Weather over western UK Sunday 6 Oct

[OntimeexceptACARS]

Was on EZY403 BRS-GLA yesterday, we had moderate turbulence from early in the flight. The crew elected to descend from FL280 to 260 abeam Liverpool, then 240 a few minutes later, for the remainder of the cruise. Crew were looking for smoother air, presumably with ATC input on reports from other crews. Maybe not too unusual, but I can see from FR24 that some domestic flights were at similar levels, though longer haul flights remained higher.

Just wanted the thoughts of those more qualified than this SLF, how rare was this?

Unsure of best place to post, thought Tech Log closest.

OTEA

[Flying Wild]

Originally Posted by OntimeexceptACARS

Was on EZY403 BRS-GLA yesterday, we had moderate turbulence from early in the flight. The crew elected to descend from FL280 to 260 abeam Liverpool, then 240 a few minutes later, for the remainder of the cruise. Maybe not too unusual, but I can see from FR24 that some domestic flights were at similar levels.

Just wanted the thoughts of those more qualified than this SLF, how rare was this?

OTEA

How rare was what? Descending out of turbulence? It's completely normal.

Where turbulence is forecast, pilots will generally speak to ATC to see whether other levels are reporting smoother conditions. For passenger and crew comfort, we'd always aim to get out of the conditions unless it's a massive difference in cruising level - i.e. cruising at FL370 with turbulence reported from FL300 upwards, we'd be unlikely to descend due to the increased fuel burn lower down. That being said, it's not really an issue on this occasion as it was such a short sector.

[OntimeexceptACARS]

Well FW rare in the sense that most UK domestic sectors I take between Scotland and the south are assigned cruise levels between 310 and 380. Just seemed inordinately low, guess what I am really asking is how unusual were the wx conditions above that level?

OTEA

[giggitygiggity]

Originally Posted by OntimeexceptACARS

Was on EZY403 BRS-GLA yesterday, we had moderate turbulence from early in the flight. The crew elected to descend from FL280 to 260 abeam Liverpool, then 240 a few minutes later, for the remainder of the cruise. Crew were looking for smoother air, presumably with ATC input on reports from other crews. Maybe not too unusual, but I can see from FR24 that some domestic flights were at similar levels, though longer haul flights remained higher.

Just wanted the thoughts of those more qualified than this SLF, how rare was this?

Unsure of best place to post, thought Tech Log closest.

OTEA

This is just speculation but I imagine this is the reason for your low level.

The first picture shows your approximate route that day, the second one is a weather chart that tells us about jetstreams, turbulence and icing conditions. I’ve annotated the relevant bits. The chart is from the date and time of your flight, it’s called a Significant Weather Chart (SIGWX Archive: AVIATION WEATHER CHARTS ARCHIVE).

The long black line that I’ve marked shows a jet stream. It was in fact a very strong one. The numbers next to it say it was centred at FL310 and was 180knots in speed (three black triangles = 150kts and the three black lines = 30 knots so together the speed was 180kts or about 200mph). The jet stream is running north to south across the U.K. and perfectly follows your route taken. Therefore If the crew fly against it (heading north), they will be flying into a 200mph headwind at that altitude. Therefore they most likely have flown lower to avoid having to fly with such a slow ground speed. Their planned speed would probably be about 500mph. With a 200mph headwind they would only be doing a ground speed of 300mph which is rather slow. Flying lower burns more fuel, but avoiding the wind is also efficient. They were running behind schedule so probably decided to fly faster at a lower speed to make up time.

Where you get jet streams, you also get turbulence. The dashed line marks the turbulence area and the numbers next to it say the turbulence will 33,000ft and below (330/XXX). Further away from the core of the jet stream is likely to be better. The worst turbulence is as you enter the jet stream. That’s probably why they went up to FL280, found it was bumpy with a lot more headwind than below, so decided to return to a lower level.

They will still certainly be suffering headwinds at FL240 but considerably less than those encountered higher. This chart was produced at midday so so the jet stream would have moved further east by 50 miles or so which would have put your flight directly in the firing line!

To answer your other question, this weather/jet stream/scenario is entirely typical and is what has brought the U.K. the rubbish weather over the last week.

Hope this helps.

[Skyjob]

Having flown that day, I can certainly say this turbulence was present.
The winds at FL200 were nearly calm, but at FL220 they had increased to ~45 knots, by FL240 ~75 knots and at FL260 and above the winds exceeded 100 knots.

The wind speed change that rapid over such a relative small distance means the air becomes turbulent.
It's like placing a hose in a paddling pool and turning it on full, then look at the water surrounding the faster travelling water from the hose, it starts to rotate and become turbulent.