You're hearing about chances of rain and thunderstorms in San Diego County's mountains this weekend, but that doesn't mean coastal and inland communities will get a break from summer heat.
That's because of monsoonal moisture and this thing called orographic lift.
What does monsoonal moisture really mean?
The southwest of the country is in the peak stage of the monsoon season. The monsoon refers to the change in the direction of the wind. In the summer, the winds blow from south to north, and pick up moisture from the Gulf of Mexico and Gulf of California.
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As that warm, moist air rises over the mountains in East San Diego County it begins to cool and condense, forming large cumulonimbus clouds. When the clouds are full of water vapor it starts to rain.
Those clouds drain as the air continues its westward push over the mountains and the air eventually starts to sink back toward sea level. As it drops, it compresses and becomes warmer.
That's orographic lift, and it's the reason why the monsoon season brings a higher chance of rain, thunderstorms, hail and strong winds to our mountains. Rain and thunderstorms during the monsoon season can become intense and even generate flash flooding.
This weekend, Southern California will get monsoon moisture that will favor showers and thunderstorms in the mountains and the deserts.
Rain to the west of the mountains this weekend is not totally ruled out, but the chances are much smaller.