[Misc] General Weather Thread

[Djmiles]

Just outside of Aberystwyth , even the sheep have pacamacs .

I’m going to take a guess at....BORTH

 

[Taybha]

I’m going to take a guess at....BORTH

Jesus I’m not that lucky , that’s quite cosmopolitan compared to Llanbadarn-fawr

 

[Djmiles]

Jesus I’m not that lucky , that’s quite cosmopolitan compared to Llanbadarn-fawr

On the bright side, at least you don’t live in Penparcau!

 

[Flex Your Head]

Hi mate,

This area of netweather might be useful to have a browse through, I think it should cover all of your questions:
https://www.netweather.tv/forum/forum/69-learners-area/

A quick one on these questions :Uppers. Toppling heights. Northerly blocking. Zonality. What is the Polar Vortex and what does it 'do'? That sorta thing really.

So when someone mentions uppers they are talking about the temperature that's at 850HPa, i.e. around 2 miles (I think that's right? Papa?).

Northerly Blocking is a term which is ideally what we need to see to get any cold weather our way. Our default weather pattern is from the West (as it is across the whole northern Hemisphere) however when we get Northerly Blocking, that means there is a high pressure over the Pole (or ideally over Greenland) which "blocks" the westerly flow of weather for us and starts turning weather to come in from the East or North East.
Generally in winter this is coming off a huge landmass so is (normally) bitterly cold and we tap into that. This is where we get the "Beast from the East" saying and generally the direction we get most of our snow.

The Polar Vortex is the killer of any cold weather in Winter! This is a huge body of extremely cold airmass from the troposphere (where clouds form) to the Stratosphere (up to the edge of space) which forms normally from September through to Feb/March due to lack of sunlight over the pole. Temps can get down to -90, so with this in place and our much milder temps over the equator and north of there, where these two airmasses meet, is where you get the jet stream. The jet stream is the dividing line between Cold airmass and milder/warmer airmass.

In winter if you want snow, you want the jet stream to head south over the Med or spilt out in the Atlantic, vice versa in summer you want it over Iceland!

Along this jet stream/boundary is where you get (generally) the Low pressures form. The faster the jet stream (if a big temp differential between the two airmasses), the bigger/windier Low Pressures form. If the jet stream is anywhere near the British Isles (which it usually is) then those low pressures go either through us or just to north.

However the Polar Vortex can be "attacked" so to speak what what's called wave 1 and wave 2 formations (these are high pressures around the Northern Hemisphere). These pump milder air into the Artic which can disrupt the Polar Vortex from being so cold and actually warm it up a little. When this happens the temp differential becomes less which reduces the strength of the jet stream, which in turn means less strong Low Pressures and it allows the jet to meander. This in turn could allow High pressure to form over us or further North/East.
A SSW basically kills the Polar Vortex in Winter and all that cold air is forced outwards to our latitude around the Northern Hemisphere, which in turn sometimes means we have a cold spell (like it did back in Feb/March).

So for weather nerds who want snow, a SSW is the Holy Grail! Next best thing is some blocking to our North/North East to get some snow.

Sorry for rattling on, but just wanted to get some points across! haha! Hopefully Papa can verify what I've said, but do have a look at that learning area, it is very useful. )

Great stuff - really useful thanks, and it provides shape and form to some of the abstract bits and bobs I've picked up lately. Much appreciated.

Will take a look at the 'learning area' too. Cheers.

If you're really lucky, I might post some charts and ask some really basic questions as how best to read 'em - something to look foreward to then!

 

[Flex Your Head]

A lovely sunny and frosty day yesterday, even colder today but with a little less sunshine. Feels right for the time of year (although [MENTION=11350]LamieRobertson[/MENTION] might not be so chuffed!)
Are we due anything more in the way of 'seasonal weather' in the run up to Christmas, or will it be a return of grey, damp and mild?

 

[casbom]

Funnily enough I was going to post a little update as things have got interesting!

So some initial cold weather rest of today and first tomorrow where we might see some snow/freezing rain before it turns to rain. It'll be horrible, wet, cold and windy yuck!

Over the next week more of the same (rain/wind) but going towards xmas it "might" turn a bit more seasonal (depending on which weather model has it right..basically none of them yet). There is a signal for an Atlantic block towards xmas which might see us have some chilly air for xmas. Some extreme versions have us seeing snow on xmas day whilst others is mild and wet. So all to play for.

Strangely there is probably more confidence in what happens after xmas as to what type of weather we'll get. Remember that Polar Vortex and how a SSW could happen? Well it's becoming clear that there will be a SSW which will displace the Vortex over Siberia/Russia just after xmas. This in itself probably won't mean cold weather for us, but interestingly the models are now starting to show a second SSW (end of Dec) which could split the Vortex. If this happens then there is a 70% chance of cold weather for us.

The Met Office are quite bullish about cold weather in Jan happening, with as they say potential for Severe weather during Jan (apparently heard on LBC radio this morning from a Met office spokesperson). Their in house models (such as Glosea) are showing a split Vortex and the EC46 (ECM long term forecasting model for the next 6 weeks) is showing Blocking in the right places for us to get cold weather.

So if you're looking for snow then patience is required, as it looks like going into Jan, it could turn into something special.

 

[Flex Your Head]

Cheers [MENTION=7321]casbom[/MENTION]. No idea how an SSW can be 'forecast', but it would certainly have the potential to liven things up a bit!
I'd love some snow at Christmas - I can only remember one white Christmas, and that was waaaaay back in the 70s - but I'm happy to wait until Jan if there's a chance of some decent wintry weather. In fact, anything but murky, dull, windy and mild will do.

 

[Flex Your Head]

Met Office long range update could be of interest...

Through the first half of January there is an increasing likelihood for it to turn colder bringing the increased risk of winter hazards, especially frost and fog. Some snow is also likely with temperatures expected to fall below normal. However, there is uncertainty in the timing of this change to turn colder, and it could come before the end of December..