The month of December featured extremely cold temperatures and frequent small snow events. The beginning of January brought much of the same, including a widespread blizzard that dropped snow from Florida to Maine. A mid season thaw finally allowed the eastern third of the US to take a break from the cold and snow, but we’re now in the process of seeing another pattern shakeup. The question is, what does that mean for weather across the nation?
Looking back at the time period from late December to early January, you can see in the temperature anomaly map above truly how chilly the country was for nearly everyone east of the Rocky Mountains.
The good news for those of you sick of this cold weather, is that a repeat of similar weather is expected for next winter. The bad news is, an extremely active pattern now setting up will still bring shots of frigid temperatures and more snow for the eastern third of the nation.
Taking a real general overarching look at the pattern that may lie ahead, you can see our global guidance (this is the 12z run of the GFS) shows multiple storm threats in the first 2 weeks of the new month. One threat at the end of this weekend, followed by a second threat during the middle of next week, and a final threat just over a week from now.
While its clearly an active pattern, there’s a defining trend that we see here with each system, and that’s the rigid rain/snow line that seems to continuously bring rain to the coast and snow to the interior.
The reason behind what some might refer to as a “gradient pattern” is that our flow is quite fast (meaning there’s nothing to slow things down a give us a longer duration storm) and the troughs that move through (cold fronts) tend to remain fairly shallow without digging very much. Comparing this to what we saw back in the beginning of the season, there’s clearly significant differences. As you can see here (above) the trough just scrapes the Great Lakes and Interior sections, while during December and early January there were troughs digging all the way down into Florida.
In translation, this type of gradient setup on average favors frequent interior snows with the coastal region either briefly mixing in snow or remaining completely wet.
Now just like with any middle to long range pattern change, the models are going to have their fair share of struggles. Just a few days back, we saw a much colder and more aggressive outcome being portrayed in the long range, so to see a rather large flip shouldn’t convince anyone on what lies ahead.
Part of the reason these long range forecasts could be flip-flopping is because of one of our major parameters – The MJO. Depending on different activity across our ocean basins, the MJO can fluctuate into different phases. You can see currently we’re entering into phase 7, and over the next few weeks the forecasts are rather widespread and erratic.
If we can manage to keep the MJO away from the COD (the center sector where the MJO has essentially no influence on the pattern) and towards phase 8, we’ll likely see a change back over to a pattern that at a minimum would increase the chances of snow events down to the coastline. The current projections among guidance make it difficult to say exactly where it will head, but certainly in a direction with slightly less influence and possibly colder and snowier.
You can see from the MJO composites above showing how the MJO typically affects temperature anomalies in the US during January, February and March. Phase 7 (our current phase) shows overwhelming warmth for nearly 2/3 of the eastern portion of the nation. Overall that lines up pretty well with what we’ve been seeing the last few weeks.
Now notice what happens if the MJO were to move into Phase 8 – A total flip of the pattern with below average temperatures for all states east of the Mississippi River, and a much warmer western US. The unfortunate news is that we won’t really have a complete grasp on what lies ahead after the first week of January for at least another few days. Even then, changes are always inevitable.
For now though, the takeaway from this is that we’re heading into another pattern change, and right now it appears to be rather gradient, supporting higher chances of snow for the interior and lower chances of snow for the east coast. But there’s a catch. If we can manage to see our MJO dip into Phase 8, we could be talking about another flip in the pattern back to something that would support more cold and snow for a large portion of the eastern third of the country. For now, it’s a waiting game.