Interitus

Ironically, if Helsinki became drastically colder, there would be the same trend on the chart. Of course that's not happening / going to happen.

Interesting that it highlights the same Kamchatka high as my post above, however it's not set in stone and has gone on the next run. Whatever, further in the convo he adds - This is interesting with regards to my post and downwards wave reflection. My speculation at the time ahead of the 2018 SSW was reflection acted to shift the heart of the troposphere vortex south towards northeast Canada (a known effect) with the centre of strat vortex attempting to follow and stretching, allowing the wave 2 to pinch it out or vis a vis his Scandinavia-Greenland dipole.

Did the MJO wave cause the UK high pressure? Easy conclusion to arrive at and it may be related but as well as a fairly short time lag, previous examples show that this was not the typical response. This graph shows three close analogues of MJO RMM1 over the 14 days to Jan 19th (x-axis day 0 - UK high pressure) - These dates show a strengthened NAO with enhanced Azores high (your MLB?) and deepened Icelandic low, troughing to UK One interesting feature they shared though appeared around 20 days later, with a significant negative EPO - 11/02/1986 - 19/02/1993 - 30/01/2007 - They share not completely dissimilar features downstream also, though actual conditions varied for the UK. Various recent runs have been trying to replicate the 20 day -EPO this year also eg - As well as battling a strong troposphere vortex, since looking at this a couple of days ago it is now being complicated by a possible wave 1 downward reflection event into the area, encouraging a strong high pressure in the Kamchatka area and the rejuvenation of the Siberian high -

Temporary split, vortex reforms, min zonal wind 13.1 ms at T228 Try 00z p15, not split but big displacement, min wind -15.1 ms and bearing in mind above post from Knocker, the window for a split may be quite small in the short term - Actually the latest GFS runs are ramping up the vortex later on as they're giving no coherent signal for other than transient wave 1 even, with the angular phase shifting in longitude all over the place.

No reversal - zonal wind 2.1 ms at T294 -

Just had to rescue a rather drowsy bumblebee off a pavement, bit early to be out yet!

Despite the recent GFS runs in long range, from the analogues there is actually a decent chance of a SSW before the end of February, maybe 30-50% at a guess. As an aside, interesting split forming on the 12z, probably won't be it, but is popping out at relatively short range so the FI is definitely not certain.

Last night the GFS was so wrong. Now they all are

Whoa!

Don't worry, one of the CFS members has the strongest reversal/early final warming on record

Well the GFS has backed down from a SSW quite a bit, here are the 1mb zonal winds on the runs since the last negative values on yesterday's 06z - The x-axis represents the 3 hourly forecast intervals and the minimum on today's 06z of 17.5 ms at T219 - day 9 - fairly accurate at that range. It's not unlikely that it could flip back beyond this, though at the moment it is looking increasingly like perhaps a first bite of the cherry. The GEOS out to T240 (one run per day) still has the 1mb wind down to 8.9 ms at the last timeslice, will be interesting to see its direction on the 28/01 00z.

More than a bit harsh, he has completed his masters and is half way to his PhD and is a published researcher alongside well known meteorologists (with particular regard to the stratosphere) such as Amy Butler, Andrew Charlton-Perez and Jason Furtado, and has a paper currently in review co-authored by sometime contributor to the strat thread Zac Lawrence (curator of stratobserve.com). His tweets are some of the more interesting out there and a world apart from some of the popular uninformed drivel which frequently graces these forums!

You might be more concerned whether a SSW is going to happen at all!

These are interesting charts, but look at the verification scores on the right hand side.

Actually the 12z backed away from an SSW, 1mb minimum wind of 11.7 ms at T261 recovering to 29.8 ms at the end. 10mb ends on 16.5 ms which is higher than the previous 3 runs.

Trying to split on 00z - Not split on 06z - Maybe tries to nip the end off, despite perhaps a better split at the higher levels, the 30 mb temperature gradient is not conducive to a 10 mb reversal on the 06z but reversal likely on the 00z. Perhaps most significantly, whilst 1mb reversals are still at the end of the forecast periods, the last three runs start to bring reductions in 1mb zonal wind closer to the reliable at 9 days rather than stuck beyond 10 days + edit: Note the strongest 1mb reversal forecast was still that from the 18th 00z (not shown)

A week on, winter 2019/20 has slipped to 16th mildest. Of recent years it has passed last winter, but has in turn been overtaken by 2013/14 and is still behind 2015/6 and 2006/7 - For lack of cold this winter is now 9th, but 2013/14 still rules the roost with basically no cold to this point whatsoever -

To update, this 18/01 00z is a bit of an outlier at the moment, there hasn't been a reversal in the 24 runs since, clustering of the windspeed graph shows that reductions are struggling to get inside the 10-12 day reliable timeframe -

Rate of change.

T375 on the 12z was the lowest 10mb 60N zonal wind of any GFS op run since before the start of November at 8.3 ms. Gone on the 18z, lowest 23.3 ms.

This graph shows the average May/June SST for the arbitrary central north Atlantic region from 1950-2019 - Clearly, there has been a downward trend counter to warming elsewhere, which represents the 'cold blob'. But the decrease is not monotonic and displays much interannual/interdecadal fluctuation. Primarily the temperatures are a response to atmospheric conditions, precipitation, evaporation, insolation etc which vary with the NAO. On top of this there is infeed of currents of varying temperature and salinity into the sub-polar gyre and levels of winter deep convection overturning the static stability. To show the contrasts in temperature compare the coldest year 2015 at 9.568°C leading to the record December CET - just five years earlier the cold December was preceded by the 5th warmest SST in the series at 11.0475°C. Here is an interesting paper comparing the winters 2009/10 and 2010/11 and highlighting the probable importance of SST anomalies in the latter - https://journals.ametsoc.org/doi/full/10.1175/MWR-D-13-00104.1 For reference, the 2009 May/June SST was cooler than average at 10.16°C which should have tended towards a warmer December.

Very interesting, but it can also tie into this other post - A couple of years back after speculation that the 'cold blob' would increase risk of early frosts and a colder winter for 2018, a rough analysis suggested that a negative May/June SST anomaly for an arbitrary 45-60°N, 10-50°W actually leads to a milder November and December, similar to the Atlantic tripole findings of Rodwell and Folland et al - https://www.netweather.tv/forum/topic/90431-uk-first-ground-and-air-frost-watch-season-2018-2019/?do=findComment&comment=3908027 The source area was not optimised for correlation and also ignored any wider tripole which may explain that the cooler the blob area, the more pronounced the effect and milder the December. For the 12 coldest May/June average blob temperatures since 1950, there was only one colder than average December, 1976 (not 2009 as wrongly stated originally). A simple 2nd order polynomial fit for the SST data 1950-2017 gives a CET prediction of 6.0°C for Dec 2018 (actual 6.9) and 5.76°C for Dec 2019 (actual 5.8) so that's only 1 colder than average December from the 14 coldest 'blobs' and 8 of these are 6+ degC. At the extreme, the second coldest blob gave the second warmest December, 1974, and the coldest gave the warmest, 2015....which brings us back to the positive IOD years. 1994 fits the pattern well with its 6.4°C December following the 4th coldest blob. 1997 and 2006 however are very much in the 'warm blob' territory. A fuller analysis taking into account patterns of SST and detrending temperatures may give better results, but there do appear to be reasonable predictions available at 6/7 months in advance.

Not really, the warming normally occurs over over troughing - the steeper the geopotential gradient of the trough below the particular vortex level, the stronger the warming, strongest of all when the geopotential contours of the two levels are perpendicular. In the corresponding 500mb charts to the animation the low heights can be seen over northern Canada and Greenland. If the EPS shows increased heights in this area later on, the warming will fade away.

Not the best of starts! Better luck with the rest.

Might be a bit cynical to point out that both locations mentioned that reached 1050+ are above 300 metres altitude thus needing a bigger pressure adjustment to sea-level.