GaWx

Here’s why (combo of things): -Don’t forget that the Weeklies are run at 0Z rather than 12Z -12Z EPS was significantly colder than 0Z 12/22-5 in the E US -The top map’s week (12/23-29) had only 2 of 7 days cold (12/23-4) at 0Z in the far E US and only 1 cold day back to the E Midwest. West of there all 7 days were mainly mild. And even in the E US most of 12/25-9 were mild. Chicago westward was mainly mild the entire 12/23-9. -Also, the E US cold of the 12Z also includes 12/20-2 with 12/22 colder vs 0Z. So, the cold is split up between two weeks and is muted in each full week by surrounding warmth.

Looking out further on the Euro Weeklies: -Still no sign of a major SSW before mid-Jan -Jan 6-19 continues the last 7 days of runs showing the lack of either a warm or cold signal. -Jan 20-26: a new week and it also has no strong signal -Although the period 1/6-26 lacks a cold signal at 2 meters, H5 maintains BN hts upper Midwest to NE US as well as in SE to SC Canada that expands westward Jan 20-6. These cold H5 anomalies are the most negative anomalies in the entire N Hem and that has been the case over the last week of runs. I wonder if that’s signaling that the risk to turning colder in later runs during some or much of 1/6-26 is higher than the risk to turning warmer. Over the last 8 or so years and although there are always a good number of exceptions, extended model periods have tended to verify warmer rather than colder (cold bias). But perhaps this winter will be different based on Dec so far and relevant analogs.

This isn’t hype, folks. The cold is really on the models and is intensifying on the GEFS/EPS as we get closer. I don’t hype. I hate hype with a passion! Edit: I also hate downplaying just for the sake of downplaying.

Per latest model consensus trends, a good portion of the first half of Christmas week (12/22-25) as well as late in the prior week (12/20-1) is increasingly likely looking to be quite cold in the E US, especially MidAtlantic south. Are you aware of this? 12Z GEFS:

The 12Z Euro is actually (fwiw) not that far off from a SE winter storm with a Miller A that forms just S of the NW Gulf coast on 12/20 between Canadian highs and scoots ENE along the Gulf coast to offshore GA on 12/21-2. It actually has light snow that falls in parts of SE LA, S MS, E SC, and E NC during 12/21-2.

The good for you/bad for me news is that as we all know the chance of this verifying closely with it currently being a huge outlier, a very highly unusual solution, and most importantly still out over a week is quite small. But with that being said, wintry precip in our area is always a huge outlier vs history. We haven’t even had a T of any kind of wintry precip in nearly 7 years, the longest wintry precip drought since at least the 1880s. One of these days we’re going to finally get the next wintry event. It could be this winter or it could still be several winters away. Because they’re so rare, it’s going to be difficult to predict more than a few days out and may be a surprise to the models. The first thing we obviously need is a good supply of Canadian air. Then we of course need moisture. The best combo for us is a split flow of cold from N jet/+PNA and WSW moist flow overrunning it from the ST jet. With us being in La Nina, a well placed ST jet may be a challenge though we’ve had wintry precip a number of times in La Niña. So far, it appears we’re likely going to have the Aleutian Low/+PNA that’s often characteristic of El Niño. But I’d also like a moist ST/WSW 500 mb flow overrunning it giving us ample Gulf moisture/deep into Gulf Miller A.

12Z GEFS, which suggests that the 12Z GFS major snowstorm is a huge outlier (no surprise of course), also suggests that the intense cold is very real. You’ve got to have the cold to have much of a chance. It suggests a cold Christmas!

12Z GEFS coldest run yet for E US 12/20-3+ with stronger mean Arctic high.

12Z GEFS coldest run yet for E US 12/20-3+ with stronger mean Arctic high! 12Z GFS was also very cold then. Edit: 12Z GEFS: has mean Aleutian Low 12/16-25+!

Also, the 12Z GFS snow starts in W TN in just 168 hours. That’s why I posted about it. If it were just another storm relegated to the 11-15 day period, I doubt I would have posted about it as those are a dime a dozen/fantasyland storms. But this run actually starts the snow a bit pre fantasyland. And the cold signal for 12/19+ has been repeatedly showing up and intensifying in recent days.

I haven’t commented too often on individual operational runs, but has anyone seen the 12Z GFS? Not only is it very cold 12/19-23++, check this out:

Looking at cold ENSO analogs: -Cold 1st 1/2 Dec in NE/SE but not cold 2nd half: 2007, 2005, 1954, 1949, 1934, 1915, 1898, 1893, and 1875. Zero out of these 9 cases (0%) were cold dominated in 1st half of Jan in either NE or SE. Of these in the SE: 2008, 2006, 1955, 1950, 1916, 1894, and 1876 were mild. Only 1935 and 1899 weren’t mild (close to normal) in the SE. In the NE 2008, 2006, 1950, and 1894 were mild. -Cold BOTH halves of Dec in NE/SE: 2010, 2000, 1995, 1962, 1955, 1944, 1917, 1910, and 1903. 6 out of these 9 cases (67%) were cold dominated in 1st half of Jan in both the NE and SE: 2011, 2001, 1996, 1945, 1918, and 1904. Of these 9, only 1911 (11%) averaged mild in 1st half of Jan. in either NE or SE. - Thus per cold ENSO cold dominated 1st half of Dec analogs: whether or not it is also cold dominated in the 2nd half of Dec appears to have significant implications on the chance for cold (much higher if cold late Dec) as well as mild domination (significantly higher if not cold late Dec) in 1st half of Jan. - Since 2024 will verify as cold ENSO and cold dominated in 1st 1/2 of Dec, whether or not it is cold dominated 12/16-31 will be quite informative as regards the chance for a cold vs mild dominated 1/1-15/2025.

After the next few days of cold and then just a couple of mild days, 18Z GFS is cold dominated starting 12/19 in SE and 12/20 in NE and this continues at least through 12/25.

Winds have been howling here for several hours. This is quite an impressive cold front!

Based on Joe D’Aleo’s research that I confirmed with my own analysis of W QBO/solar max, I now think there will likely be a major SSW, probably anywhere from mid Jan through Feb.

The 12Z EPS is Aleutian Low central Dec 16-26. Assuming it has a clue, this isn’t a mild pattern for the E US. It has only two really torchy days, 12/16-17. Other days are from modestly AN to MB. In addition to the current Arctic high coming down, the run has two more. This doesn’t average out to be mild by any means.

It is way too early for 2025 forecasts imho. I don’t want to speculate much now. All I’ve said is that TSR seems optimistic.

The more I look at the model consensus trends, the more I feel that the signs are there for an impressively cold period starting ~12/19 in the SE and ~12/20 in the NE and going at least through 12/23. Check out the 12Z GFS. Check out the last few Euro AI runs. Also, some of the Euro ops have been cold. The GEFS/EPS have at least been increasingly hinting at this possibility. With all of this in mind, I feel that the chances for a cold dominated 2nd half of Dec are increasing in the E US from the earlier low chances. They’re still not high chances yet, especially with the still mild start (12/16-18), but the trend is telling. This wouldn’t be significant just for the latter portion of Dec. That would also change the cold ENSO analog set for the first half of Jan, which would switch from little chance for cold to a much higher chance. By the way, NG is up even further (~10% over the last 26 hours)! It sees that the previous mild latter Dec model outlook is at an increasing risk to bust.

BAMwx (Michael Clark) brand new update: good update imho as it is well reasoned without the hype of last week’s super cold mid-Jan CFS based tweet. This is first public video update since Fri I believe. Last week he had you-tube updates on Wed and Fri and I had said those were pretty good presentations though I thought he had too much reliance on general CFS ideas on Wed. Today, like on Fri, he shows a better mix of multiple models rather than just focusing on CFS:

It’s way too early for me to have much of a feel, but I do think TSR is likely too optimistic going with near 1991-2020 averages considering how warm the Atlantic still is.

NG market up a whopping 8% since this time yesterday! Traders are seeing a general cooling on the EPS/GEFS in the E US for week 2, especially 12/20-24. Fwiw, the Euro-AI has been very cold on multiple runs although it is still mainly a cold outlier.

The newest BoM biweekly forecast for Nino 3.4 has cooled considerably. This is the prior one, which had -0.3 for Dec, -0.4 for Jan, -0.1 for Feb, and +0.2 for Mar: Here’s the newest one, which has -0.4 for Dec,-0.7 for Jan, -0.5 for Feb, and -0.1 for Mar: @snowman19

So for 2025 TSR is going for near average of 1991-2020 instead of anything close to hyper or anything close to 2024. I hope they are right, but I’ll still take this extremely early prediction with a humongous grain.

Thanks, Mitch. More specifically for N American 2 meter temperatures, here’s the link: https://charts.ecmwf.int/products/extended-anomaly-2t?base_time=202412100000&projection=opencharts_north_america&valid_time=202412230000

Per an analysis of cold ENSO cold first half of Dec analogs that I did today: -If current ensemble consensus of the lack of a cold dominated 2nd half of Dec. ends up verifying, analogs suggest strong likelihood of no return to cold domination in the first half of Jan although there’d still be a good chance for cold to dominate at some point later, favoring a portion of Feb. though last half of Jan would still have a shot. -However, if the current ensemble guidance is wrong and the 2nd half of Dec ends up cold dominated in the E US, then the analogs would suggest the chance for a cold dominated 1st half of Jan would rise substantially. -Fwiw since way out in fantasy range, weeks 5-6 of the Euro Weeklies (Jan 6-19) have neither a warm signal nor a cold signal. -The Euro op day 9-14 is quite cold but that is in low credibility fantasy range for an operational. It will very likely be warmer on upcoming runs since prior runs were significantly warmer and this run is a cold outlier amongst the models as a whole right now. However, it does show that a non-cold 2nd half of Dec is still too far out to be set in stone.