1991 Flagstaff Nighttime Cloudiness Summary Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr (nights) Photometric 11 4 7 8 17 13 2 2 7 14 5 4 94 Monthly Average: 7.8 Partial 5 6 3 3 4 5 1 1 3 3 4 3 41 Monthly Average: 3.4 Spectroscopic 3 7 3 11 3 1 8 9 3 5 9 3 65 Monthly Average: 5.4 Cloudy 12 11 18 8 7 11 20 19 17 9 12 21 164 Monthly Average: 13.7 -------------------------------------------------------------------------------- Clear Hours 169 84 87 74 139 118 17 21 73 153 80 64 1079 Monthly Average: 89.9 Clear+Dark Hours 84 64 36 33 74 65 5 16 31 80 33 52 573 Monthly Average: 47.8 Mean Consec 2.8 1.3 1.8 2.0 1.8 1.9 1.0 1.0 2.3 2.3 1.3 1.3 Monthly Average: 1.7 Max Consec 4 2 2 4 5 5 1 1 3 6 2 2 Monthly Average: 3.1 -------------------------------------------------------------------------------- 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.