[Surface wind map of the coastal storm; courtesy "earth.nullschool.net"]
Heavy rain continues at this hour across the New York City metro region and there is serious flooding all along coastal New Jersey. The next phase of this major coastal storm will begin early tonight as the surface low - now off the southern NJ coastline - stalls out in its northward advance near Long Island or southern New England. In this next phase, colder air in the mid and upper levels of the atmosphere will “wrap-around” the surface system into its southwest quadrant and this will increase the chances for “back end” snow showers later tonight, tomorrow and tomorrow night across much of the Mid-Atlantic region including eastern Pennsylvania and then right into the day on Thursday. The “wrap-around” snow showers can reach as far south as the DC metro region over the next 48 hours or so, but they will likely be much more numerous north of the PA/MD border.
[11:30 AM visible satellite image with surface low pressure situated off the southern NJ coastline; courtesy NASA]
Slick spots on the roadways and small accumulations are likely from "wrap-around" snow shower activity during this next phase of the storm across much of the Mid-Atlantic region. Also, there is the chance for embedded heavier snow bands to form in the unstable atmosphere and, if this happens, they would likely produce heavy snowfall amounts in a short period of time over a given area. The "wrap-around" of the colder air into the NYC metro region will be delayed some due to the positioning of the surface low pressure system to the north. Precipitation there early tomorrow will likely remain primarily in the form of plain rain, but then snow showers will threaten in NYC from later tomorrow through tomorrow night. By Thursday, even though the low pressure system will weaken as it spins over the Northeast US, the threat for snow showers will indeed continue in this long-duration event all the way along the I-95 corridor from DC-to-Philly-to-NYC.
Stay tuned...the potential for small-scale "banding" during this next phase makes this a tricky and dynamic forecast.