Brooklyn Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brooklyn Lake clear sky chart from 2005-11-06 to 2025-07-06.

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	2 5% 2 7% 5% 5% 5% 5% 8% 10% 47%	124134
	Night	1 4 2 5% 4 4 5% 5% 8% 12% 52%	123584
Transparency	Day	30% 6% 13% 25% 19% 7%	123882
	Night	24% 5% 15% 29% 19% 6%	123424
Seeing	Day	17% 28% 30% 16% 8% 1	16593
	Night	13% 32% 25% 19% 9% 1	26647

By Month

Percentage Cloud Cover SW (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	2 1 6% 5% 5% 5% 5% 9% 16% 46%	3638
	11th to 20th	Day	2 1 4 6% 7% 7% 5% 9% 20% 39%	3760
	21st to end	Day	2 2 8% 4 4 4 4 6% 11% 54%	4510
February	1st to 10th	Day	3 3 9% 8% 7% 5% 7% 10% 10% 39%	1800
	11th to 20th	Day	4 3 8% 7% 6% 7% 6% 10% 10% 40%	1819
	21st to end	Day	4 3 10% 7% 7% 7% 4 9% 9% 39%	1650
March	1st to 10th	Day	5% 4 12% 5% 4 5% 4 6% 8% 46%	4608
	11th to 20th	Day	5% 3 8% 5% 4 5% 4 9% 12% 45%	5000
	21st to end	Day	1 6% 3 8% 5% 5% 6% 5% 10% 14% 36%	5702
April	1st to 10th	Day	2 8% 4 9% 7% 5% 5% 5% 7% 9% 39%	2400
	11th to 20th	Day	3 12% 4 8% 6% 6% 6% 4 6% 9% 36%	2371
	21st to end	Day	4 12% 4 8% 6% 5% 5% 5% 7% 8% 36%	2400
May	1st to 10th	Day	5% 16% 5% 9% 6% 6% 5% 4 6% 7% 30%	6034
	11th to 20th	Day	4 8% 2 7% 4 5% 5% 5% 9% 11% 39%	6298
	21st to end	Day	3 5% 2 6% 5% 5% 6% 5% 8% 10% 45%	6925
June	1st to 10th	Day	5% 5% 2 6% 5% 4 5% 5% 8% 10% 45%	2800
	11th to 20th	Day	5% 5% 1 4 4 4 5% 4 6% 8% 52%	2800
	21st to end	Day	2 3 1 5% 4 5% 5% 5% 7% 9% 53%	2800
July	1st to 10th	Day	4 4 1 5% 4 4 5% 4 7% 8% 54%	4501
	11th to 20th	Day	3 3 2 5% 5% 5% 6% 6% 8% 9% 48%	4430
	21st to end	Day	5% 5% 2 6% 4 5% 6% 5% 8% 8% 47%	4691
August	1st to 10th	Day	3 5% 3 7% 5% 6% 6% 6% 9% 10% 40%	4092
	11th to 20th	Day	4 5% 2 6% 5% 6% 6% 4 7% 7% 50%	3891
	21st to end	Day	5% 4 2 5% 4 4 4 4 6% 7% 56%	4180
September	1st to 10th	Day	5% 6% 2 5% 4 4 4 3 5% 7% 55%	2280
	11th to 20th	Day	5% 5% 2 4 4 4 4 3 5% 6% 58%	2280
	21st to end	Day	5% 6% 2 5% 3 3 3 2 4 5% 61%	2042
October	1st to 10th	Day	3 3 1 4 3 2 3 2 4 4 70%	3170
	11th to 20th	Day	2 6% 2 5% 4 4 4 5% 7% 7% 54%	3150
	21st to end	Day	2 7% 3 5% 3 3 4 3 6% 7% 57%	3359
November	1st to 10th	Day	1 3 2 4 3 6% 5% 4 7% 9% 55%	1763
	11th to 20th	Day	1 5% 2 6% 4 4 5% 5% 8% 10% 50%	1740
	21st to end	Day	2 2 8% 6% 4 6% 4 8% 9% 51%	1600
December	1st to 10th	Day	2 1 4 5% 4 3 3 5% 12% 59%	2620
	11th to 20th	Day	3 1 5% 4 4 4 5% 9% 12% 52%	3026
	21st to end	Day	6% 2 7% 5% 5% 5% 5% 9% 16% 39%	4004
January	1st to 10th	Night	1 1 6% 6% 6% 6% 6% 9% 16% 43%	6327
	11th to 20th	Night	1 1 2 4 6% 7% 6% 9% 19% 46%	6249
	21st to end	Night	2 2 6% 4 4 4 5% 6% 11% 57%	6468
February	1st to 10th	Night	3 2 5% 5% 5% 6% 6% 11% 15% 42%	2600
	11th to 20th	Night	4 1 5% 4 4 6% 5% 13% 11% 46%	2467
	21st to end	Night	3 3 8% 5% 5% 5% 7% 9% 10% 45%	1980
March	1st to 10th	Night	3 2 7% 5% 4 5% 5% 7% 9% 52%	5269
	11th to 20th	Night	5% 3 7% 4 3 4 3 6% 12% 54%	5000
	21st to end	Night	1 6% 2 6% 4 4 5% 4 10% 16% 42%	5262
April	1st to 10th	Night	6% 2 6% 5% 4 6% 5% 7% 9% 49%	2000
	11th to 20th	Night	3 8% 3 8% 4 5% 6% 5% 6% 9% 44%	1977
	21st to end	Night	5% 9% 2 7% 3 4 4 3 7% 8% 48%	2000
May	1st to 10th	Night	5% 11% 3 7% 4 4 4 3 6% 8% 46%	3941
	11th to 20th	Night	3 6% 2 5% 4 4 4 4 9% 12% 47%	3617
	21st to end	Night	3 6% 2 5% 4 5% 5% 4 7% 9% 52%	3972
June	1st to 10th	Night	3 3 1 3 3 4 4 5% 7% 9% 58%	1600
	11th to 20th	Night	4 3 1 4 3 3 4 4 5% 8% 61%	1600
	21st to end	Night	2 4 1 4 2 3 4 4 5% 6% 65%	1600
July	1st to 10th	Night	2 2 1 4 4 4 4 4 6% 9% 60%	2580
	11th to 20th	Night	1 2 1 3 3 3 5% 5% 8% 11% 58%	2540
	21st to end	Night	1 2 1 3 3 4 6% 5% 7% 9% 59%	2869
August	1st to 10th	Night	1 3 1 5% 4 5% 5% 5% 9% 10% 52%	2847
	11th to 20th	Night	2 3 1 4 4 5% 6% 5% 9% 11% 51%	2934
	21st to end	Night	2 4 2 5% 4 4 4 4 6% 7% 58%	3487
September	1st to 10th	Night	5% 4 1 3 2 3 3 3 4 8% 63%	1900
	11th to 20th	Night	3 3 1 4 3 3 3 3 6% 8% 62%	1900
	21st to end	Night	4 4 1 3 2 3 4 3 5% 7% 65%	2136
October	1st to 10th	Night	3 3 1 2 2 2 2 2 4 5% 75%	3800
	11th to 20th	Night	2 4 2 4 4 4 4 4 6% 9% 56%	3778
	21st to end	Night	2 5% 2 4 3 3 3 3 6% 10% 59%	4166
November	1st to 10th	Night	1 4 2 3 3 3 4 4 7% 10% 60%	2535
	11th to 20th	Night	3 1 4 4 4 5% 6% 8% 12% 53%	2658
	21st to end	Night	1 4 2 6% 4 4 5% 4 7% 10% 53%	2800
December	1st to 10th	Night	2 1 3 2 2 3 4 6% 15% 61%	4570
	11th to 20th	Night	3 1 3 3 4 4 5% 9% 16% 52%	5181
	21st to end	Night	3 2 6% 4 4 6% 6% 11% 19% 38%	6974

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	24% 10% 19% 25% 19% 4	3639
	11th to 20th	Day	29% 7% 21% 25% 13% 5%	3760
	21st to end	Day	26% 5% 16% 23% 22% 8%	4510
February	1st to 10th	Day	35% 9% 19% 19% 14% 2	1800
	11th to 20th	Day	37% 7% 17% 23% 13% 4	1828
	21st to end	Day	41% 5% 15% 20% 16% 4	1650
March	1st to 10th	Day	38% 3 8% 27% 16% 9%	4608
	11th to 20th	Day	28% 8% 18% 33% 12% 1	5000
	21st to end	Day	36% 10% 18% 28% 8% 1	5702
April	1st to 10th	Day	41% 4 15% 22% 15% 4	2400
	11th to 20th	Day	45% 3 12% 23% 14% 2	2374
	21st to end	Day	43% 4 11% 31% 11% 1	2400
May	1st to 10th	Day	50% 6% 8% 18% 16% 3	6034
	11th to 20th	Day	34% 5% 13% 32% 15% 1	6302
	21st to end	Day	31% 6% 9% 32% 20% 3	6926
June	1st to 10th	Day	32% 5% 14% 26% 18% 6%	2800
	11th to 20th	Day	28% 5% 9% 20% 26% 13%	2800
	21st to end	Day	25% 5% 7% 22% 29% 13%	2800
July	1st to 10th	Day	23% 6% 8% 17% 26% 20%	4432
	11th to 20th	Day	24% 8% 10% 19% 21% 17%	4355
	21st to end	Day	28% 8% 9% 17% 22% 16%	4543
August	1st to 10th	Day	29% 9% 13% 23% 17% 9%	4078
	11th to 20th	Day	31% 6% 9% 17% 28% 9%	3930
	21st to end	Day	26% 6% 8% 19% 27% 15%	4179
September	1st to 10th	Day	28% 4 6% 19% 30% 13%	2280
	11th to 20th	Day	26% 4 9% 24% 25% 11%	2280
	21st to end	Day	26% 2 7% 31% 29% 4	2042
October	1st to 10th	Day	20% 2 6% 23% 40% 11%	3170
	11th to 20th	Day	25% 7% 11% 35% 19% 3	3150
	21st to end	Day	26% 5% 12% 37% 17% 2	3359
November	1st to 10th	Day	25% 5% 17% 29% 22% 2	1763
	11th to 20th	Day	27% 4 20% 26% 20% 3	1740
	21st to end	Day	29% 5% 16% 31% 16% 5%	1600
December	1st to 10th	Day	20% 4 20% 34% 20% 3	2620
	11th to 20th	Day	22% 7% 26% 35% 10%	3024
	21st to end	Day	31% 8% 16% 22% 16% 6%	4004
January	1st to 10th	Night	28% 7% 17% 29% 12% 7%	6327
	11th to 20th	Night	24% 5% 22% 27% 17% 5%	6249
	21st to end	Night	23% 4 17% 26% 21% 9%	6468
February	1st to 10th	Night	28% 8% 23% 26% 14% 2	2600
	11th to 20th	Night	27% 7% 19% 29% 14% 4	2468
	21st to end	Night	34% 3 17% 24% 18% 5%	1980
March	1st to 10th	Night	29% 3 10% 31% 16% 11%	5269
	11th to 20th	Night	24% 3 16% 32% 23% 2	5000
	21st to end	Night	28% 7% 21% 35% 8% 1	5262
April	1st to 10th	Night	30% 5% 18% 24% 18% 5%	2000
	11th to 20th	Night	36% 4 15% 28% 15% 2	1977
	21st to end	Night	34% 3 12% 33% 17% 1	2000
May	1st to 10th	Night	38% 4 8% 31% 16% 4	3938
	11th to 20th	Night	27% 5% 17% 36% 12% 3	3618
	21st to end	Night	27% 6% 11% 37% 19% 1	3972
June	1st to 10th	Night	21% 4 22% 29% 20% 4	1600
	11th to 20th	Night	21% 3 11% 23% 29% 12%	1600
	21st to end	Night	19% 3 7% 26% 30% 16%	1600
July	1st to 10th	Night	19% 4 9% 19% 28% 19%	2540
	11th to 20th	Night	16% 6% 11% 28% 25% 15%	2492
	21st to end	Night	19% 5% 12% 24% 23% 16%	2779
August	1st to 10th	Night	19% 9% 19% 25% 21% 7%	2838
	11th to 20th	Night	23% 11% 14% 21% 20% 12%	2961
	21st to end	Night	24% 5% 9% 19% 29% 14%	3487
September	1st to 10th	Night	21% 3 9% 20% 32% 15%	1900
	11th to 20th	Night	20% 3 11% 29% 26% 12%	1900
	21st to end	Night	20% 3 8% 28% 34% 6%	2136
October	1st to 10th	Night	15% 2 5% 24% 43% 11%	3800
	11th to 20th	Night	21% 7% 12% 33% 23% 4	3778
	21st to end	Night	20% 4 17% 35% 21% 3	4166
November	1st to 10th	Night	19% 5% 18% 30% 23% 4	2535
	11th to 20th	Night	23% 4 20% 32% 17% 5%	2658
	21st to end	Night	26% 5% 15% 34% 17% 4	2800
December	1st to 10th	Night	15% 5% 20% 37% 18% 4	4570
	11th to 20th	Night	19% 6% 24% 38% 13% 1	5182
	21st to end	Night	27% 8% 18% 29% 11% 7%	6974

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	25% 41% 16% 14% 4 1	300
	11th to 20th	Day	24% 51% 15% 7% 4	300
	21st to end	Day	18% 51% 22% 7% 3	330
February	1st to 10th	Day	35% 48% 12% 4	300
	11th to 20th	Day	34% 43% 16% 7%	300
	21st to end	Day	32% 43% 19% 6% 1	249
March	1st to 10th	Day	25% 41% 25% 7% 2	343
	11th to 20th	Day	21% 35% 34% 8% 2	500
	21st to end	Day	21% 43% 26% 8% 1	550
April	1st to 10th	Day	24% 41% 28% 6% 1	500
	11th to 20th	Day	26% 38% 28% 6% 1	492
	21st to end	Day	23% 29% 33% 12% 3	500
May	1st to 10th	Day	24% 26% 31% 14% 6% 1	607
	11th to 20th	Day	19% 19% 34% 17% 9% 2	725
	21st to end	Day	15% 21% 32% 19% 10% 2	789
June	1st to 10th	Day	9% 21% 27% 25% 15% 2	730
	11th to 20th	Day	11% 26% 35% 18% 9% 1	730
	21st to end	Day	8% 19% 35% 23% 13% 2	730
July	1st to 10th	Day	9% 10% 31% 29% 19% 3	697
	11th to 20th	Day	6% 9% 42% 25% 15% 3	668
	21st to end	Day	10% 10% 27% 34% 17% 3	677
August	1st to 10th	Day	8% 15% 41% 28% 8% 1	487
	11th to 20th	Day	8% 16% 37% 26% 10% 3	477
	21st to end	Day	9% 17% 31% 31% 10% 2	539
September	1st to 10th	Day	10% 19% 35% 21% 13% 2	490
	11th to 20th	Day	13% 22% 38% 17% 8% 2	490
	21st to end	Day	14% 24% 32% 17% 9% 5%	333
October	1st to 10th	Day	12% 25% 38% 13% 8% 4	300
	11th to 20th	Day	19% 37% 28% 9% 6% 1	300
	21st to end	Day	24% 38% 28% 7% 2	330
November	1st to 10th	Day	23% 43% 22% 7% 5%	300
	11th to 20th	Day	28% 40% 25% 5% 2	300
	21st to end	Day	19% 47% 25% 6% 2	300
December	1st to 10th	Day	30% 39% 22% 5% 2 1	300
	11th to 20th	Day	28% 46% 20% 5%	300
	21st to end	Day	30% 42% 21% 5% 3	330
January	1st to 10th	Night	18% 44% 21% 10% 6% 1	1000
	11th to 20th	Night	19% 47% 20% 9% 4 1	961
	21st to end	Night	11% 51% 24% 9% 3	880
February	1st to 10th	Night	21% 49% 20% 6% 4 1	800
	11th to 20th	Night	17% 46% 21% 12% 4	784
	21st to end	Night	22% 45% 22% 8% 2	660
March	1st to 10th	Night	14% 43% 26% 12% 4 1	800
	11th to 20th	Night	11% 37% 28% 19% 5% 1	800
	21st to end	Night	13% 38% 30% 13% 5% 1	782
April	1st to 10th	Night	11% 37% 36% 14% 2	600
	11th to 20th	Night	16% 31% 31% 16% 5%	593
	21st to end	Night	14% 26% 30% 21% 8% 1	600
May	1st to 10th	Night	14% 23% 30% 23% 10% 1	600
	11th to 20th	Night	14% 12% 29% 29% 14% 1	591
	21st to end	Night	10% 17% 27% 30% 15% 1	650
June	1st to 10th	Night	6% 13% 29% 31% 19% 1	600
	11th to 20th	Night	9% 18% 32% 32% 10% 1	600
	21st to end	Night	5% 11% 27% 40% 17% 1	600
July	1st to 10th	Night	5% 6% 18% 41% 29% 1	570
	11th to 20th	Night	3 5% 25% 39% 26% 2	552
	21st to end	Night	2 3 17% 44% 30% 4	624
August	1st to 10th	Night	4 5% 25% 43% 22% 1	567
	11th to 20th	Night	5% 5% 23% 43% 22% 2	564
	21st to end	Night	4 9% 18% 38% 28% 3	627
September	1st to 10th	Night	8% 7% 28% 33% 21% 4	570
	11th to 20th	Night	9% 9% 32% 32% 15% 3	570
	21st to end	Night	7% 19% 28% 28% 15% 4	649
October	1st to 10th	Night	10% 26% 28% 24% 12% 1	760
	11th to 20th	Night	12% 33% 28% 19% 8% 1	760
	21st to end	Night	15% 37% 31% 11% 5% 2	858
November	1st to 10th	Night	14% 47% 26% 8% 5% 1	975
	11th to 20th	Night	19% 48% 23% 8% 2	1000
	21st to end	Night	13% 46% 28% 9% 3	1000
December	1st to 10th	Night	20% 48% 22% 8% 2	1000
	11th to 20th	Night	17% 51% 21% 9% 2	1000
	21st to end	Night	23% 46% 19% 9% 3 1	1100

Page generated at 2025-07-02 23:30:17. Version ac07

Copyright © 2025 Attilla Danko.