Eagle Eye Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Eye 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	16% 6% 5% 7% 40%	8680
	Night	15% 5% 5% 7% 44%	8494
Transparency	Day	16% 13% 30% 28% 12%	5113
	Night	15% 12% 28% 27% 15%	5257
Seeing	Day	8% 16% 34% 35%	473
	Night	9% 23% 40% 25%	2549

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	22% 5% 5% 36%	563
	Night	24% 5% 6% 39%	792
February	Day	31% 5% 5% 5% 32%	570
	Night	32% 6% 5% 5% 32%	684
March	Day	20% 5% 44%	676
	Night	22% 45%	688
April	Day	17% 5% 46%	702
	Night	13% 5% 6% 50%	617
May	Day	11% 5% 6% 7% 5% 8% 40%	803
	Night	11% 7% 5% 9% 46%	550
June	Day	13% 7% 5% 8% 41%	780
	Night	13% 6% 6% 10% 43%	537
July	Day	12% 9% 6% 8% 8% 34%	801
	Night	5% 5% 6% 8% 12% 41%	558
August	Day	10% 5% 10% 6% 7% 10% 35%	1134
	Night	8% 5% 6% 8% 11% 39%	908
September	Day	14% 5% 7% 5% 6% 7% 40%	970
	Night	14% 5% 5% 8% 40%	975
October	Day	14% 7% 7% 6% 6% 8% 33%	645
	Night	9% 6% 5% 8% 5% 5% 7% 41%	714
November	Day	22% 48%	488
	Night	23% 49%	680
December	Day	13% 61%	548
	Night	9% 68%	791

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	16% 11% 37% 31%	265
	Night	15% 13% 32% 29% 10%	409
February	Day	15% 14% 35% 28% 6%	249
	Night	13% 9% 38% 29% 8%	281
March	Day	8% 10% 16% 41% 22%	365
	Night	5% 5% 25% 40% 22%	370
April	Day	9% 7% 36% 28% 19%	414
	Night	11% 7% 31% 24% 25%	371
May	Day	28% 13% 36% 14% 6%	461
	Night	23% 24% 31% 16%	351
June	Day	19% 12% 33% 26% 7%	455
	Night	24% 11% 33% 23% 7%	324
July	Day	21% 11% 29% 30% 7%	424
	Night	28% 9% 31% 25% 5%	325
August	Day	33% 21% 29% 12%	643
	Night	30% 24% 29% 13%	563
September	Day	10% 16% 28% 31% 14%	587
	Night	13% 19% 25% 24% 17%	589
October	Day	8% 14% 31% 34% 11%	527
	Night	11% 16% 27% 28% 14%	672
November	Day	5% 7% 26% 32% 28%	325
	Night	11% 5% 13% 33% 35%	411
December	Day	8% 23% 40% 23%	398
	Night	27% 40% 25%	591

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	10% 37% 41% 10%	235
February	Night	13% 35% 43% 6%	166
March	Night	8% 48% 38%	154
April	Day	14% 48% 34%	35
	Night	13% 40% 43%	159
May	Day	9% 26% 35% 26%	109
	Night	5% 25% 50% 17%	167
June	Day	13% 13% 41% 29%	107
	Night	26% 36% 32%	159
July	Day	6% 10% 34% 42% 5%	119
	Night	5% 9% 41% 39%	179
August	Day	28% 51% 10%	103
	Night	6% 26% 55% 6%	263
September	Night	7% 35% 43% 7%	251
October	Night	6% 15% 43% 31%	301
November	Night	16% 24% 40% 16%	231
December	Night	12% 24% 41% 19%	284

Page generated at 2008-08-20 17:21:01. Version ab11