GaWx
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But just 2-3 days later, look out for potential CAD cold! All ensembles have a nice sized Canadian high coming down into the N Plains on 2/24-5 and then the chance for it to wedge down to the SE just afterward. Bathing suits followed closely behind by heavy coats?
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LMAO! If need be, I'm going down with the ship!
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Yeah, it is looking bad for cold lovers for the foreseeable future. If the SSW wild card doesn't produce a big change afterward, winter may very well be over.
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The 18Z GFS fwiw has a -NAO that gets started ~2/26, becomes quite strong the next day, and stays strong through 3/3. One calculation of the NAO is based on the normalized SLP anomaly for a location in the Azores less the same for a location in Iceland. The normal Azores SLP this time of year is ~1020 mb while it is ~1005 in Iceland. So, the Azores SLP averages 15 mb higher than that of Iceland in Feb. But for the period 2/27-3/3, the 18Z GFS has the Azores at only ~1015 (~1/2 SD BN) and Iceland way up at ~1037 (~2 SD AN). So, Iceland is forecasted by this run for this 5 day period to be at a whopping 22 higher than the Azores vs the norm of 15 lower. That is a very strong -NAO, likely way up near -2.5 per this SLP based method. The point of this post is to show that some runs are showing a very strong -NAO already starting near the end of Feb. The 18z GFS is likely way overdone, but it gives an idea of the potential. I expect the 0Z GFS won't be nearly as strong. Edit for 0Z GFS: For the same period, this run looks like it has a pretty neutral NAO with averaged Azores SLP a bit higher than Iceland.
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- The GEFS based NAO forecast has slowly been trending toward the negative direction. Yesterday's 0Z GEFS had 8 members (25%) of 31 with a sub -0.25 NAO by Feb 27th. Today's has ~10 of the 31 with sub -0.25 by 2/27. Also, the mean line already gets down to 0 on Feb 26th, which is two days earlier than yesterday's showed. - The end of Feb is still out 13 days, which is still far enough out to make the model skill in the troposphere low and much lower than that for the stratosphere at day 13 (as I showed recently). Thus, confidence in even ensemble means is still low, especially considering that a major SSW is now occurring. - The major SSW is underway with the latest GFS based forecast of 10 mb 60N winds for a dip to an impressive -16 m/s on 2/18 vs -15 on yesterday's forecast. So, the GFS is staying the course. - If there is going to be significant cooling in the E US as a direct result of this SSW, it would likely not get going until at least 10-14 days after it. That would mean starting near the end of Feb at the earliest. This idea on the timing hasn't changed at all since I started talking about this newest SSW. The warmth during it and following it has been expected.
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- The GEFS based NAO forecast has slowly been trending toward the negative direction. Yesterday's 0Z GEFS had 8 members (25%) of 31 with a sub -0.25 NAO by Feb 27th. Today's has ~10 of the 31 with sub -0.25 by 2/27. Also, the mean line already gets down to 0 on Feb 26th, which is two days earlier than yesterday's showed. - The end of Feb is still out 13 days, which is still far enough out to make the model skill in the troposphere low and much lower than that for the stratosphere at day 13 (as I showed recently). Thus, confidence in even ensemble means is still low, especially considering that a major SSW is now occurring. - The major SSW is underway with the latest GFS based forecast for a dip of 60N 10 mb winds to an impressive -16 m/s on 2/18 vs -15 on yesterday's forecast. So, the GFS is staying the course. - If there is going to be significant cooling in the E US as a direct result of this SSW, it would likely not get going until at least 10-14 days after it. That would mean starting near the end of Feb at the earliest. - This idea on the timing hasn't changed at all since I started talking about this newest SSW. The warmth during it and following it has been expected.
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That makes sense. Well, at least for a change the MJO just rocketed through the MC as it took only six days! Looking back at old charts during winter, five days is the fastest to fully traverse both phases 5 and 6 near this amplitude. It more often than not takes longer than six days.
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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.
