Winter storm, snow expected in NYC on Tuesday

A winter storm will impact NYC on Tuesday, bringing the potential for mixed precipitation and accumulating snowfall. There is still a great deal of uncertainty regarding exactly how the storm will play out, resulting in a low confidence forecast overall.

Rapid Briefing: Watch our latest video update on the storm.

An area of low pressure is forecast to develop across the Mid Atlantic states late Monday into Tuesday morning. This system will amplify northward, bringing notable amounts of moisture with it. The storm is being driven by a process known as warm air advection, which is the movement of warm air aiding in lift for precipitation. This moisture and warmth will be surging towards our area from the south.

Meanwhile, cold air will be pressing down from the north across New England. The combination of the two will lead to a convergence or battleground across New England, including the NYC Metro. The battle between cold air to our north and warm, moist air to our south ensures a very difficult forecast for this storm system and a razors-edge scenario where only a few miles could mean the difference between heavy snow and cold rain.

As you may imagine, forecast models are having a terrible time with this one. Most guidance has waffled back and forth for the better part of three days regarding whether or not NYC will see notable snowfall from this storm. Conventional wisdom argues against it initially, with warm temperatures in place and a very marginal setup characterized by warm air surging towards the area.

However, as the low pressure system forms to our south, cold air will begin to wrap in towards the area on Tuesday afternoon. This could aid in changing precipitation over to snow from west to east, resulting in a few hours of accumulating snowfall across the NYC Metro area. Obviously, the difference between several hours of snow and a few hours of snow will have major implications.

After trending warmer for several days, recent model data has gone the other direction – most guidance today is colder, suggesting that precipitation will flip over to snow in NYC on Tuesday afternoon and stay that way for several hours. The result would be the potential for least a few inches of snowfall. The warmer scenario would mean very little accumulating snowfall at all.

As a result, we’re taking a middle ground with this forecast and suggesting that 1 to 3 inches of snow will fall in NYC proper, and a more notable 3 to 6 inches in the interior and higher elevations. A colder trend as we approach the event could result in these amounts increasing incrementally. The box and whisker plots, which we use to visualize uncertainty and distribution of possibilities, show an unusually large dispersion on the upper bounds of the forecast. In other words, larger and more significant snowfall totals are still on the table.

Timing: Precipitation is expected to begin late Monday evening and during the early morning hours of Tuesday, likely as rain or a wintry mix in NYC and a wintry mix or snow in Northern NJ, Upstate NY, and Connecticut. This sloppy mix will continue in NYC into Tuesday morning as snow becomes heavier in the interior.

By late Tuesday morning or Tuesday afternoon, we’ll reach the inflection point with this system. If the changeover to snow begins, we’ll be in for a long afternoon. If rain or a mix holds, we’ll likely escape any significant impacts. Regardless, a changeover to snow will occur at some point Tuesday afternoon, raising at least some concern for slippery conditions during the Tuesday evening commute. Thereafter, the system will gradually end from west to east.

In the coming 12-24 hours, we should begin to get a much better idea as to how the system will evolve. This will allow us to tighten the envelope of possibilities and gain confidence in exactly what to expect in the NYC Metro area.

Tl;dr: A winter storm will impact the area on Tuesday, but uncertainty is unusually high regarding the details. 1 to 3 inches of snow is currently forecast in NYC with 3 to 6 inches in the higher elevations and interior of Northern NJ, Southeast NY and CT. Significant adjustments to the forecast are still possible in the next 12 hours.