Colorado Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colorado Skies Observatory clear sky chart from 2005-11-05 to 2009-12-29.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	5% 5% 5% 7% 52%	16448
	Night	6% 6% 57%	16511
Transparency	Day	6% 12% 21% 25% 15%	14256
	Night	11% 24% 25% 16%	14278
Seeing	Day	15% 31% 33% 13%	935
	Night	7% 22% 36% 25%	5334

By Month

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	8% 5% 59%	1105
	Night	8% 5% 63%	1592
February	Day	6% 5% 6% 55%	1029
	Night	5% 7% 5% 61%	1365
March	Day	6% 6% 5% 5% 5% 5% 8% 44%	1361
	Night	9% 6% 5% 5% 6% 47%	1361
April	Day	5% 5% 6% 57%	1409
	Night	5% 5% 5% 6% 57%	1194
May	Day	6% 5% 8% 50%	1609
	Night	5% 6% 5% 6% 8% 51%	1088
June	Day	5% 7% 60%	1670
	Night	5% 8% 59%	960
July	Day	6% 5% 9% 9% 8% 10% 36%	1598
	Night	5% 9% 8% 8% 8% 41%	1091
August	Day	6% 5% 5% 5% 6% 10% 46%	1546
	Night	6% 5% 5% 8% 52%	1172
September	Day	5% 5% 5% 6% 5% 5% 51%	1356
	Night	5% 5% 5% 7% 54%	1244
October	Day	6% 6% 62%	1220
	Night	6% 66%	1473
November	Day	5% 6% 66%	1312
	Night	5% 66%	1855
December	Day	9% 6% 5% 7% 50%	1233
	Night	10% 7% 5% 55%	2116

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	17% 36% 22%	967
	Night	10% 39% 28%	1355
February	Day	6% 12% 28% 27%	921
	Night	12% 32% 23% 10%	1213
March	Day	5% 18% 26% 29% 5%	1063
	Night	6% 11% 28% 26% 10%	1056
April	Day	9% 21% 29% 22%	1210
	Night	5% 7% 21% 25% 27%	1008
May	Day	7% 13% 16% 28% 17%	1408
	Night	5% 15% 17% 26% 19%	933
June	Day	5% 11% 25% 36%	1549
	Night	7% 13% 18% 40%	891
July	Day	12% 14% 15% 16% 19%	1105
	Night	11% 12% 18% 16% 21%	729
August	Day	7% 12% 14% 21% 23%	1324
	Night	8% 13% 15% 17% 29%	1019
September	Day	7% 10% 16% 26% 16%	1263
	Night	6% 10% 16% 23% 20%	1167
October	Day	6% 20% 37% 13%	1115
	Night	16% 38% 23%	1348
November	Day	13% 33% 29% 8%	1215
	Night	10% 30% 31% 14%	1667
December	Day	8% 23% 31% 9%	1116
	Night	16% 32% 18%	1892

Seeing (when cloud cover <= 80%)
Color Meanings: Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month		Occurrence of each Forecast	Data Points
January	Night	8% 24% 35% 20%	475
February	Day	30% 50% 20%	10
	Night	7% 33% 32% 15%	420
March	Day	34% 36% 19% 5%	119
	Night	11% 30% 31% 19%	468
April	Day	37% 41% 14%	107
	Night	13% 30% 37% 12%	350
May	Day	18% 35% 25% 10%	139
	Night	5% 24% 36% 27%	359
June	Day	5% 25% 40% 18%	231
	Night	17% 39% 32%	339
July	Day	19% 53% 19%	108
	Night	9% 34% 43% 6%	329
August	Day	29% 43% 19%	118
	Night	8% 32% 45% 7%	357
September	Day	10% 31% 35% 15%	103
	Night	14% 39% 32% 6%	391
October	Night	7% 22% 36% 25% 5%	479
November	Night	8% 14% 42% 24% 6%	638
December	Night	8% 27% 32% 17%	729

Page generated at 2009-12-30 03:20:33. Version ab11