Good morning and merry Christmas Eve from Southern Connecticut Weather.
I'm working overtime this holiday.
A few days ago I talked about how despite the pattern change across much of the U.S. that will bring record warmth to much of the central portion of the country, we are sitting on the edge of the battle zone between warmth and cold.
This "Razor's Edge" pattern has indeed played itself out as I expected, with New England for the most part being on the colder side of that zone. While yesterday's event was a little too warm for meaningful snow for most, it did snow, and despite forecasts for mild temperatures for Christmas Eve and Christmas, here we are with seasonable temperatures for the holiday. For the most part, the trend has been toward cold, and that continues a theme that goes all the way back to August.
This coming storm has been the embodiment of that theme. A few days ago, it looked like a rain event. Then it looked like a mix event, trending colder. Now, we expect a well timed Arctic blast (another theme of the season so far) to produce an all snow event. The trick for this one however is the angle of approach and amount of blocking in place for the track.
We're on the edge of a significant winter storm. Let's talk about what we see right now.
I'm working overtime this holiday.
A few days ago I talked about how despite the pattern change across much of the U.S. that will bring record warmth to much of the central portion of the country, we are sitting on the edge of the battle zone between warmth and cold.
This "Razor's Edge" pattern has indeed played itself out as I expected, with New England for the most part being on the colder side of that zone. While yesterday's event was a little too warm for meaningful snow for most, it did snow, and despite forecasts for mild temperatures for Christmas Eve and Christmas, here we are with seasonable temperatures for the holiday. For the most part, the trend has been toward cold, and that continues a theme that goes all the way back to August.
This coming storm has been the embodiment of that theme. A few days ago, it looked like a rain event. Then it looked like a mix event, trending colder. Now, we expect a well timed Arctic blast (another theme of the season so far) to produce an all snow event. The trick for this one however is the angle of approach and amount of blocking in place for the track.
We're on the edge of a significant winter storm. Let's talk about what we see right now.
Above: The first call snow map. At this time I expect 3-6" in much of Fairfield County, with 2-4" in NW and central CT and 1-2" in eastern and NE CT. This is a highly volatile forecast where just a little trend west or east will make the difference between a significant snowstorm or minor snow event.
Overall Setup
Basically, whether or not we see a significant winter storm is all made possible by an atmospheric traffic jam. A few days ago, when some believed that we were in for a mild Christmas and especially post Christmas period, this was because guidance was effectively showing a more zonal flow on the other side of the big ridge that's developing over the central United States.
Just three days ago, this was the GFS for December 26. It had 50s in the state!
Overall Setup
Basically, whether or not we see a significant winter storm is all made possible by an atmospheric traffic jam. A few days ago, when some believed that we were in for a mild Christmas and especially post Christmas period, this was because guidance was effectively showing a more zonal flow on the other side of the big ridge that's developing over the central United States.
Just three days ago, this was the GFS for December 26. It had 50s in the state!
The signal for some type of post-Christmas storm had long existed, but with this depiction, the forecast was for rain.
So what happened? The trend in the 500mb pattern became substantially more blocked, which causes two critical things to happen. First, it allows for less of a zonal flow, meaning that cold from our source region in Canada can get shunted down into New England. Second, it forced our departed system and a follow up clipper to slow down to our northeast, jamming up the flow and forcing the next system in this fast flow regime to dive southeast. Note the "blue ball" to our northeast become stronger, and the ridge to our north into Greenland trend west and stronger.
These are massive shifts, and as a result, the shift at the surface have been massive as well. It should be noted that the Euro has generally had the right idea for longer, I am weighing that more than the GFS in this forecast.
That was a long overview of how we got here, but it's important in understanding what's happening with this storm and what's likely to happen after. While we will see storms that are too warm for snow, it is becoming increasingly likely that this blocked pattern will continue the delivery of Arctic cold and more storms into January.
Back to the storm. With the block in place, first we will get a shot of Arctic air to reach the region Christmas night into Friday. That's step one. Our fast moving storm will be running into that cold, and with the strength of the block will not be able to take a more eastward angle or intensify too much. In fact, this will be another situation where the system is probably weakening aloft or middling along as it moves into the region.
This means that the strength of the block is crucial to how far northeast the precipitation shield can get and how much space it has to gracefully deamplify. Basically, the stronger the press of the block, the further west/south the storm goes.
That was a long overview of how we got here, but it's important in understanding what's happening with this storm and what's likely to happen after. While we will see storms that are too warm for snow, it is becoming increasingly likely that this blocked pattern will continue the delivery of Arctic cold and more storms into January.
Back to the storm. With the block in place, first we will get a shot of Arctic air to reach the region Christmas night into Friday. That's step one. Our fast moving storm will be running into that cold, and with the strength of the block will not be able to take a more eastward angle or intensify too much. In fact, this will be another situation where the system is probably weakening aloft or middling along as it moves into the region.
This means that the strength of the block is crucial to how far northeast the precipitation shield can get and how much space it has to gracefully deamplify. Basically, the stronger the press of the block, the further west/south the storm goes.
Above: the 500mb evolution of the storm. Note the Christmas Day clipper to our north and how it slows down and tries to back up at the far right of the image. That's our block.
Basically, very small changes make a big difference here in CT. Let's get to the forecast.
Timing
Once again, we are dealing with a quick mover. If you plan to travel earlier in the day on Friday, you should be fine. By early evening, probably around 7pm, we're likely to have snow on our doorstep and overspreading the state afterward. The good thing for travelers is that this looks like a Friday evening to Saturday morning event, meaning that daytime travel shouldn't be impacted in CT too much. Depending on the track though, expect flight delays and possible cancellations, especially if the storm is stronger. Some guidance keeps the snow around into Saturday afternoon, and while that's plausible it is just something worth watching right now.
Basically, very small changes make a big difference here in CT. Let's get to the forecast.
Timing
Once again, we are dealing with a quick mover. If you plan to travel earlier in the day on Friday, you should be fine. By early evening, probably around 7pm, we're likely to have snow on our doorstep and overspreading the state afterward. The good thing for travelers is that this looks like a Friday evening to Saturday morning event, meaning that daytime travel shouldn't be impacted in CT too much. Depending on the track though, expect flight delays and possible cancellations, especially if the storm is stronger. Some guidance keeps the snow around into Saturday afternoon, and while that's plausible it is just something worth watching right now.
Above: Storm evolution on the 06z Euro. Snow is in and out in a hurry, which also lowers confidence in snowfall totals.
Snow & Ice Accumulation
Here's the first call map again. The further southwest you are the better odds you have of a significant snowfall. There is likely to be a narrow band of heavy snow at the front end of the system, with lighter snows the further east and northeast you are. As it stands now, SW CT is in the potential jackpot zone, with a lighter 2-4 inches possible for most of NW and central CT, and a zone of 1-2" in eastern CT. Just a 25-50 mile shift in either direction makes this a more significant winter storm or another nuisance event.
With cold air in place, despite the similar track to yesterday this is a very different outcome. This should be all snow from start to finish, unless there's a dramatic change in the track, which seems unlikely at this point.
Wind & Power Outages
Because this is likely weakening as it rolls into the region, I don't think this is a windy storm. That said, there may still be some sort of pressure gradient so it may be breezy. I don't anticipate significant power outages.
Overall Impact
This may be the most difficult question to answer. If you are in SW CT and it's snowing into Saturday morning, it may be high impact. If you are in eastern CT and this is a glancing blow it may be minor. For now, given the timing around the holiday, potential for heavy snow, and likelihood of a gradient with regard to snowfall, let's call this a moderate impact event for now. This will be refined tomorrow.
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 SCW.
-DB
Here's the first call map again. The further southwest you are the better odds you have of a significant snowfall. There is likely to be a narrow band of heavy snow at the front end of the system, with lighter snows the further east and northeast you are. As it stands now, SW CT is in the potential jackpot zone, with a lighter 2-4 inches possible for most of NW and central CT, and a zone of 1-2" in eastern CT. Just a 25-50 mile shift in either direction makes this a more significant winter storm or another nuisance event.
With cold air in place, despite the similar track to yesterday this is a very different outcome. This should be all snow from start to finish, unless there's a dramatic change in the track, which seems unlikely at this point.
Wind & Power Outages
Because this is likely weakening as it rolls into the region, I don't think this is a windy storm. That said, there may still be some sort of pressure gradient so it may be breezy. I don't anticipate significant power outages.
Overall Impact
This may be the most difficult question to answer. If you are in SW CT and it's snowing into Saturday morning, it may be high impact. If you are in eastern CT and this is a glancing blow it may be minor. For now, given the timing around the holiday, potential for heavy snow, and likelihood of a gradient with regard to snowfall, let's call this a moderate impact event for now. This will be refined tomorrow.
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 SCW.
-DB
