Friday evening sunset - Katie took this photo with her phone as we were driving south on Highway 83. Ridge to west is the north end of the Santa Rita Mountains. Earlier in the afternoon showers over metro Tucson produced a couple of sprinkles and a Trace at the house.
Unusual and somewhat strange situation today. A weak short-wave and closed low is centered out near the north end of the GoC this morning in lower levels. The circulation has a pronounced tilt toward the northeast with height and very warm upper-tropospheric air is within the upper part of the circulation. This results in a very strong inversion just above 400 mb. The above skew-T plot is the early WRF-NAM forecast for Tucson valid at 2 pm MST this afternoon. The inversion is weaker in the model forecast, as would be expected, but still provides a formidable cap to convection rooted at lower levels. The forecast sounding exhibits CAPE from just above 700 mb up to just above 400 mb. Note that the lifted parcel temperature excesses are actually quite large around 500 mb, indicating substantial vertical accelerations in any convection that develops. Any thunderstorms that occur would be fairly short and stubby towers, with bases around 11,000 feet and tops around 26,000 ft MSL. However, the updrafts should be potent enough to produce some lightning and perhaps small hail or graupel. The graphic below shows the early WRF-NAM forecast of composite radar echoes valid at 3 pm MST this afternoon.
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