I had mentioned a few blog posts back during our cold snap back in January that the airmass and pattern we were in while cold, wasn’t the ideal pattern for winter storms. We talked about the polar jet being very far south and this results in multiple rounds of winter weather across the southern United States, including to the gulf coast. I believe I made mention in that update that we would have our best chances to find winter storms on the front side of arriving cold air or on the retreating side as warmer air pushes north.
Well…… that pattern has arrived, but it has arrived in what we could call a neutral version of those two scenarios above, by that I mean we aren’t really seeing major infiltrations of cold air, nor are we seeing a massive retreat. We are in what is best described as a zonal flow. We have a very active jet stream pattern that is west to east across the region, these storms are riding a boundary between warm moist air beginning to entrain itself across the southern states as winter loses its grip, and where arctic air which is still quite plentiful across the north holds its grip.
Now, unlike in January we have both cold air and warm moist air nearby. This difference in temperature is called the baroclinic zone and it’s where storms are born. With no upper air blocking in place the jet stream is unbuckled and primed for a game of fast paced winter storms along this gradient. These storms will travel west to east and pass south of our region, in doing so the lift associated with driving warm moist air over cold dense air will result in numerous period of precipitation across our region.
The type of precipitation, the duration and intensity will differ with each system, and the exact location of the 32° boundary will be an inflection point for where the most persistent chances for snowfall will occur. Patterns like this can be prolific snowfall producers, as overrunning precipitation events can create impressive amounts of precipitation. We will get our first taste of this beginning Saturday PM into early Sunday. To truly highlight how active this pattern can be, the current data is protecting a chance of snowfall Saturday PM/Sunday AM, Tuesday PM/Wednesday AM,Thursday PM/Friday PM and again next Weekend.
Will all of these occur in those exact time frames? That will need to be determined, but what can be said about patterns such as these as they lack the complexity of coastal storms, where many things need to come together perfect to meet the forecast. When you have storms passing along a boundary that is almost stationary, the models will tend to do a better job seeing this potential. This can clearly be seen on the current ensembles for both the GFS and Euro models which current have almost every single model ensemble showing significant snowfall across parts of the region. 
In many years of forecasting, it’s not often you see this type of agreement and consistency on an upcoming pattern, this is almost 70 runs of two models, and in almost every instance the output was similar. This is what we would call a very strong signal for an active period of winter ahead. Again, all of this has its caveats, if the boundary wanders a bit north then areas along and north of i90 would see the full force of this pattern, further south and our entire region is in the action. Nothing is ever a guarantee in weather, but this is enough data for us to put out the alert that a severe period of winter weather is possible. Remember to never take long range model maps verbatim, the amounts are fun to look at, make for some good eye candy or for others great clickbait, it’s better to leverage them to identify a pattern or signal, and the one this is showing is “stormy”.
Now instead of drinking form a fire hose, and now that we’ve covered the overall potential of this longer term pattern. Let’s discuss Saturday PM/Sunday. It appears precipitation in the form of snow will overspread the region from SW to NE between 7-9 PM and continue overnight before ending from west to east between 6-8AM Sunday. Could see how some mixing may try to occur across parts of southern Orange, Westchester, Rockland and Putnam counties, these details will need to be honed down. Any mixing that occurs will hold snowfall totals down a bit across those regions. Snow will fall heavy at times overnight, with locally heavy snowfall amounts likely across areas along and north of i84. As of this evening it appears a 5”-10” snowfall is possible across the entire region with the heaviest amounts across those northern zones and higher terrain of southern and eastern facing slopes. Here’s a quick glance at the latest projections from both the GFS and Euro models. Now with that said, we have about 48 hours to go and some likely jogs north or south and those will have implications of the forecast, so don’t get hung up on exact amounts at this juncture, our preliminary will be out by tomorrow to address that. 
We will, as always be all over this system and those that may follow, and as always please remember to Keep Calm and Weather On!