Good afternoon from SCW!
In our first call yesterday, Don laid out the setup that’s coming to the state tonight into tomorrow; a strong low is cutting to our west and warming the mid levels while at the same time, high pressure to the north is causing colder air to filter down into the state. This is a classic setup for an ice storm, and if temperatures were a couple of degrees colder, we would be looking at a significant to potentially historic ice storm in the state.
The good news is that we have a warm antecedent air mass in place and the high that’s coming in isn’t positioned in quite the right spot to see really effective cold air drainage, so the impacts will be substantially reduced from what they could otherwise have been. However, we are still expecting icing across portions of the state, with the potential for a high impact icing event (0.5”+ of ice) in the northwest hills. Winter Weather Advisories are up for all of the northern counties, with the exception of northern Litchfield county where an Ice Storm Warning is in effect.
Here’s a look at our final accretion map for this event.
In our first call yesterday, Don laid out the setup that’s coming to the state tonight into tomorrow; a strong low is cutting to our west and warming the mid levels while at the same time, high pressure to the north is causing colder air to filter down into the state. This is a classic setup for an ice storm, and if temperatures were a couple of degrees colder, we would be looking at a significant to potentially historic ice storm in the state.
The good news is that we have a warm antecedent air mass in place and the high that’s coming in isn’t positioned in quite the right spot to see really effective cold air drainage, so the impacts will be substantially reduced from what they could otherwise have been. However, we are still expecting icing across portions of the state, with the potential for a high impact icing event (0.5”+ of ice) in the northwest hills. Winter Weather Advisories are up for all of the northern counties, with the exception of northern Litchfield county where an Ice Storm Warning is in effect.
Here’s a look at our final accretion map for this event.
Since yesterday, the guidance has remained relatively steady, advertising significant icing in the northwest hills, but little to nothing elsewhere. Don wrote yesterday how models tend to under-estimate surface cold, and for whatever reason often fail to “see” the high pressure to the north that will keep temps lower. The more classic depiction of scenario is when a cold airmass is already in place and models are too quick to move it out, but the same theory applies here to cold seeping in as well. In those sorts of situations you tend to see a last-minute tick colder as the models recognize the influence of the high and that surface temps will remain cooler, and interestingly here we haven’t really seen that, if anything, the guidance has wobbled slightly warmer today, and if you believe the models, this is mainly just a cold rain outside of the northwest hills. However, we are meteorologists and forecasters, not modelologists, and I’ve seen this setup enough times to not take it at face value. It is certainly possible that everyone outside of the hills wakes up to a cold rain tomorrow morning, and in fact I think it’s just as likely that we see little to no icing as it is that we see significant accretions. That said, given the impacts that even a trace of ice can have, it’s important to be aware of and highlight the possibility of an overperformer in this situation.
A notable exception to the guidance consensus is the HREF ensemble, which has accretions across most of the northern portion of the state. As an extremely high-resolution model, it may be more adept at noticing the cold air drainage than some of the other global models, and so the fact that it’s showing this scenario is worth considering.
Here’s total ice accretions from the last three runs of the NAM (showing the slight warming trend) and also from the most recent run of the HREF.
A notable exception to the guidance consensus is the HREF ensemble, which has accretions across most of the northern portion of the state. As an extremely high-resolution model, it may be more adept at noticing the cold air drainage than some of the other global models, and so the fact that it’s showing this scenario is worth considering.
Here’s total ice accretions from the last three runs of the NAM (showing the slight warming trend) and also from the most recent run of the HREF.
Given the slight warming trend and the absence of the models “recognizing” the cold, we’ve tightened up the zones a bit to focus on the inland areas above ~800 feet where we believe cold air will be more likely to hold. That said, surface temps are very terrain dependent, and we expect significant variation in icing within very small distances based on the topography of a specific town or even neighborhood. It’s entirely possible that a sheltered hollow in our glaze zone will end up with a quarter of an inch of ice, while a wide open area in our 0.3”+ zone will get just a glaze or a tenth of an inch of ice. It’s impossible to illustrate the thousands of micro-climates within the state on a map, so we’re forced to broad-brush and hope for the best, but take the ranges as guidance, not as absolutes. Unlike a snow map, this isn’t the sort of map that we’re expecting to be correct for everyone.
For the southern portion of the state, we are reasonably confident that this is a cold rain event. I wouldn’t rule out a light glaze in the elevations of Fairfield and New Haven counties, but beyond that, I think this is an annoyance more than it is a winter event.
For northern areas outside of the hills, I still think this is primarily a cold rain, but a glaze of ice is certainly possible and I do expect some totals up to about a tenth of an inch of ice or so to occur in the favored areas. In the hills, where elevation will make things just a touch colder, this will be a much higher-impact event. Guidance is in good agreement that the highest elevations of NWCT may never turn over to plain rain, and a half of an inch of ice or more is a distinct possibility there. On the fringe of the NW hills and in the NE hills, I would look for generally a tenth or two of an inch of ice accretion, but I think it is there that the biggest surprise could be in store; if guidance is under-estimating the depth of the cold even slightly, there is the potential for significant icing there as well.
All in all, we’re expecting rain/freezing rain to move into the state late this afternoon/this evening, with temperatures gradually warming throughout the day tomorrow and changing everyone outside of the hills over to plain rain. One thing to watch is whether the development of a coastal low will allow for cold air to reestablish itself in northern Connecticut, bringing more wintry precipitation. We will see rain persist through Tuesday morning, but things should clear out in time for NYE festivities; right now it’s looking like temps in the low to mid 30s for Tuesday night as shown on the hi-res NAM below.
For the southern portion of the state, we are reasonably confident that this is a cold rain event. I wouldn’t rule out a light glaze in the elevations of Fairfield and New Haven counties, but beyond that, I think this is an annoyance more than it is a winter event.
For northern areas outside of the hills, I still think this is primarily a cold rain, but a glaze of ice is certainly possible and I do expect some totals up to about a tenth of an inch of ice or so to occur in the favored areas. In the hills, where elevation will make things just a touch colder, this will be a much higher-impact event. Guidance is in good agreement that the highest elevations of NWCT may never turn over to plain rain, and a half of an inch of ice or more is a distinct possibility there. On the fringe of the NW hills and in the NE hills, I would look for generally a tenth or two of an inch of ice accretion, but I think it is there that the biggest surprise could be in store; if guidance is under-estimating the depth of the cold even slightly, there is the potential for significant icing there as well.
All in all, we’re expecting rain/freezing rain to move into the state late this afternoon/this evening, with temperatures gradually warming throughout the day tomorrow and changing everyone outside of the hills over to plain rain. One thing to watch is whether the development of a coastal low will allow for cold air to reestablish itself in northern Connecticut, bringing more wintry precipitation. We will see rain persist through Tuesday morning, but things should clear out in time for NYE festivities; right now it’s looking like temps in the low to mid 30s for Tuesday night as shown on the hi-res NAM below.
Impacts
Icing--No Impact Southern Connecticut/Low-Moderate-High Inland
There is no impact expected in southern Connecticut when it comes to icing. For most of northern CT, this should be a relatively low impact event, but in the hilly sections of NW and NE CT we are expecting more of a moderate icing impact. In the highest elevations of the NW hills (>1000’), this has the potential to be a high-impact icing event. As I explained earlier, I’d hedge towards the lower end of the ranges for most or even below that, but the possibility exists for a more impactful event and it’s important to highlight that.
Wind--None
I do not expect any significant wind with this storm.
Power Outages--Low/Moderate in NWCT
I would expect some scattered power outages in the NW hills and possibly in the NE hills should the system overperform, but do not expect widespread issues.
Timing--Low
The storm starts on a Sunday night and although Monday's morning and afternoon commute could be impacted, with kids at home for vacation and many workers doing the same, the roads should be less congested and our crews should be in a good place to keep major roadways in good shape.
Road Conditions--Low/Moderate
In areas where it's just raining, the normal level of caution should be exercised. In areas of central CT that do not receive a lot of icing, you should be careful but I expect main roads to be passable. However, it only takes a small amount of ice to cause serious issues if roads are not continuously treated, and so I expect that there will be difficult travel on secondary and tertiary roads in the hills tomorrow.
All in all, while this is likely just annoying cold rain for most of us, the potential exists for an icy day tomorrow, especially in our elevated areas, and it’s important to be aware of the potential and plan accordingly if needed. It’s worth mentioning that to our north this is expected to be a severe ice storm, with half an inch or more of accretion in the Berkshires and Hudson Valley up into Vermont and southwest NH, so I would not plan on travel that passes through those areas.
We’ll have updates through the day tomorrow as necessary, and please feel free to ask any questions you have on our social channels. Thank you for reading SCW!
-SA
Icing--No Impact Southern Connecticut/Low-Moderate-High Inland
There is no impact expected in southern Connecticut when it comes to icing. For most of northern CT, this should be a relatively low impact event, but in the hilly sections of NW and NE CT we are expecting more of a moderate icing impact. In the highest elevations of the NW hills (>1000’), this has the potential to be a high-impact icing event. As I explained earlier, I’d hedge towards the lower end of the ranges for most or even below that, but the possibility exists for a more impactful event and it’s important to highlight that.
Wind--None
I do not expect any significant wind with this storm.
Power Outages--Low/Moderate in NWCT
I would expect some scattered power outages in the NW hills and possibly in the NE hills should the system overperform, but do not expect widespread issues.
Timing--Low
The storm starts on a Sunday night and although Monday's morning and afternoon commute could be impacted, with kids at home for vacation and many workers doing the same, the roads should be less congested and our crews should be in a good place to keep major roadways in good shape.
Road Conditions--Low/Moderate
In areas where it's just raining, the normal level of caution should be exercised. In areas of central CT that do not receive a lot of icing, you should be careful but I expect main roads to be passable. However, it only takes a small amount of ice to cause serious issues if roads are not continuously treated, and so I expect that there will be difficult travel on secondary and tertiary roads in the hills tomorrow.
All in all, while this is likely just annoying cold rain for most of us, the potential exists for an icy day tomorrow, especially in our elevated areas, and it’s important to be aware of the potential and plan accordingly if needed. It’s worth mentioning that to our north this is expected to be a severe ice storm, with half an inch or more of accretion in the Berkshires and Hudson Valley up into Vermont and southwest NH, so I would not plan on travel that passes through those areas.
We’ll have updates through the day tomorrow as necessary, and please feel free to ask any questions you have on our social channels. Thank you for reading SCW!
-SA
