Brooke Stream Manor Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brooke Stream Manor Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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% 6% 2 6% 4 4 5% 4 6% 8% 41%	127327
	Night	14% 6% 2 6% 4 4 4 4 6% 7% 43%	124347
Transparency	Day	40% 4 11% 24% 17% 4	130924
	Night	40% 3 11% 25% 18% 4	128819
Seeing	Day	20% 13% 26% 23% 13% 5%	16432
	Night	18% 12% 27% 29% 12% 1	26072

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	15% 4 2 5% 4 4 4 4 5% 7% 48%	3880
	11th to 20th	Day	13% 9% 2 6% 4 4 3 3 5% 4 47%	4114
	21st to end	Day	15% 8% 2 6% 4 3 4 4 5% 7% 43%	4466
February	1st to 10th	Day	13% 9% 2 6% 5% 5% 5% 5% 5% 7% 39%	1800
	11th to 20th	Day	18% 8% 3 6% 5% 4 3 3 5% 7% 39%	1775
	21st to end	Day	17% 8% 3 6% 5% 3 4 3 4 6% 41%	1650
March	1st to 10th	Day	18% 6% 2 5% 4 4 5% 3 5% 6% 42%	4930
	11th to 20th	Day	11% 6% 2 5% 4 4 4 4 5% 7% 49%	4980
	21st to end	Day	15% 6% 2 7% 5% 4 5% 4 6% 7% 40%	5502
April	1st to 10th	Day	13% 7% 2 7% 5% 4 5% 4 6% 8% 40%	2400
	11th to 20th	Day	13% 5% 3 6% 4 3 3 3 6% 6% 46%	2374
	21st to end	Day	17% 6% 2 6% 5% 3 4 4 6% 6% 42%	2400
May	1st to 10th	Day	19% 7% 2 6% 4 5% 6% 4 6% 9% 31%	5862
	11th to 20th	Day	23% 7% 2 6% 4 4 4 4 7% 10% 31%	6061
	21st to end	Day	16% 5% 2 6% 4 4 5% 4 7% 9% 39%	6934
June	1st to 10th	Day	11% 4 2 5% 5% 4 4 5% 7% 9% 43%	2800
	11th to 20th	Day	12% 5% 2 6% 4 5% 6% 5% 7% 8% 41%	2800
	21st to end	Day	10% 3 2 4 4 5% 5% 5% 7% 11% 45%	2800
July	1st to 10th	Day	6% 5% 2 6% 5% 5% 5% 5% 7% 10% 44%	6360
	11th to 20th	Day	8% 5% 3 8% 6% 6% 6% 6% 9% 11% 32%	6049
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 10% 40%	6424
August	1st to 10th	Day	15% 6% 2 7% 5% 5% 5% 5% 7% 9% 35%	4234
	11th to 20th	Day	9% 4 2 6% 5% 4 6% 6% 7% 9% 41%	4051
	21st to end	Day	11% 4 2 5% 4 4 5% 4 6% 8% 49%	4312
September	1st to 10th	Day	15% 6% 2 5% 4 4 4 4 4 7% 47%	2400
	11th to 20th	Day	13% 5% 2 6% 3 4 3 4 5% 7% 48%	2395
	21st to end	Day	21% 7% 2 7% 4 3 4 3 5% 7% 37%	2088
October	1st to 10th	Day	16% 6% 2 5% 3 4 3 2 6% 7% 48%	2000
	11th to 20th	Day	16% 5% 2 4 4 3 4 3 4 5% 49%	2000
	21st to end	Day	14% 5% 2 5% 3 3 3 3 5% 6% 51%	2200
November	1st to 10th	Day	11% 6% 2 4 3 3 4 3 5% 7% 52%	1985
	11th to 20th	Day	14% 6% 2 5% 3 3 3 4 5% 6% 49%	1823
	21st to end	Day	15% 6% 2 5% 4 4 5% 3 4 7% 46%	1680
December	1st to 10th	Day	12% 5% 2 5% 3 5% 4 3 5% 6% 48%	2680
	11th to 20th	Day	18% 7% 2 5% 4 4 4 3 4 6% 41%	3070
	21st to end	Day	17% 8% 2 7% 4 4 4 4 6% 8% 35%	4048
January	1st to 10th	Night	11% 7% 2 5% 4 4 4 3 5% 7% 49%	6283
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 50%	5979
	21st to end	Night	14% 8% 3 6% 3 2 3 3 5% 6% 48%	6490
February	1st to 10th	Night	14% 8% 3 6% 5% 4 4 4 5% 6% 41%	2600
	11th to 20th	Night	18% 8% 2 6% 4 4 4 4 5% 5% 42%	2509
	21st to end	Night	17% 8% 3 7% 4 4 4 3 5% 6% 41%	1980
March	1st to 10th	Night	16% 6% 2 5% 4 3 3 3 4 5% 47%	4918
	11th to 20th	Night	10% 6% 2 5% 4 4 4 3 5% 6% 50%	4980
	21st to end	Night	11% 8% 2 6% 4 4 5% 4 6% 6% 44%	5429
April	1st to 10th	Night	15% 8% 2 6% 4 5% 4 4 6% 6% 39%	2000
	11th to 20th	Night	13% 6% 2 7% 4 4 4 4 6% 7% 44%	1975
	21st to end	Night	16% 5% 2 4 4 4 4 3 6% 7% 44%	2000
May	1st to 10th	Night	21% 9% 3 8% 4 5% 4 4 5% 8% 29%	4061
	11th to 20th	Night	25% 7% 2 6% 4 3 4 3 6% 8% 31%	3814
	21st to end	Night	17% 7% 2 7% 4 4 5% 5% 7% 8% 35%	3920
June	1st to 10th	Night	11% 5% 2 5% 4 5% 4 5% 6% 7% 45%	1600
	11th to 20th	Night	12% 6% 2 5% 4 5% 5% 5% 7% 8% 43%	1600
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 8% 10% 44%	1600
July	1st to 10th	Night	7% 6% 2 7% 5% 6% 6% 4 8% 10% 40%	3598
	11th to 20th	Night	7% 7% 4 9% 6% 6% 7% 7% 8% 10% 30%	3890
	21st to end	Night	8% 5% 2 6% 4 5% 6% 5% 7% 10% 42%	4427
August	1st to 10th	Night	15% 6% 2 7% 4 6% 6% 5% 7% 9% 33%	2915
	11th to 20th	Night	9% 6% 2 7% 5% 5% 5% 4 7% 8% 40%	2964
	21st to end	Night	13% 4 2 4 4 4 5% 3 6% 8% 47%	3586
September	1st to 10th	Night	15% 4 2 5% 4 4 3 4 7% 7% 45%	2000
	11th to 20th	Night	12% 6% 3 6% 4 3 4 2 4 6% 52%	2000
	21st to end	Night	21% 6% 3 6% 4 4 4 3 5% 5% 39%	2311
October	1st to 10th	Night	19% 5% 2 4 3 3 4 2 4 5% 48%	2400
	11th to 20th	Night	15% 4 2 5% 3 3 3 2 4 6% 53%	2400
	21st to end	Night	15% 5% 2 4 3 3 3 3 4 7% 52%	2640
November	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 5% 6% 53%	2530
	11th to 20th	Night	14% 7% 2 5% 3 3 3 4 5% 6% 49%	2793
	21st to end	Night	13% 4 2 6% 4 3 5% 4 5% 8% 47%	2940
December	1st to 10th	Night	10% 4 2 5% 3 4 4 3 5% 8% 51%	4720
	11th to 20th	Night	20% 6% 2 5% 4 4 4 4 5% 7% 40%	5345
	21st to end	Night	16% 7% 2 7% 5% 4 5% 4 7% 8% 35%	7150

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% 2 5% 28% 21% 7%	3881
	11th to 20th	Day	41% 2 6% 22% 20% 9%	4114
	21st to end	Day	43% 2 9% 28% 15% 4	4466
February	1st to 10th	Day	45% 4 12% 25% 13% 2	1800
	11th to 20th	Day	46% 4 7% 23% 17% 3	1784
	21st to end	Day	46% 3 10% 22% 16% 4	1650
March	1st to 10th	Day	44% 2 7% 22% 16% 8%	4930
	11th to 20th	Day	36% 2 8% 27% 21% 6%	4980
	21st to end	Day	44% 3 11% 18% 19% 6%	5502
April	1st to 10th	Day	43% 3 11% 20% 19% 5%	2400
	11th to 20th	Day	39% 2 10% 23% 20% 6%	2374
	21st to end	Day	44% 3 9% 24% 17% 4	2400
May	1st to 10th	Day	49% 4 15% 20% 10% 2	5897
	11th to 20th	Day	50% 3 11% 26% 10% 1	6065
	21st to end	Day	42% 4 13% 23% 16% 2	6949
June	1st to 10th	Day	36% 5% 14% 26% 17% 1	2800
	11th to 20th	Day	38% 7% 14% 25% 14% 2	2800
	21st to end	Day	32% 6% 16% 27% 18% 2	2800
July	1st to 10th	Day	35% 7% 16% 23% 15% 4	6290
	11th to 20th	Day	42% 7% 17% 24% 8% 1	5976
	21st to end	Day	38% 5% 10% 23% 23% 1	6240
August	1st to 10th	Day	44% 5% 15% 27% 9%	4221
	11th to 20th	Day	37% 6% 13% 28% 16% 1	4090
	21st to end	Day	34% 4 13% 29% 18% 2	4312
September	1st to 10th	Day	38% 4 11% 21% 21% 5%	2400
	11th to 20th	Day	36% 3 7% 28% 22% 3	2395
	21st to end	Day	48% 4 8% 20% 18% 2	2088
October	1st to 10th	Day	36% 2 8% 20% 28% 5%	3260
	11th to 20th	Day	27% 2 8% 30% 24% 10%	3240
	21st to end	Day	24% 2 9% 31% 29% 6%	3538
November	1st to 10th	Day	33% 2 11% 26% 22% 5%	1985
	11th to 20th	Day	36% 2 10% 24% 22% 5%	1823
	21st to end	Day	39% 4 11% 29% 16% 2	1680
December	1st to 10th	Day	37% 4 12% 29% 14% 4	2680
	11th to 20th	Day	45% 2 12% 27% 11% 3	3066
	21st to end	Day	47% 2 14% 21% 15% 1	4048
January	1st to 10th	Night	36% 2 7% 27% 25% 4	6283
	11th to 20th	Night	37% 2 8% 24% 23% 7%	5979
	21st to end	Night	39% 1 8% 30% 19% 3	6490
February	1st to 10th	Night	43% 3 12% 26% 14% 2	2600
	11th to 20th	Night	45% 3 8% 23% 16% 5%	2511
	21st to end	Night	44% 2 9% 23% 16% 5%	1980
March	1st to 10th	Night	41% 2 7% 28% 15% 9%	4918
	11th to 20th	Night	35% 2 10% 26% 20% 6%	4980
	21st to end	Night	40% 3 10% 22% 20% 5%	5429
April	1st to 10th	Night	44% 4 9% 20% 20% 4	2000
	11th to 20th	Night	39% 3 11% 21% 20% 6%	1975
	21st to end	Night	39% 4 10% 28% 15% 4	2000
May	1st to 10th	Night	54% 4 12% 18% 9% 4	4088
	11th to 20th	Night	53% 3 10% 23% 10% 1	3815
	21st to end	Night	46% 4 14% 25% 9% 3	3927
June	1st to 10th	Night	37% 5% 12% 26% 18% 3	1600
	11th to 20th	Night	38% 5% 15% 26% 14% 2	1600
	21st to end	Night	33% 5% 15% 26% 18% 3	1600
July	1st to 10th	Night	39% 7% 17% 19% 14% 3	3560
	11th to 20th	Night	47% 8% 19% 16% 9% 1	3843
	21st to end	Night	36% 5% 15% 23% 19%	4297
August	1st to 10th	Night	46% 5% 15% 24% 9% 1	2904
	11th to 20th	Night	40% 5% 11% 28% 15% 1	2991
	21st to end	Night	34% 4 13% 31% 17% 2	3586
September	1st to 10th	Night	38% 4 11% 23% 19% 5%	2000
	11th to 20th	Night	35% 3 8% 29% 23% 3	2000
	21st to end	Night	48% 3 9% 21% 17% 2	2311
October	1st to 10th	Night	40% 3 9% 23% 22% 4	3920
	11th to 20th	Night	25% 2 10% 23% 32% 7%	3899
	21st to end	Night	24% 2 9% 33% 27% 6%	4252
November	1st to 10th	Night	33% 3 9% 26% 24% 5%	2530
	11th to 20th	Night	36% 3 7% 26% 23% 6%	2793
	21st to end	Night	37% 3 11% 26% 19% 4	2940
December	1st to 10th	Night	33% 3 14% 30% 19% 2	4720
	11th to 20th	Night	45% 2 12% 20% 16% 4	5348
	21st to end	Night	47% 3 14% 20% 15% 1	7150

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	34% 24% 26% 14% 2	266
	11th to 20th	Day	37% 22% 28% 12% 1	318
	21st to end	Day	28% 30% 28% 11% 2 1	330
February	1st to 10th	Day	24% 29% 34% 10% 3	300
	11th to 20th	Day	39% 27% 28% 4 2	322
	21st to end	Day	30% 20% 32% 15% 2	414
March	1st to 10th	Day	27% 21% 30% 19% 3	500
	11th to 20th	Day	26% 24% 28% 15% 5% 2	500
	21st to end	Day	23% 21% 33% 17% 5% 1	550
April	1st to 10th	Day	25% 23% 30% 15% 7% 1	500
	11th to 20th	Day	20% 18% 29% 18% 12% 3	492
	21st to end	Day	24% 16% 31% 18% 9% 2	500
May	1st to 10th	Day	24% 17% 28% 18% 10% 3	503
	11th to 20th	Day	24% 12% 27% 21% 13% 4	527
	21st to end	Day	20% 8% 23% 24% 19% 5%	573
June	1st to 10th	Day	14% 8% 30% 24% 18% 5%	530
	11th to 20th	Day	16% 8% 24% 31% 16% 5%	530
	21st to end	Day	10% 7% 30% 29% 17% 8%	530
July	1st to 10th	Day	12% 4 16% 31% 26% 10%	525
	11th to 20th	Day	7% 3 21% 31% 29% 9%	524
	21st to end	Day	12% 4 21% 34% 20% 9%	576
August	1st to 10th	Day	13% 5% 19% 28% 20% 13%	526
	11th to 20th	Day	13% 4 22% 31% 21% 10%	519
	21st to end	Day	9% 3 22% 33% 20% 13%	583
September	1st to 10th	Day	19% 8% 17% 26% 21% 9%	530
	11th to 20th	Day	15% 5% 19% 32% 18% 11%	530
	21st to end	Day	28% 9% 23% 24% 13% 3	530
October	1st to 10th	Day	19% 8% 21% 26% 19% 8%	530
	11th to 20th	Day	18% 15% 25% 27% 12% 2	530
	21st to end	Day	17% 16% 32% 24% 11% 2	583
November	1st to 10th	Day	17% 14% 31% 25% 9% 3	496
	11th to 20th	Day	22% 16% 35% 18% 9% 1	363
	21st to end	Day	25% 20% 32% 16% 5% 1	220
December	1st to 10th	Day	21% 22% 38% 15% 3 1	220
	11th to 20th	Day	23% 25% 30% 18% 5%	220
	21st to end	Day	24% 23% 31% 17% 5%	242
January	1st to 10th	Night	22% 21% 36% 18% 3	840
	11th to 20th	Night	25% 16% 31% 24% 4	825
	21st to end	Night	20% 19% 38% 20% 2	880
February	1st to 10th	Night	19% 17% 36% 26% 2	800
	11th to 20th	Night	26% 23% 33% 16% 2	783
	21st to end	Night	26% 16% 36% 18% 3	660
March	1st to 10th	Night	22% 19% 35% 20% 3	800
	11th to 20th	Night	24% 20% 30% 20% 5% 1	800
	21st to end	Night	20% 19% 36% 20% 4 1	880
April	1st to 10th	Night	21% 19% 34% 23% 4	800
	11th to 20th	Night	18% 13% 34% 27% 7%	791
	21st to end	Night	20% 13% 29% 30% 8%	800
May	1st to 10th	Night	21% 8% 27% 32% 12%	615
	11th to 20th	Night	23% 5% 23% 38% 10% 1	503
	21st to end	Night	16% 5% 22% 39% 17% 1	433
June	1st to 10th	Night	12% 4 23% 39% 21% 1	400
	11th to 20th	Night	14% 5% 20% 39% 21% 2	400
	21st to end	Night	9% 3 22% 45% 20% 2	400
July	1st to 10th	Night	10% 4 16% 39% 27% 4	390
	11th to 20th	Night	7% 2 13% 39% 35% 4	510
	21st to end	Night	9% 2 16% 42% 27% 3	657
August	1st to 10th	Night	12% 2 11% 42% 30% 4	597
	11th to 20th	Night	11% 4 12% 41% 30% 3	644
	21st to end	Night	13% 3 15% 39% 26% 3	880
September	1st to 10th	Night	16% 2 18% 34% 26% 4	800
	11th to 20th	Night	12% 5% 18% 35% 27% 4	800
	21st to end	Night	24% 7% 18% 30% 21% 1	800
October	1st to 10th	Night	20% 6% 21% 30% 20% 4	800
	11th to 20th	Night	17% 12% 25% 31% 15% 1	800
	21st to end	Night	18% 12% 29% 29% 11% 1	880
November	1st to 10th	Night	14% 13% 31% 31% 10% 1	820
	11th to 20th	Night	19% 15% 31% 27% 8% 1	840
	21st to end	Night	17% 17% 32% 27% 7%	840
December	1st to 10th	Night	22% 16% 33% 22% 6%	840
	11th to 20th	Night	21% 13% 37% 25% 4	840
	21st to end	Night	21% 14% 34% 29% 2	924

Page generated at 2026-01-14 01:14:31. Version ac07

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