Monsoon Variability

I got a note last week from a California resident thinking about moving to New Mexico. She had a lot of great questions, including wanting to know more about this “monsoon” thing. I tried to explain that it’s not a big massive raining all the time in all the places sort of thing. Here’s the data:

In Bernalillo County, where I live, we’ve got 16 volunteer weather stations that have reported in to the COCORAHS network every day this month. The mean/median (essentially the same) is 1.1 inch (28 mm). Half the reports fall between 0.7 and 1.4 inch (18 and 36 mm). Max: 2.1 inch (53 mm). Min: 0.4 inch (10 mm).

That’s the spatial variability that happens when one small storm cell after another rakes across town. Some hit the rain gauge. Some don’t.


  1. So is it called a “monsoon” there because it makes up the majority of rainfall you get in a year?

    When I lived in Denver we would get the same “monsoonal moisture” (as the weathermen called it) and I could never quite figure out how or why it got that name.

  2. There’s actually a perennial argument about whether we should call it a monsoon at all. The technical definition meteorologists use is based on the mechanism involved – high country land surface heating that draws moist air from the ocean. In India, it’s the Himalayas. Here, it’s the Sierra Madre in Mexico and the Colorado Plateau north of the border. The key diagnostic is a reversal of wind fields – switching to onshore flow. But it’s a pretty subtle effect up here.

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