1980 Flagstaff Nighttime Cloudiness Summary Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr (nights) Photometric 7 5 6 7 10 16 9 14 17 20 16 14 141 Monthly Average: 11.8 Partial 0 3 2 2 3 3 2 3 0 1 1 2 24 Monthly Average: 2.0 Spectroscopic 3 4 1 9 3 5 0 3 3 1 2 5 39 Monthly Average: 3.3 Cloudy 21 17 22 12 15 6 20 11 10 9 11 10 162 Monthly Average: 13.5 -------------------------------------------------------------------------------- Clear Hours 75 70 60 65 79 108 70 119 136 192 166 180 1320 Monthly Average:110.0 Clear+Dark Hours 32 21 45 43 25 60 47 61 57 104 98 85 678 Monthly Average: 56.5 Mean Consec 3.5 1.7 1.5 1.8 2.0 5.3 2.3 4.7 3.4 5.0 2.0 2.0 Monthly Average: 2.9 Max Consec 5 2 2 2 5 8 3 6 9 10 5 3 Monthly Average: 5.0 -------------------------------------------------------------------------------- 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.