GaWx

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:

Wow regarding the 0Z GFS strat forecast!! Check it out (loop this for the entire run, which gets very interesting from 2/10 to the end): https://www.tropicaltidbits.com/analysis/models/?model=gfs&region=nhem&pkg=Tz10&runtime=2023020500&fh=-12 What is most needed to get out of the neverending ugly pattern is major chaos. One potential source of major chaos is the strat. The chance of strong AO/NAO blocking goes up significantly 10+ days after a major weakening of the SPV. This run's strat becomes about as chaotic as one would want. If something close to this were to verify, there'd be no telling what would happen in the SE starting as early as the last week of Feb, especially considering MJO forecasts.

1. The string of GFS runs with what appears to be a major SSW/reversal of 60N winds at 10 mb from W to E is now at 8 as of today's 12Z. As opposed to being out of touch, the GFS appears to be leading the GEFS/GEPS as they're continuing to play catch up with the GFS. See section 2, below. Also, very importantly, the modeled SSW is moving up in time, which means an earlier onset of potential impacts in the SE than thought earlier. More on this timing in section 3. 2. The GFS leading the way is evident when comparing the two images below. Going below the 0 line on the "Zonal Wind Mean" map (top map of each image) is what's needed for a "major" SSW. As of the top image from 3 days ago (1/31), the GFS was already nearly forecasting a major with it down to +1 m/s on 2/15. Note that it was an outlier with the GEFS/GEPS way up in the +15 to +20 range. Now, look at the 2nd image, which is from today. The GFS is firmly forecasting a major with a low of -10 (2/16). And look how far the GEFS/GEPS have dropped: to close to 0! So, even the GEFS/GEPS are bordering on a major. Based on these trends, the GEFS/GEPS appear to be heading to showing a major. 3. Now I'll address the earlier timing: On the older map the GFS winds don't get to its low of +1 til 2/15. In contrast, today's map has the GFS already to a major on 2/13 due to a steeper drop and lower starting point. That's 2+ days earlier! The old GFS was still up at +15 on 2/13. Regarding temperatures (bottom map of each image), the old GFS showed warming not starting til 2/13 (from 221 K). In contrast, the new GFS' warming starts on 2/9 (4 days earlier) and from a warmer starting point of 224. As of 2/13, the new GFS was already up to 230 or 9 warmer than the old GFS. Also, the old GFS was still warming as of 2/16 (reaching 230 three days later than the new GFS). The new GFS has already peaked on 2/15 (at 237), when the old GFS was still down at 225. 4. Summary: - Chances for a major SSW continue to increase as the GFS leads the way. As of today's 12Z run, 8 in a row have had a major SSW. - The timing of the forecasted SSW has moved ~2-3 days earlier vs what models were showing just three days ago. This means an increased chance vs what was earlier thought for cooling effects on the SE, should they occur, to start during the last week of Feb as opposed to the first week of March. Images of strat winds/temps: GFS in orange Older (based on 1/31 runs): New (based on 2/3 runs):

Even way on down here near the coast, where there's a T+ of wintry precip on average for the entire winter only once per 4 years, I don't give up til after the first week or so of March if the pattern is cold: - SAV's 2nd biggest snow on record was on March 4th! CHS also had a significant snow that day. - Since 1890, there has been wintry precip (most but not all were traces) within the CHS-JAX corridor 15 years during the 1st week of March or once every 9 years on average. That's pretty notable for way down in this stretch at the coast. So, it isn't all that far-fetched to hope for wintry precip in this area in early March. *Edit: Meanwhile, based on the projected MJO timing as well as the increasingly possible midmonth SSW that could exert its influence on the SE more quickly than the average lag, I'm not at all discounting the possibility of a cold last week of Feb. IF that were to happen, many more doors would open regarding the chance for SE wintry precip. A cold 2/22-3/7 or so would be quite interesting. The highly expected strat warming along with a very much weakened and displaced SPV introduces a lot of chaos and thus the possibility of a real pattern change! Buckle up, folks!

Because it is a potentially a game changer for the seemingly never-ending dreary SE pattern late this month into early March, especially when combined with what may very well be a favorable MJO and considering that wintry precip climo is still near peak into the first 3 or so days of March, I expect to keep talking about a *potential* major SSW at midmonth as long as the threat shows on the models. The 12Z GFS is the 4th run in a row with a *major* SSW on it. Keep in mind that the SSW that just occurred didn't make "major" status, which requires a reversal of 10 mb winds from W to E at 60N. Typically that requires a high dominating the Arctic instead of the SPV. This last one's high didn't get there and allowed the SPV to remain too close/too strong despite the impressive warming. We'll need to see if the GFS holds onto a "major" SSW as we get closer. If it is still there 5 days from now, I'd then be very excited. In the meantime on the GEFS, the N Pole at 10 mb has warmed as of 0Z 2/15 from -64 C on the 0Z 1/26 run to -34 C on today's 12Z run. So, it has warmed a whopping 30 C (54 F) just within 7.5 days of runs at the N Pole for the same forecast point (2/15). So, the GEFS continues to trend in a SSW direction as the crucial period gets closer and the ensemble gets more of a clue. Edit: 18Z GFS appears to me to be 5th in a row with major SSW

Phil (not Hogtown Phil lol @pcbjr) must have seen the 6Z GFS' ~35C (63 F) 10 mb warming at the N Pole within 60 hours (6Z on 2/14 to 18Z on 2/16). That's pretty sudden! It also appears to have a 60N wind reversal at 10 mb from W to E with the high in the Arctic. So, I have these four GFS runs with a major SSW (60N wind reversal) very likely being depicted at 10 mb at midmonth: 18Z of 1/31, 18Z of 2/1, 0Z and 6Z of 2/2. So, three GFS runs in a row. **Edit: 12Z GFS makes four GFS runs in a row

Although earlier in the month (like the timing of the current minor SSW) would have been optimal, this later one definitely wouldn't be too late to potentially have significant downstream effects in the SE outside of the mountains. Yes, likely ~2/25 or later for first effects should they occur. The key would be getting the effects in the first place and then getting them to start quickly enough. If they can start 2/25ish, that would give many in the SE still another week or so of prime climo to work with. After all, March 2nd has had more SN/IP at RDU than any other day if I'm not mistaken. If the start of any effects is delayed til, say, March 10th, then it likely wouldn't do much good though even then there could be some benefit. Edit: The 0Z GFS joins the prior two 18Z GFS runs in having what appears to be a major SSW at midmonth.

If this isn't a major SSW on the 18Z GFS at 10 mb, then I don't know what one is: high in the Arctic has replaced the SPV with E winds at 60N all around it, the Arctic is much warmer than normal, and the SPV has plunged WAY south to 50N with it stretched/splitting. I know this is just the GFS late in the run (very unreliable), but the trends the last few days have been headed toward a midmonth disruption/warming. If this were an isolated GFS run showing this with no prior support of strat changes at midmonth, I wouldn't have posted thi:

The high at KSAV was 82, three shy of the record and the warmest since Dec 8th's 82.

The table (SSW plus MJO) per models is being set for this scenario though it could start during the last part of Feb. I just did a time lapse on Tropical Tidbits of 0Z GEFS runs at 10 mb for the forecast date of 2/15 starting with the 1/26 run and ending with the 2/1 run. It clearly shows a continuing trend of a further S SPV along with a further N high. The further S the SPV and the further N the high, the more the disruption/warming. The 2/1 run location of the SPV on 2/15 is ~700 miles S of the 1/26 run's position, which was near Svalbard (80N). Now it is over N Norway (70N). Also, the main high as of 2/15 has moved 700 miles N from S of Alaska (55N) on the 1/26 run to Alaska (65N) on the 2/1 run. Along with this, the N Pole at 10 mb has warmed as of 2/15 from -64 C on the 1/26 run to -42 C on today's run. So, it has warmed 22 C just within 6 days of runs for the same forecast point (2/15). So, the GEFS has gone from showing nothing interesting in the strat 6 days ago (cold SPV over the Arctic) to a significant disruption/warming today for 2/15. That's why I didn't start talking about this new warming til yesterday. And the trend toward more disruption/warming on future runs may not be over.

The main hope I have for a cold last week of Feb into early March largely hinges on the degree of strat Arctic warming and disruption of the SPV at midmonth. GEFS runs since 12Z yesterday have continued to show significant warming along with a southward displacement of the SPV to N Scandinavia at midmonth. This is the kind of strat chaos that can shake up the pattern enough based on past cases to lead to a couple of week+ colder pattern in the SE that would start within 10-14 days of the "onset" of a SSW. With that kind of timing, any SSW generated cold could make it to the SE as early as during the last week of Feb. The MJO would likely be in a more favorable position at late month into early March to help out. Meanwhile, model consensus is still suggesting a short moderate cold snap ~2/11. The 12Z Euro *fwiw* even gives parts of NC several inches of snow then.

I agree to some extent since any cooling effects from a possible major SSW in mid Feb could easily extend into mid to late March when normals are a good bit higher. However, there'd still be hopes for a colder late Feb into early March. First, looking at non-El Nino years with a SSW in mid-Feb: Consider the cold that followed the 2/17/2002 SSW, which was 2/22-3/6. Also, the 2/11/2001 and 2/12/2018 SSWs had cold follow 3/5-4/3 and 3/3-3/15, respectively. So, there's some early March cold included with those last two. Looking a bit away from mid Feb: Late Feb: 2/22/1979 and 2/22/2008, I couldn't find any cold dominated period of note. But 2/21/1989 had cold dominate 2/23-3/9. Early Feb: 2/6/1981 had cold dominate 3/6-25. So, in summary, this all tells me that if there's a major SSW, potential cold could come in as early as the last week of Feb. The last week of Feb and first few days of March are still pretty cold on average (within only 5-6 of the coldest week in January) and are also within the climo active period for SE wintry. By the way, the 0Z GFS is another run with an impressive displacement of the 10 mb SPV!

Fwiw, the 18Z GFS, like the 0Z, has what may be a real live major SSW on it late in the run fwiw. For those curious, check out the N Hemispheric maps at 10 mb late in the 18Z/0Z GFS runs to show what I'm seeing. They show a significantly displaced SPV along with massive Arctic strat warming. These are both bordering on a 60N wind direction reversal from W to E, especially the 18Z.

If RDU's total were to remain at a T, it would be the first time that low since 2005-6 for those who didn't know.