Charlotte
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charlotte 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	12% 5% 5% 8% 43%	12269
	Night	13% 5% 5% 5% 7% 42%	12164
Transparency	Day	6% 15% 26% 25% 5%	9306
	Night	5% 14% 24% 25% 7%	9058
Seeing	Day	5% 18% 27% 22% 17%	722
	Night	6% 26% 34% 21%	3735

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	18% 6% 5% 5% 6% 41%	832
	Night	19% 5% 5% 43%	1208
February	Day	14% 6% 5% 8% 44%	782
	Night	16% 5% 5% 8% 44%	997
March	Day	12% 6% 5% 5% 9% 44%	1022
	Night	10% 5% 7% 6% 46%	1020
April	Day	13% 5% 5% 5% 6% 7% 40%	1068
	Night	13% 7% 5% 6% 7% 43%	909
May	Day	7% 6% 5% 8% 50%	1208
	Night	8% 5% 5% 7% 9% 45%	837
June	Day	9% 6% 5% 6% 10% 44%	1170
	Night	9% 7% 5% 9% 8% 6% 10% 28%	810
July	Day	9% 5% 6% 6% 7% 7% 7% 10% 30%	1209
	Night	6% 5% 6% 7% 7% 8% 7% 7% 10% 30%	834
August	Day	11% 5% 5% 6% 6% 8% 13% 31%	1167
	Night	8% 6% 5% 5% 7% 9% 11% 31%	862
September	Day	13% 7% 5% 8% 41%	994
	Night	14% 6% 6% 5% 7% 42%	982
October	Day	16% 56%	933
	Night	14% 5% 6% 54%	1101
November	Day	12% 8% 56%	1047
	Night	13% 5% 7% 49%	1396
December	Day	19% 5% 7% 47%	837
	Night	17% 5% 5% 5% 44%	1208

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	10% 29% 26% 10%	578
	Night	11% 25% 27% 12%	811
February	Day	19% 29% 22% 5%	593
	Night	17% 29% 25% 6%	731
March	Day	11% 15% 33% 18% 5%	753
	Night	7% 16% 27% 27% 7%	741
April	Day	5% 14% 24% 23% 10%	798
	Night	5% 14% 24% 24% 10%	694
May	Day	5% 14% 30% 30%	956
	Night	5% 14% 30% 28% 5%	635
June	Day	9% 25% 26% 25%	824
	Night	12% 20% 29% 14%	501
July	Day	14% 18% 17% 21%	662
	Night	8% 23% 18% 15% 7%	446
August	Day	9% 19% 25% 14%	967
	Night	10% 21% 23% 13%	711
September	Day	8% 10% 19% 25% 7%	836
	Night	7% 11% 17% 25% 7%	817
October	Day	6% 25% 32% 8%	813
	Night	9% 19% 33% 9%	970
November	Day	12% 29% 34% 6%	864
	Night	12% 24% 31% 9%	1106
December	Day	18% 24% 23% 9%	662
	Night	13% 26% 24% 10%	895

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	12% 40% 33% 6%	319
February	Day	12% 25% 62%	8
	Night	14% 46% 30%	290
March	Day	7% 40% 37% 7%	88
	Night	10% 43% 35% 5%	353
April	Day	8% 28% 27% 14% 9%	83
	Night	7% 35% 31% 15%	317
May	Day	21% 28% 21% 21%	89
	Night	5% 25% 37% 23%	272
June	Day	6% 6% 22% 35% 25%	76
	Night	13% 39% 35% 5%	238
July	Day	5% 8% 10% 35% 29%	78
	Night	34% 48% 5%	238
August	Day	10% 19% 17% 37%	86
	Night	25% 48% 11%	286
September	Day	6% 8% 27% 24% 19%	83
	Night	10% 34% 37%	331
October	Day	6% 15% 27% 29% 6%	86
	Night	20% 30% 25% 6%	352
November	Day	17% 46% 17% 8%	45
	Night	7% 31% 36% 16%	408
December	Night	6% 29% 41% 12%	331

Page generated at 2008-11-27 13:47:33. Version ab11