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 2005-11-06 to 2025-09-04.

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	14% 7% 2 6% 5% 4 5% 4 6% 8% 39%	126160
	Night	14% 7% 2 6% 4 4 4 4 5% 7% 41%	122551
Transparency	Day	41% 6% 12% 23% 16% 3	129754
	Night	40% 5% 11% 23% 17% 3	127026
Seeing	Day	19% 15% 28% 22% 12% 4	15993
	Night	18% 13% 31% 27% 11% 1	25400

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	14% 6% 3 5% 4 5% 6% 4 5% 5% 43%	3597
	11th to 20th	Day	13% 9% 3 10% 6% 4 3 3 4 5% 40%	4042
	21st to end	Day	15% 8% 3 7% 5% 4 4 3 6% 5% 39%	4466
February	1st to 10th	Day	14% 9% 2 6% 5% 5% 5% 5% 6% 6% 37%	1800
	11th to 20th	Day	16% 8% 2 7% 5% 4 4 3 5% 7% 38%	1808
	21st to end	Day	18% 10% 3 6% 5% 4 3 2 4 5% 39%	1650
March	1st to 10th	Day	18% 6% 2 5% 4 4 4 4 5% 7% 42%	4796
	11th to 20th	Day	11% 6% 2 7% 4 5% 4 4 5% 7% 45%	4980
	21st to end	Day	15% 7% 2 7% 5% 6% 4 4 5% 6% 40%	5592
April	1st to 10th	Day	14% 9% 3 6% 4 4 5% 4 6% 7% 37%	2400
	11th to 20th	Day	14% 6% 2 6% 5% 5% 4 3 5% 7% 43%	2374
	21st to end	Day	17% 7% 3 6% 3 5% 3 4 6% 5% 41%	2400
May	1st to 10th	Day	22% 7% 2 6% 4 4 5% 5% 6% 9% 30%	5787
	11th to 20th	Day	22% 7% 3 7% 4 4 5% 4 6% 9% 30%	6267
	21st to end	Day	16% 5% 2 6% 4 5% 5% 4 7% 9% 37%	6934
June	1st to 10th	Day	13% 6% 2 5% 5% 4 5% 4 7% 10% 39%	2800
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	2800
	21st to end	Day	10% 4 2 4 5% 5% 5% 4 7% 10% 45%	2800
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 10% 42%	6360
	11th to 20th	Day	9% 7% 2 8% 5% 6% 6% 6% 8% 11% 31%	6319
	21st to end	Day	9% 6% 3 7% 4 5% 5% 4 7% 9% 40%	6424
August	1st to 10th	Day	17% 6% 2 7% 5% 4 6% 5% 6% 9% 34%	4234
	11th to 20th	Day	11% 6% 2 7% 4 5% 6% 4 7% 9% 39%	3996
	21st to end	Day	11% 5% 2 5% 4 4 4 4 6% 7% 47%	4312
September	1st to 10th	Day	15% 6% 2 5% 4 4 3 4 5% 7% 45%	2316
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 6% 8% 48%	2280
	21st to end	Day	20% 8% 2 6% 4 4 4 3 5% 7% 38%	2005
October	1st to 10th	Day	17% 5% 2 4 5% 3 4 4 4 7% 45%	1900
	11th to 20th	Day	16% 7% 2 6% 3 3 3 3 4 5% 48%	1900
	21st to end	Day	14% 7% 3 5% 3 3 4 3 6% 6% 46%	2090
November	1st to 10th	Day	11% 6% 2 5% 3 3 3 3 6% 7% 50%	1816
	11th to 20th	Day	14% 6% 2 4 5% 3 4 4 5% 6% 46%	1765
	21st to end	Day	16% 6% 3 6% 4 4 5% 4 5% 6% 43%	1600
December	1st to 10th	Day	13% 6% 2 6% 5% 6% 4 4 6% 7% 40%	2600
	11th to 20th	Day	18% 10% 3 7% 4 3 3 3 4 6% 38%	2990
	21st to end	Day	17% 10% 3 6% 4 4 5% 4 6% 8% 34%	3960
January	1st to 10th	Night	11% 8% 3 7% 4 5% 4 4 5% 7% 42%	6349
	11th to 20th	Night	14% 7% 2 5% 4 4 4 3 5% 6% 46%	5903
	21st to end	Night	15% 8% 2 5% 4 4 4 3 5% 5% 44%	6490
February	1st to 10th	Night	15% 9% 3 6% 5% 4 4 3 6% 7% 39%	2600
	11th to 20th	Night	17% 9% 3 6% 4 4 4 3 5% 5% 40%	2478
	21st to end	Night	16% 9% 3 6% 4 5% 4 4 5% 6% 38%	1980
March	1st to 10th	Night	16% 6% 2 6% 4 4 4 3 4 5% 46%	5053
	11th to 20th	Night	10% 5% 2 6% 5% 5% 4 3 5% 6% 49%	4980
	21st to end	Night	11% 9% 3 7% 4 4 4 3 5% 6% 44%	5338
April	1st to 10th	Night	16% 9% 3 6% 6% 4 4 4 6% 7% 36%	2000
	11th to 20th	Night	13% 7% 2 6% 4 4 4 4 5% 8% 43%	1975
	21st to end	Night	16% 6% 3 5% 4 4 4 4 6% 7% 42%	2000
May	1st to 10th	Night	23% 9% 3 7% 4 5% 4 4 6% 7% 28%	4137
	11th to 20th	Night	21% 9% 3 6% 4 4 5% 3 6% 8% 31%	3622
	21st to end	Night	18% 7% 2 7% 4 4 4 4 6% 8% 36%	3920
June	1st to 10th	Night	11% 6% 2 5% 4 4 5% 4 6% 8% 46%	1600
	11th to 20th	Night	11% 6% 2 6% 5% 4 5% 5% 6% 10% 39%	1600
	21st to end	Night	7% 6% 2 6% 4 5% 5% 4 7% 10% 43%	1600
July	1st to 10th	Night	7% 6% 3 8% 5% 6% 6% 5% 7% 10% 39%	3598
	11th to 20th	Night	9% 8% 4 10% 6% 6% 6% 5% 8% 9% 30%	3634
	21st to end	Night	9% 7% 2 6% 4 5% 5% 4 6% 9% 44%	4427
August	1st to 10th	Night	18% 7% 2 6% 4 5% 5% 4 7% 9% 34%	2915
	11th to 20th	Night	9% 8% 3 8% 5% 5% 4 5% 6% 7% 39%	3006
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 8% 47%	3586
September	1st to 10th	Night	12% 6% 3 6% 4 4 4 4 6% 7% 46%	1931
	11th to 20th	Night	11% 5% 2 5% 3 4 4 3 4 7% 53%	1900
	21st to end	Night	19% 6% 2 5% 4 4 4 3 4 6% 41%	2169
October	1st to 10th	Night	18% 7% 3 5% 3 4 4 3 5% 6% 44%	2280
	11th to 20th	Night	14% 6% 2 4 3 3 4 3 4 6% 50%	2280
	21st to end	Night	15% 6% 2 5% 3 3 4 3 5% 6% 48%	2508
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 5% 7% 52%	2480
	11th to 20th	Night	14% 8% 2 6% 4 3 4 3 5% 6% 46%	2631
	21st to end	Night	14% 5% 2 5% 5% 4 4 4 6% 6% 45%	2800
December	1st to 10th	Night	11% 6% 2 6% 4 4 5% 4 6% 7% 45%	4580
	11th to 20th	Night	20% 7% 2 5% 4 5% 5% 4 5% 6% 37%	5205
	21st to end	Night	17% 9% 2 7% 5% 5% 5% 5% 6% 7% 33%	6996

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	38% 4 9% 26% 19% 4	3598
	11th to 20th	Day	46% 3 9% 20% 16% 6%	4042
	21st to end	Day	44% 5% 11% 23% 14% 3	4466
February	1st to 10th	Day	46% 6% 13% 25% 10% 2	1800
	11th to 20th	Day	46% 5% 9% 23% 14% 3	1817
	21st to end	Day	48% 4 11% 21% 13% 4	1650
March	1st to 10th	Day	41% 4 11% 23% 15% 7%	4796
	11th to 20th	Day	36% 4 11% 26% 16% 6%	4980
	21st to end	Day	44% 5% 9% 19% 19% 5%	5592
April	1st to 10th	Day	45% 5% 12% 19% 16% 4	2400
	11th to 20th	Day	40% 6% 11% 21% 18% 4	2374
	21st to end	Day	43% 6% 10% 21% 18% 3	2400
May	1st to 10th	Day	49% 7% 13% 19% 10% 2	5821
	11th to 20th	Day	50% 7% 10% 22% 9% 1	6271
	21st to end	Day	42% 7% 12% 23% 15% 2	6949
June	1st to 10th	Day	38% 8% 14% 24% 15% 2	2800
	11th to 20th	Day	40% 8% 13% 23% 13% 2	2800
	21st to end	Day	34% 9% 14% 25% 17% 1	2800
July	1st to 10th	Day	35% 10% 15% 20% 17% 3	6290
	11th to 20th	Day	42% 10% 17% 21% 8% 1	6244
	21st to end	Day	38% 7% 11% 22% 21% 1	6240
August	1st to 10th	Day	45% 8% 13% 25% 9%	4221
	11th to 20th	Day	38% 7% 12% 27% 15% 1	4035
	21st to end	Day	35% 6% 12% 28% 18% 2	4312
September	1st to 10th	Day	39% 6% 10% 20% 20% 4	2316
	11th to 20th	Day	34% 5% 9% 26% 22% 3	2280
	21st to end	Day	47% 5% 8% 19% 19% 2	2005
October	1st to 10th	Day	38% 4 7% 20% 27% 5%	3160
	11th to 20th	Day	29% 3 10% 27% 21% 10%	3140
	21st to end	Day	26% 4 10% 29% 29% 3	3428
November	1st to 10th	Day	34% 5% 12% 25% 21% 4	1816
	11th to 20th	Day	36% 6% 11% 23% 21% 3	1765
	21st to end	Day	41% 5% 11% 29% 12% 2	1600
December	1st to 10th	Day	40% 5% 16% 27% 9% 3	2600
	11th to 20th	Day	47% 4 12% 27% 9% 1	2986
	21st to end	Day	46% 5% 17% 17% 14% 1	3960
January	1st to 10th	Night	38% 4 10% 25% 20% 3	6349
	11th to 20th	Night	37% 3 10% 26% 17% 6%	5903
	21st to end	Night	41% 3 10% 27% 17% 2	6490
February	1st to 10th	Night	43% 5% 13% 24% 13% 2	2600
	11th to 20th	Night	46% 4 9% 21% 17% 4	2480
	21st to end	Night	45% 4 11% 20% 15% 5%	1980
March	1st to 10th	Night	41% 4 8% 26% 12% 9%	5053
	11th to 20th	Night	35% 4 12% 30% 14% 6%	4980
	21st to end	Night	41% 4 9% 19% 23% 4	5338
April	1st to 10th	Night	46% 5% 11% 18% 17% 3	2000
	11th to 20th	Night	39% 5% 11% 22% 18% 5%	1975
	21st to end	Night	40% 5% 11% 22% 18% 4	2000
May	1st to 10th	Night	54% 6% 10% 16% 11% 3	4165
	11th to 20th	Night	49% 8% 11% 21% 10% 1	3623
	21st to end	Night	45% 8% 12% 24% 10% 2	3927
June	1st to 10th	Night	36% 8% 10% 26% 18% 2	1600
	11th to 20th	Night	38% 10% 12% 24% 15% 1	1600
	21st to end	Night	35% 8% 12% 25% 18% 2	1600
July	1st to 10th	Night	39% 10% 15% 19% 14% 3	3560
	11th to 20th	Night	46% 11% 14% 19% 9% 1	3589
	21st to end	Night	36% 7% 12% 23% 21% 1	4297
August	1st to 10th	Night	44% 8% 18% 21% 8% 1	2904
	11th to 20th	Night	40% 8% 10% 28% 13% 1	3033
	21st to end	Night	34% 6% 11% 30% 17% 2	3586
September	1st to 10th	Night	37% 6% 11% 21% 20% 5%	1931
	11th to 20th	Night	33% 5% 9% 26% 24% 3	1900
	21st to end	Night	44% 7% 9% 19% 19% 3	2169
October	1st to 10th	Night	42% 5% 10% 19% 21% 3	3800
	11th to 20th	Night	25% 4 10% 26% 27% 7%	3779
	21st to end	Night	25% 4 10% 32% 24% 5%	4120
November	1st to 10th	Night	33% 4 11% 25% 22% 5%	2480
	11th to 20th	Night	39% 4 9% 24% 20% 5%	2631
	21st to end	Night	37% 5% 12% 26% 18% 2	2800
December	1st to 10th	Night	36% 4 15% 30% 13% 1	4580
	11th to 20th	Night	46% 4 13% 19% 15% 3	5208
	21st to end	Night	47% 6% 13% 18% 16% 1	6996

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	30% 28% 30% 11% 3 1	200
	11th to 20th	Day	29% 27% 32% 10% 1	297
	21st to end	Day	23% 32% 30% 12% 4	330
February	1st to 10th	Day	26% 27% 35% 10% 2	300
	11th to 20th	Day	36% 26% 31% 5% 1	355
	21st to end	Day	29% 25% 30% 13% 2	414
March	1st to 10th	Day	24% 26% 30% 17% 3	500
	11th to 20th	Day	25% 24% 31% 15% 4 1	500
	21st to end	Day	24% 24% 31% 15% 5% 1	550
April	1st to 10th	Day	25% 22% 33% 14% 5% 1	500
	11th to 20th	Day	20% 22% 29% 16% 10% 2	492
	21st to end	Day	24% 15% 34% 17% 8% 1	500
May	1st to 10th	Day	25% 16% 31% 17% 9% 2	503
	11th to 20th	Day	23% 16% 29% 21% 9% 2	527
	21st to end	Day	17% 8% 26% 26% 19% 5%	573
June	1st to 10th	Day	15% 12% 30% 23% 15% 5%	530
	11th to 20th	Day	17% 9% 30% 27% 13% 4	530
	21st to end	Day	12% 8% 26% 34% 16% 5%	530
July	1st to 10th	Day	11% 5% 22% 31% 20% 10%	525
	11th to 20th	Day	6% 3 24% 34% 25% 8%	524
	21st to end	Day	11% 6% 22% 35% 21% 5%	576
August	1st to 10th	Day	13% 5% 21% 30% 23% 8%	526
	11th to 20th	Day	12% 4 23% 33% 21% 8%	519
	21st to end	Day	11% 5% 21% 32% 21% 11%	583
September	1st to 10th	Day	17% 9% 18% 24% 22% 11%	502
	11th to 20th	Day	11% 5% 23% 30% 22% 9%	490
	21st to end	Day	26% 12% 23% 23% 12% 4	490
October	1st to 10th	Day	20% 10% 24% 24% 16% 6%	490
	11th to 20th	Day	18% 16% 27% 25% 12% 2	490
	21st to end	Day	17% 14% 36% 21% 9% 2	539
November	1st to 10th	Day	17% 14% 32% 23% 11% 2	423
	11th to 20th	Day	19% 20% 34% 18% 9% 1	365
	21st to end	Day	23% 22% 33% 17% 6%	200
December	1st to 10th	Day	24% 24% 36% 13% 4 1	200
	11th to 20th	Day	26% 27% 29% 16% 4	200
	21st to end	Day	20% 22% 34% 18% 6%	220
January	1st to 10th	Night	18% 23% 40% 16% 2	800
	11th to 20th	Night	23% 20% 33% 21% 3	800
	21st to end	Night	18% 20% 43% 18% 1	880
February	1st to 10th	Night	20% 20% 36% 23% 2	800
	11th to 20th	Night	26% 25% 34% 14% 1	783
	21st to end	Night	25% 20% 39% 14% 3	660
March	1st to 10th	Night	20% 19% 40% 18% 3	800
	11th to 20th	Night	21% 21% 34% 19% 5%	800
	21st to end	Night	20% 16% 42% 18% 4	880
April	1st to 10th	Night	22% 21% 35% 18% 4	800
	11th to 20th	Night	17% 16% 37% 23% 7% 1	791
	21st to end	Night	20% 15% 33% 25% 7% 1	800
May	1st to 10th	Night	19% 11% 33% 28% 9%	653
	11th to 20th	Night	20% 8% 31% 32% 8% 1	415
	21st to end	Night	15% 6% 26% 35% 17% 1	433
June	1st to 10th	Night	11% 3 31% 34% 21%	400
	11th to 20th	Night	14% 5% 28% 38% 16% 1	400
	21st to end	Night	9% 5% 26% 44% 17%	400
July	1st to 10th	Night	8% 4 21% 39% 25% 4	390
	11th to 20th	Night	9% 2 19% 40% 28% 3	399
	21st to end	Night	10% 2 19% 40% 26% 3	657
August	1st to 10th	Night	12% 2 12% 47% 24% 2	597
	11th to 20th	Night	12% 4 17% 40% 25% 2	673
	21st to end	Night	12% 4 18% 37% 25% 4	880
September	1st to 10th	Night	14% 3 22% 33% 25% 3	773
	11th to 20th	Night	11% 4 18% 36% 26% 4	760
	21st to end	Night	23% 5% 23% 30% 17% 2	760
October	1st to 10th	Night	22% 6% 22% 29% 17% 3	760
	11th to 20th	Night	16% 11% 29% 30% 12% 1	760
	21st to end	Night	18% 11% 34% 25% 12%	836
November	1st to 10th	Night	14% 11% 35% 31% 8% 1	780
	11th to 20th	Night	19% 18% 32% 24% 6% 1	800
	21st to end	Night	15% 18% 37% 23% 7% 1	800
December	1st to 10th	Night	23% 14% 38% 18% 6%	800
	11th to 20th	Night	20% 15% 40% 21% 5%	800
	21st to end	Night	20% 17% 36% 25% 3	880

Page generated at 2025-09-01 01:51:06. Version ac07

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