NEFAS Swamp Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NEFAS Swamp Site clear sky chart from 2005-11-05 to 2008-11-27.

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	11% 6% 6% 5% 6% 5% 6% 8% 34%	12264
	Night	10% 5% 5% 6% 5% 9% 41%	12167
Transparency	Day	5% 15% 20% 21% 8%	8884
	Night	5% 19% 22% 20% 9%	9262
Seeing	Day	6% 14% 23% 26% 20%	751
	Night	8% 26% 34% 21%	3781

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	16% 9% 5% 6% 5% 5% 5% 6% 33%	840
	Night	18% 6% 5% 5% 6% 7% 34%	1199
February	Day	12% 5% 5% 48%	813
	Night	12% 5% 6% 6% 48%	966
March	Day	6% 5% 8% 52%	1022
	Night	7% 5% 7% 53%	1020
April	Day	8% 5% 5% 5% 5% 6% 8% 43%	1038
	Night	6% 5% 6% 9% 49%	939
May	Day	7% 6% 5% 7% 5% 7% 41%	1208
	Night	6% 5% 6% 11% 49%	837
June	Day	8% 7% 7% 6% 9% 8% 7% 10% 24%	1170
	Night	7% 5% 8% 6% 10% 12% 34%	810
July	Day	10% 7% 6% 8% 9% 5% 11% 7% 8% 10% 14%	1209
	Night	5% 5% 7% 6% 11% 8% 8% 16% 20%	834
August	Day	16% 7% 9% 7% 6% 7% 8% 11% 16%	1124
	Night	12% 6% 7% 7% 5% 7% 11% 28%	904
September	Day	11% 8% 9% 6% 8% 6% 5% 9% 25%	987
	Night	11% 6% 5% 6% 6% 6% 10% 35%	990
October	Day	15% 8% 7% 5% 5% 5% 36%	953
	Night	12% 6% 5% 6% 6% 43%	1080
November	Day	8% 5% 8% 52%	1063
	Night	10% 5% 5% 7% 51%	1380
December	Day	16% 5% 5% 6% 8% 37%	837
	Night	16% 5% 5% 9% 39%	1208

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	11% 21% 23% 13%	544
	Night	14% 20% 22% 12%	790
February	Day	11% 19% 34% 16%	594
	Night	12% 18% 28% 20%	728
March	Day	14% 31% 29% 8%	794
	Night	17% 32% 21% 10%	818
April	Day	18% 19% 22% 18%	789
	Night	5% 25% 19% 23% 14%	734
May	Day	12% 28% 31%	854
	Night	24% 26% 30%	667
June	Day	9% 31% 19% 12%	729
	Night	10% 38% 25% 9%	586
July	Day	11% 29% 12%	578
	Night	19% 32% 13%	453
August	Day	9% 23% 12%	898
	Night	11% 27% 17%	774
September	Day	6% 13% 12% 15% 6%	821
	Night	6% 18% 22% 13% 5%	832
October	Day	5% 15% 20% 14%	821
	Night	11% 16% 22% 10%	949
November	Day	9% 25% 28% 16%	891
	Night	10% 23% 26% 17%	1116
December	Day	11% 32% 26% 7%	571
	Night	14% 27% 29% 7%	815

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	17% 32% 31% 10%	328
February	Day	75% 25%	4
	Night	13% 36% 40% 6%	291
March	Day	10% 25% 32% 23%	88
	Night	9% 40% 35% 9%	354
April	Day	10% 24% 33% 19% 9%	87
	Night	7% 37% 40% 9%	329
May	Day	5% 27% 18% 24% 18%	90
	Night	6% 28% 38% 22%	274
June	Day	8% 11% 32% 42%	80
	Night	13% 30% 38% 10%	246
July	Day	12% 35% 43%	78
	Night	27% 47% 15%	236
August	Day	7% 11% 25% 36%	88
	Night	23% 41% 13%	285
September	Day	9% 17% 28% 23%	85
	Night	18% 33% 30% 5%	336
October	Day	8% 14% 33% 21% 6%	90
	Night	5% 22% 37% 20%	357
November	Day	8% 18% 34% 29%	61
	Night	7% 33% 34% 16%	422
December	Night	10% 27% 40% 15%	323

Page generated at 2008-11-27 13:47:42. Version ab11