Cima
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cima 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	6% 69%	12254
	Night	6% 69%	12178
Transparency	Day	6% 16% 28% 38%	10819
	Night	6% 16% 29% 36%	10822
Seeing	Day	15% 28% 41% 12%	762
	Night	8% 18% 32% 30% 7%	4009

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	7% 65%	850
	Night	5% 67%	1187
February	Day	5% 8% 58%	809
	Night	9% 61%	970
March	Day	7% 62%	986
	Night	5% 7% 61%	1053
April	Day	70%	1091
	Night	68%	885
May	Day	6% 76%	1209
	Night	6% 73%	837
June	Day	5% 82%	1170
	Night	83%	810
July	Day	5% 5% 7% 57%	1208
	Night	5% 5% 7% 60%	833
August	Day	5% 5% 70%	1133
	Night	5% 74%	903
September	Day	79%	1002
	Night	82%	973
October	Day	80%	956
	Night	80%	1077
November	Day	7% 63%	1003
	Night	5% 6% 64%	1443
December	Day	5% 8% 60%	837
	Night	5% 6% 60%	1207

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	11% 24% 39% 10%	760
	Night	10% 24% 32% 18%	1079
February	Day	10% 25% 36% 15%	691
	Night	10% 21% 40% 16%	854
March	Day	9% 23% 36% 20%	824
	Night	6% 8% 23% 33% 23%	890
April	Day	7% 21% 32% 32%	940
	Night	5% 7% 21% 30% 33%	753
May	Day	13% 30% 45%	1125
	Night	15% 31% 40%	769
June	Day	15% 76%	1083
	Night	5% 17% 73%	746
July	Day	9% 15% 16% 46%	799
	Night	6% 13% 23% 47%	551
August	Day	12% 22% 45%	1108
	Night	12% 24% 47%	886
September	Day	8% 28% 51%	988
	Night	10% 27% 53%	947
October	Day	9% 24% 55%	897
	Night	6% 24% 58%	1005
November	Day	7% 20% 36% 22%	897
	Night	7% 19% 33% 26%	1319
December	Day	12% 29% 29% 14%	707
	Night	13% 23% 32% 17%	1023

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	Day	26% 33% 33%	15
	Night	17% 28% 32% 14%	368
February	Day	18% 44% 25% 8%	79
	Night	11% 21% 39% 20%	315
March	Day	31% 34% 24% 8%	91
	Night	12% 27% 34% 18% 5%	366
April	Day	32% 37% 24% 5%	87
	Night	15% 29% 35% 16%	336
May	Day	14% 35% 38% 10%	90
	Night	9% 18% 31% 35%	278
June	Day	5% 26% 50% 16%	90
	Night	5% 11% 32% 46%	253
July	Day	11% 57% 25%	78
	Night	30% 55% 8%	240
August	Day	20% 62% 14%	89
	Night	29% 52% 12%	331
September	Day	9% 19% 53% 18%	88
	Night	13% 25% 38% 19%	349
October	Day	25% 27% 36% 9%	55
	Night	6% 19% 32% 30% 10%	363
November	Night	6% 20% 33% 29% 7%	442
December	Night	10% 22% 38% 21%	368

Page generated at 2008-11-27 10:47:43. Version ab11