Cold Behind the Storm (Dec 18-20)

Discussion: The upper jet will stay to the S of NJ from now until Saturday evening. This is because the departing mid-latitude cyclone and approaching high to our SW are pulling colder air downwards from our N. The jet should then should return N of NJ for Sunday-Monday before a transient narrow trough swings through Monday night into Tuesday morning. That trough swing could connect with a weak ocean disturbance and drop some snow/rain showers across NJ Mon PM-Tues AM. But with a marginal surface temperature profile I wouldn’t expect much accumulation if any. Then it’s back to positive heights over NJ for Wednesday and Thursday. A very deep trough, in a favorable EC winter storm pattern, is then setting up for the weekend beginning with Christmas Day. If the trough swings through without a winter storm then we’re at least looking at much colder temperatures. There’s currently a strong lobe of the PV influencing E Canada. Some of that Arctic air should spill down and propagate to the surface into the Christmas weekend trough regardless. There’s ridging in the W US, a deep E US trough, and blocking downstream. Because the blocking is a little S of Greenland, the trough wants to bring its stormy side through NJ with a positive tilt. If the blocking should occur higher in latitude (over Greenland) it would force a negative tilting trough for a higher impacting NJ winter storm. In any case, there’s a recipe for another winter storm Christmas weekend. I’ll only follow casually through the weekend and will address seriously if the overall signal is still showing on Monday morning.

Note: Unless specifically mentioned by location (Example: NNJ elevations, SENJ immediate coast, Interior CNJ/SNJ, etc.) assume the following forecast language is statewide for New Jersey. When I say “from elevations to sea” I mean from NWNJ mountains spreading down to immediate ECNJ/SNJ coastal areas. Directions are shortened (N = North, S = South, W/SW = West/SouthWest, etc.).

Thursday (tonight) looks clear and cold. Overnight lows should range from near-10 to mid-20s from elevations to sea. All of NJ should dip below freezing even extreme Cape May County. If you still have snow on the ground (mostly NNJ and parts of CNJ), watch out for black ice. There should be some snow melt, especially if you made it into the mid-30s, today that, if untreated, will refreeze once temps return below freezing this evening.

Friday (Dec 18) high temperatures should max out in the 30s statewide. NWNJ elevations might struggle to rise above freezing. Skies should be mixed with sun and clouds. Winds should be light out of the N. Overnight lows should range from single-digits to mid-20s from elevations to sea. All of NJ below freezing again. Black ice an issue again for areas of daytime snowmelt.

Saturday (Dec 19) high temperatures should range from near-30 to near-40 from elevations to sea. Skies should be mixed with sun and clouds. Winds should be light out of the NW. Overnight lows should range from near-20 to near-30 from elevations to sea.

Sunday (Dec 20) high temperatures should range from mid-30s to mid-40s. Skies should start partly sunny then become mostly cloudy by PM hours. Winds should be light out of the W/SW. Overnight lows should range from mid-20s to mid-30s from elevations to sea.

An early look at next week indicates high temperatures ranging from near-40 to near-50 through Thursday (Christmas Eve). Mostly decent weather. A few snow/rain showers possible Monday night into Tuesday morning. Friday (Christmas Day) and into next weekend is the next synoptic wintry storm signal I’m monitoring (Dec 25-27). Will revisit Sunday night to see weekend evolution of such. Just a long-range signal to watch for now. If it drops off it drops off. Have a great weekend. Please stay warm and be safe! JC  

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Jonathan Carr

Jonathan Carr (JC) is the founder and sole operator of Weather NJ, New Jersey’s largest independent weather reporting agency. Since 2010, Jonathan has provided weather safety and forecasting services for New Jersey and immediate surrounding areas through the web, social media, and app spaces. Originally branded as Severe NJ Weather (before 2014), Weather NJ is proud to bring you accurate and responsible discussions ahead of high-stakes weather scenarios that impact the garden state. All Weather. All New Jersey.™