Predominantly Colder Pattern Could Develop Across Heartland Of U.S. By Late Next Week

Brief Discussion On Early to Midweek Weather:

We’re about to briefly shift out of the pattern that has been responsible for the recent colder weather across the eastern United States and warmth out west. The pattern has previously been characterized by an amplified ridge that has extended from the western U.S. through western Canada and into Alaska. Downstream of the ridge, deep troughing has persisted and in fact, even brought colder conditions all the way into Florida. Remarkably, parts of the panhandle of Florida and over the open waters of the Gulf had snow on the backend of the system that dumped copious amounts of snow across parts of the Southeast. This amplified pattern is going to flatten out next week, allowing for relatively warmer conditions to prevail across most of the U.S. through mid-week. With that said, there will be a quick-moving trough that’ll trek across the Northern Plains early next week and then eastward over New England by mid-week. That’ll bring a quick intrusion of cold air from the Northern Plains over into the Great Lakes and over parts of New England, but that cold will remain mostly confined to those regions. We will eventually have to discuss that system on Firsthand Weather, since it will most likely be bringing a swath of precipitation (rain) across the eastern third of the U.S. Parts of the Northern Plains, Great Lakes, and inland regions of New England could get some snow out of the system, so we’ll have to watch that.

Overview Of Long-Range Forecast Discussion For Late Next Week Through Just Beyond Christmas:

Let’s go ahead and fast forward to the end of next week through the Christmas timeframe and just slightly beyond that. That’s really the entire purpose of this article, and I want to begin digging into how the pattern could begin to evolve after the early to mid-week warmup. Temperatures have mostly been below average across the majority of the eastern third of the nation over the last seven days, while the core of the warmth (relative to climatological averages) has been centered over the Northern Plains and has extended westward into Montana, Wyoming, and Colorado. Additional parts of the western third of the U.S. have also been quite warm. Now if you read Firsthand Weather’s winter forecast that was published about a month ago, you probably noticed that we were bullish on the cold across the Northern Plains and into the Rockies, so if you’re located across any of those locations, you might be wondering what’s going on with the forecast. Get ready, changes are on the way!

It’s not all that uncommon to hear a lot of talk about the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) in many of the medium and longer-range forecast discussions that get published on the internet; however, the eastern Pacific Oscillation (EPO) is a lesser known index that honestly should be discussed more often than it is in the U.S. The negative phase of the EPO is characterized by ridging over Alaska with troughing to its south. It’s simply a dipole pattern similar to the NAO, but its location is in the northeastern Pacific. Any atmospheric feature(s) that is present upstream of the U.S. can have important implications for how our weather in the U.S. may evolve with time.

It’s important to note that simply determining whether the EPO is negative or positive doesn’t give the whole picture. It’s just as important to determine the position of the Alaska ridge or trough, its orientation, and its amplitude. For example, a ridge can extend well into Alaska, but its position may be far enough offshore that the downstream trough centers itself over the western and central U.S. This, in effect, can open the door for ridging to develop across the Southeast and along the East Coast. The moral of the story is that a negative EPO pattern is one to watch closely in the U.S. since it can oftentimes signal widespread cold, but it’s important to dig a bit deeper to fully determine where those coldest anomalies will be located. That’s what we’ve been in the process of doing at Firsthand Weather and will continue doing through the weekend and early next week.

How Will This Impact The Weather In The United States:

While the GFS model is generally more aggressive with the development of Southeast ridging, the European features a weaker ridge. Nonetheless, the pattern that will likely evolve from very late next week into Christmas will feature widespread cold across the heartland of the country. The coldest anomalies should be centered over the Northern Plains and upper Midwest, and it won’t be uncommon for that Arctic air to spill southward into the Rockies and the central/southern Plains. Additional regions to watch for very cold conditions will be the Ohio Valley, northwestern parts of the Tennessee Valley, and Northeast (especially inland regions away from the coast). The Pacific Northwest could also get in on some of these colder conditions, and that colder air could spill into the Mid-Atlantic at times, too. To summarize this into one sentence, this pattern will likely feature widespread cold, which differs quite drastically from the eastern-focused cold earlier in the month.

european model 500 mb height anomalies
Figure 1: Latest European model features long-wave trough centered over the central U.S.

The next image from the Climate Prediction Center (NOAA) shows the probability that temperatures will be above or below average from December 21 to December 27. That’s not a bad compromise across the Southeast, given that the guidance does tend to develop ridging across the Southeast but at times, colder air will make it into those regions. Notice that the probability for below-average temperatures is depicted over a large region of the U.S. Keep in mind that this particular graphic tells you nothing about the magnitude of the cold. Its purpose serves to show you which regions could simply have above or below average temperatures.

8-14 day temperature anomaly probabilities
Figure 2: The latest 8-14 day (Dec. 21 to 27) temperature probability outlook from the CPC

The next analysis takes GEFS forecast model data and produces a temperature anomaly map (from December 23 to 25, in this case) based on previous similar pattern setups. Based on this kind of setup, you’d generally expect storm systems to swing southeastward through the Rockies, into the central/southern Plains and then hook northeastward across the mid-south, the northwestern Tennessee Valley, Ohio Valley, and across inland regions of the Northeast. Even though I didn’t draw in that storm track, I mostly agree with this analysis. The region to watch most closely for wintry weather (including ice) over this period will generally extend from the central/southern Plains over into the Ohio Valley and into inland regions of the Northeast. That puts parts of the Tennessee Valley and the mid-south (parts of Arkansas, western Tennessee, far northward Mississippi) in a zone that could swing either way; however, it’s a region to watch nonetheless. To make it easy, take a glance at the map, and if you’re relatively close to the storm track drawn on the map and located on the northern/northeastward side, take notice. This is meant to give you a general overview of what the dominant storm track could look like, so please understand that this isn’t depicting a particular system.

Cold in central U.S. with storm track
Figure 3: Projected temperature anomalies (for Dec. 23 to 25) from CIPS Analog Guidance using GEFS model data and analogs

I suspect that most of the Southeast (the red-shaded zone across parts of the South in the image above) will transition to a predominantly wetter and a warmer pattern through Christmas and maybe just a bit beyond. With that said, some of the guidance does have the colder air spilling into the Southeast at times through the period (notice the back and forth in temperature anomalies depicted in the two images below), which seems realistic to me. Essentially, this is a pattern that favors wetter and warmer conditions, which can then be followed by colder and drier conditions, and then the cycle continues. If you’re located just east and southeast of the Appalachians, it’s worth noting that surface high pressure moving across the Northeast can result in surface temperatures being at freezing just outside of the mountains across those locations as precipitation is moving across the Southeast. That’s a scenario to watch for with this kind of pattern and can cause icy conditions (not snow though); however, that’s a very localized threat that often doesn’t even reach into cities like Birmingham or Atlanta and doesn’t occur across locations west and southwest of the Appalachians. Unless the ridging that is expected to build into Alaska is farther east than I’m anticipated, I expect most of the wintry weather to occur across the locations I specified in the previous paragraph.

european model temperature anomalies 1
Figure 4: Projected temperature anomalies from latest European model on Friday morning, Dec. 22

european model temperature anomalies 2
Figure 5: Projected temperature anomalies from latest European model on Saturday morning, Dec. 23

Chris is planning on posting an article for the Pacific Northwest and one for the Southern Plains sometime soon. In the meantime, I’ll also be working on regional forecasts across additional areas. Hopefully this article gives everyone a general overview of the pattern we’re going to be dealing with, and we’ll get into the nitty-gritty specifics throughout the month. Of course, any changes to the overall pattern could require me to make revisions to this forecast, so most definitely be aware of that! I don’t have all of the answers and do make mistakes, so please follow Firsthand Weather continuously.

Bitter Cold Will Continue Into February

If winter ended today, I would say that this was an awesome winter! Many of you have gotten the snow that you wanted, and January ended up being very cold for many across the United States. Now, let me be clear that winter is far from over, and as I have stated on the Facebook page many times, February is going to be active. We are going to be dealing with a bit of a different pattern than what we had in January, but I do expect another month of brutally cold temperatures. Many areas across the United States could end up getting a lot of wintry weather this month with some regions getting multiple storms in the upcoming weeks.

Last month, temperatures ended up being well-below normal for much of the eastern U.S., while the western U.S. stayed mild and dry. The Deep South was also finally able to get that big winter storm that I had been predicting for the end of January. All in all, the winter has been good for all of you lovers of cold, and many of you got to see snow for the first time in several years. At this point, most of you want to know if this cold is going to continue and whether or not you’re going to get more snow. Many of you are, and the one’s who do could get a lot of it.

For a good portion of last month, there was a lot of troughing in the eastern half of the United States, while there was strong ridging out West. I explained earlier in January why we weren’t going to need the NAO index to be strongly negative to get a lot of cold air in the eastern U.S. That’s why many were forecasting in early January that the cold would be over after that first outbreak, but I ended up being one of the crazy ones that went against the crowd. We’re about to have a bit of a change in the pattern for February, but that doesn’t mean we’re about to move into a warmer pattern. In January, the PNA index was mostly positive, and with that, you usually get ridging out West and troughing and stormiest out East. Of course, there are other factors that play into that, but that’s typically what you get during the winter months with a positive PNA. In February, it’s looking like the PNA will be negative, at least for the first half of the month. Since that is going to occur, that could really start to break down some of that ridging out west and allow for an increase in stormiest particularly in the Pacific Northwest.

Now, many of you saw my rant about how these “weather” pages were sharing one forecast model run from the European model and calling for 5 feet of snow. That was not me saying that I didn’t think that certain areas will get a lot of snow, but it is frustrating when people cause hype without truly being able to interpret the forecast models. Like I’ve said many times, forecast models should be used as a tool and not as a forecast. I do think that the forecast models are on to something with showing an increase in storminess from the Southern Plains to the Ohio River Valley on up to the Northeast. The pattern is going to favor this, and the cold air is going to be in place.

Now, one thing that I am keeping a close watch on is the possibility of a ridge building in from the west into the Southeastern United States. For those of you that know a little bit about meteorology, the SE ridge is something that sometimes will build into the Southeast during the winter months and cause well above average temperatures for that region, but it all depends on the strength of the ridge. Earlier model guidance had this ridge being quite strong, but I never really bought into that. Later model guidance is a lot weaker with this ridge, and actually if it stays very weak, it could help give some areas increased chances of getting wintry weather later in the month. Because I don’t think this ridge will be particularly strong and because there will be plenty of cold air coming south from the Arctic, some areas could actually benefit from this. This is something that I am going to have to watch very closely.

Again, areas from the Plains to parts of the Tennessee River Valley/Ohio River Valley to the Northeast could be impacted by multiple storms this month. The track of these systems will determine who gets the heavy wintry precipitation or just rain, but there is going to be a lot to watch! Many of you know that I am a believer in cycles and trends and often use these trends to make my long-range forecasts. Things could get very interesting later in the month, and depending on the pattern at that particular time, someone could get a big winter storm. Pinpointing the location will be difficult at this time, but the possibility is definitely there.

Anyways, that’s all I have for you tonight. Please give Firsthand Weather a like on Facebook if you haven’t already. I’m always putting new updates on there on a daily basis!!

CPC's Temperature Probability Map For the Next 6 to 10 Days

CPC’s Temperature Probability Map For the Next 6 to 10 Days