GaWx

1. That looks like a major SSW (with a split) on the 12Z GFS. The 0Z was right at 0. 2. The 0Z CDN ens mean dropped way down to -16 vs -3 yesterday (see below). A -16 for an ensemble mean 14 days out is extremely impressive! Anything -15 or under would be a record breaker for late Dec through mid Jan and there have been many in early Jan, alone. 3. The 0Z GEFS mean dropped way down to +7 vs +17 yesterday (see below):

That Atlanta to Carolinas major snowstorm was on Jan 2-3 and the SSW was on Jan 2nd. So, it’s likely that the snowstorm occurring had little to do with the SSW.

Agreed 100% about the difficulty in estimating what would have occurred without a SSW should one actually occur.

The MJO progs from the model consensus of early Dec were much too weak for late Dec: near circle (top image) vs actual well outside the circle (bottom image):

The model consensus continues to go in the direction of a split major SSW in early January. Almost all of the El Niño years with them had following the splits significant periods of notable cold and/or winter storms, including some wintry precip quite far south (like N Florida).

Following up on this, the GEPS mean had a major 14 days out yesterday and 13 days out today vs having to wait til 10 days out in advance of the 2/16/23 major. So, its signal is much stronger than then. OTOH, the GEFS mean in advance of 2/16/23 was ~+10 or less from 15 days out before also going major 10 days out. But with it still up at +17, it is a much weaker signal than that of GEPS vs having a stronger signal than GEPS 15-14 days in advance of 2/16/23. So, there are mixed signals between the GEFS (less bullish) and GEPS (more bullish) vs last year. Based on my memory, the EPS is stronger than it was then. So, two of the three ensemble means are more bullish currently vs 2/16/23 and one is less bullish. I expect the GEFS to get more bullish on the coming days.

0Z 12/24 (orange) barely makes major SSW status with it a hair under 0 m/s at the end and still dropping. The 0Z CDN ens mean (blue) is at 2 days in a row at a major. But the 0Z GEFS mean never gets below +17.

The 0Z 12/24/23 EPS holds onto the very good chance for a major SSW Jan 3-9. Also, I count ~12 extreme cases (sub -15) throughout the run:

And we can now add the 12Z GFS op to the split SSW list. Here’s the way I look at the SPV: -Weak much better than strong -SSW better than not -Major SSW better than minor. E 1/3 of US affected most. -Split major seems to be somewhat better than displacement major -Split during El Niño may be best of all though displacement during Nino normally good enough

Here is a screenshot of a list of major SSWs broken down by split vs displacement: noteworthy splits include 1/30/58 (El Nino), 1/8/68, 2/2/73 (El Nino), 1/9/77 (El Nino though not listed), 1/2/85, 12/8/87 (El Nino), 1/18/03 (El Nino), 2/9/10 (El Nino), and 1/2/19 (El Nino; too recent to be listed here but was a split). Note that there have been 7 split SSWs since 1958 during El Nino that were early enough to impact met. winter and all 7 were notable in terms of subsequent cold and/or historic E US winter storms:

The 0Z EPS is also hinting at a split per this that just came out from BAMWx (left map is 0Z EPS hour 360 at 50 mb) meaning all three of the latest major ensemble means are leaning toward a split now:

So does the 0Z GEPS (CDN ens):

The 3.4 OISST is not going in the right direction if you want a super Nino:

This 0Z 12/24 GFS is almost definitely a major SSW (we'll find out by afternoon) and is the first run I can recall with an actual split of the SPV.

I found this but have no details about it. What do they mean by “following”? The 1-3 week period immediately following is sometimes mild in the E US. Is that period included. If so, the average cold anomaly would be colder than this once past 1-3 weeks. And is this just for majors? Are these C or F? But this suggests that the coldest over land in the entire hemisphere between 30 and 40N by far is over the E US vs the warm anomalies over much of Eurasia/W US. The coldest is over the MidAtlantic/SE/lower MW. That’s why I don’t think about where the coldest will end up. So, get the major and the cold should come, especially during El Niño:

The potential major SSW is getting closer! Once again, the EPS has numerous major SSWs 1/3-9 with the highest concentration 1/4-7. So, the Euro and CDN are both are both saying very good chance for one 1/3-9 with the GEFS at ~ half as high a chance as the other two for then. I see ~17 sub -15:

12Z GEPS still has strong signal/much stronger signal than 14 days prior to 2/16/23 for a major SSW ~1/6. But for same timeframe the 12Z GEFS still has a much weaker signal than GEPS. Model battle! I expect GEFS signal will strengthen in coming days.

Today’s 0Z CDN ens mean has gone from yesterday’s +2 to +1 for 1/6-7 to today’s -3 to -5 for 1/7-8 (lt blue line), solid signal for a major SSW within a few days of 1/6 or 14 days out: To compare, what did the GEPS mean show in advance of the 2/16/23 major? At 14 days out or the 2/2/23 run, it still had it way up at ~+15 on 2/16 (see below). It didn’t show it negative until 2/6/23, only 10 days out. So, the current GEPS signal out 14 days is much stronger vs where it was 14 days before the 2/16/23 SSW:

Regarding the periods in El Niño Jans with outside circle MJO phase 4-6 for 5+ days, were they all dominated by mildness in the SE? I’ll look at RDU: 1. Jan 17-30, 2019: no as it averaged 2 BN 2. Jan 1-13, 2015: No as it averaged 3 BN 3. Jan 4-6, 18-21, 2010: No as it averaged 3 BN 4. Jan 1-15, 26-30, 2007: Yes as it averaged 7 AN 5. Jan 1-12, 15-19, 30-31, 2005: Yes as it averaged 5 AN 6. Jan 1, 8-12, 2003: Yes as it averaged 4 AN 7. Jan 12-28, 1995: Yes as it averaged 5 AN 8. Jan 20-31, 1978: No as it averaged 8 BN ——————— So, for the 8 El Niño Jan periods with 5+ days of outside COD phases 4-6, RDU was mild during only half of them. To be fair when averaging the 108 days, I do get 1.5 AN. However, even that is only slightly warmer than normal. Conclusion: Although it could very well be mild during non-weak phases 4-6 in El Niño Jans in the SE, don’t assume it will because that was the case for only half of the 8 cases: 2007, 2005, 2003, and 1995. The years 2018, 2015, 2010, and 1978 were cool to cold. This tells me to not assume either way.

The answer just came out based on the following chart: 0Z 12/22/23 GEPS mean (light blue line) has a mean 60N 10 mb wind of +1 m/s on 1/6-7:

New Euro Weekly 10 mb mean wind: though likely not quite as many there are still lots of members with a major SSW in early Jan, especially Jan 3-9. Also, for the full run, the # of extreme SSWs (sub -15) increased back up to ~15:

In the E US, I found that the SE US and lower Mid Atlantic have been most affected on average. As I’ve posted before, I did an analysis of major SSWs that affected El Niño winters since 1957-8 (excluded the two in late Feb because that’s too late to impact met. winter) and found all of them to have had a 3-7 week long period of BN temp domination in those areas starting 1-3 weeks after the major SSW date. The NE is also usually affected though not always.

Today’s 0Z GEPS mean at 384 looks very close to a major SSW. If not, I think the mean wind is only a little over 0. I’ll find out later:

1. Today’s WCS OISST dropped slightly to +2.01. It continues to not move much overall (no real trend). It remains to be seen whether or not the ERSST based NDJ ONI ends up +2.00+. Keep in mind that the Nov ERSST was slightly warmer (less than 0.10) than the Nov OISST: 2. OHC has been dropping sharply since late Nov per this. So, barring another sharp warmup soon, Nov will end up the peak month:

Don’t forget that the great cold snap of 12/23-26/22 was actually during a high amplitude phase 5: