A few days ago, snow rumors abounded. Multiple weather models showed the potential for accumulating snow to impact the region. We tweeted out that there was the potential, but that everything would have to come together perfectly for it to be a threat, and that it is extraordinarily unlikely that anywhere in Fairfield, New Haven, or Westchester counties will see actual accumulating snow. We stand by that still.
What has changed through all this time is the weather model output, and thus the forecasts that many have put forward. The forecast is especially tricky due to the difference that minute upper level differences in the upper level will make at the surface. This post will just briefly elaborate on some of the scenarios that remain plausible with this storm, again ending with what we think is most likely. Similarly, we remind all users that come November 1st, in just two days now, our website will go through an entire suite of upgrades, with a significant amount of content going over to subscription-based. Still, blog posts with slightly less content will be available for free, and blog posts that will expand much more on the points made here and include more timing/technical analysis will be available to paid subscribers. We will have more on this at the end.
First impacts from this storm may be felt as soon as late Halloween evening. The first part of this storm to emphasize is that there will actually be two centers of low pressure, one that will impact the region Friday night into Saturday, and then another one that could impact the region later on Saturday into Sunday as it steals energy from the primary low pressure center. In the upper levels of the atmosphere, however, the transition is much more fluid, with a singular upper level trough digging deeply across the region, injecting energy into these systems and potentially even cutting off entirely for a period of time, allowing for the slow moving nature of the storm.
So, we are confident that later tomorrow evening light showers will break out, alongside some drizzle, as low pressure begins to organize out at sea and slightly destabilize the atmosphere. Through 8 AM Saturday, all major weather models align in saying that there is no significant precipitation, so nothing should be seriously impacted until the day on Saturday. This is where differences begin to present themselves. A low pressure center will begin to form and strengthen to the south of Cape Cod. As this strengthens, it may throw back showers into cooler air across our three counties, resulting in showers. The model differences start here in how heavy the Saturday rain is, as they differ on the strength of the primary low. A stronger low out to sea brings in heavier rain, and vice versa. While most models have this low pressure center further out to sea and weaker, a few models have come in recently showing more rain possible on Saturday. The 18z GFS weather model, for example, came in showing the potential for up to an inch of rain on Saturday with the low pressure center forming much closer to the coast. At this time this is not forecast, and the Saturday forecast is scattered showers with less than a quarter of an inch of rain through Saturday afternoon with the potential for a little more in the evening, but there does remain an outside possibility of a stronger primary storm on Saturday bringing in heavier rain during the day. We estimate the chance of that is around 25%.
The second variable is the second storm, called a secondary low pressure center, which will be forming to the southwest of this primary low pressure center and then riding up to the northeast much more like a classic Nor’ Easter. This low pressure center will be stronger and throw back more wind. It will also have a much more defined precipitation shield, with rain wrapping in closer to it. As a more defined Nor’ Easter, it will also pull in colder air, which is why some thought there may be a potential for accumulating snow across the region. I’ll get to that in a second. Currently, the GFS is the weather model that is furthest west with this secondary low pressure center, moving it very close to Cape Cod. The latest SREF weather models (brand new run) have it move pretty far out to sea. Similarly, the 18z NAM weather model had it move out to sea, and I would be surprised if the 0z came in changed. The CMC weather model threw in a curveball, having it form so late that it would not really impact the region (I could go into a long meteorological explanation about how the bias of the weather model is impacting both the 500mb and surface output, and that this scenario in real life is not actually plausible, but I will save the time here, so just know that this scenario is not going to occur). The ECMWF weather model does have some rain from the main shield scrape the region. So the overall consensus here seems to either be a scrape or a miss from this secondary storm.
So why is it still worth watching? Well, it was the latest run of the GFS that showed impacts possible, and a significant number of its ensemble members also agreed. And the NAO remains negative, and models are notoriously poor with secondary low pressure placement within a closer upper level 500mb low opening up (a rare scenario regardless). With all the moving parts, the weather models may have not captured every scenario available here, leaving open the possibility for a second round of rain Saturday night. Regardless, at this time the storm looks to move far away from the region to spare us the worst of the rain and most of the winds as well, so unless there is a significant trend towards the GFS weather model overnight, there are no severe impacts to worry about, and by Sunday morning we should certainly be seeing some clearing.
In terms of other real impacts, this means that after the scattered showers on Saturday (some could be heavy at times depending how that first low pressure center acts) we could again see some showers Saturday evening, with the small chance of that steady rain overnight. If the low pressure passes close enough, some wrap-around showers very early Sunday morning actually could mix with snow as cold air is pulled down across the region, which is why we are forecasting around a 30% chance that the region sees its first snowflakes early Sunday morning. Again, the odds that this would accumulate are very low as surface temperatures are still fairly warm and the ground has certainly not frozen through yet, but there could be some flakes flying based on the placement of this low pressure center. We will continue to track this through the next few days.
As we track this, though, we want to remind all viewers that in just two days our site will be taking a new look as we upgrade to a premium service. This premium service will feature 7-day forecasts broken down by county, alongside 15-day weather discussions for the entire county (and even some brief investment discussions based upon the implications of various weather patterns). Premium posts will contain content much like we have above, but it will be supplemented with additional graphics, more details/timing, and more impact assessments, to keep subscribers one step ahead of every scenario and every storm. We will continue to offer free blog posts as well, that will just be paired down versions of what we have offered above, and the standard 5-day forecasts and storm alerts will remain available for all free viewers as well. The premium site is going up just in time to track that early Sunday morning snow potential, so if that continues to appear it may be worth grabbing that subscription early on Saturday to track that potential through the day!
That’s all we have to report from here on the storm. In brief summary, light showers/sprinkles start late tomorrow evening with off and on light rain on Saturday that could get moderate at times depending on low pressure placement/strength, and then showers will likely continue into the evening. Overnight it should dry out unless a couple weather models are correct, in which case the low pressure center would correct westward and impact us with some heavier rain and stronger winds into early Sunday morning, maybe ending with a few scattered snow showers around sun-up. Should any of this change we will publish an update, but as has been our tone we continue to err on the side of lower-impact versus higher-impact for the three counties we cover.