Why is it so clear today?
Usually because a cold front or a storm just passed. Rain washed the particles out of the air, a fresh, dry air mass moved in, and high pressure behind the front sinks and keeps clouds away. With so little haze, you can see mountains you normally can't.
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What makes air look hazy
On most days the air holds tiny particles (dust, salt, smoke, pollution) and water clinging to them. Together they scatter light and wash out distant views. Humid air makes it worse, because the particles swell with water.
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What clears it out
- Rain sweeps particles out of the air as drops fall.
- A new air mass from the north or from over the ocean replaces the old, dirty air.
- Dry air keeps particles small and stops haze from forming.
- Wind mixes and carries away pollution that builds up on calm days.
Deep blue skies
Clean, dry air scatters mostly blue light from the air molecules themselves, so the sky looks deeper blue and the horizon stays sharp. In very clean, dry air, visibility can stretch beyond 100 miles. In Southern California the clearest days often come with offshore Santa Ana winds or right after winter storms.
Questions people ask
- Why can I see the mountains today?
- The air is unusually clean and dry, often right after rain or a cold front, so the haze that normally hides them is gone.
- Why is the sky a deeper blue in winter and at altitude?
- There's less water and fewer particles in the air, so the blue scattered by air molecules dominates.