Winer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Winer Observatory 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	7% 6% 6% 55%	8681
	Night	6% 5% 6% 56%	8488
Transparency	Day	8% 7% 18% 30% 35%	6535
	Night	8% 8% 20% 31% 30%	6462
Seeing	Day	13% 38% 34% 13%	505
	Night	5% 18% 37% 35%	2864

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	10% 6% 8% 5% 7% 44%	549
	Night	11% 6% 5% 7% 5% 42%	804
February	Day	18% 6% 5% 5% 5% 6% 38%	558
	Night	15% 5% 5% 44%	687
March	Day	9% 5% 60%	681
	Night	5% 6% 57%	681
April	Day	6% 5% 62%	698
	Night	5% 65%	622
May	Day	9% 64%	802
	Night	11% 61%	562
June	Day	74%	780
	Night	81%	537
July	Day	9% 5% 7% 6% 5% 8% 39%	795
	Night	6% 6% 8% 8% 8% 9% 39%	558
August	Day	10% 5% 11% 6% 7% 8% 34%	1165
	Night	8% 5% 7% 5% 6% 13% 36%	876
September	Day	7% 5% 64%	969
	Night	7% 62%	977
October	Day	69%	630
	Night	70%	734
November	Day	5% 5% 62%	505
	Night	8% 61%	660
December	Day	7% 5% 63%	549
	Night	5% 6% 61%	790

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	14% 12% 29% 32% 11%	325
	Night	13% 10% 35% 28% 12%	452
February	Day	11% 12% 31% 27% 17%	302
	Night	10% 10% 30% 32% 16%	387
March	Day	7% 7% 29% 34% 20%	495
	Night	8% 12% 33% 25% 20%	486
April	Day	10% 36% 44%	511
	Night	8% 17% 36% 34%	475
May	Day	13% 35% 43%	670
	Night	5% 22% 32% 36%	462
June	Day	5% 27% 60%	678
	Night	7% 39% 51%	460
July	Day	15% 8% 19% 18% 37%	461
	Night	25% 9% 18% 16% 29%	332
August	Day	20% 18% 28% 22% 9%	637
	Night	20% 20% 27% 22% 7%	534
September	Day	5% 7% 14% 34% 38%	776
	Night	6% 6% 10% 41% 34%	769
October	Day	5% 19% 35% 35%	786
	Night	5% 7% 19% 38% 29%	922
November	Day	8% 6% 16% 23% 44%	467
	Night	7% 16% 31% 39%	571
December	Day	6% 17% 25% 46%	427
	Night	8% 6% 15% 22% 48%	612

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	8% 20% 46% 23%	230
February	Day	39% 42% 12% 6%	33
	Night	12% 28% 44% 14%	198
March	Day	25% 35% 26% 12%	56
	Night	6% 21% 40% 28%	240
April	Day	25% 50% 23%	51
	Night	10% 36% 38% 14%	196
May	Day	10% 51% 31% 6%	58
	Night	21% 41% 33%	181
June	Day	8% 43% 45%	60
	Night	11% 41% 43%	179
July	Day	13% 33% 43% 10%	60
	Night	7% 40% 45%	180
August	Day	5% 24% 41% 27%	87
	Night	5% 19% 59% 13%	264
September	Day	39% 35% 22%	87
	Night	7% 31% 52% 6%	354
October	Day	7% 38% 38% 15%	13
	Night	5% 18% 35% 38%	368
November	Night	27% 41% 25%	240
December	Night	10% 24% 33% 25% 5%	234

Page generated at 2008-09-01 23:07:43. Version ab11