Yesterday the rain guage at Onion Creek/Hwy.183 at Austin, TX, operated by the Lower Colorado River Authority (LCRA), recorded 14.39 inches of rain (365.5 mm). In one day.
A Texas man, whose car was overcome by flood, escaped by jumping out of his car and climbing a tree. You can see a report here:
That amount of rainfall in one day, at that location, is staggering. The question is, how staggering?
Unfortunately I haven’t found historical data for that specific location. But I have found data, from the Global Historical Climate Network (GHCN), for nearby stations in Austin, TX. One should be advised that they don’t represent the exact location measured by LCRA, and it’s possible that there’s something unusual and unique about the Onion Creek/Hwy.183 location that induces storms to drop excessive rainfall amounts at that exact spot. But … what are the odds?
Let’s look at daily precipitation amounts for Austin’s Camp Mabry:
These data cover Jun. 1, 1938, through Oct. 8, 2015. Within that time range the maximum daily rainfall was 191.8 mm (7.55 inches) on Nov. 15, 2001. The amount recorded at Onion Creek/Hwy.183 yesterday was nearly twice as much.
The “survival function” of daily rainfall in Austin, for large values, very nearly follows an exponential distribution. If we fit an exponential distribution to the tail of the distribution, we can estimate the likelihood of getting 14.39 inches in a single day. It turns out to be a once-in-170,000-years event. But we should really fit a generalized Pareto distribution (according to extreme value theory), in which case 14.39 inches of rain in one day would only be a once-in-40,000-years event.
As I say, that’s applying the statistics for the nearby Austin-Camp Mabry station to the observation at Onion Hill/Hwy.183. And it’s possible the statistics don’t really translate from one location to the other, no matter how nearby they may be.
But any way you look at it, the rainfall measured in Onion Hill, TX, near Austin, was apocalyptic. The only thing less likely, is that Texas congressman Lamar Smith or Texas senator Ted Cruz will “get it.”