Good evening from Southern Connecticut Weather!
Winter looks poised to start off quickly, with our first winter storm of the season coming in the next 48 hours. As is usually the case with early season storms, there is high uncertainty over what looks to be a mixed bag event. Our first winter storm watch of the season is up for northern Litchfield County, and while there are no other winter weather headlines up for the state at the time of this forecast, they're likely coming (winter weather advisories most likely) as confidence increases. What can we expect? Let's dive in.
Winter looks poised to start off quickly, with our first winter storm of the season coming in the next 48 hours. As is usually the case with early season storms, there is high uncertainty over what looks to be a mixed bag event. Our first winter storm watch of the season is up for northern Litchfield County, and while there are no other winter weather headlines up for the state at the time of this forecast, they're likely coming (winter weather advisories most likely) as confidence increases. What can we expect? Let's dive in.
Above: Our first call snow map for the coming winter storm. In the southern CT zone, we expect a coating to 2" with the least at the immediate shoreline. There we expect a snow to mix to rain event. For much of central and eastern CT we expect 2-5" of snow, with the higher amounts focused the further north and west you are. Here we think the storm stays mostly snow, but it's an extremely close call along the gradient between C-2 and 2-5. Finally, we have a 3-6" zone for NW CT. This is the area most likely to stay below freezing and snow the entire time.
Overall Setup
There isn't much change from what we described yesterday. As expected, our pre-frontal rain is moving through the state and will clear later tonight. A cold front will bring our antecedent air mass, and our Monday--the first day of December and Meteorological Winter, will be colder than normal. Get used to hearing that for the first half of December.
As our storm approaches early Tuesday, the high pressure holding the cold air in the region will begin retreating, which will open the door for our mixed bag system. Again, that's a totally normal evolution for a winter storm, especially this early in the season.
The differences between the 500mb evolution of our storm are subtle between the GFS and Euro, but they're significant enough to mean very different things for our weather on Tuesday.
Overall Setup
There isn't much change from what we described yesterday. As expected, our pre-frontal rain is moving through the state and will clear later tonight. A cold front will bring our antecedent air mass, and our Monday--the first day of December and Meteorological Winter, will be colder than normal. Get used to hearing that for the first half of December.
As our storm approaches early Tuesday, the high pressure holding the cold air in the region will begin retreating, which will open the door for our mixed bag system. Again, that's a totally normal evolution for a winter storm, especially this early in the season.
The differences between the 500mb evolution of our storm are subtle between the GFS and Euro, but they're significant enough to mean very different things for our weather on Tuesday.
Above: the 18z GFS showing the 500mb evolution of our system from late Monday through early Wednesday. Below is the 18z Euro depiction for the same time frame. In the images, you can see how the shortwave in the GFS continues to be a bit more robust and north, while the Euro is a bit flatter and further south.
The result of these differences plays itself out in critical ways. With the GFS more amplified and north, it introduces more southerly flow in advance of our system, warming the surface and the column of air all the way up to 850mb. That is a recipe for mixing and rain for a substantial portion of the state, especially southern CT where Long Island Sound temperatures are still approximately 50 degrees. This is much less pronounced on the Euro, as a flatter system doesn't have nearly as much inland push of warmth.
The best way to see this is by looking at temperatures aloft. This is 850mb at about 7pm on the GFS (top) and Euro (bottom). The Euro is much colder even down to the coast. That would increase the odds of staying snow for longer even down to the coast. The GFS would probably bring rain well inland.
The best way to see this is by looking at temperatures aloft. This is 850mb at about 7pm on the GFS (top) and Euro (bottom). The Euro is much colder even down to the coast. That would increase the odds of staying snow for longer even down to the coast. The GFS would probably bring rain well inland.
Remember though, models are guidance not gospel. And those 10:1 ratio snow maps are the devil. A forecaster needs to sift through the noise to understand the trend and environment. Of the three scenarios presented yesterday, it now looks like the most common forecast method of blending guidance is the best way to go. With that overview out of the way, let's get to the forecast.
Timing
Regardless of what happens with the rain/snow line, the guidance is already in good agreement on the timing for this storm. Snow will begin across the state Tuesday morning from SW to NE as the storm moves into the region. Exact timing TBD. The worst of the storm is likely mid-afternoon into mid-evening, and the precipitation likely starts shutting off late Tuesday night into early Wednesday morning.
Timing
Regardless of what happens with the rain/snow line, the guidance is already in good agreement on the timing for this storm. Snow will begin across the state Tuesday morning from SW to NE as the storm moves into the region. Exact timing TBD. The worst of the storm is likely mid-afternoon into mid-evening, and the precipitation likely starts shutting off late Tuesday night into early Wednesday morning.
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Snow & Ice Accumulation
As you saw at the beginning of the discussion, a blend of the guidance gives us our first call snow map. In the southern CT zone, we expect a coating to 2" with the least at the immediate shoreline. This is because we expect a snow to brief mix to rain event.
For much of central and eastern CT we expect 2-5" of snow, with the higher amounts focused the further north and west you are. Those are the areas least likely to have the surface and mid levels warm above freezing. Here we think the storm stays mostly snow, but it's an extremely close call.
Then the easiest part of the forecast. In NW CT we expect 3-6". This may be a touch conservative, but the speed of the storm and potential for this to shuffle further south or less amped means we don't feel the need to go with bigger totals. This is the area most likely to stay below freezing and remain snow the entire time.
Finally, it's important to note that even though we may have periods of mixing in the state on Tuesday, we expect any mixing to be sleet rather than freezing rain, and for any icing from mixed precipitation to be minor at best.
As you saw at the beginning of the discussion, a blend of the guidance gives us our first call snow map. In the southern CT zone, we expect a coating to 2" with the least at the immediate shoreline. This is because we expect a snow to brief mix to rain event.
For much of central and eastern CT we expect 2-5" of snow, with the higher amounts focused the further north and west you are. Those are the areas least likely to have the surface and mid levels warm above freezing. Here we think the storm stays mostly snow, but it's an extremely close call.
Then the easiest part of the forecast. In NW CT we expect 3-6". This may be a touch conservative, but the speed of the storm and potential for this to shuffle further south or less amped means we don't feel the need to go with bigger totals. This is the area most likely to stay below freezing and remain snow the entire time.
Finally, it's important to note that even though we may have periods of mixing in the state on Tuesday, we expect any mixing to be sleet rather than freezing rain, and for any icing from mixed precipitation to be minor at best.
Wind & Power Outages
Although this is a modestly strong coastal low as coastal lows go, the lack of a significant pressure gradient and the lack of a closed off and well organized low means that we do not expect significant wind or power issues.
Overall Impact
Now, some will say that this is a nothing burger and that's fine, but we do this every year: that perspective is not entirely true.
Timing often makes a big difference in impact, and the fact that we will likely have accumulating snow starting Tuesday morning and the worst of the storm happening in the afternoon/evening means that this is probably a higher impact event than it'd otherwise be if you just looked at the snow map. While yes it is New England and we certainly get bigger snowfalls, everybody knows that there are big impacts on many if there are widespread school delays and cancellations, and if the roads are a mess when you're commuting to or from work.
In southern CT we expect a minor impact event, but even there we could see widespread school delays. For inland areas that are in the 2-5" or 3-6" zone, widespread school cancellations and road delays are possible, triggering a moderate impact event.
Expect our final call forecast tomorrow.
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 SCW.
-DB
Although this is a modestly strong coastal low as coastal lows go, the lack of a significant pressure gradient and the lack of a closed off and well organized low means that we do not expect significant wind or power issues.
Overall Impact
Now, some will say that this is a nothing burger and that's fine, but we do this every year: that perspective is not entirely true.
Timing often makes a big difference in impact, and the fact that we will likely have accumulating snow starting Tuesday morning and the worst of the storm happening in the afternoon/evening means that this is probably a higher impact event than it'd otherwise be if you just looked at the snow map. While yes it is New England and we certainly get bigger snowfalls, everybody knows that there are big impacts on many if there are widespread school delays and cancellations, and if the roads are a mess when you're commuting to or from work.
In southern CT we expect a minor impact event, but even there we could see widespread school delays. For inland areas that are in the 2-5" or 3-6" zone, widespread school cancellations and road delays are possible, triggering a moderate impact event.
Expect our final call forecast tomorrow.
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 SCW.
-DB
