Wednesday, July 01, 2009

Another Active Storm day in Southeast Arizona

Heavy storms moved across the Tucson area for the second straight day yesterday. The radar loops show several pronounced outflows played roles in the detailed evolution of the storms. photo above shows a large thunderstorm moving across the east flanks of the Catalinas. This storm produced a strong outflow, again with lots of blowing dust. Winds at house were around 40 mph but there was only 0.03” of rain as the storm moved to the south and weakened over downtown. New and more intense cells formed to the west and south.
Data from the Pima County ALERT network indicated that ~70% of the sites had measurable rainfall, with 4 stations reporting over an inch of rain. Brawley at three Points (west of downtown on the other side of the Tucson Mountains) reported 2.20 inches of rain and there was wind damage associated with this storm cell.
Heavy clouds and continuing showers are between here and Phoenix this morning. The TWC sounding was modified by the deep clouds and is not representative of the larger-scale environment – making the forecast situation difficult. A special sounding at 18Z might prove very useful today.
Regardless, precipitable water values are now very large – about 1.75 inches or 45 mm. The NAM predicts that a weak shortwave at 500 mb will be affecting south-central Arizona this evening and that vertical wind shear will again be favorable for strong storms. It appears that storms will occur over a larger portion of the south half of state and that the Phoenix area may be affected today. The details, of course, depend upon the evolution of the current messy cloud/shower situation and how much sunshine and heating occur this afternoon. But definitely another interesting weather day.

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