Deerlick Astronomy Village
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deerlick Astronomy Village clear sky chart from 2005-11-05 to 2012-05-10.

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	12% 5% 5% 5% 5% 7% 43%	25452
	Night	11% 5% 7% 46%	25187
Transparency	Day	7% 12% 21% 21% 6%	22954
	Night	6% 11% 20% 23% 8%	22998
Seeing	Day	18% 23% 27% 13%	1523
	Night	9% 24% 31% 20%	8361

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	17% 5% 5% 6% 46%	1665
	Night	16% 6% 47%	2405
February	Day	15% 5% 6% 46%	1909
	Night	14% 6% 48%	2313
March	Day	16% 5% 6% 47%	2370
	Night	11% 7% 50%	2403
April	Day	8% 5% 5% 6% 52%	2491
	Night	7% 8% 55%	2123
May	Day	9% 5% 6% 5% 6% 9% 41%	2461
	Night	8% 5% 5% 6% 5% 8% 7% 44%	1716
June	Day	6% 5% 7% 7% 8% 11% 40%	2340
	Night	6% 5% 7% 7% 7% 13% 39%	1620
July	Day	8% 6% 8% 8% 7% 8% 9% 30%	2413
	Night	5% 5% 5% 6% 6% 7% 8% 11% 35%	1667
August	Day	12% 5% 6% 7% 7% 6% 8% 9% 28%	2324
	Night	9% 5% 6% 7% 6% 7% 7% 10% 32%	1759
September	Day	14% 6% 6% 5% 6% 5% 5% 38%	1980
	Night	16% 5% 5% 5% 5% 5% 5% 39%	1980
October	Day	16% 53%	1920
	Night	13% 5% 54%	2172
November	Day	11% 5% 54%	1905
	Night	11% 6% 55%	2611
December	Day	16% 5% 5% 6% 43%	1674
	Night	14% 5% 6% 48%	2418

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	8% 19% 30% 7%	1683
	Night	6% 20% 28% 9%	2401
February	Day	8% 23% 26% 6%	1680
	Night	9% 22% 26% 10%	2024
March	Day	6% 11% 24% 20% 6%	2105
	Night	7% 13% 20% 24% 8%	2147
April	Day	5% 11% 22% 29% 7%	2231
	Night	5% 9% 25% 27% 11%	1954
May	Day	8% 16% 26% 15%	2222
	Night	10% 15% 25% 17%	1554
June	Day	12% 19% 26% 16%	2016
	Night	12% 20% 26% 17%	1364
July	Day	14% 17% 17% 12% 5%	1876
	Night	12% 20% 19% 12% 6%	1270
August	Day	11% 16% 18% 10%	2084
	Night	11% 17% 20% 11%	1563
September	Day	7% 10% 17% 19%	1805
	Night	7% 11% 15% 18% 6%	1826
October	Day	6% 14% 32% 12%	1824
	Night	7% 12% 31% 14%	2064
November	Day	7% 23% 28% 13%	1688
	Night	7% 18% 29% 16%	2330
December	Day	6% 11% 19% 19% 8%	1740
	Night	5% 10% 23% 22% 7%	2501

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	18% 32% 27% 7%	817
February	Night	17% 37% 28%	734
March	Day	8% 26% 30% 20%	194
	Night	12% 32% 31% 11%	852
April	Day	9% 28% 19% 29%	209
	Night	12% 30% 31% 15%	730
May	Day	25% 25% 19% 15%	187
	Night	26% 32% 25%	568
June	Day	10% 22% 31% 27%	173
	Night	14% 36% 35% 7%	521
July	Day	8% 16% 42% 25%	171
	Night	8% 36% 43% 5%	507
August	Day	11% 19% 29% 23%	177
	Night	9% 33% 39% 7%	569
September	Day	14% 22% 30% 10%	176
	Night	13% 34% 28%	702
October	Day	6% 16% 28% 19% 8%	184
	Night	7% 23% 29% 21%	733
November	Day	28% 25% 26% 7%	52
	Night	10% 27% 29% 19%	796
December	Night	16% 27% 31% 10%	832

Page generated at 2012-05-11 19:54:03. Version ac01