MetStat is a company that provides “detailed precipitation analysis” and “weather frequency analysis” to industries like utility companies that need to know where to put their infrastructure so it won’t be damaged by extreme weather events. It has now released an analysis of Hurricane Harvey, which finds that the storm was a once in 25,000 year event. In some locations, it resulted in an almost unimaginable once in 500,000 year event, which translates into a 0.0002% chance of such an enormous deluge happening in any given year. Probabilities that extreme “are calculated by extrapolating the distribution curves for precipitation observed over the last century,” MetStat’s Shauna Bokn explains.
To do its analysis, MetStat used an approach based on “average recurrence intervals.” The analysis looks at how long we would have to wait for a Harvey-level deluge to occur again in a given area, based on historical rainfall records. Bokn notes that “although extremely rare, rainfall statistics of this nature are routinely computed by companies like MetStat to ensure the safe operation and design of large dams and nuclear power plants.”
According to Think Progress, MetStat’s post-storm analysis found “an interesting atmospheric setup was present that allowed it to stay alive for so long; bringing devastation over such a widespread area.” In particular, “the jet stream was located at very high latitudes, allowed for very light wind shear over Texas, and this aided in the lack of movement for Harvey.” Noted climatologist Michael Mann explained while Harvey was happening: “The kind of stalled weather pattern that is drenching Houston is precisely the sort of pattern we expect because of climate change.”