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.
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.
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.
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.
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.
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.
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!