Good evening from Southern Connecticut Weather.
As the headline states, we are expecting a major and long duration winter storm to impact Connecticut beginning on Sunday. We expect a mixed bag of precipitation types, and both snow and icing are likely to cause significant travel delays and cancellations Sunday and Monday, with the possibility of delays or cancellations continuing into Tuesday.
Before diving into the details, here's our First Call map for the entire storm. I have moderate confidence in this forecast. Keep in mind that these are ranges. No one is guaranteed the maximum value.
Let's examine the first winter storm of the season.
As the headline states, we are expecting a major and long duration winter storm to impact Connecticut beginning on Sunday. We expect a mixed bag of precipitation types, and both snow and icing are likely to cause significant travel delays and cancellations Sunday and Monday, with the possibility of delays or cancellations continuing into Tuesday.
Before diving into the details, here's our First Call map for the entire storm. I have moderate confidence in this forecast. Keep in mind that these are ranges. No one is guaranteed the maximum value.
Let's examine the first winter storm of the season.
The National Weather Service is beginning to issue Winter Storm Watches for much of Connecticut. More watches, and eventually, warnings, are likely to to be issued today and tomorrow.
The storm that has brought significant weather across much of the western United States is the culprit for our upcoming winter weather event. It has been traversing the nation for days, and is expected to reach our region on Sunday. I view this system as having two parts:
Part I--Sunday into Early Monday
This part will feature overrunning precipitation. Essentially, as the storm approaches, warmer air will rise over the colder surface air and produce snow. Snowfall should begin between approximately 9am and 1pm from SW to NE. This part should produce accumulating snowfall during the afternoon, but as the warm air begins to erode the mid levels of the atmosphere, a change to mixed precipitation and even rain, in SE CT, is likely.
The critical questions here are how much snow falls before mixing begins, and how prolonged a period of icing (sleet and/or freezing rain) occurs.
The storm that has brought significant weather across much of the western United States is the culprit for our upcoming winter weather event. It has been traversing the nation for days, and is expected to reach our region on Sunday. I view this system as having two parts:
Part I--Sunday into Early Monday
This part will feature overrunning precipitation. Essentially, as the storm approaches, warmer air will rise over the colder surface air and produce snow. Snowfall should begin between approximately 9am and 1pm from SW to NE. This part should produce accumulating snowfall during the afternoon, but as the warm air begins to erode the mid levels of the atmosphere, a change to mixed precipitation and even rain, in SE CT, is likely.
The critical questions here are how much snow falls before mixing begins, and how prolonged a period of icing (sleet and/or freezing rain) occurs.
Above is the latest high resolution NAM, showing the onset of snow statewide on Sunday and the start of mixing. Snowfall may be heavy at times on Sunday before the mixing begins, causing travel delays.
My current thinking is that for interior portions of the state, the northern four counties, this is a fully frozen precipitation storm. Temperatures there will drop below freezing. For southern portions, temperatures will hover near freezing or just below depending on proximity to the coast.
Part I should produce accumulating snow for virtually everyone before the mixed precipitation line creeps northward. I think it's likely that most areas outside the NW hills will see mixed precipitation. Icing is possible as a result, and it may be a prolonged period of icing.
I think the mixed precipitation is predominantly sleet, but there may be a period of freezing rain. That could cause significant problems later on Sunday and into early Monday. At this time, I expect widespread cancellations on Monday.
Below is a quick primer on precipitation types during winter storms. I think the mixed precipitation, rather than snowfall, is the main story of Part I.
My current thinking is that for interior portions of the state, the northern four counties, this is a fully frozen precipitation storm. Temperatures there will drop below freezing. For southern portions, temperatures will hover near freezing or just below depending on proximity to the coast.
Part I should produce accumulating snow for virtually everyone before the mixed precipitation line creeps northward. I think it's likely that most areas outside the NW hills will see mixed precipitation. Icing is possible as a result, and it may be a prolonged period of icing.
I think the mixed precipitation is predominantly sleet, but there may be a period of freezing rain. That could cause significant problems later on Sunday and into early Monday. At this time, I expect widespread cancellations on Monday.
Below is a quick primer on precipitation types during winter storms. I think the mixed precipitation, rather than snowfall, is the main story of Part I.
Part II--Monday Afternoon into Tuesday Morning
Although all generally the same system, Part II is more of the snow element of the winter storm.
Overnight Sunday into Monday, a coastal low develops off the coast. As it does so, it intensifies rather quickly and as a boundary bringing colder air pushes through the state, the entire region changes over to snow. You can see it clearly via the high resolution NAM animations below, which cover approximately 1am Monday morning into 1am Tuesday morning.
Although all generally the same system, Part II is more of the snow element of the winter storm.
Overnight Sunday into Monday, a coastal low develops off the coast. As it does so, it intensifies rather quickly and as a boundary bringing colder air pushes through the state, the entire region changes over to snow. You can see it clearly via the high resolution NAM animations below, which cover approximately 1am Monday morning into 1am Tuesday morning.
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On the left, we are looking at a forecast of 850mb temperatures. These are temperatures in a layer above the surface. Notice how over most of CT at the start of the animation, temperatures are above freezing. That is a signal for mixed precipitation. As the animation continues you see those temperatures crash below freezing toward the coast. That's where we see the coastal wrap up and everything changes to snow via the depiction on the right.
Monday is snowy as a result, statewide. Note that on this NAM run, we see evidence of banding. The NAM is not my model of choice here--I am showing it because of how easily viewable it is. I expect stronger lift, which would result in a more robust precipitation shield/banding. I expect snow will be heavy at times.
Monday is snowy as a result, statewide. Note that on this NAM run, we see evidence of banding. The NAM is not my model of choice here--I am showing it because of how easily viewable it is. I expect stronger lift, which would result in a more robust precipitation shield/banding. I expect snow will be heavy at times.
This is the Euro depiction of precipitation early Monday afternoon. Even though we see parts of southern CT as rain and mixed precipitation, a look at the surface, 925mb, and 850mb tells the same story--most are likely to be snowing and possibly snowing heavily as the day progresses on Monday. Image courtesy of weathermodels.com
This part of the storm may also be the long duration piece. It is unanimous on the guidance that there is a mini "stall" of this low as it wraps up, which could prolong snowfall into early Tuesday. If that is the case, Tuesday could begin with significant delays, if not cancellations.
Below is the very latest GFS model run. This is posted to to show a depiction of the event. I do not expect rain in northern CT, so do not take this depiction verbatim.
This part of the storm may also be the long duration piece. It is unanimous on the guidance that there is a mini "stall" of this low as it wraps up, which could prolong snowfall into early Tuesday. If that is the case, Tuesday could begin with significant delays, if not cancellations.
Below is the very latest GFS model run. This is posted to to show a depiction of the event. I do not expect rain in northern CT, so do not take this depiction verbatim.
Bottom Line
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-DB
- A major and long duration winter storm is expected to impact Connecticut from Sunday morning/afternoon through Monday night/Tuesday morning. This is expected to be a moderate (SE CT) to high impact (rest of CT) winter weather event, especially on the roads.
- Even with lower projected snowfall amounts in southern portions of the state, a period of icing is expected that will likely cause significant travel delays and possible isolated to scattered power outages as breezy conditions occur Sunday night into Monday.
- There is still significant uncertainty over how quickly the mixed precipitation line pushes north, how far it pushes north, and how long mixed precipitation lasts. This will have a significant impact on eventual snowfall totals, but not on the overall impact of the storm.
- Everyone is expected to transition back to accumulating snow on Monday which is increasingly likely to last into Tuesday morning.
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
