Good evening from Southern Connecticut Weather.
There haven't been many changes to the winter storm watches today. The only addition has been a Winter Weather Advisory issued for Windham County and coastal Fairfield County. There's a reason for that.
Although we are closer in time to the start of this winter storm, uncertainty for Connecticut has increased quite noticeably in the last 24 hours. Here is our latest update.
There haven't been many changes to the winter storm watches today. The only addition has been a Winter Weather Advisory issued for Windham County and coastal Fairfield County. There's a reason for that.
Although we are closer in time to the start of this winter storm, uncertainty for Connecticut has increased quite noticeably in the last 24 hours. Here is our latest update.
There are a couple of things to highlight here. The ranges have been maintained but shifted quite a bit.
2-4 Inch Zone
Our 2-4 inch zone has been expanded. In this zone, we are expecting most of the snow to fall during Part I, when the state receives a burst of snow and temperatures are most conducive for SE CT accumulation. This zone was expanded because the guidance is now unanimous in having some sort of dry slot aloft that would limit precipitation on Monday, particularly in the afternoon when we previously expected Part II to get going.
4-8 Inch Zone
Our 4-8 inch zone has been expanded to cover much of the state, up into much of Tolland and Windham County. This zone could easily be reduced, but I do still believe that the guidance, which shows a massive dry slot in Connecticut, is overdone. As a result, most end up getting about what we originally thought, but there's a lower floor and lower ceiling with Part II.
6-12 Inch Zone
Our 6-12 in zone has been reduced to the norther tier of Fairfield County, Central and northern Hartford County, and a smaller sliver of Tolland and Windham Counties. There is higher confidence that both Part I and Part II will produce as originally expected.
8-14 Inch Zone
Our 8-14 inch zone was reduced slightly. There are no significant changes in our expectations for conditions here.
2-4 Inch Zone
Our 2-4 inch zone has been expanded. In this zone, we are expecting most of the snow to fall during Part I, when the state receives a burst of snow and temperatures are most conducive for SE CT accumulation. This zone was expanded because the guidance is now unanimous in having some sort of dry slot aloft that would limit precipitation on Monday, particularly in the afternoon when we previously expected Part II to get going.
4-8 Inch Zone
Our 4-8 inch zone has been expanded to cover much of the state, up into much of Tolland and Windham County. This zone could easily be reduced, but I do still believe that the guidance, which shows a massive dry slot in Connecticut, is overdone. As a result, most end up getting about what we originally thought, but there's a lower floor and lower ceiling with Part II.
6-12 Inch Zone
Our 6-12 in zone has been reduced to the norther tier of Fairfield County, Central and northern Hartford County, and a smaller sliver of Tolland and Windham Counties. There is higher confidence that both Part I and Part II will produce as originally expected.
8-14 Inch Zone
Our 8-14 inch zone was reduced slightly. There are no significant changes in our expectations for conditions here.
Above: GFS trend for Monday evening since yesterday. Note how the dry slot was only introduced recently with a much more ragged precipitation shield appearance. I am not fully buying, but with the other guidance showing something similar at this time, it would be hard to discount. Let's take a look at Part I and Part II in more detail.
Part I
Timing
The storm will start off as snow statewide. The timing remains more or less the same, though with the current dew points outside it is possible that onset is a bit slower with snow having trouble reaching the ground early. Snow should begin between 9am to 2pm from SW to NE. After a burst of snow that should drop a couple of inches, we will transition to sleet and freezing rain for most over the course of the afternoon. By evening, most should be mixing. Rain is likely for SE portions of the state during the overnight hours, and the mixing will likely continue and taper a bit into Monday morning. We should begin to see more influence from Part II begin in the afternoon.
Impacts
As mentioned above, Part I should drop a few inches before icing via sleet and freezing rain begins. Roads should not be too bad at first, so those traveling in the morning will likely be ok. Once we get into the afternoon and evening road conditions will deteriorate. Given the uncertainty about how much mixing occurs, it is an open question as to whether schools and businesses are closed Monday. I think the further away from the coast you are, the more likely widespread cancellations are. There may be significant icing that occurs away from the coast.
Part I
Timing
The storm will start off as snow statewide. The timing remains more or less the same, though with the current dew points outside it is possible that onset is a bit slower with snow having trouble reaching the ground early. Snow should begin between 9am to 2pm from SW to NE. After a burst of snow that should drop a couple of inches, we will transition to sleet and freezing rain for most over the course of the afternoon. By evening, most should be mixing. Rain is likely for SE portions of the state during the overnight hours, and the mixing will likely continue and taper a bit into Monday morning. We should begin to see more influence from Part II begin in the afternoon.
Impacts
As mentioned above, Part I should drop a few inches before icing via sleet and freezing rain begins. Roads should not be too bad at first, so those traveling in the morning will likely be ok. Once we get into the afternoon and evening road conditions will deteriorate. Given the uncertainty about how much mixing occurs, it is an open question as to whether schools and businesses are closed Monday. I think the further away from the coast you are, the more likely widespread cancellations are. There may be significant icing that occurs away from the coast.
Above: HERF Ensemble view of accumulated freezing rain. This is a fairly robust signal for freezing rain for much of the state into Monday morning.
Part II
Timing
Part II is likely to begin taking over late Monday morning into Monday afternoon, as a secondary low develops off the coast. Just like yesterday, this is expected to be a mostly snow event as temperatures drop. Part II will likely start off light because of the potential for dry slotting, but snow is likely to last in some fashion into Tuesday morning.
Impacts
This is where a lot of the uncertainty lies as of this discussion. Usually, I would be more bullish given the conditions--a rapidly deepening low just underneath the state as temperatures crash--but with strong banding comes strong subsidence. The guidance has converged on dry slotting encompassing much of Connecticut, but I do not buy that fully yet.
Slight shifts would put us on the higher end of the projected totals, if not exceed them. The dry slot coming to fruition would likely put us on the lower end of totals. We'll have to watch closely. We're still nearly 48 hours from Part II beginning. That's a lot of time for more changes to occur.
Widespread delays and cancellations are possible on Tuesday, but that will need to be reevaluated on Monday once we see how Part II produces.
Part II
Timing
Part II is likely to begin taking over late Monday morning into Monday afternoon, as a secondary low develops off the coast. Just like yesterday, this is expected to be a mostly snow event as temperatures drop. Part II will likely start off light because of the potential for dry slotting, but snow is likely to last in some fashion into Tuesday morning.
Impacts
This is where a lot of the uncertainty lies as of this discussion. Usually, I would be more bullish given the conditions--a rapidly deepening low just underneath the state as temperatures crash--but with strong banding comes strong subsidence. The guidance has converged on dry slotting encompassing much of Connecticut, but I do not buy that fully yet.
Slight shifts would put us on the higher end of the projected totals, if not exceed them. The dry slot coming to fruition would likely put us on the lower end of totals. We'll have to watch closely. We're still nearly 48 hours from Part II beginning. That's a lot of time for more changes to occur.
Widespread delays and cancellations are possible on Tuesday, but that will need to be reevaluated on Monday once we see how Part II produces.
Above 12z European model depiction for Tuesday morning. Light snow may still be falling at that time as Part II is slow to depart.
Bottom Line
Thank you for reading SCW.
-DB
Bottom Line
- A major and long duration winter storm is still expected to impact Connecticut from Sunday morning/afternoon through Monday night/Tuesday morning. This is expected to be a moderate (SE and southern CT) to high impact (northern CT) winter weather event, especially if Part II is more robust.
- 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 Sunday night. Monday is an open question depending on whether there is continued mixing at the shoreline.
- 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.
- In addition, there is significant uncertainty over the intensity of Part II. Where the banding sets up is critical in overall snowfall totals and how widespread delays and/or cancellations there are on Tuesday.
Thank you for reading SCW.
-DB
