10:45 AM (Monday) | ***An icy mess tonight across much of PA, northern NJ, and NYC…’plain’ rain for the most part in the DC metro region***
Paul Dorian
12Z NAM 2-meter temperature forecast map for early tonight with temperatures hovering near the freezing mark in many spots in the Mid-Atlantic at a time when the precipitation intensities will be picking up; map courtesy NOAA, tropicaltidbits.com
Overview
There will be two different parts to the current winter weather event with phase one already well underway and phase two coming from later today through Tuesday morning. Phase one featured some accumulating snow south of the PA/MD border earlier today and has had very limited precipitation so far north of the Mason-Dixon Line. Phase two will involve heavier precipitation amounts from later today into tomorrow morning as low pressure heads towards the region from the Lower Mississippi Valley. This second phase will generally feature ‘plain’ rain across the immediate DC metro region, but icing will be a big concern across much of PA, northern NJ and NYC where temperatures will hover around the freezing mark throughout the night as precipitation intensities pick up.
12Z NAM surface forecast map for early tonight with lots of sleet/freezing rain (pink, purple) near and north of the PA/MD border; map courtesy NOAA, tropicaltidbits.com
Details
After a lull in the precipitation during the mid-day hours, phase two of this winter weather event will get underway later in the afternoon as the intensifying low pressure system over the Lower Mississippi Valley heads northeast and towards the central Appalachians. This developing system is very energetic and is generating severe weather in the Deep South today including a threat of tornadoes. With support from an upper-level jet streak, precipitation will increase in intensity later today and it can come down hard at times tonight and into Tuesday morning. [Note - any burst of heavy precipitation later this evening and overnight is likely to be accompanied by strong upward motion and this can produce some dynamic cooling in the lower atmosphere which can result in a change back to snow and sleet from freezing rain].
Forecast map of accumulated freezing rain as depicted by the high-resolution (3-km) NAM computer forecast model; map courtesy NOAA, Weather Bell Analytics
Temperatures have pushed above freezing in the DC metro region at mid-day and precipitation in that area should fall mainly in the form of ‘plain’ rain through tonight although a few pockets of freezing rain will be possible well to the north and west of the District. It’ll be a different story, however, to the north of the PA/MD border for the second phase of this event. While there may be a slight warming aloft tonight with the arrival of an upper-level jet streak, temperatures at the surface will continue to hover near the freezing mark across much of PA, northern NJ and NYC. As a result, much of the precipitation later today and tonight north of the Mason-Dixon Line will be a mixture of snow, sleet and freezing rain and there is likely to be an ice buildup on untreated surfaces (e.g., trees); especially, in suburban locations. Some snow small accumulations are possible before it mixes with sleet and freezing rain, but it’ll be quite variable depending on elevation. In addition, some high-resolution forecast models (e.g., 3-km NAM, HRGPS) are actually predicting rather significant accumulating freezing rain amounts for this second phase of the storm. Slick spots on untreated roadways are quite possible not only tonight, but also going into the AM commute on Tuesday in PA, northern NJ and NYC. The rain will shut off later tomorrow as a cold front passes through and it’ll remain quite cold tomorrow night and Wednesday. There can be some rain or snow shower activity as the frontal system pushes through the region and winds will gust up to 25 mph or so.
An Arctic air mass will push into the Mid-Atlantic/NE US for Wednesday night and Thursday with way below temperatures for the middle of December; map courtesy NOAA, tropicaltidbits.com
An Arctic cold frontal system will cross the region later Wednesday with possible strong wind gusts, snow showers and maybe even a snow squall or two and it’ll usher in very cold air for Wednesday night and Thursday. In fact, temperatures on Thursday will likely hold in the 20’s across the NYC and Philly metro regions and struggle to reach the freezing mark in DC.
Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com
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