This page made possible by the sponsorship of: , .

Bear Branch Nature Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bear Branch Nature Center 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	19% 5% 5% 6% 5% 5% 7% 33%	8728
	Night	19% 5% 5% 5% 5% 6% 36%	8445
Transparency	Day	19% 15% 41% 21%	4533
	Night	18% 14% 42% 21%	4598
Seeing	Day	12% 30% 26% 22% 9%	533
	Night	16% 32% 31% 17%	2430

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	24% 6% 5% 7% 7% 28%	531
	Night	22% 5% 5% 5% 37%	822
February	Day	16% 5% 8% 5% 6% 6% 38%	535
	Night	15% 5% 7% 5% 5% 7% 39%	719
March	Day	19% 7% 7% 5% 7% 5% 5% 6% 28%	682
	Night	22% 9% 7% 5% 33%	682
April	Day	22% 5% 5% 6% 41%	720
	Night	24% 5% 7% 33%	600
May	Day	17% 5% 6% 5% 6% 7% 35%	838
	Night	14% 6% 7% 6% 6% 6% 37%	516
June	Day	12% 5% 5% 8% 7% 7% 8% 32%	840
	Night	11% 5% 7% 5% 5% 11% 36%	476
July	Day	16% 6% 5% 5% 5% 9% 6% 6% 7% 25%	842
	Night	14% 7% 5% 7% 5% 6% 8% 32%	520
August	Day	19% 6% 5% 5% 6% 5% 5% 8% 29%	1160
	Night	16% 5% 7% 7% 10% 33%	879
September	Day	22% 6% 5% 7% 37%	1019
	Night	20% 5% 5% 5% 40%	925
October	Day	25% 6% 8% 37%	618
	Night	27% 5% 6% 38%	744
November	Day	18% 7% 5% 6% 6% 38%	457
	Night	23% 5% 5% 5% 7% 32%	710
December	Day	18% 5% 6% 7% 40%	486
	Night	16% 6% 5% 6% 5% 5% 41%	852

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	34% 12% 34% 17%	203
	Night	26% 16% 40% 15%	376
February	Day	17% 13% 44% 22%	284
	Night	21% 8% 43% 18% 8%	379
March	Day	23% 22% 39% 14%	277
	Night	15% 13% 47% 21%	303
April	Day	13% 8% 43% 28% 6%	395
	Night	11% 8% 41% 30% 7%	279
May	Day	23% 16% 43% 15%	430
	Night	24% 12% 46% 15%	285
June	Day	22% 10% 45% 21%	441
	Night	23% 12% 50% 13%	263
July	Day	27% 12% 36% 20%	355
	Night	21% 20% 36% 15% 5%	274
August	Day	19% 25% 41% 13%	528
	Night	29% 22% 30% 16%	466
September	Day	12% 11% 34% 36% 6%	555
	Night	7% 11% 39% 36% 5%	510
October	Day	14% 13% 46% 24%	494
	Night	14% 13% 45% 25%	587
November	Day	18% 21% 42% 16%	313
	Night	14% 17% 48% 18%	418
December	Day	23% 15% 40% 20%	258
	Night	21% 15% 43% 18%	458

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	36% 43% 16%	192
February	Day	33% 50% 11% 5%	18
	Night	25% 42% 25% 6%	197
March	Day	19% 40% 31% 8%	47
	Night	27% 44% 25%	197
April	Day	20% 40% 24% 6% 8%	49
	Night	17% 44% 27% 10%	190
May	Day	7% 35% 35% 13% 7%	53
	Night	8% 41% 37% 12%	136
June	Day	27% 27% 36% 7%	55
	Night	31% 46% 15%	107
July	Day	5% 22% 38% 18% 14%	54
	Night	7% 22% 34% 34%	132
August	Day	10% 15% 29% 30% 15%	79
	Night	5% 12% 41% 34% 5%	285
September	Day	12% 20% 20% 30% 17%	70
	Night	8% 22% 38% 29%	296
October	Day	13% 40% 14% 24% 6%	74
	Night	13% 31% 28% 21%	293
November	Day	14% 32% 23% 29%	34
	Night	18% 30% 33% 16%	201
December	Night	25% 39% 28% 5%	204

Page generated at 2008-08-29 16:03:11. Version ab11