Yesterday (Monday 20 September 2010) thunderstorms stayed mostly on higher terraing from the southwest to south to northeast of the Tucson metro area. Nogales had a strong outflow from the south and then thunderstorms with 0.32". Two stations in the ALERT network had rain down toward Nogales, with Tubac reporting 0.67".---------------------------------------------------------
A large outflow passed TUS right before 7 pm (see top graphic) with a temperature drop of about 15F and a dewpoint rise of about 20F. This outflow helped push low-level moist air back into much of southeast Arizona as winds gusted 30 to 40+ mph from the south. It is likely that the large outflow had its origins with the large MCS in northern Sonora that had redeveloped to the north several times during the day (see 00 UTC IR image middle), with re-enforcement from the storms that developed as the outflow moved across the border. The bottom plot shows surface observations at 9 pm. The outflow covered southeastern Arizona, while air with Tds in the 50s was moving back into southwest and south-central Arizona as a precursor to a significant Gulf surge. The dewpoint at Yuma this morning is 37F higher than it was 24-hours ago - quite an amazing change!
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