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 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.
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.
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.
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 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.
- 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.
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