Clouds are a fascinating topic around here. Especially since they are poised for a major makeover.
Most of the world has a rainy season. From California to Bombay, three months of the year deliver most of the annual rainfall. What makes our region fascinating is that we do have a cloudy season — but not a rainy season.
We receive 36 to 40 inches of rain annually. About three-and-a-half inches a month. This is distributed pretty evenly among the 12 months. You’d think that our cloud cover would be just as even. It isn’t. We enjoy a distinct period of mostly blue skies that envelops the summer and especially runs from May through October. Meaning right now. We get 65% of available sunshine during this period.
But a very interesting if depressing thing happens around November 1. Climate statistics show that our daily average cloud cover suddenly jumps from 35% to 65% virtually overnight. We go from mostly sunny to mainly overcast. This alteration is now just a couple of weeks away.
Another thing changes cloud-wise for us. In summer, clear mornings with perhaps some early valley fog turns into afternoons with the sky peppered with individual puffy cumulus clouds. These are driven by convection — rising warm air created by the strong sun unevenly heating the ground. By late afternoon these puff-balls dissipate, leaving the sky mostly clear once again by sunset.
In September and October, with the sun less strong, the cumulus tend to be scarcer and have much less vertical development. The thunderstorm potential similarly plummeted these past six weeks.
But watch what happens a couple of weeks from now when mother nature switches to its cold weather mode. Quite suddenly in November — and lasting right through March — the weak sun and cold ground no longer produce upward moving air. Individual puffy clouds become somewhat rare. Thunderstorms are therefore scarce too. Instead, the cloud cover tends to be stratus or overcast. Visually this is far less interesting. We no longer see detailed, mutating cauliflowers but a single featureless gray sheet.
It›s odd that this striking annual pattern, parading overhead throughout our lives, tends to go unnoticed. However, since this dramatic increase in cloudiness and concomitant absence of sunshine happens at the same time that the very hours of daylight shrink to their yearly minimal, the gloom factor is psychologically inescapable. No wonder 15% of us suffer from SAD — Seasonal Affective Disorder.
For most of us, the solution is obvious. We must fill our leisure hours by going to more restaurants. We must get fatter.
Another quarry can be the legendary CZA. That’s the circumzenithal arc. It’s a vivid upside down “rainbow” seen straight up against high, thin, icy cirrus clouds. They get more numerous this next month, but remain a rare treasure. Spotting a CZA once a year counts as a success. Try for it!
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