GaWx

There hasn’t even been one 3+ day long Dec MJO phase 8 since 2017 and the one before that was way back in 2009! So, if the models are right with their 3++ day long phase 8, it would the first time in 8 years and only the 2nd time in 15 years! A whopping nearly 80% of 3+ day long Dec phase 8 periods averaged colder than normal at Raleigh though with lots of variation. When amplitude is <1.5, that rises even further to 85% along with an average of 5.2 F BN. If it’s a pretty strong amplitude (1.5+), it actually averaged only 0.5 F BN at Raleigh. At Baltimore, it’s pretty similar for Dec phase 8 with 4.8 F BN for amp <1.5 but only 0.3 F BN for amp >1.5. Fortunately, most Dec phase 8 are <1.5 amp.

Today’s Euro Weeklies 10 mb zonal wind mean is slightly weaker early and allows most to reverse unlike yesterday. However, afterwards it looks like yesterday’s significantly stronger run: Today’s: Yesterday’s: Two days ago: significantly weaker

Thanks, Don. One thing helping 2025 vs 1983 is that 1983 didn’t have a weak SPV as it didn’t get <25 m/s through Nov and Dec:

Today’s GEFS gets to phase 7 a day earlier than yesterday’s (11/28 vs 11/29) and three days earlier than the run from 2 days ago. The 11/19/25 Euro-ext gets it to phase 8 ten days earlier (12/5) than the prior run (12/15): Prior run (11/18/25):

Based on H5 height comparisons (not H5 height anomaly comparisons), I strongly doubt that H5 temps on 11/11/2025 were as cold as those of 11/26/1950: 11/26/1950 0Z: N NC ~520 dm per upper right map 11/11/2025 6Z: N NC 528 dm However, in terms of H5 temperature anomalies for any date in Nov back to 1950, I feel it’s likely because NC H5 ht anomalies on 11/11/2025 were as low as -45 dm vs 11/26/1950’s lowest being ~-41 to -42 dm per the comparisons of these two maps. Had the 11/11/2025 pattern instead occurred 2 weeks later, I believe it likely would have broken the Nov H5 temp. record. Keep in mind that H5 heights are directly related to air temps from H5 down to the surface.

Why not? Other long range models run daily like GEFS. Long range should always be taken with a grain, regardless, due to high levels of forecast uncertainty. But why not run them daily since despite unreliability they can at least hint at potential trend changes past 2 weeks. The EW have been halfway decent imho. For one thing, they had very early hints about the upcoming very weak SPV. For another, they’ve done pretty well with hints about general levels of Atlantic tropical activity weeks out.

Today’s Euro Weekly 2m temp anomalies vs yesterday’s run: Dec 1-7: ~same Dec 8-14: similar for most/slightly stronger cold in Lakes region Dec 15-21: similar for most/slightly colder NNE Dec 22-28: similar for most/slightly colder NE/slightly less cold Lakes region:

Today’s Euro Weeklies 10 mb 60N mean zonal wind isn’t as weak as recent runs: Today’s run (11/19): Yesterday’s (11/18): Does anyone else see what I’m referring to? I’m not just talking about whether it actually reverses. I’m talking more about the period afterward.

This is a good post imho and mirrors my general thinking:

12Z ensemble means at H5 just after the cold shot at the end of Nov: GEFS: EPS: more amplified including much stronger SE ridge than GEFS: We’ll see which verifies more closely. Lately, cold has had the edge.

Thanks Don, I see your point about the unpredictability of upcoming NE snow. Moreover, this thread isn’t strictly about NE snow (as you know). It’s of course also about NE and other areas’ temperatures, wintry precip in other areas, and many other things. Wintry precip, which is usually more variable/localized than the cold influence of Arctic airmasses, is thus often less predictable than temperatures. Therefore, regarding the potential lagged effects of an SSWE, I’m guessing that temperatures in the NE US as well as for other areas for whatever period would be less unpredictable than snowfall. From what I’ve learned, there’s a significantly better chance than normal for a multi week long period of cold domination in the E US usually starting 2-3+ weeks after an SSW. More often than not the cold will appear in the E US. Most likely that would naturally mean increased wintry precip in parts of the E US, but where is the question? Especially if there’s a decent sized sample, I do like to look back at specific cities’ stats (temps and wintry precip) to give me some idea of the potential, regardless.

Natural gas is up 4.5% on colder model trends.

AAM forecast (CFS ensemble): big change for mid Dec vs forecast from two days earlier (warning: these are highly volatile on right side of graph): 11/18/25 AAM forecast: suggests it may go + (El Ninoish) in mid-Dec?!? 11/16/25 AAM forecast: 11/11/25 AAM forecast: @snowman19

More stuff related to weak to moderate Dec phase 8 having been the coldest Dec phase 8 MJO on average: Dec 9-18 of 1989 was frigid/~tied for the coldest Dec phase 8 in the E US since 1974 along with 5.5” of snow at Baltimore (2 events) and it was weak/near the circle and slow moving: also note that it stayed frigid through this very weak phase 1 and the moderate phase 2: About tied with the frigid 1989 was the very cold 12/6-9/2002. Note that this phase 8 wasn’t too far outside of the circle (moderate phase 8): Temperatures are based on Baltimore as an E US proxy.

IF the 11/18 bc version of the extended EPS were to be right, you couldn’t ask for a better position of the MJO in Dec/Jan: just outside the circle in phase 8 (and very slow moving making it last longer would be a big bonus) is about the coldest on average in the E US as it’s colder than strong phase 8 on average (though there’s always lots of variation of course): if you asked me to place it in a better place and speed of movement in Dec or Jan I couldn’t:

Latest (yesterday’s) Euro Weeklies for 12/1-7 fwiw shows it warmer than normal in much more than FL though we’ll see whether this cools off today considering the colder end of Nov (lots of model volatility currently):

Today’s 2 week GEFS MJO progressed significantly more quickly vs yesterday’s run into phase 7! Today’s 2 week GEFS (11/19) is 2 days faster making it into phase 7 vs yesterday’s run and is already halfway through phase 7 as of 12/3! Yesterday’s 2 week GEFS (11/18) didn’t get to phase 7 til 12/1 vs today’s 11/29: Yesterday’s extended GEFS (11/18) didn’t have it halfway through phase 7 til 12/7 meaning today’s 2 week GEFS gets to halfway through phase 7 four days faster (12/3) than yesterday’s extended GEFS (not til 12/7)!

How much snow did Baltimore get during the 13 phase 7 Dec periods that were during La Niña? I’ll check now: 12/16-19/1974 (temps 1 AN): 0.4” 12/7-9/1988 (temps 1 BN): 0.8” 12/23-25/1988 (temps 5 AN): none 12/9-19/1995 (temps 7 BN): 1.5” (3 snows) 12/20-23/1998 (temps 4 AN): 3.0” on 12/23, which was very cold 12/20-30/1999 (temps 3 BN): 0.2” 12/11-14/2000 (temps 5 BN): T 12/14-21/2008 (temps 2 AN): T 12/16-20/2010 (temps 11 BN): 1.2” 12/9-11/2017 (temps 5 BN): 2.8” 12/17-20/2017 (temps 5 AN): none 12/19-31/2021 (temps 7 AN): T 12/28-31/2024 (temps 13 AN): none ———- From this list: -Temps averaged right at normal -9.9” snow over 77 days or on avg 0.13”/day How does 0.13” snow per day of phase 7 in Dec La Niña compare to all of 1974-2025 Dec climo at Baltimore? They averaged 2.2”/Dec 1974-2025 or 0.07”/day. Compare the 0.13”/day to 0.07”/day: that’s 185% of the average for all Dec days since 1974 and the conclusion is that Baltimore did quite well overall with snow during phase 7 in Dec for La Niña vs the avg for all Dec days. @stadiumwave

I’d call it average. At Baltimore since 1974 during 3+ day long phase 7 periods during Dec (32 of them adding to 185 days), they’ve averaged 0.5 F warmer than normal with the coolest tending to be somewhat weak and warmest tending to be somewhat strong though with much variation. The range during La Niña has been as cold as 11 BN (12/16-20/2010), 7 BN (12/9-10/1995), and 5 BN (12/9-11/2017) to as warm as 13 AN (12/28-31/2024) and 7 AN (12/19-31/2021). Breakdown of these 13 phase 7 periods during La Niña in Dec: 1 MB, 4 B, 2 N, 5A, 1 MA

That’s pretty amazing considering that Brooksville, FL, got down to an incredible 27 on Nov 12th!! Here’s where Brooksville is located, well on down into C FL! To be fair though, elevations are 100-180 feet, quite high for FL.

Today’s Euro Weeklies 2m temp anomalies vs prior run in E US Dec 1-7: slightly cooler NE US but still mild overall Mid-Atlantic and especially SE/warmest week of Dec Dec 8-14: NE cooled slightly from slightly AN to NN but SE ~same Dec 15-21: slightly warmer SE (was NN); ~same NE Dec22-28: slightly warmer but still coldest week of Dec

~Dec 14-16th is my hope for a change to cold domination in most of the E US based on the MJO being progged to then get into 8 and allowing ~2.5 weeks following an SSWE to start a cold dominated pattern in the E US. In the meantime, the weekend after Thanksgiving giving has cooled a lot and looks a bit chilly as of now vs having looked mild just 3 days ago.

This only recently seen on the models cold shot is for the weekend after Thanksgiving. So, this is technically during the last days of Nov. Then I still expect a mainly mild first half of Dec. while the MJO crosses 7 and we wait to see what the SSWE does just afterward. Of course expectations and reality sometimes don’t match well.

That’s quite the cooldown! The EPS has also cooled down over the last 48 hours of runs for the weekend after Thanksgiving though not to as cold as GEFS.