The autumn equinox happens at 1:02 p.m. Friday, the official end to a Modesto-area summer that has been unusually hot.
But did it set a record, as measured by the number of days at 100 degrees or more? Yes and no.
The National Weather Service says yes, based on its thermometer at Modesto Airport at the city’s southeast corner. It has hit at least 100 degrees on 36 days, breaking the record of 34 in 1961.
The Modesto Irrigation District says no. Its downtown weather station has tallied 27 days over 100, but the record for that site is 33 days — in 1960, 1961 and 1984.
It might seem strange that the two stations vary so much in their counts of 100-plus days. But remember that it takes just a 1-degree swing to keep a given day from qualifying.
The hair-splitting aside, it’s clear that summer 2017 was a scorcher. What made it so hot?
“We just had a few high-pressure systems that were very persistent and didn’t allow for any air flow,” said meteorologist Hannah Chandler at the Weather Service office in Sacramento.
Our summers tend to have a few days here and there where the highs stay in the 80s or even the 70s. Not this year. The Weather Service has recorded 103 days at 90 or more this year. The average over the past 30 years is 86.
The hot summer came right after a winter and spring that brought the second-largest snowpack on record to the central Sierra Nevada. “It’s been a year of these anomalies,” Chandler said.
The equinox is considered summer’s end based on observation’s of Earth’s tilt. But the Modesto area can have 100-plus days into October, so it’s possible that the MID and Weather Service numbers will grow.
The extra demand on air conditioners meant more power generation by MID. It peaked at 697 megawatt-hours on Aug. 28, tying a record set in 2006, spokeswoman Melissa Williams said.
The Turlock Irrigation District had a record of 548.7 megawatts on Aug. 28, spokesman Calvin Curtin said.
“High temperatures create more demand for electricity, but we are well-positioned with a very diverse portfolio of generation assets and met the demand with no curtailments to our customers,” he said.
John Holland: 209-578-2385