Monday, July 25, 2011

Thunderstorm Semaphore

My sister texted last night from Albuquerque, with news of two storms, and a power outage that was forcing her to shuffle frozen materials to her neighbors. Hardship!

Looking late last night, it looked like there was the remnants of a series of storms, perhaps a mesoscale convective complex (MCC) moving west, just south of the city. It's unusual to see these kinds of storms in Albuquerque. If anything, it's usually a symptom of high summer, when the tropical easterlies make their northernmost approach. These storm complexes mimic the sort of MCCs you see boiling off the Sierra Madre in Sonora, and other points further south.

I was so excited about NM storms, that I forgot all about the Arizona storms. On Sunday, there was also a much-larger easterly, much-better-organized high-summer MCC spilling off the Mogollon Rim, and heading west, just north of Phoenix. The Zonians are naturally excited this morning about this storm complex.

I learn new things all the time. Last week, I realized the National Weather Service (NWS) radar displays are sensitive enough to show gust fronts, which catalyze new storm cell growth. Now, it's possible to see the effects of these things in real time!

I became rapt watching the old storms triggering new storm growth near ABQ: I'm sure they do the same kind of signalling in AZ. The upshot appears to be, if it doesn't rain in the mountains first, followed by abrupt storm collapse, it will not rain in ABQ that day. The torch must pass first!

On Thursday, the trigger for ABQ precipitation came from the storms east of Acoma. On Friday, the trigger came in a relay, from the Jemez, to Zia, then to town. Every day is a little different, in part because the overall wind direction can be a little different, and the trigger can come from storms over any high ground anywhere near town, but I'm sure there are persistent themes: Mt. Taylor, the Manzanos, the Sandias, the Jemez, even areas farther away, etc.

In Arizona, the coherent unifying presence of the Mogollon Rim favors the development of MCCs: the storms can advance in unison towards lower elevation to the south and west.

It's just all this semaphore that's going on: convection signals are flashing and echoing all over the Southwest during hot summer afternoons. It's like hearing the gods on Mt. Olympus having a spirited debate. With the NWS radars it's like getting a radio that's finally tuned to this fascinating frequency, and listening in....

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