Mt. Cuba Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mt. Cuba Astronomical Observatory 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	13% 5% 6% 5% 5% 8% 39%	12252
	Night	15% 5% 5% 5% 8% 39%	12141
Cloud Cover	Day	13% 5% 6% 5% 5% 7% 40%	12268
	Night	16% 5% 5% 5% 8% 39%	12165
Transparency	Day	9% 18% 26% 19%	9077
	Night	9% 18% 25% 19%	8940
Seeing	Day	6% 26% 29% 20% 5%	771
	Night	10% 34% 32% 11%	3562

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	13% 6% 6% 6% 5% 6% 38%	785
	Night	19% 5% 5% 5% 5% 7% 35%	1255
February	Day	15% 6% 5% 44%	773
	Night	15% 6% 5% 5% 5% 5% 5% 6% 39%	1018
March	Day	13% 7% 6% 5% 7% 40%	993
	Night	13% 6% 5% 7% 5% 7% 38%	1004
April	Day	15% 5% 5% 5% 5% 5% 6% 38%	1078
	Night	19% 7% 5% 5% 5% 5% 37%	899
May	Day	11% 8% 6% 6% 8% 40%	1264
	Night	11% 5% 6% 7% 8% 40%	785
June	Day	12% 5% 7% 6% 7% 9% 36%	1251
	Night	13% 5% 5% 5% 10% 40%	718
July	Day	9% 5% 5% 9% 5% 7% 9% 36%	1287
	Night	9% 5% 7% 6% 9% 11% 34%	753
August	Day	10% 6% 6% 6% 8% 40%	1141
	Night	13% 5% 6% 8% 41%	892
September	Day	15% 5% 6% 8% 42%	1042
	Night	13% 5% 8% 50%	935
October	Day	14% 5% 5% 7% 48%	917
	Night	15% 6% 7% 47%	1116
November	Day	21% 6% 5% 6% 36%	977
	Night	20% 7% 5% 5% 6% 7% 30%	1469
December	Day	14% 5% 7% 6% 5% 8% 37%	744
	Night	17% 6% 5% 5% 8% 37%	1297

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	13% 7% 5% 5% 6% 7% 38%	784
	Night	20% 5% 5% 5% 5% 7% 36%	1256
February	Day	16% 6% 5% 5% 44%	771
	Night	15% 6% 6% 5% 6% 39%	1009
March	Day	13% 5% 5% 5% 5% 8% 40%	1014
	Night	13% 6% 5% 5% 7% 7% 37%	1027
April	Day	15% 5% 5% 6% 5% 7% 38%	1077
	Night	21% 6% 5% 5% 6% 37%	899
May	Day	11% 7% 5% 7% 8% 41%	1263
	Night	11% 5% 5% 5% 5% 5% 9% 40%	785
June	Day	12% 5% 7% 6% 7% 9% 36%	1260
	Night	12% 6% 5% 9% 40%	720
July	Day	9% 5% 6% 7% 5% 6% 10% 36%	1287
	Night	10% 5% 8% 5% 8% 11% 35%	754
August	Day	11% 6% 5% 5% 6% 8% 41%	1135
	Night	12% 5% 5% 6% 5% 5% 7% 41%	894
September	Day	16% 5% 7% 43%	1041
	Night	13% 7% 50%	936
October	Day	13% 5% 6% 49%	917
	Night	16% 5% 7% 47%	1116
November	Day	21% 6% 5% 6% 37%	975
	Night	20% 7% 5% 5% 6% 7% 31%	1468
December	Day	14% 6% 7% 5% 6% 7% 37%	744
	Night	17% 6% 5% 5% 8% 37%	1301

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	9% 22% 28% 15%	527
	Night	9% 21% 31% 17%	817
February	Day	8% 23% 28% 13%	588
	Night	7% 22% 25% 18%	751
March	Day	7% 18% 28% 22%	728
	Night	11% 21% 27% 15%	709
April	Day	9% 17% 15% 24% 7%	766
	Night	5% 17% 20% 23% 5%	632
May	Day	12% 16% 29% 21%	973
	Night	13% 16% 23% 23%	581
June	Day	16% 24% 34% 10%	868
	Night	14% 25% 31% 15%	492
July	Day	9% 16% 27% 18%	708
	Night	15% 23% 18% 18%	411
August	Day	8% 13% 23% 19% 5%	978
	Night	6% 13% 24% 21%	752
September	Day	6% 13% 22% 28%	854
	Night	5% 11% 26% 31%	790
October	Day	6% 13% 26% 24%	801
	Night	5% 12% 25% 25%	969
November	Day	5% 18% 29% 11%	752
	Night	9% 18% 23% 12%	1081
December	Day	11% 25% 24% 13%	534
	Night	9% 25% 28% 13%	955

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	17% 47% 23%	323
February	Day	20% 46% 23%	39
	Night	22% 45% 21%	296
March	Day	14% 37% 30% 9%	83
	Night	18% 45% 23%	346
April	Day	13% 37% 24% 10%	83
	Night	11% 39% 30% 8%	323
May	Day	27% 35% 21% 5%	88
	Night	7% 37% 36% 12%	219
June	Day	5% 21% 31% 31% 5%	73
	Night	28% 46% 17%	156
July	Day	16% 30% 34% 9%	75
	Night	20% 47% 23%	168
August	Day	5% 12% 22% 31% 16%	87
	Night	14% 42% 24%	312
September	Day	14% 35% 24% 9%	82
	Night	16% 43% 26%	328
October	Day	22% 30% 20%	84
	Night	6% 28% 34% 14%	347
November	Day	5% 35% 28% 7%	77
	Night	9% 37% 28% 9%	402
December	Night	14% 45% 25%	342

Page generated at 2008-11-27 13:47:51. Version ab11