If you’ve seen them, believe us when we say, we’ve seen them too! The elephant in the room, or the one trampling through your news feeds. It’s become common practice for online and mainstream weather sites to post pictures of snowfall maps for storms some 300+ hours away. Some of the worst offenders use these images while also promoting the answers to those images are hidden behind a paywall or membership fee. Can we blame them? No… fact is, drama sells and we consume a lot of drama filled, fact-less, click bait every single day.
When you see a snow map for a storm that’s seven or even 10 days away, you are looking at the output from a storm that will form from multiple pieces of energy that are somewhere out over the western Pacific Ocean, and will be under the influence of upstream and downstream atmospheric currents that change like currents in a stream of moving rocks and boulders.
The supercomputers behind these outputs are amazingly powerful, incredibly useful when used as the tools they are, and do a pretty damn good job at giving a general idea of what the future weather may hold. They do so with a steadily increasing accuracy with each day closer to the storm, with their highest accuracy being between 3-5 days out from a storm. Why 3-5 days? Because that’s about the time frame that our east coast weather enters the west coast of the United States. So in short, while long range snow maps are fun to look at and help to conjure up the imaginations hopes or worries of what could be, they hold very little value in terms of actual outcome, most of the time.
If you’ve been with us for a while, you’ll know we don’t usually begin discussing or even teasing these things until we get within 7 days or less, and we don’t start committing to real details until 3 days or so with an ever increasing focus on the finer details with each day that passes. Now, behind the scenes….. lol… we are sharing those same snow maps, hypothesizing, comparing notes, trying to understand the likelihood of the scenario and the ingredients required for it to actually occur, including all the reasons it can’t or won’t, so please don’t ever think we’re just asleep at the wheel. We are simply saving you from the daily roller coasting of waffling forecasts about storms from the move Day after tomorrow, that end of being partly cloudy and cold.
Now…. It’s Sunday.. and we have a storm signal that has been flashing on and off since about ten days ago that focuses around the period of this upcoming weekend. Abiding by our code of honor above, we will not put out our first formal thoughts.
The ingredients for a powerful winter storm along the East Coast will be on the table this week, whether or not these ingredients will all come together at the right time, in the right places, to spark the evolution to a large cycle off the Northeast coast between Jan 11th/12th is very much “in the air”. Let’s take a look at some of the data and highlight the current volatility and why it’s simply way too soon to say much more than “the threat is there”.
Above are projected surface maps from both the GFS and Euro for next weekend, first two are from the EURO and the last two are from the GFS. They are all showing the same exact moment in time, but they are displaying runs that are 6-12 hours apart from one another. So in just a single day of data, you can see both models go from showing a weak, flat system that scoots out the mid-Atlantic coast with nothing more than some clouds and maybe light snow. Then in the very next run, these models show a powerful coastal storm, parked just off the NE coast with heavy snow and powerful winds. This is just one day’s worth of data, this back and forth has been occurring for days, and there have even been multiple days where data has lost the storm entirely. Those snow maps and drama filled images are simply cherry picked snow maps from some of the worst case scenarios that have popped up in the long range. Here’s an example on just how vast the outcomes of these scenarios play out in terms of snow accumulations. 
Yes…. This is just today’s data. Zero to thirty inches! Post the 30” map and you’re bound to get lots of likes, and maybe some new subscribers. The reality is this volatility exists because there is ALOT that needs to be resolved before the models can even begin to get a clearer picture of what may occur next weekend. Now let me be clear, BOTH of these outcomes are possible, they currently both hold much different probabilities of occurring. Why the volatility? Why such violent swings in the outcomes from run to run? Simple… there’s a lot of noise, first being the storm hitting areas to our south tomorrow, as this storms energy will get absorbed into a larger area of low pressure over the Canadian Maritimes and play a part in the pattern later in the week. In addition, the two pieces of energy that will become the storm have not even come ashore on the west coast yet, and they are currently in the data hole of the pacific. You heard correctly, TWO pieces of energy, and if these two pieces don’t phase together at the perfect time, then there is no storm. In order to get major storms like the one shown above, many things need to come together perfectly, which is why they are rare, and don’t occur regularly. Also, a good reason to always stay ground when their ghosts show up on a long-range model, as they do every winter, multiple times a winter, yet only actually occur once every few seasons. 
Above you will find the GFS ensembles, another great tool for forecasting, as instead of just one run as seen above, which we call the operational run, you get many runs. It allows you to see how many scenarios does the model see where a storm occurs. This helps build probabilities and confidence. What do you see? The model ran 30 times, only twice did it see a major snowfall? The European ensembles continue to be quite similar. This tells us that at 6 days out, the probability of the worst case scenario remains low, and the likelihood of a storm that simply slides off the east coast like tomorrow storm is the higher probability. With that said, the probability of a major east coast storm next weekend is about 25%, as of now and that will likely change as we start to get players on the field and others off of it.
So what do we need for a big storm to occur? Skip this if you’re not in the mood to nerd…
These fancy images are showing atmosphere at 500mb and it’s showing the pieces of energy that help spark Cyclogenesis.
Image 1 early next week, two distinct pieces of energy, one diving in from Montana and one rolling through northern Mexico.
Image 2 these two pieces pace each other perfectly and phase together into one piece of energy, notice I made the arrow vertical? That is mark that the trough is currently neutral. A neutral trough does not allow the energy to consolidate along the east coast, it would simply allow a weaker storm to pass from west to east and off the mid Atlantic coast, like the storm on Monday.
Image 3 because the two energies phased together, it allows all the energy to consolidate and move the trough into negative. See how the arrow is now tilted 45°. That helps produce rapid cyclogenesis along the eastern seaboard and the outcome is a deep area of low pressure.
If those two pieces of energy remain disconnected, this storm will remain weaker and simply pass to our south, which is what 28 of those ensemble members are seeing. If those two pieces of energy, that aren’t even on shore yet, can phase together at the right time, and turn the trough negative, we could see a powerful storm system develop along the coast. Both of these scenarios are plausible, but currently the data favors a storm that passes to our south. We won’t be able to plant a flag, nor should anybody, until about Tuesday PM. Hope this helps answer some of the questions, clear up some of the stuff floating around out there. As always, we will be here for each step along the way, and don’t forget to keep calm and weather on..
-Alex