Lake Murray Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Murray 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	13% 5% 5% 5% 8% 41%	16501
	Night	13% 5% 5% 7% 42%	16464
Transparency	Day	6% 13% 21% 23% 6%	13339
	Night	6% 12% 20% 23% 9%	13349
Seeing	Day	22% 26% 20% 13%	963
	Night	8% 28% 31% 18%	5114

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	20% 6% 5% 43%	1100
	Night	16% 7% 6% 42%	1598
February	Day	15% 5% 6% 48%	1066
	Night	15% 6% 6% 46%	1329
March	Day	15% 5% 6% 46%	1363
	Night	11% 5% 5% 5% 6% 47%	1361
April	Day	9% 5% 5% 6% 8% 47%	1400
	Night	11% 5% 6% 50%	1206
May	Day	9% 5% 7% 6% 6% 8% 41%	1598
	Night	8% 5% 5% 6% 8% 9% 40%	1100
June	Day	9% 7% 6% 8% 13% 35%	1552
	Night	9% 5% 5% 6% 7% 7% 13% 34%	1078
July	Day	8% 5% 7% 6% 5% 8% 6% 7% 12% 27%	1595
	Night	9% 6% 6% 5% 8% 6% 7% 10% 30%	1097
August	Day	14% 5% 5% 7% 7% 9% 8% 31%	1553
	Night	12% 5% 7% 7% 7% 8% 11% 29%	1156
September	Day	14% 6% 6% 5% 5% 8% 36%	1303
	Night	15% 5% 5% 5% 6% 8% 38%	1301
October	Day	19% 6% 46%	1245
	Night	16% 6% 6% 47%	1449
November	Day	14% 5% 54%	1357
	Night	14% 5% 53%	1811
December	Day	18% 5% 5% 5% 5% 6% 39%	1369
	Night	16% 6% 5% 5% 5% 43%	1978

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	8% 20% 30% 9%	823
	Night	5% 8% 17% 30% 13%	1206
February	Day	11% 23% 31% 8%	843
	Night	9% 23% 28% 12%	1056
March	Day	11% 30% 23% 6%	1061
	Night	5% 15% 23% 27% 7%	1074
April	Day	6% 10% 22% 29% 10%	1147
	Night	9% 24% 27% 13%	993
May	Day	6% 17% 22% 23%	1346
	Night	8% 17% 21% 22%	930
June	Day	11% 22% 29% 14%	1176
	Night	12% 20% 28% 17%	784
July	Day	12% 18% 16% 15%	1018
	Night	13% 17% 16% 13% 6%	690
August	Day	9% 16% 19% 14%	1341
	Night	11% 17% 20% 10%	976
September	Day	6% 9% 18% 19% 7%	1137
	Night	7% 13% 17% 18% 6%	1146
October	Day	17% 30% 7%	1129
	Night	7% 18% 27% 9%	1317
November	Day	10% 23% 29% 10%	1162
	Night	8% 20% 29% 14%	1521
December	Day	12% 17% 21% 8%	1156
	Night	10% 19% 23% 9%	1656

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	18% 40% 24% 6%	435
February	Day	42% 42%	7
	Night	16% 43% 27%	389
March	Day	11% 40% 25% 12%	117
	Night	12% 39% 29% 9%	468
April	Day	6% 40% 17% 20% 5%	115
	Night	12% 37% 28% 11%	426
May	Day	5% 29% 25% 16% 14%	120
	Night	5% 32% 34% 19%	352
June	Day	15% 23% 26% 23%	102
	Night	20% 37% 30% 5%	326
July	Day	7% 34% 30% 22%	102
	Night	12% 44% 33%	312
August	Day	11% 19% 23% 30%	113
	Night	6% 31% 40% 8%	373
September	Day	10% 32% 27% 8%	111
	Night	14% 38% 27%	448
October	Day	20% 33% 12% 9%	117
	Night	5% 24% 30% 18%	474
November	Day	6% 20% 33% 18% 8%	59
	Night	7% 32% 30% 17%	541
December	Night	14% 28% 30% 10%	570

Page generated at 2009-12-30 05:20:57. Version ab11