Winter 2024/2025 December Thread

[*Flash*]

ePac ridging and Hudson Bay low position/strength will be a fun tandem to watch this winter. I think we'll get some cooperation from places we didn't expect a month ago.

Side note: It hit me today how when people inquire our thoughts about a given winter, we can simply say 'I'm mildly optimistic' and we'll be right every time. 

[Carvers Gap]

Pretty clear signal in LR ext models of the ridge retrograding into the Aleutians, ridge tucking into the Mountain West, and SER establishing around the first week of January.  Now, that is a LONG way out there.  However, that fits climatology and fits the recent Nina winters.  I have my suspicions as to whether that can hold long term.  It is likely a January thaw with winter returning later that month.  This pattern coming up has an almost extreme EPO ridge, and that is not sustainable as a long term pattern.  The ridges and troughs need to be flatter.  JB mentioned today that there should be some upwelling of cooler water in the ENSO regions which should bring La Nina into play.  We want that.  We don't want a Nada which is "dud winter territory" for this area.  If we can get the weak La Nina, I think we see more cold later in winter.  For now, it looks like cold through roughly December 20th(give or take 3-4 days), then seasonal as the trough retrogrades, then a return flow from the GOM due to incoming HP, and then a great big question mark.  So, I think we have a pretty good idea of cold duration now.  I think!

[Carvers Gap]

The 12z ECMWF AIFS is picking up on a really cold shot around the Dec 8-10.  That would be a second very cold shot in addition to the Dec 2-6 timeframe.  The CPC maps this afternoon are dark purple for temps for this area.  Apparent temps during the second cold shot are showing up in the single digits for valleys and below zero for mountains.  I would almost think and ana front is probably going to be embedded within future models runs at some point.  That cold means business.

[nrgjeff]

Yeah that AIFS has sniffed out trouble before and been right. That could be the final core dump before the said January thaw starts in mid-December. This could have December 2005 vibes with the cold start and then torch.

I was in KCMO in 2005 and we got a great snow the middle of December. Unfortunately I see nothing like that in the cards for southeast Tenn. Never know I-40 north. Otherwise a waste of a pattern on cold and dry is a Southeast tradition right up there with the Iron Bowl.

[Daniel Boone]

1 hour ago, Carvers Gap said:

The 12z ECMWF AIFS is picking up on a really cold shot around the Dec 8-10.  That would be a second very cold shot in addition to the Dec 2-6 timeframe.  The CPC maps this afternoon are dark purple for temps for this area.  Apparent temps during the second cold shot are showing up in the single digits for valleys and below zero for mountains.  I would almost think and ana front is probably going to be embedded within future models runs at some point.  That cold means business.

Agree. Should get at least a couple minor snow events in the first 2 weeks of December probably for the famous I-40 North Jeff alluded to.

Usually you get a relaxation in a Cold Pattern after a full unload. It is possible a full Pattern flip but not completely sold on that due to Webber's abna research. That Pacific Ridge may end up shifting back east and poleward after the retrogression. The PV is expected to strengthen so, will lend to a +AO. So, not good there irt strong cold coming south but, if a +TNH Pattern restablishes during that, we could still get cold enough air into the area to support Snow. The NAO will probably be neautral to positive late December and January due to the + QBO but, a +TNH works well with that. Those SST'S Around Nova Scotia are supportive of LP in that area of which could assist a tall PNA Ridge and mitigate a +NAO. Jan.2015 and Feb. 2015 once again used as great examples here. Those type Patterns can blow the typical mild +AO/NAO guaranteed Torches out of the Water. The Pattern is a rarity so, you can't bank on it but, Webber's research does lend support for a greater likelihood of it this Winter. Food for thought.

[Carvers Gap]

2 hours ago, nrgjeff said:

Yeah that AIFS has sniffed out trouble before and been right. That could be the final core dump before the said January thaw starts in mid-December. This could have December 2005 vibes with the cold start and then torch.

I was in KCMO in 2005 and we got a great snow the middle of December. Unfortunately I see nothing like that in the cards for southeast Tenn. Never know I-40 north. Otherwise a waste of a pattern on cold and dry is a Southeast tradition right up there with the Iron Bowl.

Thanks for the info on the AIFS.  I have been meaning to ask how good it is.   I never know what to think of it.  It has a little bit of DGEX in it, but it has been really decent during the recent weeks I have been following it - I really have just started to use it.

[Carvers Gap]

1 hour ago, Daniel Boone said:

Agree. Should get at least a couple minor snow events in the first 2 weeks of December probably for the famous I-40 North Jeff alluded to.

Usually you get a relaxation in a Cold Pattern after a full unload. It is possible a full Pattern flip but not completely sold on that due to Webber's abna research. That Pacific Ridge may end up shifting back east and poleward after the retrogression. The PV is expected to strengthen so, will lend to a +AO. So, not good there irt strong cold coming south but, if a +TNH Pattern restablishes during that, we could still get cold enough air into the area to support Snow. The NAO will probably be neautral to positive late December and January due to the + QBO but, a +TNH works well with that. Those SST'S Around Nova Scotia are supportive of LP in that area of which could assist a tall PNA Ridge and mitigate a +NAO. Jan.2015 and Feb. 2015 once again used as great examples here. Those type Patterns can blow the typical mild +AO/NAO guaranteed Torches out of the Water. The Pattern is a rarity so, you can't bank on it but, Webber's research does lend support for a greater likelihood of it this Winter. Food for thought.

Good info.  JB says the MJO warm tax will have to get paid after Dec 20.  If the Niña comes to pass, prob more cold finds its way here per JB.  Typical Nina winters have periods of warm accentuated by severe cold.

[Daniel Boone]

3 hours ago, Carvers Gap said:

Good info.  JB says the MJO warm tax will have to get paid after Dec 20.  If the Niña comes to pass, prob more cold finds its way here per JB.  Typical Nina winters have periods of warm accentuated by severe cold.

An excerpt from Webb on X :

While there are many reasons this winter is starting out so cold in the Eastern US this year… Imo, the -EPO/+TNH pattern in early Dec is largely being driven by low frequency variability (not the MJO) from the Indo-Pacific Warm Pool. Namely, the Indo-Pacific Warm Pool is rectifying long-term observed changes since the early-mid 20th century that conflict with most climate model forecasts: the Indian & West Pacific oceans warming at a faster rate than the East-Central Pacific (in part as a response to AGW), which changes the downstream waveguide over the N Pacific & N America to resemble the +TNH pattern.

[John1122]

The Euro has light snow with clipper one but a bit more with a second clipper early next week. The icon has the clipper but way north. Hopefully the Euro is onto something. So far it's actually been less grinchy with snow chances than the GFS.  

[Jed33]

We need one of these systems to actually come through and produce a good rainfall across the area. Yes, we’ve been getting rain, but it’s been falling well short of forecast. Tomorrow’s system is no exception. It was originally a widespread 1-2in rainmaker across the area. Now, we’re looking at 0.25 to 0.50 at most. So far I’ve recorded 1.09in for November and 1in exactly for October. Hopefully that changes at some point in the near future.

[jaxjagman]

Seemingly right now its typical Nina,cold into the early season then crap as we get into towards the holidays.Even the CFS,JMA shows something similar.Maybe it will change,but it definite needs to get out of there

[Daniel Boone]

8 minutes ago, jaxjagman said:

Seemingly right now its typical Nina,cold into the early season then crap as we get into towards the holidays.Even the CFS,JMA shows something similar.Maybe it will change,but it definite needs to get out of there

Check out Eric Webbs Write-up regarding how that might not work out like usual on X. The +TNH Pattern. The ABNA Connection. I'm not sold on it totally changing the MJO effects but, his research shows possibility.

[Carvers Gap]

56 minutes ago, jaxjagman said:

Seemingly right now its typical Nina,cold into the early season then crap as we get into towards the holidays.Even the CFS,JMA shows something similar.Maybe it will change,but it definite needs to get out of there

I concur.

[Daniel Boone]

If the " cold" pattern we're going into lessens in severity or longevity, that will be crucial in determining what kind of Winter ensues i.m.o.. Also, it is possible even if it lasts until late Month ala,1989. If I remember correctly, blocking broke down then and allowed the Western Ridge to suddenly come East. 

     That MJO Plot is still worrisome as it usally Trump's other Drivers if they're not very prominent or if the MJO Wave itself is very weak low Amp.. As rehashed in earlier post, hopefully Webb is onto something and it plays out if you want at least an average Winter overal imo.

[Carvers Gap]

For now, I am sticking with ensembles in the d7-16 range.  Operational modeling has trended warmer for the past couple of days.  Wild swings like that tend to signal very cold air beginning to work its way into the pattern.  That type of low level, Arctic air wrecks complete havoc on modeling.  Ensembles OTH are quite cold with little change to the EPO ridge and downstream EC trough.  I thought I would add the graphic below just for kicks and giggles.  This is the Euro control from the Weeklies run this afternoon.  It probably doesn't have much(if any) skill.  But what is interesting is that if North America gets that cold, the MJO won't matter nearly as much.  It will simply mean "less cold" as it goes through warm phases, i.e. just different variations of cold. 

One final note, modeling will often be too quick with cold, and then bring the hammer later.  The above map shows "what could" happen as we see a very La Nina temp structure for North America, but cold just overwhelms the pattern.  It has been a long time since we have seen cold that encompassing over NA.  Again, it is just an example of one pathway that the weather could take.  There are many, many options on the table for that timeframe, especially at this range.

 

[Carvers Gap]

I think operational modeling is under-doing d8-16 temps. 

[Daniel Boone]

1 hour ago, Carvers Gap said:

For now, I am sticking with ensembles in the d7-16 range.  Operational modeling has trended warmer for the past couple of days.  Wild swings like that tend to signal very cold air beginning to work its way into the pattern.  That type of low level, Arctic air wrecks complete havoc on modeling.  Ensembles OTH are quite cold with little change to the EPO ridge and downstream EC trough.  I thought I would add the graphic below just for kicks and giggles.  This is the Euro control from the Weeklies run this afternoon.  It probably doesn't have much(if any) skill.  But what is interesting is that if North America gets that cold, the MJO won't matter nearly as much.  It will simply mean "less cold" as it goes through warm phases, i.e. just different variations of cold. 

One final note, modeling will often be too quick with cold, and then bring the hammer later.  The above map shows "what could" happen as we see a very La Nina temp structure for North America, but cold just overwhelms the pattern.  It has been a long time since we have seen cold that encompassing over NA.  Again, it is just an example of one pathway that the weather could take.  There are many, many options on the table for that timeframe, especially at this range.

 

Map looks to be showing hidson bay to Greenland blocking signature. Has Lp look near 50-50. That would probably need adjusted West of there if the SST'S are same then as now. Looks like an Aleutian Ridge. That may be or be further East. Should oscillate during Winter imo. due to the +QBO and ABNA if it manifests through the Winter at times.

[jaxjagman]

6 hours ago, Daniel Boone said:

Check out Eric Webbs Write-up regarding how that might not work out like usual on X. The +TNH Pattern. The ABNA Connection. I'm not sold on it totally changing the MJO effects but, his research shows possibility.

I'm not sure,might be a Jeff question.If i'm not mistaken the 2013-2014 winter that was the year the TNH was positive,the 2nd highest on record that was when Atlanta got crippled by a winter storm and that was the winter the snow dome came out for Nashville.Met might know if that was the year but i'm pretty sure it was for the Atlanta storm

[jaxjagman]

Here it is Daniel

 

https://en.wikipedia.org/wiki/2013–14_North_American_winter

 

 

[jaxjagman]

 

[jaxjagman]

When discussing "TNH index" with "La Niña,"it refers to the potential impact of a La Niña event on the Tropical Northern Hemisphere (TNH) weather pattern, which is a climate index that describes large-scale atmospheric pressure variations across the North Pacific and North Atlantic, often leading to specific weather patterns across North America, especially during winter months; During a La Niña phase, the TNH pattern can be amplified, potentially causing colder and wetter conditions in certain regions depending on the specific atmospheric conditions. 

Key points to understand:

TNH Index:

This index measures the strength of the TNH pattern, which is characterized by high pressure over the Gulf of Alaska and low pressure over the eastern North Atlantic. 

The Girl:

A climate phenomenon where the central and eastern equatorial Pacific Ocean experiences cooler than average sea surface temperatures, impacting global weather patterns. 

Connection:

During a La Niña event, the jet stream can become wavy, sometimes enhancing the TNH pattern, which can lead to colder temperatures and increased precipitation in certain parts of North America. 

How to interpret:

Positive TNH with La Niña:

A strong positive TNH index during a La Niña phase could indicate a higher chance of colder and wetter winter conditions in parts of the United States.

Negative TNH with La Niña:

A weaker or negative TNH index during a La Niña might lead to less pronounced weather impacts related to the TNH pattern. 

[Daniel Boone]

7 minutes ago, jaxjagman said:

When discussing "TNH index" with "La Niña,"it refers to the potential impact of a La Niña event on the Tropical Northern Hemisphere (TNH) weather pattern, which is a climate index that describes large-scale atmospheric pressure variations across the North Pacific and North Atlantic, often leading to specific weather patterns across North America, especially during winter months; During a La Niña phase, the TNH pattern can be amplified, potentially causing colder and wetter conditions in certain regions depending on the specific atmospheric conditions. 

Key points to understand:

TNH Index:

This index measures the strength of the TNH pattern, which is characterized by high pressure over the Gulf of Alaska and low pressure over the eastern North Atlantic. 

The Girl:

A climate phenomenon where the central and eastern equatorial Pacific Ocean experiences cooler than average sea surface temperatures, impacting global weather patterns. 

Connection:

During a La Niña event, the jet stream can become wavy, sometimes enhancing the TNH pattern, which can lead to colder temperatures and increased precipitation in certain parts of North America. 

How to interpret:

Positive TNH with La Niña:

A strong positive TNH index during a La Niña phase could indicate a higher chance of colder and wetter winter conditions in parts of the United States.

Negative TNH with La Niña:

A weaker or negative TNH index during a La Niña might lead to less pronounced weather impacts related to the TNH pattern. 

Exactly. That's what I had read up on too. Interesting. So, if Webb's right about the ABNA and the greater likelihood of a + TNH Lanina could work out fine for us. 

[Daniel Boone]

31 minutes ago, jaxjagman said:

Here it is Daniel

 

https://en.wikipedia.org/wiki/2013–14_North_American_winter

 

 

I'd forgot about what year that happened in Atlanta but, yeah that was one heck of a cold January ! Feb 2015 had the big +TNH Pattern as well and was historic here snowfall and cold wise.

[jaxjagman]

4 minutes ago, Daniel Boone said:

I'd forgot about what year that happened in Atlanta but, yeah that was one heck of a cold January ! Feb 2015 had the big +TNH Pattern as well and was historic here snowfall and cold wise.

Yeah i believe that was the year we had a Winter Weather Warning here in the 2013-14 for that storm but i believe we got warm nosed in our parts it ended up being just liquid rain,thats when the snow dome started.

[Daniel Boone]

1 hour ago, jaxjagman said:

Yeah i believe that was the year we had a Winter Weather Warning here in the 2013-14 for that storm but i believe we got warm nosed in our parts it ended up being just liquid rain,thats when the snow dome started.

It was. We had a record snowy February in 2015. I recorded about 34 inches in Jonesville. Northern section's of Lee County over 50" !

[John1122]

Just had a heck of a rumble of thunder. It's not quite winter but I'm hoping the T.I.Ms index fires. 

[John1122]

2013-14 was frigid in January and cold/snowy in February. We had a particularly big snow around Valentines day here. 

[Daniel Boone]

20 minutes ago, John1122 said:

2013-14 was frigid in January and cold/snowy in February. We had a particularly big snow around Valentines day here. 

Yeah it was here too. The Valentines day Storm was 6-9" in Valley locations here . A Miller A. 

  Several 2-4 inch deals in January, mainly Clippers as I recall. 

[*Flash*]

It's a one year sample but if you go back and look at the last strong +TNH pattern (I.e. 2013-14), I-40 between Memphis and Nashville was shut out consistently. The 'Snowdome' winter as they call it locally (for BNA, the #1 worst winter in terms of mean temp/total snow) preceded my first year on this forum. I'm not suggesting a repeat at all; however, unless we get some eastern blocking mechanism, I'm not sure all parts of TN will capitalize. That said, December continues to look more encouraging by the day as new data comes in, but the long term is still iffy. As several have already mentioned on here, how the TNH/EPO combo develops will be telling moving forward. 

HAPPY THANKSGIVING, EVERYONE!

[matt9697]

20 minutes ago, *Flash* said:

It's a one year sample but if you go back and look at the last strong +TNH pattern (I.e. 2013-14), I-40 between Memphis and Nashville was shut out consistently. The 'Snowdome' winter as they call it locally (for BNA, the #1 worst winter in terms of mean temp/total snow) preceded my first year on this forum. I'm not suggesting a repeat at all; however, unless we get some eastern blocking mechanism, I'm not sure all parts of TN will capitalize. That said, December continues to look more encouraging by the day as new data comes in, but the long term is still iffy. As several have already mentioned on here, the TNH/EPO combo develops will be telling moving forward. 

HAPPY THANKSGIVING, EVERYONE!

Wonder what specific pattern is good for the entire forum area? I can recall as a kid, the trifecta of winters, 76/77, 77/78 and 78/79 I believe were good for the entire state but not really sure what types of patterns existed upper-air wise that produced them.