San Francisco chilled by coldest July in years, after hottest February temperatures in three decades

Video: Friday Morning Forecast With Julie Watts

The coldest winter I ever knew was July of 2016 in San Francisco. Literally, we had warmer evenings back in mid-winter. With the month's climate data now in, the average high temperature for July only hit 65.2--the coldest July in six years--while February's average daily high was 66.4 degrees as measured in downtown San Francisco.

While July felt downright chilly, August so far is on track to have colder afternoons than February too, averaging just 65.7 for the daily high temperatures so far.

Now, to be clear, we're talking about the temperatures we notice -- the daily high.

February's lows still get colder than July's lows, bringing the overall average temperatures down, but most people aren't awake to feel the daily low temperature overnight. It's those afternoon highs that feel so frigid. February enjoyed 77 degrees one sunny afternoon this year, while we had one July afternoon where it never got above 59.

As I walked upwind from the Chronicle toward BART on a "hot August night" this week, face pelted by a fog so heavy it could be more accurately called drizzle, and with hands in my pockets to avoid the chill, I wondered just how cold our summer will remain.

Today, I actually put my coat on. Indoors.

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The real story though is not the summer cold, but the winter heat. Downtown had the hottest average high temperatures in February in 28 years.

Blame the ocean. The sea surface temperature off the coast is like setting your home's thermostat to either "Heat or Cool."

The cooler the ocean, the cooler the city by the ocean. Even as the Central Valley broils under 105+ degree heat.

The ocean water has been around 52 degrees off our coast this summer.

The difference in summer and winter temperatures is most noticeable in downtown San Francisco. If you explore the official climate records using the weather station at San Francisco International Airport, you won't find the same phenomenon, because the cold blasts in July don't impact the airport as much as they do downtown.

The coldest July average high temperatures on record for Downtown San Francisco? 1962, when the average high temperature barely made it out of the fifties: 60.4. (Records have been kept for this station since 1921.)

September and October are coming, for all your heat seekers. Those are our warmest months of the year.

EDITOR'S NOTE: An earlier version of this story referenced a correlation between El Niño and La Niña conditions influencing our coastal ocean temperatures. After studying conflicting analyses of the impacts of the equatorial ocean waters on our local micro climates, we have chosen to remove that discussion. Continue reading for why.

While forecasters draw many different conclusions about the cause of our incredibly complex ocean temperatures and their influence on our micro climates, one meteorologist says 40 years experience suggests caution.

Jan Null from Golden Gate Weather Services tells SFGATE, "When you have a long pervasive El Niño, you are warming up the entire Pacific, but we're much more influenced than normal wind patterns than anything going on in the tropics."

He cautions that all the stories about warm water fishes or other warm water irregularities spotted along the California coast are not necessarily because of El Niño, and our summer's cold ocean temperatures this year and in other years are not necessarily directly correlated to La Niña's colder ocean conditions either.

Null explains that the warmer water we had this past winter actually pre-dated El Niño occurring, and he says the biggest phenomenon influencing our warm winter was the "warm blob" -- a strange mass of warmer water that lurked off the coast, up into the Gulf of Alaska, dramatically influencing local conditions.

As for La Niña right now?

The colder ocean temperatures have already formed along the equator indicating a La Niña is forming, but it must continue to be colder than normal for three months before a La Niña condition is officially called.

So, parsing the weather speak, you could say "a La Niña appears to be forming, and the ocean is at La Niña levels, but it's not yet a La Niña, because it hasn't lasted for three months."

With that, we'll just say, enjoy what Jan Null calls "Fogust" in San Francisco.