Summer 2017 - General Discussion

hatrickpatrick wrote: »

Seems that the root of the upcoming change in Weather is that the Jet Stream is about to take a southward plunge. I have very little knowledge of how the jet stream works (as in, what factors determine where it will be positioned at a given time) but to those who do, what conditions have to be in place to cause it to push northward and therefore allow high pressure to build from the south?

You have to know what the Jet Stream is first of all. The Jet Stream is a ribbon of air high up in the atmosphere that brings all the low pressure systems across Ireland. It's typical of the Jet Stream to go straight through Ireland which would bring very unsettled weather. However, the temperatures are very changeable with this kind of setup and there is no guarantee what sort of temperatures you can see. When the Jet Stream is on a northerly track so up to Iceland or Scotland, it gives away to high pressure building up from the south and with this, temperatures are above average because winds are coming from a southwesterly, southerly or southeasterly direction. As a result of course, the source of air is coming from southern Europe which can be very warm. December 2015 had winds coming from a straight southerly which meant for its extraordinarily warm nature. When the Jet Stream is on a southerly track, it means that high pressure either builds over us or to the north. This in turn leads to northerlies or easterlies. For northerlies, high pressure has to be over Greenland and Iceland with low pressure to the east of the UK or over Scandinavia. For easterlies, high pressure has to be up to the north of Ireland or over Scotland. May 2017 just gone was a very easterly month for example. If this is the case, the temperatures will normally be on the cool or cold side. The odd one out to this however is when the winds are coming from the east in Summer, especially so in July, August and September. May and June less so. Winds are coming off a cold continent in Winter thus why easterlies are cold then but in Summer, winds are coming off a warm continent thus why easterlies are warm or even hot then. When there is a large contrast between the temperatures in the Atlantic Ocean or North America aka the warm air and cold air fighting against each other, the Jet Stream tends to get powered up. Winter 2013/14 was a very cold Winter in the eastern seaboard of the USA. This deep cold air did not mix well with the mild air trying to push up from the south of the USA at the same time thus why the Jet Stream became more powerful. As a result, our Winter 2013/14 was exceptionally stormy thanks to this. A southerly tracking Jet Stream, like in much of 2010, Summer 2012 and March 2013, is more frequently to happen if the Jet Stream is not that powerful.

With all that considered, I think it's time to truly answer your question on what causes the Jet Stream to be in the position it does be in like on a northerly track this past week. Well first thing is the Season you are in. You might be like, how does Season affect the Jet Stream as you have seen plenty of different "seasons" in Ireland as in March 2013 be Winter or December 2015 be Summer :pac:. Well in Winter, the Jet Stream tends to be more powerful as a result of a large temperature gradient/contrast between Arctic and tropical air masses. This goes back to on why I think we're getting stormier winters because of Global Warming. The warming adds energy to the Jet Stream - and creating an even larger contrast between the air masses. In the Summer, the Jet Stream tends to be weaker as a result of a much less extreme contrast between air masses. The Jet Stream is said to follow the sun as it moves north with warm air and south with cold air. A powerful Jet Stream has the frequency to change position more so than a weak Jet Stream - thus why you can see these big swings in Winter from like daytime temperatures of 13-15c one day then 4-6c the next day.

Another thing is the Coriolis Effect - basically Earth spinning on its axis if you don't know what it is. The Jet Streams flows east all the time. In other words, you won't see the Jet Stream flowing towards the west of Ireland from the east. However, whilst the Jet Stream flows east all the time, it often meanders across the atmosphere. These meanders flow slower than the rest of the air. They are called Rossby Waves. They move slower as a result of the Coriolis Effect and turn west in respect to the flow that they are embedded in.

There is no specific factor on why the Jet Stream can change position but there are plenty of signs showing that a more powerful Jet Stream has the ability to change position a lot. It all depends on how tight the gradient between the air masses are, the Season and the Coriolis Effect.

EDIT: Btw, it's not impossible to have powerful Jet Streams outside of Winter just that it's much more difficult to do so as the Arctic or cold air masses are less intense to contrast with the tropical air masses.

DOCARCH wrote: »

27c at Phoenix Park at 1200.

Can't tell you what temp it is in Dublin 16 due to the fact that I am in Lanzarote....where it is not as warm as the Phoenix Park!

Ditto, although I'll be able to pull my up weather station history when I go back.

DOCARCH wrote: »

27c at Phoenix Park at 1200.!

I reckon it should go north of 30c so. Peak heat on days like this seems to be 5pm so a long way to go.

28C at Phoenix Park

27C at Casement

A slightly less warm 25C at Dublin Airport with a 12 knot SE breeze

Currently at 27.2c here and my June record is 27.8c. Only thing that is holding me back is that breeze.

Dr Crayfish wrote: »

I can't remember it ever feeling this warm in Dublin, it's great. Going to get my last sea swim in of the nice spell this evening. Can any experts here see any more of this weather this year or is that us done for the year? I wonder which is rarer... weather like this or persistent snow and cold temperatures?

Did you see my Summer forecast I posted on May 29th?

Dr Crayfish wrote: »

I don't know, I find it difficult to remember everything I've read on the internet

http://www.boards.ie/vbulletin/showpost.php?p=103654646&postcount=110

squarecircles wrote: »

met eireann going for 29 degrees maximum



the cool air is already here on the coast in Mayo.
horrible overcast day with a chilly breeze.

I'll send over the fella I just met wearing a parka jacket, I don't know how he hasn't melted in it.He's dressed for Mayo weather,not Wexford weather.

Well despite the passage of that active cold front this morning, skies and atmosphere continues to be heavy here. Really quite dark under a dense stratus layer that hasn't shifted all day.

Hooter23 wrote: »

A nice chill in the air in Galway

There is? Send it up this way please...

4pm now. I'll give it another hour or two before I call today a dud. Cloud cloud cloud sums it up. Very disappointing. Reaching 26, sure, an achievement during an Irish summer but Saturday/Sunday we got there WITH sunshine.

Was hoping today would go that little step further based on the buzz generated. Won't rule out a 2nd temperature peak here anyway, just need the cloud to break.

Good to see some spots getting a bit more luck and heat though. Hopefully we can beat 28 this summer.

Still 28 at the Phoenix Park, getting sunnier now so a long term record could be broken? 28.7c on June 6th 1950 is the one to beat.
Records began there as long ago as 1855.
Interesting that the June record there wasn't made in 1976 or 1995 when both months had hot endings.
Edit; just saw murrisk post above, I was looking at the 1500 reports so no record broken today.

Well my June forecast was shhht first half good second half

unfortunately the second half wont be all good as downhill for the rest

July forecast starting psss poor then picking up slowly until the middle of the month and then thunderstorms till the end. ... more or less