Very Deep Boundary Layer

This morning's 12 UTC 500 mb chart has a very summer-like look to it (above from Univ. of Wyoming upper-air page). There is a broad, amorphous cyclone over northern Mexico and an anticyclone centered over the Great Basin. The mid-level temperatures, however, are cooler than they'd be in mid-summer. Temperatures associated with the cyclone are around -15 to -16C. The morning sounding for Tucson (12 UTC skew-T below from the SPC) indicates that by afternoon the boundary layer will reach to nearly 500 mb. However, there is not much CAPE apparent, except perhaps a bit over the high elevations. So there may be moderate buildups on some of the mountains. When half of the troposphere ends up with a dry-adiabatic lapse rate, strange things can happen even with very limited moisture availability.

At Atmo the early run of Mike Leuthold's version of the WRF-GFS forecasts some strange things during the night. The above graphic is the model forecast of composite radar echoes valid at 4 am MST, early tomorrow morning. The TUS sounding forecast at 3 am (below) indicates that the model develops a bit of elevated CAPE during the early morning hours. If showers do develop they'll have high bases (near 600 mb) and wuld be occurring above a very dry and hot, residual boundary layer. So, the model indicates that it could be an interesting sunrise tomorrow and I'll be out taking a look.