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Pont Cantin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pont Cantin 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	25% 9% 5% 5% 5% 5% 6% 24%	12243
	Night	24% 10% 5% 5% 5% 5% 5% 25%	12145
Transparency	Day	9% 17% 21% 9%	7723
	Night	9% 17% 21% 9%	7629
Seeing	Day	13% 29% 25% 13%	807
	Night	17% 31% 27% 8%	3245

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% 14% 8% 6% 7% 5% 6% 17%	740
	Night	22% 14% 7% 7% 5% 7% 6% 18%	1300
February	Day	12% 12% 9% 10% 7% 5% 5% 6% 20%	748
	Night	12% 13% 8% 8% 7% 7% 5% 6% 22%	1041
March	Day	18% 11% 9% 7% 6% 7% 23%	979
	Night	18% 12% 6% 5% 6% 7% 5% 6% 24%	1017
April	Day	30% 8% 5% 32%	1119
	Night	29% 9% 6% 5% 5% 28%	858
May	Day	24% 5% 5% 6% 5% 6% 27%	1287
	Night	27% 8% 5% 5% 29%	761
June	Day	27% 7% 6% 5% 6% 7% 5% 7% 20%	1335
	Night	27% 8% 5% 5% 6% 5% 5% 23%	632
July	Day	24% 6% 5% 5% 6% 7% 7% 24%	1301
	Night	24% 5% 5% 6% 6% 7% 28%	740
August	Day	21% 6% 5% 6% 5% 5% 5% 7% 28%	1212
	Night	15% 5% 5% 7% 9% 37%	821
September	Day	26% 5% 8% 33%	1025
	Night	22% 6% 5% 6% 37%	952
October	Day	30% 11% 5% 5% 5% 21%	892
	Night	31% 9% 5% 24%	1141
November	Day	30% 15% 6% 7% 5% 17%	939
	Night	33% 12% 5% 6% 5% 18%	1507
December	Day	24% 19% 6% 6% 5% 20%	666
	Night	26% 16% 9% 6% 5% 18%	1375

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	14% 12% 22% 9%	399
	Night	10% 18% 17% 10%	696
February	Day	9% 17% 23% 9%	452
	Night	7% 22% 21% 10%	602
March	Day	11% 18% 16% 14%	545
	Night	11% 17% 20% 11%	610
April	Day	5% 15% 23% 20% 5%	679
	Night	7% 13% 26% 18%	513
May	Day	8% 18% 25% 16%	777
	Night	8% 15% 27% 16%	437
June	Day	12% 21% 14% 9%	785
	Night	10% 22% 19% 9%	372
July	Day	16% 21% 15% 5%	650
	Night	15% 25% 14% 9%	376
August	Day	8% 18% 24% 6%	999
	Night	10% 22% 26% 8%	693
September	Day	7% 20% 27% 7%	831
	Night	8% 18% 28% 10%	756
October	Day	5% 13% 21% 5%	672
	Night	8% 14% 20% 5%	882
November	Day	6% 11% 18%	559
	Night	8% 13% 17%	935
December	Day	6% 20% 18% 7%	375
	Night	10% 16% 15% 8%	757

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	23% 32% 27% 6%	314
February	Day	24% 33% 24% 8%	45
	Night	22% 38% 24% 8%	297
March	Day	17% 32% 24% 10%	87
	Night	22% 40% 19%	330
April	Day	16% 30% 22% 11% 6%	72
	Night	17% 31% 31% 7%	257
May	Day	20% 40% 26%	83
	Night	17% 44% 20% 7%	170
June	Day	7% 29% 30% 14%	142
	Night	10% 27% 36% 8%	151
July	Day	8% 21% 36% 16%	73
	Night	7% 23% 45% 10%	155
August	Day	12% 26% 21% 17% 6%	88
	Night	6% 27% 36% 18%	244
September	Day	8% 24% 24% 20%	79
	Night	11% 31% 28% 10%	328
October	Day	11% 27% 25% 10%	80
	Night	14% 26% 25% 7%	333
November	Day	17% 24% 15% 17%	58
	Night	18% 25% 23% 7%	368
December	Night	24% 34% 24%	298

Page generated at 2008-11-27 13:47:35. Version ab11