Absolute Vorticity

I'll go ahead and get the December thread going as we continue to track mounting evidence of a nice stout -NAO.


GEFS


EPS


EPS continues to try and retrograde the GOA trough some to pop a +PNA while the GEFS may show a more transient +PNA. Either way it is not a text book look but it isn't a warm torchy look either.

Toward the end of the GFS range, but the attached graphic illustrates my thinking of a warm to very warm middle of the month. Les I believe you are in agreement with that as well. That could be one heck of a torch! The stage is certainly set for it on some of the models.

Trevor wrote: ↑Fri Nov 24, 2023 3:13 am Toward the end of the GFS range, but the attached graphic illustrates my thinking of a warm to very warm middle of the month. Les I believe you are in agreement with that as well. That could be one heck of a torch! The stage is certainly set for it on some of the models.

Trev, if the Pacific does not cooperate, then yes. I am in total agreement. Yes, we will have a -NAO, but if the EPO stays positive then we will certainly have a trough in the West and a ridge in the East for the torchy period. Also of note is the MJO which looks to die out in Phase 3 and not take a tour into the warmer phases 4-6. So honestly, it does remain to be seen how long the warmer period may last. It may not last as long as I once thought (2 weeks). If the MJO comes back out in Phase 7 or 8 which I am seeing some hints of after mid December then that could set us up for a nice Holiday period this year.

Back to the medium range period here and we will start December off on a quiet note with warming temps into the 50s by the weekend (Dec 2-3). However, our first system to deal with looks to arrive sometime Saturday or Sunday the 3rd in the form of rain with a cold front. We may see another rain maker shortly thereafter as well with the STJ beginning to make its presence known.

Good Morning Les and Trev. The warmup and most believe this will happen and I agree. Just not sure how warm we get and one reason is the flow looks like its out of the GOM and like we have been mentioning for months the GOM is loaded with moisture and we just need a transport to bring it north. I can see some low and maybe mid-60's ahead of a front but getting much warmer may be hard if we get the moisture transport which would mean some decent rains. The MJO is another wild card and where does it go. Going to head into phase 3 late next week and that is a warmer phase but models trying to bring it into the COD.That will keep milder temps around until it moves into another phase. Just not sure what phase that is and will it just remain in the COD and keep us status quo for a week or so.

Late November and early December has always been a rough ride for models as the northern hemisphere heads toward winter. Looks no different this year and expect more wild swings in the models.

tron777 wrote: ↑Fri Nov 24, 2023 8:02 am

Trevor wrote: ↑Fri Nov 24, 2023 3:13 am Toward the end of the GFS range, but the attached graphic illustrates my thinking of a warm to very warm middle of the month. Les I believe you are in agreement with that as well. That could be one heck of a torch! The stage is certainly set for it on some of the models.

Trev, if the Pacific does not cooperate, then yes. I am in total agreement. Yes, we will have a -NAO, but if the EPO stays positive then we will certainly have a trough in the West and a ridge in the East for the torchy period. Also of note is the MJO which looks to die out in Phase 3 and not take a tour into the warmer phases 4-6. So honestly, it does remain to be seen how long the warmer period may last. It may not last as long as I once thought (2 weeks). If the MJO comes back out in Phase 7 or 8 which I am seeing some hints of after mid December then that could set us up for a nice Holiday period this year.

I agree with you that the longevity of the above average period (and possible torch) will be less than I expected as well. I'm now thinking max 10 days, but probably more like 5-7 days. December as a whole is not looking nearly as warm as I was expecting.

Both the GEFS and Euro Weeklies support a return to below normal around the 15-16th and lasting through the holidays.

Good morning gents and no doubt! The operational models will continue to flip and flop esp. beyond Day 10 so we must continue to look at the Ensemble guidance for trends. The trends on the last few runs have been for a -PNA to start December but after the 5th, it may start to trend positive. GEFS Tellies has a +PNA, -NAO, -AO combination that could deliver legit below avg temps after December 10th. This is all speculative this far out but that has been the trend as of late. The STJ will be active either way as we have been expecting but the storm track is up in the air for Week 2 of December IMO should the trends hold. I can say with fairly good confidence that Week 1 will avg mild. Originally, Weeks 2 and 3 were my mild weeks but now I am beginning to question it. I don't think we will see a raging -PNA with troughs digging down into the Baja like last year. While we may see some milder weather, it won't be historic warmth like last year. I am tossing that out the window. With an El Nino, you typically don't see -NAO's in December so this is actually a very encouraging sign that it is continuing to show up on the guidance and it may bode well for winter as we get deeper into the season. It is currently the Pacific side that holds the most concern for me. The EPO is positive as previously stated but if we can flip the script on the Pacific side, we may certainly get some December fun at some point during the month. I'd consider that a bonus if it were to occur.

tron777 wrote: ↑Fri Nov 24, 2023 8:33 am Good morning gents and no doubt! The operational models will continue to flip and flop esp. beyond Day 10 so we must continue to look at the Ensemble guidance for trends. The trends on the last few runs have been for a -PNA to start December but after the 5th, it may start to trend positive. GEFS Tellies has a +PNA, -NAO, -AO combination that could deliver legit below avg temps after December 10th. This is all speculative this far out but that has been the trend as of late. The STJ will be active either way as we have been expecting but the storm track is up in the air for Week 2 of December IMO should the trends hold. I can say with fairly good confidence that Week 1 will avg mild. Originally, Weeks 2 and 3 were my mild weeks but now I am beginning to question it. I don't think we will see a raging -PNA with troughs digging down into the Baja like last year. While we may see some milder weather, it won't be historic warmth like last year. I am tossing that out the window. With an El Nino, you typically don't see -NAO's in December so this is actually a very encouraging sign that it is continuing to show up on the guidance and it may bode well for winter as we get deeper into the season. It is currently the Pacific side that holds the most concern for me. The EPO is positive as previously stated but if we can flip the script on the Pacific side, we may certainly get some December fun at some point during the month. I'd consider that a bonus if it were to occur.

Good post. I think we are both in agreement on how December is looking now versus how we originally had things mapped out. I mentioned the 15/16th for the return to below normal but I think that may be too late. Somewhere earlier in week two would be a better guess like you suggested.

Week one definitely looks warm the way things have trended and that will likely be thanks to a cutter. But that cutter will also help usher in some cold weather and like you said, the remainder of December does look mostly below normal. Much different than I had originally planned on thanks to what looks to be some good blocking setting up shop. Essentially from the 12th through the rest of the month both the GEFS and the Euro keep us locked in what is honestly a very impressive persistent ridge in the west/trough in the east pattern. Snow prospects for December are increasing.

Being that we are in the long range, we have "time to get the timing" ironed out.

Fantasy range of the GFS but this would be a setup that would promote the development of a strong cutter that ultimately helps get the ball rolling for a pattern shift. Like I said I think you are spot on with an above average week one with the pattern change happening some time in week two after a potential cutter.

With such a strong baroclinic zone setting up in that cutter scenario and us being on the warm side, we’d have increased potential for strong storms before the flip to cold.

Great posts Trev! We could absolutely get that severe wx event that you had in your bold prediction for sure. I am confident on the -NAO being there. It is the Pacific side that we need to continue to watch for the change to a more sustainable colder pattern.

Good Afternoon and the final mow of the year is done and just need to clean up the mower and move to the back of the garage. Back to the weather and saw Brian's video and again he always has a wonderful grasp of the overall pattern and long term and that fits well with this forum. Item he mentioned and one that is true every winter is we need to have a nice warm spell to get into the colder spell. Yes warmth=cold with this equation. We need the PV to get strong and this helps in supplying the cold in the polar regions. When we get a relaxation of the PV then we wait and see where the stored up cold finally heads. Sometime it can be release in Euro and the USA at the same time or maybe Asia. If we get the PV to head towards the southeast half of Canada that is normally the best for us in terms of cold air. This does mean it will bring snow but the chances go up and usually snow is part of the equation. Many times the cold is delayed per the model output but not always and we need to look at other factors that may help deliver the cold air.

Yes we can get snow and some cold without the PV but usually in long term cold is usually when the PV gets weak and heads south plus the more snow in the lower 48 the longer it takes to warm up. We have a piece of the PV Sunday through about Wednesday next week but its quick in quick out and again this cold is not the coldest you will ever see in late November and early December but cold enough. Models are showing a stormier pattern for us with mainly rain later next week but always just after a cold spell is gone I look to see if the leading edge of the new storm can bring a quick bout of snow and/or frz/rain for a few hours before the warmth takes over. Then the models tend to keep us busy but mainly rain events through mid-month. Then do we get that surge of warm air about the 3rd week of December and longer term models are showing this and I agree but the timing can be off and sometimes off by a week or 10 days. Lets hope the cold starts to enter the picture locally about the 22-24 of Dec just before Christmas because I love cold around the Christmas holiday. We have plenty of time to watch this play out but once we hit December the fun and games should really get going around here.

12Z GFS today shows the -NAO / +EPO / -PNA combo to kick off December and thus the mild pattern we've been talking about. As soon as Dec 5th that begins to change on the GFS with the +PNA starting to build and it really goes to town in the fantasy range around the 10th. If correct, we are warm the first week of December with rain chances kicking in as early as Friday Dec 1st on into the weekend. Then, the t-storm maker around the 9-10th that Trev eluded to earlier which may bring about the colder pattern.

tron777 wrote: ↑Fri Nov 24, 2023 12:15 pm 12Z GFS today shows the -NAO / +EPO / -PNA combo to kick off December and thus the mild pattern we've been talking about. As soon as Dec 5th that begins to change on the GFS with the +PNA starting to build and it really goes to town in the fantasy range around the 10th. If correct, we are warm the first week of December with rain chances kicking in as early as Friday Dec 1st on into the weekend. Then, the t-storm maker around the 9-10th that Trev eluded to earlier which may bring about the colder pattern.

Hey guys and it seems the back and forth could continue for a few weeks but not sure if a true pattern change to colder is here before the last week or so of the month. So this pattern is one that we see warm-up- then rain and then cool for a few days before another rinse and repeat. Getting the PNA to a positive stage is one of the keys as this will slow down the pacific flow into the USA. The latest mjo is one that is giving us a few clues but nothing strong that would say cold or warmth is in our extended. What I do like though for this winter is the -NAO that has been there for many months and yes it heads towards neutral at times but has been mostly negative and this is no doubt a good thing for the winter around here to at least get storms to slow down as they head east. Still believe the northeast USA is in for one heck of a winter and hopefully and can at least get in on some of that action.

tpweather wrote: ↑Fri Nov 24, 2023 12:29 pm

tron777 wrote: ↑Fri Nov 24, 2023 12:15 pm 12Z GFS today shows the -NAO / +EPO / -PNA combo to kick off December and thus the mild pattern we've been talking about. As soon as Dec 5th that begins to change on the GFS with the +PNA starting to build and it really goes to town in the fantasy range around the 10th. If correct, we are warm the first week of December with rain chances kicking in as early as Friday Dec 1st on into the weekend. Then, the t-storm maker around the 9-10th that Trev eluded to earlier which may bring about the colder pattern.

Hey guys and it seems the back and forth could continue for a few weeks but not sure if a true pattern change to colder is here before the last week or so of the month. So this pattern is one that we see warm-up- then rain and then cool for a few days before another rinse and repeat. Getting the PNA to a positive stage is one of the keys as this will slow down the pacific flow into the USA. The latest mjo is one that is giving us a few clues but nothing strong that would say cold or warmth is in our extended. What I do like though for this winter is the -NAO that has been there for many months and yes it heads towards neutral at times but has been mostly negative and this is no doubt a good thing for the winter around here to at least get storms to slow down as they head east. Still believe the northeast USA is in for one heck of a winter and hopefully and can at least get in on some of that action.

It's all speculation Tim as you know this far out. But it is interesting to track nonetheless. Concerning the +PNA, it's position will also be important. If the ridge axis is more over the Rockies that would benefit New England more then it would us. We want the ridge axis further West along the West Coast of North America.

It's fantasy range but near the end of the 12Z GEFS run, it is a workable pattern with the -EPO returning and the +PNA not quite as far East as some guidance shows. A nice -AO too.

0Z EPS vs the new 12Z run. This is centered on the Dec 3rd - 8th five day mean. Note more Western US ridging. I wish it was a little further West with the ridge axis though. That is really the only problem that I have with it.

tron777 wrote: ↑Fri Nov 24, 2023 4:04 pm 0Z EPS vs the new 12Z run. This is centered on the Dec 3rd - 8th five day mean. Note more Western US ridging. I wish it was a little further West with the ridge axis though. That is really the only problem that I have with it.


Nov24_EPScompare.thumb.gif.2a0eb1781e875a54a0bf23a51c2fbe7c.gif

Seems to me guidance has been trending colder and colder the closer we get to December. It has been a good number of years, not sure how many it's been so long, since the models have trended colder like we have been seeing the last week or so. I have no doubt that warm ups are going to occur in December, but I'm beginning to get the feeling they may be brief with colder air winning out the majority of the time. The MJO seems to finally be in our favor which we haven't seen for several years. The El Nino looks to be trending more and more El Modiki like the more this thing evolves. There's still time for everything to blow up like we are used to seeing, but this is the most objectively optimistic I have been going into winter for many many years.

dce wrote: ↑Fri Nov 24, 2023 6:09 pm

tron777 wrote: ↑Fri Nov 24, 2023 4:04 pm 0Z EPS vs the new 12Z run. This is centered on the Dec 3rd - 8th five day mean. Note more Western US ridging. I wish it was a little further West with the ridge axis though. That is really the only problem that I have with it.


Nov24_EPScompare.thumb.gif.2a0eb1781e875a54a0bf23a51c2fbe7c.gif

Seems to me guidance has been trending colder and colder the closer we get to December. It has been a good number of years, not sure how many it's been so long, since the models have trended colder like we have been seeing the last week or so. I have no doubt that warm ups are going to occur in December, but I'm beginning to get the feeling they may be brief with colder air winning out the majority of the time. The MJO seems to finally be in our favor which we haven't seen for several years. The El Nino looks to be trending more and more El Modiki like the more this thing evolves. There's still time for everything to blow up like we are used to seeing, but this is the most objectively optimistic I have been going into winter for many many years.

Great Post Doug and everything you mentioned as tons of merit. The mjo is tricky and looks like phase 2-3-cod but does it head to phase 1 or back to 2 and I just don't know. Next week the AO is really getting negative and the Nao also negative which is normally a good sign for us during the winter. The El Nino and just not sure how strong and exactly where the warmest waters will set up for the winter period but further west helps us. Last winter there were signs for both warmth and cold and we saw after Christmas the warmth took over until March and then we got cold of course. So far this season more signs point to cold over warmth and like you mentioned the closer we get to December the models are tending at least somewhat colder than say 2-4 weeks ago. Still believe a warm spell is in the offing but with the STJ starting to get its act together the jet may keep us from getting to warm as systems move along the jet. I still believe a day or two of low-mid 60's is possible but not seeing any long term warmth at this moment.

tpweather wrote: ↑Fri Nov 24, 2023 6:57 pm

dce wrote: ↑Fri Nov 24, 2023 6:09 pm

tron777 wrote: ↑Fri Nov 24, 2023 4:04 pm 0Z EPS vs the new 12Z run. This is centered on the Dec 3rd - 8th five day mean. Note more Western US ridging. I wish it was a little further West with the ridge axis though. That is really the only problem that I have with it.


Nov24_EPScompare.thumb.gif.2a0eb1781e875a54a0bf23a51c2fbe7c.gif

Seems to me guidance has been trending colder and colder the closer we get to December. It has been a good number of years, not sure how many it's been so long, since the models have trended colder like we have been seeing the last week or so. I have no doubt that warm ups are going to occur in December, but I'm beginning to get the feeling they may be brief with colder air winning out the majority of the time. The MJO seems to finally be in our favor which we haven't seen for several years. The El Nino looks to be trending more and more El Modiki like the more this thing evolves. There's still time for everything to blow up like we are used to seeing, but this is the most objectively optimistic I have been going into winter for many many years.

Great Post Doug and everything you mentioned as tons of merit. The mjo is tricky and looks like phase 2-3-cod but does it head to phase 1 or back to 2 and I just don't know. Next week the AO is really getting negative and the Nao also negative which is normally a good sign for us during the winter. The El Nino and just not sure how strong and exactly where the warmest waters will set up for the winter period but further west helps us. Last winter there were signs for both warmth and cold and we saw after Christmas the warmth took over until March and then we got cold of course. So far this season more signs point to cold over warmth and like you mentioned the closer we get to December the models are tending at least somewhat colder than say 2-4 weeks ago. Still believe a warm spell is in the offing but with the STJ starting to get its act together the jet may keep us from getting to warm as systems move along the jet. I still believe a day or two of low-mid 60's is possible but not seeing any long term warmth at this moment.

I will also agree with the both of you. We will see some warmth of course but it won't be for weeks on end and it won't be historic. I do not see frigid air for December but I do see air cold enough for snow with the right storm track. Honestly, that is all most people care about anyway. For months, we have been discussing the reasons why this El Nino is not acting like a typical Strong El Nino and that is beginning to manifest itself with the Ensemble Guidance. The upcoming winter is not going to be like the last several. 2009-2010 continues to be the lead analog too. We had a warm November which we had this year. The forcing of the Nino is almost identical to what we've seen thus far. We had avg snow in December at CVG, slightly above avg snow for Jan and a whopping 26.1" in Feb which still stands as the snowiest Feb on record for a total of 38.4" for the season!!! Sign me up!

Good morning! We still look to start off December on a wet note Fri the 1st thru the weekend with a couple of systems working thru. Then, the pattern looks to turn colder behind this system. The -NAO is already there when we kick off December and we finally start to see the +PNA pop on Dec 5th as a southern slider works thru the area via the STJ. A weak snow signal is showing up on the Ensemble guidance. The signal to me looks a little better east of us for the Mid Atlantic region. This is just starting to get into the Day 10 range now so lots of changes on the modeling is ahead. What I find really interesting is how much faster this pattern has developed then anyone envisioned. December was supposed to be a torch with a +NAO, +AO, +EPO etc and that is not the case right now. The trends have been for a big -NAO and a +EPO to begin the month quickly changing to a more neutral EPO with a retrograding GOA Low which helps pop the +PNA by Dec 5th. Unlike most winters when good patterns seem to be getting can kicked, this one has been trending faster! Definitely something to watch folks over the next week IMO.

tron777 wrote: ↑Sat Nov 25, 2023 7:53 am Good morning! We still look to start off December on a wet note Fri the 1st thru the weekend with a couple of systems working thru. Then, the pattern looks to turn colder behind this system. The -NAO is already there when we kick off December and we finally start to see the +PNA pop on Dec 5th as a southern slider works thru the area via the STJ. A weak snow signal is showing up on the Ensemble guidance. The signal to me looks a little better east of us for the Mid Atlantic region. This is just starting to get into the Day 10 range now so lots of changes on the modeling is ahead. What I find really interesting is how much faster this pattern has developed then anyone envisioned. December was supposed to be a torch with a +NAO, +AO, +EPO etc and that is not the case right now. The trends have been for a big -NAO and a +EPO to begin the month quickly changing to a more neutral EPO with a retrograding GOA Low which helps pop the +PNA by Dec 5th. Unlike most winters when good patterns seem to be getting can kicked, this one has been trending faster! Definitely something to watch folks over the next week IMO.

Great Post Les!!! The Nao has been negative for the most part this year though a few times in the positive. Greenland had a very cold and snowy summer compared to normal so my guess and only a guess is snow cover is rather deep. This does not mean we get hammered with cold and snow but it can be a big roadblock for systems heading east. The AO has been neutral since summer which is normal but in the recent week or so going negative and forecast to go even more over the next week or so. I agree about the snow signal further east and in my winter forecast the mid-Atlantic and northeast could have a banner year for snow and cold and we are on the western edge which will give us chances to cash in as well. The mjo is in phase 2 and heading to phase 3 but weakening and then to the COD. Where we go from there is still up n the air but being weak may not play a big part in determining the current weather. I do believe models have gotten a colder look or at least more cold shots as the forecast in the past few weeks was for the MJO to head into 3 which should happen but it retreats instead of heading into the warm phases of 4-6.

Just to add a little more info and this is key imo and that is the temps in Siberia. The coldest I could find was -47 and coldest in northern Canada was -41. Okay so Siberia is colder and they usually are but when I start seeing temps this time of year -60 and colder over there then I know the cold is taking up shop on that side of the planet and we usually have a milder spell. Likewise if I start seeing temps at -30 and warmer in Siberia that usually means the PV is more than likely on this side of the planet. Does not mean its in southern Canada but more of the cold is on this side of earth

Looking around the world and eastern Europe getting hammered with cold and snow. They had been rather warm for much of November but that 180 degree change is happening and will expand to western Europe next week. Not always but many times when we see Europe get cold this happens in the eastern USA 2-3 week later. Again this cold outbreak is centered more over the eastern part of Europe at the moment so not sure this is any indication that we get hit 2-3 weeks later. They had a very mild winter last year like the eastern half of the USA so is this the forerunner of a much colder winter for them and hopefully for us as well.

Wonderful posts as well from you Tim! From a snow cover standpoint, S Canada and the Upper Midwest still need some help. Parts of the Rockies are off to a good start though.


N. Hemispheric shot of snow and ice coverage. Remember this is not snow or ice depth / thickness, it is just showing where there is coverage. It could be feet or just a 1/2" or something.

GFS and Euro NAO forecasts from yesterday thru Dec 4th.


The CFS forecasts a -AO for the entire month of December! Wow... wouldn't that be something if correct???

Les that would be great and then a little help from the pacific. The NAO has been negative for much of the year but the effects locally are felt from late fall to spring for the most part. I will roll the dice if the nao stays negative all of December.