1989 Flagstaff Nighttime Cloudiness Summary Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr (nights) Photometric 10 2 1 5 10 13 5 9 12 11 14 14 106 Monthly Average: 8.8 Partial 6 3 4 5 1 3 2 7 4 2 8 3 48 Monthly Average: 4.0 Spectroscopic 3 3 15 7 8 7 8 1 6 8 1 8 75 Monthly Average: 6.3 Cloudy 12 20 11 13 12 7 16 14 8 10 7 6 136 Monthly Average: 11.3 -------------------------------------------------------------------------------- Clear Hours 162 37 28 68 76 103 43 108 129 129 210 195 1288 Monthly Average: 107 Clear+Dark Hours 81 12 14 40 39 76 15 98 67 96 104 95 737 Monthly Average: 61 Mean Consec 2.0 2.0 1.0 1.4 2.5 2.2 1.2 3.0 2.4 2.2 2.0 2.3 Monthly Average: 2.0 Max Consec 5 2 1 3 4 3 2 6 3 4 4 6 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.