I just finished a flight from RKSI to RJAA( using ASN) at FL390, where I encountered winds  246/204KTS, that is insane! I've never seen such a strong tailwind before. Are winds aloft like these common in that part of the world?

Jet Stream

Ohh yes, they can. Quite common down my part of the world ( Roaring Forties )

Jet Stream

Wow, been simming since 07, that was the first time I caught a ride in it!

http://earth.nullschool.net/#current/wind/isobaric/250hPa/orthographic=-12.36,40.66,671

Great link Doudou, now I can see why the uk gets all the bad weather from the US. Ha ha

 

 

Wow, been simming since 07, that was the first time I caught a ride in it!

 

Because you're finally getting accurate and complete wind data...

 

I know OPUS and ASN weather addons use the World Area Forecast System (WAFS) wind model with a high degree of resolution, usually 1x1 or even 0.6x0.6 degrees lat/lon at all the standard forecast wind levels. That means you get accurate coverage even in oceanic regions while minimizing or eliminating [horizontal] interpolation issues found with the relatively sparse or nonexistent upper level wind reporting stations in the default FS weather.  ASN also does a great job of vertical interpolation to avoid sudden wind shifts as you transition through different wind levels.  

 

That's also what makes a model, like Edouard posted, possible. 

 

Note: The WAFS wind model is sometimes referred to as GRIB winds, which is a misnomer.  GRIB is an acronym for GRIdded Binary, the file structure format used to store the data.

Because you're finally getting accurate and complete wind data...

 

I had a similar thing happen in Feb 2008 a few days before I bought Active Sky.  I was flying with the default, built-in weather and caught the tailwind from hell over China on a flight from London to Sydney.  I beat Qantas time on their first 747 flight by a couple of hours. 

 

Hook

 

 

I was flying with the default, built-in weather and caught the tailwind from hell over China on a flight from London to Sydney.

 

Other than shaving a couple hours off your flight, that had to be unpleasant with default FS weather wind shifts...LOL.

Because you're finally getting accurate and complete wind data...

 

I know OPUS and ASN weather addons use the World Area Forecast System (WAFS) wind model with a high degree of resolution, usually 1x1 or even 0.6x0.6 degrees lat/lon at all the standard forecast wind levels. That means you get accurate coverage even in oceanic regions while minimizing or eliminating [horizontal] interpolation issues found with the relatively sparse or nonexistent upper level wind reporting stations in the default FS weather.  ASN also does a great job of vertical interpolation to avoid sudden wind shifts as you transition through different wind levels.  

 

That's also what makes a model, like Edouard posted, possible. 

 

Note: The WAFS wind model is sometimes referred to as GRIB winds, which is a misnomer.  GRIB is an acronym for GRIdded Binary, the file structure format used to store the data.

ASN should get  a Gold Star award, since I began using it a little over a month ago, I have yet to experience a single wind shift, cloud pop or temperature fluctuations. I did a flight from Moscow to Sochi, Russia bout a week ago. On the approach plate for runway 6, it notes expected turbulence and downdrafts on final due to high terrain east of the airfield. Prior to ASN I would disregard such data....not anymore, as expected I hit a chop about 8 miles out from the airport that got my attention. Think I'll give Madeira a go next.

Other than shaving a couple hours off your flight, that had to be unpleasant with default FS weather wind shifts...LOL.

 

Actually, I don't recall any wind shifts at all.  It's been my experience that the worst of the wind shifts occur on the boundary between two weather layers.  For example, the weather layers change at 24000, 30000, 34000, 38000, so you'd get shifting at 27000, 32000 and 36000. I know it works this way when flying lower:  for example, layers at 3000, 6000 and 9000, wind shifts at 4500 and 7500.

 

Hook

Actually, I don't recall any wind shifts at all.  It's been my experience that the worst of the wind shifts occur on the boundary between two weather layers.  For example, the weather layers change at 24000, 30000, 34000, 38000, so you'd get shifting at 27000, 32000 and 36000. I know it works this way when flying lower:  for example, layers at 3000, 6000 and 9000, wind shifts at 4500 and 7500.

 

Hook

 

Yep, you are correct...and that's what I kinda figured might've happened to you as you transitioned those levels with such a strong jet stream using default weather.  Things must've been well-behaved that day. 

I just finished a flight from RKSI to RJAA( using ASN) at FL390, where I encountered winds 246/204KTS, that is insane! I've never seen such a strong tailwind before. Are winds aloft like these common in that part of the world?

I just looked at the North Pacific winds aloft chart at the aviationweather.gov site, and those winds are right on the money... It shows a 190 knot jet stream just east of Japan.

 

The jet stream is strongest in the northern hemisphere in winter, and it often reaches its peak velocity near Japan, or just to the east, over the North Pacific Ocean. There are a variety of factors that cause the jet stream wind velocities to be at their highest in this particular geographic area.