RainWatch 24hr storm totals

The first true storm of the season was a respectable one. While rainfall intensities were not statistically significant, the event did set a new daily precipitation record at Seatac (0.72″). It also provided more rainfall (1.52″) in 24 hours than is normal for the entire month of September (1.50″).

Running totals citywide ranged from 1.35″ (Maple Leaf Reservoir) to 1.77″ (West Seattle Reservoir). Maximum rainfall intensity appears to have occurred at Myrtle Edwards Park, where 1.31″ fell in a 12 hour period ending around 8:30 AM, when the cold front passed. (That 12-hour rate is 0.25″ short of a 2-year recurrence.)

Given the steady, long duration nature of the event, Seattle RainWatch issued just two alerts throughout, each for 1-hour accumulations just greater than the 0.30″ threshold. (See 24-hour RainWatch accumulation image above.)

A weekend forecast update will be published tomorrow, but another 6- to 12-hour burst of similarly intense rainfall is possible on Friday evening.