Snow and ice expected Monday night

John Cifelli, Meteorologist | December 16, 2019 | Weather
  • Low/no impactful weather expected through daytime Monday
  • Snow, sleet and freezing rain overtake the northern half of the state Monday night
  • Serious icing potential exists north of Route 78 through Tuesday morning

A significant winter weather event will unfold for northern New Jersey Monday evening, bringing accumulating snowfall and ice accretion. A weak wave of low pressure is moving through the lower Ohio Valley towards the mid-Atlantic, bringing a surge of moisture from the Gulf of Mexico. A few flakes and raindrops will fall at times throughout the day today, but this initial round of precipitation is being eaten up by very dry air in the lower levels of the atmosphere. While that is a good thing for today, it spells problems for tonight. Dry air near the surface helps keep temperatures near the surface below freezing, which in this case will set the stage for an icing event. Additionally, our surface low in this setup is very weak. While temperatures will gradually increase above freezing aloft, without that strong surface low to drive warmer air across New Jersey at the lower levels, sub-freezing temperatures will remain in place, amplifying the icing threat.

After the commute Monday evening, precipitation will intensify across the state. South of 195 this is mostly a rain event, other than maybe a few flakes or some sleet at the start. South and east of the Route 1 corridor, look for a coating of snow and sleet before a change to freezing rain, and then plain rain. Little to no ice accretion is expected here and that includes right into New York City. It’s along and north of Route 202 where conditions will be more hazardous overnight and into the morning. Hunterdon, Somerset and Union counties on north will see the same transition from snow to sleet to freezing rain, but the transition will be more gradual, allowing more frozen precipitation to fall. Look for snow to begin between 7 and 10 p.m. across northern New Jersey tonight.

After an inch of sleet and snow for the the 202 and 78 corridors, I expect light freezing rain by midnight. Gradually the surface temperature should creep above freezing or at least close enough to it that ice can’t accrete. Temperatures had been above freezing for the past couple of days and nights, so surfaces, especially brined or salted roads, are not going to immediately lend themselves to icing. That will likely be the saving grace for this part of the state. Up to .2″ of ice accretion is possible after the change from snow, but I think things should be relatively manageable here than further north. The Route 80 corridor is where there will be major issues. Temperatures at the surface and just aloft will not rise above freezing until the event winds down mid-morning Tuesday. Expect 1-3″ of snow, followed by up to .5″ of ice accretion. This is potentially a very dangerous situation with hazardous road conditions and power outages. Northern Bergen, Passaic, Sussex, northern Warren and Morris counties make up the region of the state under threat for greatest impact.

By midday Tuesday, all precipitation is sliding east and out of our picture. On the other side of this event it gets really darn cold. Look for high temperatures in the 20s and 30s through the weekend, moderating by Sunday.