Rainy portent in a scruff of cloud

….that scruff of cloud topping Mt. Sara Lemmon around dawn this morning, to finish the thought.   This:

Why?

Because seeing a cloud topping Mt. Lemmon instead of well above it indicates that the air is very moist and cloud bases are going to be realtively low, substantially lower than yesterday.  This in turn means even more rain will reach the ground after falling from cloud base today, more of the terrain will be involved with launching deep clouds later this morning,  with their crayola black bases and impenetrable rainshafts scattered around the area this afternoon and evening.

Will we get one of those rainshafts?

Well, no one knows exactly where they will be, but my best guess, based on a few summers here, is that Catalina will at least get measurable rain today, and a real dump of a half an inch or more is well within range.  Yesterday, two brief light showers only gave us a “trace” of rain.  Darn.  But, if you noticed, the rainshafts from the clouds yesterday were denser than the day before, and that trend will continue today.  Sometimes these dumps, just like the 4 PM shower yesterday, are invigorated and started by the gush of winds from dead showers off in the distance.  One of the patterns here is for a gush of wind to blast out of the N or NE, and suddenly, the clouds overhead start filling in in response to the gush of air.  The gush causes the air over it to be pushed up.   And, this can happen very rapidly, going from clouds that draw a yawn, to “Oh, my gosh, look how dark it is over us now!”  Better lie down now for a moment until this gush of excitement passes over.   But, this is going to be a GREAT day for Cumulus and Cumulonimbus clouds!

And what a sunrise display of lightning and a cumulonimbus clouds!

By Art Rangno

Retiree from a group specializing in airborne measurements of clouds and aerosols at the University of Washington (Cloud and Aerosol Research Group). The projects in which I participated were in many countries; from the Arctic to Brazil, from the Marshall Islands to South Africa.