Thursday, June 25, 2009


The plume of subtropical, middle-level moisture covers all but northwest Arizona this morning. However, the Tucson sounding (above) illustrates that very little low-level moisture has accompanied the plume. It appears that high values of low-level moisture have reached north to the Guaymas and Hermosilla areas and the only cold cloud tops are isolated in the southern half of the Gulf of California. Thus, we start the day again with no CAPE at low elevations, thick middle cloud layers, and a hope that the high elevations will heat and convect much more this afternoon than happened yesterday.
The current situation illustrates the importance of moisture recycling during the summer out here. If the mountains in southeast Arizona and northern Sonora had been active yesterday with heavy storms, then significant, cool moist outflows would have brought more moisture to lower elevations this morning. Further, it is not clear whether there will enough convection and/or cool advection and pressure rises with the upper-level trough over northwestern Mexico to trigger a low-level moisture surge. Note that this feature has also been mostly devoid of deep convection! A piece of it will shear northward across Arizona later today, but most of this feature will move off to the southwest over the Pacific.
Thus, we are left mostly at the mercy of small and mesoscale convection at higher elevations to bring enough moisture to low elevations to fuel thunderstorms. My outlook for here at the house is not very positive for storms today – barring a miraculous low-level surge by mid-afternoon – chances here are about zero for meaningful rain. Perhaps a few light middle level sprinkles and spits, but mostly hopes that things will come together better tomorrow.

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