GaWx

Related to this is the -PNA Dec to +PNA Jan transitions for -ENSO that have been happening during the last 40 year period. That transition has been strongest when the Dec -PNA was strongest. Examples of cold Jans were during these winters: 1983-4, 1984-5, 2008-9, 2010-1, 2013-4, and 2021-2 where Jan was cold though not always colder than Dec.

Indeed, and look at the trend of just the last 3 GEFS for 12Z on 12/18: E trough deepening/W ridge strengthening. It’s important to keep watching these trends as the models in general have been much too warm in the E US since the runs starting 3 weeks ago though at some point this trend is likely to end at least temporarily:

I’ll give him the benefit of the doubt and assume he’s not counting weak phase 8 (inside circle). But even so, these had outside the circle phase 8 in Dec since 2001: 2017: 2009: 2007: 2002: @mitchnick

There’s no question that the CAD wedge has been the big winner in the SE US so far this month. My area has had almost every day mainly cloudy, rain on most days, and every day 12/1-7 has had highs only in the 50s! That’s very hard to do on every day for a week in early Dec with normal highs 10 degrees warmer. As a matter of fact, it’s so hard that this is the first time on record that it has happened with records going all of the way back to 1874! Interestingly, the highs have ticked down each day this month: 59, 58, 55, 54, 53, 52, and 50. I see that GSO has had all highs only in the 40s Dec 1-7. I wonder if that’s ever on record happened there. Anyone know? Edit: If that’s not enough, the forecast is calling for 2 more days of 50s highs, which will make it Dec 1-9! Same idea for GSO with 2 more sub 50 highs for Dec 8-9! Edit: I just checked GSO. Only once on record back to 1903 did they have not get out of the 40s Dec 1-7: 1910. However, they did get to 50+ on Dec 9th, So based on the forecast, Dec 1-9th, 2025 will be the first on record not having even one day get out of the 40s at GSO!

Which are y’all going with for Saturday’s (12/13) low? The GFS sticks out as much colder than the others at ATL with upper teens there, which tells me it’s likely too cold there. It has had a cold bias over snowcover in recent years (which is well above average in the Midwest). That’s probably a factor as I don’t know that that has been fixed. 6Z GFS: pipe busting cold with upper teens ATL/RDU: likely too cold 0Z Euro: slower with the cold and thus is much warmer on Sat AM with upper 30s: likely too warm though it has 20s the subsequent few days 0Z ICON: mid 20s RDU to upper 20s ATL: looks like a reasonable middle-ground 0Z CMC: coldest at RDU with mid teens (CMC has a well-known cold bias) though only down to mid 20s ATL 0Z UKMET: only down to low 30s though it has a warm bias/very likely too warm though it is headed for 20s on Sunday

I’m not using Dec 2022 as a heavily weighted analog because of snowcover. On this date in 2022, there was only 1% snowcover in the Midwest: Compare that to today’s 46%, the 3rd highest only to 2013’s and 2007’s 53% and just ahead of 2005’s 45%. The 2003-24 average is only ~15% meaning today’s is ~3 times the average for Dec 7th: @donsutherland1you may want to keep this in mind for your forecasts. https://www.nohrsc.noaa.gov/nsa/index.html?region=Midwest&year=2025&month=12&day=7&units=e

I created a new thread for tomorrow’s wintry event in mainly NC/VA:

I created this for the Monday (12/8) wintry threat for mainly NC and VA so as to leave the longer term for the main Dec thread. @buckeyefan1please pin this. Thank you.

Regarding the Januaries overall in the NE US following the last 11 -ENSO -PNA Decembers, only 2 were mild (2017 and 2023) while 3 were within a few degrees of normal and 6 were cold (1984, 1985, 2009, 2011, 2014, and 2022). So, 3 times as many mild were cold. *Edited for correction: 6 Jans were cold, not just 5.

But the idea of a big Arctic plunge 12/12-17 deep down into the US (possibly from two highs per GFS) is becoming increasingly likely based on model guidance. This is very believable considering it would be during an EPS progged longest phase 8 in 50 years along with the highest % Dec 5th snowcover in the Midwest since at least 2002. This is also setting the table for a potential quite cold Dec/Jan considering the -PNA Dec -ENSO analogs suggesting a +PNA Jan, which would make it likely that DJF would end up colder than normal for much of the E US even if we get the favored mild Feb. The Euro Weeklies would have to bust badly to allow for a +PNA, but it’s been too strong with the SER since just before Thanksgiving.

18Z GFS: 2m anomalies for 0Z on 12/14:

Highest US snow-cover as of Dec 5th 2003-25 (%)(2003-24 avg 27%): ‘05 48 ‘25 45 ‘18 43 ‘10 39 ‘13 38 ‘19 37 ‘06 33 ‘16 32 But more importantly for E US cold prospects is the Midwest snowcover: highest % as of Dec 5th (2003-24 avg 12%): ‘25 65 ‘05 45 ‘18 32 ‘06 31 ‘10 27 ‘16 25 ‘03 23 ‘08 20 https://www.nohrsc.noaa.gov/nsa/index.html?region=Midwest&year=2025&month=12&day=5&units=e

US snowcover as of Dec 5th is way higher now than it was in ‘16 and even moreso vs ‘22.

Followup: this is only 8 days out 12Z GFS

All 0Z ensembles are much colder in the E US 12/13-17 vs earlier runs.

New weeks 3-4 outlook makes sense since it’s similar to the Euro Weeklies. But hopefully they will end up too warm:

Chicago per model consensus is on track for a top tier cold Dec 1-20. Here are the 15 coldest Dec 1-20 at Chicago of the last 75 years (top 20 %) in reverse chronological order: 2016, 13, 10, 08, 05, 00, 89, 85, 83, 76, 72, 63, 58, 56, 50 2025 appears at this time like it might compete with many of these.

At 1PM, there was a whopping 26F diff. between Valdosta’s 76 and Tifton’s 50. Tifton is a mere 45 miles N of Valdosta!

The yucky rainy pattern continues here. Luckily during a short break in the light rains yesterday evening, I squeezed in a walk. Today so far has been different. The rains at times have been heavy, with my measurements suggesting ~0.75”. There’s been enough to be wary of hydroplaning if going too fast. This is the heaviest I’ve seen in several months. Thus, it’s the first minor test of my completed yard drainage projects as well as the city’s redug nearby street drainage ditch project. But it’s still not yet a complete tear as I need even heavier rains. Regardless, there will be more on and off rains through Sunday. My temps have been mainly in the mid to upper 50s after dipping to the rain cooled upper 40s last night. Temps are 12 warmer in Brunswick 75 miles to the S.

9 of the last 11 of the Jans following -PNAs in Dec for -ENSO were either cold or pretty close to normal. You’ve been harping on the only two warm Jans of the 11. Feb will more than likely be mild. It’s not necessarily Jan and Feb being similar as you’ve been thinking. This indicator suggests that’s unlikely as of now.

I’ll be rooting for a strong -PNA this month. Why? For -ENSO: Strongest -PNA Decs since 1983-4: -2021-2: -2.56; Jan was +1.01/cold -2010-11: -1.78; Jan was +1.29/cold -1984-5: -1.60; Jan was +1.63/cold -2008-9: -1.41; Jan was +0.61/cold ——— The Euro Weeklies continue with a pretty strong SER/-PNA in the first half of Jan. But it’s recently been correcting to a weaker one in late Nov/early Dec.

Agreed. But also keep in mind that the 15 days on that model (0Z EPS) preceding the map you showed are very cold in the NE 1/4 of the US and suggest one of the coldest 1st 19 days of Dec anomalies on record in the NE 1/4 of the US: Days 1-10: Days 11-15:

Today’s 2 week ensemble MJO forecasts: -12/5 EPS steady as a rock with a 17+ day long phase 8, second (back to 1974-5) only to the 18 days of 1975-6: a cold E US weenie couldn’t place it any better though keep in mind that the MJO, itself, is only one index of many despite it having notable tendencies: 12/5 GEFS: though not steady like EPS with only a 5 day phase 8 followed by 3 days of weak phase 1 (which also is often cold in Dec) followed by 5 more days in phase 8 and then 4 days barely in phase 7, this is on the whole still favoring dominating cold in the E US: Related to the very cold Dec forecasts, natural gas is up a whopping 6% today, alone! Knowledgeable NG investors don’t normally go long NG in winter unless the forecast is for a cold E US.

I still feel that Jan and Feb should be analyzed separately for the NE US. Since 1983-4 as regards -PNA Decs: -3 times as many -ENSO -PNA Decembers were followed by cold Jans as mild Jans including the recent Jan of 2022. In addition, there were cold Jans in 2014, 2011, 2009, 1985, and 1984. Related to this, 9 of 11 of these Jans were either cold or pretty close to normal. -But OTOH there were 6 times as many mild Febs vs the only cold Feb (2014) of these analogs in the NE.

I don’t feel 1989-90 is an -ENSO analog to 2025-6. That’s because: -Dec was slightly +ENSO per RONI (+0.09) and only a hair -ENSO per ONI (-0.01). -Jan was already a solid +ENSO per RONI (+0.39) and slightly +ENSO per ONI (+0.11). -Feb was +0.31 to +0.34.