2001 Flagstaff Nighttime Cloudiness Summary Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr (nights) Photometric 6 2 5 9 8 19 3 4 14 7 8 5 90 Monthly Average: 7.5 Partial 2 5 4 2 4 2 4 3 5 4 5 6 46 Monthly Average: 3.8 Spectroscopic 5 3 8 2 7 2 3 2 4 1 0 0 37 Monthly Average: 3.1 Cloudy 18 18 14 17 12 7 21 22 7 19 17 20 192 Monthly Average: 16.0 ------------------------------------------------------------------------------- Clear Hours 85 52 70 89 82 140 39 54 151 94 114 97 1067 Monthly Average: 88.9 Clear+Dark Hours 38 28 43 70 36 50 32 32 78 54 73 60 594 Monthly Average: 49.5 Mean Consec 1.5 1.0 1.3 3.0 2.0 6.3 1.0 4.0 4.7 1.8 2.0 1.3 Monthly Average: 2.5 Max Consec 3 1 2 4 3 10 1 4 7 2 4 2 Monthly Average: 3.6 ------------------------------------------------------------------------------- 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.