Chabot Space and Science Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chabot Space and Science Center clear sky chart from 2003-08-01 to 2005-11-07.

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	10% 8% 53%	8697
	Night	12% 5% 5% 8% 45%	8473
Transparency	Day	6% 10% 29% 32% 21%	6206
	Night	8% 12% 27% 28% 23%	5515
Seeing	Day	14% 26% 40% 17%	656
	Night	8% 10% 32% 41% 6%	2723

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	18% 5% 5% 7% 10% 33%	539
	Night	21% 5% 5% 5% 6% 6% 5% 32%	815
February	Day	28% 9% 6% 6% 5% 5% 26%	530
	Night	26% 7% 6% 6% 5% 6% 27%	715
March	Day	17% 5% 5% 7% 46%	681
	Night	12% 5% 9% 49%	681
April	Day	8% 5% 5% 6% 7% 52%	720
	Night	9% 5% 6% 7% 56%	600
May	Day	13% 5% 7% 48%	824
	Night	13% 9% 54%	539
June	Day	10% 61%	840
	Night	5% 6% 8% 58%	478
July	Day	8% 66%	816
	Night	5% 6% 5% 8% 7% 7% 10% 40%	536
August	Day	9% 65%	1155
	Night	5% 6% 5% 5% 13% 45%	887
September	Day	7% 68%	1018
	Night	6% 7% 63%	927
October	Day	7% 6% 5% 5% 8% 50%	620
	Night	8% 5% 6% 6% 51%	744
November	Day	14% 6% 9% 45%	466
	Night	14% 5% 5% 9% 44%	701
December	Day	25% 5% 6% 5% 34%	488
	Night	28% 5% 5% 5% 5% 31%	850

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	19% 16% 40% 21%	261
	Night	26% 21% 28% 19%	349
February	Day	37% 13% 18% 22% 7%	196
	Night	26% 16% 24% 20% 12%	259
March	Day	7% 10% 31% 36% 14%	415
	Night	9% 12% 35% 24% 18%	426
April	Day	8% 22% 27% 18% 22%	488
	Night	9% 16% 29% 21% 23%	412
May	Day	8% 9% 42% 23% 15%	509
	Night	6% 16% 29% 30% 15%	359
June	Day	9% 43% 41%	642
	Night	7% 40% 42% 6%	333
July	Day	14% 35% 44%	661
	Night	16% 34% 46%	362
August	Day	6% 23% 37% 31%	953
	Night	9% 21% 35% 31%	618
September	Day	23% 40% 31%	832
	Night	20% 29% 44%	732
October	Day	5% 16% 27% 32% 18%	668
	Night	18% 22% 28% 26%	783
November	Day	16% 22% 35% 22%	347
	Night	17% 16% 36% 18% 11%	498
December	Day	9% 18% 38% 20% 11%	234
	Night	19% 8% 32% 29% 10%	384

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	15% 17% 28% 30% 8%	46
	Night	11% 8% 32% 44%	210
February	Day	26% 34% 21% 14%	41
	Night	16% 11% 38% 27% 5%	178
March	Day	20% 22% 37% 18%	53
	Night	5% 13% 34% 42%	220
April	Day	29% 32% 30% 7%	55
	Night	12% 20% 30% 33%	230
May	Day	24% 37% 31% 7%	54
	Night	10% 12% 38% 34%	149
June	Day	14% 26% 51% 7%	56
	Night	11% 6% 35% 41% 5%	117
July	Day	16% 64% 17%	62
	Night	23% 54% 15%	163
August	Day	19% 57% 19%	91
	Night	5% 29% 51% 8%	324
September	Day	8% 27% 42% 21%	90
	Night	6% 8% 34% 41% 9%	357
October	Day	14% 31% 34% 19%	88
	Night	7% 10% 28% 43% 10%	355
November	Day	35% 25% 15% 25%	20
	Night	10% 13% 40% 33%	233
December	Night	9% 16% 32% 36% 5%	187

Page generated at 2008-05-11 01:45:51. Version ab11