Yet Another Moisture-Starved Short Wave

Another moisture-starved short wave is approaching the Southwest this morning - as has been the trend for several months. The 12 UTC analysis for 500 mb (above from NCAR RAL) shows this feature approaching northern Baja within the distinct, southern branch of the flow. Water vapor image below (for 1430 UTC) shows considerable upper-level moisture with and ahead of the short wave.

The view of the Catalinas (below at 0753 am MST) shows the thick clouds, bringing us a partly to mostly cloudy morning. The NWS ASOS system at the airport tells us that skies are currently clear - but this inaccurate observation is because the system detects only clouds below 12,000 ft above the surface. Because of automated systems, the most accurate sky cover observations these days are those from major airports, where human observers add additional detail to the automated data. So, while Tucson is "clear", Phoenix has broken cloud cover at 24,000 ft AGL. So it goes.