GaWx

Indeed, I do. At 2-3 weeks from now, the SE is still at the tail end of prime winter storm season that goes into early March. Also, keep in mind that there were big SE winter storms in the first half of March during 1924, 1927, 1934, 1942, 1948, 1960 (3 of them), 1962, 1969, 1980, 1993, and 2009 along with quite a few more that were sub 4". We're actually due for the next one. Even way down here, there was 1"+ on 3/1/1986. Also, SAV's 2nd biggest snow on record was on Mar 3-4. The second half of March had big SE storms in 1940, 1971 and 1983 along with others that were sub 4". It is still too early to give up per climo! *Edited to add more early March storms

Don and others, It surely isn't what I want to see but it is still very early when you consider: 1. Despite relatively high forecast skill at the strat level way out at 1.5 months (note dark colors in top of image below), the skill goes down quickly in the much more difficult to forecast troposphere (note the light colors on the bottom of the image below starting out only two weeks). Thus, how it will play out in the troposphere likely won't be clearly seen for quite some time: 2. A warm E US is actually pretty common during and for much of the two week period following a SSW. This SSW still wont hit its peak for another ~4 days (~2/16). So, adding two weeks take us to ~3/2. It is only after this period when any change to a cold pattern typically takes hold in the E US, if it is ever going to do so. That's when I hope for a change to a -AO/-NAO regime. So far, the jury is out as the models have limited skill that far out, especially with the unusual situation of a major SSW. 3. As I posted about earlier, the greater than 40 mb Scandinavian-Greenland dipole of late Feb 6th, is based on Simon Lee's studies usually an indicator that any SSW will propagate to the troposphere within a few weeks of it: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030940 4. MJO forecasts in combination with this give a lot of hope that the SE ridge domination will end by early March. 5. This major SSW may very well end up failing to lead to a colder E US in March. I'm open-minded about it. But it is too early to make that call (I realize you're not yet) and there's still reason to remain hopeful.

There's still no -AO/-NAO late on the ensemble means near the end of the month. If that were to verify along with no prospects for it in early March (say, on model runs two weeks from now), only then would I start to think that a multi-week long SSW generated -AO/-NAO isn't going to happen. But it is still very early with the major SSW not even becoming official (shift of 60N 10 mb winds from W to E) for another 3-4 days. Then there's the typical 2 or so week lag. So, we're still a good ~2-3 weeks from when this hypothetical SSW generated -AO/-NAO would typically get started. And as I've shown, the troposphere is notoriously much more difficult to forecast than the strat out just two weeks. So, the 12Z EPS like the others has no -AO/-NAO of significance at the end based on my eyeballing it. However, it and the 12Z GEFS do fwiw have a Scandinavian block that forms on Feb 25th as have the last 3 runs. What is needed for SE cold lovers is for that block to instead be 1,500 miles to the west.

I've had the heaviest 24 hour rainfall since the ~4" of 9/4/22 and it is still coming down (pretty heavy now) with several more hours of steady rain likely! I'm somewhere over 3", which together with some during the day yesterday and ~4.25" 1/22-2/3 has me at ~8" over the last 3 weeks. After a typical dry La Niña 9/12/22-1/21/23 with only 5-6", the 8" has been welcomed. I have breezy NE winds and temps have fallen into the lower 50s.

You're welcome. Glad you like them! I'm now going to repost an image put together by Weather Desk with temperature maps from some past SSW cases that shows that it is often warm in the SE US for the 15 days starting with the SSW followed by sharply colder on days 16-30. Some good examples with that pattern shown below: 1/2/19, 2/12/18, 1/7/13, 3/24/10 (to an extent), 1/21/06, and 2/11/01 (to an extent). So, of these 9 recent cases, 4 are strong examples and 2 others are modest examples. Of the recent La Niña examples shown here, 2/12/18 and 1/21/06 are 2 of the strong cases and show very well the warm SE 1-15/cold SE 16-30. Those two La Niña SSWs, like the current case, had 40 mb+ Scandinavian-Greenland dipoles prior to an SSW and later were downward propagating (they're the only 2 of these 9 cases like that). In the current case, days 1-15 would likely be either 2/15-3/1/23 or 2/16-3/2/23. So, days 16-30 would likely be either 3/2-16/23 or 3/3-17/23. I suppose they may even call the SSW date 2/17/23. These are just guidelines, of course, as the timing of effects of no two SSWs are exactly alike:

A midmonth major SSW is about to occur. It has been very well predicted by the GFS: 1. Something to keep in mind is that despite relatively high forecast skill in the strat out several weeks after a SSW (note dark colors in top of image below), the skill goes down quickly in the much more difficult to forecast troposphere (note the light colors on the bottom of the image below starting out only two weeks) in the aftermath of one and thus likely won't be clearly seen for quite some time: 2. A warm E US is actually pretty common during and for much of the two week period following a SSW. It is only after this period when any change to a cold pattern typically takes hold in the E US, if it is ever going to do so. So far, the jury is out, but long range signs remain promising for the start of a multi-week long significant -AO/-NAO (as per yesterday's Euro weeklies) around the last days of Feb and then dominating March. Also, the greater than 40 mb Scandinavian-Greenland dipole early this week is based on Simon Lee's studies usually an indicator that any SSW will propagate to the troposphere within a few weeks of it. Finally, MJO forecasts in combination with this remain favorable to end the SE ridge domination by early March.

Thanks and you're welcome. I forgot to add that the MJO will (as you probably already realize) on its own be favorable to get rid of the SE ridge/torch by late month and into March if model consensus is correct. That hopefully will help out the Pacific side. So, it appears that we may have a combo of a much improved Pacific thanks to the MJO and the end of La Niña in combo with -AO/-NAO from the SSW to make a cold March a very realistic possibility in the SE US. If that happens, it won't be out of the realm of possibilities for March to be the coldest one since at least 2013.

It is now near a certainty that the SSW of next week will be a major. Supporting this are today's Euro weeklies, which show 100% of the 51 members now having the 60N 10 mb winds go below 0 m/s (westerly). The mean gets down to an impressive -12 m/s, down from the prior run's -10 m/s. Also, the new run's mean switches to westerly on 2/16 and stays that way for 3 weeks! The old run's mean was westerly only for one week. Consistent with this is the transition of the Arctic's H5. After the next 13 or so days of continued solid +AO/NAO and above normal H5 in the E US, which is not unusual near and somewhat after a SSW, a transition toward a -AO/NAO begins during the week of 2/20 although the E US stays mainly mild. This transition starts several days earlier than the prior run. On ~2/25, it goes to -AO and ~2/27 it goes to -NAO with both quicker than the old run. H5 hts rise along the west coast. The NE US cools to BN near the end of Feb and the SE NN. There's a full fledged -AO/-NAO for all of March, similar to the old run but starting a few days sooner. The E US is BN to NN the entire month, vs NN on the old run. In summary, the Euro weeklies are even more on board for a downward propagation of the major SSW into the troposphere getting started late month. That's what the greater than 40 mb Scandinavia-Greenland dipole of early this week had suggested.

Significantly heavier snow accumulations on 12Z Euro vs 0Z NE GA/NW SC/ W NC per Pivotal

12Z Euro has significantly more snow over N GA/upstate SC vs 0Z so far despite a weaker H5 low.

I was just looking back at old maps for 3/1-2/2009 to see how 2/12/2023 compares: 1) Similar strength of H5 low in low 540s at strongest in SE US but it is progged to remain that strong til well out in the Atlantic vs 2009 opening up: 3/1/2009 H5: https://www.wpc.ncep.noaa.gov/dailywxmap/dwm_500ht_20090301.html 3/2/2009 H5: no longer closed: https://www.wpc.ncep.noaa.gov/dailywxmap/dwm_500ht_20090302.html 2) In 2009 there was a big, strong (1044 mb) high to the NW centered over the Plains feeding in cold air: https://www.wpc.ncep.noaa.gov/dailywxmap/dwm_stnplot_20090301.html The upcoming case has no high to the NW to speak of to feed in cold air. However, this time there's moderate CAD from a 1027 mb VA high vs no CAD high in 2009. 3) Related to point #2, temperatures were ~10 colder in 2009 to the NW in the area from St. Louis to Chicago (near normal) vs well above normal this time. However, this time out ahead of the low it is ~5-10 colder (like in VA): https://www.wpc.ncep.noaa.gov/dailywxmap/dwm_minmax_20090301.html

An increasingly high chance at a major peaking in at or just over a week. Now that the progged warming peak is only 7-8 days away and the start of the rapid warming is only 4 days out, the chances of it not happening are dropping rapidly as we're now within a pretty forecast-able timeframe.

The 12Z EPS has a gradually developing -AO starting ~Feb 22nd. The 12Z GEFS is similar. Monday's weeklies also had something similar along with a full fledged -AO/-NAO getting established by the first few days of March. That's what I'm going to be looking for starting around then in response to the upcoming SSW.

I don't recall finding anything special about phase 4-5 over other phases for NC. But what I can tell you about MJO tendencies regards RDU 6"+ snows (and by extension a good number of major SE winter storms in general including at ATL) and is this: low amp (within COD...most of them) to moderately low amplitude (between 1 and 1.5) was present for an amazing 93% of the big RDU storms since the daily MJO index started (13 of 14)! Only 1/17-18/2018 had an amplitude higher than 1.5 and it just happened to be in phase 4. It had an amp of 1.9. So, even that wasn't a high (2+) amp. So, I can say that none of RDU's fourteen 6"+ snows since the MJO started getting tracked daily had a high amplitude MJO (2+). The odds of any DJFM day having an amp of 2+ are 20%. So, the expectation if there were no tendency based on that would be for three of those fourteen 6"+ snows to have an amp of 2+. Having no high amp together with the fact that most of the 14 were when the MJO was within the circle tell me that the lower the amplitude the better the odds of a big snow in RDU and vicinity. Edit: Aside: Every ATL major IP or ZR since 1979 was within the circle entirely (all but one) or partially (one that was on two calendar days)! More evidence that being either inside or barely outside the circle is best for major wintry precip chances. Edit #2: The MJO forecasts have a 1.0 to 1.50 amp (low end moderate) for Feb 12th, which is the day with the highest threat for snow. So, although not ideal since it isn't inside the circle, it is not bad either since it isn't too far outside.

This wouldn't surprise me at all for at least the first half of March should the upcoming (very likely major) SSW propagate downward into the troposphere to a significant degree. That propagation chance is pretty high as of now based on the Scandinavian-Greenland index (SLP difference) peak that just occurred late Monday. It appears to have exceeded the threshold of 40 mb. You can go here to learn about the S-G index/dipole and the 40 mb threshold: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030940 So, with good odds of a significant downward propagation, I'm currently expecting a significant drop in the AO (and probably also the NAO) to start most likely either during the last few days of Feb or first few days of March. It wouldn't surprise me at all if March were to be snowy in much of the E US, but that's highly speculative at this early point. If the models were to not forecast the AO to start dropping significantly by ~March 5th or soon afterward, I'd only then start to think the SSW was likely not going to propagate strongly downward.

While we're waiting on the 0Z runs for the potential Feb 12th snow, I'm going to go back to the much longer range in this post, specifically related to the upcoming SSW. Check out the tweet below, which is a reason to closely follow Arctic stratospheric progs of the EPS (including weeklies), GEFS, and others. The strat, after a SSW, is more predictable than the upper tropospheric pattern starting with day 5 and is much more predictable by day 15 in the Arctic. Note the lighter colors (lower correlation) in the lower levels meaning more difficulty. From this, one can infer that the models tend to have a very hard time predicting AO/NAO indices and other possible downward reflections into the Arctic troposphere after an SSW, despite the SSW, itself, being highly predictable. Look at day 23, for example. Whereas the strat above 100 mb still has an impressive anomaly correlation of 0.6 to 0.8, the upper troposphere (300 mb) has already plunged to under 0.2! So, keep this in mind as regards the extended models getting a good handle on where our sensible wx may go late this month. It is very highly unpredictable at this point in time even though the strat is much more predictable. So, expect a lot of change on the models as we get closer. From the same Twitter thread: "... so even though the winter stratosphere is relatively predictable, the models can't effectively translate that skill down to the surface. Nevertheless, the *potential* predictability linked to the stratosphere is good reason for following these forecasts closely." Or put another way by Dr. Simon Lee: "The stratosphere can be extremely predictable -- particularly after SSWs -- but both model deficiencies *and* unrelated tropospheric noise means this doesn't perfectly translate to tropospheric skill."

I think it is getting close to new thread time for this 2/12 threat since it is now dominating the medium to long range pattern thread and it is only 5 days out. Opinions?

Zero Atlantic blocking wouldn't be unusual for a big RDU snow. Here is the NAO for the 23 Raleigh 6"+ SN/IP storms since 1950. (I'm calling neutral NAO to be from +0.25 to -0.25):-1/19/1955: -NAO- 12/11/1958: neutral NAO- 3/2-3/1960: neutral NAO- 3/9/1960: neutral NAO- 2/26/1963: neutral NAO- 1/25-7/1966: -NAO- 2/9/1967: +NAO (+0.5)(9.1")- 3/1/1969: -NAO- 1/7-8/1973: -NAO- 2/18-9/1979: neutral NAO- 3/1-2/1980: +NAO (+0.4)(11.1")- 1/13-14/1982: neutral NAO- 3/24/1983: neutral NAO- 2/6/1984: +NAO (+1.1)(6.9")- 1/7-8/1988: +NAO (+0.5)(7.3")- 2/17-8/1989: +NAO (+1.7 )(6.2")- 1/24-5/2000: -NAO- 1/2-3/2002: -NAO- 2/26-7/2004: -NAO- 12/25-6/2010: -NAO- 2/24-6/2015: +NAO (+1.0)(6.5") - 1/17-8/2018: +NAO (+1.2)(6.1") - 12/9-10/2018: +NAO (+0.9)(8.9")Tally:-NAO: 8Neutral NAO: 7+NAO: 8 Moreover, note that RDU had 5 big snows, including the last 3, with an NAO much more positive (see bolded five NAOs of +0.9 to +1.7) than the +0.6 that is being predicted by the GEFS for 2/12. So, RDU hasn't had a 6"+ snow with NAO under +0.9 since 12/25-6/2010! Furthermore, the other 3 +NAO 6"+ snows were only barely lower (+0.4 to +0.5). By the way, the big SE bowling ball snow (RDU got 3.2", ATL got 4") of 3/1-2/2009 had a +1.0 NAO along with AO of +2.1 and PNA of -0.4. So, 3/2009 had a strong +NAO/+AO! The GEFS is forecasting for 2/12/23 an NAO of +0.6, AO of +2.0, and PNA of +0.1. If there were a strong -PNA being forecasted, then I'd have much more doubt. But a neutral PNA doesn't at all hamper the odds. The MJO was on 3/1-2/2009 in phase 4 and is predicted to be in phase 5 or 6 on 2/12/23. I'm not predicting either yes or no for a 2/12/23 RDU snow. It may end up too warm as we all know. I'm just saying that the progged indices on their own, especially NAO, are not at all a hampering factor per history, especially recent. ---------------------------------- NAO daily data: https://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.nao.cdas.z500.19500101_current.csv RDU data: https://www.weather.gov/wrh/Climate?wfo=rah

Yesterday (2/6), the S-G dipole (Scandinavian SLP minus NE Greenland SLP) was very strong and likely exceeded 40 mb. The following link is to the article from which I learned about the S-G dipole and its predictive ability for major SSWs within 15 days when it exceeds 40 mb: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030940 From this: "When 2018 is included, 78% of the major SSWs preceded by an amplified S-G dipole were downward propagating (Karpechko et al., 2017), with only March 1981 and February 2008 otherwise. This is larger than the observed ratio of 57% (although the sample is too small to draw robust conclusions) but is in agreement with Birner and Albers (2017), who note larger tropospheric impacts following SSWs preceded by enhanced tropospheric wave activity." ----------------------- So, for the SSWs preceded by a 40+ mb S-G dipole that were downward propagating (78% of them), here were the AOs for the week centered on that day, on the week centered on two weeks later, and on the week centered on three weeks later: * = during La Niña - 2/22/1979: -0.3, +0.8, -2.7 - 2/29/1980: -0.5, -1.3, -2.8 * - 2/24/1984: -0.7, -2.5, -3.1 * - 1/1/1985: -2.1, -3.4, -3.5 - 1/23/1987: -1.1, -0.3, -2.8 * - 1/21/2006: -0.1, -1.8, 0.0 * - 2/12/2018: +1.5, -1.9, -3.3 - Average of the seven: -0.5, -1.5, -2.6 - This tells me that assuming the upcoming SSW downwardly propagates, look for an AO plunge to most likely start within two weeks and possibly within 10 days of the SSW (likely during last few days of Feb to first few of March). Then look for it to most likely last at least 2 weeks. - Look for the strongest -AO week to most likely be the week centered on 3 weeks after the SSW. So, in the upcoming case, ~Mar 5-11, although the prior week could also have a strong -AO. - Note that the only year with a strong week of +AO during the SSW (2018, a La Niña) similar to now was still able to plunge to a strong -AO 2-3 weeks later. Despite the strong +AO initially, the -AO for those two weeks averaged out actually ended up significantly stronger than 4 of the other 6 weeks! Only 1984 (barely) and the historic 1985 had a stronger -AO. The 2018 AO plunged fastest starting 13 days after that SSW. 2006 took 10 days to start dropping its fastest while 1987 took 17 days, 1985 took 12 days, 1984 took 10 days, 1980 took 12 days, and 1979 took 15 days. So, range of 10-17 days after SSW date for the AO to accelerate downward. For the four La Niña events, alone, the range was 10-13 days. The four La Niñas propagated a good bit more quickly (average of just 11 days) than the average of the other three (15 days). So, for the upcoming case assuming it propagates downward, look for the AO to start dropping the most rapidly for a sustained period of time most likely starting ~2/24-2/28 although it may wait til 3/5. If there's no big AO drop by 3/5 and none forecasted, I'd then be thinking it probably won't propagate downward.

Courtesy of Dr. Simon Lee's Twitter, the 0Z EPS mean is also now forecasting a major SSW and a rather stout one at that with a 60N 10 mb wind low of -10 m/s on 2/19 (see image below). That would be a whopping 33 m/s below the climo mean of +23 for the date. It is currently +30. The run from four days earlier had it dipping down only to +3 (on the same date). So, now all of the major ensemble means have a major. Most importantly, note that over 90% of the 50+ EPS members show a major. Also, note that the bottom 10% of members are in the -25 to -30 range, which is where the 0Z GFS is and would be near a record low for Feb. ------------------------ 0Z 2/6/23 EPS mean prog (thick blue line) of 60N winds at 10 mb showing a major SSW (below the pink line from 2/16 through 2/22) with it dipping all of the way down to -10 m/s on 2/19: Here's a tweet from Dr. Lee from earlier today: Edit: To compare, the prior runs available at the website never had anything lower than +5 m/s for the low in advance of the recent minor SSW.

1. The 0Z GFS is likely overdone since it is predicting a near record Feb low 10 mb wind at 60N of -27 m/s on 2/18/23 and is an extreme outlier vs ensemble members. But fwiw you can see it in the top graph of the first image below in orange. More importantly and to the GFS' credit since it has had a major SSW on its last 20 runs often as an outlier, the same image shows that all of the ensemble means have followed the GFS' lead that started five days ago and for the first time now have a major (at -4 m/s on 2/18). 2. The 2nd image shows Arctic strat temperatures this winter to date along with the GFS forecast through Feb 22nd. Looking at the winter through Jan 23rd, which was just prior to the minor SSW of late Jan, you can see the dominance by blue (cold) anomalies. The peak cold strat near New Year's was near a record low strat temp as well as anomaly, which equated to a near record strong SPV. That's a key reason this winter has been so warm to date. But then note the late Jan minor SSW. And on the right, you can see the forecasted major SSW, the polar opposite extreme (even though it is likely overdone as already stated). That along with the forecasted MJO is why I feel there's a good chance for a change to a much colder pattern in the E US overall possibly starting as early as during the last week of Feb. Image 1 top graph shows GFS (orange) with near record Feb low 10 mb 60N wind of -27 m/s and also ensemble means having a major SSW for first time: Image 2 shows how cold it was in the stratosphere through 1/23 (especially near New Year's) along with the strong warming from the minor SSW and the forecasted major SSW:

The CFS is terribly unreliable. It typically changes wildly from run to run. Also, it is too cold over snowcover. However, because it an operational that goes out much further (which is one reason it shifts wildly), it like the Euro control is fun to look at for "what if" possibilities. The last 3 runs, especially the last 2, go from +AO/+NAO for the next 2+ weeks to a strong -AO/-NAO starting in late Feb. That's interesting because that's what a major SSW would often lead to starting 7-10+ days later. The result in the SE from that is often a colder pattern following soon afterward. That's precisely what these CFS runs are showing. Today's 12Z is late Feb-early March of 1960 all over again in the SE with MB temps and 3 winter storms within just one week. ATL doesn't get above low to mid 40s 2/25-3/7. They don't get above 35 F 2/28-3/4. These are very similar to early March of 1960. Also, this would easily be the longest strong cold stretch there and throughout the SE since early January of 2018! This shows that if the right atmospheric ingredients are there, the SE can have a lengthy very cold and wintry period even in early March. **Edit: I should add that the MJO is looking favorable to allow for cold later this month, a very important ingredient. Yes, it is likely overdone even if there is a strong -AO/-NAO then. But this does at least give an idea of the type of thing that a major SSW at midmonth can do.

Walt, 1. The GFS is explicitly calling for a major SSW in mid-Feb per the first image I posted. I can't speak for others, but that's what I'm paying attention to. It is highly doubtful imho that it could also end up as an SFW because none have occurred as early as Feb. 2. Major SSWs have occurred as late as March 23rd per this: https://en.m.wikipedia.org/wiki/Sudden_stratospheric_warming#Classification_and_description Also, regarding the 9 major SSWs that occurred within 15 days of a 40+ mb S-G dipole event, the following 5 of the 9 were near or later than the upcoming event, which looks to occur ~2/15: 2/22/1979, 2/29/1980, 3/4/1981, 2/24/1984, and 2/12/2018

SSWs have had varying effects on the SE. What may very well turn out to be different from the prior one is that the upcoming strat warming is looking increasingly likely to be "major" (see 1st image, in which the GFS is showing quite the major event with 60N 10 mb winds dropping to well below 0 m/s). Before anyone says anything about the unreliability of the GFS vs ensemble means, it has been leading the way, which is quite evident when looking back to 1/31 runs at the Stratobserve website at the following: https://stratobserve.com/ens_ts_diags Another thing to keep in mind is the Scandinavian-Greenland (S-G) dipole, which looks to me like it is forecasted to exceed 40 mb per the 2nd image below. Learn about the S-G dipole here: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030940 "The correlation field indicates that ensemble members with lower MSLP over eastern Greenland and higher MSLP over Scandinavia forecast weaker U1060." "Of the 23 SSWs (Karpechko et al., 2017), we find eight (35%) followed a similar evolution to 2018 and were preceded by an S-G dipole exceeding 40 hPa within 15 days of the start date of the SSW. Given the total of 345 days preceding the 23 events (and assuming independence), this is 2.3 times larger than the climatological likelihood (since 40 hPa is approximately the 99th percentile, it would be expected that it was exceeded on 3-4 days)." "We therefore suggest the S-G dipole should be monitored operationally as a precursor to SPV weakening." "When 2018 is included, 78% of the major SSWs preceded by an amplified S-G dipole were downward propagating (Karpechko et al., 2017), with only March 1981 and February 2008 otherwise. This is larger than the observed ratio of 57% (although the sample is too small to draw robust conclusions) but is in agreement with Birner and Albers (2017), who note larger tropospheric impacts following SSWs preceded by enhanced tropospheric wave activity." Per table 1 from this article, the following 8 SSWs had a 40+ mb S-G dipole peak during the 15 days prior: Feb of 1979, Feb of 1980, March of 1981, Feb of 1984, Jan of 1985, Jan of 1987, Jan of 2006, and Feb of 2008. Also, Feb of 2018, which this article highlighted, had a 40+. So, one might want to focus on the tropospheric impacts of the above listed 9 SSWs to get a better idea of how the upcoming SSW may affect the SE US late this month into March+. I say late this month because I believe based on the timing of past cases that any potential cold resulting from this may start as early as the last week of this month. Image 1 showing that today's 0Z GFS is forecasting a major SSW: Image 2 suggesting likelihood of S-G dipole peak of 40+ mb coming tomorrow:

Don and others, What may very well turn out to be different from the years listed is that the upcoming strat warming, whether final or not, is looking increasingly likely to be "major" (see 1st image, in which the GFS is showing quite the major event with 60N 10 mb winds dropping to well below 0 m/s). Before anyone says anything about the unreliability of the GFS vs ensemble means, it has been leading the way, which is quite evident when looking back to 1/31 runs at the Stratobserve website at https://stratobserve.com/ens_ts_diags Another thing to keep in mind is the Scandinavian-Greenland (S-G) dipole, which looks to me like it is forecasted to exceed 40 mb per the 2nd image below. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030940 "The correlation field indicates that ensemble members with lower MSLP over eastern Greenland and higher MSLP over Scandinavia forecast weaker U1060." "Of the 23 SSWs (Karpechko et al., 2017), we find eight (35%) followed a similar evolution to 2018 and were preceded by an S-G dipole exceeding 40 hPa within 15 days of the start date of the SSW. Given the total of 345 days preceding the 23 events (and assuming independence), this is 2.3 times larger than the climatological likelihood (since 40 hPa is approximately the 99th percentile, it would be expected that it was exceeded on 3-4 days)." "We therefore suggest the S-G dipole should be monitored operationally as a precursor to SPV weakening." "When 2018 is included, 78% of the major SSWs preceded by an amplified S-G dipole were downward propagating (Karpechko et al., 2017), with only March 1981 and February 2008 otherwise. This is larger than the observed ratio of 57% (although the sample is too small to draw robust conclusions) but is in agreement with Birner and Albers (2017), who note larger tropospheric impacts following SSWs preceded by enhanced tropospheric wave activity." Per table 1 from this article, the following 8 SSWs had a 40+ mb S-G dipole peak during the 15 days prior: Feb of 1979, Feb of 1980, March of 1981, Feb of 1984, Jan of 1985, Jan of 1987, Jan of 2006, and Feb of 2008. Also, Feb of 2018, which this article highlighted, had a 40+. So, one might want to focus on the tropospheric impacts of the above listed 9 SSWs to get a better idea of how the upcoming SSW may affect the E US late this month into March+. I say late this month because I believe based on the timing of past cases that any potential cold resulting from this may start as early as the last week of this month. Image 1 showing that today's 0Z GFS is forecasting a major SSW: Image 2 suggesting likelihood of S-G dipole peak of 40+ mb coming tomorrow: