It is looking increasingly likely that a burst of snow will be followed by a burst of sleet and freezing rain across Southwestern Connecticut and New York Saturday night. Travel could be severely impacted inland through Saturday evening before the storm turns over to rain. In this post, I look to hone in on a number of details with the upcoming storm. Should you wish a more detailed forecast that breaks down our weather models and offers insight on the January 6th snow threat and long-range patterns, you can purchase the Premium forecast here. And should you want frequent updates on this storm, exact travel impacts, and any school impacts, do consider subscribing to Premium here. I bring this up as as there is a special 2015 offer where all subscriptions and purchases are 10% off if you use the coupon code “newyear”. But enough about premium services, I want to outline all the threats with the storm freely here too so that everyone reading can be kept one step ahead of what is coming this weekend, especially as the potential threats have not been as well publicized as I would have liked.
The storm this weekend continues to prove quite a mess to forecast, as key very small-scale differences in model timing have resulted in very different pieces of forecasting analysis. Winter storms have always been known in the meteorology business as the hardest to forecast. Not only do you have to figure out the duration and intensity of precipitation, but you have to figure out the type. And not just the type, you also have to determine if the type will “stick,” or even be observed at the surface. The result of this always is highly volatile forecasts. And this storm is no different, with our weather models all being so similar but yet just different enough to cause some fairly major forecasting headaches. I have an overall idea of what I expect this storm to do, and I will say that I am becoming increasingly concerned about travel impacts inland Saturday evening into Saturday night before poor travel conditions ease into early Sunday morning. A combination of snow, sleet, and freezing rain looks even more likely in front of the rain to move through, and I want to outline exactly why here.
In general, I am siding with some of the slightly colder weather model guidance, mainly due to the intensity of the cold air that we are seeing now across the region. Coastal areas will be getting into the low to mid 20s Friday night, and that cold air is not something that easily gets kicked out. Long-range models have been known to not accurately forecast cold air damming, and I believe that in such a scenario, especially with the potential for a very weak secondary low pressure center to form south of Long Island, there is a possibility of severe icing far inland. However, this is far from a lock. The long-range models do not show cold air damming not because they are missing it, but rather because they are less robust with a secondary low pressure center trying to form south of Long Island. It would not be strong enough to significantly impact the movement of air aloft, but this small secondary could be just strong enough to move winds more east of south for a period of time, which could keep the cold air in inland areas through 11 PM, 12 PM, or maybe even 1 AM. It is in these scenarios that the worst icing would be possible, and travel Saturday evening would be some of the worst of the last few years.
At this time, I am not yet ready to predict icing to that level. I am worried that the short-range models may be over-amplifying the storm, potentially requiring it to create a secondary low pressure center that will not be as prominent in the actual storm. Yet, I do believe that surface temperatures begin in the storm colder than a few models show. In terms of real conditions, my expectations are that precipitation now starts between 3 and 6 PM across the entire region as snow. By 7 PM, snow will have turned to sleet in all except maybe New Haven county. Between 8 or 9 PM, sleet mixes freezing rain. Freezing rain at the coast quickly turns to rain as temperatures rise above freezing. North of the Merritt Parkway, sleet/freezing rain lasts until around 10 PM. Around Interstate 84, the changeover to plain rain happens around 11 PM, and north of Interstate 84 is where it could wait until around midnight or so. After midnight or 1 AM at the latest, plain rain is falling across the entire region and ice is melting, so travel conditions gradually improve through morning. Rain then continues off and on through the night and into Sunday morning. One burst of rain between 9 AM and 1 PM on Sunday is possible as pockets of instability move through, and then ahead of the cold front another burst of rain between 4 PM and 8 PM may be possible. After 8 PM I don’t see much precipitation falling, although that final burst late in the afternoon/early in the evening has been hard to predict and could move through a little later. Overnight Sunday night everything dries out and temperatures plummet. With low temperatures below freezing across the entire area, there could be some minor icing issues, so it will be important for road crews to treat roadways Sunday night. Winds will still be gusting a little bit overnight, so that should keep a lot of the standing water from freezing as it will evaporate, but some roads may still be icy.
In terms of accumulations, the previous snowfall forecast stands of up to 1 inch at the cost and up to 2 inches north of the Merritt Parkway. The “up to” means that some areas could very well see no snow or sleet, though I think that is fairly unlikely, as at least a dusting or coating or snow and sleet pellets looks likely before we change to freezing rain and then rain. Then, in terms of freezing rain, at the coast I see only a couple hundredths of an inch of freezing rain possible if any freezing rain falls at all. Instead, a little ice from sleet could accumulate with the snow, and that may be it. Most models indicate that icing will not be nearly as much of a threat as temperatures quickly rise above freezing, and in coastal areas travel begins getting better by 9 or 10 PM I believe. Inland is a different story, where between a tenth and a quarter of an inch of ice could be possible around or north of Interstate 84, and in between those areas .05 to .15 inches of ice could be possible as well. A quarter of an inch of ice, though not very likely, is enough to close roadways and bring down small limbs and power lines when winds gust into the 20 or 30 mph range. This is just one of many reasons I am so concerned about this icing. After all this dies down, around an inch of rain looks probable too. This rain should not be heavy enough to cause flooding or many concerns like that, and the main concern of the rain will be the standing water sitting into Sunday night that could freeze and cause patchy icy conditions on untreated roadways into Monday morning.
Overall, I believe that Winter Weather Advisories will need to be issued for inland areas due to the freezing rain threat, and there is a chance they are issued for the coast, though surface temperatures should be warm enough there that those likely will not be needed. The National Weather Service has not yet outlined any freezing rain threat in its forecasts, but I think that in future updates it will be needed. Sleet will dominate inland for a period but freezing rain looks to eventually come as well, and I feel the NWS will have to update forecasts accordingly. At the coast, it will be much more of a snow to sleet to just rain event. Winds no longer look to be as bad, with gusts only up to 30 or maybe 35 mph likely.
That’s really it for this storm, and I’ll have another forecast update tomorrow night after the next Premium update is published. The Premium forecast out now had additional weather model and travel impact analysis for those interested, and again I encourage you to take advantage of the 2015 special to sign up for Premium services here. If not, stay tuned for upcoming free updates!