This morning higher moisture contents are positioned to the east, over southern New Mexico. Dry air (with PW values of an inch or less) is located over southwest Arizona. Tucson lies in the zone between the two areas - above comparison of GPS and raob PW shows that PW has increased some over the past several hours and is currently a bit over 30 mm. The 6:15 am visible satellite image (below) shows widespread cloudiness at sunrise over eastern Arizona and western New Mexico. It was a nice purple to orange sunrise this morning, with the rising sun illuminating a deck of middle clouds.
There will be a bit of a clash between these air masses today (winds are light aloft, so diurnal, terrain driven winds will prevail). Atmo's early run of the WRF-GFS indicates that the dry air from the west will prevail this afternoon, with PW values below 25 mm over Pima County (forecast valid at 5 pm MST below). Note that the model is currently running about 3 mm too dry relative to observations - so the GPS trend of PW will be something to watch today. The model forecasts keep storms to the east and south today, with activity increasing both Saturday and again Sunday..
Finally, a look at this morning's (Friday, 6 July 2012) 12 UTC soundings at Phoenix and at TUS. The Phoenix sounding (above - from a Vaisala sonde) indicates a strong and dry inversion right at 500 mb. The TUS sounding (below - data from the NWS RRS sonde) have a strong super-adiabatic layer near 500 mb due to wet-bulbing. The result is temperatures too cool by several degrees at 500 mb, with the inversion layer weakened, and the warmest air aliased to a higher level by the slowly responding RRS instruments. The problems with the Tucson data result in inaccurate calculations of thermodynamic parameters by automated sounding analysis programs (compare CAPE values for the two soundings). Again, let the user beware. Vertical wind profiles are just a pathetic mess of L/V winds - especially here at Tucson.
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