Tuesday, September 04, 2012

Difficult Forecast Today

At sunrise skies were covered with heavy clouds, and I could see lightning to the south and southwest when I walked along the Rillito. The 7 am TUS radar composite image (above) indicates that an area of storms had developed quickly this morning (no storms when I checked the radar around 5 am MST) to the south and west of Tucson. The morning skewT plot for the 12 UTC sounding (below from SPC) shows that the storms have developed aloft, above the surface layer, where a layer just below 700 mb has substantial CAPE (~1500 J/kg). Winds aloft are light and variable so there's serious threat of heavy rains.

The graphic below is the early WRF-GFS forecast from Atmo of rainfall through midnight tonight, showing a region of heavy rain amounts that arcs from southwest Cochise County into east and central Pima County. However, the initialization did not have the heavy cloud cover, nor did the forecast have the observed early development of storms. So the spatial and temporal aspects of the forecast are questionable - but the heavy rains are already underway. High temperatures are forecast in the mid-to-upper 90s today, but that degree of heating seems unlikely, since clouds may persist much of day (note that the anvils from the current storms will spread eastward over the metro area). So, a check of the 12Z WRF forecasts is needed today.

No comments:

Post a Comment