Scott Overpeck
While all of you were chasing cold core storms, down in SE Texas we had what resembled more of a warm core tropical system. Or so it seemed. Flash flooding is not as glamorous as a good supercell, but 6 inches of rain in one hour may raise a few eye brows. Just to explain the set up, aloft we had a very diffluent jet with the polar jet wrapping around the closed cold core low and the sub tropical jet screaming off to the east across Mexico and S Tx. At the surface we had outflow boundaries from the previous day's convection which with the aid of another line of convection Friday night/Sat morning set the stage for strong sfc convergence. And for good measure we'll throw in a 40kt LLJ from the SSE off the Gulf. Precip water values over the area were approaching 1.8 inches which is 2 standard deviations above normal for this time of year. The end result was a cluster of storms with very high rain rates. We also had a few storms that were spinning, one reported EF0 tornado in Galveston Co that had a nice couplet with it that afternoon. The cluster of storms moved into the Houston area where radar estimates hour rain rates around 4-5 inches. This cluster eventually started to become more organized, with some bowing segments, one of which causing damage across SE Houston and parts of Galveston Co. A meso low had developed in the vicinity of the coma head of the bow. Training storms back to the SW had quickly developed on outflow from these storms. In the end, these storms produced observed rainrates of 6 inches in an hour. Some stations reported an inch or more of rain in just 10-12 minutes. Our office had 7.88 inches of rain with other areas around League City/Dickinson picking up as much as 10 inches in just 1.5 to 2 hours. I had not seen that much rain fall so quickly. Some areas flooded more than Hurricane Ike (those not prone to storm surge). Drainage systems backed up since they could not handle the high rain rates. Below is the PNS from the office of the rainfall totals which are 24 hour totals. I also included a couple of composite rainfall maps to give you an idea of the impacts.
Public Information Statement
Public Information Statement
