GaWx

If you were hoping for a Euro run with implications for cold to dominate the SE in early Feb, the just out 12Z isn't the run for you as the SE ridge holds the cold back. Prior runs looked better, especially yesterday's 12Z. And this isn't a surprise based on the frequent overzealousness of models bringing cold to the SE this winter. But then again, there's the usual high uncertainties with operational runs out past a week or so. So, take with a grain as it is still early.

Longest -AO streaks back to 1950 along with RDU temperature anomaly 12/25/1959-4/4/1960: 102 days/ 5 BN 2/2-4/11/1958: 69 days/ 6 BN 2/5-4/9/2013: 64 days/ 4 BN 12/23/1962-2/23/1963: 63 days/ 6 BN 11/23/2022-1/23/2023: 62 days/ 3 AN The recent -AO streak apparently ended yesterday at 62 days. What's very notable is how much warmer it has been in the SE US vs during other very long -AO streaks with an anomaly of +3 at RDU vs the other four having had anomalies of a very cold -4 to -6! And on top of that, I'm using updated 30 year normals in the calculations, meaning a warmer normal for the current streak.

12Z Euro is delayed due to maintenance being done:

Note that the GEFS forecast is for a +NAO in early Feb. Since 1950, 6"+ snowstorms at RDU have occurred equally frequently between +NAO (~1/3), neutral NAO (~1/3), and -NAO (~1/3) as I've posted in the past, which admittedly was a surprise to me. So, a +NAO, alone, should not be a reason to feel there's virtually no chance for a big snow there and in the SE in general in early Feb. The hard data says that's not the case. That doesn't at all mean I'm predicting one though.

Indeed, that's what the model consensus has been showing for several days now with the 60N wind dropping from 50 m/s now to ~10 on 1/28-29. (See model consensus forecast image below.) It would need to get to below 0 to be called "major" as I understand it. That's looking very unlikely now since the models have hardly budged. But this still begs this question: With a drop-off of the winds of 80%, would that be close enough to allow for any potential cooling effects on the SE US to possibly be somewhat similar to what a "major" SSW would tend to cause, especially considering that the Arctic warming looks to be very strong? I mean if it doesn't get all the way to 0, why would that totally cancel out the potential effects?

Yesterday's 12Z EPS mean had been the coldest run yet for the SE in the 11-15. Then today's 0Z backed off some. But now the new 12Z is back to at least as cold as yesterday's 12Z, and even slightly colder at times. For example, yesterday I had noted that the 12Z mean had Charlotte at 30 as of 12Z on 2/4, which was 10 colder than just three runs earlier. Then today's 0Z backed off some to 33. The brand new run has 29. This is significant because this is near the period that some GFS runs/GEFS members are sniffing out a somewhat elevated chance for wintry precip. Looking at wintry precip., this new run's mean has a good bit more than yesterday's almost as cold run and this is mainly for inland areas though the NC coast, especially upper, has a bit of a signal.

The 12Z GEFS mean has about the most wintry precip over the well inland SE overall (not for my and other coastal/deep SE areas) as any other GEFS run in early Feb. The precip falls anywhere from Feb 2nd through 7th depending on the member/area. That doesn't mean there will necessarily be anything significant or that it is necessarily likely. I'm just saying what the mean has compared to earlier runs. This doesn't say what % of the members have it nor does it take into account model bias this season. But it probably means a slightly increased chance vs earlier for well inland areas of the SE.

Yeah, cluster 1 (31%) is sort of the statistical "mode" of the four clusters. However, if ensemble mean bias were to also be taken into account, I think the true chance would be lower than 31% as there's often been too much west coast ridging/E US troughing overall this winter in the 11-15 resulting in a cold bias in the SE/E US. In other words, I think that if model bias were to be incorporated, the bias corrected cluster 1 would be reduced substantially from 31% and some or all of the other three clusters increased.

The 6Z GEFS mean is the coldest GEFS mean yet for Feb 3-5 in the SE (mainly MB) though the 0Z EPS isn't as cold as yesterday's 12Z, which was the coldest EPS so far. The 6Z GEFS is actually colder than yesterday's 12Z EPS. Edit: The mean Arctic surface high track on the 6Z GEFS during that potentially very cold period is through the Ohio Valley to the NE US, which is pretty close to the optimal track for potential widespread SE wintry precip though that doesn't at all mean it would likely occur as I don't think many members actually have widespread wintry precip.

Well Tony, don't shoot the abacus lol. In the first week of Feb for whatever reason, I could find no major snow or sleet officially at Atlanta! I found nonmajor ones, of course, and several bad icestorms. And I'm sure you know there have been a good # of major snows/sleets both the week before and the week after. (Peak at Atlanta is near mid-Feb.) One of these days that will change for the first week of Feb. Maybe that's what you're alluding to for this year as that would be highly anomalous!

This area had a severe thunderstorm go through ~an hour ago. This caught me by surprise. But I didn't detect any lightning/thunder. Just heavy rain and gusty winds. Since last night, we've had very beneficial rains in the general vicinity of 1". I haven't seen my measurement yet. Edit: It was near 1" for me.

Thanks. If it occurs, I think it would be near or just after the end of the rapid 10 mb Arctic warming or, say, ~1/28 or a little later. The 60N winds will drop drastically per models from their pre SSW near 50 m/s to under 15. If they would get to below 0, that would be considered a reversal as I understand it. But what if it were to stop at, say, 10? That would be 80% of the way to 0. Would that be close enough effectwise to result in similar changes to what an actual "major" typically causes?? The N Pole is progged to warm up at 10 mb from near -75 C to ~-35 C on 1/28. Normal/average for that date is ~-55 to -60 C. But then it is progged to warm further to -20 C on 2/2, which would be 35 C AN for the date and 10 C AN for mid summer high normals! *Edited for corrections

Tomorrow will be when the SSW starts in the Arctic. This has been the timing on the GEFS since I started following it closely a week ago. It still looks about as strong as it ever has on the GEFS. The N Pole is still progged to warm at 10 mb a whopping 40C/72F+ during just a 5 day period ending 1/28! And then it warms even more into early Feb. What's still in doubt is whether it gets classified as a "major" SSW or a "minor" SSW. "Major" requires a wind shift from W to E at the 10 mb level at 60N. Regardless, it will be a strong SSW (rapid, strong warming). The eventual effects on the SE remain to be seen. However, the history of actual "major" SSW events suggests that the bulk of potential significant, persistent cooling in the SE US related to this would most likely not occur til at least 10-15 days after the SSW (per the maps I posted two days ago) when a -AO dominates. These same maps as well as stats I looked at suggest that the 1-2 week period right after the SSW would typically average near to AN prior to the cold with a +AO prevailing. Looking at the MJO forecasts, the GEFS is still largely on its own with a forecast of a moderate phase 4 within two weeks. The others turn back into the COD, which wouldn't be a warm signal. We'll see how this evolves, especially since it may not reach the "major" SSW classification. But would that matter much with this strong of a warming? We'll see.

I'd say we're already in the midst of a pattern shift from torch dominating most of the month to averaging near normal (some BN and some AN) for the rest of this month and possibly further in the SE and in much of the E US. Ironically, the 12Z EPS is significantly colder overall vs prior runs in the SE (coldest run in quite awhile) in the 11-15 day. The last couple have been colder than prior runs. Also, the 12Z GEFS is as cold as any of the last few days. Neither ensemble now has it mild in early Feb. with near to a little BN on the 12Z EPS/GEFS in most of the SE. The colder model trend could be a psyche/wrong, of course, especially with them being too cold overall this winter to date, but regardless, I didn't see a model cooling trend coming. 12Z EPS mean of 51 members is a whopping 10 F or so colder in not only the SE US but also almost the entire E 1/3 of the US vs just three runs ago in much of the 11-15! Example: the ensemble mean at Charlotte for 12Z on 2/4 was an AN 40 just three runs ago and is now a BN 30!

A once in 125 year series of deep SE winter storms that suddenly appears on a GFS run out 12-14 days gone on the next run? I'm absolutely shocked and stunned! But it is entertaining to see these fantasies. The extreme inaccuracy of models that far out allows for crazy fantasies to appear every once in a while. Based on the timing of the upcoming SSW and considering ensembles, I'm expecting this period and a bit beyond to be dominated by near to warmer than normal. The start of a cold dominated pattern related to the SSW would probably not be before ~Feb 10th at the earliest based on analogs (shown on maps I posted yesterday). Around then winter will most likely be restarting! Far from over imo!

Yeah, like 1899 that 12Z GFS fantasy winter storm was all the way down to (and past) Phil @pcbjr in Hogtown/Gainesville with ~1/4" of ZR. Unlike 1899, this fantasy is from a series of lows and a large portion of the heaviest SE US qpf is actually ZR with some sleet. The precip in N FL, and SE GA/SC/NC is nearly 100% ZR/IP with the 850 mb 0C line to the NW. It would be a massive/historic icestorm for much of that area but fortunately it isn't real. The odds actually favor near or above normal temperatures around that time based on ensembles and the typical timing of SSW effects on the SE.

The following maps from Weather Desk (**Due to member limitations on attachments, on 2/10/23 I deleted the attached image that was here so I'd have room to repost it in a 2/10/23 post about the mid-Feb 2023 major SSW**) show how often the first 15 days after a SSW in the SE have been mild and how often the subsequent 15 days have been cold. (2009 is actually much colder than its 2nd map when you start the 15 day period 11 days later. 2010 was also cold immediately due to other factors/near record blocking the entire winter in that moderate El Niño). In other words, should warmth dominate in early Feb as models are suggesting, that would actually be an encouraging sign that things are going according to plan of the typical SSW pattern in the SE of warmth followed by lengthy cold. So, while seeing that warmth on the models would be (is already) leading to "winter cancel" proclamations among some, it would actually tell me the opposite. I'd then be looking with even more confidence for a new cold pattern to start around mid Feb and dominate for several weeks: * 2/10/23 edit: As stated above, I deleted the attachment to make room in my account to allow me to repost it later in this thread.

Today it is very pleasant here with highs closer to normal in the 60s and much lower dewpoints (30s). No more torchy days for awhile thank goodness!

"@We've not had a day with above normal (cold) national gas-weighted HDDs since Dec 27. The ensuing Dec 28-Jan 17 period yields the fewest GWHDDs on record since 1950 for the period (467.6 vs 30-year normal 630.0)." From Weatherdesk's Twitter -------------- So, this is pretty much saying that the E US, where HDD weighting is highest based on population/energy usage, has overall been about as warm as any Dec 28-Jan 17 since 1950 when averaged out over that 3 week period. Other than the several day long mid Jan cold snap largely associated with that very strong upper low, most days have been mild in the SE. In stark contrast and to the relief of cold lovers, the next 10 days or so look to average pretty close to normal overall in the SE with a mix of BN and AN...typical midwinter stuff. After this, indications/model consensus favor mild to return to the SE for early Feb. This is actually typical for the period near and immediately following a strong SSW. Subsequently, we'll see if the SSW helps to sharply reverse that warmth as we go further into Feb. I think it will based on prior cases of La Niña winters with major SSWs around this time of year and shortly after per the hard data in my prior post as the impending strong SSW/much warmer Arctic strat persists on the models. In my mind, it will likely be a totally new ballgame as much better players (from a cold lover's standpoint) take the field. Edit: I forgot to add that other than the GEFS, no model is forecasting the MJO to get into the warm phases outside of the COD. The bc extended Euro, in contrast, has a very inviting track back to inside the COD that then gets to the left side in mid Feb while still inside. That's pretty significant.

Followup on the 5 La Niña winters with a major SSW within late Jan to early Feb As mentioned, all 5 had multi week cold dominated periods in the SE 10+ days later within Feb/Mar due largely to a -AO/-NAO: 1971 (cold first half of Feb), 2001 (cold March), 2006 (cold Feb), 2009 (cold 2nd half of Feb to early March), and 2018 (cold March) AO on day of and immediately following the major SSW was neutral to positive before turning predominantly negative: 1) 1/18/1971: day of SSW +0.3; + to neutral for 10 days (peak of +1.5); then - on 34 of next 41 days with low of -2.8 2) 2/11/2001: day of SSW +1.5; + for 10 days (peak of +2.9!); then - on 29 of next 35 days with low of -4.9! 3) 1/21/2006: day of SSW -0.2; neutral for 3 days (peak of +0.5); then - on 13 of next 15 days with low of -2.7 4) 1/24/2009: day of SSW +1.1; + to neutral for 7 days (peak +1.9); then - on 14 of next 16 days with low of -3.2 5) 2/12/2018: day of SSW +1.7; + to neutral 12 of next 13 days (peak of +1.9); then - on next 22 days with low of -4.4! ----------------------------- Based on the above, I'm educatedly guessing the following after the SSW: - 1-2 weeks dominated by neutral to +AO with a good chance for it peaking at +1+. The La Niña favored SE ridge would likely be in control. I expect some cries of "winter cancel" over the next 1-2 weeks as this likely mild early Feb period gets closer. Don't let this initial 1-2 week mild dominated period in early Feb fool you into thinking winter is over! - 3-6 weeks dominated by -AO starting by mid Feb with lowest dipping to -2.5 or lower - In the SE, mild dominating early Feb. Cold domination starts ~mid-Feb and continues through the last half of Feb and probably into at least early March. Could extend through mid March.

Since 1958 as mentioned before, there have been 13 winters with a major SSW in the late Jan to early Feb timeframe (5 during La Niña): 1958, 1960, 1963, 1971, 1973, 1981, 1987, 2001, 2003, 2006, 2009, 2010, 2018 They tended to be cold in the SE during multi week long periods within the Feb-March period. I checked the average of three of the indices in Feb/March to see if there was a notable difference between years with and without a late Jan to early Feb major SSW: 1. AO - With SSW: -1.0; 7 were sub -0.9; only 2 of 13 were positive with highest +0.7 - Without SSW: -0.1 2. NAO - With SSW: -0.4 - Without SSW: +0.2 3. PNA - With SSW: +0.2 -Without SSW: 0.0 Conclusions: Years with a late Jan or early Feb major SSW tended to have a -AO/-NAO when averaged through Feb/Mar whereas other years averaged neutral. The PNA averaged neutral for both with and without one. Thus, it appears that the -AO/-NAO combo tendency is a major driving force in tending to make a good portion of Feb/Mar chilly in the SE soon after a major SSW. So, as we go toward Feb 10th or so and beyond, I'll be looking at the AO/NAO forecasts with extra interest.

The model consensus continues (as they have for many days now) to insist that a very strong 10 mb Arctic warming is on the way starting early next week. This will mean going from much below normal 10 mb Arctic temperatures/very strong SPV of recent days to way warmer than normal/southward displaced SPV afterward. The 12Z GEFS and other runs have been showing a 40C/72F warming at the North Pole during a mere 120 hours (0Z 1/23 to 0Z 1/28)! Some GFS runs have had 5 day warming there up to 50C/90F! In addition, GFS suite consensus suggests a peak in very early Feb that I think would be AN even for summer! What does this mean? A strong SSW late this month is pretty much a certainty. What's unknown is whether it will be called a "major" strong SSW or a "minor" strong SSW. The very impressive degree and speed of warming are there. But to be considered "major", the 10 mb winds at 60N+ have to reverse from W to E. That part is uncertain but GEFS continues to go in that direction. The 12Z GFS may actually have it. Regardless, with this strong of a SSW and it close to "major", it may not matter much. As far as the timing of effects on the SE based on past events, it appears that a multi week long cold dominated period could start as early as ~~Feb 10th and possibly last into March. Nobody knows as details are highly speculative. The potential cold shot for late next week is independent of this (SE cold doesn't normally occur at the same time as the SSW) as a mild period will most likely follow that.

It could very well be a mainly dry, cold weekend after next for most of the SE as is quite common with Arctic highs that plunge assuming the plunge occurs. However, NW flow would be favorable for another good upslope mountain event (even if not as good as the great one that just occurred) as the Arctic air comes in and this is on the models. Also, we're still 9-10 days out and there's still plenty of time for change as that's a semi-eternity in model accuracy time as you know. For a not as dry outcome, it would probably be better if the Arctic high moved through the Ohio Valley instead of a deep plunge.

If the 12Z GFS/Euro/CMC and 0Z Euro have the right idea (it is still out in semi-fantasyland), this past below normal cold weekend will have a chance to be exceeded by an even colder weekend/the second coldest Arctic plunge of the winter to date the weekend after the upcoming one! The consensus of the models has easily the 2nd coldest Arctic airmass of the winter to date coming out of S Canada and agreement is rather strong for that far out. Also, the 12Z GEFS mean is the coldest run so far for the SE that weekend. I didn't even consider a very cold last weekend of January that much of a possibility until the last couple of days and figured this past weekend would likely be the coldest one of the month.

Interestingly, if the 12Z GFS/Euro/CMC and 0Z Euro have the right idea (it is still out in semi-fantasyland), this past below normal weekend will have a chance to be exceeded by an even colder weekend/the second coldest Arctic plunge of the winter to date the weekend after the upcoming one! I'm the meantime to keep this on topic, it is now 75 with dews in the semi-muggy low 60s. What a contrast to just two days ago, when it was in the 60s with dews only in the low 20s!