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Moderate Snowfall to Blanket Northeast this Week. 2/25

A weak low pressure is expected to slide south of the region on Wednesday and deliver a nice burst of snowfall Wednesday night into Thursday morning. It will likely create travel disruptions for Thursday morning and slippery travel as temperatures will be cold enough to coat roadways. More updates will be on the way as the storm develops.

This setup is rather zonal and progressive so there is a cap on how much snow will blanket the region. Besides the bad atmospheric flow, there are a few other limiting factors that I will cover later in the blog. The 500mb pattern shows a weak shortwave diving down and slightly intensifying and will create a swatch of snow from the midwest to the northeast.

As you can see above, there is a weak shortwave moving into the upper mid-west and dropping down into the northeast. In northern New England there is a good amount of confluence to hold the precipitation from expanding too much and the lack of a positive PNA ridge on the west coast means the storm will not dig down south and intensify. That does not mean there could be a good 3-6" of snow in some places as clippers can be weak yet potent storms that drop heavy snow in a few short hours.

Over the past day the majority of models have shifted the heaviest totals south a good deal. We can visualize this with the NAM precipitation map.

Above is a 4 run trend of the NAM mesoscale model for Wednesday night. As you can see precipitation has moved south considerably and now includes New York City and Boston in snowfall. It will be vital over the next day to see if this trend continues. The NAM and the GFS suite both agree on a more southerly track while the ECMWF has honed in on a more northerly track keeping the heaviest totals just north of Connecticut. It is worth noting that the ECMWF has preformed poorly this year with weak zonal systems and I strongly believe the GFS and NAM have a better handle on this system as they sniffed out the impacts first.

One thing I am certainly concerned about with this system is the dry air in place ahead of the storm. Models struggle with dry air and virga and they may be over doing the total precipitation that will fall. Currently I am not thinking this will be too much of an issue but it is something to keep an eye on.

As you can see precipitation water values are not particularly high, but some other models are showing good venting aloft and humidity high enough for good snow growth.

High humidity values shown by the GFS will help the show shield expand aided by the strong 250mb jet. A. strong jet over the area will help vent the atmosphere and push against the dry air to expand the snow shield north. I will monitor trends for all these parameters over the next few days leading up to the storm.

Finally after all the analysis we can get to my forecast. Attached below is my snowfall forecast for the region currently.

I have the heaviest axis of snowfall from northeast Pennsylvania into the Hudson Valley and into nearly all of Connecticut and Rhode Island. All of these areas will see 3-5" of snow. Currently I am leaning to the lower end of this range as I believe that dry air will cut back on these areas somewhat. In the 1-3" zone I have northern New Jersey, New York City and Long Island. If the southern trend continues I expect the heaviest snow axis to possibly move into these zones but for right now I like where I stand. These areas have the highest potential to hit the high end of their ranges or over preform as dry air will not be as much of an issue as they will be closer to the storm center but too close to receive the heaviest snow. I have a coating to 1" spanning from central Pennsylvania into central New Jersey. Once again these areas could slightly over preform if the southern trend continues tomorrow.

I will update you as the latest observations come out. Any questions can be directed to @mikebweather on Twitter, Facebook or Instagram!