We’ve discussed for a few days the threat for wintry weather this coming weekend – and while the evolution of the forecast has changed in the atmospheres mid and upper levels, the threat for wintry weather still does exist. With that being said, forecast model guidance continues to offer little help in regards to consistency and confidence as we move forward. A complicated situation is set to evolve across the Great Lakes and Northeast States this weekend.
An initial disturbance is still likely to drop southward into the Great Lakes, well from the northwest, associated with Pacific energy. It will undercut a piece of what is known as the “tropospheric polar vortex” – or the polar vortex that exists in our troposphere, where we experience most of our weather. The interactions between these two disturbances will be critical, and forecast model guidance is struggling with exactly how the two of them will behave.
It’s important to note a few things about the weather pattern, especially before we analyze individual forecast model guidance and ensembles. This is a critical part of forecasting the weather – we have to understand the preexisting conditions before we utilize computer guidance to move forward. The weather pattern in the short and medium term is a rather progressive one, especially in the Pacific. In other words, there is not a whole lot of “amplification” out in the Western part of North America.
Instead, the Pacific Ocean continues to send multiple disturbance into the Western United States, which kills the amplitude of ridging. This leads to a mid level atmospheric flow that is more progressive in nature down over the United States. This will be critical as the two disturbances interact, as instead of “digging” southward the tropospheric polar vortex will have a tendency to slide eastward over time.
In addition, forecast models are indicative of “confluence” over the Northeast United States. In other words, a compressed height field in the mid levels of the atmosphere that would act as a “block” for storm system amplification further north. The GFS in particular is very strong with confluence across New England, preventing the storm from gaining any northward ground and amplifying near or east of New England.
But forecast model guidance has trended toward a more amplified Pacific Ocean in the past several runs, and the ECMWF in particular seems to suggest that a piece of the tropospheric polar vortex will have plenty of room to amplify southward into the Great Lakes and Ohio Valley. This would force the development of a low pressure system off the coast of the Mid Atlantic and New England which, depending on the systems exact track, could strengthen and bring snow to the Northeast states late this weekend.
Other forecast models, like the GFS, are much more progressive with the evolution of the storm system, taking the low pressure system hundreds of miles offshore with minimal impacts in the Northeast states at all. Given the state of the pattern, and propensity for a progressive mid and upper level evolution, our current forecast package continues to favor a more progressive solution – although snow is not out of the question altogether. A stripe of light-impact snow still appears possible as the upper level disturbance moves through the Northeast later this weekend.
We’ll be keeping a very close eye on how things evolve over the next few days. Stay tuned for the latest data, information and thoughts.