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Black Rock Desert
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Rock Desert clear sky chart from 2005-11-05 to 2008-11-20.

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% 7% 57%	12216
	Night	5% 5% 7% 54%	12071
Transparency	Day	14% 23% 23% 22%	9773
	Night	5% 16% 25% 21% 17%	9537
Seeing	Day	16% 31% 25% 21%	759
	Night	6% 19% 38% 25% 6%	3712

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% 7% 9% 8% 6% 5% 8% 11% 30%	764
	Night	5% 5% 8% 7% 5% 6% 6% 7% 39%	1273
February	Day	5% 7% 7% 9% 11% 38%	779
	Night	5% 5% 7% 5% 7% 5% 7% 6% 43%	1000
March	Day	7% 5% 7% 13% 40%	1002
	Night	6% 7% 7% 7% 10% 42%	1036
April	Day	6% 6% 5% 6% 5% 8% 46%	1078
	Night	5% 6% 6% 8% 49%	897
May	Day	7% 58%	1267
	Night	5% 5% 6% 5% 57%	778
June	Day	6% 68%	1260
	Night	5% 5% 5% 64%	720
July	Day	79%	1301
	Night	8% 74%	741
August	Day	86%	1146
	Night	5% 86%	891
September	Day	82%	1036
	Night	77%	939
October	Day	5% 8% 61%	912
	Night	5% 7% 66%	1121
November	Day	5% 5% 5% 6% 5% 7% 7% 44%	927
	Night	5% 5% 5% 5% 5% 7% 51%	1375
December	Day	9% 5% 11% 8% 5% 8% 7% 8% 8% 24%	744
	Night	6% 8% 5% 9% 6% 8% 5% 6% 8% 30%	1300

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	15% 36% 23%	547
	Night	9% 36% 26%	932
February	Day	7% 36% 28% 11%	584
	Night	8% 27% 29% 13%	733
March	Day	7% 25% 41% 11%	729
	Night	8% 28% 32% 13%	752
April	Day	19% 36% 24%	757
	Night	26% 32% 20%	643
May	Day	12% 28% 30% 10%	1070
	Night	10% 32% 27% 11%	646
June	Day	6% 17% 36% 35%	1045
	Night	8% 20% 35% 28%	569
July	Day	7% 23% 63%	887
	Night	7% 28% 55%	510
August	Day	9% 28% 56%	1107
	Night	10% 29% 55%	874
September	Day	16% 29% 42%	1013
	Night	13% 27% 46%	904
October	Day	12% 33% 27% 5%	849
	Night	8% 38% 27% 9%	1046
November	Day	10% 18% 26% 23%	712
	Night	8% 19% 26% 22% 6%	1093
December	Day	14% 30% 23%	473
	Night	10% 26% 27% 9%	835

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	Day	10% 40% 25% 15% 5%	20
	Night	7% 23% 40% 19%	366
February	Day	9% 23% 29% 31%	72
	Night	8% 20% 32% 30%	308
March	Day	22% 43% 17% 13%	87
	Night	10% 26% 38% 19%	365
April	Day	32% 27% 27% 7%	80
	Night	11% 23% 36% 20%	344
May	Day	18% 25% 29% 18%	87
	Night	7% 21% 38% 26%	219
June	Day	22% 34% 20% 16% 5%	87
	Night	18% 50% 26%	164
July	Day	8% 33% 42% 12%	78
	Night	14% 40% 40%	161
August	Day	14% 32% 25% 23%	89
	Night	13% 47% 33%	321
September	Day	8% 22% 24% 40%	87
	Night	8% 31% 38% 14%	350
October	Day	13% 37% 13% 29%	72
	Night	13% 36% 28% 12%	363
November	Night	5% 18% 41% 19% 11%	404
December	Night	9% 25% 38% 19%	347

Page generated at 2008-11-20 21:15:41. Version ab11