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Spring Mill Pond
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spring Mill Pond 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	16% 8% 6% 6% 5% 6% 5% 7% 29%	12211
	Night	19% 8% 5% 6% 5% 5% 6% 30%	12181
Cloud Cover	Day	16% 8% 6% 6% 5% 6% 5% 7% 29%	12230
	Night	19% 8% 5% 6% 5% 5% 6% 30%	12203
Transparency	Day	9% 19% 22% 14%	8050
	Night	8% 19% 23% 14%	8077
Seeing	Day	9% 28% 26% 21% 7%	755
	Night	12% 32% 30% 11%	3624

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	24% 15% 11% 5% 8% 5% 5% 5% 9%	764
	Night	28% 12% 8% 9% 5% 6% 14%	1276
February	Day	20% 13% 11% 11% 6% 8% 5% 5% 10%	776
	Night	20% 11% 8% 6% 7% 7% 21%	1015
March	Day	20% 11% 10% 10% 5% 6% 19%	974
	Night	21% 9% 7% 6% 5% 5% 5% 5% 26%	1023
April	Day	16% 7% 5% 6% 38%	1122
	Night	18% 7% 5% 5% 5% 6% 6% 34%	858
May	Day	17% 7% 6% 6% 7% 33%	1211
	Night	16% 6% 5% 5% 5% 9% 34%	834
June	Day	8% 5% 5% 5% 8% 5% 7% 11% 32%	1250
	Night	8% 6% 9% 10% 41%	719
July	Day	8% 5% 5% 6% 10% 42%	1280
	Night	7% 5% 5% 5% 5% 10% 45%	762
August	Day	12% 6% 5% 6% 6% 5% 5% 7% 37%	1193
	Night	8% 5% 5% 5% 5% 8% 46%	843
September	Day	14% 6% 6% 9% 39%	999
	Night	14% 7% 5% 48%	975
October	Day	17% 7% 5% 6% 5% 5% 6% 35%	918
	Night	16% 6% 6% 5% 5% 6% 37%	1115
November	Day	21% 12% 6% 7% 6% 5% 5% 22%	996
	Night	23% 10% 6% 6% 5% 6% 25%	1449
December	Day	23% 12% 11% 11% 6% 6% 12%	728
	Night	29% 13% 8% 8% 6% 5% 14%	1312

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	25% 16% 9% 5% 7% 6% 5% 10%	763
	Night	29% 13% 7% 8% 6% 15%	1276
February	Day	20% 13% 11% 10% 8% 7% 5% 11%	774
	Night	20% 10% 8% 7% 7% 7% 21%	1006
March	Day	20% 12% 9% 10% 6% 6% 19%	996
	Night	23% 8% 7% 6% 5% 5% 6% 5% 26%	1046
April	Day	16% 8% 5% 5% 5% 5% 38%	1121
	Night	18% 7% 5% 5% 5% 6% 6% 34%	858
May	Day	17% 7% 5% 5% 6% 7% 34%	1210
	Night	17% 7% 5% 5% 9% 34%	834
June	Day	8% 5% 5% 6% 8% 5% 7% 11% 32%	1260
	Night	8% 7% 9% 10% 42%	720
July	Day	9% 5% 6% 10% 43%	1280
	Night	7% 5% 6% 5% 11% 45%	763
August	Day	11% 6% 5% 5% 6% 5% 5% 7% 38%	1188
	Night	8% 5% 5% 8% 46%	844
September	Day	14% 5% 6% 9% 39%	998
	Night	15% 6% 5% 48%	976
October	Day	17% 7% 5% 5% 5% 6% 35%	918
	Night	16% 6% 5% 5% 5% 6% 37%	1115
November	Day	21% 13% 6% 6% 5% 6% 5% 22%	994
	Night	24% 11% 5% 6% 6% 25%	1449
December	Day	24% 11% 13% 11% 5% 6% 12%	728
	Night	29% 12% 7% 8% 5% 6% 14%	1316

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	12% 20% 11%	379
	Night	9% 21% 13%	659
February	Day	15% 15% 12% 5%	396
	Night	12% 20% 19% 5%	610
March	Day	11% 25% 15% 6%	536
	Night	9% 22% 23% 9%	626
April	Day	8% 21% 27% 18%	744
	Night	8% 20% 26% 21%	556
May	Day	8% 22% 24% 14%	799
	Night	8% 18% 29% 15%	577
June	Day	11% 25% 25% 14%	915
	Night	11% 27% 28% 17%	546
July	Day	9% 19% 27% 21% 5%	708
	Night	7% 20% 31% 20%	430
August	Day	8% 14% 20% 20%	990
	Night	7% 12% 27% 23%	713
September	Day	7% 15% 31% 19%	796
	Night	13% 29% 22%	792
October	Day	7% 13% 22% 19%	738
	Night	5% 14% 25% 18%	915
November	Day	9% 16% 17% 9%	679
	Night	8% 19% 20% 8%	996
December	Day	11% 22% 10%	370
	Night	13% 24% 12%	657

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% 41% 22%	354
February	Night	19% 40% 22%	287
March	Day	10% 40% 23% 8% 5%	59
	Night	16% 40% 23% 6%	329
April	Day	16% 27% 32% 13%	81
	Night	15% 36% 32% 7%	246
May	Day	10% 34% 17% 22% 7%	88
	Night	10% 30% 35% 13%	257
June	Day	9% 33% 27% 19% 5%	168
	Night	27% 45% 19%	246
July	Day	10% 22% 35% 19% 9%	129
	Night	21% 46% 24%	234
August	Day	18% 29% 28% 12%	88
	Night	23% 46% 19%	256
September	Day	26% 13% 37% 9%	82
	Night	8% 20% 28% 28%	320
October	Day	10% 31% 25% 20%	60
	Night	14% 30% 33% 10%	343
November	Night	14% 36% 23% 7%	395
December	Night	20% 38% 23%	357

Page generated at 2008-11-27 13:47:44. Version ab11