GaWx
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Based on what I've read by pro mets, near record warm SST anomalies in the Maritime Continent for the last few years have been favoring a SE ridge more by increasing the % of winter days in the MC of the MJO, increasing the magnitude of the MJO when in the MC, and causing tropical forcing patterns to sometimes be MC-like even when the official MJO wasn't in the MC. Therefore, the MC waters would need to cool relative to surrounding waters to reduce the domination of the SE ridge.
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Thank you and lmao! Keep in mind that for the first time this winter there's about to be a major SSW. Don't forget that the prior SSW, which is what got me excited and thus posting a lot more starting in mid January, ended up being a "minor" SSW and it lead to limited effects on the E US. Now this time we have the "real deal" about to occur, which increases the chance to lead to -NAO/-AO/colder E US/increased wintry wx in the E US as compared to the after effects of a minor SSW. Edit: I think it is important to not get so emotionally tied to the outcome. Edit 2: Even stronger indication of -NAO starting Feb 28th on 18Z GEFS vs 12Z
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Great questions: 1. We don't know if it will downwell. However, last week there was a S-G dipole max above 40 mb, which per Dr. Simon Lee, is a positive indicator for it to go down into the troposphere. And the models are suggesting a -NAO in two weeks. 2. Nobody knows the specifics on which areas of the world would be affected the most if it downwells. But if the -NAO that models are hinting at starting in two weeks actually occurs, that would obviously bode well for chances for cold in the E US. 3. The timing varies with each SSW but effects including an -NAO/-AO often start within 1.5-2 weeks of the SSW date, which would be either very late Feb or very early March. So, imho, IF there is to be a colder pattern from this, it would very likely start earlier than mid to late March.
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Same thing
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You're making a good point that can't be ignored. The models' cold bias is important to keep in mind. However, there's one key difference ahead that we haven't seen so far this winter: we now have the unpredictability of the sometimes favorable aftermath of a major SSW to consider. And this is looking to be a solid major with the latest GFS prediction of a -15 m/s 10 mb 60N mean wind now being predicted. While not near the record strongest, which is well down into the -20s, a -15 is no slouch and probably is stronger than the average major SSW by that measure.
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On the 0Z GEFS mean, 25% of the members had a sub -0.25 NAO (what I consider the threshold for an -NAO) already by Feb 27th. With the 12Z GEFS mean being even closer to a -NAO on Feb 27th than was the 0Z mean, I feel that the chance of a -NAO starting in very late Feb as opposed to waiting til the first days of March is increasing. Edit: Remember that nice looking -NAO on the Euro weeklies from last Thursday that then didn't look as good on yesterday's weeklies? The latest trends are heading back to that Thursday weeklies look.
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A -NAO may even start as early as very late Feb per GEFS trends. 25% of the 0Z GEFS members had it below -0.25 by Feb 27th and the 12Z mean as of Feb 27th is closer to a -NAO than was the 0Z mean.
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The 12Z GEFS mean has a pretty impressive -NAO that gets going late on 2/28 and then strengthens. The chance of a -NAO getting started very late Feb/start of March is increasing. Edit: Regarding the 0Z GEFS mean, 25% of the members had a sub -0.25 NAO by Feb 27th. The 12Z GEFS mean is even closer to a -NAO on Feb 27th than was the 0Z. This tells me that the chance of a -NAO starting already in very late Feb is increasing. Edit again: Remember that nice looking -NAO on the Euro weeklies from last Thursday that then didn't look as good on yesterday's weeklies? The latest trends are heading back to that Thursday weeklies look.
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Excellent point. I think as brooklynwx said that it is going to come down to whether or not there is a solid -NAO (say sub -0.5) averaged out in March and early April. The model trend fwiw is going in the direction of a -NAO for at least early March. Keep in mind that despite the prior SSWs, none of the four cases you bolded had a -NAO dominated March: 1999: +0.23 2002: +0.69 2007: +1.44 2008: +0.08 Also, in 2018, NYC averaged 7 AN for the period 2/10-3/6 fwiw.
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GFS/GEFS trends through 12Z are clearly going in the -NAO direction late in the runs with a -NAO being suggested by March 1st. The trend is also suggesting that it may start in very late Feb as 25% of the 0Z GEFS members have a -NAO by Feb 27th.
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Following the 2018 major SSW, NYC for the period 3/7-4/11 averaged 5 BN and had a whopping 17" of snow. This followed the very mild 2/10-3/6 that was 7 AN. They were able to be this cold and snowy despite an average PNA down at -0.5 for that 36 day period. On the days of the 3 main snows (3/7, 3/21, and 4/2) the PNA was -0.7, -0.8, and -1.8, respectively. They had a -PNA on 24 days, a neutral (-0.25 to +0.25) PNA on 9 days, and a +PNA on only 3 days. GFS/GEFS trends through 12Z are clearly going in the -NAO direction late in the runs with a -NAO being suggested by March 1st. The trend is also suggesting that it may start in very late Feb as 25% of the 0Z GEFS members have a -NAO by Feb 27th. *Edited for typo
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The 12Z EPS as well as 0Z GEFS/GFS/GEPS all are suggesting a -NAO period starts ~3/1-2. Based on the last weeks worth of 0Z GEFS runs, which go out much further than other runs, 3/1-2 has been the start of a -NAO. So, it isn't slipping back. Let's see what the 0Z EPS does.
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Thanks. Also, isn't NAM more precisely the AO rather than the NAO? The diagram refers to NAM, but she refers to NAO.
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Don and others, I have my skepticism about the statistical significance of the study referenced in this Dr. Amy Butler tweet, but am posting it anyway to see what others think. Even Amy Butler, herself, says this: "A word of caution: this analysis is based on the relatively few events in the historical record, so sampling is likely an issue"
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Not a good run of the Euro weeklies today if you want a cold March. This new run has a much weaker -AO/-NAO 2/27+ vs the prior run and is warmer than the old run. Not what I wanted to see although not surprising based on the fact that the prior run's 360 (for 2/24) already had a developing -AO/-NAO vs the 0Z of today still having what appears to me to still be a +AO/+NAO or at best neutral as of its end on 2/28. There's still time for it to change back but I'd like to see it trend back in that direction by the next run (Thursday). Don Sutherland agrees for the NE and you can see in his tweet on the maps that it is ~2 F warmer in the SE 2/27-3/5 on the new run vs old run with ~2 AN instead of NN.
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And as you probably already realize, this new run also has a much weaker -AO/-NAO 2/27+ vs the prior run. Not what I wanted to see although not surprising based on the fact that the prior run's 360 (for 2/24) already had a developing -AO/-NAO vs the 0Z of today still having what appears to me to still be a +AO/+NAO or at best neutral as of its end on 2/28.
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Here the winter to date is tied for the all-time worst of no wintry precip. Of course, that's not saying much since the majority have been like that. Meanwhile, the major SSW is on schedule. What still isn't clear is whether or not a significant and longlasting -AO/-NAO period will follow by early March. There have been hints of that on certain runs, but nothing definitive.
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I was just looking back in this forum's discussion when the Feb of 2018 major SSW was starting, which was 3-4 days earlier in Feb than the current one. Mid to late Feb, itself, was similar to this month looking mild with a solid -PNA projected. However, what was different then was that a new strong -NAO/-AO was already appearing late in the model runs, which was attributed to that month's SSW. So, there was already a suggestion based on the models that the overall pattern would likely cool down significantly by the end of Feb or early March vs the higher level of uncertainty today.
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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
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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.
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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.
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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.
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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:
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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.
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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.
