GaWx

The latest available bias corrected extended EPS, CFS, and BOMM ensemble means all have the MJO reaching the left side of the diagram mainly at moderate to weak amplitude in early Jan, which though not nearly always have more often than not been associated with a cold dominated pattern in the E US in the first half of Jan during non-Nino ENSO: EPS bc: CFS: BOM: Here are non-Nino ENSO weak (near or inside circle) to moderate left side MJO dominated E US 1st half of Jan with diagrams shown for coldest: 2023 mild 2022 cool NE/mild SE 2002 slightly AN NE/cold SE 1999 cold: 1997 normal 1996 cold: 1994 cold: 1985 cool:

Charlie, doesn’t a weaker PV usually mean overall colder for the middle latitudes since the cold wouldn't be as locked up in the more N latitudes?

Indeed, the 0Z GFS is significantly warmer for 12/19-20 than almost all other runs the last few days. But cheer up, today’s Euro Weeklies were the coldest run yet for Jan 6-12. Edit: However, the consensus has also cooled some for 12/22-5/6.

It’s interesting that we’re having the coldest first half of Dec in the E US overall in a good number of years (since 2010 in many cases) and that this is during a robust MJO 4-5, which has more often than not been mild in Dec and averages mild. The +PNA has been one of the strongest for this period on record. *Edit: For non-Nino since 1950 only these had a similarly strong +PNA during 12/1-15: 2020, 2017, 1989, 1988, and 1960. *Edit 2: Of the above 5 strong non-Nino +PNA during 12/1-15, only 2020 and 1960 held on with a solid +PNA most of the rest of the month like is progged by the GEFS for 2024.

Plus strong non-Nino +PNA/cold Dec analogs suggest to at least be wary about the slightest hint for cold in Jan. Indeed the week 1/6-12 is the coldest for it at sfc and at H5 in the E US of any run yet (going back 16 runs) by a good margin. More strikingly, look at how much the 1/6-12 BN H5 in E NA sticks out on this global view, which tells me it is a very strong signal especially for being still out at week 4 (a rare occasion that far out on EWs to see that large/intense BN H5 in the current warming era): Note fwiw that the ridge is centered W of this month’s W NA ridging allowing a stronger -EPO, which may mean even colder anomalies especially up north.

Parts of upstate NY, Ontario and Quebec appear to be near or at all-time Dec record high SLP with the Massena to Ottawa corridor at ~1050 mb near records for any month: these are from 10AM EST: CITY SKY/WX TMP DP RH WIND PRES REMARKS MASSENA SUNNY 18 10 71 NE3 31.01S MONTREAL MOSUNNY 16 7 67 N5 31.00R WCI 9 TC -9 _____REGIONAL ONTARIO LOCATIONS_____ CITY SKY/WX TMP DP RH WIND PRES REMARKS OTTAWA MOSUNNY 14 9 79 NE7 30.99R https://ca.news.yahoo.com/record-breaking-pressure-over-ontario-012208535.html

Parts of upstate NY, Ontario and Quebec appear to be near or at all-time Dec record high SLP with the Massena to Ottawa corridor at ~1050 mb near records for any month: these are from 10AM EST: CITY SKY/WX TMP DP RH WIND PRES REMARKS MASSENA SUNNY 18 10 71 NE3 31.01S MONTREAL MOSUNNY 16 7 67 N5 31.00R WCI 9 TC -9 _____REGIONAL ONTARIO LOCATIONS_____ CITY SKY/WX TMP DP RH WIND PRES REMARKS OTTAWA MOSUNNY 14 9 79 NE7 30.99R https://ca.news.yahoo.com/record-breaking-pressure-over-ontario-012208535.html

From FFC: WILL BRING FLOW AT 850MB FROM THE EAST TO THE SOUTHEAST AS A MASS RESPONSE TO THE DEVELOPING LOW. HOWEVER, SIMULTANEOUS TO THIS, STRONG SURFACE HIGH WILL SET UP SHOP OVER THE NORTHERN APPALACHIANS, WHICH THE WEATHER WEENIES WILL KNOW BRINGS COLD AIR DAMMING (THE WEDGE) TO OUR CWA.

Newest from BAMwx: I haven’t watched it yet. Hoping it like the last couple provides sound reasoning for cold Jan and doesn’t hype:

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+!