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 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	18% 6% 5% 5% 5% 6% 36%	16485
	Night	18% 6% 5% 5% 6% 37%	16450
Cloud Cover	Day	18% 6% 5% 5% 6% 36%	16494
	Night	18% 6% 5% 6% 37%	16471
Transparency	Day	8% 15% 24% 15%	12818
	Night	7% 15% 25% 15%	13011
Seeing	Day	13% 34% 24% 10%	1106
	Night	16% 37% 23% 6%	4741

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	19% 5% 5% 5% 6% 39%	979
	Night	16% 8% 6% 5% 5% 5% 7% 35%	1720
February	Day	13% 7% 6% 5% 7% 6% 6% 33%	1065
	Night	15% 8% 5% 7% 38%	1342
March	Day	17% 6% 5% 6% 42%	1310
	Night	16% 6% 5% 5% 5% 40%	1368
April	Day	19% 5% 5% 5% 5% 7% 35%	1458
	Night	20% 5% 5% 5% 5% 5% 37%	1146
May	Day	23% 5% 5% 5% 6% 33%	1660
	Night	22% 7% 5% 5% 5% 5% 6% 32%	1053
June	Day	30% 6% 5% 5% 7% 8% 23%	1663
	Night	26% 7% 6% 6% 7% 23%	956
July	Day	13% 6% 6% 6% 7% 7% 6% 7% 29%	1716
	Night	16% 5% 7% 7% 5% 5% 7% 32%	974
August	Day	12% 5% 6% 5% 6% 5% 5% 7% 39%	1562
	Night	14% 6% 5% 6% 8% 40%	1152
September	Day	13% 5% 7% 48%	1345
	Night	16% 7% 49%	1259
October	Day	15% 5% 5% 6% 42%	1209
	Night	19% 6% 7% 41%	1485
November	Day	24% 6% 5% 37%	1299
	Night	25% 7% 5% 34%	1873
December	Day	19% 8% 5% 5% 36%	1219
	Night	17% 7% 5% 6% 40%	2122

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	18% 5% 5% 5% 6% 39%	977
	Night	16% 9% 5% 5% 5% 7% 35%	1721
February	Day	13% 7% 6% 5% 7% 5% 5% 6% 34%	1062
	Night	15% 8% 5% 7% 38%	1334
March	Day	18% 5% 6% 41%	1331
	Night	16% 6% 5% 5% 5% 5% 39%	1392
April	Day	19% 5% 5% 5% 5% 7% 35%	1457
	Night	21% 5% 5% 5% 5% 5% 37%	1146
May	Day	23% 6% 5% 5% 5% 5% 6% 33%	1654
	Night	23% 6% 5% 5% 5% 6% 31%	1047
June	Day	30% 5% 5% 5% 7% 7% 23%	1672
	Night	25% 8% 6% 5% 6% 5% 7% 23%	958
July	Day	14% 6% 5% 6% 8% 6% 6% 7% 29%	1716
	Night	16% 5% 5% 7% 7% 5% 5% 7% 32%	975
August	Day	12% 5% 5% 6% 6% 5% 5% 6% 39%	1556
	Night	13% 6% 5% 6% 7% 40%	1155
September	Day	13% 5% 7% 48%	1344
	Night	16% 7% 48%	1260
October	Day	15% 5% 5% 6% 43%	1209
	Night	18% 6% 5% 7% 41%	1485
November	Day	24% 6% 5% 36%	1297
	Night	25% 7% 5% 34%	1872
December	Day	19% 8% 5% 5% 6% 36%	1219
	Night	17% 8% 6% 6% 40%	2126

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	7% 21% 27% 15%	733
	Night	7% 18% 27% 14%	1258
February	Day	10% 15% 28% 10%	817
	Night	8% 17% 29% 12%	1049
March	Day	7% 15% 28% 17%	1025
	Night	6% 12% 28% 17%	1081
April	Day	7% 13% 23% 20% 5%	1069
	Night	7% 12% 24% 21%	847
May	Day	7% 14% 25% 12%	1224
	Night	9% 15% 20% 13%	788
June	Day	12% 21% 20% 5%	1185
	Night	13% 19% 16% 8%	653
July	Day	11% 15% 21% 11%	1100
	Night	10% 19% 27% 7%	626
August	Day	7% 13% 23% 17%	1376
	Night	10% 14% 26% 16%	1025
September	Day	5% 9% 24% 29%	1184
	Night	6% 10% 24% 28%	1115
October	Day	7% 14% 25% 15%	1092
	Night	6% 15% 24% 15%	1332
November	Day	5% 16% 25% 14%	1020
	Night	6% 15% 21% 14%	1469
December	Day	7% 21% 17% 15%	993
	Night	6% 18% 27% 12%	1768

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	22% 46% 18%	426
February	Day	22% 37% 20% 5%	87
	Night	26% 38% 18%	403
March	Day	23% 30% 21% 7%	117
	Night	24% 42% 18%	460
April	Day	14% 39% 19% 13%	103
	Night	22% 37% 19% 7%	379
May	Day	13% 39% 23% 7%	109
	Night	17% 39% 21%	273
June	Day	5% 32% 26% 11%	103
	Night	40% 33%	205
July	Day	6% 36% 30% 13%	107
	Night	5% 28% 42% 11%	214
August	Day	5% 35% 31% 8% 6%	117
	Night	33% 36% 14%	388
September	Day	10% 33% 21% 9% 14%	113
	Night	8% 31% 32% 12%	445
October	Day	11% 31% 29% 11%	117
	Night	14% 36% 19% 10%	460
November	Day	14% 32% 16% 12%	131
	Night	16% 32% 23% 7%	516
December	Day	100%	2
	Night	22% 43% 12%	572

Page generated at 2009-12-30 05:20:40. Version ab11