griteater

Mid Jan and on IMO, yes

Euro Weeklies trend loop...7-day avg for Jan 14-21...last 6 model runs including today's

Still good with this. Agree with @CAD_Wedge_NC that chances for a big one are elevated. But it's' going to take a little time. The Pacific pattern is straight awful the first 10 to 12 days of Jan, then it should gradually improve. We have what looks to be a strong -NAO episode coming in 8-10 days. Meanwhile, we have a legit, downwelling SSW (strat warming) on the doorstep - Euro is locked in on Jan 5 which is earlier than I anticipated would happen. In addition, the lower stratosphere is already in a very weakened state. Research from Simon Lee states that the Arctic High regime (-AO / -NAO) is 7 times more likely to occur when the lower stratosphere is in a weakened state, and the SSW will only reinforce the weakness. Thinking we may see something like a heavy blocking period here in early to mid-Jan, then a bit of a relax period at some point, followed by another heavy blocking period. We should see an improving Pacific pattern mid-Jan and after, though suspect it will be variable. Good luck to all

The whining thread will be hot and heavy for sure. Hopeful that we can see a better pattern emerge or in sight by mid-Jan. The Greenland blocking and Strat Warming (and likely official SSW) are things we haven't see much of at all in the past 10 years, so that is interesting to see. Hopefully, that will be something that sticks around for much of the winter (at least off and on), and we get into a better Pac pattern down the road. We are going to need a little GNR Patience though I think, as it may take some weeks.

Yeah, the Pac side is just essential for the cold air. We can't have a bad Pac side. I guess it is something like this (thinking out loud, ha)...For number of winter storms / winter storm threats, we've gotta have the Pac side. The Atlantic side then gives you a better chance at having higher quality storm features like 50/50 lows, surface highs that don't race off the NE coast, sfc highs with CAD, suppressed 500mb wave track, amplifying and slower moving waves (storms)

NOAA CPC is predicting a new MJO event will emerge over the Indian Ocean in Week 2. It would then move east, but we would have to see with how much amplitude. Strat warming should help with propagation if it does indeed form. See the MJO Weekly Update - https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjoupdate.pdf

^ I gave some thoughts regarding the culprit for the problems with the Pacific pattern in a thread here: https://twitter.com/griteater/status/1342941989696905218

As good a retrograding Greenland block as we've seen in 10 years getting ruined simultaneously by an awful Pacific pattern. These are in complete opposition to one another in terms of what we are looking for.

Canadian has the same setup as the GFS, but after the wave digs in TX, it gets squashed/weakened as it moves east so there is no storm east of TX/LA

The GFS keeps trying with the storm in early Jan

raindance - I've never picked up on that, but you are correct on the sign difference there. This page indicates that the "EP/NP index replaces the old EP index which is no longer maintained by CPC" - https://psl.noaa.gov/data/climateindices/list/ -EPO means ridging over Alaska. Here is a site for the EPO. It gives a definition for the EPO, but it looks like the data links are broken - https://psl.noaa.gov/data/timeseries/daily/EPO/ Here is an EPO site that was constructed by Alan Marinaro, but the data hasn't been updated since 2016 - http://www.wxmidwest.com/epo/ Back to the EP/NP Index, here is a composite of all January's in which the EP/NP Index was +1.00 or higher. Basically, it looks just like the EPO, but with reversed sign. In this case, +EP/NP Index means ridging over Alaska

Just watching the ensemble model runs, this -AO/-NAO looks and feels legit. I'm sure it will wax and wane, but I think the signal is more real this time than normal. The near constant ridging in NW Asia with corresponding troughing in E Asia / NW Pacific is a configuration that will continually attack the stratospheric polar vortex and lend support to the tropospheric high latitude blocking. I think we will eventually see an official SSW, but it make take some time (late Jan?)...and the chances of the SSW yielding favorable results are better when the troposphere and lower stratosphere are already experiencing blocking and are weaker than normal. The ideal scenario would be for the tropospheric blocking to continue well into January, then we get the SSW that gives it an additional kick - it's not a far fetched scenario this time.

A few long range thoughts. I believe early to mid January will be favorable for a winter storm or 2 for the mid-Atlantic and north...and same for all of the east coast including our forum for mid to late January as enhanced convection should begin to move out of Indonesia during the 2nd week of January, improving the pattern over Western Canada / Eastern Alaska. I would say that the chances of a large and widespread winter storm for our forum to be much higher than normal for mid-January to early February. Time will tell, we can revisit down the road. Here is today's Euro Ensemble Mean for days 10-15...

RGEM trend loop with the wave. It is trending south and more energetic. This is a good setup for snow showers across North Bama and North GA IMO (even some in central Bama/GA). Localized light accumulations too. More renegade snow showers east of the there.

^ Another thing on that GEFS loop, you can see how waves would be launched into California in the southern stream with that big North Pacific low (subtropical jet would be located between the blue negative anomalies in the N Pac and the yellow positive anomalies to the south).

End of the GEFS looks great with the NAO - that's classic NAO placement for winter storms in our forum with the max positive anomalies centered from the southern tip of Greenland and west toward Hudson Bay. The EPO, on the other hand, looks bad with the big low in Alaska.

The big -AO/-NAO winters/periods are kind of legendary, so that's what elevates interest I'd say. Dec-Jan 2010-2011, Winter 2009-2010, Dec-Jan 1995-1996, Jan-Feb 1987, Dec-Jan 1981-1982, Winter 1978-1979, Winter 1976-1977, Winter 1969-1970, Winter 1968-1969, Jan 1966, Jan-Mar 1960, Winter 1939-1940, Winter 1935-1936

Not a fan of it either...think we can still see something with a bit of luck though. Hopefully the -AO/-NAO hang on in Jan (along with a boost from a legit SSW), and the Pac improves in due time

The models are currently trending toward a bit more vigorous trough passage. Keep that trend going, and you'll have flakes flying late on Christmas Eve and overnight in Atlanta / North GA / North Bama. Here's the 12z Canadian which is currently the most energetic with the trough, closing it off over TN. Temperatures really crash as it moves through.

The pattern developing late Dec into Jan is close to being a very good one. It looks full of 50/50 lows, split flow, southern stream waves, and negative Arctic Oscillations. The one thing I'd like to see more of is what you've touched on here which is a bit more amplification into Western Canada and Alaska to give us a little more cold air. The pattern of descending highs from Siberia into East Asia should continue the subtropical jet feed for several weeks and we should continue to see temporary +PNA spikes (there is a large Siberian High that peaks at 1076mb on Dec 29 on today's GFS). Anthony M has indicated that in order to get larger and more sustained ridging into Alaska and Western Canada we'll need to move the MJO / tropical convection out of Indonesia / Maritime Continent, and he thinks we may see that occur as early as the 2nd week in Jan. That's obviously way out there, but something to look for. Regarding ENSO, the west to east pattern you mention that we're in is really more indicative of a -AO/El Nino pattern. As I'm learning more and more, having El Nino type patterns during La Nina and La Nina patterns during El Nino really isn't that uncommon as subseasonal factors can overwhelm typical ENSO seasonal patterns at times. Anyway, here is the 500mb pattern that has occurred for Dec 1 to Dec 20. The PNA has been positive every day so far this December (though not always strongly so), which is El Nino like. Also, you can see here on this chart of 200mb wind anomalies, that since Dec kicked off, the subtropical jet stream along ~30N has been stronger than normal (orange/red colors), and the polar jet stream along ~60N has been weaker than normal (blue colors)...that's very representative of a -AO / El Nino regime. As others have mentioned, it takes many things to align to get a good storm down here, but we're not far off as we go forward into January.

12z CMC has a southern stream wave that tracks from central/southern California to Texas Dec 28-31, with snow and ice deep into TX and surface low in NW Gulf

@Isotherm - thanks for posting your updates in here. I hope you will continue to do so. Yeah, I'm not sure what to make of this big incoming +EAMT. Following the descent of the Siberian High, I would expect to see a strong low kick out into the northwest Pacific, with a downstream large -EPO and/or +PNA ridge...but the current modeling acts like it wants to somewhat flood AK with low pressure. I wasn't sure if that's a situation where models will correct in time, or if the large nature of the +EAMT could lead to that type of result. I'd also expect to see solid split flow develop following the development of the -EPO/+PNA ridge. Do you recall other scenarios / analogs with this type of large Siberian High descent?

Yes. It's really just a cold front passage, but it's very amplified and there's a piece of upper level energy there at the base of the trough where a low rides north up the front. But for us east of the mountains, we would need a piece of energy to drop in after the cold air has moved in. The mountains would do well with upslope post frontal snow.

GFS drops a lobe of the TPVortex into the Great Lakes this run. Has temperatures below zero in the mountains Christmas morning, and 4PM temperature of 21 in Greensboro