For most of you who follow Firsthand Weather on a daily basis, you know that I’ve been discussing the coming pattern change for a very long time. On December 23rd, I decided to introduce the southern winter storm threat on Firsthand Weather’s social media pages and came out with an article on the site on the 27th. So, I realize that I’ve been discussing this potential storm for a while now but have purposely not gotten too specific details just yet. Before I get into this discussion that will include a lot more details, I want you to understand from the start that it’s important not to focus on individual forecast model runs this far out as a way to predict the outcome of individual storm systems. In fact, it’s pretty pointless. What I try to do is identify and forecast the upcoming pattern, and by doing that, I’m able to point out which regions need to be monitored most closely. With that said, the model guidance is starting to come into agreement with the Firsthand Weather long-range predictions.
A Pattern Change Is On The Way:
As I have mentioned a lot in December, the change in the overall pattern across the United States is going to take some time. The unbelievably warm December across a large portion of the U.S. was due to a very strong El Nino, a warm Pacific overall (not only in the El Nino regions but overall), and a well-placed and strong polar vortex over the North Pole. It’s worth noting that the waters along the East Coast and Gulf of Mexico also remain very warm. There really was no reason that December shouldn’t have been very warm, and that’s what was predicted.
The sub-tropical jet stream has been incredibly active, transporting deep tropical moisture into the United States. With the tendency for troughing to build over the western U.S. in December and a persistent ridge over the eastern U.S., this was a favorable setup for a large area of the U.S. to get flooding rains, and that wasn’t confined to just the southern U.S. As we progress into January, the flooding threat will continue for the southern U.S. but over time, it could dry out some farther to the north. The pattern is going to remain very active across the South with storm systems having a greater chance of moving from Mexico and the southwestern U.S. into the Southern Plains and Southeast and oftentimes cutting northeast into the Mid-Atlantic. This was not the dominant storm track in December thanks to the pattern that I just described above.
The first intrusion of Arctic air is going to move into the eastern third of the U.S. at the beginning of next week. This will likely be the coldest air of the season so far, and it’s going to feel really cold since December was so warm.
Monday Morning – January 4th, 2016:
Tuesday Morning – January 5th, 2016:
Now this gets back to what I was saying about it taking a little time for a pattern change to occur with the kind of setup that we have. After the cold air rushes into the East, it’ll be warm again by the end of the week. But compared to this past December, even that’ll probably seem cool. Keep in mind that these maps are temperature anomaly maps (expected departures from average temperatures), not actual temperatures!
Friday Morning – January 8th, 2016:
While all of this is going on over the next 7 to 10 days, there will be a few storm systems to watch. Even much of California will be getting some beneficial rainfall and the Southwest will be getting hit very hard. An end of the week storm system may develop and take a similar track to what a lot of the systems did in December. I’ll cover all of that this upcoming week.
Southern Winter Storm Threat Looking More Likely With Next Cold Surge:
The pattern will get extremely interesting after January 10th. All indicators point to extensive warming taking place over the Arctic, beginning the process of the breakdown and elongation of a well-placed and strong polar vortex. An amplified ridge is going to build over western Canada into Alaska, and this will favor an Arctic air mass pushing into the eastern two-thirds of the U.S. This will be, by far, the coldest air of the season. At this point, there will be expansive blocking over the Arctic, and the active storm track will be much more suppressed to the south.
If this pattern persists over any period of time, this will set the stages for southern regions of the U.S. to be at risk of getting more than one winter storm. There are currently two winter storm potentials on the table for the January 11th to 20th timeframe that I’ll discuss momentarily.
Before I discuss these two potential systems, I want to briefly bring your attention to something else. During El Nino winters, you often hear a lot about “split flow.” The reason so many meteorologists have been so adamant about this winter being warm overall is because of the strength of the current El Nino episode. During El Nino winters, the Pacific jet stream often becomes stronger and extends farther east across the Pacific. It’s pretty common for the jet stream to split closer to the West Coast. The southern split (the sub-tropical jet) is usually the more dominant and active jet stream with this setup, and it can transport deep moisture and Pacific warmth into parts of the U.S., depending on its placement, which is basically what we saw in December. The northern jet can often be weaker, and the Arctic air stays bottled up north.
A good example of the active sub-tropical jet stream and split-flow pattern:
I have discussed extensively why El Nino is only one component of many parts to consider, even during the super El Nino years of the past that were warm overall. Other variables must be considered, and that has been particularly pivotal this winter. There is going to be a tendency for ridging to build into western Canada and Alaska and with a more elongated and weaker polar vortex that will evolve over time (it’s been stubbornly strong), this will set the stages for colder air masses to drop into the eastern U.S. With an active sub-tropical jet stream transporting moisture into the southern regions of the U.S., this sets up a scenario that’s pretty unusual for such a strong El Nino event. If you’ve been following my forecasts since July, you already should know what’s going on, to an extent.
The first winter storm on the table could occur right around January 11th-12th. Of course, exact dates and timelines will change some. This first threat is going to occur around the time that a big Arctic air mass is pushing into the U.S. The eastern U.S. will be coming off of a brief warmup, and a piece of energy will likely move into Mexico from the Pacific and merge with a long-wave trough that will develop in response to a building ridge over western Canada and Alaska. This could eventually merge with a piece of energy moving in from the north, but I’ll hash all of that out in future updates.
Notice the big trough over the U.S. and the blocking over the Arctic regions:
A surface low pressure system could develop along the Gulf Coast in response to a favorable mid and upper level pattern and active sub-tropical jet stream, and be the first real winter storm threat for parts of the Southeast, Tennessee Valley, parts of the Appalachians, and Mid-Atlantic. This kind of mid and upper-level pattern favors primarily an all snow or all rain event (determining rain/snow line will be important) for most areas with possibly a transition zone in between. Although there’s a chance that there could be some ice, I’d say there’s a better chance at this primarily being a snowstorm. As I said, warm air will be moving out of the eastern U.S. and be replaced by a colder pattern. The rain/snow line will probably be somewhere extending from Birmingham to Atlanta into Upstate SC and central NC. Parts of the Tennessee Valley and the Mid-Atlantic will probably get some decent snowfall from this. If moisture extends farther west of the regions that I just mentioned, then areas farther west could get some wintry precipitation, too. At this point, I have a difficult time seeing wintry precipitation falling much farther to south than the areas I just mentioned, but this far out, it could very well have to be adjusted. Unfortunately, it’s difficult to say what side of the line some of these areas will fall on, but if I mentioned your region above, just keep a close eye on this potential system.
The next winter storm potential could occur farther to the south than the first one. The cold air should be more established over the eastern U.S., and the sub-tropical jet stream will likely be more suppressed to the south during this period. This means that wintry precipitation could fall over some areas that typically don’t get to see a lot of winter weather from the Southern Plains into the Southeast. Since this is a potential at the end of the time period that I wrote this discussion for, it’s a little too soon to get as detailed as I did with the first system. But if you miss getting anything with the first storm, chances are higher that many locations in the South will get wintry precipitation with this second system.
I’ll continue to monitor how this pattern will evolve over the next two to three weeks. I definitely included enough detail in this article that I will probably have to make some changes along the way, so be sure to visit Firsthand Weather daily on the website and social media.