Ice Jam continues, wintry mix tomorrow morning, and a major storm on Saturday

The ice jam along the Delaware River has continued to worsen, as Flash Flood Watches have been upgraded to Flash Flood Warnings in Mercer County in New Jersey, and Bucks County in Pennsylvania. Flooding has been reported at Route 29, and some roads have been closed. For more details on the Flood Warning, click this link. Otherwise, a Flash Flood Watch still exists in Mercer, Northwest Burlington, Philadelphia, and Lower Bucks County. For more information on ice jams and their potential severity, check out our article from yesterday, and today’s video discussion, which also highlights the storm potential on Saturday.

Moving forward to the weather for the rest of today, it certainly feels more comfortable than it has been with sunny skies and temperatures around or just above freezing. Continued warm air advection will prevent temperatures from dropping too much during the overnight. However, the warm and moist air approaching the still relatively cool airmass will help to trigger a weak warm front. Out ahead of this warm front, light precipitation will be falling and considering temperatures will still be around freezing, a light round of wintry precipitation can be expected late tonight and tomorrow morning.

Today’s RGEM model valid for 6am tomorrow morning shows some light snow passing just to the north of NYC.

It’s a bit of a tricky forecast due to the fact that the precipitation is relatively light, scattered, and disorganized — so the exact location and timing of precipitation is uncertain. The earlier it arrives, the more wintry the scenario; the later it arrives, the rainier the scenario. Warm air moving in both aloft and at the surface will eventually change any light precipitation over to liquid by later Friday. Today’s 12z RGEM model shows the snow remaining to our north, with only a few passing flurries for NYC. However, today’s European model showed the early-morning batch of precipitation a tad further south, which allows our area to pick up a coating to 1″ of snow.

Moving forward a few hours later, the RGEM model suggests things will be getting a bit icy.

Today’s 12z RGEM valid for 11am tomorrow morning shows some significant icing for the NYC area.

Later on Friday morning, the RGEM model suggests a period of significant icing for the NYC area. Warm air advection continues at the mid-levels of the atmosphere, which warms temperatures to above freezing at those levels. But the surface warmth is a bit more stubborn to move out, which allows what melts above the ground to re-freeze as ice at the ground — or freezing rain. Freezing rain can be very dangerous to travel — moreso than snow. The RGEM, if correct, would imply 0.25 to 0.50″ of freezing rain, before changing over to rain.

We are a bit skeptical on the RGEM’s significant ice output for our area due to a couple of factors: a southerly component to the winds that will develop when the high pressure system moves east, and a relative lack of moisture from the storm system to begin with.

Total ice accumulation from today’s 12z RGEM model, in millimeters. The conversion is 25.4 millimeters to 1 inch.

That being said, winds will be relatively light at the surface, so it is certainly conceivable that warm air advection will be much slower at the surface than aloft. Additionally, ocean temperatures have cooled a bit thanks to the recent cold shot, so the source of surface warm air advection may not be all that warm to begin with.

All of that said, some light snow can be expected to move in early tomorrow morning for the rush-hour, but primarily to the north of the city. A coating to 1″ of snow is possible in areas that do receive snow. Afterward, some freezing rain can be expected, and a threat for enough icing for treacherous roads certainly exists for areas west of NYC, especially in the western half of New Jersey. We do not have enough confidence to be on high-alert for Long Island, but thinking now is that Long Island should be fine due to southerly flow from the Atlantic Ocean warming the surface temperatures.

Confidence Increasing in a Major Storm System on Saturday: 

Computer modeling data continues to trend stronger with our storm system on Saturday. The potential for 2″ of rain exists from Saturday afternoon through early Sunday morning. What has also becoming interesting to note is the potential for very strong winds and even some thunder. Temperatures will also surge into the upper 50s.

Forecast model soundings for New York City on the GFS model paint an interesting scenario:

Forecast model sounding on the GFS model for Saturday afternoon shows some elevated instability, supportive of thunderstorms. It also shows very strong winds just above the surface.

The first thing to note is the very strong wind profile on the right. The wind barbs on the right are showing winds of 60-70 knots just above the surface. It may be hard for those to mix down to the ground because of the inversion near the surface, which promotes stability, but there may be a few ways around that.

One way to get around that is convection, which would help to force strong winds downward. There will not be any surface-based convection in this setup, but elevated convection is certainly possible, based on the relatively steep lapse rates that we see from 850mb and higher. These steep lapse rates along with a very impressive moisture tongue throughout the whole atmosphere, and very strong unidirectional winds may allow for a squall line to become embedded within the heavy rain — or at the very least some thunderstorms. These thunderstorms could help mix some of the strong winds down to the surface, potentially with gusts between 50 and 60 miles per hour. This, combined with torrential downpours will create many significant weather and travel hazards on Saturday.

As always, stay tuned to our website and our social media accounts for more updates.