eduggs

We could have gotten a coastal snowstorm this weekend if the multiple shortwaves interacted just a little differently. The trof axis has good amplitude and orientation and there is sufficient cold air available. Snowstorms are local phenomena that depend on nuances in features and their evolution. Yes the background airmass and longwave jet structure is important, but it's usually the minor details that deliver snow.

I think you attribute too much causal certainty to ENSO, MJO, and other climate indices. Most of the correlations are weak, and the indices themselves, broadly defined. There is a lot of randomness in weather outcomes.

It amazes me that people keep looking at ensemble charts out beyond 14 days. They have effectively no skill. We have seen it over and over, yet people don't learn the lesson. If there's light way out there at the end of tunnel, you won't see it coming until it's much closer. Often it will just surprise you in the mid-range.

I don't remember any winters like this. Back then there were low snow years and warm periods, but the temperature still went below freezing regularly. This winter is not comparable in that regard.

I'm feeling uneasy about my predictions. We'll probably need a big event to get close.

You can squirm and twist all you want. But facts are facts.

Not correct that there's no cold available. <10C 850mb temps to the Carolinas and sub 530dm heights at 500mb throughout the mid-Atl on Saturday. We even have a very high amplitude longwave trof with a nearly perfect alignment and orientation. Our problem is in the nuances of the height structure... the evolution of the shortwave interactions. Snow vs. no-snow outside the mountains is almost always due to the nuances of mid- and upper-level features.

If you loop like 168hr - 216hr on the 12z GFS North Atlantic view it looks like two hurricanes moving westward in September. I don't remember seeing such well defined mid-level lows in that region during the winter, but I don't usually look for it either.

Not trending colder per say. Clearly the initial phase and SLP track into Ontario has trended sharper with a quicker scouring of antecedent cold. But one thing that's changed from 3+ days ago is that there's a fresh cold air source to the west that isn't being immediately pushed out by the next wave. Days ago a modeled negatively tilted ULL was pinching off and being separated from the longwave flow, resulting in a complete emptying of subfreezing surface temps east of the Mississippi. With CAA behind the "front," at least there's a longshot chance of developing a new SLP on what's left of the baroclinic zone that could potentially produce snow somewhere along the east coast.

Radiational cooling conditions are decent tonight. It's just fake (i.e., low level) cold. Check a sounding. The airmass is warm for January.

Every major midrange model - UK, CMC, EC, ICON, NAVGEM - with the GFS as the only exception, gets snow into or near our region on Saturday. That's 5 days out. It's a tenuous setup for sure, but it's something. I haven't looked at individual ensemble members, but I'd suspect there are a few that drop significant snow for our region.

The 12z CMC, EC, UK, and 18z ICON all get snow to our area or near NW this weekend in the manner I speculated about yesterday. Unfortunately the scenario is less than ideal because the early, initial phase and SLP to Ontario has pushed the initial antecedent cold air far to the NE and we are left waiting for fresh cold to seep in from the W. IMO prospects for some snow have increased since yesterday. I do not believe this scenario is hopeless, although we would need a lot to go right. Inland, elevated areas would be favored and significant snow is unlikely. It would be nice to get the GFS on board, but it trended away at 18z.

The 18z GFS gets a vortmax and 546dm 500mb heights to the FL panhandle with a slightly negatively tilted trof. That should mean potential. The problem is how we get there and the residual 500mb low center in Ontario.

At least the 18z ICON and RGEM don't match the GFS with the clean phase and SLP into Ontario.

The 18z GFS continues with a northern stream shortwave that is too sharp and too closely spaced with the southern wave, which allows wave phasing and a SLP into southern Ontario. This scours the cold air, shunts the baroclinicity offshore behind the front, and taints the 500mb height structure and any follow up coastal.

The 12z CMC shows the coastal low that I believe we need to deliver a miracle for us. It grazes Cape Cod at day 6 and then dumps heavy snow on downeast Maine.

I think the ICON is somewhat close to a longshot scenario that could bring snow to our area or the NW fringes. At day 3 there is one shortwave over CO and another over MN. If they stay longitudinally separated far enough, the more northerly wave can interfere somewhat with the maturation of the southerly wave and shunt any surface reflection further southeast. Wave amplification typically occurs when a shortwave is on the downstream side of a longwave trof. In the ideal scenario, a 3rd follow up wave (upper Midwest at day 4) phases with the southern wave, dropping into the backside of the trof, leading to amplification and negative tilting. If we can avoid an initial wave phasing and resulting SLP into western NY, there may be enough cold air relatively close by to tap into a coastal low. We would still need the trof to take on a significant negative tilt, without pinching off the cold air source, to wrap some moisture back into the cold air. I believe a few ensemble members have shown something like this. But the UK, EC, and GFS are pretty far off.

Yeah the recent model cycles show it cooling down for a day or two around the weekend. But if there are clouds behind the ULL or if guidance switches back to the pinched off ULL that might change. I think it could be a close call for the urban centers.

I'm not rooting against NNE snow. And we would probably all take whatever snow we can get. I just don't agree with the interpretation that the 12z EC is a good snow outcome for anybody outside of Maine considering the potential setup and time of year.

6" in the mountains on a clown map in mid January is not impressive, especially with a high amplitude trof and copious moisture available. Plus many south of NNE flip to heavy rain anyway.

EC and UK are both hideous for anybody outside of Northern Maine.

It looks like there's a small chance some NYC urban areas won't hit freezing all January. I think we'll get a seasonably cold day or two at least, but it's not a given.

CMC is northern stream dominant. That feature has to be way out ahead or flat. Only NNE can cash in with a surface low anywhere near the Lakes.

Detroit - Rochester SLP primary track on the 12z GFS is not what most want.

Keep that primary slp south and east of PA and it's game on for all of NNE and possibly further south. As many have noted, the key is to avoid an early phase.