GaWx

Followup to followup: So, the above suggests a good shot at a +0.75+ PNA in Jan. These 9 non-Nino Jans since 1950 had a +0.75+ PNA (all cold ENSO except RONI neutral 1961 and 1981): Year/PNA/E US temps 1961 +1.41 cold 1981 +2.42 cold 1984 +0.97 cold 1985 +1.63 cold 1986 +0.97 normal 2001 +1.51 normal 2011 +1.29 cold 2014 +0.97 cold 2022 +1.01 cold So, the current cold and strongly +PNA Dec has totally changed my thinking for Jan to a good chance for much colder than I originally thought using the Dec to Jan analog method.

Followup: The 5 highest tabular Dec +PNAs for non-Nino on record (2024 progged to have good chance to be new highest): 2020: +1.58 1960: +1.46 1985: +1.39 2005: +1.38 2000: +1.23 Where were the subsequent Jan tabular PNAs for these non-Nino high +PNA Dec? 2021 +0.19 1961 +1.41 (4th highest on record for non-Nino) 1986 +0.97 (tied for 7th highest on record for non-Nino) 2006 +0.43 2001: +1.51 (3rd highest on record for non-Nino) Avg Jan for these 5: +0.90 So, as I think @Stormchaserchuck1was suggesting (actually he was suggesting for all ENSO), +PNA in Dec tends to carryover into Jan for non-Nino. Three of the 5 did strongly and one weakly. The other (2020-1) went to neutral. So, none even went to a weak -PNA. @Terpeast

Based on the GEFS chart’s PNA mtd as well as the 0Z GEFS 14 day PNA prog, we have a chance to break the all-time record (since 1950) +PNA for a non-Nino Dec. I estimate based on dailies that the (tabular equivalent) MTD is ~~+1.8. The prog avg (tabular equiv) for the next 2 weeks is near that meaning the progged MTD through Dec 27th is ~~+1.8. *Keep in mind that the tabular equivalent is ~~twice the dailies.* Also, keep in mind that the 10 day GEFS progs have verified significantly too low since late Nov as they’ve averaged only ~half as high as verifications. Current highest tabular Dec +PNA for non-Nino: 2020: +1.58 1960: +1.46 1985: +1.39 2005: +1.38 2000: +1.23 Highest tabular Dec +PNA for El Nino: 2006: +1.86 1969: +1.84 1963: +1.77 2002: +1.59 1986: +1.37 0Z GEFS prog through 12/27 and mtd: ~+1.8 Tabular monthly PNA 1950+: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.pna.monthly.b5001.current.ascii.table

That’s the power of the Aleutian Low/+PNA, the most efficient delivery mechanism of MB anomalies to the deep SE as opposed to New England. That’s why I always prefer an Aleutian Low/+PNA in the means, something we hadn’t had that much of the last few winters til the last 2 weeks.

OISST is very close to its lowest anomaly of the year, which was set ~Sept 20th. This means the equivalent RONI daily is likely now back to low end moderate:

Here in the SE I always prefer the El Ninoish mean Aleutian low dominating as that’s typically part of (or at least associated with) a +PNA and minimizes a SE ridge.

It appears to me that the models initially missed in the E US the intensity of both the 11/30-early Dec and upcoming pre-Christmas cold periods. Also, the current and last couple of days of cold based on memory appear to have been initially well forecasted pretty far back before being warmed a bit too much prior to returning to accuracy. So, overall the models have been under doing cold periods. But they’ve also not been warm enough during the mild periods in between including the upcoming one 12/16-8.

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.