized phase will lead to a stronger storm that will track closer to the coast, bringing more impacts to our area.

Here’s the bottom line: The likelihood that a significant Nor’Easter will develop late this weekend is increasing rather quickly. However, where the storm develops, where it rapidly deepens, and how it does so will have huge impacts on the sensible weather that we experience. Yes, a significant snowstorm is on the table here as a possible solution. Yet, so is a glancing blow with minimal impacts.

The best advice we can give you over the next few days is to stay tuned, check out the latest information, and make sure to check back for updates as we continue to analyze the latest data and information.