1979 Flagstaff Nighttime Cloudiness Summary N.B.: only 24 nights included in June. Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr (nights) Photometric 4 5 10 15 9 16 13 12 10 9 7 11 121 Monthly Average: 10.1 Partial 3 5 4 6 5 0 3 3 4 7 3 4 47 Monthly Average: 3.9 Spectroscopic 3 9 3 4 4 2 7 3 6 10 8 5 64 Monthly Average: 5.3 Cloudy 21 9 14 5 13 6 8 13 10 5 12 11 127 Monthly Average: 10.6 -------------------------------------------------------------------------------- Clear Hours 50 60 90 120 60 95 95 95 85 100 80 130 1060 Monthly Average: 88.3 Clear+Dark Hours 35 20 50 65 25 45 55 65 45 45 45 70 565 Monthly Average: 47.1 Mean Consec 1.0 1.3 1.7 2.5 1.5 4.0 2.2 3.0 2.0 1.8 1.4 2.8 Monthly Average: 2.1 Max Consec 1 2 3 7 4 7 5 4 4 4 3 7 Monthly Average: 4.3 -------------------------------------------------------------------------------- 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.