Mixed Conditions (Dec 21-25)

Jonathan Carr
By December 21, 2020 14:56

Mixed Conditions (Dec 21-25)

Discussion: A very meridional upper jet pattern with a lot of below-average geopotential height anomaly periods is expected through the rest of this year and into January. The AO and NAO teleconnections continue to model negative for this period. This means an active pattern of synoptic-scale mid-latitude cyclones moving through the E US (generally from SW to NE)—systems capable of producing snow in New Jersey if the cold air mass timing is right and the low tracks just to the SE of NJ. There is a lot to keep our eye on IMO.

But for this week (Christmas week), we have mixed conditions. A very weak upper-level disturbance should move through between tonight (Monday night) and Tuesday afternoon. This should bring some cold air with it and eventually make for a colder Tuesday night. For Tuesday, the surface should remain unorganized but feature enough lifting to produce a mix of isolated-to-scattered snow and rain showers. NWNJ would be most favored for snow showers and SENJ for rain. The snow/rain line would likely cut across NJ near 95 with little to no accumulation. It’s out of here by Tuesday afternoon and then high pressure moves in for Tuesday night through most of Wednesday (colder and dry).  

Thursday (Christmas Eve) then looks interesting. High pressure should depart into the Atlantic with its return flow meeting up with a very strong warm sector and cold front approaching from the W. This is the most meridional trough I’ve seen in a while but we’re going to be on the warm side of it for the precip dump. We’re likely looking at periods of heavy rain, gusty winds out of the S, and possibly thunderstorms with just a small chance of ending flurries/snow showers later Thursday night/Friday AM. Again, most precipitation should fall stormy and mild ahead of the front. But once the front is through, Friday (Christmas Day) looks much colder and more traditional of Christmas time. The trough-associated cold air mass would then remain overhead for Saturday and Sunday. The next storm signal is early the next week with several more storm signals heading into January. Again, a very active pattern.

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.).

Monday (Dec 21) high temperatures are reaching the low-to-mid 40s. Skies should remain mostly cloudy with a few isolated snow/rain showers around. Winds should remain light out of the W. Overnight lows should fall into the 30s for most of the state with snow/rain showers at the coldest point of the night. Little to no accumulations are likely.  

Tuesday (Dec 22) high temperatures should reach the low-to-mid 40s. Skies should be mostly cloudy with periods of light snow/rain possible (divide near 95). Winds should be breezy out of the W/NW. Overnight lows should range from near-20 to near-30 from elevations to sea.

Wednesday (Dec 23) high temperatures should reach the low-to-mid 40s. Skies should be mostly sunny. Winds should be light out of the SW. Overnight lows should range from near-30 to near-40 from elevations to sea.

Thursday (Dec 24 – Christmas Eve) high temperatures should reach near-60 for most areas. Skies should be mostly cloudy with periods of heavy rain possible and maybe even thunderstorms. Heavy rainfall on areas still having a snowpack could lead to additional flooding concerns. Winds should be breezy-to-gusty out of the S/SE. Overnight lows should drop into the 30s with periods of rainfall continuing. A very strong and sharp cold front is expected. It’s possible that rainfall ends as snowfall for some areas. The ground however will likely be too warm for stickage. NWNJ would be favored the coldest.

Friday (Dec 25 – Christmas Day) high temperatures should reach the mid-30s for most areas and likely occur during AM hours. A noticeably cold air mass should be present behind the cold front. Skies should gradually improve throughout the day but could remain cloudy in some spots until afternoon. Snow flurries/lake effect streamers are possible but with little to no accumulation…more of a visibility hazard if anything. Winds should be light-to-breezy out of the W/NW. Overnight lows should range from single digits to teens from elevations to sea.

An early look at the weekend indicates colder conditions with highs failing to escape the 30s and overnight lows well below freezing statewide. After the frontal passage this Thursday-Friday, there are 4-5 synoptic storm signals before Jan 5. The specific dates of such are likely irrelevant but I just want to point out that the pattern is modeled very active in the near future. Let’s get through Christmas and revisit accordingly. Everyone have a wonderful week and please be safe! JC

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Jonathan Carr
By December 21, 2020 14:56