Jet stream

[Cookie]

I hope I will be able to explain this well and hope posted it in the right place.

I have a very basics knowledge of the jet stream and how it works etc.

I was wondering if someone could explain to me why the jet is a further south as the moment and has been for a while and which is sending the Low pressures further south.

By the standers of last winter where I stay has been very calm, last year we had low pressure after low pushing in, sometimes more then 1 a week.

I have also noticed that in the previous 3 winter I have been on lewis, ( this being my 4th) the winter was again very windy 2004/05 with the huge wind storm on 11 and 12 jan, then the following winter 05/06 was very calm compared to the previous winter. as mentioned above last winter 06/07 was very windy and what calmac called their worst winter in 30 years.

also what would cause the jet to move further north again?

thanks any response will be very helpful.

Richard.

Edited January 15, 2008 by cookie

[tropical madness]

heya,

my knowledge of the jet stream is rather limited aswell but a thought popped into my mind. I may be completely wrong so sorry if i am lol but i thought its worth mentioning.

Isnt the jet stream in the Atlantic strongly influeced by the North Atlantic Oscillation??? im sure i read somewhere that if the NAO index is in the +ve regime, the pressure gradient between the Icelandic Low and the Azores High is large, hence strengthening westerly winds (jet stream) and bringing all the crap towards the UK. Saying that ive just checked on wikipedia for a quick explanation (i know its not professional, but a university student relies on it for a quick answer hehe)!

It says "A large difference in the pressure at the two stations (a high index year, denoted NAO+) leads to increased westerlies and, consequently, cool summers and mild and wet winters in Central Europe and its Atlantic façade"

ive also looked into the current NAO index (attached) to see if it is indeed in the +ve regime...and it does reveal that this is the case, despite being weak, since ~December 23rd of last year. Which would I guess explain a strengthened jet stream bringing all the onionse in one after another from late last year. pardon my language! but you have to agree with me on that one! lol

As for why its further south than usual or its meridional movement, i havent got a clue as of yet but Im guessing its partially to do with the NAO again and the balance of these pressures. Im guessing that the Icelandic low is stronger than usual, dominating the region and pushing the jet stream further south! anyways i hope this brought a perspective on what might be causing all this wind and rain!

[BrickFielder]

The jetstream is where cold air from the north meets warm air from the south up in the atmosphere and is a strong ribbon of high winds. How far north it is is determined by a mixture of factors of which the artic oscillation is one, but you also need to look at sea surface temperatures and la nina as well as the state of the stratosphere and where the winter polar vortexes set up. Your best chances of change during winter are from blocked patterns upstream which is likely to happen soon and from stratospheric warming which looks like it may be on the cards. Be warned that wet and windy can change to icy cold when the pattern does change.

What goes on aloft

[dogs32]

I hope you dont mind me asking a Q here Cookie......The jet stream as been on my mind too.

If the Jet stream as been this low now for a long time...Does it mean its got a good chance of moving North before summer...meaning a long hot summer??

[Cookie]

The jetstream is where cold air from the north meets warm air from the south up in the atmosphere and is a strong ribbon of high winds. How far north it is is determined by a mixture of factors of which the artic oscillation is one, but you also need to look at sea surface temperatures and la nina as well as the state of the stratosphere and where the winter polar vortexes set up. Your best chances of change during winter are from blocked patterns upstream which is likely to happen soon and from stratospheric warming which looks like it may be on the cards. Be warned that wet and windy can change to icy cold when the pattern does change.

What goes on aloft

thanks mate great link

I hope you dont mind me asking a Q here Cookie......The jet stream as been on my mind too.

If the Jet stream as been this low now for a long time...Does it mean its got a good chance of moving North before summer...meaning a long hot summer??

no I don't mind

[BrickFielder]

I hope you dont mind me asking a Q here Cookie......The jet stream as been on my mind too.

If the Jet stream as been this low now for a long time...Does it mean its got a good chance of moving North before summer...meaning a long hot summer??

As the jet is the boundary between cold and warm air it depends on how much cold air builds up in the artic , how much spills out and when the stratospheric vortex breaks up. Residual La nina does not bode well according to many forecasts for a dry summer, in other words I don't know of any statistical link between winter and summer jet stream patterns other than through sea surface temperatures.

[dogs32]

As the jet is the boundary between cold and warm air it depends on how much cold air builds up in the artic , how much spills out and when the stratospheric vortex breaks up. Residual La nina does not bode well according to many forecasts for a dry summer, in other words I don't know of any statistical link between winter and summer jet stream patterns other than through sea surface temperatures.

Thanks...I just thought seeing how the jet stream is swaying this low for such a long time that the chances are higher for a long hot summer.....One can hope its about time we had one ..cheers

[Stratos Ferric]

Thanks...I just thought seeing how the jet stream is swaying this low for such a long time that the chances are higher for a long hot summer.....One can hope its about time we had one ..cheers

Mean latitude is only one factor. The jet does indicate the point in the atmosphere where the thermal gradient is steepest, the wind effectively blowing at right angles across the gradient. A number of factors are at play, and as BF infers, in simple terms the location of the jet represents the budgetary balance between cold air to the north and warm to the south, that's why the average movement is always towards the summer pole on average (or, more specifically, it drifts with the thermal equator which tends to lag the apparent movement of the sun by around 6-8 weeks).

At the surface, however, what matters as much is the general nature of flow of the jet, specifically speed and sinuosity. If the jet is running at, say, around 53N at our longitude, then we are close to the boundary of polar and tropical air masses. The condiitons at the surface, however, could be wide ranging. If the jet is unstable (sinuous or broken) we might have HP at the surface, and dependoing on whether we are ahead of, or behind, the loop in the jet, the HP might be W or E of us, meaning a surface flow could either be from a cold or a warm source, depending on the season as well. A flatter jet, as we saw last summer, will tend to introduce a loing series of depressions at the surface, much as we have also seen this past week.

It's too far out to say what summer might do, though a long continued run of relatively close to average months would be unusual.

[Cookie]

are their any signs of the jet moving further north?

[Gibli]

are their any signs of the jet moving further north?

Try looking here on the netweather site for the next 10 days or so

http://www.netweather.tv/secure/cgi-bin/pr...21297dd6ada6e10

Or

http://www.meteociel.fr/modeles/gfse_carte...de=0&mode=5

Click on 'anim' at top left of the map and wait. Also shows the whole northern hemisphere (Carte Hemi nord) - final option above the chart. These will give a good indication if the jet is likely to move north. (Suite) belowT+180 leads to T+ 192 -384.

Good luck

Gibli

[Cookie]

dose look to be on a more northerly direction from middle of next week.