Aviation In Canada

Monday, April 25, 2005


Well, according to the public forecast, the thunderstorm season is upon us here in the maritime provinces. I saw "risk of thundershower" in yesterday's forecast, and again today. The storms we see tend to be short and weak compared to other areas. We have our occasional doozies, and I enjoy every minute of them -- when I'm not working. Personally, I hate hearing about lightning anywhere near an airplane I'm working, especially the light aircraft. A lightning strike can not only reduce electrical systems to a pile of smouldering circuitry, but the shear force of a lightning strike can rip holes in airplane skin. The heat could, if it struck a moving surface, weld it to the nearest non-moving surface, compromising the control of the airplane. The turbulence within a cell can be deadly, too.

BTW, there is no such thing in aviation weather as a "thundershower". TSSHRA, the METAR reporting code often read as thundershower, is actually "thunderstorm and rainshower." In the old days of SAs, before METAR, TRW was the code for the same phenomenon, and one thing that I appreciate about that is that the intensity ('-' for light, '+' for heavy) would describe the individual items. For example, T-RW was "thunderstorm and light rainshower" -- in SAs there was no such thing as -T-RW, which would have been read as "light thunderstorm and light rainshower". Thunder was either considered moderate or heavy (for a particularly active storm) but there was no "light thunderstorm". In the METAR sense, -TSSHRA exists as a notation, since the intensity (the '-' sign in this example) applies to the precipitation, not the individual phenomena descriptors (the TS and the SH) within a phrase. This leads people to read it as "light thunderstorm and rainshowers".

One of the most detailed pages I've encountered yet about METAR coding and reporting can be found here: