Wilder Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wilder Skies 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	18% 5% 5% 5% 5% 6% 36%	12271
	Night	18% 5% 5% 7% 37%	12123
Cloud Cover	Day	18% 5% 5% 5% 6% 36%	12286
	Night	18% 6% 5% 5% 7% 37%	12150
Transparency	Day	9% 17% 26% 16%	8611
	Night	9% 18% 27% 17%	8685
Seeing	Day	14% 35% 25% 10%	813
	Night	17% 40% 24% 6%	3385

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% 5% 5% 5% 6% 35%	740
	Night	17% 7% 5% 5% 6% 5% 8% 34%	1300
February	Day	15% 8% 5% 5% 7% 7% 6% 32%	792
	Night	17% 7% 5% 5% 8% 36%	999
March	Day	16% 6% 5% 5% 6% 41%	976
	Night	14% 6% 5% 5% 6% 41%	1020
April	Day	22% 5% 5% 6% 35%	1108
	Night	22% 5% 5% 5% 38%	869
May	Day	22% 5% 5% 5% 7% 32%	1252
	Night	24% 5% 5% 5% 6% 32%	797
June	Day	25% 5% 5% 5% 7% 9% 25%	1251
	Night	21% 6% 5% 5% 5% 7% 5% 9% 26%	718
July	Day	12% 6% 6% 6% 8% 7% 6% 6% 30%	1301
	Night	14% 5% 5% 7% 8% 6% 6% 7% 30%	740
August	Day	12% 5% 6% 5% 6% 6% 7% 39%	1170
	Night	13% 6% 6% 8% 41%	863
September	Day	13% 5% 5% 6% 49%	1020
	Night	17% 7% 48%	957
October	Day	15% 5% 6% 45%	913
	Night	17% 6% 7% 45%	1121
November	Day	24% 6% 5% 37%	1002
	Night	24% 6% 5% 5% 34%	1445
December	Day	18% 6% 5% 5% 38%	746
	Night	16% 6% 5% 7% 40%	1294

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	20% 5% 5% 5% 5% 5% 36%	739
	Night	17% 8% 5% 5% 5% 7% 34%	1301
February	Day	15% 8% 6% 5% 7% 5% 5% 5% 32%	789
	Night	16% 8% 6% 7% 36%	991
March	Day	16% 6% 5% 5% 5% 6% 41%	997
	Night	14% 5% 5% 5% 5% 5% 5% 40%	1044
April	Day	21% 5% 5% 5% 6% 35%	1107
	Night	22% 5% 5% 5% 37%	869
May	Day	22% 6% 5% 5% 5% 5% 6% 32%	1251
	Night	23% 5% 5% 5% 5% 6% 32%	797
June	Day	25% 5% 6% 7% 8% 26%	1260
	Night	19% 7% 5% 5% 6% 7% 5% 5% 9% 25%	720
July	Day	12% 6% 5% 6% 9% 5% 6% 8% 30%	1301
	Night	14% 5% 5% 7% 8% 5% 6% 7% 30%	741
August	Day	12% 5% 5% 6% 6% 6% 5% 6% 39%	1164
	Night	12% 6% 7% 8% 41%	866
September	Day	13% 5% 6% 49%	1019
	Night	16% 7% 48%	958
October	Day	15% 5% 6% 45%	913
	Night	16% 6% 5% 7% 45%	1121
November	Day	24% 6% 5% 37%	1000
	Night	24% 6% 5% 5% 34%	1444
December	Day	18% 6% 5% 5% 6% 37%	746
	Night	16% 6% 5% 7% 39%	1298

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% 26% 14%	494
	Night	9% 22% 28% 15%	838
February	Day	11% 15% 26% 13%	544
	Night	10% 17% 29% 15%	706
March	Day	8% 17% 29% 19% 5%	699
	Night	7% 16% 32% 19%	733
April	Day	8% 16% 23% 22% 8%	719
	Night	7% 13% 25% 26% 6%	573
May	Day	9% 17% 29% 11%	817
	Night	12% 17% 22% 14%	530
June	Day	15% 27% 25% 6%	773
	Night	16% 28% 20% 10%	415
July	Day	13% 18% 25% 11%	685
	Night	13% 24% 28% 5%	392
August	Day	7% 13% 26% 18%	984
	Night	10% 14% 28% 17%	736
September	Day	8% 25% 32%	859
	Night	5% 9% 26% 29%	813
October	Day	6% 14% 28% 17%	794
	Night	6% 17% 23% 19%	968
November	Day	6% 18% 28% 14%	723
	Night	8% 17% 23% 15%	1041
December	Day	8% 28% 21% 13%	520
	Night	8% 23% 31% 10%	940

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	26% 47% 17%	306
February	Day	22% 39% 19%	63
	Night	27% 42% 16%	291
March	Day	26% 33% 22% 6%	86
	Night	26% 44% 18%	336
April	Day	14% 37% 18% 14%	74
	Night	25% 38% 18% 8%	275
May	Day	16% 40% 23% 10%	80
	Night	18% 41% 24%	198
June	Day	8% 35% 31% 13%	74
	Night	45% 40%	146
July	Day	7% 37% 35% 10%	78
	Night	5% 33% 46% 8%	156
August	Day	6% 36% 30% 9%	86
	Night	5% 34% 38% 13%	285
September	Day	12% 31% 23% 9% 12%	85
	Night	8% 32% 32% 11%	332
October	Day	12% 31% 31% 12%	87
	Night	12% 39% 20% 12%	340
November	Day	16% 35% 16% 13%	98
	Night	18% 34% 24% 7%	385
December	Day	100%	2
	Night	20% 51% 12%	335

Page generated at 2008-11-27 13:47:34. Version ab11