Good afternoon from Southern Connecticut Weather.
With the overall upper level pattern settling into a conducive state for winter storm chances and guidance in unanimous agreement about two distinct events, we are declaring the week ahead a SCW Period of Interest.
This post is intended to provide a brief overview of what we're seeing and provide early thoughts. Expect a lot more posts here, on Facebook, and on Twitter @southernctwx in the coming days as the forecast comes into better focus.
If you haven't joined any of our pages yet, this would be a good time.
Now, with that shameless plug out of the way, let's dive in. :)
With the overall upper level pattern settling into a conducive state for winter storm chances and guidance in unanimous agreement about two distinct events, we are declaring the week ahead a SCW Period of Interest.
This post is intended to provide a brief overview of what we're seeing and provide early thoughts. Expect a lot more posts here, on Facebook, and on Twitter @southernctwx in the coming days as the forecast comes into better focus.
If you haven't joined any of our pages yet, this would be a good time.
Now, with that shameless plug out of the way, let's dive in. :)
Above: the EPS (European Ensemble) depiction of the upper level pattern on Thursday morning. This is a textbook look for a winter storm in New England.
The Overall Setup
As I mentioned in our Facebook update this morning, this is probably the best December winter storm pattern we've seen in quite some time. The image above is a snapshot of that pattern, but it's easy to see why I'm writing this post. If you recall in our winter forecast, we said that there might be a window for some teleconnection support. Here it is. You have higher heights (look toward the red shading) in the Arctic which reflect negative states of the NAO and AO, and in the Pacific, while not perfect, you have some ridging (raised lines) in the Pacific that helps cut off the flow of warm air.
This is an evolving pattern. Which means while we're socked in with a cold rain today and tomorrow we will be warmer than normal, we will be dealing with our first potential system on Monday and likely second and much colder system by midweek, and maybe another system by the weekend.
The Overall Setup
As I mentioned in our Facebook update this morning, this is probably the best December winter storm pattern we've seen in quite some time. The image above is a snapshot of that pattern, but it's easy to see why I'm writing this post. If you recall in our winter forecast, we said that there might be a window for some teleconnection support. Here it is. You have higher heights (look toward the red shading) in the Arctic which reflect negative states of the NAO and AO, and in the Pacific, while not perfect, you have some ridging (raised lines) in the Pacific that helps cut off the flow of warm air.
This is an evolving pattern. Which means while we're socked in with a cold rain today and tomorrow we will be warmer than normal, we will be dealing with our first potential system on Monday and likely second and much colder system by midweek, and maybe another system by the weekend.
Above is the GEFS (GFS Ensembles) depicting our two main systems. The first comes on Monday and the next is looking more Wednesday PM into Thursday. Timing for the second is still up in the air. Note the areas of low pressure (red numbers) below CT. Both are good tracks for wintry precipitation for CT, though Monday doesn't have the best upper level setup.
Wave 1--Monday System
This first one is the classic thread the needle scenario not that much unlike our first winter storm earlier in December. We will see an area of low pressure develop in the south and slide off the coast on Monday. How far north it gets is critical to our chances for snow.
Now, this one is a thread the needle setup because there isn't any real cold air in place to allow for an easy one type precipitation call, and we don't yet know the northern extent of the storm track. Small differences here can make a meaningful difference in what we see on Monday.
This afternoon, the European model, which had been leading the way for a light snow event for CT backed down, while the GFS, which had been totally disinterested in any precipitation let alone snow in CT amped up to bring a period of snow for most of CT on Monday afternoon.
This first one is the classic thread the needle scenario not that much unlike our first winter storm earlier in December. We will see an area of low pressure develop in the south and slide off the coast on Monday. How far north it gets is critical to our chances for snow.
Now, this one is a thread the needle setup because there isn't any real cold air in place to allow for an easy one type precipitation call, and we don't yet know the northern extent of the storm track. Small differences here can make a meaningful difference in what we see on Monday.
This afternoon, the European model, which had been leading the way for a light snow event for CT backed down, while the GFS, which had been totally disinterested in any precipitation let alone snow in CT amped up to bring a period of snow for most of CT on Monday afternoon.
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On the left you see a Monday whiff. We don't see any rain or snow on this run of the Canadian model. On the right, we have the 12z GFS, which was robust and drops a few inches in CT. The Euro, not shown, was in the middle. Note how even on the GFS, verbatim temperatures may be warm enough for rain at times.
Right now we think the snow ceiling is low for this system. A further south track means we see nothing. Further north and we could see a mix of rain and snow that has some accumulation, albeit minor. A lot needs to be sorted out here before we put out forecast numbers tomorrow.
Regardless of what happens, Wave 1 is important. If you remember the very first image, to the northeast of Canada there is a huge blue ball. That's Wave 1! After it passes us it blows up into a huge system that provides blocking for our next system...
Right now we think the snow ceiling is low for this system. A further south track means we see nothing. Further north and we could see a mix of rain and snow that has some accumulation, albeit minor. A lot needs to be sorted out here before we put out forecast numbers tomorrow.
Regardless of what happens, Wave 1 is important. If you remember the very first image, to the northeast of Canada there is a huge blue ball. That's Wave 1! After it passes us it blows up into a huge system that provides blocking for our next system...
Wave 2--Wednesday/Thursday
Let me start off by saying there is higher confidence in Wave 2 than Wave 1. Why? Because the pattern will have matured enough to provide us with relatively stable features to support a potentially major winter storm.
With Wave 1 and the teleconnections serving as a block, the next wave on the heels of Monday has a lot going for it. First, there's cold air in place.
Let me start off by saying there is higher confidence in Wave 2 than Wave 1. Why? Because the pattern will have matured enough to provide us with relatively stable features to support a potentially major winter storm.
With Wave 1 and the teleconnections serving as a block, the next wave on the heels of Monday has a lot going for it. First, there's cold air in place.
Above you'll see EPS (again, Euro Ensemble) high temperatures on Wednesday. It's near to below freezing across the state. This is important because unlike Wave 1, or the system in early December, there's an Arctic high to our north locking in cold air. This makes it less likely we see mixing issues even at the coast, though coastal folks really need to watch where this tracks to feel confident in snow type. Image courtesy of weathermodels.com.
Second, the dynamics of the storm are sound.
Second, the dynamics of the storm are sound.
Let's walk through this GFS Ensemble image above. This covers Wave 2's progression. First, you will see a low (blue) develop in the south and then ride up the coast while deepening. That's a good track for a winter storm, near our "Benchmark", though a little south for our blockbuster storms. But note the high on top--that locks in our cold air and keeps the storm from cutting to our west. Timing matters quite a bit here, as well as the track. If the best dynamics take off to our south at the right location, watch out. If not, this is a more run of the mill type of storm.
Looking at some of the ensemble probabilities, there is a very strong signal for a significant snow event out of this.
That said, we're still a ways out, and we need to see how Wave 1 impacts Wave 2.
Now is not the time to lock in snow totals, no matter what you see on ensembles or operational guidance.
Looking at some of the ensemble probabilities, there is a very strong signal for a significant snow event out of this.
That said, we're still a ways out, and we need to see how Wave 1 impacts Wave 2.
Now is not the time to lock in snow totals, no matter what you see on ensembles or operational guidance.
Above: the 12z EPS probabilities of 12+ inches between now and Friday morning. As of this run, it's a 40-50% probability for most, which may not seem like much, but is a huge signal for a significant winter weather event at this range. Image courtesy of weathermodels.com.
This could still end up less dynamic or shunted further south, but one thing is clear: Wave 2 has a high ceiling, statewide. Stay tuned.
As always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
Thank you for reading.
-DB
This could still end up less dynamic or shunted further south, but one thing is clear: Wave 2 has a high ceiling, statewide. Stay tuned.
As always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
Thank you for reading.
-DB
