GaWx

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.

MJO model progs: -11/18 GEFS/EPS runs similar to yesterday day by day along with good progression into 7(GEFS) and well into 7 (EPS). -11/17 extended EPS remains consistent with recent runs with it getting into 8 on 12/14. But the big news is that the extended GEFS is its most progressive yet and with it actually moving into 8 a day earlier than the EPS (12/13). At RDU/BWI since 1974 for the 23 three+ day long Dec phase 8 periods averaged out: lots of variation but with solid tendencies -78%/61% of Dec phase 8 were cold -Compare that to only 22%/13% that were mild -Phase 8’s three+ day long periods have averaged 5 days with the longest being 13 days -Phases 1 and 2 have also averaged cold at BWI but with again lots of variation but with solid tendencies Based on all of this as well as a typical couple of weeks+ lag of cold in the E US after an SSWE, I’m hoping for E US cold domination to start around Dec 15th. Until then, I expect mild to dominate much of the E US, especially mid-Atlantic south. 11/17 GEFS extended: 11/17 EPS extended:

To me, NYC has a very snowy climate. Then again, my avg annual snow is only 0.2” with most winters getting none. My area hasn’t received a foot+ of snow for an entire season since 1800. I’ve also lived in Atlanta, where their avg is still “only” 2”. So, when I see a city’s average at 20”+, ten+ times as much as ATL and 100+ times as much as SAV, that there is very snowy! Atlanta’s never even gotten close to 20” in a season! Aside: Cloudflare problems had been causing widespread outages this morning, including here.

From JB today: Euro MJO closest analogs 1983 and 1989 The severe cold Decembers of 1983 and 1989 both raise the spectre of a cold shot letting loose into the Texas Citrus areas, with Fla secondary concern had a major stratwarm in mid to late November, almost identical to now —————- The only problem with this is that there was no major stratwarm in mid to late Nov of 1983 or 1989 or anytime during early to mid winter for both for that matter: https://www.researchgate.net/figure/The-SSW-and-SFW-event-onset-date-year-and-type-identified-in-the-NCEP-NCAR-dataset-The_tbl1_267063738 ———- Also, I checked to see if the 60-90N temperatures in the strat. in mid to late Nov were notably warm and they weren’t. Lastly, I checked the zonal winds at 60N in both Novs to see if they were weak despite no actual reversal. They weren’t as they were pretty close to normal. https://acd-ext.gsfc.nasa.gov/Data_services/met/ann_data.html#ncep_clim_stats_nh

This is by a good margin the weakest SPV on any run. If this verifies closely, this would be the weakest late Nov to early Dec SPV by a good margin since way back in 1987! We know that one month later there was a historic SE winter storm, which gave Atlanta 4” of sleet, very heavy snowfall in some other areas, and ZR down all of the way down here.

Per this EW run’s weekly 2m maps directly from the source, it remains a step down process from a mild E US start: Dec 1-7: mild Dec 8-14: cools some to slightly mild to normal Dec 15-21: cools to normal Dec 22-28: cold comes in around Christmas!

I still wouldn’t give up on a net neutral NAO (between -0.25 and +0.25) DJF averaged out, especially because of the very weak SPV to start. Although solid +NAOs have been dominant recently other than 20-21 (near minimum), there was a net neutral NAO DJF during the weak SPV, -ENSO, active solar winters in 2000-1 and 2001-2.

That’s honestly nearly impossible to predict with much confidence. But I’d lean toward at least a slightly warmer than avg Dec overall, especially this far south, due to the expected mild start.

Anthony, 1. Where are you seeing a weak phase 7 being forecasted? The GEFS and EPS haven’t been and still aren’t. 2. I’m well south of the Mason Dixon line. As I said, I was giving you my perspective. A prevailing SE ridge is typically mild in the SE other than when there’s strong low level CAD. I prefer it not be mild. I prefer BN temps year round. Even NN would be ok. At the very least I like to see comfy dewpoints, especially in winter! I hate sweating during winter walks because it’s so humid much of rest of year. 3. I continue to expect a mainly mild lower Mid Atlantic and especially SE the next 4 weeks as is clearly shown by a good # of Euro Weeklies runs. 4. But as you said, we shall see!

Hey Anthony, What’s wrong from my perspective? prevailing SE ridge/-PNA. The MJO is then forecasted by GEFS to be strong near phase 6/7 border, which is typically mild in the E US. Strong phase 7s in Dec have often been mild in the E US. A big key will be whether or not it eventually makes it to phase 8 like the extended EPS has been showing. There’s been only ONE 3+ day Dec MJO phase 8 period the last 15 Decembers!

11/17/25 MJO forecasts is mixed bag: 1) 11/17/25 GEFS backtracked to ~2 days slower than yesterday’s slightly more progressive/weaker run to being nearly identical to the more lethargic and stronger run of 11/15 (not what I wanted to see): GEFS 11/17: stronger/less progressive vs GEFS 11/16 and close to GEFS 11/15 GEFS 11/16: was slightly more progressive/weaker than GEFS 11/15 GEFS 11/15: ————— 2) However, 11/17/25 EPS remains similar to yesterday’s slightly more progressive run and continues to be a good bit more progressive/weaker than GEFS, two things I like: 11/17 EPS: similar to 11/16 EPS and more progressive/weaker than 11/17 GEFS 11/16 EPS: slightly more progressive than 11/15 EPS 11/15 EPS:

1. AAM is now dropping back from neutral and is forecasted to be in a solid -AAM (solid Ninaish) through the next 30 days per this CFS ens run: 2. WCS daily PDO has risen steeply the last 6 days and is up to -0.83, the highest daily since May:

This shows that the Euro is now leaning toward that later period for the actual reversal (~11/28 instead of 11/25). Add in a several week lag and a potential of a phase 8 MJO followed hopefully by 1-2 and we’d have a realistic chance for a several week long period of cold domination in the E US starting as early as near mid-Dec. Prior to this potential, there’d also likely be a mild dominated next 30 days, which shouldn’t be ignored.