Winter 20/21 - General Discussion

Where I was born in dunlavin in wicklow there Is hill fort .
,couple of times as a child I was brought up to it by both my father and or brother.
If the weather conditions were perfect you could just make out part of wales with the naked eye.

That horizon chart is great GL . Never knew it increased so much at a few meters . Cheers

sryanbruen wrote: »

If you feel that way then fair enough. However, I will continue to post about the stratosphere ‘til the end of time or as long as I’m a weather enthusiast anyway as I find its variability and dynamic nature quite interesting irregardless of what happens at a tropospheric level. How it can vary from a very strong SPV to a very weak SPV in a matter of days via stratospheric warmings. It’s just all fascinating to me. It’s a continuously researched phenomena too so there’s always something new to learn and nothing is concrete. The stratosphere never “promised” anything, I think it’s people’s expectations getting the best of them (and I have done that before too *sigh*).

It’s unfortunate it is now used as another source that the media can “justify” their nonsense on that they pull out of their arse because of events like 2018. I do find that quite frustrating knowing that was the extreme end of tropospheric impacts and will highly unlikely see again anytime soon.

Is there any historic strat data available Syran to allow us to to maybe run a few correlation tests with SSW events and potentially colder weather down the line? I see much talk on Twitter about this but I always find explanations about SSW vague at best, which just increases my apathy towards it.

Is there a way of predicting when a SSW might occur? From what little I know, they nearly always seem to triggered around the far west of the greater Med area? Is there a reason for that and is there any particular synoptic pattern in the north/central Atlantic that would help trigger such large scale atmopheric phenomenon?

Has this become the Official Tell Us What You Can See thread? :pac:

mcburns07 wrote: »

Has this become the Official Tell Us What You Can See thread? :pac:

I spy on roids

Oneiric 3 wrote: »

Is there any historic strat data available Syran to allow us to to maybe run a few correlation tests with SSW events and potentially colder weather down the line? I see much talk on Twitter about this but I always find explanations about SSW vague at best, which just increases my apathy towards it.

Is there a way of predicting when a SSW might occur? From what little I know, they nearly always seem to triggered around the far west of the greater Med area? Is there a reason for that and is there any particular synoptic pattern in the north/central Atlantic that would help trigger such large scale atmopheric phenomenon?

The following link shows geopotential height anomaly cross sections at 60-90N for every winter back to 1979-80 which was the first year of the ERA5 record. This is a basic way of trying to see if downwelling does occur although not perfect and does not necessarily show a favourable cold pattern for us either which you need to look at the actual synoptics for of course.

https://fh004579.webs.act.reading.ac.uk/pcap_xc/

I have done one here as an illustrated example with the major SSW in February 2018 being very visible at the top of the stratosphere which would downwell quickly towards the surface.



Other sites with stratospheric related data include that might be of interest:

https://csl.noaa.gov/groups/csl8/sswcompendium/
https://ozonewatch.gsfc.nasa.gov/meteorology/wind_2018_MERRA2_NH.html
https://www.geo.fu-berlin.de/en/met/ag/strat/produkte/northpole/index.html
https://acd-ext.gsfc.nasa.gov/Data_services/met/ann_data.html

A paper that I always find myself coming back to for anticipating SSW events in advance outside of modelling is Cohen's "Tropospheric Precursors and Stratospheric Warmings".

Yes, these warming events are caused by tropospheric patterns sending atmospheric waves to stratosphere via upwelling. This results in the stratospheric polar vortex getting disturbed and being weakened - this has been known for a long time but what has been studied more recently is for these stratospheric phenomena to then downwell back to the troposphere and result in blocked patterns that mean for a more meridional jet stream.

What are these tropospheric patterns that cause upwelling to the stratosphere? It's blocking over the Urals and low pressure over the Aleutians. The figure below shows mean sea level pressure anomalies averaged between 45-0 days prior to/after displacement and split major SSW events respectively in the study. Both Ural blocking or ridging and low pressure over towards the Aleutians is evident pre-displacements and pre-splits with blocking in the Arctic following both types of events. The European low is further west and deeper with displacement events as compared to split events so not quite as conducive to cold weather conditions for Ireland.

Zonal wavenumbers (number of troughs and ridges in a full circle around the globe) are another way of looking at these events but in spite of theories, an interesting new study which GL posted in the stratosphere thread discussed that a wave-2 split is no more likely to propagate downward or downwell than a wave-1 split or a wave-1 displacement which I find riveting to ponder at.



I have updated the table in the paper named to include the recent major SSW events since 2010. 5 January 2021 is an estimated central date. The central date is when the zonal mean zonal wind at 10 hPa 60N reverses from westerly to easterly.



I've said it very simply I can but if you would like more details, I'd recommend to indulge in more papers like that one.

I wouldn't even be reading papers like it if it weren't for recommendations given to me over the years from fellow enthusiasts on here or on other mediums.

sryanbruen wrote: »

The following link shows geopotential height anomaly cross sections at 60-90N for every winter back to 1979-80 which was the first year of the ERA5 record. This is a basic way of trying to see if downwelling does occur although not perfect and does not necessarily show a favourable cold pattern for us either which you need to look at the actual synoptics for of course.

https://fh004579.webs.act.reading.ac.uk/pcap_xc/

.

Absolutely epic Syran. Thanks! It is explanations like this, and from someone that is genuinely invested and interested in the topic that helps myself and others gain a better understanding of things like this the most.

Birdnuts wrote: »

Would u believe the lad giving that forecast is my Nephew!!:eek:

Feck off, that's a small world we live in, aiden is my favourite forcaster next to Philip Avery

Where I'm living now in Poland.
It's been snowing lightly to at times moderate since 3PM yesterday.
Roughly just over 10cms of snow -6 at the moment but to drop further during the day to-15 or below.
Temperatures are forecasted to drop below -20 over the weekend.

surprisingly very frosty in Dublin 5, didn't expect it.

The only thing that is certain is uncertainty and that is truer now than ever.

What we do know, is that the tropospheric pattern is modelled to be very disturbed and amplified over the northern hemisphere as a whole, as far as the medium range NWP models can show. The NH pattern as a whole is actually all over the place from run to run, HLBs popping up everywhere, bits if vortex going east to west and west to east. It's a mess, with very little consistency in the predicted long wave pattern.

No deep cold consistently modelled at the moment. And mild/cool is always more likely than deep cold than Ireland. But I wouldn't rule out anything in the next 6 weeks.

Honestly this place has been worse than netweather with the amount of toys and towels being thrown this week. I'm certainly not going to say a big freeze is definitely on the way, but the overall predicted pattern leaves many doors open.

I'm not sure if it's just temper tantrums, but the certainty that some on here are speaking with, is just foolish.