Colorful announcement of a storm

This glorious sunrise today about 7:30 AM announces in its way that a strong storm is on the way.


First of all the clouds, “altocumulus lenticularis” are the lower, rippled clouds, combined with a higher,  solid layer of altocumulus and altostratus clouds demonstrates that the air is moist to saturated over a great depth above those lowest clouds.

The lenticulars highlighted by the rising sun just above the Catalina Mountains generally occur when the wind speed at their level is at least 30-40kts.  Thus, lenticular clouds have always been a sign of being around and under strong upper level winds we sometimes call the “jet stream.” While lenticulars might hover over the same spot for minutes to hours, watching how fast the elements in it move, or other cloud movements can tell you something about how strong the jet stream is over you.  Today, the clouds were racing across the peaks, consistent with the very strong jet stream and storm systems that is about to pounce on us.  The NWS balloon sounding from Tucson this morning, a couple of hours before this shot, indicated the winds were 30-35 kts at the level of the Ac len clouds.

The second photo, kind of dull compared to our glorious sunrise, has something to say in it, too. The wind at cloud level is at the photographer and its strong,   What happens in these “pre-frontal” situations is that the air ahead of the cold front can be relatively stable, that is resistant to moving up and down, and in resisting doing that when hills and mountains are present in the path of the air movement, something akin to gigantic ocean swells are produced.  Here you see darker bases off in the distance that are PERPENDICULAR to the wind just like huge ocean swells might be.  A time lapse camera would show the movement of these “swells” beautifully as they peak and die, going through ridges and troughs, that is, slight rises and falls of the air in its movement toward the camera.

At the same time, those clouds, due to the Catalina Mountains and the higher terrain downwind from Catalina, also forces these cloouds to deepen, a process that will continue as the upper low pressure trough approaches.  As this happens, clouds such as these that are not precipitating now, start to precipitate.  The rain often doesn’t move in, but begins to fall from these deepening layer clouds overhead.  I think that is going to happen here in the next couple of hours (its about noon now).

Here in Catalina, AZ, the rainfall (17.5 inches per year) is considerably more than that in and around Tucson (12 inches per year), and this difference largely comes in winter storms like these that are subjected to the lift zone described above out ahead of the higher terrain here in Catalina,  and downwind of us.

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.