Ritter Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ritter 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	17% 8% 5% 5% 5% 5% 5% 7% 30%	12277
	Night	20% 8% 5% 5% 5% 6% 31%	12116
Cloud Cover	Day	18% 8% 5% 5% 5% 5% 5% 6% 31%	12297
	Night	20% 8% 5% 5% 5% 6% 31%	12137
Transparency	Day	9% 18% 22% 14%	8135
	Night	9% 17% 22% 15%	7988
Seeing	Day	6% 26% 28% 21% 10%	740
	Night	12% 30% 30% 13%	3604

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	26% 17% 10% 5% 6% 5% 13%	775
	Night	29% 13% 7% 5% 5% 6% 16%	1265
February	Day	21% 14% 7% 8% 8% 5% 6% 5% 5% 13%	778
	Night	22% 13% 8% 8% 7% 5% 17%	1012
March	Day	24% 16% 8% 8% 19%	975
	Night	24% 9% 7% 5% 6% 26%	1022
April	Day	15% 8% 6% 5% 6% 37%	1118
	Night	18% 8% 5% 5% 7% 34%	862
May	Day	18% 5% 5% 6% 5% 8% 32%	1209
	Night	21% 6% 5% 7% 5% 8% 30%	837
June	Day	10% 5% 5% 7% 6% 10% 35%	1240
	Night	7% 5% 6% 5% 7% 10% 41%	728
July	Day	10% 5% 7% 5% 9% 43%	1271
	Night	8% 5% 6% 6% 9% 50%	772
August	Day	12% 5% 5% 5% 5% 6% 5% 7% 39%	1191
	Night	10% 5% 5% 7% 49%	845
September	Day	13% 5% 5% 6% 6% 45%	997
	Night	12% 5% 5% 49%	977
October	Day	18% 6% 5% 6% 37%	924
	Night	17% 6% 5% 5% 5% 6% 40%	1109
November	Day	26% 12% 5% 5% 5% 6% 21%	1002
	Night	23% 9% 6% 6% 5% 5% 7% 24%	1444
December	Day	22% 16% 8% 8% 5% 6% 6% 14%	797
	Night	30% 13% 7% 6% 5% 5% 5% 13%	1243

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	26% 16% 10% 5% 6% 6% 13%	774
	Night	29% 13% 7% 6% 5% 6% 17%	1265
February	Day	21% 14% 7% 8% 8% 6% 5% 13%	776
	Night	21% 13% 8% 8% 6% 18%	1003
March	Day	25% 15% 8% 7% 5% 19%	998
	Night	26% 9% 6% 6% 6% 25%	1044
April	Day	16% 7% 6% 5% 6% 38%	1117
	Night	18% 7% 5% 6% 34%	862
May	Day	17% 5% 6% 5% 6% 6% 7% 32%	1208
	Night	20% 5% 5% 5% 6% 5% 8% 30%	837
June	Day	11% 5% 5% 7% 5% 6% 9% 35%	1250
	Night	7% 5% 6% 5% 6% 7% 9% 41%	729
July	Day	10% 5% 7% 5% 9% 43%	1271
	Night	8% 6% 5% 6% 8% 50%	773
August	Day	12% 6% 5% 5% 6% 5% 8% 39%	1186
	Night	10% 5% 5% 7% 49%	846
September	Day	14% 5% 6% 6% 45%	996
	Night	13% 5% 5% 48%	978
October	Day	18% 6% 5% 5% 5% 38%	924
	Night	18% 5% 5% 5% 6% 40%	1109
November	Day	26% 12% 5% 5% 5% 5% 5% 21%	1000
	Night	23% 9% 6% 6% 5% 5% 6% 24%	1444
December	Day	21% 16% 8% 9% 5% 5% 7% 14%	797
	Night	30% 13% 7% 7% 5% 5% 14%	1247

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	9% 21% 14%	367
	Night	8% 19% 18% 5%	630
February	Day	13% 23% 11%	422
	Night	15% 19% 15% 5%	586
March	Day	10% 19% 20% 5%	523
	Night	9% 19% 23% 8%	621
April	Day	9% 20% 25% 21%	741
	Night	9% 16% 23% 22%	549
May	Day	10% 19% 29% 12%	801
	Night	8% 17% 24% 16%	556
June	Day	11% 21% 25% 15%	913
	Night	11% 19% 31% 17%	546
July	Day	9% 20% 29% 20%	688
	Night	12% 18% 25% 24%	450
August	Day	9% 13% 20% 20%	998
	Night	8% 13% 24% 25%	713
September	Day	5% 17% 28% 20%	806
	Night	7% 13% 26% 22% 5%	803
October	Day	6% 11% 27% 19%	744
	Night	5% 13% 25% 22%	900
November	Day	11% 14% 15% 11%	691
	Night	7% 18% 16% 12%	1001
December	Day	15% 25% 9%	441
	Night	14% 20% 13%	633

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	Night	23% 39% 21%	345
February	Night	18% 43% 20%	285
March	Day	7% 45% 22% 15%	57
	Night	16% 38% 23% 7%	333
April	Day	15% 34% 27% 11%	85
	Night	15% 35% 33% 8%	257
May	Day	32% 19% 22% 13%	83
	Night	31% 34% 15%	249
June	Day	6% 26% 36% 17% 10%	160
	Night	23% 44% 23%	246
July	Day	25% 31% 21% 14%	119
	Night	15% 50% 26%	230
August	Day	12% 25% 30% 17%	88
	Night	17% 43% 26%	256
September	Day	16% 22% 33% 13%	84
	Night	6% 19% 29% 30% 5%	327
October	Day	9% 26% 34% 17%	64
	Night	11% 27% 32% 14%	343
November	Night	16% 33% 24% 7%	398
December	Night	20% 37% 23%	335

Page generated at 2008-11-27 13:47:33. Version ab11