Carvers Gap

December thread has been started. If December wx is slow, I will just convert it to Part I of probably multiple, winter threads.

We will soon find out if the high latitude blocking signatures pay dividends for our area. May need a boat and may also need snow shovels. We'll try separating this into threads by month. If that doesn't work, I will simply switch this to Part I of winter. Have fun and good luck!

As you can see above, the source regions are frigid. One cutter, and much of that cold comes eastward. The NAO is strongly negative. I noticed that Bob Chill in the MA forum notes that often when the NAO is that negative, it tends to hang around and the overall pattern is very tough to break down. Food for thought. NOTHING IS A CERTAINTY. This is spitballing, and should be noted this is in the 10-15 day range. We all know the rules. Probably time for a December thread. Edit...I will get the thread started.

This is what corresponds to those above...Euro is about 36 hours slower.

Temps are cold from the Apps west, northwestward. That is a strong high latitude blocking signature. If true, I expect severe cold to ensue. Pretty easy to see where the storm track battle line is drawn. As noted above, flooding is a possibility as well as an extended overrunning event in the areas where cold and GOM moisture intersect.

Woof at the 18z GEFS. Looks more like the Canadian and EPS now. That is a COLD look.

The 12z EPS has a MONSTER -NAO. It is so strong that it nearly overcomes a PAC that is the exact opposite of what we need it. BN temps still relatively on target for mid-December...could begin during week 2 of December. Huge grain of salt right now as this is a wonky set-up...could be much colder or much warmer.

Patterns is very blah after what looked like something promising. I still think mid-December looks like a good window for the beginning of cold. Nailing down that timeframe has not been easy. Certainly looks like the trough will pull into the West in January, if not before. But really, I have no crystal ball on that. The Pacific is so hostile, I am not sure the trough can hold in the east at all for more than a few days. That said, January climatology normally does the trick.

The ensembles are spitting out a pretty nice pattern from mid-December onward. Cosgrove has been doing pretty well this late fall...he has a nice write-up about it on social media. How long does the cold last? TBD. As John noted, there are some similarities to '89, but there are also some similarities to some winters which saw cold come back after a brief January thaw. The bridge over the top of HL blocking is a pretty good signal for winter here.

12z GEFS does not support the operational after d10. I think the idea of the next cold shot coming around mid-December looks about right.

12z GFS today has the bridging of the HL PAC and Atlantic blocks now at hour 288, roughly beginning Dec3-4. Guessing part of the TPV gets trapped and sent southward. Impressive look. 12z GFS w/ a hold my beer run compared to yesterday's incredible look at 12z.

Looking at the 0z CFSv2extended/seasonal, 6zGEFS, and Weeklies(careful as today's runs don't look overly similar...), I am beginning to feel more comfortable that a window of cold/wintry weather will make its appearance around mid-December. And that might be our shot. That window has been tough to nail down. Duration is incredibly tricky as well. This is just spitballing. The cold could show up anywhere between Dec 7-15th, and maybe last 10-20 days(if pressed I would say Dec 10th...earlier if the 6z GEFS is correct, but it is prob rushed). Christmas is too far out to say anything with certainty. Some LR model runs show cold...some not. The third week in December seems almost universally cold on modeling though.

Pretty nice run of the Weeklies and looks to really repeat what we have seen during November. Cold shots followed by ridging....wash, rinse, repeat. NAO gives way to an EPO ridge later in the run - displaced slightly westward but still will work. I have seen MUCH WORSE runs than that. We are almost out of shoulder season, so the "trust factor" of the Weeklies edges upward with each run now.

It is 384 for kicks and giggles. That traps the PV. Blockimus Maximus.

I mean really for MBY, we are five to six weeks away from prime climatology, so even tracking at this time of year(my elevation) is a bonus! The early snows of the past decade were not something I even saw as a kid at lower elevations. Now the Apps and Plateau, snow is not uncommon beginning now.

Regarding the NAO, some runs it appears it is headed for an alignment which would benefit us. On others it is east based which would favor cold for Nova Scotia and the extreme NE. With the Pacific being hostile (PNA/EPO included), the NAO from what I have seen is only blunting what would otherwise be a record setting torch. As is, the NAO will keep us seasonal. Even marginal help out west would create very cold conditions here. OTH, if the NAO backs off....torch city. I tend to lean towards a period of moderation during the early half of December, an idea shared by many. I then think that we see the end of December turn cold before flipping to a potentially winter-ending pattern in January. Not saying that is a certainty BTW, but that is on the table. The other option is winter just ratchets down and never warms back up truly. There is the potential for a modified 95-96 pattern. In NE TN and the mountains, we are long overdue for that. 14-15 is on the table as well.

Looks like we are going to see a cutter(unless something abruptly changes) on Friday. We could still see some snow showers and flurries along the Plateau and mountains. I would think the valleys have a shot if the Euro is accurate. The reason for the cutter? Well, climatology supports that track as Nina is in place. It also looks like the energy for this storm(to my eyes anyway), is coming out in several pieces with the main energy cutting int middle and west TN.

The 12z GFS is a doozy of a solution. That is rain changing to snow in the northwest quadrant. Mountains would get hammered.

1. The overal northern stream dominance reminds me a lot of 14-15. 2. 12z EPS looks much better than this morning.

12z Euro w/ same wave-along-a-front set up.

The 12z GFS...Pretty good look around the 26th. Cosgrove was money with that comment on social media.

Cosgrove noted on FB just a few mins ago that he thinks the morning operational runs might have been in error w/ re: to the absence of snow and a storm.

Remind me of late Nov/early Dec 1975.....

That is the textbook look we need. Ensemble is continuing the meh look from the past several runs which sends a ridge into the middle of the country and builds eastward. This could be a time where the operational may lead the way. It seems like the GFS operational does handle early season cold better.

Just to tag onto my post above. Blocking over Greenland is not far enough southwest to fight the upcoming PAC pattern which is nearly opposite of optimal for cold in the East. It is not a classic Greenland block on the GEFS. Need it centered closer to the Davis Straits. Otherwise, Michigan benefits and cold doesn’t press.