This page made possible by the sponsorship of: .

Observatoire de Mirabilis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Mirabilis 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	23% 10% 5% 6% 5% 5% 6% 26%	16459
	Night	21% 10% 5% 6% 5% 6% 27%	16473
Cloud Cover	Day	23% 10% 5% 6% 5% 5% 5% 26%	16470
	Night	21% 10% 5% 6% 5% 5% 6% 27%	16492
Transparency	Day	14% 22% 10%	11946
	Night	5% 15% 22% 10%	12089
Seeing	Day	13% 27% 22% 14%	949
	Night	16% 28% 26% 9%	4480

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	22% 15% 7% 7% 6% 6% 19%	979
	Night	18% 16% 8% 9% 6% 5% 6% 15%	1720
February	Day	14% 17% 8% 8% 7% 5% 6% 20%	1022
	Night	15% 15% 7% 8% 5% 5% 6% 6% 6% 18%	1383
March	Day	19% 11% 6% 6% 6% 28%	1322
	Night	19% 9% 5% 5% 5% 6% 6% 31%	1356
April	Day	26% 8% 5% 6% 31%	1451
	Night	27% 6% 6% 5% 31%	1157
May	Day	25% 6% 5% 5% 5% 6% 29%	1726
	Night	21% 5% 5% 6% 36%	984
June	Day	22% 7% 6% 5% 7% 6% 5% 6% 23%	1663
	Night	19% 6% 6% 5% 5% 5% 5% 7% 29%	956
July	Day	25% 8% 6% 5% 6% 5% 6% 6% 23%	1716
	Night	17% 6% 5% 6% 5% 7% 35%	974
August	Day	13% 6% 6% 5% 5% 5% 8% 36%	1598
	Night	10% 6% 5% 5% 7% 43%	1113
September	Day	21% 5% 7% 39%	1373
	Night	16% 5% 7% 44%	1231
October	Day	32% 12% 5% 5% 22%	1178
	Night	27% 9% 6% 6% 24%	1515
November	Day	26% 16% 6% 5% 5% 22%	1214
	Night	27% 13% 6% 7% 5% 20%	1958
December	Day	25% 18% 9% 7% 5% 5% 5% 13%	1217
	Night	25% 17% 8% 8% 5% 16%	2126

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	22% 14% 7% 8% 5% 5% 20%	977
	Night	19% 16% 8% 8% 6% 6% 17%	1721
February	Day	15% 16% 9% 7% 7% 5% 5% 20%	1020
	Night	15% 13% 8% 8% 5% 6% 6% 5% 6% 18%	1374
March	Day	20% 11% 7% 6% 5% 5% 28%	1343
	Night	20% 9% 5% 6% 6% 6% 31%	1380
April	Day	26% 9% 5% 5% 31%	1450
	Night	27% 6% 6% 5% 31%	1157
May	Day	26% 7% 5% 5% 5% 6% 28%	1720
	Night	22% 6% 5% 6% 36%	978
June	Day	23% 7% 5% 6% 6% 5% 5% 6% 23%	1672
	Night	19% 8% 7% 7% 8% 29%	958
July	Day	25% 7% 6% 5% 6% 6% 5% 24%	1716
	Night	17% 7% 5% 6% 6% 5% 36%	975
August	Day	13% 6% 7% 6% 5% 8% 36%	1593
	Night	11% 6% 5% 5% 7% 43%	1115
September	Day	22% 5% 6% 39%	1372
	Night	18% 6% 45%	1232
October	Day	32% 11% 5% 5% 23%	1178
	Night	27% 9% 6% 6% 24%	1515
November	Day	26% 14% 7% 5% 5% 5% 23%	1212
	Night	27% 12% 5% 7% 6% 21%	1957
December	Day	24% 19% 8% 7% 5% 5% 14%	1217
	Night	25% 17% 8% 7% 7% 17%	2130

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	14% 22% 7%	653
	Night	14% 20% 7%	1102
February	Day	13% 27% 5%	674
	Night	6% 20% 21%	950
March	Day	15% 27% 12%	901
	Night	17% 25% 14%	982
April	Day	13% 25% 14% 7%	981
	Night	13% 24% 19%	789
May	Day	13% 24% 16%	1231
	Night	5% 12% 27% 18%	720
June	Day	7% 17% 18% 10%	1185
	Night	9% 19% 22% 11%	700
July	Day	5% 19% 18% 5%	1092
	Night	6% 28% 19% 7%	659
August	Day	15% 25% 13%	1420
	Night	16% 29% 15%	997
September	Day	14% 32% 13%	1126
	Night	14% 36% 14%	1032
October	Day	12% 17% 9%	962
	Night	12% 20% 8%	1271
November	Day	13% 17% 11%	864
	Night	12% 16% 9%	1398
December	Day	12% 15%	857
	Night	12% 17%	1489

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	20% 36% 20% 7%	408
February	Day	12% 40% 15% 10%	40
	Night	20% 33% 23% 5%	387
March	Day	20% 31% 24% 8%	112
	Night	21% 37% 19%	436
April	Day	17% 34% 21% 10% 6%	100
	Night	16% 30% 28% 8%	367
May	Day	18% 41% 12% 11%	108
	Night	13% 35% 27% 8%	217
June	Day	14% 26% 26% 15%	99
	Night	11% 22% 40% 13%	210
July	Day	8% 21% 27% 13% 6%	103
	Night	18% 45% 14%	212
August	Day	7% 25% 23% 17% 12%	118
	Night	8% 24% 32% 21%	349
September	Day	5% 17% 19% 28% 9%	107
	Night	7% 22% 36% 17%	429
October	Day	10% 25% 18% 19%	109
	Night	14% 23% 26% 9%	446
November	Day	18% 15% 39% 5%	53
	Night	20% 21% 21% 10%	494
December	Night	22% 32% 16%	525

Page generated at 2009-12-30 05:20:38. Version ab11