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 2009-12-29.

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% 5% 63%	16476
	Night	12% 5% 59%	16483
Transparency	Day	10% 21% 29% 19%	14058
	Night	10% 20% 27% 20%	13940
Seeing	Day	16% 37% 33%	1066
	Night	10% 34% 32% 8%	4939

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	21% 6% 50%	1050
	Night	20% 5% 5% 48%	1644
February	Day	26% 9% 7% 36%	1042
	Night	23% 8% 6% 37%	1353
March	Day	16% 8% 8% 43%	1349
	Night	19% 6% 6% 45%	1373
April	Day	18% 6% 5% 50%	1414
	Night	15% 5% 48%	1189
May	Day	7% 6% 64%	1651
	Night	9% 5% 64%	1047
June	Day	5% 70%	1669
	Night	71%	960
July	Day	86%	1688
	Night	83%	1003
August	Day	88%	1521
	Night	85%	1198
September	Day	85%	1378
	Night	86%	1222
October	Day	7% 5% 66%	1220
	Night	6% 5% 72%	1473
November	Day	11% 6% 56%	1278
	Night	11% 6% 56%	1893
December	Day	22% 8% 6% 40%	1216
	Night	24% 6% 6% 41%	2128

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	10% 22% 21% 15%	865
	Night	11% 17% 22% 19%	1357
February	Day	14% 26% 16% 5%	798
	Night	10% 24% 17% 9%	1044
March	Day	6% 22% 25% 20%	996
	Night	7% 15% 27% 21% 7%	1013
April	Day	20% 32% 23%	1038
	Night	5% 20% 28% 24% 5%	851
May	Day	15% 37% 21% 8%	1500
	Night	18% 31% 22% 11%	941
June	Day	13% 17% 31% 23%	1519
	Night	12% 16% 32% 25%	869
July	Day	8% 33% 50%	1299
	Night	7% 29% 57%	755
August	Day	10% 45% 36%	1500
	Night	11% 42% 39%	1174
September	Day	19% 37% 31%	1364
	Night	17% 36% 35%	1204
October	Day	7% 25% 30% 16%	1150
	Night	6% 23% 34% 19%	1411
November	Day	12% 20% 30% 14%	1076
	Night	13% 20% 22% 21%	1602
December	Day	14% 21% 24% 6%	953
	Night	5% 12% 18% 22% 9%	1719

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	19% 29% 27%	62
	Night	8% 19% 34% 17%	455
February	Day	22% 20% 29% 7%	94
	Night	7% 11% 32% 23%	383
March	Day	33% 35% 16%	106
	Night	8% 13% 35% 25%	436
April	Day	36% 37% 17%	99
	Night	9% 11% 44% 21% 8%	420
May	Day	17% 36% 35%	119
	Night	11% 29% 38% 9%	306
June	Day	12% 44% 33%	116
	Night	37% 47% 8%	227
July	Day	40% 54%	109
	Night	23% 57% 15%	248
August	Day	45% 45%	120
	Night	32% 53% 10%	442
September	Day	9% 39% 41%	117
	Night	6% 28% 44% 17%	458
October	Day	14% 40% 24% 11%	122
	Night	12% 35% 30% 11%	481
November	Day	100%	2
	Night	11% 40% 27% 8%	545
December	Night	6% 16% 32% 19% 6%	538

Page generated at 2009-12-30 02:20:38. Version ab11