What causes the 10 degree temperature change between Miramar Way and Mira Mesa Boulevard?

Matt:

A while ago I was coming home from a job downtown, heading north on the 15. When I got to about Miramar Way, I noticed the temperature dropped what felt like ten degrees Then it seemed to warm up at about Mira Mesa Boulevard again. Other motorcycle riders have commented on this too. What might cause this?

-- Biker B, on the road

If you can find your thinking cap -- if it's not in the laundry or the junk drawer or balled up under your bed or something -- dig it out and put it on. Let's see if we could have figured this out without bothering Matt and the elves. So what's between Miramar and Mira Mesa? That's roughly the south-north boundaries of the Marine Corps Air Station. Lots of development south and north of there, but in between we have the Southern California version of wide open spaces. Smells like a clue to me. Let's call the U.S. Weather Service for their take on this microclimate zone.

"Weather Service..."

"Yeah, hi. We have a question here. Traveling north on I-15 at night, you get to Miramar Way and -- "

"...and the temperature drops."

"Well, yeah." Figure they get this question a lot?

"We get this question a lot."

"The answer better have something to do with the Marine base, or I'm out of a job." As luck would have it, it does. During the day, buildings absorb heat; at night they release it. All that dreary Mira Mesa and Kearny Mesa construction radiates more warmth than do the wilds of the air base. The coolness you feel might be enhanced by several canyons west of the base that funnel breezes toward the freeway. And cold air sinking down off Miramar Hill might settle in that stretch of freeway as well.