WEATHER
south-easterly flow. Meanwhile, north- western parts were under the influence of a much cooler airmass with Atlantic origins. This led to an exceptionally strong
thermal gradient across the UK, which created a very unstable atmosphere, giving rise to CB (Cumulonimbus) and thunderstorm development along this gradient, and the risk of severe turbulence for aviation in association with these storms. The boundary of the hot, to rather cool
conditions is represented by the warm front on the chart, with most of the storm development being just east of this along the trough line, running from the Midlands to south-east Scotland. Met Office Aviation Meteorologists,
had forecast the risk of thunderstorm development across the Midlands area, as seen in the following TAFs issued for East Midlands Airport.
TAF EGNX 131102Z 1312/1412 08007KT CAVOK PROB30 TEMPO 1313/1317 VRB15G25KT 3000 +TSRAGR BKN045CB PROB30 1322/1403 8000 PROB30 1403/1408 3000 BR=
TAF AMD EGNX 131728Z 1318/1418 07008KT CAVOK TEMPO 1318/1319 VRB15G25KT 3000 +TSRA BKN045CB BECMG 1321/1324 8000 PROB40 1323/1408 3000 BR BECMG 1408/1411 CAVOK=
SIGMETs were in force for embedded thunderstorm activity throughout the day, and there were thunderstorm warnings in force for many civil airports across England. (The amended TAF came out just after Jonathan had completed his planning for the flight back.) The list of
‘Despite the thunderstorms being further est than the pilot as ing the eects could still be felt an iles aa’
THE METARS FOR EAST MIDLANDS 13/09/2016 16:50 -
13/09/2016 17:20 - 13/09/2016 17:50 -
METAR EGNX 131650Z 02005KT CAVOK 23/19 Q1009=
METAR EGNX 131720Z 28018KT 9999 6000W VCTS SCT023 22/18 Q1010=
METAR EGNX 131750Z 32011KT 9999 SCT023 21/17 Q1010=
METARs below show the conditions at East Midlands Airport around the time the severe turbulence was reported: As shown above, between 16:50Z and 17:20Z (18:20 local time), there was a large change in wind speed and direction at the airport, while VCTS (thunderstorm in the vicinity) was being reported. This is likely to have been caused by strong downdraughts from the storm, hitting the surface and spreading out, reaching the airport despite the thunderstorm not being overhead. For this reason, the TAF had VRB15G25KT in the PROB group, because when these downdraughts spread out they can reach the airport from any direction, depending on where they have hit the surface in relation to the airport. It’s likely these winds being observed at
the surface will have been even stronger at 1000ft where the aircraft was flying. This sudden change in wind speed and wind direction, or ‘wind shear’, would lead to sudden turbulence, which could be severe for small aircraft. As can be seen from the METARS, the
18 CLUED UP Autumn/Winter 2016
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36