1998 Flagstaff Nighttime Cloudiness Summary Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr (nights) Photometric 3 4 5 6 10 19 8 3 14 9 8 7 96 Monthly Average: 8.0 Partial 2 2 4 5 5 1 2 2 2 6 8 8 47 Monthly Average: 3.9 Spectroscopic 8 3 6 8 4 5 5 7 2 4 7 6 65 Monthly Average: 5.4 Cloudy 18 19 16 11 12 5 16 19 12 12 7 10 157 Monthly Average: 13.1 ------------------------------------------------------------------------------- Clear Hours 51 53 71 78 75 136 64 34 145 126 131 139 1103 Monthly Average: 91.9 Clear+Dark Hours 30 38 35 35 49 83 24 24 116 56 98 81 669 Monthly Average: 55.8 Mean Consec 1.0 1.3 1.3 1.0 2.0 3.2 2.7 1.0 3.5 1.8 1.6 2.3 Monthly Average: 1.9 Max Consec 1 2 2 1 3 6 4 1 5 3 3 3 Monthly Average: 2.8 ------------------------------------------------------------------------------- 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.