After a morning with light icing due to freezing fog, more wintry weather involving icing is one the way.
On Tuesday, warm air advection associated with a warm front will enter our region. The warmer air will ride over the Arctic Air being held in place by an area of high pressure. This will cause precipitation to break out on late Monday Night and especially on Tuesday Morning. This is what we call overrunning in meteorology. The precipitation will begin as snow or a mixture of snow and sleet. The latest models suggest the heaviest precipitation across Northern and Central New Jersey. There could be some light rain at the coastline mixing with sleet, but the models actually do not show much precipitation in this area with part one. The “540 Line” will slowly push northward throughout the day. After the morning round of precipitation, the precipitation will be lighter during a lull between this event and the big inland low for Wednesday. The arrival continued infiltration of warmer air aloft along with lighter precipitation intensity will result in the snow and sleet switching over to rain. There could be a window of opportunity for temperatures to rise above freezing, before falling back a few degrees once the sun sets. Once the temperature falls back, Tuesday Night could feature freezing drizzle and light freezing rain. I have included a snow map as Northern and Central New Jersey could pick up several inches of wet snow. It is a good idea to clean off your roofs as the snow liquid content is very high.
On Wednesday, a very strong low will cut up through the Great Lakes region. This means we will be on the “warmer side” of the storm system. This will draw in warmer oceanic air. Therefore, the chances of this system bringing snow or sleet are low. This looks like freezing rain to rain for many areas. The question will be how many hours of below freezing temperatures and what will be the intensity during that time frame. It is possible some areas receive up to one-half inch or more of liquid before plain rain comes in. The criterion for an ice storm is one-quarter of an inch. So even if you see plain rain by the end of the event, you may have an ice storm prior to the switch to rain. Each storm seems to be colder than the models predict initially, so we will have to watch how the models handle the departure of the cold air at the surface and a high pressure area to our north. The high pressure area could lock the below freezing surface air in for quite a few hours in the interior. The snow on the ground will also aid in keeping the cold air at the surface. This would be classic cold air damming. Areas in Northwestern New Jersey could see wet snow on Wednesday which could changeover to heavy freezing rain.
All in all, widespread icing amounts of 0.25” to 0.50” is likely in interior portions of Central and Southern New Jersey, before any change to plain rain. The most icing will occur close to the Delaware River. Then we will have to nail down whether this ice will linger for more hours during the Wednesday storm or whether this plain rain takes over. Still, 0.25” could down trees and power lines and make travel impossible. I have inserted another map indicating where I feel the best chance of icing will be.
Areas that observe heavy, plain rain have the potential to see widespread and significant poor drainage flooding. Some creek, stream, and even river flooding would be possible should heavy, plain rain fall for several hours around the Delaware River and Raritan River Basins. This rain will combine with a ground loaded with moisture and snow-cover. In addition, the ground is frozen which will increase the runoff further. Needless to say, if you are flood prone you need to watch for the latest forecasts.
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