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I’ll start with the scenario that has the least impacts, which would be the most recent 18z NAM. This far out from a storm it can generally change rather dramatically, so I would not put too much stock in this output just yet. However, it is a realistic scenario that a number of models are beginning to trend towards. The model shows some flurries as early as 9 or 10 AM on Sunday, as seen here. Surface temperatures will generally be near freezing. However, at no point does it ever get heavier than that. In the mid-afternoon light snow moves nearby again, as seen here. But total snow accumulations here through mid-day Monday are less than a half inch across the entire region. Essentially, the entire storm would miss with virtually no impacts.
Oftentimes, the high definition version of the NAM model will be more amplified and present scenarios that are more realistic. All winter it has also been performing better. With this storm, however, it is relatively similar. Over the next 60 hours, it shows less than an inch of snow across the region, as seen here. Some parts of SWCT/NY could see no accumulating precipitation at all (especially inland) while Long Island and points further south could see slightly more, seen here. But this agreement is worth noting, especially as the storm has continued to jog off to the south on most models this afternoon.
Meanwhile, the closest model suite to the NAM, the SREFs, disagree. As seen here, they show widespread amounts of 3-4 inches of snow across the region through Monday. A couple members have the storm entirely miss, but most show at least a decent hit. Through 8 PM on Sunday they have around a 65% chance of an inch or more of snow and a 23-35% chance of 4+ inches of snow, as seen here. These are relatively impressive probabilities, though it is worth noting that by 2 AM or so they are declining as the storm is generally shown moving out slightly earlier than before. Here, the consensus appears to be that 2-4 or 3-6 inches of snow region wide should be considered most likely.
Next, we have the GFS guidance which has continued to gradually trend southeast in line with the NAM. The model has light snow overspread the region by 9 or 10 AM on Sunday, as seen here, with temperatures generally right around freezing. During the day, however, the strong March sun angle might melt a majority of this. A brief burst of moderate snow is seen from 2-5 PM, as seen here, but again temperatures are right by freezing, and much of this snow is likely to compact. From there the storm moves out of the region by 2-3 AM at the latest, with only light snow showers after 5 PM. As seen in the bottom middle here, this scenario generally brings .1-.3 inches of liquid, some of which would likely melt on impact as almost all precipitation would fall during the day. This would thus amount to around .5-2.5 inches of snow on Sunday that would be relatively low impact, struggling to stick to roads and never getting all that heavy. The worst impacts would be across coastal New Haven County, where the slightly higher accumulations would be possible, but again no real lingering impacts into Monday would be expected besides potentially delays from icy roads should any snowmelt freeze over.
Next we have the Canadian model guidance, which is notorious for overdoing snow storms and moisture. Here on the bottom right we see that total amounts of liquid from .5-.8 are shown across the region, amounting generally to 4-7 inches of snow with much falling overnight Sunday night as the storm takes longer to get its act together but is much stronger. However, the higher resolution RGEM version of the Canadian model is less convinced on this widespread snow, though admittedly it is not entirely in range. Generally, the model shows only snow showers that don’t stick on Sunday, with moderate snow Sunday evening and heavy snow from 10 PM Sunday through 4 AM Monday. Snow then moves out between 5 and 9 AM on Monday with 4-7 inches region wide and schools closing with travel significantly impacted. This scenario is the worst case scenario overall, but at this time is not seen as all that likely.
Finally, the ECMWF appears to be split between the GFS and the CMC. It does show the storm strengthen far more rapidly than the GFS does, but does not have it quite as strong or west as the CMC. The result is a strip of 3-5 inches of snow across New Haven and parts of Fairfield County, with instead closer to 2-3 inches of snow inland. The timing is a little quicker than the CMC as well, but regardless the snow clears out by Monday sunup, which models are very consistent in.
As I mentioned yesterday, I do not love this storm setup. The upper level pattern just does not look primed for a large snow storm, and alongside that unless things look perfect in March it is hard for it to really come together for significant snow. With much of the accumulation poised for Sunday afternoon, I feel much of it could melt on impact, limiting total accumulations and impacts from the storm and not making it much of a deal at all. I said yesterday that most of the crazy snowfall amounts of 8-10+ inches were likely overdone, and today we saw just that as a bunch of models backed off the storm. I even think there is a chance that the NAM could be right, and we see nothing more than flurries and snow showers through the day Sunday into Sunday night with no real accumulations, but I am not yet ready to forecast just that.
Instead, I think 1-3 inches of snow starting Sunday afternoon and winding down overnight appears most reasonable. It seems quite likely that we do see light snow starting between 9 and 11 AM on Sunday across much of the region but it is unlikely to stick or cause much trouble. Any steadier snow likely waits until Sunday evening when it should begin to stick, but whether that is just for a few hours or for a more extended period of time is unclear. I do not see the CMC scenario with widespread amounts of 4+ inches verifying, though the fact that the SREFs do have such a high chance of 4+ inches being widespread has be concerned that there does remain some upside risk to the forecast despite the southeastern trend today. Similarly, my forecast is below the National Weather Service, which appears to be forecasting anywhere from 2-6 inches across the region, but given that surface temperatures at first are only marginal, some models show the storm entirely missing, and it is going to be late March, I just do not see much coming together for widespread amounts of more than 2-3 inches.
Additional updates to this forecast will come as necessary. Premium subscribers will receive updates as soon as they are made, and another Free update will be released Saturday evening if necessary.