Yesterday, Tucson was hit with a strong microburst as captured by our cloud camera. The sub-tropical high, or monsoon ridge, is well to our south in Mexico so we are not in a monsoon flow pattern. Instead, Arizona was in a region of weak upper-level divergence, between two troughs, one off the west coast and one impacting the mid-west. This coupled to the moisture in place and the synoptic scale push from remnants of tropical storm Mario aided in thunderstorm development yesterday. It was highly uncertain as to whether the storms could develop in spite of the mid-level cloud cover, but the favorable wind shear meant storms that persisted on the Catalina mountains eventually propagated to the south. <\/p>\n\n\n\n