Rancho Del Sol Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rancho Del Sol 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	11% 5% 63%	12271
	Night	13% 5% 58%	12159
Transparency	Day	12% 22% 30% 20%	9854
	Night	11% 20% 28% 21%	9610
Seeing	Day	17% 38% 34%	782
	Night	5% 10% 35% 33% 8%	3556

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	23% 7% 43%	793
	Night	22% 6% 5% 43%	1244
February	Day	24% 6% 5% 7% 41%	773
	Night	21% 6% 7% 41%	1006
March	Day	17% 8% 5% 9% 36%	1011
	Night	20% 7% 5% 7% 41%	1029
April	Day	21% 6% 6% 45%	1077
	Night	18% 6% 5% 5% 42%	899
May	Day	6% 5% 66%	1247
	Night	8% 5% 65%	798
June	Day	5% 77%	1260
	Night	75%	720
July	Day	86%	1276
	Night	82%	765
August	Day	89%	1139
	Night	86%	898
September	Day	88%	1041
	Night	87%	932
October	Day	7% 5% 5% 64%	920
	Night	7% 5% 71%	1113
November	Day	13% 7% 52%	990
	Night	12% 5% 6% 51%	1455
December	Day	26% 6% 5% 5% 38%	744
	Night	28% 5% 40%	1300

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	14% 25% 21% 7%	608
	Night	14% 18% 27% 8%	956
February	Day	17% 34% 19% 7%	529
	Night	6% 12% 28% 21% 12%	697
March	Day	8% 24% 24% 21%	667
	Night	10% 17% 26% 23% 8%	669
April	Day	5% 24% 33% 20%	703
	Night	6% 24% 29% 21% 5%	561
May	Day	18% 36% 23% 9%	1088
	Night	22% 31% 22% 13%	687
June	Day	12% 19% 38% 26%	1110
	Night	9% 18% 36% 27%	629
July	Day	10% 35% 47%	887
	Night	9% 32% 52%	517
August	Day	9% 46% 38%	1118
	Night	9% 41% 44%	874
September	Day	19% 36% 33%	1027
	Night	16% 36% 36%	914
October	Day	8% 21% 29% 20%	848
	Night	7% 18% 33% 24%	1051
November	Day	5% 15% 20% 27% 14%	788
	Night	16% 19% 21% 20%	1164
December	Day	19% 28% 24%	481
	Night	6% 16% 24% 19% 10%	891

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	20% 33% 24%	45
	Night	8% 18% 38% 16%	335
February	Day	21% 19% 34% 9%	66
	Night	7% 11% 35% 30%	271
March	Day	37% 37% 16%	75
	Night	10% 15% 35% 25% 5%	312
April	Day	40% 36% 16%	72
	Night	10% 9% 47% 21% 7%	304
May	Day	20% 36% 34%	88
	Night	5% 13% 31% 37% 9%	231
June	Day	10% 47% 38%	86
	Night	5% 34% 50% 7%	169
July	Day	36% 59%	79
	Night	21% 59% 15%	184
August	Day	46% 47%	89
	Night	33% 52% 10%	328
September	Day	11% 42% 40%	88
	Night	7% 29% 43% 16%	346
October	Day	13% 41% 23% 11%	92
	Night	10% 38% 28% 12%	361
November	Day	100%	2
	Night	11% 39% 29% 9%	413
December	Night	9% 18% 34% 20% 5%	302

Page generated at 2008-11-27 10:47:33. Version ab11