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Sacramento Mountains Astronomy Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sacramento Mountains Astronomy Park clear sky chart from 2005-11-05 to 2008-11-27.

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	6% 5% 5% 5% 8% 53%	12250
	Night	5% 8% 59%	12176
Cloud Cover	Day	5% 6% 5% 5% 8% 52%	12243
	Night	5% 5% 8% 58%	12184
Transparency	Day	7% 10% 19% 29% 20%	10175
	Night	6% 10% 18% 32% 22%	10349
Seeing	Day	17% 27% 31% 17%	638
	Night	17% 26% 29% 19%	3826

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	5% 5% 8% 5% 6% 56%	835
	Night	6% 6% 6% 6% 54%	1203
February	Day	5% 8% 66%	807
	Night	5% 5% 8% 69%	971
March	Day	5% 5% 56%	1017
	Night	5% 7% 59%	1021
April	Day	5% 68%	1077
	Night	5% 5% 5% 68%	899
May	Day	5% 6% 6% 8% 54%	1138
	Night	5% 6% 7% 60%	906
June	Day	7% 8% 8% 9% 47%	1255
	Night	11% 6% 5% 7% 49%	724
July	Day	18% 5% 6% 10% 7% 8% 12% 19%	1202
	Night	12% 7% 8% 9% 15% 27%	839
August	Day	15% 6% 8% 7% 7% 6% 8% 26%	1108
	Night	10% 5% 8% 12% 38%	929
September	Day	10% 6% 5% 5% 8% 48%	1043
	Night	8% 8% 57%	931
October	Day	5% 72%	926
	Night	6% 73%	1106
November	Day	6% 74%	1042
	Night	7% 69%	1402
December	Day	8% 66%	800
	Night	9% 67%	1245

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	7% 7% 7% 55%	834
	Night	5% 5% 7% 6% 53%	1206
February	Day	5% 8% 65%	807
	Night	6% 8% 69%	971
March	Day	5% 6% 6% 56%	1018
	Night	5% 7% 58%	1023
April	Day	5% 6% 67%	1077
	Night	6% 5% 5% 67%	899
May	Day	5% 7% 5% 6% 8% 52%	1137
	Night	6% 7% 59%	906
June	Day	7% 8% 7% 10% 45%	1255
	Night	11% 6% 6% 7% 48%	724
July	Day	17% 5% 6% 9% 9% 7% 10% 18%	1202
	Night	12% 6% 9% 9% 9% 15% 26%	840
August	Day	14% 5% 6% 9% 8% 6% 7% 7% 25%	1102
	Night	8% 6% 5% 7% 13% 37%	930
September	Day	9% 5% 6% 8% 46%	1045
	Night	7% 5% 9% 54%	931
October	Day	5% 71%	927
	Night	6% 73%	1106
November	Day	6% 73%	1039
	Night	8% 68%	1402
December	Day	8% 65%	800
	Night	9% 66%	1246

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	10% 12% 22% 28% 18%	720
	Night	8% 13% 18% 35% 16%	1009
February	Day	20% 45% 21%	710
	Night	16% 49% 22%	879
March	Day	6% 10% 20% 31% 22%	837
	Night	5% 9% 17% 36% 24%	839
April	Day	5% 6% 8% 32% 44%	933
	Night	6% 6% 8% 32% 42%	780
May	Day	10% 10% 13% 26% 30%	936
	Night	8% 10% 13% 35% 27%	744
June	Day	9% 15% 15% 22% 28%	985
	Night	10% 16% 14% 19% 31%	561
July	Day	16% 18% 18% 11%	665
	Night	17% 31% 21% 12%	473
August	Day	13% 18% 22% 11%	851
	Night	11% 23% 29% 10%	742
September	Day	6% 11% 19% 29% 11%	948
	Night	8% 13% 24% 25% 11%	857
October	Day	6% 15% 36% 30%	861
	Night	5% 14% 32% 34%	1028
November	Day	7% 29% 37% 14%	1008
	Night	22% 39% 21%	1326
December	Day	6% 6% 28% 41% 11%	721
	Night	5% 23% 39% 20%	1111

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	34% 31% 23% 6%	359
February	Night	30% 30% 25% 8%	303
March	Day	37% 51% 9%	66
	Night	22% 38% 26% 8%	332
April	Day	48% 43% 6%	80
	Night	29% 36% 27% 7%	262
May	Day	25% 38% 24% 9%	105
	Night	14% 34% 32% 15%	270
June	Day	8% 19% 37% 29%	167
	Night	6% 16% 41% 30%	253
July	Day	18% 49% 23%	77
	Night	6% 33% 46% 6%	235
August	Day	5% 48% 27% 9%	88
	Night	21% 51% 14%	260
September	Day	30% 38% 14%	55
	Night	6% 9% 37% 37%	254
October	Night	13% 22% 34% 19% 8%	353
November	Night	11% 28% 32% 17% 6%	501
December	Night	25% 36% 26% 7%	444

Page generated at 2008-11-27 11:47:53. Version ab11