Tierra del Sol
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tierra del Sol 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	6% 66%	8662
	Night	5% 5% 62%	8505
Transparency	Day	15% 33% 41%	7106
	Night	6% 5% 15% 30% 42%	6862
Seeing	Day	15% 37% 35% 11%	614
	Night	8% 19% 33% 31% 6%	3017

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% 8% 5% 5% 5% 43%	578
	Night	10% 5% 5% 6% 5% 6% 44%	775
February	Day	22% 6% 5% 5% 9% 6% 5% 30%	561
	Night	17% 5% 6% 6% 9% 5% 5% 32%	684
March	Day	6% 6% 61%	659
	Night	5% 5% 61%	701
April	Day	68%	720
	Night	5% 5% 5% 6% 5% 58%	600
May	Day	5% 6% 69%	803
	Night	5% 10% 62%	561
June	Day	91%	780
	Night	92%	537
July	Day	74%	788
	Night	71%	564
August	Day	5% 7% 67%	1114
	Night	6% 69%	929
September	Day	82%	989
	Night	81%	957
October	Day	8% 71%	653
	Night	6% 5% 68%	709
November	Day	7% 5% 58%	468
	Night	5% 60%	698
December	Day	10% 5% 6% 54%	549
	Night	9% 8% 5% 51%	790

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	7% 6% 32% 35% 19%	313
	Night	12% 7% 26% 32% 19%	456
February	Day	15% 10% 25% 37% 10%	231
	Night	10% 14% 32% 25% 16%	316
March	Day	5% 11% 17% 35% 31%	480
	Night	6% 9% 18% 29% 36%	500
April	Day	5% 5% 21% 38% 29%	580
	Night	8% 15% 34% 38%	444
May	Day	15% 36% 39%	681
	Night	6% 12% 26% 49%	445
June	Day	9% 39% 48%	768
	Night	9% 34% 54%	518
July	Day	7% 14% 28% 46%	681
	Night	5% 5% 12% 23% 52%	480
August	Day	5% 5% 16% 35% 37%	891
	Night	20% 34% 36%	774
September	Day	6% 21% 66%	932
	Night	5% 5% 21% 66%	888
October	Day	13% 35% 45%	817
	Night	16% 33% 43%	899
November	Day	6% 7% 23% 36% 26%	369
	Night	6% 9% 24% 30% 29%	595
December	Day	12% 33% 48%	363
	Night	10% 9% 33% 42%	547

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	12% 60% 24%	25
	Night	14% 23% 32% 25%	236
February	Day	42% 44% 12%	50
	Night	14% 36% 34% 13%	195
March	Day	23% 33% 23% 20%	60
	Night	13% 21% 33% 23% 7%	242
April	Day	26% 44% 25%	56
	Night	12% 29% 35% 17%	231
May	Day	12% 52% 31%	57
	Night	8% 27% 40% 21%	188
June	Day	10% 40% 43% 6%	60
	Night	17% 38% 38%	180
July	Day	37% 54% 8%	62
	Night	35% 55%	190
August	Day	26% 51% 16%	87
	Night	29% 52% 11%	368
September	Day	14% 32% 41% 12%	90
	Night	12% 30% 43% 10%	358
October	Day	17% 28% 29% 23%	67
	Night	8% 13% 33% 35% 8%	359
November	Night	12% 36% 31% 16%	248
December	Night	13% 24% 35% 20% 6%	222

Page generated at 2008-10-12 17:06:01. Version ab11