December 2020 Medium/Long Term Pattern Discussion.

[John1122]

The ICON has a snow event starting at 159-162 for the eastern half or so of the forum.  

[John1122]

The Euro has a storm in the same timeframe as the ICON that has more of an Apps runner look, it's wintry with snow/sleet in western areas of the Valley followed by upslope snow showers for the Plateau and Mountains.  

[Holston_River_Rambler]

John covered the Nov 30 - Dec 1 storm, so I'm gonna look at the pattern after that for the oddball cutoff. 

Looks like the Euro is also trying to do that big ridge bridge at the end of its run:

so it's op would probably support, after day 10, a similar cut off solution to what the GFS has been showing for a few days (yesterday's 18z run shown here, by popular request):

 

Even the smoothed EPS mean has a pretty strong signal for over-the-top ridging:

 

[Holston_River_Rambler]

I'd also add that the EPS has a healthy number of members that see both windows (Nov 30 - Dec 1 and Dec 4 - 6), but many of those members see ways to make both or at least one storm, mostly rain. Still, one of the most interesting patterns I've seen since I've been on Americanwx. After the past couple of years, hard not to expect it all to disappear as we get within a few days. 

[Carvers Gap]

The system early next week is probably going to have to be watched.  Euro is amped more and it cuts through TN.  GFS is more progressive, and jogs eastward.  CMC sort of splits the difference.  The pattern from d7-15 has several pieces of energy with blocking over the top.   Just need to reel in one of these(and there are multiple systems) during the next couple of weeks.  Would appear that major changes(to our current pattern) are potentially on the way.  Great overnight discussion.  

[Reb]

Gfs looks like it’s going to be a hit 

[Holston_River_Rambler]

After the Nov 30 - Dec 1 storm, the 12z GEFS haz a confuzelment regarding the cut off that the op has now lost:

 

 

 

[John1122]

The pattern is good at this point and that's about the best we can hope for. Blocking over the top, cold air around, very low sun angle/short days this time of year, and systems working their way west to east.

[Holston_River_Rambler]

Ukie is almost there, but further W in its evolution (my access only goes out to 144 hrs)

[John1122]

It amps up faster on the UKIE and turns north faster because of it.

[Wurbus]

Euro has the Nov 30th/Dec 1st system cutting up through Nashville with some plateau/mountain love and flurries/light snow for most of East TN after it moves through. Looks to be chilly, regardless of precip.

[Wurbus]

That low just gets cutoff over Michigan and spins for days. If that happens, some of those totals in MI are going to be insane, especially with lake effect snow.

[tnweathernut]

This could be a bias of the Euro as we watch it roll in.  Since their last upgrade it has a tendency to over-intensify storm systems.  A further west track as a result (as shown on 12z) makes a lot of sense.....

Odds of a Miller A are increasing.  Likely wet, but the chances for first flakes for some are not out of the question.  At the very least it will probably FEEL like winter as early as next week.

[tnweathernut]

Just now, Wurbus said:

That low just gets cutoff over Michigan and spins for days. If that happens, some of those totals in MI are going to be insane, especially with lake effect snow.

Yeah, lake effect totals would be enormous for some!

[John1122]

The Euro slows the wave in the SW, which is one of it's classic biases at this range. We will see in the next few days if it keeps that up. Right now I'd say we are going to have a system for sure but I could see it anywhere from the central Carolinas to Memphis as it turns north.

[BullCityWx]

I noted on our side of the mountains that the GFS is giving us our coldest early december stretch since 2000. The first 10 days could have some serious negative anomalies if this holds. 

[John1122]

Another Apps runner on the Euro at the end of the run. Too much S/SW flow ahead of it to produce frozen outside of Arkansas initially. The back size frozen eventually works it's way into Tennessee but I've rarely seen the backside stuff work out very well but if it moves due north or even slightly NW it could cause wrap around snow down into our backyard. The Great Appalachian snow storm in 1950 happened when a massive block over Eastern Canada forced a storm to move west. There's plenty of blocking in the NE on the 12z Euro at 240. Just not a ton of cold air. The 1950 system was brutally cold.

[Carvers Gap]

The Euro after d10 has them lined-up across the Pacific cutting and likely cutting right under that PNA ridge which gets hooked into a block over Greenland.   If that d7-10 is even remotely close to being correct, then cold air from the Arctice would be released southward.  The blocking on the Euro after 200 is insane.  Again, that has been a huge red flag that the run was going to fail(in the past).  Thing is, that look is all of the way to 200 now.  For kicks and giggles look at the 500 map from the North Pole view...and just watch that block evolve.  

[Carvers Gap]

If the Euro is a bit over-amped.....look out.

[John1122]

The PNA is very very positive all the way through December 9th, the SE ridge looks like it might come back towards mid-month per Eric Webb, which would lead to possibly icy solutions in that environment.

[Holston_River_Rambler]

EPS means:

MSLP:

500mb:

 

850 temps:

 

precip:

 

whether any of this plays out or not, that was a pretty 12z EPS run

 

[tnweathernut]

26 minutes ago, Holston_River_Rambler said:

EPS means:

 

whether any of this plays out or not, that was a pretty 12z EPS run

 

Other than looking great as you mention, I also like the part about moisture gathering again to our SW at the end of the run.........

[BullCityWx]

Didnt want to reupload the images over here but it's safe to say the OP euro was too amped if you believe the EPS.

[John1122]

18z GFS cuts to Indiana and Ohio and does a loop. Indiana gets buried. A few snow bands would possibly up somewhere in parts of our forum region with it, but overall not our best look by any means.  

Modeling is coming into agreement today with the low being on our side of the mountains. Unfortunate if it sticks that way, as our path to snow becomes a less conventional one.  

[Holston_River_Rambler]

Queen City posted this in the SE forum, but here are the EPS member surface lows over the course of the potential storm:

It's hard to see, on my gif, but there are quite a few ~1000 mb and some sub 1000 mb lows to out SE on the 12z run. NAVGEM is, well, the NAVGEM, but it seems to show a compromise like the EPS mean:

 

It really wants to cut, badly, but that N stream energy bullies it S and E and it turns into an inland runner. 

18z GEFS is further east than the OP, likely it is splitting the difference between the two camps:

And there are some members that cut the 500 mb energy off SE of us or at least push it east of us as the N stream energy rushes in and phases. 

I think a lot is going to depend on the speed and timing of the N stream energy as to how much latitude the S stream energy can gain before it passes our longitude. 

I think the N. Stream energy is over Kamchatka or Mongolia now. 

[John1122]

Interesting tweet from Ventrice today. He said a Siberian stratospheric warming event was shaping up for week 2. The 7 day lag map he posted feature major blocking in Eastern Canada and BN heights nearly nationwide. Some of the biggest height anomalies in the lower 48 were based in the South and Southeast. 

[Carvers Gap]

18z GEFS is basically several waves running a boundary after the initial storm.  E TN saw a fairly strong uptick in the snow mean compared to 12z, especially NE TN and SW VA.  Where is @BlunderStorm?

[Met1985]

2 hours ago, Carvers Gap said:

18z GEFS is basically several waves running a boundary after the initial storm.  E TN saw a fairly strong uptick in the snow mean compared to 12z, especially NE TN and SW VA.  Where is @BlunderStorm?

Yeah thats a great signal for upslope snow for our area. Im cautiously optimistic. 

[John1122]

The 00z GFS is so weird I posted about it in banter. The low cuts into the block, then gets stuck and goes from Michigan to Illinois to West Virginia to Pennsylvania back to Michigan. Then it sits in SE Ontario for a while before getting kicked north. 

[John1122]

The Euro bombs out an Apps runner that retrogrades a bit to the NW. It  was kind to the Eastern 2/3rds of the valley with wrap around snow, unfortunately not for the western areas that run. It almost followed the grand divisions in the state.  It has a second system that's a Miller A running just east of the Apps that sees rain to snow in the higher elevations of the Plateau and Mountains. The Euro pops a massive -NAO later in the run too. Lots of storms in the pipeline, some cold air but it's not extremely cold, as is often the case this early in winter season. Still with very low sun angle and very short days this time of year, it can work out pretty well for us. 

All that of course could change. The first storm and it's behavior will heavily influence what happens behind it, and if we get the blocking as advertised we could have some very good times for the next two weeks or so.