Aussie Bot

Here's a scan-by-scan breakdown of the thunderstorm cell that N722BD flew into. We've contoured the 30 dBZ surface, which signifies where moderate precipitation was present. The thunderstorm cell grew to 48,300 feet by 12:56 p.m., meaning that, at 12:48 p.m. when the plane flew through, it was still rapidly growing vertically. 15,000 feet of growth in under 20 minutes is a VERY intense updraft. Now what about icing? It's true that the ambient temperature OUTSIDE the storm was around minus-45 degrees Fahrenheit. That's generally too cold for icing, which requires supercooled water droplets – i.e. water droplets that remain a liquid at temperatures below freezing. Water sometimes is slow to freeze UNLESS it has something to freeze onto – like a cold surface (a plane). At minus-45, moisture would have already frozen into ice crystals, i.e. snowflakes, which aren't really dangerous to aviation. HOWEVER, the rapid growth of this thunderstorm cell 1.) carried LOTS of heat upwards, bending temperature surfaces and probably making the core of the thunderstorm cell 15 to 20+ degrees warmer. That warmth was probably amplified by the latent heat release of water droplets freezing, as my colleague Roger Edwards adroitly pointed out, and 2.) the swift updraft probably transported large, tropical raindrops upwards so quickly that some liquid remained even at altitude. A study in the journal "Nature" found that deep convective (thunderstorm) clouds regularly have supercooled water droplets down to minis-38 degrees, and it's probable that, at 35,000 feet, the temperatures inside this cloud were warmer. Therefore, while this wouldn't ordinarily be an "obvious" icing case, the forensic meteorology suggests icing as a probable contributing factor or cause. The NTSB will continue to investigate.