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The more I visit this site the more I love it , plus Simon updated the site with this new data, which I have not seen anywhere else ( lower stratospheric anomalies ) : New product online at https://simonleewx.com/polar-vortex-forecasts/… GEFS forecasts of tercile anomaly categories of 100 hPa 60°N zonal-mean zonal wind. These lower stratospheric anomalies are important for influencing the what happens in troposphere, and are often more relevant than 10 hPa. Polar Vortex Forecasts All charts are updated once daily between 8:30-10:30 AM London time. Please feel free to share any images from this site on social media or elsewhere. 00Z GFS 0.5° & GEFS 1.0° 10 hPa 60°N ensemble plume 00Z GFS 0.5° 10 hPa 60°N forecast evolution White crosses indicate a strong vortex event (>41.2 m/s) following Tripathi et al. 2015. CFSv2 1.0° 10 hPa 60°N bias-corrected ensemble plume This is produced by taking the 4-member ensembles from 00, 06, 12 and 18Z yesterday and combining into a 16-member ensemble, out to 45 days. The bias is calculated as the difference between the 1999-2009 hindcasts (available from the S2S database) and ERA-Interim reanalysis. The CFSv2 has a significant bias toward a weak vortex, especially for forecasts launched in early winter, so accounting for this drift is necessary. It should be noted that a simple linear bias correction does not necessarily solve the problems produced by the bias, as the bias can interfere with the model dynamics. 00Z GFS 0.5° & GEFS 1.0° 1000 hPa Northern Annular Mode (NAM) ensemble plume This is calculated using the method of Gerber and Martineau (2018) using standardized anomalies of 65-90°N geopotential height (with respect to 1979-2018 ERA-Interim climatology) with the global mean anomaly removed. I thank Zac Lawrence for calculating the filtered ERA-Interim climatology used here. 00Z GEFS 1.0° 100 hPa 60°N tercile categories The tercile-category anomaly of the lower-stratospheric polar vortex, defined by the 100 hPa 60°N zonal-mean zonal wind, has been used as a diagnostic for the behaviour in the ‘coupling layer’ between the stratosphere and troposphere, i.e. the level in the stratosphere where circulation anomalies are important for influencing tropospheric weather regimes (e.g. Charlton-Perez et al. 2018, Lee et al. in review). The chart below shows the percent of GEFS members in each tercile anomaly category, based on daily 1979-2018 ERA-5 climatology. 00Z GFS 0.5° & GEFS 1.0° Scandinavia-Greenland dipole ensemble plume This dipole pattern, defined in Lee et al. (2019) as the MSLP difference between a grid box over Scandinavia and a grid box over north-east Greenland, can be used as a diagnostic of anticyclonic wave breaking in the north-east Atlantic which can enhance vertically-propagating wave activity and weaken the stratospheric polar vortex. In the paper, we use 40 hPa as a threshold (strong Scandinavia high + deep Greenland low) as this is similar to what occurred before the February 2018 major SSW, but values above 30 hPa are noteworthy.

Soon we will know how smart the seasonal models are with the NAO call. The post by Tony is interesting. Of note, if you click and close up on the image I do tend to see what Isotherm mentioned and someone else at 33andrain, a deeper NAO after the bottom of the solar min. Also, not related to this post by Tony , but read as well, next winter we reap the benefits of an established Easterly QBO . Personally I have seen the cycles go slower and then other times quicker. DT has something online that when the QBO is -10 to -20 it corresponds to a very cold Eastern winter. As Isotherm mentioned as well we are not dropping fast enough to reap the benefits of the changing QBO in the early winter , but will tend to at least increase the odds it helps us when we get to Feb and March

Of interest ....... hopefully it has a clue. Or , another way to look at it ..... Bob > CFSv2

Looking good, I have seen worse

A little twist here on time lines . When I watched a great webinar from BAMMWX a week ago they talked about how the PV was ahead in the progression versus some other years in their analog package and research. Also, the Siberian High is robust and off to a good start due to the abundance of Siberian snowfall. So, taken a step further everything happened so quickly , including the ramp up of the PV we are indeed ahead of historical timetables. ( per Webb - ahead by a month or so ) It is natural for the PV wanting to get stronger just as it is typical for it to undergo pressure and disruptions, which happens every year. The players are starting to work on the PV . Of course there is the lag to take into account. There are many outcomes possible in the next several weeks. HM's post for example. ( may not have to wait for a top down ) This post below is of interest and touches on this very thing.

Agreed. Seems Isotherm's sticking point, or one of several, was the PDO and the general Pac. ( And, I do acknowledge he did say Feb and March might be good for our area, but not good enough to get us above his snowfall projections ) I hope we get the changes you are talking about. It would be ironic if we time the STJ and the cold even for a week correctly, and then one storm alone can have a huge impact on the seasonal snowfall totals . aka Jan 2016.

I am surprised he posted something "positive " . Most of the things recently were negative. Being in the South I think, and maybe he is just tired of the warmth. Grown a little tired of hearing him focus on the roll forward MJO and the warmth coming for December. I will take a -NAO in December though.

Some decent thoughts here about the NAO from Webb, and what may happen. Plus, a quick one from HM on the same topic.

Check this out, really impressive.

There are signs that a real - NAO may get going to extend the colder pattern in the NE later in November. There always has been talk that later November/early December it could occur. Looks of retrogression in the pattern along with several indicators such as the MJO, Aleutian low, Scand block.

Something else to ponder. A +PDO versus the Victoria mode. You can see the image at the bottom for a representation of the associated SST anomaly . I need to research this more. Maybe Bob can chime in on this. To me the Victoria mode looks like a + PMM a little . I refer you to this https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014JD022221 The Victoria mode (VM) represents the second dominant mode (empirical orthogonal function, EOF2) of North Pacific variability, independent of the Pacific Decadal Oscillation and is defined as the EOF2 of SST anomalies in the North Pacific poleward of 20°N. The present study indicates that the VM is closely linked to the development of El Niño–Southern Oscillation (ENSO). The VM may effectively act as an ocean bridge (or conduit) through which the extratropical atmospheric variability in the North Pacific influences ENSO.

Heard that BAMMWX is entering warmer risks into December, but what I also heard was they mentioned the +IOD a a means of possibly lessening the warmer phases of the MJO we are destined for in December. Then this evening I saw something online by DT stating it was good news that in December the highly + IOD is forecasted to weaken. Hmm, I need to think about that more. WXRISK.COM 23h A good point about the positive IOD. The good news for winter wx lovers is that it looks like the IOD breaks down pretty significantly in December

Priceless !!!!!!!!!! I almost needed the Heimlich maneuver as I watched this while eating my dinner .

Hope your new grass survives the winter torch...... keep watering

Yes, that is true for the Atlantic , Matt posted on that earlier. HM posted weeks ago about the coming wave breaking events. Here you go -

@poolz1 You might enjoy this link. There is even a bias corrected 45 day CFS-v2 U10-60 forecasts. Pretty neat! https://simonleewx.com/polar-vortex-forecasts/

Something to keep an eye on during the next few weeks, as it appears to be an interesting set-up .

I know you touched on this already, to a degree, but do you have specific research that shows in this semi-new climate era from say 2010, that when November is winter-like then the winter attempts to mirror that outcome in the following March as well ? If anything, it seems winter starts later, taken into account the November head fake and then lingers longer. The linger longer part I imagine has to do with delayed seasonal blocking and any related lag effects from possible PV weakening. Last March many thought it was going to deliver, but it really didn't to the full potential some said it would, but oh boy April was cold. The year before was an epic March I even think the maturing of the event was responsible for the less hot June and July, relatively speaking. Thanks

For someone with Weather Bell access I am not privy to what the Euro ensemble shows for the AO, but the lastest CPC AO forecast shows more spread today. Can't post the 11/7 update here is the link https://origin.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao.shtml

I don't have an answer for this. I know last year Isotherm had mentioned he thought we might be nearing a period of more frequent - NAO cycles. Some research points to the sun effecting the ocean currents in the NAO domain, which can lead to a seasonal - NAO, but in this area I think the lag might be as long as 2 to 3 years. I know HM wrote something a few weeks ago about the NAO , and I personally thought it implied he did not seeing long periods of NAO . Whether he meant that for this month or this coming winter, I am not sure. I would have to search for the post. Here is what Isotherm wrote " There are other factors forcing the mode as well. Furthermore, as a general and practical matter, the descent of the solar cycle tends to force a greater frequency of positive NAO periods. My NAO formula suggests that the mean will be positive for DJF. This is not a deviation from most winters of the past decade. "

Very true. He also highlights on AAM, atmospheric angular momentum and the momentum budget and stuff like that. Hard to say if we go towards his solution. Last year Tom thought we did not need a SWWE , and I believe he might have hedged against a wind reversal and a true SSWE. In the end that did happen. Did it take full responsibility last year for the poor performance of many humans and machines, not sure. Some mets commented last winter the models saw the warming at HL and went with the idea that blocking would indeed develop over the AO and the NAO regions due to the Dec SSWE. It never happened and hence the awesome look by the weeklies and other models never occurred. We have mentioned many reasons why , the pure lack of tropical forcing, the ocean and atmosphere not coupling, the December SOI which was positive not negative. Not what you would expect. The MJO being effected in the warm cycles by the SSWE. The basin wide Nino and the very fast Pac jet, and High pressure in the Central Pac that enhanced a SE ridge. ( Nina like ) Everything went haywire and there was no cooperation and sync if you may. You would have thought the blocking should have descended to effect our sensible weather but many blame the QBO as a road block to that not happening. last Jan. This year we have a more favorable QBO. I also think I read in Tom's winter outlook where he stated in low solar min the NAO is more so positive, not sure but I think I read that, if so, I wonder what makes some solar min winters so freaking cold when I looked at previous solar min winter since 1950.

I liked your post but then I got it ....... so here you go

Looking like maybe we do not lose the trough in the East later in the month. I like the signal for the Kara Sea ridge Also, the consider the MJO as well for later in the month and then continuation of the progression would lead to a warm up in early December.

I don't follow Larry, but I can tell you Isotherm does have a good record at predicting the seasonal trends. His forecast for the next winter is anticipated by many every late Fall.

I post the positives and negatives - for those that wonder why - simply to make sure I am not biased cold and snowy. I love snow, but I attempt to be more realistic as I age. Chatting with bluewave about this November, just like last November we are doing great in terms of almost record high NH snow cover. I use to think that was awesome. What was viewed before as a great signal to a colder winter ( Judah SAI) has waned. We lost the snow last December and might lose the snow again this December if the warm December forecasts are correct. The changing Pac along with lower sea ice and other features are acting to put down rapid snow cover in October leading into November only to fall back versus above normal values in December. Damn I hate looking at those maps. from bluewave: <<< The cold November followed by a mild December has been a very persistent pattern this decade. So the snow extent charts are just reflecting this new regime. >>>