Although the big snowstorm that some models had for Wednesday night and Thursday is definitely not going to happen, the NYC Metro area may still see its first snowflakes of the season tomorrow morning during the rush-hour commute. Yes, this does include coastal areas.
The main culprit for this is the Arctic cold front that will move through the area. There is not a whole lot of moisture with this front, as the main story will be the falling temperatures, as temperatures will struggle to get out of the 30s tomorrow and Wednesday. However, there is some moisture; particularly behind the front, where temperatures will be colder. This is called an anafront, as opposed to the more typical katafront, where most of the moisture is out ahead of the front in the warmer, more unstable airmass.
Current surface observations in the Great Lakes show the frontal boundary quite well, with many observations of snow on the cold side of the boundary. This front will cross our area during the overnight hours and should give most of the area its first snowflakes of the season.
Normally, it is much easier to generate precipitation ahead of a front rather than behind it, due to the airmass being warmer and having more moisture ahead of the front. But sometimes, due to jet stream dynamics among other things, the best source of lifting actually occurs behind the front. Of course, the colder airmass and lack of a strong storm system will somewhat mitigate the amount of precipitation that does fall; but the temperature gradient, lift, and moisture aloft do support some precipitation.
This morning’s high-resolution NAM model shows a band of light to moderate snow moving into the area around 6:00 a.m.
Precipitation should start as light rain around 2:00am in further northwest areas, and closer to 4:00am in coastal locations. As temperatures cool, the rain should change to snow about an hour or two after the initial onset of precipitation, fall lightly to at times moderately, and then end between 9:00am and 11:00am from west to east. This means that the immediate NYC Metro area could see a period of steady snow between 6:00am and 7:00am. Accumulations will be very light and limited to only the cold surfaces. Perhaps a dusting to a coating in coastal sections, and a coating to as much as an inch further north and west. The main roads should primarily be just wet, but it may be a good idea to save a bit of extra time tomorrow morning, as some colder roads could be a bit white and slick. It may appear quite wintry at times, due to the strong winds blowing around any snow that does fall.
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