GaWx

Holy cow! That 82 F at KATL is also the warmest so late in the season by 6 days! They missed the warmest for all of Nov by only 2 F! Here it wasn’t a record, but it was the 4th day in a row with low 80s. Being back autumn! It will be arriving just in time to give us a cool Thanksgiving!

Hopefully the MJO won’t turn sharply left along the 7/8 border like these: Dec of 2014 was mild: Dec-Jan 2019-20 was mild:

Whereas there can be a lag, the diagrams by phase are based on concurrent temps. So, phase 8 being the coldest in Dec is based on temps during phase 8 being the coldest of any phase rather than with a lag. Perhaps, it’s phase 7 in some cases being the cold generator that takes til phase 8 to show up in the E US.

12/9-14/91 also was a mild strong phase 8 in the E US though it cooled afterward:

The Weeklies have it mainly mild in the SE first 3 weeks of Dec, not the NE, thanks to a SE ridge. Anthony asked where’s the warmth? The maps he posted had SE warmth.

You don’t see any warmth, Anthony?

Why? I’m not going crazy. We look at long range guidance ITT every day. This is mainly a long range thread. You just posted weeks 3-4, for example. I’d rather have the most up to date.

Today’s Euro Weeklies 2m temp changes vs yesterday aren’t good for the E US overall if you prefer cold: Dec 1-7: warmer SE to Mid-Atlantic due to even stronger SE ridge: Dec 8-14: ~unchanged Dec 15-21: warmer SE/very slightly warmer NE Dec 22-28: slightly warmer Mid-Atlantic/very slightly warmer SE: Dec 29-Jan 4: warmer NE

Today’s Euro Weeklies update on the SPV compared to last run keeps the reversal (or near reversal) but it’s a fair bit stronger Dec-early Jan. Keep in mind that the prior two runs were already significantly stronger for that period: Today’s EW mean zonal wind at 10 mb (11/21): significantly stronger than 11/18 run with, for example, 12/12 at +29 vs +11 on 11/18 run: EW run from just 3 days ago (11/18): 12/12 had been at only +11

To add: -1983 doesn’t fit -1985 strong 2nd half of Oct -1989 was fairly stout last 1/3 of Oct -2000 wasn’t strong but was stronger than avg

The 6 coldest La Niña to neutral ENSO Decembers in the E US as a whole since 1974 have been 1983, 1985, 1989, 2000, 2005, and 2010: Here are the respective Dec MJOs: 1983: mainly inside COD or just outside/no strong 1985: almost all inside COD 1989: most of 8/1 just outside COD or inside it/no strong 2000:almost all just outside or inside COD 2005: all inside COD 2010: all just outside or in COD What do these 6 have in common regarding the MJO? No strong and most days just outside to inside COD. Below are the extended progs that have the Dec 1-21 MJO: look how strong they are, especially GEFS but even the Euro is solid compared to the six cold Decembers posted. My concern is that the MJO amplitude will be too strong, based on history, to allow for a widespread intense cold dominated E US in Dec. Thus, I’m hoping the progs remain going into 8, but weaken. My hypothesis as to why strong MJO has had a tendency (though not always, of course) to not be as cold as weaker MJO is because the higher amp may tend to bring up too much warmth from the tropics, where the MJO is measured: Any opinions?

Domination in the SE by mild/SE ridge in the first half of Dec has been forecasted by the Euro Weeklies for over a week. They’ve been steady as a rock. I’d be very surprised if it isn’t mild in the means. After that it is up in the air though recent runs have been suggesting a weaker version of a SE ridge/slightly warmer than normal for 12/15-21 lingering for the SE. We’ll see.

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 5.0 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: