Interitus

And I perhaps should have called them isohypse

For ease of viewing they've halved the isopleths for the 30mb chart by doubling the contour interval so a misleading comparison. The take-out from those charts may be how closely co-located the vortex centres are - little vortex tilt/baroclinicity and warming at that time.

Following on from the Simon Lee tweet, here is the GFS vs GEFS 12z ZMZW. Spot the GFS - And the 18z - GFS not quite as strong towards the end but the ensembles shifting en masse towards the op. Notable that under the suggested SPARC/SNAP criteria for assessing NWP skill, the GFS forecast wouldn't even register as a weak vortex - courtesy A. Charlton-Perez

Interesting ~2.5 week periodicity in the tropospheric NAM in which case the strat probably irrelevant in the forecast. Note on that run the NAM was influenced by a large cut-off high in the Arctic giving -ve AO, but there was a +ve NAO.

Just for fun, a quick look at CET for the +/- IOD years and other years since 1960 - Negative years - Dec 3.94, Jan 4.46, Feb 5.42, Winter 4.61 Neutral years - Dec 4.86, Jan 3.95, Feb 3.89, Winter 4.23 Positive years - Dec 5.38, Jan 4.86, Feb 4.59, Winter 4.94

It's been 'temporarily' mild in Barrow for at least a year lol

Today - Anchorage, Alaska - November mean temperature -5°C, average monthly snowfall 13 inches

They will record them almost certainly. For example see the "Workshop on Predictability, dynamics and applications research using the TIGGE and S2S ensembles" from April 2019 - https://www.ecmwf.int/en/learning/workshops/workshop-predictability-dynamics-and-applications-research-using-tigge-and-s2s-ensembles Scroll down to 'Presentations and recordings'. Lots of interesting presentations on subseasonal to seasonal forecasting (MJO, QBO, sea ice etc) including one on forecasting the 2018 SSW from Alexey Karpechko. Some of the previous events have simple videos and PDF files of the presentations but this TIGGE/S2S one uses Adobe Connect which neatly combines the video of the speaker with the slides they're presenting (as well as having separate PDFs).

Briefly returning to 3-D plotting, Unidata Integrated Data Viewer (IDV) has made this available for a decade. Here is an isosurface of model absolute vorticity of the above image - Slight drawback in that it cannot natively create the potential temperature levels as used on stratobserve, here it is the GFS isobaric levels between 100 mb - 3 mb approximating the 400-1200K. Find out more about IDV and download - https://www.unidata.ucar.edu/software/idv/

Confirms the tenuous link between ENSO and NAO which can be gleaned from elementary investigation. Compare with this other recent paper - The Linear Sensitivity of the North Atlantic Oscillation and Eddy-Driven Jet to SSTs https://journals.ametsoc.org/doi/full/10.1175/JCLI-D-19-0038.1 As shown below (and with particular regard to winter) the ENSO region appears to affect NAO as part of a tropic/sub-tropic Pacific dipole. The Atlantic tripole is also in evidence, but interestingly seems to exert little more influence, though it captures most variance in reconstructed NAO time-series. However, the modeling confirms previous works, that in theory NAO is most sensitive to Indian Ocean SSTs but the influence cannot be detected interannually (eg. month to month). Rather a long term warming trend may foster periods of more positive NAO years. It is seen that prescribed Indian Ocean temperatures can be responsible for Pacific and Atlantic wave trains affecting the NAO but in reality the SSTs in the region are most sensitive to ENSO with warming forced by the atmosphere instead of SSTs forcing and preventing the teleconnection.

Yes, posted links relating to this a few times, for example, never mind 2014, this 2013 paper from Peings et al showed that using an extended dataset, the snow cover / AO relationship is non-stationary - https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012GL054083 Other papers from Yannick Peings examine this concept further which suggests that the snow/AO correlation may just be an artefact of other processes rather than a cause itself.

The paper referenced above, which reviews the February 2018 SSW, can be found here - http://ifurtado.org/wp-content/uploads/Publications/LeeCharltonFurtadoWoolnough.pdf Jason Furtado kindly makes available papers he's involved with, a great resource - http://ifurtado.org/published/

Except last year when the vortex was average until SSW at start of New Year. And 2015 when the vortex was strong throughout Autumn and early winter. But, yeah.

The English record for February is -20.6°C at Woburn, 25/02/1947. Chance of beating that must be about zero.

Not really, what is the contour interval? Can see a 700 metre depression in geopotential height at the 500mb level in the image above, whilst it is up to 800 metres at the 10mb level with a suitable contour resolution -

Yes, the Kryjov paper, was going to repost this link. At the time back in 2015, way up this thread, it was paywalled. By using 500mb data at an arbitrary random location on the Taymyr peninsula it was possible to get an October geopotential - winter AO correlation of 0.62 over the 1976-2013 period, not quite the 0.9 touted for the mythical OPI but promising nonetheless. The method used in the paper above was alluded to in a follow up which shows it as calculated slightly differently - area averaged and at different altitude. Importantly their results appeared to be stationary over time which gives some hope that it may retain its utility. The main raft of papers commonly refer to Arctic sea ice or northern hemisphere snow cover, either individually or in combination with various other indices eg QBO etc Work such as the Cohen SAI have famously shown strong links to winter AO though have since been questioned as non-stationary - the correlations may be more an artefact of a causative link rather than the cause itself. Also the proposed trop-strat-trop pathways have been difficult to reproduce in modeling studies. To single out one author as a starting point, the works of Yannick Peings are a treasure trove - Yannick Peings - Google Scholar Citations SCHOLAR.GOOGLE.CO.UK His work on Ural blocking for example demonstrates that as well as generating the wave driven strat response, also leads to the Kara sea ice and Siberian snow cover which are suggested as possible causative factors by others.

Once again, this is weather vs climate!

This is weather vs climate. If looking only at UK weather or climate maybe, but obviously there have been many studies which have demonstrated statistical correlations between October circulation patterns and the following winter.

This is probably unlikely. The geopotential anomaly plot shows the combined effects of virtual temperature in the stratosphere and all the levels of the troposphere below. In this instance it does indicate a warmer stratosphere, but looking at all the charts shows that in the 1980s there was a positive stratospheric anomaly more or less every summer, many stronger than 1981. In the 1990s it is more mixed around the average, whilst since the millenium there has been a persistent negative anomaly. This is consistent with the recorded stratospheric cooling as expected from global warming and greenhouse theory. With regards to December, note there was a SSW on December 4th.

Bit of a nonsense calling it a weaker than average vortex, the vortex hasn't reformed yet.

? Southern hemisphere

The Cambridge Botanic Gardens weather station is an official Met Office climate station which reports daily values on a monthly basis as opposed to synoptic stations reporting each day or indeed in real time. The station is valuable for climatic studies as data goes back to 1898, and also as such exact precise values are less important than the homogeneity and length of the data series. However, from appearances the site certainly wouldn't be immune to criticism, despite the assertions that the MO know best and sly digs at 'amateurs'. If in any doubt read the article from the journal Weather by Stephen Burt and the late Philip Eden linked to earlier - The August 2003 heatwave in the United Kingdom. Part 2 - The hottest sites - https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1256/wea.10.04B Sites such as Heathrow, Northolt, Gravesend, Kew Gardens and Wisley all appear to be less than perfect at the time of their analyses. Meanwhile, the Brogdale/Faversham record was considered to be possibly an anomaly of 2 degrees,- but the site looks state of the art compared to the photos of the Cambridge one.

It's possible, but unlikely because the temperature is due to the air at high altitude descending to the surface and warming by compression. So all things being equal and the same heat burst occurred, to beat the record, the air at altitude would also have to be six or seven degrees warmer in the daytime than at night which isn't the case.

Purely guessing that they happen fairly frequently with suitable shower activity, but as they are very localised, getting them to coincide with an official recording station must be very unusual.

Yes well worth noting some discrepancies with regards some of the other readings. They proposed that the 38.1°C at Kew Gardens be the official record (thus equaled yesterday) though the screen height was too low which would produce an artificially high reading. Gravesend's same value of 38.1°C originally thought to be the record was anomalous with readings from other dates and considered to be up to 1°C too high. As is often suspected, Heathrow and Northolt are unrepresentative of non-airfield locations by perhaps 0.5°C. The Wisley site has become more sheltered by a neighbouring orchard and now features more often in the tables of highest values - though of course if the orchard was there in the first place would it even be considered an issue?