one is never bored due to being puzzled by how much one does not know . Looks like everyone except me knows about jet stream that makes long distance flight duration longer or shorter depending on which way is headwinds. So I educated myself with the help of the most comprehensive educational resource (W of course) and read through this The Jetstream - What It Is and How It Affects Our Weather - Netweather.tv and maybe someones with experience would care to explain if the jet stream is predictable enough to know before you take off, or will one know when up there?
It is reported and forecast like any other weather phenomenon, including likely areas of turbulence, and the likely intensity of the turbulence so you can adjust planned flight levels, and therefore, planned fuel loads prior to departure. The forecast is usually pretty good.
Routes are often changed to take advantage of a good tail wind, or to avoid a severe headwind, even on shorter routes nowadays. Fuel efficiency is king given the current fuel prices!
I am not sure if there is a free website that will allow you to see the relevant charts with the jetstream marked up, but I am sure that someone can point you in the right direction.
probes - Yes, Jet Streams are predictable and are shown on the weather charts that pilots collect at briefing, they are usually shown as a thick black line with an arrow head and the flight level(s) and speeds that it can be expected at.
In the airline world, long before the pilot sees the chart, the briefing officers will have fed the flight plan into the computer, which has also been fed all the met. information, and the flight plan produced will pick a route that either maximizes the tail wind component or minimizes the head wind component, subject to any rules governing the airways and any overfly restrictions published by the various nations.
Problems can and do arise when the head wind component is a lot stronger than forecast, personal experience is a JS of 220kts over the North Pacific that was forecast at 170kts, we had to stop off in Osaka for fuel when on our way from San Francisco to Hong Kong.
Not at home at the moment so can't reproduce a chart for you showing the JS and where you can expect to find it. Plenty of expertise here on PPRuNe so hopefully they will be along shortly!
The North Atlantic tracks vary from day to day according to the position of the Jet......and get devised and promulgated by ATC.
This can have a profound effect on the pattern of domestic airspace traffic here in the UK......we often talk of a "northabout" day for example when everyone and his dog wants to head North over the UK to start their North Atlantic crossing up near Stornoway or somewhere similar, a few days later, and aircraft will be going out through Lands End or thereabouts
Slightly off topic, Probes, but jetstreams are sometimes, but not always, accompanied by an area of severe clear air turbulence (CAT) on either side (think of the jetstream as the motorway, and the areas of CAT as the hard shoulders.) Once you are in the jetstream, the CAT is not a problem, and you are either zooming along happily anticipating a cold beer an hour earlier than usual, or else crawling across the chart, wondering if you're ever going to get there (see parabellum's post above).
that's another thing that's the source of constant awe. So, even the regular flights are different depending on what's going on 'up there'? And, as you know now I'm dumb anyway, I could as well confess I used to think planes fly mainly because they've got wings... and never thought about the pilots' and ATCs' component in the lot.
The funny little arrows point into wind and the markings are a chevron for every 50 kts, a large tick for 10 kts and half a tick for 5 kts. The speed of the jet over Newfoundland is 150kts. South of Ireland, it's 85kts.
The jet is a strange beast with the strongest winds being found in the polar night jet i.e. the months when the pole is in permanent darkness. I think I was told that 300kts is not unknown and the jet can be sometimes found at extreme altitudes at around the 50mb level. 300mb (30,000 feet or so) is more common.
Riding The Jetstream by John Christopher is an excellent book describing balloonists attempts to use the jetstream to fly as far as possible culminating in Bertrand Piccard and Brian Jones (great bloke) making it all the way round the world in Breitling Orbiter III. A quick trip to the south american river website is well worth the money.
Roughly speaking the surface stuff, eg Atlantic depressions are usually dragged along under the jet. that's why we've had a mostly mild winter, the polar jet has been to the north of the UK allowing SW'lies to dominate.
If you look at the current jet stream analysis (Saturday afternoon) together with this satellite animation, you'll see a strong airstream south of Ireland sweeping into France directly below the jetstream:
Their paper balloon bombs certainly were helped by the jetstream although I doubt the Japs knew anything about it. The B-29 pilots reported being helped or hindered by strong winds at altitude although they too didn't really understand what was happening. I recall a post war Avro Lancastrian on a westbound flight over the Andes descending through cloud at the appointed time only to find that they had yet to cross the mountains due to flying into a headwind jetstream. They probably didn't have more than a second to realise they were heading into cumulo-granite.
Probes. Getting a flight in the air is a bit like a Formula 1 team effort. There are lots of people in lots of disciplines who bring bits of information together with the pilots making the final decisions, and the final execution of the flight. Unlike F1 who do it every other weekend airlines do it many times every day.
It is not unusual for a flight to be about to close the doors prior to departure to be given a change of route by the flight operations or flight planning department at the airline HQ because of a late change of conditions along the route. Reasons can be things like: thunderstorms causing a lot of small diversions (a bit like negotiating potholes in an otherwise straight road); an airport closure causing diversions, thereby taking up controller capacity and airspace; a change in forecast weather conditions a bit like parabellum described. At that point the crew have to make a decision about whether they have sufficient fuel for the new flight plan, or if they need to uplift a bit more. A high speed jet stream headwind may not warrant rerouting, but may be better overcome by changing flight level, usually to a lower level, but a lower level means a higher fuel burn. If the aeroplane is at or near it's maximum take off weight, or maximum performance for the departure airport then something else might have to give, ie unload some luggage, or recalculate performance or departure technique. In almost all instances something can be done quite, but one has to be aware of the options that one has, and to think fairly quickly through which one will be most appropriate.
The japanese certainly noticed the jet stream as early as the 1920s, but their meteorological science was pretty much ignored by everyone else.....a German probably coined the term in 1939 or thereabouts, but here in the West a certain gent called Wiley Post first made use of the phenomenon between the wars.
To some extent, one can actually SEE the Jet Stream acting locally, as viewed from the ground. The Jet typically runs much higher than most clouds that are visible due to holding a lot of water vapour condensation, but the presence of high-velocity winds "herds" these lower level clouds and entire weather systems in long-reaching streams and curves that the eye can discern. View from above is much more informative than below, of course, which is one great benefit of those orbiting thingies we have now. Using those an armchair Jet-spotter can probably approximate a fair percentage of the forecast patterns that the Meteo folks turn out from more rigorous analysis.
One can imagine that Japanese fishermen, watching systems of clouds moving east across the Pacific and perhaps following while sailing under long-duration Jet Stream patterns could infer the potential speeds and stretch of distances that balloons might follow.
Some fair number of the things reached US coasts, IIRC.
Once done a TPE - LAX in the 74' with 220 knots right up our clacker - and not much CAT either. The TAT barely moved the whole trip. With 730 knots average GS we were really bloody whistling!
. Looks like everyone except me knows about jet stream that makes long distance flight duration longer or shorter depending on which way is headwinds. So I educated myself with the help of the most comprehensive educational resource (W of course) and read through this 
and never thought about the pilots' and ATCs' component in the lot.
