At 1:18 UTC (10:18 EDT), a United flight en route from Houston to LaGuardia encountered severe turbulence along the coast of TX, just west of the LA border. Injuries of both crew and several passengers were reported, and the pilot was forced to make an unplanned landing in St. Charles, LA.
The composite radar reflectivity at 0110 UTC, several minutes before the event, showed echoes of only around 25 dBZ, which if noted on the pilot's radar would likely not have caused concern. In fact, the pilot may have chosen this route as a way to get between the broad area of convection to the north and the already developed cell in the very SW portion of LA.
IR imagery also showed similar features, with the the coldest returns well north in the broad area of convection and in the cell in SW LA. Again, given this imagery, the route which the plane took would seem to be the 'best' place to fly the gap.
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| 120613 115 UTC IR imagery |
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| 120613 110 UTC Radar composite reflectivity |
What the IR imagery did not pick up on, however, was a rapidly developing cell buried beneath the large cirrus shield of the broad area of precipitation over SE TX. This cloud cover also prevented algorithms such as the UW-CIMSS Cloud Top Cooling (CTC) and the UAH SATCAST from picking up on this developing convection. By 0145 UTC the radar imagery showed echoes in the 50 to 55 dBZ range. Additionally, the IR imagery was showing a small area of cooler temperatures in the same area.
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| 120613 145 UTC IR imagery |
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| 120613 145 UTC Radar composite reflectivity |
By 0200 UTC, the radar imagery showed a mature cell of 60 dbZ.
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| 120613 200 UTC Radar composite reflectivity |
It looks as if this incident was an very unfortunate case of 'wrong place, wrong time'. Based on the IR and radar imagery shortly before the incident, the area actually looked relatively docile, making it a good place to fly the gap. However, the cirrus shield hid the rapid development occurring the lower levels, and the United flight looks to have crossed into the area during the worst possible moment...the time in which the updraft would have been significantly intensifying.
It should also be mentioned that the incident took place at 0120Z which is right at sunset. Add to that the cirrus deck from the storms to the north and west and it was getting to that near-dark time where it is more difficult to pick out features like clouds. Also, the storm didn't start producing lightning until after the aircraft had passed so that wasn't available to aid the pilots.
ReplyDeleteThe aircraft was on its ascent flying between FL180 and 240 which would have been the area of near maximum updraft speeds. The convection itself formed along an apparent outflow boundary which aligned itself with the path of the aircraft. So the turbulence would have lasted for several minutes.
The aircraft could have avoided the turbulence if it had flown 10 miles to the north or south but given no visual reference, no echoes on the aircraft radar and no lightning, the pilots were almost flying blind.
It really was a case of being in the wrong place at the wrong time.