Turbulence
 

Heading for Heathrow from Jersey last night we were warned it might be a rough flight. About halfway the captain announced with a certain urgency that the seat belt signs were coming back on, and a few seconds later it was obvious why. Even at it's worst it was no doubt 'mild turbulence' in the great scheme of things, water bottles flying off tables ETC, and it only lasted a few seconds. But how did the captain know? Could he tell from the feel of the initially scarcely noticeable turbulence that it was going to get worse or was he warned of the bad patch of weather a couple of miles before we reached it?

There are a few ways.
1. Ride reports from aircraft ahead. ATC can forward the info to you as well.
2. Doppler radar can pick up horizontal shifts in rain = turbulence. (Not all aircraft have that capability. X band wx radar)
3. Conventional radar with amber or red returns. Good chance it'll be bumpy.
4. Preflight. Note the significant weather chart and the turbulence areas. Flight plan will have predicted turbulence on it (Ours do).
5. Wake turbulence. Often you can see the vortices.

If it was a few seconds, I'd go with a wake vortex or it was a smallish Cu cloud they couldn't get a vector around.

Thank You redsnail most informative.

Thanks for that. Given that it was dark and there were thunderstorms about I reckon the cu.

For those of you who don't speak Aviation-speak, X-band is 8.4 - 12,4 GHz radar and wx means weather.

Wx is an abbreviation from the days when radio communication was by morse, rx=receive tx=transmit are still used today, the other exes have fallen out of use. X-band was from WWII, the allies had the technology to transmit high-power radar at these frequencies using klystrons, the axis powers did not, so the band that was used was called X, X for secret. The other letters for frequency bands are equally cryptologic, except L ('low') band, 1240 - 1300 MHz. Some allies were confused between K and Q bands (there's no Q in Cyrillic, and the USSR were our allies in WWII, so these bands are known as Ka and Ku band.

Ku band radars can detect windshear directly, but are too short-range, heavy, thirsty, unreliable and expensive to mount inside aircraft radomes as yet. Expect to see Ku band radars in aircraft from the 2040s onwards, as the science progresses.

Dr Jeykl
Was there not the tail end of a Hurricane in Biscay yesterday. Mrs Mac in Porto reported torrential rain and high winds on Tuesday \ Wednesday night with flooding and substantial trees down. Not surprisingly you may have had a bumpy ride the other night as I believe it routed up Western Approaches and over NW France.

Cheers
Mr Mac

It was certainly gusty in Jersey and apocalyptically wet at times. But the captain specifically mentioned thunderstorms as a possibility before we took off.