1990 Flagstaff Nighttime Cloudiness Summary Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr (nights) Photometric 7 6 2 1 8 14 3 6 2 19 10 13 91 Monthly Average: 7.6 Partial 8 5 7 4 7 3 4 2 10 3 3 4 60 Monthly Average: 5.0 Spectroscopic 3 5 5 4 5 6 2 6 2 3 5 2 48 Monthly Average: 4.0 Cloudy 13 14 17 21 11 7 22 17 16 6 12 12 168 Monthly Average: 14.0 -------------------------------------------------------------------------------- Clear Hours 126 101 59 33 93 114 42 58 77 210 133 185 1223 Monthly Average: 102 Clear+Dark Hours 67 52 30 14 38 59 36 49 29 120 62 68 622 Monthly Average: 52 Mean Consec 1.8 1.2 1.0 1.0 1.3 2.8 1.5 3.0 2.0 4.8 2.0 1.9 Monthly Average: 2.0 Max Consec 2 2 1 1 2 6 2 5 2 8 4 5 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.