Processes leading to a severe wind-shear incident at Hobart Airport

At 0149 UTC on 21 January 1997 an abrupt southerly wind change moved through Hobart Airport (see Fig. 1 for all place names used in this paper), with the surface wind shifting from 310/22 kn (gust 34 kn) at 0130 UTC to 160/15 kn (gust 31 kn) at 0156 UTC. With this change the temperature dropped from 37.2°C to 24.6°C over the same interval. At 0230 UTC 21 January 1997, Qantas flight QF617 was approaching Hobart Airport from the northwest and encountered extreme turbulence at approximately 500 ft altitude (the imperial units used here are those transcribed from the flight recorder records). Wind (temperature) changed from 315/31 kn (37.5°C) at 472 ft to 178/11 kn (32.8°C) at 396 ft. After descending through the wind-shear layer into cooler southerlies, the plane climbed rapidly and passed through a zone of southwesterly winds, with the temperature increasing rapidly again to the mid-30s (°C) at around 1200 ft altitude. A tabulated extract from the flight recorder data is shown in Table 1. The purpose of this paper is three-fold. In the first part, the frequency with which such wind shear events occur at Hobart Airport is reviewed, and the subsynoptic evolution of the low-level wind, temperature, and pressure fields around southern Tasmania on that day is documented. In the second part of the paper a high resolution mesoscale numerical weather prediction (NWP) model simulation of the event is used to both demonstrate the predictability of the event with Aust. Met. Mag. 52 (2003) 171-188