Arctic Weekend NJ Snowstorm Developing

Discussion: Remember, deep breaths everyone. We’re still 36 hours away from this snowstorm beginning. Historically, we’ve seen large changes that drastically affect the outcome in less time than that. We are, however, gaining consistency on the idea of a high-impact wintry event, featuring Arctic air, for New Jersey between about midnight (12:00am) Sunday, January 25 morning and noon (12:00pm) on Monday, January 26. Many are already preparing for the weekend snowstorm NJ is expected to experience.

At this point, we try to look for everything we can think of that could go wrong. I can mention two off the bat. First is Warm Air Advection (WAA). With the northern trend of this system, which appears to have halted for now, comes the ability for warmer air off the ocean to invade the low-mid levels of the atmosphere. It might not take the surface above freezing but it takes the air that’s a few thousand feet above you above freezing in a shallow layer. This layer typically resides between where the snowflake is formed higher up and the surface. So that snowflake is formed in below-freezing air, falls through a layer of above-freezing air, and then re-enters below-freezing air closer to the surface. So, it starts as a snowflake, melts into a raindrop, and refreezes into a sleet pellet or hits the below-freezing ground and freezes as freezing rain. This type of occurrence then produces less snowfall accumulations.

Another thing worrying many forecasters right now is a Miller-B transfer. Because the cold suppressive high-pressure forces and locations to the N, low pressure, which loves to cut and turn N, gets to a point and then disappears and reforms a low to the E of it. Some of the current models are doing this by sending a primary low into the W PA area before transferring to a low off the E coast. When this happens, you get a dry slot between the lows where precipitation dries up. You then get a booming area of precipitation near/to the NW of the new secondary low. Right now, we feel this will be most likely a W PA or Central PA thing, it could very well happen closer to EPA and NJ.

I do think we’re well past this thing being suppressed to the S though. We crossed that line yesterday with the weaking SE Canadian high allowing the system to come further up the coast. If this system is going to perform below expectations, it will be because it is too far N not too far S. And that would mean mixed precipitation (sleet/freezing rain/rain) making it a lot further inland than just to the I-95 corridor. I think areas N of I-78 are most shielded from that. Areas between I-195 and I-78 are most subject to wild swings in either direction…basically the Philly across Trenton and over towards NYC/NE Monmouth County area.  The rest of NJ SE of the I-95 corridor are staring at a snow to mix situation at this point. When does it mix? How long does it mix for? How far does the mixing get into NJ? These are the questions that we hope to iron out as much as possible before our first call snow map tomorrow with expected amounts. Before we get to the snow map, let’s talk about the models.

The GFS adjusted N the other night when hurricane hunter dropsonde sensors were dropped into the upstream energy near the Baja upper low. Since then, it has remained the most consistent. consistency since flight drop. It has less of a Miller-B snowstorm idea (a transfer of low pressure) and more of a singular low that spawn off OBX and tracks to the 40N/70W benchmark. This keeps the mixed precipitation to the SE of I-95 and never introduces freezing rain or plain rain. Most areas, especially closer to I-95, actually never change completely over to sleet. They snow and sleet a mix. With how cold the overall environment will be, a shallow warm layer could collapse quickly along I-95 and even areas SE of that. This is likely the reason why the GFS has been outputting 8-12+ for SNJ and 12-18+ for NNJ. Other model guidance (Canadian and Euro) has the Miller B transfer and quicker retreating SE Canadian highs which allows the storm to send in a warm layer as far NW as EPA/NWNJ.

Temperatures are going to remain very cold given the Arctic air involved. If you are NW of the warmer air intrusion, you will likely stay well-below freezing. Some areas that mix over might stay in the 20s or even upper-teens as the warmth will only be moving over you not through you at the ground. There will be a very tight gradient along the mixing line where it goes from just above freezing to well-below freezing. This is why areas that do snow will still be in the 15:1 to 20:1 range of snow ratios.

We’re always trying to see which model is handling the pattern best so we can apply a weight to it when creating forecasts. You must respect the GFS’s persistence. However, you must allow for the WAA and/or Miller-B transfer process to possibly mess things up like the Canadian and Euro. Therefore, after analysis of all data today, we’ve put together a probability-based map. What we are doing here is setting the low end/floor meaning this is the least amount of snow you can expect. The best chance to remain all snow is Area A, greater than 16″. Area B could see some mixing with sleet, but if not, it ends up more like Area A. Low floor amounts accounting for sleet mixing is still greater than 12″. Area C we expect a change to sleet, but still at least 10″ snow there too. If that snow holds on longer, that could very easily be 14… 16 inches of snow. But 10 is the low point. Area D is 8″+ sleet/freezing rain, and the others are minimum 6″ before the other p-types. This is how probability works… start with the low/floor amounts and work bottom up. Ranges of snow expectations will be introduced tomorrow with the first official call. For Area A, presently this would be a 16-22″ swath, for example.

In English: The weekend snowstorm is still a go and still expected to bring high wintry impacts to NJ between midnight Sunday morning and noon on Monday. Initial snow could break out earlier Saturday night, but that snow will take time to saturate the dry air. So, it might be closer to midnight by the time it starts making it down to the surface. The above map describes the least amount of snow you should see before any changeovers to sleet, freezing rain, or rain. NWNJ has the best chance to stay all snow. SENJ has the best chance to mix over to plain rain. The I-95 corridor between is the most uncertain regarding staying mostly snow or mixing over to at least sleet. The three main parts of this storm are looking like:

1) Saturday night (closer to midnight likely) through about 8am Sunday: Starts as all snow for everyone (even Cape May) in a very cold environment. This is when SENJ should see the majority of their snow accumulations from this system.

2) Sunday 8am to Sunday 8pm: A mix of at least sleet, but possibly freezing rain and or plain rain, works its way off the ocean into SENJ first. How far this advances to the NW (all the way past I-95, just to I-95 or possibly just SE/before I-95) will have significant impact on snow accumulations, especially for areas right along I-95/NJTP. For areas that stay N and W of this warmer air intrusion, you are most likely to KABOOM from this storm (12 inches on the ground or greater) as you’ll just keep snowing. And since you will remain in Arctic air, the snow will really stack up.

3) Sunday 8pm to Monday 8am: Once the low is established offshore, it will rip colder air back downwards behind it and change areas that mixed back over to snow. This is where SENJ can pick up a few more inches of snow after changing back over to snow before everything tapers off on the ECNJ/SENJ coast.

Tomorrow (Friday), we’ll have an updated snow map posted at 5pm which will feature expected amount ranges instead of “the least you can expect” like above. We’ll update that again on Saturday at 4pm and then we will begin live observations Saturday night. In the meantime, we’ll be geeking out in KABOOM Club with model run-by-run analysis (see below ways to join). I might try to put a video out later tonight. Also, there’s a winter storm signal gaining strength around Jan 31-Feb 2. Have a great rest of Thursday evening and please be safe! JC

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