Sometime this week you will probably note from your calendar, read in the newspaper or hear on radio or television that it’s the first “official” day of summer. But is it really? And what makes it “official”?.jpg)
First, take a look at your calendar. It probably has a notation on Sunday, June 21st to the effect “First Day of Summer” or sometime “Summer Solstice”. This is true if you live east of the Mountain Time zone. Otherwise, your calendar is wrong! Charts showing the dates and times of the solstices and equinoxes are usually expressed in terms of Greenwich Mean Time (GMT). But with an eight hour time difference between Greenwich (i.e., London) and the Pacific coast, about a third of the time the solstice may occur a day ahead on some calendars. That is the case this year, when the solstice is at 5:45 am GMT on Sunday, June 21, 2009 which means 10:45 pm on Saturday, June 20th.
Confused? But should the solstice be the beginning of summer, official or otherwise? After all, the solstice is an astronomical not a meteorological or climatological event. It’s when, in the case of the summer solstice, when the earth’s orbit has reached its farthest north, and highest in the sky, position. However, some scientists argue that summer should be the three warmest months.
Sounds logical, IF every place has the same three warmest months. In most locales that works just fine with June, July and August (in the Northern Hemisphere) being the warmest. But when you are dealing with the complexities of the California’s Mediterranean climate these conceptions go right out the window. If we start in Vacaville, about 50 miles northeast of San Francisco, we do indeed see that June, July and August are the warmest months. But, going 50 miles south to San Jose, the warmest months are July, August and September. And in San Francisco, the three warm months are in fact August, September and October!
So remember, summer starts Saturday night, at 10:45 pm. Maybe.
Jan Null, CCM
SF Weather Examiner
jnull @ ggweather.com
For More Information
Definition of Solstice
Equinoxes and Solstices
SF Bay Area Climates
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