1999 Flagstaff Nighttime Cloudiness Summary Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr (nights) Photometric 4 4 7 5 12 14 1 2 12 23 9 6 99 Monthly Average: 8.2 Partial 8 4 6 3 1 6 6 1 2 6 7 12 62 Monthly Average: 5.2 Spectroscopic 5 8 5 5 9 2 1 3 2 0 6 4 50 Monthly Average: 4.2 Cloudy 14 12 13 17 9 8 23 25 14 2 8 9 154 Monthly Average: 12.8 ------------------------------------------------------------------------------- Clear Hours 100 67 98 61 92 123 33 22 126 284 143 150 1299 Monthly Average: 108 Clear+Dark Hours 45 41 39 53 51 52 8 19 47 146 93 82 676 Monthly Average: 56 Mean Consec 1.0 1.3 1.4 1.7 2.0 2.3 1.0 2.0 6.0 4.6 1.8 2.0 Monthly Average: 2.3 Max Consec 1 2 2 3 4 6 1 2 7 16 4 3 Monthly Average: 4.2 ------------------------------------------------------------------------------- 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.