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Wind River Special Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wind River Special Observatory 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	5% 6% 10% 55%	12250
	Night	6% 10% 59%	12181
Transparency	Day	10% 24% 27% 17% 7%	10208
	Night	11% 25% 29% 17% 6%	10367
Seeing	Day	16% 37% 29% 11%	803
	Night	10% 43% 29% 12%	4051

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% 13% 61%	798
	Night	6% 11% 60%	1243
February	Day	5% 13% 60%	735
	Night	5% 7% 12% 55%	1044
March	Day	5% 5% 5% 6% 12% 47%	1020
	Night	5% 6% 7% 12% 49%	1020
April	Day	5% 6% 7% 7% 9% 44%	1106
	Night	5% 6% 11% 55%	868
May	Day	6% 5% 6% 8% 11% 41%	1270
	Night	7% 5% 6% 8% 55%	776
June	Day	5% 6% 10% 59%	1260
	Night	8% 71%	720
July	Day	5% 6% 7% 7% 61%	1272
	Night	5% 9% 67%	768
August	Day	7% 64%	1185
	Night	5% 76%	852
September	Day	5% 5% 6% 59%	1024
	Night	5% 5% 62%	949
October	Day	7% 7% 58%	920
	Night	6% 7% 5% 57%	1113
November	Day	5% 11% 63%	916
	Night	6% 10% 62%	1528
December	Day	5% 5% 14% 51%	744
	Night	6% 5% 7% 15% 48%	1300

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	13% 40% 37%	709
	Night	10% 36% 36% 9%	1067
February	Day	11% 46% 32%	626
	Night	13% 38% 33% 6%	884
March	Day	14% 37% 29% 7%	808
	Night	15% 37% 30% 10%	792
April	Day	16% 25% 34% 10%	832
	Night	15% 30% 31% 15%	701
May	Day	11% 26% 32% 10%	1013
	Night	6% 23% 35% 17%	663
June	Day	7% 17% 29% 25% 13%	1095
	Night	6% 16% 27% 30% 14%	642
July	Day	8% 12% 16% 25% 32%	821
	Night	6% 12% 14% 25% 36%	533
August	Day	5% 6% 15% 37% 21%	1102
	Night	7% 21% 34% 28%	813
September	Day	7% 14% 27% 25% 7%	928
	Night	9% 14% 30% 24% 8%	853
October	Day	7% 18% 27% 25%	824
	Night	5% 16% 31% 19% 5%	948
November	Day	13% 30% 29% 16%	837
	Night	13% 29% 27% 18%	1370
December	Day	17% 35% 25% 7%	613
	Night	21% 28% 27% 11%	1101

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	13% 62% 18%	404
February	Day	100%	1
	Night	18% 56% 16% 5%	319
March	Day	30% 43% 20%	91
	Night	10% 53% 26% 8%	365
April	Day	33% 35% 23%	89
	Night	12% 47% 32% 6%	271
May	Day	12% 29% 36% 12%	149
	Night	6% 27% 37% 19%	274
June	Day	12% 34% 27% 19%	173
	Night	5% 32% 39% 20%	254
July	Day	7% 28% 34% 26%	130
	Night	20% 43% 32%	243
August	Day	10% 50% 34%	88
	Night	21% 50% 23%	266
September	Day	17% 51% 24%	82
	Night	27% 37% 20% 6%	299
October	Night	11% 36% 26% 13%	360
November	Night	13% 57% 19% 5%	537
December	Night	16% 48% 25% 7%	459

Page generated at 2008-11-27 11:47:38. Version ab11