7.1.1 At Altitude
At level 500 hPa (around 5 500 m), a depression associated with a pocket of cold air (temperature < -16 °C) was centred over the Gulf of Gascony. It was moving from the southwest towards the northeast and arrived over the Paris region during the night. It was associated with the rear of the disturbance covering the southwest of the country.
An analysis of the meteorological situation at 12 h 00, performed using the Météo-France, Aladin model, with a mesh of 0.1° at heights of 100, 200 and 500 m above the ground, showed a small anti-cyclonic cell centred on the Seine et Marne which was moving north-east at forecast times of 15 h 00 and 18 h 00. Because of its progression, this cell maintained an easterly flow over the whole Paris region during the afternoon.
7.1.2 On the Ground
A succession of low-pressure areas stretched from La Coruna to Leningrad. At midday one of these low-pressure areas was centred over the Poitou and Auvergne regions and was moving northeast. In front of its warm front, in the cool wet air left by the previous day¹s disturbance, the cloud cover was essentially made up of cumulus and stratocumulus with little vertical development.
This slightly subsiding intermediate zone had a weak pressure gradient. Consequently, it produced variable winds of less than 10 kt, locally calm.
After the dispersal of morning mist at around 10 h 00, the increase in temperatures provided visibilities and ceilings which removed any operating restrictions on the aerodrome.
At 14 h 43, visibility was 15 km, the sky was cloudy with 2/8 Cu at 540 m, 2/8 Cu at 720 m and 5/8 SC at 1 020 m. The temperature was 19 °C and the humidity 74 %. The average wind at the threshold of runway 26 was 090°/3 kt and 320°/3 kt at the threshold of runway 08.
At 14 h 44, the average wind at the threshold of runway 26 was 020°/3 kt and 300°/3kt at the threshold of runway 08.
Note: wind measurements are taken every half a second and averaged over two minutes.
Between 14 and 15 h, the surface wind varied in strength at the two thresholds between calm and 9 kt and between 330° and 170° in direction. The runway was dry.
The meteorological dossier supplied to the crew consisted of wind and temperature charts with forecasts at flight levels 300, 390 and 530 at 12h and 18 h, two TEMSI charts for the north Atlantic between flight levels 250 and 360 for the same times and TAF, METAR and SIGMET reports valid for the destination and alternate aerodromes.