GaWx
-
Posts
15,994 -
Joined
Content Type
Profiles
Blogs
Forums
American Weather
Media Demo
Store
Gallery
Everything posted by GaWx
-
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.
-
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.
-
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.
-
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.
-
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
-
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.
-
Thanks. Also, isn't NAM more precisely the AO rather than the NAO? The diagram refers to NAM, but she refers to NAO.
-
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"
-
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.
-
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.
-
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.
-
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.
-
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.
