Santa Barbara
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Santa Barbara 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% 7% 62%	12265
	Night	5% 6% 66%	12161
Transparency	Day	7% 13% 21% 28% 23%	10618
	Night	6% 10% 20% 29% 27%	10575
Seeing	Day	57% 7% 16% 15%	879
	Night	56% 6% 12% 17% 5%	4002

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	12% 5% 62%	817
	Night	10% 5% 64%	1220
February	Day	7% 7% 6% 8% 51%	807
	Night	10% 7% 55%	971
March	Day	5% 6% 5% 6% 8% 56%	1009
	Night	6% 5% 7% 61%	1030
April	Day	7% 6% 7% 58%	1077
	Night	6% 5% 6% 63%	899
May	Day	9% 5% 9% 57%	1177
	Night	11% 8% 60%	867
June	Day	10% 8% 65%	1260
	Night	11% 5% 9% 62%	720
July	Day	10% 5% 5% 9% 58%	1242
	Night	9% 5% 6% 8% 62%	799
August	Day	10% 9% 63%	1108
	Night	8% 5% 6% 70%	929
September	Day	7% 72%	1037
	Night	5% 6% 76%	937
October	Day	76%	935
	Night	81%	1097
November	Day	6% 68%	1015
	Night	6% 68%	1430
December	Day	7% 5% 9% 58%	781
	Night	6% 8% 61%	1262

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	13% 17% 28% 18%	713
	Night	7% 20% 26% 25%	1086
February	Day	15% 12% 29% 25% 6%	672
	Night	7% 10% 27% 33% 11%	780
March	Day	11% 15% 24% 29% 15%	779
	Night	9% 14% 30% 27% 13%	835
April	Day	14% 14% 28% 27% 11%	856
	Night	12% 13% 26% 25% 21%	719
May	Day	13% 16% 25% 24% 12%	1082
	Night	10% 18% 20% 30% 17%	795
June	Day	5% 15% 17% 29% 31%	1159
	Night	6% 18% 12% 25% 37%	653
July	Day	7% 17% 22% 19% 28%	866
	Night	7% 9% 21% 24% 33%	565
August	Day	15% 14% 33% 29%	1075
	Night	10% 14% 30% 38%	901
September	Day	6% 13% 37% 34%	1004
	Night	16% 33% 38%	914
October	Day	7% 19% 21% 40%	881
	Night	14% 24% 48%	1028
November	Day	5% 9% 19% 33% 23%	909
	Night	5% 8% 19% 32% 25%	1299
December	Day	9% 13% 27% 29% 13%	622
	Night	8% 12% 24% 31% 18%	1000

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	68% 6% 14%	74
	Night	66% 8% 8% 6%	372
February	Day	68% 8% 10% 8%	80
	Night	67% 5% 10% 9%	319
March	Day	69% 13% 12%	93
	Night	66% 10% 13% 7%	371
April	Day	70% 8% 15%	90
	Night	66% 8% 10% 12%	359
May	Day	68% 11% 14% 5%	92
	Night	67% 6% 12% 11%	309
June	Day	67% 18% 7%	90
	Night	64% 12% 12% 5%	170
July	Day	62% 10% 25%	79
	Night	62% 20% 12%	217
August	Day	37% 15% 44%	89
	Night	37% 5% 39% 15%	356
September	Day	34% 9% 22% 32%	88
	Night	34% 13% 37% 10%	350
October	Day	36% 10% 26% 23%	92
	Night	34% 10% 19% 26% 8%	366
November	Day	41% 16% 25% 8%	12
	Night	50% 6% 20% 15% 5%	444
December	Night	66% 5% 15% 7%	369

Page generated at 2008-11-27 10:47:34. Version ab11