This page made possible by the sponsorship of: .

Starburst Meadows Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starburst Meadows 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	20% 6% 5% 5% 7% 35%	16399
	Night	20% 7% 5% 5% 6% 35%	16530
Cloud Cover	Day	20% 5% 5% 5% 7% 36%	16408
	Night	20% 7% 5% 7% 36%	16551
Transparency	Day	8% 15% 24% 16%	12613
	Night	7% 15% 25% 14%	12920
Seeing	Day	45% 15% 12% 8%	1204
	Night	46% 17% 15% 6%	5102

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	18% 6% 5% 5% 6% 35%	979
	Night	17% 8% 5% 5% 5% 7% 34%	1720
February	Day	12% 9% 7% 8% 5% 6% 7% 30%	1048
	Night	16% 7% 7% 5% 38%	1358
March	Day	17% 5% 5% 6% 42%	1304
	Night	17% 8% 5% 6% 39%	1374
April	Day	20% 5% 6% 40%	1479
	Night	23% 6% 7% 6% 33%	1124
May	Day	25% 5% 5% 6% 6% 6% 28%	1652
	Night	23% 7% 5% 5% 5% 6% 7% 27%	1062
June	Day	29% 7% 5% 5% 5% 7% 22%	1663
	Night	31% 6% 5% 5% 5% 7% 21%	956
July	Day	17% 6% 9% 6% 7% 9% 28%	1716
	Night	18% 5% 5% 6% 8% 5% 7% 8% 26%	974
August	Day	13% 5% 5% 6% 5% 7% 8% 38%	1585
	Night	14% 6% 5% 5% 7% 7% 39%	1128
September	Day	14% 8% 50%	1333
	Night	14% 5% 6% 52%	1271
October	Day	18% 6% 6% 5% 42%	1205
	Night	19% 6% 5% 5% 39%	1488
November	Day	26% 6% 5% 38%	1297
	Night	24% 6% 6% 35%	1873
December	Day	21% 9% 5% 6% 35%	1138
	Night	22% 9% 5% 5% 5% 35%	2202

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	19% 6% 5% 5% 7% 35%	977
	Night	18% 6% 5% 9% 34%	1721
February	Day	13% 9% 6% 8% 5% 5% 8% 30%	1045
	Night	16% 7% 7% 6% 37%	1350
March	Day	18% 6% 42%	1325
	Night	19% 7% 5% 6% 39%	1398
April	Day	20% 5% 6% 41%	1478
	Night	23% 6% 5% 5% 5% 35%	1124
May	Day	25% 5% 5% 6% 5% 5% 6% 29%	1646
	Night	24% 7% 5% 6% 5% 7% 28%	1056
June	Day	31% 5% 6% 5% 6% 24%	1672
	Night	31% 7% 5% 5% 5% 5% 8% 21%	958
July	Day	16% 5% 6% 8% 6% 7% 10% 29%	1716
	Night	19% 5% 5% 6% 7% 5% 6% 8% 27%	975
August	Day	13% 6% 5% 6% 7% 41%	1579
	Night	15% 6% 5% 5% 6% 8% 38%	1131
September	Day	15% 7% 51%	1332
	Night	15% 7% 51%	1272
October	Day	19% 5% 5% 5% 43%	1205
	Night	19% 6% 6% 39%	1488
November	Day	26% 6% 5% 39%	1295
	Night	23% 6% 6% 35%	1872
December	Day	22% 8% 5% 6% 35%	1138
	Night	22% 9% 5% 5% 36%	2206

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	10% 20% 27% 13%	714
	Night	8% 17% 30% 13%	1273
February	Day	7% 18% 25% 9%	817
	Night	7% 19% 29% 10%	1067
March	Day	6% 17% 26% 19%	1033
	Night	7% 14% 28% 18%	1058
April	Day	7% 10% 27% 22% 6%	1096
	Night	6% 10% 24% 22%	776
May	Day	7% 14% 22% 14%	1160
	Night	9% 17% 21% 13%	765
June	Day	11% 16% 20% 8%	1093
	Night	11% 19% 14% 7%	670
July	Day	13% 21% 20% 10%	1130
	Night	9% 24% 17% 6%	644
August	Day	9% 14% 26% 15%	1391
	Night	8% 12% 28% 16%	997
September	Day	5% 10% 28% 28%	1187
	Night	11% 31% 24%	1128
October	Day	12% 25% 17%	1072
	Night	6% 12% 24% 17%	1300
November	Day	5% 16% 24% 16%	1025
	Night	7% 16% 23% 13%	1485
December	Day	7% 16% 21% 14%	895
	Night	6% 15% 26% 12%	1757

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	56% 21% 10%	491
February	Day	59% 9% 15%	104
	Night	57% 13% 11%	430
March	Day	58% 17% 9%	124
	Night	58% 16% 11%	495
April	Day	54% 13% 8% 8%	119
	Night	55% 16% 10% 7%	412
May	Day	53% 16% 10%	122
	Night	53% 13% 15%	322
June	Day	50% 6% 12% 7%	113
	Night	50% 6% 17% 7%	228
July	Day	45% 8% 16% 14%	110
	Night	45% 7% 18% 12%	220
August	Day	28% 14% 17% 15% 9%	121
	Night	27% 15% 26% 16%	375
September	Day	29% 15% 17% 11% 12%	116
	Night	28% 19% 23% 11%	463
October	Day	30% 29% 8% 13%	121
	Night	31% 23% 18% 8%	487
November	Day	45% 15% 11% 6%	144
	Night	42% 20% 15%	573
December	Day	60% 20% 10%	10
	Night	52% 18% 9%	606

Page generated at 2009-12-30 05:20:24. Version ab11