Coastal storm has arrived in NJ – will it be snow or rain?
As the first bands of showers enter South Jersey on Saturday evening, the forecast is holding steady for minor snow, rain, and coastal flooding through Sunday.
Our "big, bad" coastal storm system is here. And, as expected, we are already seeing showers in South Jersey as of Saturday afternoon. With air temperatures in the lower 40s, all precipitation so far has been rain.
These are just the outer bands of the system - the bulk of the rain and snow will come on Sunday, especially during the second half of the day. Of course, the big question is how much of the precipitation will be rain and how much will be snow? We're still talking only minor snow accumulations, due to the numerous late-season challenges I've enumerated in previous blogs.
The 12Z afternoon models are in, and suggest a slight drift westward and northward to the storm. Not a surprise, and not alarming in the slightest. We're still only receiving a glancing blow.
Allow me to share a pair of graphics to further illustrate my latest forecast and the difficulties in putting it together:
These two maps represent the latest GFS and NAM model output showing the QPF, or Quantitative Precipitation Forecast. It represents the liquid and liquid equivalent (i.e. melted snow) that is forecast to fall between now and Monday morning. You will notice 1.) these two graphics show remarkably similar solutions, and 2.) there is a sharp gradient ranging from little to no precipitation in North Jersey to about an inch along the southern coast.
Note: I can't post the European model here due to copyright issues, but I can tell you that the QPF output is very similar to the two American models above. Meanwhile, the Canadian model puts almost an inch of precipitation across the entire state - this track is clearly an outlier, and so I'm throwing it out the window.
If it were the middle of summer, with nice warm temperatures, this would be an easy forecast. Up to an inch of rain would be expected across New Jersey through Sunday, especially along the southern coast.
If it were the dead of winter, with subfreezing temperatures for the duration of the storm, this would also be a straightforward forecast. Since the general rule of thumb is that 1 inch of liquid precipitation generally equates to 10 inches of snow (although not always), we would expect 6 to 10 inches of accumulation for parts of Ocean, Burlington, Atlantic, Cumberland, and Cape May counties.
But this forecast is way more difficult, especially due to the expected transitions from rain to snow to rain to snow, etc. Additionally, the warm ground will prevent any snow from accumulating immediately, especially on manmade surfaces like asphalt and concrete. And the relatively warm ocean water (50 degrees off Cape May this weekend) will moderate air temperatures along the coast.
So where does the rain-snow line end up at any given time? And how much snow will fall and how much rain will fall for any given location? It's an educated guess, based on my research of the latest model data, knowledge of how the atmosphere works, experience with similar storms and similar forecasts, and gut instinct. Meteorology is an inexact science, full of assumptions and estimations. I'm actually feeling pretty comfortable with this forecast. If the storm wiggles left (west/inland)a bit more, we could see slightly higher snow totals. Similarly, if the storm wiggles right (east/out-to-sea) again, snow and rain totals will go down.
The Bottom Line
--Saturday night, Sunday, and early Monday morning will be messy and uncomfortable for most of New Jersey - whether you see snow, cold rain, or a combination of the two.
--The peak of the precipitation is expected during Sunday afternoon and evening.
--A maximum of 1 to 3 inches of snow is expected for inland portions of central and southern New Jersey, with the highest accumulations occurring on cold surfaces (not necessarily on the roads). Lesser amounts will fall in far North Jersey and along the south coast.
--Roads may be wet or icy at times, but travel won't be impossible. Just be careful and slow down if you encounter slick road conditions.
--Minor flooding (on the order of 1 to 2 feet) may occur from tidal waterways at the time of high tide.
--As of this writing, no watches, warnings, or advisories have been issued by the National Weather Service in New Jersey.
Unless conditions change dramatically, my next blog entry is scheduled for Sunday morning by around 8 a.m.
Dan Zarrow is the Chief Meteorologist for Townsquare Media New Jersey. Follow him on Facebook or Twitter for the latest forecast and realtime weather updates.