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Eckley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eckley 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	21% 5% 5% 5% 6% 7% 32%	8733
	Night	23% 5% 5% 6% 34%	8440
Transparency	Day	23% 17% 37% 19%	4266
	Night	21% 17% 39% 19%	4345
Seeing	Day	16% 30% 25% 18% 9%	517
	Night	20% 33% 28% 16%	2345

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% 7% 7% 6% 5% 5% 6% 28%	517
	Night	29% 6% 5% 32%	836
February	Day	18% 6% 5% 6% 5% 5% 7% 35%	539
	Night	16% 5% 6% 7% 5% 8% 35%	715
March	Day	25% 6% 7% 7% 7% 6% 5% 24%	678
	Night	27% 5% 6% 5% 31%	686
April	Day	24% 5% 6% 5% 41%	720
	Night	27% 6% 5% 33%	600
May	Day	19% 6% 6% 5% 8% 35%	848
	Night	19% 5% 7% 8% 37%	506
June	Day	15% 5% 5% 7% 6% 6% 9% 31%	840
	Night	15% 5% 5% 6% 8% 5% 6% 34%	476
July	Day	17% 7% 6% 5% 7% 6% 8% 28%	860
	Night	14% 5% 5% 5% 10% 37%	501
August	Day	23% 5% 5% 5% 9% 5% 7% 27%	1155
	Night	21% 6% 5% 5% 5% 7% 34%	884
September	Day	23% 5% 5% 40%	1024
	Night	24% 5% 6% 41%	921
October	Day	25% 6% 6% 6% 6% 33%	612
	Night	27% 7% 5% 6% 33%	750
November	Day	21% 5% 6% 7% 6% 7% 31%	454
	Night	28% 5% 6% 6% 30%	713
December	Day	24% 5% 6% 5% 5% 6% 7% 27%	486
	Night	19% 5% 5% 5% 5% 6% 8% 32%	852

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	31% 14% 38% 12%	188
	Night	29% 15% 44% 10%	363
February	Day	28% 8% 39% 19%	261
	Night	22% 8% 41% 20% 6%	343
March	Day	28% 19% 36% 14%	233
	Night	21% 20% 42% 14%	305
April	Day	13% 10% 38% 30% 7%	372
	Night	15% 8% 38% 33%	270
May	Day	25% 22% 45% 7%	424
	Night	21% 25% 42% 11%	268
June	Day	23% 11% 44% 20%	425
	Night	18% 15% 42% 22%	234
July	Day	26% 16% 38% 13%	381
	Night	28% 20% 29% 17%	292
August	Day	26% 25% 35% 12%	508
	Night	22% 23% 33% 16%	436
September	Day	10% 16% 30% 39%	574
	Night	11% 14% 34% 36%	520
October	Day	23% 17% 37% 21%	421
	Night	21% 15% 42% 19%	541
November	Day	25% 20% 35% 18%	277
	Night	21% 22% 40% 15%	372
December	Day	35% 18% 34% 9%	202
	Night	25% 18% 44% 9%	401

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	47% 35% 14%	171
February	Day	13% 65% 21%	23
	Night	27% 45% 22%	194
March	Day	23% 34% 41%	43
	Night	27% 45% 22%	193
April	Day	31% 31% 21% 8% 6%	47
	Night	19% 44% 24% 10%	181
May	Day	17% 34% 34% 9%	52
	Night	15% 44% 29% 10%	123
June	Day	6% 37% 25% 27%	48
	Night	10% 32% 39% 15%	108
July	Day	7% 28% 19% 30% 14%	56
	Night	24% 36% 36%	119
August	Day	6% 18% 26% 30% 18%	72
	Night	23% 32% 35%	280
September	Day	9% 26% 18% 28% 16%	71
	Night	11% 21% 37% 27%	293
October	Day	21% 27% 20% 17% 13%	69
	Night	21% 27% 26% 20%	296
November	Day	33% 22% 33% 8%	36
	Night	24% 30% 31% 12%	188
December	Night	32% 39% 23% 5%	199

Page generated at 2008-05-11 04:45:49. Version ab11