Stormchaserchuck1

If this verifies, we could be looking at our first winter storm threat around or after Thanksgiving. Maybe more 40N-north. 18z GFS ensemble mean at 384hr also had a pretty strong -EPO developing. Basically, the NAO is negative for the next 15 days, then the block retrogrades to NE Canada, just when the Pacific changes to more -epo/+pna around Nov 24-25 and after. That actually creates a window for a trough to track across the US, under the -NAO ridge in NE Canada, giving us a chance for a storm to hit colder air after Thanksgiving. The H5 in the map below is good, but we probably need a few days to flush out the old slightly warmer pattern. Still a long way to go, but it's looking good for at least below average temps beyond Day-15, based on current long range models. That cross polar ridge, with a GOA trough and 50/50 trough (although both are weak) is what you want to see -- especially good ridging over Alaska. It's a winterystorm pattern, although early in the year.

Yeah, it was a private school. I used to do weather forecasts at chapel everyday.

Jan 25, 2000 is very underrated. Literally that morning, the forecast was for partly sunny with a chance of a flurry and later that day 20" fell here. My school principal used to call me for weather updates when they would consider closing the school or not. I was watching the radar at 6:30am that day, watching a huge area of precip moving NW from the ocean, and I told them, "close the schools, I think we are getting 6-12". A few hours later when it started snowing everything went 12"+.

30-day is the highest since December 2022! It had actually gone 31 straight months without passing +10, now it's up to +15. Between that, the Oct-Nov N. Hemisphere 500mb pattern, and now a -3c pocket developing in the ENSO subsurface.. you can make a case for a La Nina presence this Winter. I'm curious to see how it goes with the fact that 21 of the last 29 months have been +PNA (CPC), and what happens there going forward.

From what I've seen Gawx post, it was a pretty big one-day jump. Like, top 15 percentile. Maybe he can confirm though.

They have had pretty decent success the last few years. I believe they kept showing cold in 23-24 that never panned out, but Gawx has been posting long range ACE forecasts and they have been very good over the last 2 years. It nailed a few Stratosphere warmings in early 2024.

That's a really good point -- the total N. Hemisphere 500mb pattern has been a very close match for October and November this year, about as close as it gets. Going forward, December typically holds the November -NAO, then the NAO switches to positive for January and February

18z GFS ensembles has a strong -NAO through the whole run.. we haven't seen something like that in a while.. we've had -NAO's but they've had problems sustaining. GEFS says 15 days and going, which is a good trend! It doesn't rapidly switch back to positive at the end of the run right now. At 84hr we have <-360dm 500mb going through PA/MD/VA. That's a big negative anomaly!

24-25 was the coldest Winter since 14-15. Something similar to last year is possible this year, as lot of the same conditions are reoccurring. We had 2 favorable patterns in 22-23, in December and March. 6/7 times out of 10, those patterns would deliver a SECS. It just didn't happen that way that year - a repeat of 22-23 though may not be as bad as you would think. Jan and Feb were really warm that Winter though: +QBO coupled with La Nina to have a strong 10mb vortex in 22-23.. we have a -QBO this Winter, and the long range Euro ensembles are already looking like they want to do a Stratosphere warming in a few weeks (which would correlate with -AO late Dec into early Jan (about 70% likely)).

Yeah, the Nina is weak sauce right now. Going back to June 2023, 21/29 months have been +PNA (CPC). It's surprising because we've had 2 "most negative monthly PDO on record" periods during that time, and the last 15 months have been cool ENSO.. but tracking 500mb all the time, the -PNA tendency has not been the same since the 23-24 Strong Nino -- it was happening all the time before then, now it's not sustaining more than a short period of time. It would have to kind of come out of nowhere to be a -PNA Winter this year, possible, but not as likely as the 2017-2023 period. Precip is definitely not a El Nino STJ right now, but I don't see why we can't have storms track across the Tenn valley and then into the Mid Atlantic this Winter. I think there is a -AO tendency with negative SLP 60-90N over the warm season (strong Summer -> Winter correlation since 2012) this year. Lots of cold H5 across the N. Hemisphere this year too, including the lowest 500mb reading on record for August this last August. 2020-2023 was not cold at H5 in the Northern Hemisphere at all. The strongest leading correlation I've found to Winter cold/snow is preceding year total H5 cold across the N. Hemisphere.

Is there a place that does the 2-6 week forecasts for GEFS and EPS for free, or do you have to pay for it?

We haven't had a Week 3-4 this cold since January last year.

+WPO is actually cooler pattern in the extreme Southeast. It's main effect is a ridge in SE Canada and around the Great Lakes/Midwest/Northeast. I think the digging trough that was +wpo/+pna related, and the fact that it happened 1 day from the coldest of the year on average (Jan 27). Surprisingly, the NAO/AO was not negative for that event.. so in the optimal scenario, it could have gone even further south!

Nice -NAO pattern Nov 7-23.. through hr384 on the 00z GFS ensemble mean. That's what you want to see as a wintery pattern, constant sustained High pressure west of Greenland and over the Davis Strait through the entire model run. That's a good sign for Winter, and does correlate at about 55% to -AO the rest of the Winter. We aren't super cold in the east because of a N. Pacific High pressure in that time... but since the 23-24 Strong Nino, since June 2023, the PNA has been positive 21/29 months (CPC)! It's been hard for -PNA's to sustain..

There is a really strong timelag between Stratosphere warming and -NAO at different times of the year: Nov 1-15: +45 days Nov 15-30: +40 days Dec 1-15: +35 days Dec 15-30: +30 days Jan 1-15: +25 days Jan 15-30: +25 days Feb 1-28: +20 days March 1-31: +15 days Cold Stratosphere has a +0-day timelag to corresponding +NAO at all times of the cold season.

Some long range confusion on the long range GEFS right now. It's the only model that has a strong MJO Phase 7 wave occurring But it's developing a -PNA look You guys are keeping track of this more than I am.. Has strong Phase 7 in late November been hard to happen the last several years?

We've had a good amount of PNA blocking (-PNA). December 2021 shattered records in this regard. -NAO's have not sustained at all. 15 days or less then it always goes back to neutral or positive, since I think 11-12. The 60s and 70s were not like that at all. EPO has also come in short periods, but that is more typical of the region to be like that than the NAO.

Well the 18z GFS isn't close to any snow. You guys made me look.

That's a time that correlates with -NAO from around Christmas to the 1st week of January

I haven't been talking about it as much because it's been near neutral.. the May-Sept total N. Atlantic SST indicator for Winter (DJFM) NAO came in at +0.08. It has a normal standard deviation of 0.54, so that makes it 50% likely to have a Winter NAO -0.46 to +0.64.

Kind of a big trend on today's models to -NAO conditions in the medium/long range. Yesterdays models had the NAO very positive for the next 15 days. I like that trend, I think we're wanting to go colder this year. Not huge Winter cold but at least a decent shift to normal Winter conditions unlike so many Winters in the last 10 years.

October SOI came in at +12.. which was the highest monthly reading since December 2022! Here's how that rolls forward to the following Winter:

October SOI came in at +12.. which was the highest monthly reading since December 2022! Here's how that rolls forward to the following Winter: Cooler December, warmer February

Lamar has almost a perfect QB rating in Miami in 5 games there.. that's where he grew up. The dude loves warm weather

La Nina effects on the Winter Northern Hemisphere pattern actually puts a High pressure over the North Pacific High, which is just off the west coast of the US. A lot of people think its main effect the PNA, which is actually only the case for extreme west-based events. Last Winter despite +PNA we did see a +NPH pattern. It was Weak-Nina like. I think we could be looking at a similar pattern here, at least to start this Winter, going into November and early December. Beyond early December, I wonder if the now neutral ENSO subsurface will make the La Nina less impactful. If the SOI stays strong through next month (it's been positive now 15 months in a row), we could see more a of a east-based La Nina like composite for the Winter, which is usually cold in the Upper Midwest and sometimes Great Lakes. La Nina December's also have a tendency to be cool in the Upper Midwest, Great Lakes, and Northeast - that's if the SOI stays moderately positive through next month and December.