The Labor Day Heat Wave of 2017

Last weekend, the high temperatures around coastal California set many new records. Here in San Geronimo Valley, the same was true, but equally remarkable were the nighttime lows above the inversion layer--there were three nights near 80 degrees! On the valley floor, below the inversion, the minimum temperatures were close to 60 on the days when it was near 80 on the ridges, and warmed each day until a peak of 70 on Tuesday September 5th. This nighttime heat wave on the valley floor peaked two days after the daytime heat wave ended--and insects such as wasps seemed busier than ever that 70-degree morning. 70 was the highest minimum temperature I recorded in the last five years, beating 65 in 2014. Also remarkable--on Monday September 4th, the high temperature of 82 in Woodacre occurred before 8 am!

High and low temperatures each day for two ridge locations and one valley floor location.

The high of 107 on Friday was the highest temperature I've recorded in my five years of recordkeeping, and three other days this summer also beat the previous record of 99 in August 2015. The number of days in the 90s is steadily climbing, with 9 days in 2012 and 2013, 12 in 2014, 14 in 2015, 21 in 2016, and 23 in 2017. Since I miss 30-60 days per year, this is just a sampling, but it is clear that there has been a steady warming trend since 2012 for the warmest daytime highs.