GaWx

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.

Per the new 12Z EPS for the SE US, the 8th-9th has some precip but only very limited cold air and thus practically no wintry precip. Then the 11th has much more significant precip along with a low that then tracks offshore the SE for many members. Whereas that's often favorable for SE wintry precip in mid January, it is still not cold enough in most areas except the NC mountains and possibly parts of N NC into VA. As of now, this looks like a minor deal at most but should be watched especially since there's an outside chance that it trends colder and the more N areas might have a decent shot at something. But then we come to 1/13-15, which is a totally different story. This period is the highest threat level for SE wintry of the run by a good margin. Like the 11th, the run has many members with a low that either tracks offshore from the NE GOM or inland or forms offshore the SE US and there is a strong signal for significant precip over the SE. Unlike the 11th, this period has ample cold air to potentially work with depending on the low's track. Thus, several members bring snow to the SE, especially NE GA, SC (heaviest upstate and E), and NC (heaviest E) along with VA. This run has by a good margin the highest threat yet for 1/13-15 for the SE overall. There's nothing boring about this run for the SE. ----------- Edit fwiw since this is the very unreliable GFS this far out and cold air is still limited: 18Z GFS has the Jan 11th low move NE from the E GOM and then wind up offshore strongly and pretty far south giving much of the E Carolinas several inches of snow 1/11-12.

I looked at February temperature anomalies of 34 La Niña Febs to see what are the chances based on the last 140+ years for a torch (using respective 30 year averages) in the SE using ATL stats as representative: 1887: +8 1890: +10 1893: +1 1894: 0 (major snow) 1904: -3 1909: +4 1910: -3 1911: +5 1917: -2 1925: +5 1934: -6 (major snow) 1939: +4 1943: +1 1950: +5 1955: +2 1956: +5 1971: -1 1974: +1 1975: +2 1976: +7 1985: -1 1989: +3 1996: -1 1999: +1 2000: +3 2001: +2 2006: -4 2008: 0 2009: -1 2011: +2 2012: +3 2018: +9 2021: 0 2022: +3 If I use +5 as minimum required for torch, I count 8 torches (MA) (24%), which is a lot. There are also 10 A (+2 to +4)(29%). So, a whopping 18 of 34 (53%) are A to MA. Normally, A to MA would comprise no more than ~35-40%. There are 11 near N (+1 to -1)( 32%). I count only 4 B (-2 to -4)(12%) and just 1 MB (-5 or colder)(3%). But that still means 47% (nearly half) were near normal or colder. So, whereas we often read about the assumption (likelihood) of a mild Feb in a La Niña, the reality is that that chance is only a little over 50% and the average of the 34 Niña Febs was only +2 at ATL. That's because the largest # in any category is actually near normal. In fairness though, the chance of cold is much lower than mild. Conclusion: During any La Niña, there is a high chance that Feb won't be cold. However, there actually isn't a high chance but rather more or less only a coin flip type chance that Feb will be mild. --------------- ENSO data: Pre 1950 from Eric Webb: https://www.webberweather.com/ensemble-oceanic-nino-index.html 1950+ from NOAA: https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php ATL temperature data: https://www.weather.gov/wrh/climate?wfo=ffc

For those like myself who want the progged mid January chill to be the start of a long period of cold domination, the 0Z EPS and now even more emphatically the 12Z EPS is saying the chances of that are dropping. Whereas the 12Z EPS looks a bit colder than the 0Z toward midmonth with the cold period thanks to a decent +PNA, it is also showing it to be only a ~3 day long chilly period as the +PNA quickly transitions to a zonal/strong Pacific jet/warming pattern to at least near normal with no new cold then in sight. That progged quick end to the chill is still two weeks out and can obviously change drastically. However, today's ensemble consensus changes are clearly moving away from the possibility of the start of an extensive, long duration cold pattern at midmonth. Based on how often model consensus has been doing this kind of thing since late November outside of the big cold of late December, this isn't at all what I wanted to see. Edit: I should reiterate it does look pretty cold on the 12Z EPS for ~3 days near midmonth. That would possibly be a period to look for the chance of snow from an off the coast storm for mainly NC north just taking the run at face value. The run is showing a pretty good number of members with off the coast storms centered at the start of this cold period late 1/13 to early 1/14. If there is a low there then, would enough cold air get entrained before the moisture is gone?

I wonder whether this underestimation of the Pacific jet/overdoing the +PNA by the models in the 11-15 often since late November is partially related to near record high SSTs in Indonesia/Maritime Continent. I was told by a pro met a couple of years ago that the record high SSTs in the MC likely sometimes cause the Pacific to act as if there's a pseudo MC MJO phase (4 and 5) even when the MJO, itself, isn't officially in the MC. It seems as if this has been occurring a lot over the last several years and the MC has been near record highs for several years.

Since yesterday, the EPS (along with the GEFS) has warmed in the SE/much of the E US near midmonth and is now suggesting that the midmonth cooling may not last more than a few days or be as strong with the +PNA then quickly dropping back. Today's 0Z day 14 GEFS PNA forecast took a hit from yesterday's ~+0.5 to today's ~0. That's a drastic change for just one day. The day 14 GEFS NAO rose from yesterday's ~0 to today's ~+0.2. Though the AO still looks solidly negative and the strong Dec -AO favors a sub -1 AO this month, it doesn't look as strongly negative late in today's GEFS run as yesterday's nearing -2. Today's isn't much lower than -1 along with most members then rising. The MJO does still look favorable for cold with a phase 8 though with a little higher amp. (I prefer low amp.) Yesterday I said this: "For those preferring cold domination, the hope is that the EPS won't backtrack like it did for the period near 1/9-10 about five days ago." Unfortunately for cold lovers, today's 0Z EPS backtracked somewhat for midmonth though it is just one run. We'll see whether or not the 12Z EPS agrees. The following link from a knowledgeable NYC forum poster "bluewave" shows very well how much the EPS and GEFS (especially the EPS) have backtracked from a return to cold/solid +PNA for January 10th on the 0Z/6Z 12/26 runs (what I was referring to yesterday) to a warm E US for January 10th on today's 0Z runs due to underestimating the strength of the Pacific jet: I mentioned last week that the Indonesian waters/MC are near record highs (similar to last several years) and that this along with La Niña would likely mean periods favoring the SE ridge. I wonder if this is the main reason for underestimating the Pac jet.

The above two posts make it sound like AN temps will dominate the SE through the somewhat foreseeable future (say 15 days). If I read them and didn't look at any data, I'd be inclined to think that. Also, if I saw it that way, I wouldn't be afraid to suggest similarly as my style is to post with objectivity as a prime goal. But I don't see it that way. In a nutshell, the current torch will end abruptly all areas by 1/5 followed by a couple of chilly days. There will likely be a return to AN a few days later that is expected to last no more than 5 days. After that, the prospects for significantly colder starting ~1/13-4 are coming into better focus. Below is a link to the entire run of 12Z EPS 850 mb temperatures, which illustrate all of this quite well. The chance of a return to a solid +PNA by midmonth looks as high on this run as any in the last 5 days. For those preferring cold domination, the hope is that the EPS won't backtrack like it did for the period near 1/9-10 about five days ago. Based on midmonth GEFS progs of the combo of strong -AO (nearing -2), which is supported by the 3rd strongest Dec -AO on record since a strong Dec -AO tends to have a memory; a drop in NAO toward zero; and a favorable MJO for +PNA/cold SE, I feel that the EPS is probably on the right track this time as opposed to my saying this just based on my desire:

This shows 850 mb temperature anomalies for the entire 12Z EPS. It shows at 850 mb (5K foot elevation) in the SE US a torch 1/1-4, a cooldown to BN 1/5-6, a warmup to AN 1/8-12, and then a cooldown to BN 1/14-5 in most of the US due mainly to a combo of the strengthening +PNA/-AO. Keep in mind these are 850s rather than ground temperatures. Ground temperature changes often lag 850 changes. Also, low level features like CAD are often not reflected well up at 850 mb:

This is mainly a rehash of old news for the SE with it showing a torch for 1/1-5 followed by downs and ups into the first half of week 2 with a lean toward AN. But it then shows a gradual transition to BN by the end of week 2 and the start of week 3. This is fully in line with recent days' expectations/model consensus. By the way, my take on RonH is that he's pretty objective in his Twitter posts with him mainly sticking to objective wx model output, whether warm, cold, or whatever from day to day.

The 12Z EPS is a bit warmer through early week 2 than prior runs and has a mild SE through 1/13 overall in the means. However, it then quickly evolves to much colder with actual BN mean by 1/14-5 thanks to the strongest +PNA late in any EPS run since the runs from 12/27. IF this were to end up real this time (keep in mind we're talking way out in the unreliable late week 2 and that the BN/solid +PNA late in the 12/27 runs (for 12/9-11) has since changed to AN) and when considering my post above with progged favorable AO/MJO along with NAO finally dropping back to 0, mid January and potentially beyond would very likely be much colder than the first 12 days of the month. Keep in mind that the very strong December-AO has a memory of sorts per analogs and that mid to late Jan being dominated by a strong -AO is a distinct possibility.

Today's update vs yesterday on the 5 indicators I've been following with first 3 being 0Z GEFS 2 week based: 1. PNA: less + with it now dropping to neutral ~1/7 before slowly rising to ~+0.3 at end of week 2 (vs +0.6 yesterday) 2. AO: slightly + on/near 1/7 vs previously having been - through entire run a few days ago but then still goes back to solidly - (sub -1) by the end of week 2; strongly -AO Dec analogs do favor sub -1 Jan AO overall (more on that in another post) 3. NAO: strong + week 1 but now drops to ~0 by end of week 2 vs +0.5 yesterday 4. MJO: still progged to be in a supportive position to allow for cold to dominate once into mid January with very slow moving low amp in/near phase 8 5. EPS: 0Z little changed with weak to borderline moderate +PNA after day 10 ---------------------- Summary vs yesterday from SE cold preferring standpoint (I know some prefer warm): Worse: PNA overall; AO for week 1 Same: AO late week 2, MJO, EPS Better: NAO Conclusion: probably no return to cold domination through next 10 days but significant drop in NAO to neutral by day 14 (first time in many days showing this) along with solid -AO, beautiful looking MJO, and back up to a weak +PNA by then tells me that the potential remains for mid to late January to be when cold domination returns. Remember that mid January is still a virtual eternity away in terms of model forecasting abilities.

I see nothing exciting on the entire 12Z EPS as well as other ensembles through the end of the runs suggesting a return to a cold pattern. If accurate, that would mean that a new cold pattern would not be until midmonth at the earliest. Let's see what happens.

Sharp contrast in airmass here (and in the SE overall) vs 48 hours ago, when it was 59/27. Now it is a somewhat sticky 73/60. I'd enjoy 73/45 much more.