2021 Flagstaff Nighttime Cloudiness Summary Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr (nights) Photometric 2 10 8 5 14 4 0 10 12 10 10 6 91 Monthly Average: 7.6 Partial 7 9 3 6 9 4 1 4 3 5 10 3 64 Monthly Average: 5.3 Spectroscopic 6 1 1 5 1 1 2 2 2 1 3 3 28 Monthly Average: 2.3 Cloudy 16 8 19 14 7 21 28 15 13 15 7 19 182 Monthly Average: 15.2 ------------------------------------------------------------------------------- Clear Hours 72 172 91 68 161 50 4 111 133 138 173 100 1273 Monthly Average: 106 Clear+Dark Hours 43 83 26 35 98 45 4 46 66 57 105 48 656 Monthly Average: 55 Mean Consec 1.0 1.7 2.7 1.3 1.8 1.3 0 2.5 3.0 2.5 2.0 2.0 Monthly Average: 1.8 Max Consec 1 3 5 2 4 2 0 6 4 4 5 3 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.