The monsoon has arrived! A huge thunderstorm complex in northern Mexico spilled plenty of clouds and smaller thunderstorms into southern Arizona. Mt. Bigelow missed out on this activity, but lightning was seen to the east, south, and even west of the observatory before midnight. Over three hours of the night were lost to various degrees of cloud cover. The seeing was anywhere from 1.5 to 3.5 arcsec when observing in clear patches and through the thinner clouds. Ten blazars were successfully observed for polarization during this very sloppy night. Little differential photometry was attempted.
The weather forecast calls for a very high probability for thunderstorms tomorrow night and we'll get to see how robust the early monsoon will be. Hopefully, these first storms will come with a lot of rain to ease the extreme fire danger around the observatory. The almost certain lightning strikes that will occur over the next few days could make the situation too exciting for comfort if little rain falls.