Early WRF Forecasts Down Day For Southern Arizona

This morning's 12 UTC sounding for TUS (from SPC) is shown above. Things to note almost no winds below 600 mb; mostly southerly flow above; PW down some relative to yesterday; some cooling in low levels and some warming in mid-levels; substantial CAPE still present. As the boundary layer re-develops there will be a layer of CIN above (meaning some kind of low-level forcing needed for storm development at lower elevations). Visible satellite image below shows clear skies across most of southern Arizona. But the early WRF (forecast of composite radar echoes for 3 pm this afternoon 2nd below) forecasts almost no convective development across all of southern Arizona this afternoon - i.e., a totally down day.

So, the main issue is whether we can can buy into this forecast from the early WRF. There is an interesting smaller mesoscale issue in play today. The model forecasts clear skies through the day (forecast of solar irradiance w/m**2 at noon is above) and very intense radiative heating. However, some areas of the metro are very wet after yesterday's heavy rains (see previous post) BUT other areas remain bone dry. With light winds, this means  some significant low-level temperature gradients will likely develop, as the wet areas remain cooler due to evaporation. However, the WRF-GFS surface forecast valid at 3 pm below indicates uniformly hot temperatures across the metro. The model forecasts a slow decrease in PW during the day but may not be incorporating the evaporation correctly. Adds up to a complex situation. Southerly steering flow is not good. But it is hard to accept that the western and northern portions of the Catalinas won't produce some storms that move off to the north. Clearly a close look at the 12 UTC model forecasts will be needed.