Edward Knight Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edward Knight 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	22% 5% 6% 5% 5% 7% 33%	8740
	Night	23% 5% 5% 5% 6% 35%	8430
Transparency	Day	18% 16% 41% 21%	4443
	Night	18% 16% 41% 21%	4290
Seeing	Day	14% 34% 27% 16% 5%	539
	Night	20% 36% 29% 12%	2276

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	26% 6% 43%	490
	Night	23% 7% 5% 5% 38%	863
February	Day	13% 6% 5% 5% 44%	555
	Night	18% 5% 5% 46%	698
March	Day	27% 5% 5% 5% 34%	666
	Night	21% 5% 5% 6% 6% 6% 5% 34%	697
April	Day	27% 6% 37%	742
	Night	31% 5% 35%	578
May	Day	27% 5% 6% 7% 27%	830
	Night	29% 9% 5% 6% 5% 7% 24%	524
June	Day	16% 6% 5% 5% 7% 6% 6% 9% 30%	840
	Night	17% 7% 7% 7% 5% 37%	476
July	Day	20% 5% 5% 6% 6% 8% 5% 6% 8% 24%	866
	Night	20% 5% 5% 5% 5% 7% 6% 7% 8% 24%	496
August	Day	20% 5% 7% 8% 7% 9% 24%	1177
	Night	24% 5% 6% 5% 5% 6% 30%	861
September	Day	20% 6% 7% 42%	1003
	Night	17% 5% 45%	942
October	Day	28% 5% 7% 32%	609
	Night	29% 5% 5% 7% 29%	752
November	Day	14% 6% 5% 6% 7% 40%	475
	Night	21% 5% 5% 7% 39%	692
December	Day	25% 6% 7% 32%	487
	Night	22% 6% 7% 6% 36%	851

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% 42% 25%	243
	Night	14% 12% 49% 21%	414
February	Day	18% 10% 40% 28%	333
	Night	15% 11% 45% 22% 5%	390
March	Day	23% 21% 44% 10%	317
	Night	28% 16% 37% 17%	338
April	Day	15% 9% 38% 28% 8%	377
	Night	11% 13% 38% 33%	258
May	Day	26% 13% 40% 18%	347
	Night	30% 13% 27% 27%	197
June	Day	14% 14% 46% 24%	387
	Night	19% 13% 35% 28%	230
July	Day	17% 19% 42% 15%	338
	Night	30% 13% 41% 12%	214
August	Day	25% 25% 29% 15%	531
	Night	21% 22% 37% 16%	359
September	Day	13% 49% 32%	574
	Night	9% 16% 45% 25%	555
October	Day	17% 20% 46% 15%	449
	Night	19% 19% 45% 15%	509
November	Day	19% 16% 36% 23%	305
	Night	15% 25% 36% 21%	410
December	Day	26% 23% 35% 11%	242
	Night	17% 18% 42% 18%	416

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	33% 46% 18%	187
February	Day	23% 43% 25% 7%	39
	Night	19% 49% 22% 7%	188
March	Day	24% 42% 24% 8%	45
	Night	27% 39% 25% 6%	191
April	Day	13% 31% 36% 13% 5%	38
	Night	17% 47% 26% 7%	149
May	Day	15% 31% 35% 17%	45
	Night	25% 33% 33% 7%	118
June	Day	13% 37% 31% 13%	51
	Night	13% 46% 32% 7%	108
July	Day	8% 44% 24% 16% 8%	50
	Night	14% 25% 41% 14%	109
August	Day	10% 33% 24% 25% 6%	78
	Night	12% 32% 31% 22%	250
September	Day	6% 34% 26% 21% 10%	73
	Night	11% 24% 41% 21%	306
October	Day	16% 32% 20% 17% 13%	68
	Night	20% 32% 25% 18%	283
November	Day	23% 23% 37% 15%	51
	Night	23% 34% 32% 7%	197
December	Day	100%	1
	Night	25% 40% 29%	190

Page generated at 2008-09-30 05:41:18. Version ab11