Brunswick
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brunswick clear sky chart from 2005-11-06 to 2025-10-04.

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	9% 5% 2 6% 5% 5% 5% 4 7% 9% 42%	126298
	Night	10% 6% 2 6% 4 4 5% 4 6% 9% 43%	123090
Transparency	Day	34% 9% 17% 20% 15% 5%	129996
	Night	36% 8% 14% 19% 17% 7%	127461
Seeing	Day	10% 6% 21% 30% 23% 9%	16668
	Night	12% 6% 20% 32% 25% 5%	26702

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	8% 6% 2 5% 4 4 3 3 4 6% 55%	4056
	11th to 20th	Day	16% 7% 2 6% 4 4 4 3 5% 6% 43%	4060
	21st to end	Day	11% 7% 3 7% 4 4 3 3 5% 8% 46%	4466
February	1st to 10th	Day	15% 8% 2 5% 3 4 4 4 5% 7% 43%	1950
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 6% 47%	1948
	21st to end	Day	13% 6% 2 5% 3 3 3 3 4 8% 49%	1725
March	1st to 10th	Day	16% 8% 3 6% 4 4 4 3 5% 7% 39%	4935
	11th to 20th	Day	7% 3 1 4 3 3 4 3 5% 8% 57%	4980
	21st to end	Day	13% 6% 2 6% 4 3 4 3 5% 6% 48%	5465
April	1st to 10th	Day	8% 5% 2 5% 4 4 3 3 6% 8% 52%	2200
	11th to 20th	Day	10% 5% 3 5% 4 3 4 4 5% 7% 50%	2272
	21st to end	Day	5% 3 2 4 4 4 4 4 5% 8% 57%	2455
May	1st to 10th	Day	8% 4 2 6% 4 5% 4 5% 7% 11% 45%	5862
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 7% 10% 43%	5861
	21st to end	Day	4 2 1 4 4 5% 6% 5% 8% 11% 48%	6433
June	1st to 10th	Day	9% 6% 2 6% 5% 6% 6% 6% 10% 11% 33%	2600
	11th to 20th	Day	5% 5% 1 7% 6% 7% 7% 5% 9% 13% 36%	2600
	21st to end	Day	7% 5% 2 8% 6% 7% 8% 8% 9% 12% 30%	2600
July	1st to 10th	Day	6% 6% 2 9% 7% 8% 9% 8% 10% 11% 23%	5900
	11th to 20th	Day	3 2 2 4 5% 6% 7% 7% 10% 15% 37%	5900
	21st to end	Day	3 3 2 6% 6% 6% 6% 6% 9% 12% 40%	6424
August	1st to 10th	Day	13% 6% 3 8% 6% 7% 7% 5% 9% 11% 26%	4234
	11th to 20th	Day	5% 4 2 6% 5% 6% 6% 6% 9% 12% 40%	4156
	21st to end	Day	9% 6% 3 8% 5% 6% 6% 6% 8% 10% 33%	4054
September	1st to 10th	Day	12% 7% 3 8% 6% 7% 7% 5% 7% 9% 30%	2200
	11th to 20th	Day	13% 7% 3 9% 6% 6% 6% 5% 6% 8% 31%	2200
	21st to end	Day	13% 7% 3 7% 5% 5% 4 4 6% 9% 37%	2200
October	1st to 10th	Day	12% 7% 2 7% 5% 5% 6% 3 6% 8% 40%	2066
	11th to 20th	Day	7% 4 2 4 3 4 4 3 6% 7% 55%	1900
	21st to end	Day	10% 5% 2 5% 4 3 4 3 5% 8% 52%	2090
November	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 5% 7% 49%	1957
	11th to 20th	Day	10% 7% 2 5% 4 4 4 3 4 7% 49%	1980
	21st to end	Day	12% 7% 2 6% 4 3 4 3 6% 8% 46%	1800
December	1st to 10th	Day	6% 4 1 5% 5% 4 4 3 5% 7% 56%	2930
	11th to 20th	Day	14% 7% 2 7% 4 3 4 4 5% 6% 43%	3373
	21st to end	Day	14% 8% 3 7% 5% 4 4 3 4 6% 41%	4466
January	1st to 10th	Night	10% 5% 2 5% 3 2 3 3 5% 6% 56%	5889
	11th to 20th	Night	13% 8% 3 7% 4 4 5% 4 6% 7% 40%	5900
	21st to end	Night	12% 7% 3 7% 4 4 3 3 5% 8% 44%	6490
February	1st to 10th	Night	15% 7% 3 6% 3 4 4 3 5% 6% 43%	2445
	11th to 20th	Night	14% 8% 2 6% 4 4 3 3 5% 5% 45%	2338
	21st to end	Night	13% 6% 2 5% 4 4 5% 4 6% 6% 46%	1902
March	1st to 10th	Night	17% 10% 3 5% 3 3 4 3 4 5% 42%	4918
	11th to 20th	Night	6% 5% 2 4 3 3 4 3 6% 10% 53%	4980
	21st to end	Night	10% 6% 2 6% 3 4 4 3 5% 7% 49%	5467
April	1st to 10th	Night	9% 5% 1 5% 4 4 5% 4 6% 8% 49%	2200
	11th to 20th	Night	9% 6% 2 5% 4 3 4 3 5% 6% 53%	2075
	21st to end	Night	5% 3 1 4 4 4 4 3 7% 9% 55%	1960
May	1st to 10th	Night	5% 5% 2 6% 4 5% 5% 4 7% 10% 46%	4033
	11th to 20th	Night	12% 5% 2 5% 4 4 5% 4 7% 9% 43%	4032
	21st to end	Night	6% 4 2 6% 5% 4 5% 5% 8% 11% 43%	4421
June	1st to 10th	Night	9% 5% 2 6% 5% 7% 6% 5% 8% 12% 34%	1800
	11th to 20th	Night	6% 5% 2 8% 6% 5% 6% 5% 10% 13% 36%	1800
	21st to end	Night	7% 4 2 5% 5% 6% 7% 6% 9% 14% 34%	1800
July	1st to 10th	Night	7% 6% 3 9% 7% 7% 8% 6% 9% 11% 26%	4058
	11th to 20th	Night	3 4 2 7% 5% 6% 8% 7% 10% 14% 33%	4057
	21st to end	Night	4 5% 2 7% 6% 6% 7% 6% 11% 13% 32%	4427
August	1st to 10th	Night	15% 6% 2 7% 6% 6% 7% 5% 8% 11% 26%	2915
	11th to 20th	Night	4 4 2 6% 6% 5% 7% 5% 8% 13% 40%	2875
	21st to end	Night	8% 5% 2 7% 5% 6% 6% 5% 7% 10% 38%	3822
September	1st to 10th	Night	12% 7% 3 8% 6% 6% 5% 5% 8% 10% 30%	2200
	11th to 20th	Night	14% 7% 2 8% 6% 6% 6% 5% 7% 10% 29%	2200
	21st to end	Night	12% 6% 4 8% 5% 4 4 4 7% 8% 37%	2200
October	1st to 10th	Night	13% 6% 2 7% 4 4 4 4 6% 9% 41%	2178
	11th to 20th	Night	7% 4 1 5% 3 4 4 4 5% 7% 56%	2280
	21st to end	Night	8% 4 2 5% 3 4 4 3 5% 7% 53%	2508
November	1st to 10th	Night	10% 5% 2 6% 5% 4 4 3 5% 7% 48%	2341
	11th to 20th	Night	12% 7% 2 6% 4 4 5% 4 4 6% 47%	2417
	21st to end	Night	12% 7% 2 5% 4 4 4 3 6% 7% 45%	2600
December	1st to 10th	Night	9% 5% 2 5% 3 3 3 3 4 8% 55%	4250
	11th to 20th	Night	12% 8% 3 8% 5% 4 4 3 4 5% 44%	4822
	21st to end	Night	15% 8% 3 7% 4 4 4 3 5% 6% 41%	6490

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	30% 5% 7% 14% 33% 10%	4057
	11th to 20th	Day	42% 3 6% 14% 22% 12%	4060
	21st to end	Day	38% 7% 6% 22% 16% 11%	4466
February	1st to 10th	Day	40% 5% 11% 15% 21% 8%	1950
	11th to 20th	Day	38% 5% 8% 17% 22% 10%	1958
	21st to end	Day	35% 5% 10% 20% 19% 11%	1725
March	1st to 10th	Day	43% 6% 9% 17% 20% 6%	4935
	11th to 20th	Day	24% 6% 14% 17% 17% 22%	4980
	21st to end	Day	36% 6% 9% 19% 19% 11%	5465
April	1st to 10th	Day	29% 7% 13% 24% 18% 10%	2200
	11th to 20th	Day	32% 6% 10% 22% 20% 10%	2272
	21st to end	Day	24% 6% 15% 27% 23% 5%	2455
May	1st to 10th	Day	30% 9% 18% 29% 12% 2	5897
	11th to 20th	Day	34% 8% 18% 29% 10% 1	5865
	21st to end	Day	24% 10% 20% 28% 17% 2	6447
June	1st to 10th	Day	37% 13% 20% 21% 9%	2600
	11th to 20th	Day	32% 14% 21% 26% 8%	2600
	21st to end	Day	36% 16% 24% 17% 6%	2600
July	1st to 10th	Day	39% 18% 29% 12% 1	5835
	11th to 20th	Day	22% 17% 45% 14% 2	5831
	21st to end	Day	26% 17% 30% 23% 4	6240
August	1st to 10th	Day	44% 13% 29% 12% 1	4221
	11th to 20th	Day	27% 14% 26% 24% 9%	4195
	21st to end	Day	38% 14% 22% 24% 2	4054
September	1st to 10th	Day	43% 15% 18% 16% 8% 1	2200
	11th to 20th	Day	46% 10% 16% 18% 9% 1	2200
	21st to end	Day	41% 8% 17% 18% 13% 3	2200
October	1st to 10th	Day	45% 7% 11% 12% 14% 11%	3417
	11th to 20th	Day	18% 6% 8% 21% 33% 13%	3140
	21st to end	Day	21% 5% 8% 23% 34% 10%	3428
November	1st to 10th	Day	34% 6% 12% 19% 18% 10%	1957
	11th to 20th	Day	35% 4 10% 18% 23% 9%	1980
	21st to end	Day	35% 7% 10% 21% 20% 7%	1800
December	1st to 10th	Day	29% 5% 10% 25% 23% 8%	2930
	11th to 20th	Day	40% 7% 11% 17% 19% 5%	3370
	21st to end	Day	44% 6% 8% 21% 16% 4	4466
January	1st to 10th	Night	28% 4 7% 12% 37% 11%	5889
	11th to 20th	Night	43% 4 6% 14% 24% 8%	5900
	21st to end	Night	40% 6% 8% 18% 18% 11%	6490
February	1st to 10th	Night	41% 5% 8% 16% 20% 10%	2445
	11th to 20th	Night	41% 4 9% 16% 18% 12%	2339
	21st to end	Night	38% 5% 10% 20% 16% 11%	1902
March	1st to 10th	Night	42% 6% 10% 15% 16% 11%	4918
	11th to 20th	Night	25% 6% 12% 19% 20% 19%	4980
	21st to end	Night	34% 5% 9% 18% 21% 13%	5467
April	1st to 10th	Night	30% 7% 14% 20% 18% 11%	2200
	11th to 20th	Night	30% 6% 8% 25% 21% 9%	2075
	21st to end	Night	24% 5% 16% 26% 23% 5%	1960
May	1st to 10th	Night	30% 11% 19% 26% 12% 2	4060
	11th to 20th	Night	36% 8% 20% 26% 10% 1	4033
	21st to end	Night	31% 10% 15% 27% 15% 1	4429
June	1st to 10th	Night	38% 11% 20% 20% 11%	1800
	11th to 20th	Night	35% 13% 22% 22% 8%	1800
	21st to end	Night	35% 13% 27% 18% 6% 1	1800
July	1st to 10th	Night	43% 16% 28% 12% 1	4015
	11th to 20th	Night	33% 19% 35% 11% 2	4006
	21st to end	Night	36% 16% 25% 21% 2	4297
August	1st to 10th	Night	47% 15% 27% 10% 1	2904
	11th to 20th	Night	31% 14% 24% 23% 8%	2902
	21st to end	Night	37% 12% 21% 27% 2	3822
September	1st to 10th	Night	45% 13% 17% 15% 8% 1	2200
	11th to 20th	Night	46% 12% 17% 16% 9%	2200
	21st to end	Night	42% 9% 14% 18% 14% 3	2200
October	1st to 10th	Night	47% 6% 9% 12% 14% 11%	3607
	11th to 20th	Night	21% 4 7% 19% 31% 18%	3779
	21st to end	Night	20% 5% 8% 19% 34% 13%	4120
November	1st to 10th	Night	36% 6% 9% 18% 20% 11%	2341
	11th to 20th	Night	38% 6% 7% 17% 22% 9%	2417
	21st to end	Night	38% 5% 10% 20% 19% 9%	2600
December	1st to 10th	Night	29% 5% 10% 21% 25% 10%	4250
	11th to 20th	Night	40% 6% 9% 21% 16% 8%	4824
	21st to end	Night	44% 6% 10% 17% 20% 3	6490

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	10% 15% 44% 24% 7%	300
	11th to 20th	Day	7% 13% 35% 33% 11% 2	300
	21st to end	Day	16% 17% 41% 22% 4	330
February	1st to 10th	Day	16% 12% 31% 32% 9%	300
	11th to 20th	Day	20% 10% 41% 23% 5%	300
	21st to end	Day	12% 12% 35% 35% 5%	324
March	1st to 10th	Day	13% 13% 34% 29% 11%	500
	11th to 20th	Day	12% 13% 32% 31% 9% 3	500
	21st to end	Day	12% 11% 35% 30% 10% 2	550
April	1st to 10th	Day	9% 13% 33% 30% 13% 1	500
	11th to 20th	Day	10% 9% 29% 31% 16% 4	492
	21st to end	Day	5% 5% 28% 37% 19% 6%	500
May	1st to 10th	Day	5% 7% 24% 38% 21% 6%	503
	11th to 20th	Day	7% 2 22% 36% 26% 7%	527
	21st to end	Day	8% 3 13% 32% 30% 13%	573
June	1st to 10th	Day	13% 2 10% 32% 32% 12%	530
	11th to 20th	Day	7% 2 13% 29% 30% 19%	530
	21st to end	Day	7% 2 7% 30% 36% 18%	530
July	1st to 10th	Day	6% 2 5% 23% 41% 23%	525
	11th to 20th	Day	5% 1 2 21% 44% 27%	524
	21st to end	Day	6% 1 6% 23% 45% 19%	576
August	1st to 10th	Day	8% 2 6% 23% 41% 21%	526
	11th to 20th	Day	5% 2 3 22% 41% 27%	519
	21st to end	Day	11% 3 8% 23% 35% 20%	583
September	1st to 10th	Day	14% 3 9% 26% 31% 17%	530
	11th to 20th	Day	12% 4 13% 32% 29% 10%	530
	21st to end	Day	14% 2 11% 28% 33% 12%	530
October	1st to 10th	Day	15% 5% 20% 35% 19% 6%	502
	11th to 20th	Day	7% 6% 25% 33% 23% 6%	490
	21st to end	Day	12% 5% 18% 40% 23% 4	539
November	1st to 10th	Day	16% 6% 23% 32% 18% 4	495
	11th to 20th	Day	16% 8% 30% 32% 12% 2	480
	21st to end	Day	13% 12% 29% 35% 11%	300
December	1st to 10th	Day	10% 9% 36% 32% 10% 3	300
	11th to 20th	Day	19% 10% 31% 32% 8%	300
	21st to end	Day	15% 11% 30% 34% 10% 1	330
January	1st to 10th	Night	14% 12% 36% 29% 8% 1	800
	11th to 20th	Night	12% 10% 30% 35% 12% 1	800
	21st to end	Night	16% 10% 37% 31% 5%	880
February	1st to 10th	Night	17% 9% 30% 34% 11% 1	800
	11th to 20th	Night	18% 11% 31% 32% 8%	783
	21st to end	Night	15% 9% 31% 39% 6%	660
March	1st to 10th	Night	11% 9% 32% 37% 11%	800
	11th to 20th	Night	12% 9% 29% 37% 12% 1	800
	21st to end	Night	11% 8% 29% 39% 13% 1	880
April	1st to 10th	Night	10% 8% 32% 37% 13% 1	800
	11th to 20th	Night	10% 8% 29% 34% 18% 2	791
	21st to end	Night	6% 4 22% 45% 21% 2	760
May	1st to 10th	Night	8% 4 19% 42% 25% 3	600
	11th to 20th	Night	7% 2 20% 35% 30% 7%	591
	21st to end	Night	9% 3 9% 33% 40% 6%	650
June	1st to 10th	Night	9% 2 9% 38% 36% 7%	600
	11th to 20th	Night	7% 1 7% 32% 39% 13%	600
	21st to end	Night	9% 1 6% 29% 44% 11%	600
July	1st to 10th	Night	8% 1 6% 24% 47% 14%	585
	11th to 20th	Night	5% 1 3 21% 50% 19%	582
	21st to end	Night	5% 1 5% 23% 54% 12%	657
August	1st to 10th	Night	9% 1 6% 21% 50% 13%	597
	11th to 20th	Night	8% 1 4 17% 52% 18%	594
	21st to end	Night	13% 2 7% 23% 40% 15%	863
September	1st to 10th	Night	12% 2 9% 25% 43% 10%	800
	11th to 20th	Night	14% 3 10% 26% 40% 7%	800
	21st to end	Night	15% 4 9% 27% 39% 7%	800
October	1st to 10th	Night	17% 3 18% 30% 28% 5%	773
	11th to 20th	Night	8% 6% 18% 36% 29% 4	760
	21st to end	Night	10% 5% 20% 33% 30% 2	836
November	1st to 10th	Night	13% 4 22% 36% 22% 2	780
	11th to 20th	Night	14% 9% 26% 31% 19% 2	800
	21st to end	Night	15% 9% 26% 32% 16% 2	800
December	1st to 10th	Night	12% 9% 26% 33% 18% 1	800
	11th to 20th	Night	14% 10% 26% 31% 16% 3	800
	21st to end	Night	17% 9% 26% 33% 14%	880

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