GaWx

My post above based on 3rd year cold ENSO analogs said that the best bet for this DJF was for one mild, one near normal, and one cold. Dec was near normal. Jan, based on actual first week and forecasts through midmonth, will very likely be 7-9 AN for the first half. Combined with more warmth forecast by model consensus to dominate 1/16-1/21 means that Jan will almost certainly end up mild. So, that means one near normal and one mild for DJ. One might then think based on the original best bet to look for Feb to be cold. Maybe that will happen but La Niña climo will make that quite the challenge. I looked at the 34 La Niña Febs over the last 140+ years at ATL: - 18 AN - 11 NN - only 5 BN (15%): 2006, 1934, 1917, 1910, 1904 So, La Nina climo says bet heavily against a cold Feb. But my original best bet suggested one cold month. Will 2023 be one of the unusual cold La Niña Febs? Nobody knows. By the way, Feb of 1895 (3rd year cold ENSO) was record cold, but it was during cold neutral ENSO rather than La Niña.

To an extent it still does

12Z EPS is consistent with the model consensus trend away from a SE winter storm threat during 1/13-15. So, the January of 1933 scenario of warm practically all month surrounding an isolated two day cold that included a big RDU January 13th snow is now looking highly unlikely.

And in case anyone is wondering lol, the 12Z JMA (which also had a SE wintry threat at 12Z yesterday) joins the other models with a warmer solution and no widespread SE wintry threat.

Preliminary 12Z Euro maps suggest to me that this run will be more similar to today's non-wintry 0Z than yesterday's wintry runs. Let's see what it ends up showing.

12Z ICON has no SE wintry precip as the low is way too far north and there's no strong precursor low to lock in the cold from the Canadian high. This allows for way too much warmth ahead of it for SE wintry precip.

0Z EPS has similar change to the 0Z Euro with much weaker or no precursor surface low to help bring down and lock cold air in the SE. Thus, I expect this run won't be as wintry as the last one. Let's see.... Edit: confirmed to have less wintry precipitation

So far (hour 132), the 0Z Euro doesn't look as threatening as the 12Z, mainly because there's no surface low on the way to being the very strong low that the 12Z had that helped lock in cold in the SE ahead of the SE storm, itself. Also, H5 isn't so far as strong for the storm, itself. Going further out, the SE Canadian high is weaker and there's no precursor storm to help bring down cold air into the SE. The H5 for the potential SE storm is weaker, too. Edit: not surprisingly, a big fail on this run

However, this run doesn't have the 970 mb low off SE Canada that the 12Z had and is thus not nearly as cold ahead of the storm. The 12Z looked like it was heading toward a huge mess in the SE after the end. This run isn't as threatening for especially more southern areas.

But the 0Z CMC has the low back way far south on the Gulf coast and thus is back to wintry precip just like two, three, and four runs ago.

0Z GFS and ICON say no widespread SE winter storm 1/13-15. Surface low tracks further north/way too far north and thus way too warm.

To clarify when I say wintry, much of that pivotal accumulation appears to actually be ZR for GA/SC/NC with 850s well above 0C in many cases. This is a major icestorm signature vs the EPS having much more snow in the mix due to a much further south mean surface low track.

Contrary to what the 18Z GFS has, the 18Z GEFS per clown maps is actually the most wintry GEFS yet for much of NC, N SC, and N GA (as of 12Z on 1/14).

The chance for any one D, J, or F at RDU to be snowy (say, 3"+ of SN/IP) is between 1/4 and 1/5 per records that started in 1887. As is intuitive, the correlation of snowy to how cold is the month is strong. With the forecast for RDU to be ~11 AN MTD as of 1/11 and with the models looking warm again after the midmonth winter storm threat, this month is almost certainly going to end up AN. So, that got me wondering how rare and cool it would be IF RDU were to get 3"+ from this storm with it a mild month: -~37% of BN months had 3"+ SN/IP -~21% of NN months had 3"+ SN/IP -only ~4% of AN months had 3"+SN/IP I was surprised at how low is the AN month %. So, should we assume that RDU has only a 4% chance of getting 3"+ this month? If there were currently no threat showing, I'd say that would be a good guideline. But based on the threat the models are showing just 8-10 days out, the chance is clearly much higher. This may very well be one of those very rare mild snowy/sleety months! They're kind of due for one fwiw. I found 5 AN winter 3"+ SN/IP months at RDU and 3 of them were during La Niña fwiw. Going from warmest down: 1. Jan of 1933 (cold neutral ENSO): 10" on 1/13 and a whopping +9 F for month, 6th warmest on record; warm through 1/12 and then the big snow; after a cold 1/13-4, warm returned 1/16-26 What's interesting about this analog is how similar it appears to be to 1/2023! 2. Dec of 1971 (moderate La Niña similar to now): 3.7" on 12/3-4 and +7 for month; warm 12/7-17 including high of 77 on 12/16 3. Jan of 1911 (weak La Niña and a 3rd year Niña like we're in now): 3.3" on 1/17 and +5 for month after warm 1/11-15 including highs in 70s on 1/12-5 4. Jan of 1930 (weak El Niño): 3.6" (3.5" 1/29-30) and +3 for month 5. Feb of 1984 (weakening from moderate La Niña): 6.9" on 2/6 and +2 for month with a warm 2/11-20 ----------------------- In summary, RDU had 3"+ during a mild winter month in 1911, 1930, 1933, 1971, and 1984. So, these have occurred ~once every 27 years on average. It has been 39 years. Will 2023 be the next one? Stay tuned!

The 12Z GFS' surface low needs to adjust further south to produce widespread SE wintry precip as it has the low going across N GA. With the GFS trending stronger and further south with the H5 low, the 12Z Euro holding onto to the Gulf coast to S GA to offshore track, and the 168 12Z UKMET setup suggesting something similar had it gone out further, I think it is just a matter of time before the inferior GFS does something similar. Indeed, the AO and MJO for 1/13-15 are looking favorable. The PNA drops to neutral then, but I don't see that as a negative. The +NAO, indeed, is dropping from an earlier strong. However, the GEFS has it still moderate (~+0.9) 1/13-15. But as the research I posted two days ago showed, folks hoping for a big SE snow shouldn't fret about it. Why? Because in looking at big RDU snows since 1950, there was no correlation to NAO with only ~1/3 during a -NAO, ~1/3 during neutral, and ~1/3 during +NAO. Moreover, the 2/6/1984, 2/17-8/1989, 2/24-6/2015, 1/17-8/2018, and 12/9-10/2018 big RDU snows all had an NAO of +0.9 or higher (range +0.9 to +1.7). RDU hasn't had a big snow during a -NAO since 2010.

The 12Z EPS is the 7th of the last 8 runs with a significant wintry precip signal for a good portion of the SE for 1/13-5. This signal goes all of the way back to the 0Z 1/2 run. Only the 0Z 1/3 run lacked this.

12Z Euro 198 has wintry mix Atlanta NE to SW NC!

The 12Z Euro as of 180 looks like it may be headed to something similar to yesterday's 12Z. Edit: wintry mix far N GA to NC.

It is too bad that the UKMET doesn't go out past 168. The 12Z 168 has both the surface and H5 lows well to the south, near Dallas, TX, producing heavy QPF east/SE of there. Then there's the strong (1040 mb) Canadian high already inducing CAD way down into the favored SE region on the backside of very strong (970 mb) low winding up just off SE Canada. At that time, the 0C 850 line is dropping south of Columbia. There's little doubt in my mind that had this run gone to 192 that it would have shown a big wintry mess over a good portion of the SE on 1/13.

Regarding the 12Z GFS (which indeed is trending more impressively at H5), a much further south surface low track similar to the last two extended Euro runs would be most helpful to make it much colder at low levels and allow for widespread and significant SE wintry precip prospects. Whereas those two Euro runs had the low go offshore E of Brunswick, GA, on January 13th, and thus produce wintry precip in parts of the SE, the 12Z GFS has it way north of that north of Augusta. Let's see whether or not the GFS sfc low track adjusts southward over the next couple of days. The 12Z CMC is by far the warmest of the last 4 runs due to the surface low being 700 miles further north (IL to OH to VA) vs the prior three runs. Those prior three CMC runs had the surface low go offshore GA and thus produce wintry precip in part of the SE. As a result, the new (12Z) CMC is much warmer with all rain in the SE. So, the key for the best chance for a big deal wintry precip wise in the SE is for the surface low to track much further south than the 12Z CMC/GFS with off of Brunswick being near ideal.

The 12Z EPS, consistently with the 12Z Euro, has the strongest signal yet for a SE winter storm on 1/13-14. The 12Z Euro has a closed upper low that is associated with this over MO early on 1/13 that strengthens and moves SE/ESE to the SE and hits max strength just offshore the SE US early on 1/14. At that time, the center is a whopping 25 dm below normal at 500 mb. So, plentiful cold air from above gets into this. In addition, strong CAD from a large SE Canadian high gets involved and imparts low level cold air. On the 12Z EPS, the winter storm signal is mainly for VA, NC, NE GA, and the N half of SC. It is important to point out that though this is the strongest signal from the EPS for 1/13-14, it isn't the first run with a significant signal for then as this is the 3rd in a row and 5th of the last 6 runs going back to the 0Z 1/2 run.

Agreed. This was also on the 0Z CMC and 0Z Euro as well as recent EPS runs as noted earlier. In addition, the 12Z CMC has wintry precip in the SE 1/13-14.

Both the 0Z Euro and CMC have wintry precip in portions of the W Carolinas and NE GA late on 1/13 as a result of the system highlighted on the 12Z EPS. This system, no matter how it ends up evolving, has the makings of quite an energetic one in the upper levels.

I've got more to say about a -NAO not even being close to being required for major SE snow chances. I brought this up due to the moderate +NAO (~+0.6) forecasted during 1/13-15, which could become a threat period for a SE winter storm per the EPS. Here is the NAO for the 23 Raleigh 6"+ SN/IP storms that I found since 1950. (I'm calling neutral NAO to be from +0.25 to -0.25):-1/19/1955: -NAO- 12/11/1958: neutral NAO- 3/2-3/1960: neutral NAO- 3/9/1960: neutral NAO- 2/26/1963: neutral NAO- 1/25-7/1966: -NAO- 2/9/1967: +NAO (+0.5)(9.1")- 3/1/1969: -NAO- 1/7-8/1973: -NAO- 2/18-9/1979: neutral NAO- 3/1-2/1980: +NAO (+0.4)(11.1")- 1/13-14/1982: neutral NAO- 3/24/1983: neutral NAO- 2/6/1984: +NAO (+1.1)(6.9")- 1/7-8/1988: +NAO (+0.5)(7.3")- 2/17-8/1989: +NAO (+1.7 )(6.2")- 1/24-5/2000: -NAO- 1/2-3/2002: -NAO- 2/26-7/2004: -NAO- 12/25-6/2010: -NAO- 2/24-6/2015: +NAO (+1.0)(6.5") - 1/17-8/2018: +NAO (+1.2)(6.1") - 12/9-10/2018: +NAO (+0.9)(8.9")Tally:-NAO: 8Neutral NAO: 7+NAO: 8 Note that RDU had 5 big snows with an NAO much more positive than the +0.6 that is being predicted for 1/13-15! Honorable mention since Raleigh didn't get heavy snow from it but many others did: 3/12-3/1993 Storm of the Century: +NAOConclusion: results like this on a pretty nice sized sample tell me that any correlation of -NAO with heavy SE US SN/IP is likely low, if any. NAO daily data: https://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.nao.cdas.z500.19500101_current.csv RDU data: https://www.weather.gov/wrh/Climate?wfo=rah

Regarding the potential 1/13-15 SE wintry threat, the consensus has the MJO then at a moderate level mainly in phase 8 but possibly still in 7 during part of it. The GEFS has a weak +PNA (though the EPS' PNA may be up to moderate), a moderate -AO (~-1.5), and a moderate +NAO (~+0.6). So, moderate phase 7 to mainly phase 8 MJO, weak to moderate +PNA, moderate -AO, and moderate +NAO. For those fretting about the +NAO, a good number of major SE snowstorms have occurred with a +NAO per my research. I may post these later if I were to get the chance and if this threat were to grow.