GaWx

OHC continues to plunge:

Also, 1986-7 and 2015-6 El Nino winters had both under an inch through Dec and 20”+ Jan+. So, there have been four and all four had 11.6”+ in January, alone. Since 1939-40, there have been 10 El Niños with <1” through Dec. That’s out of 28 total El Ninos. So, 36% of them had <1” meaning not highly unusual. Thus out of those 10, four (40%) had 20”+ Jan+. That’s not that low of a %. I’ll now compare to non-Nino winters. Regarding non-Nino winters since 1939-40, I count 13 with <1” through Dec. That’s 13 out of 56 non-Nino or 23% of them. So, having <1” through Dec has been significantly more unusual during non-Nino (23%) than during Nino (36%). Out of those 13 during non-Nino, only 4 (31%) ended up with 20” Jan+ vs the 40% for El Niño. So, being in El Niño helped some for the slow starters. Out of all 84 winters since 1939-40, 41 of them (49%) had <20” Jan+. So, not getting 20”+ Jan+ is nearly a coin flip for all winters. Out of the 23 total winters with <1” through Dec, 15 (65%) had <20” Jan+. That means that out of the 61 total winters with 1”+ through Dec, 26 (43%) had <20” Jan+ vs the 65% for winters with 1”+ through Dec. So, having <1” through Dec does increase the chance somewhat for Jan+ to have <20”.

The # of members with a major during just Jan 5-12 went from the 0Z 12/24 GEFS’ one (3%) to the 0Z 12/25 GEFS’ 11 (36%)! I’m getting very close to the @40/70 Benchmarklevel of confidence that there will be one in early Jan.

So, the 12Z EPS is implying a most likely major SSW (when winds reverse) centered on Jan 6th. Per the 0Z, the most likely reversal dates appear to be for Jan 5th-8th. The 0Z was the first 0Z EPS with the mean touching 0 m/s. The lowest prior to that had been yesterday’s +2.5. And now this 12Z drops it to -5! A Jan 5-8 SSW date would suggest the period of greatest potential cooling from it on the E US would start ~Jan 20th and go at least well into Feb meaning covering a large portion of the best climo period for E US winter storms, especially.

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: