2009 Flagstaff Nighttime Cloudiness Summary Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr (nights) Photometric 11 3 6 11 6 3 3 10 8 10 10 4 85 Monthly Average: 7.1 Partial 3 4 5 4 5 5 8 5 5 3 3 3 53 Monthly Average: 4.4 Spectroscopic 5 8 6 4 2 6 3 4 2 6 4 5 55 Monthly Average: 4.6 Cloudy 12 13 14 11 18 16 17 12 15 12 13 19 172 Monthly Average: 14.3 ------------------------------------------------------------------------------- Clear Hours 146 61 86 119 71 41 60 105 113 120 127 66 1115 Monthly Average: 92.9 Clear+Dark Hours 72 32 48 68 15 26 19 60 76 65 73 23 577 Monthly Average: 48.1 Mean Consec 2.2 1.0 1.0 2.2 3.0 1.0 3.0 2.5 4.0 1.7 3.3 2.0 Monthly Average: 2.2 Max Consec 5 1 1 4 4 1 1 4 7 4 5 2 Monthly Average: 3.3 ------------------------------------------------------------------------------- Definitions: Photometric - cloudfree dusk-to-dawn. Partial - at least 3 consecutive cloudfree hours during the night. Spectroscopic - less than about 1 mag. extinction throughout the night. Cloudy - cloudy. Clear+Dark Hours = photometric hours with moon absent. Mean Consec = mean number of consecutive photometric nights during the month. Max Consec = maximum number of consecutive photometric nights during the month.