Overview
This may be one of the longest weeks of the winter. In the words of the legendary winter weather expert, Paul Kocin, nothing like a new model run (cough cough EURO) to dampen enthusiasm. After a remarkable period in which virtually all computer guidance agreed that a major snowstorm from Richmond to Boston was likely, a substantial shift southward happened today on our two most reliable pieces of guidance—the GFS and the Euro. In addition, these operational models were backed up by their ensembles, which are a series of similar models with slightly different initialization schemes and physics calculations that are run to account for the inherent errors that take place both when a model is initialized (begins running) and out in time. For this reason, there is substantially higher uncertainty over what will unfold over the next few days.
Let’s dive in…
First, a couple of things need to be said before moving forward:
Alright, tonight the shortwave in question that will develop into a major storm for someone is entering the west coast. Over the next few days, it will gradually work its way across the country and begin a southward dive.
This may be one of the longest weeks of the winter. In the words of the legendary winter weather expert, Paul Kocin, nothing like a new model run (cough cough EURO) to dampen enthusiasm. After a remarkable period in which virtually all computer guidance agreed that a major snowstorm from Richmond to Boston was likely, a substantial shift southward happened today on our two most reliable pieces of guidance—the GFS and the Euro. In addition, these operational models were backed up by their ensembles, which are a series of similar models with slightly different initialization schemes and physics calculations that are run to account for the inherent errors that take place both when a model is initialized (begins running) and out in time. For this reason, there is substantially higher uncertainty over what will unfold over the next few days.
Let’s dive in…
First, a couple of things need to be said before moving forward:
- The synoptic, or large-scale, setup has been well forecasted so far. A combination of factors will allow for a major storm to develop over the next 72 hours. This storm will impact the east coast with heavy snow, strong winds, and coastal erosion and flooding in spots.
- Even with this known, very small details will make a significant difference in sensible weather in your area. Nothing is set in stone. We are still over 72 hours from the most likely onset, which means that trends one way during an afternoon can easily shift the next day. If you get caught up chasing model run after model run, you will go crazy.
- I would still be wary of snowfall accumulations given by anyone. With this much uncertainty injected into the overall evolution of the next few days, the most accurate forecasts will be the ones made much closer to onset of any event. The calls that you hear today can be different tomorrow. That isn’t being wrong on a forecast or not knowing anything—that is adapting to a dynamic setup and unknown evolution. You have to keep checking weather updates (hopefully with us but with whoever you follow) to stay ahead of any changes.
Alright, tonight the shortwave in question that will develop into a major storm for someone is entering the west coast. Over the next few days, it will gradually work its way across the country and begin a southward dive.
The two images above show the latest GFS projection of our storm. The first image shows the 500mb (18,000 feet) vorticity digging all the way into Texas, with a corresponding upper level low over the region. Just as Greg said last night, this is a classic feature on all of the biggest Northeastern United States snowstorms, as it dives south and begins to effectively feed off of the southern branch of the jet stream and the contrast in temperature. There is total agreement among the guidance on the overall setup at this point in time.
Shortly after is where things begin to get tricky. In order for a classic northeast snowstorm to end up hitting everyone up and down the coast, you need everything to come together at the right time and in the right place. For Connecticut, you not only want a “benchmark” track, but you want the area of low pressure to be at it’s most dynamic strengthening phase when it is near you. That is highly unlikely in this instance. This too was well modeled.
Shortly after is where things begin to get tricky. In order for a classic northeast snowstorm to end up hitting everyone up and down the coast, you need everything to come together at the right time and in the right place. For Connecticut, you not only want a “benchmark” track, but you want the area of low pressure to be at it’s most dynamic strengthening phase when it is near you. That is highly unlikely in this instance. This too was well modeled.
In the first image, notice the black lines, or isobars. There is one that is closed. There’s your first sign of trouble. This low is closing off earlier than is ideal for Connecticut. A closed low is a low-pressure area that has a distinct center of cyclonic circulation. What is key here is that in addition to setting the stage for rapid development once it hits the coast, closed lows aloft are usually partially or completely detached from the main westerly current. This allows them to move more slowly.
If you look at the surface map, you see that the eastern US is primed for snow, with cold high pressure systems in great position to feed in cold air as a storm passes. Precipitation type is no concern in this event.
The Flies in the Ointment for a Large Event
With a closed low moving slowly along the Mid-Atlantic, that region is most likely to receive a major to historic event. The low will transfer from the continental US to the Atlantic, and once it does it will explode. The location of this rapid deepening combined with the slow movement of the low will allow for the best dynamics—the cold conveyor belt (think of the classic comma head of precipitation), and midlevel frontogenesis—key components to big time snowfall amounts, to be effectively spent in that region.
All that said, that doesn’t preclude New England from good snow. Because of the sheer size of the storm and really strong mid level organization, even as the low tracks toward New England, snow would fall. This has been consistent on all the models. You see this on the latest GFS, which has snow solidly in Connecticut in about 96 hours or 1pm Saturday.
If you look at the surface map, you see that the eastern US is primed for snow, with cold high pressure systems in great position to feed in cold air as a storm passes. Precipitation type is no concern in this event.
The Flies in the Ointment for a Large Event
With a closed low moving slowly along the Mid-Atlantic, that region is most likely to receive a major to historic event. The low will transfer from the continental US to the Atlantic, and once it does it will explode. The location of this rapid deepening combined with the slow movement of the low will allow for the best dynamics—the cold conveyor belt (think of the classic comma head of precipitation), and midlevel frontogenesis—key components to big time snowfall amounts, to be effectively spent in that region.
All that said, that doesn’t preclude New England from good snow. Because of the sheer size of the storm and really strong mid level organization, even as the low tracks toward New England, snow would fall. This has been consistent on all the models. You see this on the latest GFS, which has snow solidly in Connecticut in about 96 hours or 1pm Saturday.
All that makes sense, right? So what is the problem? The breadcrumbs that I left from earlier in the discussion—the early cutoff, the rapid deepening in the Mid-Atlantic, lead us to a less than ideal spot for big snow, but it can still be overcome. The key, just as in many a storm, becomes the track.
In what would be the irony of ironies, the thing that would have helped New England last week when a coastal storm passed could be the thing that is its undoing. On the image above, which is a 500mb European ensemble plot, you see higher heights (orange shading). What you see is confluence and a high near Quebec. If you want a big storm, you need that in place in many cases. The problem here is that we have too much, which in the end, shuttles the storm further south. Not only did the European operational model go south midday with the storm, but it’s ensembles, the afternoon GFS, and the GFS Ensembles went south. The strength of the high to the north and confluence was a key factor. It is a subtle change, but a big one.
Before my snow-disliking friends begin spiking the football, what the models giveth the models can taketh away. The trend at this time is a movement further south, and that could continue. With all the pieces finally lining up however, and models moving from fantasy range to unreliable range to useful range for sensible weather impacts, there could be shifts. In a number of instances, models shift one way on a storm at this range, just to tick back to their original solutions in the very near term. This is something to watch.
Bottom Line
Before my snow-disliking friends begin spiking the football, what the models giveth the models can taketh away. The trend at this time is a movement further south, and that could continue. With all the pieces finally lining up however, and models moving from fantasy range to unreliable range to useful range for sensible weather impacts, there could be shifts. In a number of instances, models shift one way on a storm at this range, just to tick back to their original solutions in the very near term. This is something to watch.
Bottom Line
- Currently, I believe that we are still looking at a 60% chance of a plowable event, and the largest winter weather event Connecticut has seen this winter. All options remain on the table. I can see a foot for Connecticut or a non event. This is how much small changes matter.
- Because there has been a significant southern trend with the area of low pressure, which would substantially impact the snow totals that Connecticut receives, it is unwise to speculate on specific numbers. By this time tomorrow, this could be a complete non event.
- I do believe that the southern trend could stop however, or even tick further northward over the next 72 hours, which would make this a more impactful event. I believe there is a 50% chance of this happening.
- Even with lower snow totals, wind and coastal flooding would make this a high impact event for many within the state. This is something that needs to be monitored. Slight shifts in details will have a large impact.
We understand the need to give you the information you need to make informed decisions about the upcoming weekend. We will be here every step of the way to answer questions that you have. We encourage you to ask questions.
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-DB
