Carvers Gap

The EPS is on an island right now. The Euro Weeklies, after being locked-in for weeks, have flipped to AN temps for week one of December and normal for week 2. It is definitely "can kicking." On the other hand, the GFS and Canadian ensembles and LR ext models have assumed the Euro Weeklies former "cold is king" spot. Welcome to shoulder season modeling. The CFSv2 at lunch was just ridiculously cold w/ the ridge heights and trough lows. We are talking subtropics to the NP. That is not a stable pattern, and probably why we see differences. But....that is a pattern which could deliver insanely cold air into the Lower 48. The December which Boone referenced and 89 would be on the table as ensembles. I "think" cold is coming, but going into battle with the Weeklies flipping doesn't give me great confidence. I often wonder if the Euro Weeklies are about 1-2 days ahead of other LR ext models w/ better data. With the Weeklies trending away from a cold start to December, I would think other LR ext models will do the same during the next couple of days - if they are actually going to flip. BTW, the 500 pattern isn't terrible on the Euro Weeklies, but it isn't cold either. The SSW....has screwed up more than one great cold snap during the past decade. That event often wrecks havoc on modeling and can inflict damage on what looked like a promising event. The SSW....most likely we are looking at modeling bouncing around due to low level cold air being underneath those 500 patterns. Might as well drop a cat in a bathtub - cause all you know what is gonna break loose. Overall, I think cold is coming just after thanksgiving, but with a strong word of caution. FWIW, I generally like the CMC when cold is in the forecast at medium and long range. It often over-does the cold, but it actually "sees" it. I would feel a bit better if the Euro and EPS hadn't been right about this last system, and "at range" to boot. But the GEFS was sneaky good as well - just not the GFS. The GEFS looks like a good compromise for the two weeks after Thanksgiving.

Whew. Not often that I see an ensemble look that cold at range. The 12z GEFS looks similar, but with lighter blues. That is most of the continent. 384 map...so proceed with caution.

The 0z GEPS and 6z(edit...) GEFS are frigid at the ends of their runs today. The EPS is lagging as it kicked the can by about 3-5 days yesterday. It still "should" get there, but have to be careful for the Charlie Brown football deal. When ensembles get that cold, chances start to go way up. Those ensembles are cold for about 75% o NA and almost all of the Lower 48. Pretty impressive.

Just checked. Nope, not December 2020. Though this current projected cold looks remarkably similar in its progression. I am looking for the year where an epic December(way better than what weeklies have now) delayed by about three weeks. It might be that late December/early January cold snap where it didn't snow much - 17 or 18'? I remember sitting in a movie theater and seeing the Weeklies flip warm. I know...get a life right? I had been banging the cold drum for weeks, and it was like someone turned the lights off! LOL. Seems like it has been 7-10 years since that time. I can remember really two places where I connect weather models going nuts(good and bad) and a specific location. The other one(besides the movie theater) is in Hampton. We had been back in the boondocks with no cell service. When we got to the hill overlooking Hampton, I got several texts from @tnweathernutw/ snowmaggedon maps that originally included us. To this day, I hate missing a 12z suite because of that. Those maps were flat out nuts. DC got most of our snow, but the model runs for a few days were epic.

I honestly don't use the MJO much in November and early December. I wonder if modeling is over-emphasizing it. Either way, a delay would probably allow for the cold to last into early January - good recipe! I will say that I track an "eastern" cold shot only to have it dump West...and then come eastward around Christmas. It was delayed by about three weeks. I need to check the thread, but that might be the Christmas Eve anafront year.

The Euro Weeklies today use the first week as a transition week(as opposed to full blown cold) and repay us with cold the rest of the month. I am seeing a bit of a trend to dump cold in the west and then it spreads eastward. We have seen this trend on modeling(and it be correct) more times than I can count during the past decade. The 12z GEPS absolutely slams the cold into the West and it quickly spreads eastward. With all the bouncing around today, this may be a very wicked shot o cold air - lots of bouncing around with very cold air. It is worth noting that the Canadian model suite will often "see" the extreme of cold air first. While the Euro is sidestepping a bit, the GEFS and Canadian ensembles at 12z are quite cool. Remember it is shoulder season and possibly VERY cold air in the mix for December....so no surprise today.

Thanks, @John1122. Great stuff. And JP Estrella looked good last night!

All three 0z global ensembles show the transition to an EPO and/or PNA ridge by very late this month. Operationals don't have it at 0z, but that could easily change. Ensembles are the choice for now. Hopefully, we see further runs over the next 2-3 days which sporadically show major cold out breaks at least heading SE out of Canada along with big highs.

Today's 8-14 analog package from CPC... 19611207 20001106 20001111 19521122 19831124 19671210 20041119 19981106 19711115 19691110 The one that really stands out is the 83-84 winter due to the cold which came early during that winter. It was just brutal. I remember riding to town in our Toyota, and the windows froze up on the inside! @John1122will have to fill in the blanks for the 1960s. Generally, if I see winters from the 1960s showing up...those are gonna have some decent analogs(not all). We may have some others with knowledge of those winters as well. Keep in mind, these analogs are centered-on a warm time frame. So, let's see where these go as we get deeper into winter, and see if we see a particular analog which survives from week to week. I like to look at analogs during forecasted warm-ups. If they turn cold later on, that may tell us something.

We are starting to sporadically see deterministic modeling (at very long range) spotting the potential for a massive EPO/PNA ridge. The 12z Euro is just the latest iteration. That ridge connects to a ridge over into eastern Asia. Europe goes into the ice box which teleconnects well to a cold eastern half of NA. That is the type of nechanism which can send bitterly cold air into North America, particularly the East Coast. Way out there and huge grains of salt.

I like watching the daily run of the CFSv2 seasonal. I generally watch trends. It does bounce a round quite a bit, so be forewarned. Today's run was an extreme run. Cold December, followed by a colder January, followed by a colder February. This is about the time of year that we can peek into early winter and see if our thoughts over the summer were correct. We can also begin to sort through analogs. I think Cosgrove's ideas have some merit in that winter will have a cold finish. He is just one of these guys who has seen a lot of weather, and has experience of decades of forecasting. But what if he is right, AND those of us(who are calling for a cold start to winter) are both correct? It has been a while since we have had a wall-to-wall winter. While I think wall-to-wall is unlikely, I do think a cold 2-3 weeks to start December, followed by 3-4 weeks of meh, followed by mid-late Jan into Feb cold...is on the table. But here is the extreme. And that might not look overly extreme, but given the configuration of the surface pressure maps below...there is an increasingly strong possibility of very cold temps being released into the lower 48. During a La Nina, the SE extent of the cold will often be more blunted than below. However, during weak La Nina winters...we can see that SE extent do exactly as modeled below. Not always, but there are precedents for that look. Over time, I have learned to look at surface pressure maps. I do this in order to see where the coldest air is. They are counter intuitive in that we look for BN heights at 500mb for but we look for AN heights at the surface. During winter, that can be a strong signal for cold air. Cold air anchors itself into the Canadian Prairies, and builds. As the season modeled progresses(below), the cold pushes. This is an "old school" winter setup where winter just kept coming. FTR, I am not saying this will happen, but it does catch my attention when modeling shows it - even LR ext modeling during shoulder season.

Today's GFS is the first of the operationals to get Nov 27th in range, albeit waaay out there. That is generally the earliest part of the potential window for sustained winter cold. Some modeling waits a few more days. The 12z GFS fits with what LR ext models have been saying. Now, we have seen head fakes at exaclty this range and at exactly this time of year during prior years. We have also seen LR ext models nail the forecast 4-6 weeks out. The GFS has a knack for spotting patterns at d16 during early winter. Here is a collection of maps from the morning and afternoon suites. 1. You can see the cold air configuration for DJF. The CFS flips flops between front loaded and back loaded winters, but generally this shows up regardless. I title this one "Remember when everyone used to talk about International Falls during cold outbreaks?" 2. The CFS daily runs 4x per day and can offer some fun solutions. I title this one, "Send it all to Cuba." This was from 6z. 3. The CFS at 0z gave us this lovely west PAC ridge. I title this one "Cold and dry." 4. As noted in the intro to this post, the 12z GFS now has Thanksgiving week in range. I title this one "Didn't we just do this yesterday?"

Wind chills at TRI dropped to 10F early this morning. I went running at a local state park this morning, and froze my tail off!!! Strava said the wind chills were 24F. Nope - they were 17F!!! That is probably the second coldest run I have done, but felt worse as I was exposed to the wind much more than other running routes. Last night, we had light snow until 10:00PM and likely much longer. This system was a powerhouse. We rarely get NW flow in Kingsport. We had several streamers. If this had fallen at night, we would have easily gotten 2-4" of snow. Just looking at some of the dates being kicked around for November snows...'93 and '14. Those went on to be benchmark winters for cold and snow. Will this winter follow suit? Time will tell.

Definitely some level of convective rotation. I have noticed it off and on today. Honestly, I am a little surprised there have not been reports of rumbles of thunder. Might just be too cold.

No particular order. Just thought I would share some LR ext maps and maybe throw in a seasonal. I am mainly looking at the time frame from Thanksgiving to Christmas. I tend to think the cold arrives just after Thanksgiving and holds to just before or right to Christmas. I think we have a very slight ridge or at least something to turn storms slightly northward if they slide across. I did throw in one turd burger control run just to show you how different the Euro Weeklies mean and control are. Pretty strong cold signal overall for early and mid December. There are much cooler weeks embedded within those 30 day maps.