Stratosphere watch 2020-21

bazlers wrote: »

Hi Sryanbruen, the SPV flipped westerly yesterday although quiet weak. Do you know if there will be further warmings soon?

Replying to this in the respective thread, yes there will be a succeeding warming that occurs later in the week and is reflected by a a drop back to reversal from this GFS forecast.

The latest GFS does show an eventual recovery in the SPV which you would expect. Warming events cannot go on forever. This is normal with mid-winter major warming events.



All eyes right now are on if tropospheric impacts will be felt now that the major SSW event was officially declared on 5th January. The likely route if we see any impacts is a mid-Atlantic ridge, North American trough and the main lobe of the vortex over Eurasia. This initially sounds all positive for a cold/snow lover but there are lots of complexities surrounding it. However, Iberian heights might prove an issue with depressions forming in the North Atlantic due to the vortex lobe over North America.

Models are on a rollercoaster at the moment with these stratospheric developments. They have no clue. Some runs show the likely route I mentioned whilst others show something completely different or nothing at all. This is definitely more uncertain than what happened in 2018 but even that event was not fully certain all the time with some rollercoaster moments such as models (notably the ECM) showing the high latitude blocking too far south to allow a direct feed of the severe cold polar continental airmass or the period of "lift off" would backdate on runs.

What is different this time to 2018 too is that we have high latitude blocking already or a weakened tropospheric polar vortex. Does the SSW prolong this blocking, does it intensify the blocking or does it give the atmosphere a bit of a shake to a different pattern?

Lots to keep a close eye on for sure.

nacho libre wrote: »

https://twitter.com/TradeWpower/status/1351270507522486272?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1351270507522486272%7Ctwgr%5E%7Ctwcon%5Es1_&ref_url=https%3A%2F%2Fwww.netweather.tv%2Fforum%2Findex.php%3Fapp%3Dcoremodule%3Dsystemcontroller%3Dembedurl%3Dhttps%3A%2F%2Ftwitter.com%2FTradeWpower%2Fstatus%2F1351270507522486272%3Fs%3D19

Sryan, what are your thoughts about this?

Well the tropics might finally be on the move so that'd be a start... and away from Nina wavelengths.

First post here in a while. The major sudden stratospheric warming (SSW) happened in early January with an estimated central date of 5th January when the zonal mean zonal winds at 10hPa 60N went into reversal from westerly to easterly. This central date is to be confirmed in reanalysis towards the end of the season or next winter. It was primarily wave-1 driven and the stratospheric polar vortex (SPV) was displaced from its habitat. Through succeeding warming events in mid-January, wave-1 splitting did occur with further reversals but this did not evolve into a wave-2 major SSW event. All of these constitute as 1 major SSW event as for multiple major SSW events for historical consistency and various reasons, there must be a period of at least 20-30 consecutive days with positive zonal mean zonal winds i.e. westerly.



This has been a downward propagating SSW (dSSW) event going by the below cross section with clear negative Northern Annular Mode (also known as the Arctic Oscillation) in the stratosphere in early January associated with the major SSW event.

What may make it more difficult or confusing at first to tell when there was downward propagation exactly, using this data specifically, is how there was already blocking in the Arctic in the troposphere pre the SSW event and during it. However, the -AO has peaked during this cold spell giving away to extreme negativity of the index and extensive blocking over the Arctic. The second time-series I have given shows the propagation more clearly as it's the geopotential height anomaly for this year so far. There is a clear smooth propagation occurring from early January right at the top of the stratosphere (1-10hPa), in the lower stratosphere through mid-January (30-50hPa) and down to the troposphere (between 70-400hPa) coming up to late January.

The GFS is forecasting a readily strengthening SPV through the rest of February which you would expect as the very weak stratospheric polar vortex cannot go on forever and typically with major SSW winters, there is a later than normal final stratospheric warming (FSW) when the zonal mean zonal winds reverse to easterly for summertime before reforming in late August with the mean date being April 15th.

There is the likelihood for the -AO to significantly pay back a touch next week but there is no sign of going into positivity for the foreseeable future, at least on current model runs. Therefore, we should expect further blocking around the pole, just not as extensive or as extreme as we see now on synoptics at the moment.