Brodhead
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brodhead clear sky chart from 2005-11-06 to 2025-03-12.

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% 9% 3 7% 5% 4 4 4 6% 7% 36%	109190
	Night	14% 9% 3 7% 4 4 4 3 5% 6% 39%	109844
Transparency	Day	45% 5% 10% 22% 15% 2	112934
	Night	44% 5% 10% 22% 16% 3	114238
Seeing	Day	19% 12% 25% 22% 15% 7%	15124
	Night	19% 9% 25% 28% 17% 2	25282

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% 17% 8% 12% 4 3 3 3 5% 6% 24%	4056
	11th to 20th	Day	14% 15% 7% 14% 3 4 2 2 3 4 31%	4060
	21st to end	Day	20% 10% 5% 7% 4 4 4 3 4 5% 33%	4466
February	1st to 10th	Day	18% 13% 5% 8% 4 2 4 3 5% 6% 31%	1965
	11th to 20th	Day	23% 10% 4 9% 5% 4 4 3 4 5% 30%	1948
	21st to end	Day	20% 13% 3 7% 4 4 4 4 5% 5% 32%	1650
March	1st to 10th	Day	23% 13% 3 7% 4 3 4 3 4 5% 31%	3271
	11th to 20th	Day	15% 6% 3 6% 4 4 4 3 4 6% 45%	3491
	21st to end	Day	14% 9% 3 7% 5% 5% 4 4 5% 7% 38%	3815
April	1st to 10th	Day	14% 8% 3 7% 4 4 5% 3 6% 7% 39%	2213
	11th to 20th	Day	14% 10% 3 7% 4 4 3 3 5% 5% 41%	2277
	21st to end	Day	16% 7% 3 6% 5% 4 5% 4 6% 6% 37%	2470
May	1st to 10th	Day	20% 10% 4 7% 5% 4 5% 4 6% 7% 29%	4082
	11th to 20th	Day	17% 10% 4 7% 5% 4 4 3 5% 5% 35%	4081
	21st to end	Day	11% 6% 3 7% 5% 5% 5% 4 7% 9% 36%	4476
June	1st to 10th	Day	11% 6% 3 7% 6% 6% 5% 4 7% 9% 38%	2470
	11th to 20th	Day	7% 5% 2 7% 5% 6% 5% 5% 7% 9% 42%	2470
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 8% 11% 38%	2470
July	1st to 10th	Day	9% 5% 2 8% 6% 5% 6% 5% 7% 10% 36%	4120
	11th to 20th	Day	9% 6% 2 7% 5% 5% 5% 4 7% 11% 39%	4120
	21st to end	Day	18% 11% 4 10% 6% 6% 6% 5% 6% 7% 22%	4466
August	1st to 10th	Day	8% 4 2 6% 5% 5% 6% 5% 8% 9% 41%	4104
	11th to 20th	Day	9% 7% 2 7% 5% 6% 6% 4 8% 10% 36%	3982
	21st to end	Day	5% 3 2 5% 3 4 5% 4 7% 9% 53%	4180
September	1st to 10th	Day	13% 7% 3 6% 4 5% 6% 4 6% 7% 40%	2142
	11th to 20th	Day	12% 6% 3 6% 4 4 4 3 6% 8% 44%	2090
	21st to end	Day	16% 6% 2 5% 4 4 4 4 5% 6% 44%	2090
October	1st to 10th	Day	11% 4 2 5% 3 3 4 3 5% 8% 52%	2090
	11th to 20th	Day	13% 6% 2 6% 4 3 4 3 4 5% 51%	1949
	21st to end	Day	19% 7% 2 4 4 3 3 3 5% 6% 44%	1995
November	1st to 10th	Day	12% 7% 2 4 4 3 3 3 4 6% 51%	1762
	11th to 20th	Day	16% 9% 2 6% 3 3 4 3 4 7% 43%	1800
	21st to end	Day	16% 10% 4 8% 3 3 4 3 4 6% 39%	1800
December	1st to 10th	Day	18% 12% 3 6% 5% 4 3 3 4 5% 37%	2930
	11th to 20th	Day	21% 14% 5% 8% 4 4 4 3 5% 5% 26%	3373
	21st to end	Day	18% 15% 5% 11% 5% 5% 5% 3 4 6% 23%	4466
January	1st to 10th	Night	16% 16% 7% 15% 5% 3 3 3 4 5% 25%	5889
	11th to 20th	Night	18% 13% 5% 10% 6% 4 4 2 3 4 31%	5900
	21st to end	Night	19% 10% 4 6% 4 3 3 3 4 5% 38%	6490
February	1st to 10th	Night	19% 11% 4 9% 5% 4 4 4 5% 5% 29%	2433
	11th to 20th	Night	22% 11% 4 8% 4 4 4 2 4 5% 32%	2338
	21st to end	Night	23% 11% 3 9% 5% 4 4 3 3 4 31%	1980
March	1st to 10th	Night	19% 15% 3 7% 4 4 4 3 4 5% 31%	3799
	11th to 20th	Night	12% 7% 2 4 4 4 4 3 4 6% 49%	3498
	21st to end	Night	13% 9% 3 7% 5% 5% 5% 4 5% 6% 38%	3817
April	1st to 10th	Night	12% 9% 3 5% 4 4 4 4 5% 7% 43%	1981
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 7% 43%	1851
	21st to end	Night	16% 8% 2 7% 4 4 4 4 5% 8% 38%	1710
May	1st to 10th	Night	18% 9% 3 9% 6% 5% 5% 4 5% 6% 30%	2813
	11th to 20th	Night	17% 9% 3 5% 4 4 4 4 6% 7% 37%	2812
	21st to end	Night	7% 6% 2 6% 5% 5% 5% 4 6% 9% 43%	3079
June	1st to 10th	Night	9% 5% 2 6% 4 4 4 6% 8% 9% 43%	1710
	11th to 20th	Night	5% 3 2 5% 4 4 6% 5% 7% 13% 46%	1710
	21st to end	Night	7% 6% 2 5% 4 4 6% 5% 9% 11% 41%	1710
July	1st to 10th	Night	7% 5% 2 7% 5% 5% 5% 6% 7% 10% 41%	2840
	11th to 20th	Night	7% 5% 2 6% 3 4 4 3 7% 10% 48%	2840
	21st to end	Night	15% 10% 3 7% 6% 7% 6% 4 7% 9% 26%	3087
August	1st to 10th	Night	7% 5% 2 6% 5% 4 5% 4 6% 9% 46%	2825
	11th to 20th	Night	8% 7% 3 7% 4 5% 5% 4 7% 9% 41%	2842
	21st to end	Night	4 3 1 4 3 3 4 3 6% 9% 61%	3476
September	1st to 10th	Night	12% 6% 2 5% 4 3 5% 3 7% 7% 47%	2019
	11th to 20th	Night	11% 6% 3 6% 4 4 5% 4 5% 7% 47%	2090
	21st to end	Night	11% 7% 2 5% 4 3 3 2 4 6% 51%	2090
October	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 5% 6% 55%	2090
	11th to 20th	Night	15% 6% 2 5% 4 3 3 4 5% 6% 49%	2229
	21st to end	Night	16% 7% 2 6% 3 3 4 2 4 6% 46%	2598
November	1st to 10th	Night	12% 7% 3 5% 4 3 3 3 4 5% 50%	2536
	11th to 20th	Night	15% 9% 3 6% 3 3 3 3 3 6% 45%	2600
	21st to end	Night	17% 10% 3 5% 4 3 4 3 4 5% 41%	2600
December	1st to 10th	Night	18% 13% 4 9% 4 3 3 2 3 4 36%	4250
	11th to 20th	Night	22% 12% 5% 9% 3 3 3 2 4 5% 32%	4822
	21st to end	Night	16% 15% 5% 10% 6% 7% 5% 4 5% 6% 22%	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	61% 3 8% 19% 7% 1	4057
	11th to 20th	Day	59% 2 5% 17% 15% 2	4060
	21st to end	Day	54% 3 7% 21% 13% 2	4466
February	1st to 10th	Day	55% 4 8% 18% 13% 2	1965
	11th to 20th	Day	57% 4 6% 19% 11% 2	1958
	21st to end	Day	53% 4 8% 17% 13% 4	1650
March	1st to 10th	Day	56% 4 7% 17% 13% 4	3271
	11th to 20th	Day	40% 4 11% 24% 19% 2	3491
	21st to end	Day	45% 6% 11% 27% 11% 1	3815
April	1st to 10th	Day	43% 5% 11% 24% 14% 3	2213
	11th to 20th	Day	44% 4 9% 21% 18% 4	2277
	21st to end	Day	45% 7% 10% 24% 11% 2	2470
May	1st to 10th	Day	53% 7% 11% 21% 8% 1	4120
	11th to 20th	Day	50% 6% 10% 21% 12% 1	4085
	21st to end	Day	41% 8% 14% 18% 17% 2	4489
June	1st to 10th	Day	41% 8% 10% 23% 16% 2	2470
	11th to 20th	Day	36% 8% 13% 23% 18% 2	2470
	21st to end	Day	38% 9% 14% 19% 18% 3	2470
July	1st to 10th	Day	41% 8% 18% 21% 12% 1	4055
	11th to 20th	Day	38% 7% 14% 31% 9% 2	4051
	21st to end	Day	60% 6% 11% 13% 8% 1	4324
August	1st to 10th	Day	36% 7% 15% 30% 12%	4091
	11th to 20th	Day	39% 7% 12% 27% 13% 2	4021
	21st to end	Day	26% 7% 12% 39% 14% 2	4179
September	1st to 10th	Day	42% 8% 11% 18% 16% 5%	2142
	11th to 20th	Day	38% 6% 11% 22% 21% 2	2090
	21st to end	Day	39% 6% 10% 24% 20% 3	2090
October	1st to 10th	Day	23% 4 7% 23% 40% 3	3480
	11th to 20th	Day	26% 3 9% 26% 31% 5%	3215
	21st to end	Day	31% 3 8% 28% 20% 10%	3271
November	1st to 10th	Day	35% 3 8% 24% 24% 4	1762
	11th to 20th	Day	41% 4 7% 23% 20% 5%	1800
	21st to end	Day	47% 3 8% 21% 17% 3	1800
December	1st to 10th	Day	51% 3 5% 22% 18% 1	2930
	11th to 20th	Day	60% 3 8% 16% 11% 2	3370
	21st to end	Day	61% 5% 10% 17% 6% 1	4466
January	1st to 10th	Night	63% 3 7% 17% 9% 1	5889
	11th to 20th	Night	58% 3 5% 16% 13% 4	5900
	21st to end	Night	50% 3 7% 20% 17% 3	6490
February	1st to 10th	Night	56% 4 10% 17% 11% 1	2433
	11th to 20th	Night	56% 4 7% 18% 13% 3	2339
	21st to end	Night	58% 4 8% 15% 12% 4	1980
March	1st to 10th	Night	55% 4 7% 18% 13% 2	3799
	11th to 20th	Night	36% 5% 9% 30% 14% 6%	3498
	21st to end	Night	45% 5% 12% 22% 15% 1	3817
April	1st to 10th	Night	40% 6% 10% 22% 18% 4	1981
	11th to 20th	Night	41% 5% 10% 19% 19% 6%	1851
	21st to end	Night	43% 6% 12% 25% 13% 1	1710
May	1st to 10th	Night	53% 7% 11% 21% 7% 2	2840
	11th to 20th	Night	45% 8% 12% 23% 11% 1	2813
	21st to end	Night	35% 9% 12% 24% 18% 2	3087
June	1st to 10th	Night	33% 9% 13% 26% 15% 4	1710
	11th to 20th	Night	28% 9% 17% 24% 20% 2	1710
	21st to end	Night	33% 9% 16% 21% 16% 5%	1710
July	1st to 10th	Night	35% 8% 15% 27% 13% 2	2795
	11th to 20th	Night	31% 6% 16% 32% 12% 3	2786
	21st to end	Night	52% 7% 12% 18% 9% 1	2988
August	1st to 10th	Night	34% 6% 13% 30% 16% 1	2814
	11th to 20th	Night	37% 7% 12% 29% 13% 1	2869
	21st to end	Night	19% 6% 13% 36% 21% 3	3476
September	1st to 10th	Night	34% 8% 14% 19% 18% 6%	2019
	11th to 20th	Night	36% 5% 11% 24% 21% 2	2090
	21st to end	Night	35% 4 9% 23% 25% 4	2090
October	1st to 10th	Night	25% 4 7% 22% 39% 4	3480
	11th to 20th	Night	25% 3 7% 24% 31% 9%	3702
	21st to end	Night	28% 3 9% 22% 28% 10%	4272
November	1st to 10th	Night	36% 4 6% 25% 23% 5%	2536
	11th to 20th	Night	41% 4 7% 19% 23% 6%	2600
	21st to end	Night	46% 4 7% 24% 18% 3	2600
December	1st to 10th	Night	54% 2 7% 20% 15% 1	4250
	11th to 20th	Night	56% 3 7% 20% 13% 1	4824
	21st to end	Night	62% 5% 10% 14% 8%	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	26% 22% 35% 13% 4	300
	11th to 20th	Day	30% 25% 31% 12% 2	300
	21st to end	Day	25% 27% 35% 11% 2	330
February	1st to 10th	Day	26% 20% 37% 13% 3	300
	11th to 20th	Day	39% 23% 29% 6% 1 1	300
	21st to end	Day	38% 20% 32% 8% 1	249
March	1st to 10th	Day	29% 22% 34% 10% 5%	325
	11th to 20th	Day	23% 22% 33% 16% 4 1	464
	21st to end	Day	27% 20% 30% 17% 6%	506
April	1st to 10th	Day	21% 21% 27% 21% 9% 1	460
	11th to 20th	Day	19% 19% 31% 19% 10% 3	452
	21st to end	Day	19% 17% 32% 21% 10% 3	460
May	1st to 10th	Day	20% 15% 31% 21% 10% 3	463
	11th to 20th	Day	18% 11% 26% 27% 13% 6%	487
	21st to end	Day	15% 9% 19% 28% 19% 11%	529
June	1st to 10th	Day	14% 6% 23% 27% 21% 10%	490
	11th to 20th	Day	9% 4 22% 31% 25% 10%	490
	21st to end	Day	11% 4 23% 30% 20% 12%	490
July	1st to 10th	Day	12% 3 17% 24% 24% 21%	485
	11th to 20th	Day	11% 4 18% 26% 27% 15%	484
	21st to end	Day	15% 3 16% 29% 24% 13%	532
August	1st to 10th	Day	14% 2 15% 28% 26% 14%	486
	11th to 20th	Day	13% 3 19% 32% 23% 10%	479
	21st to end	Day	11% 2 10% 26% 32% 19%	539
September	1st to 10th	Day	14% 3 14% 23% 32% 14%	490
	11th to 20th	Day	13% 4 16% 24% 30% 13%	490
	21st to end	Day	19% 6% 17% 29% 21% 8%	490
October	1st to 10th	Day	13% 4 21% 32% 22% 7%	490
	11th to 20th	Day	14% 13% 28% 27% 12% 6%	490
	21st to end	Day	22% 10% 31% 25% 11% 1	444
November	1st to 10th	Day	19% 10% 34% 25% 9% 3	300
	11th to 20th	Day	22% 16% 35% 21% 5% 1	300
	21st to end	Day	24% 17% 32% 20% 7% 1	300
December	1st to 10th	Day	28% 23% 28% 15% 5%	300
	11th to 20th	Day	26% 18% 30% 18% 7%	300
	21st to end	Day	28% 20% 35% 12% 5%	330
January	1st to 10th	Night	25% 18% 32% 20% 4	800
	11th to 20th	Night	30% 18% 29% 19% 3	800
	21st to end	Night	23% 16% 38% 21% 2	880
February	1st to 10th	Night	25% 15% 36% 21% 3	800
	11th to 20th	Night	30% 19% 33% 16% 2	783
	21st to end	Night	30% 14% 38% 16% 1	660
March	1st to 10th	Night	24% 15% 32% 24% 5%	800
	11th to 20th	Night	24% 14% 34% 22% 6%	767
	21st to end	Night	21% 14% 30% 28% 8%	836
April	1st to 10th	Night	18% 12% 33% 27% 9%	651
	11th to 20th	Night	18% 11% 33% 26% 11% 1	563
	21st to end	Night	19% 8% 34% 28% 10%	570
May	1st to 10th	Night	19% 9% 27% 30% 13% 2	570
	11th to 20th	Night	17% 6% 21% 34% 20% 3	561
	21st to end	Night	7% 3 19% 35% 30% 5%	617
June	1st to 10th	Night	9% 3 16% 42% 27% 4	570
	11th to 20th	Night	7% 2 17% 40% 30% 5%	570
	21st to end	Night	9% 3 16% 41% 28% 3	570
July	1st to 10th	Night	12% 1 10% 34% 34% 8%	555
	11th to 20th	Night	7% 2 11% 31% 43% 6%	552
	21st to end	Night	12% 3 10% 33% 37% 5%	624
August	1st to 10th	Night	11% 1 10% 29% 42% 6%	567
	11th to 20th	Night	9% 2 11% 38% 34% 5%	564
	21st to end	Night	8% 1 7% 34% 42% 8%	627
September	1st to 10th	Night	13% 2 12% 32% 36% 5%	689
	11th to 20th	Night	14% 2 14% 28% 36% 6%	760
	21st to end	Night	16% 2 20% 29% 29% 4	760
October	1st to 10th	Night	12% 5% 17% 30% 30% 5%	760
	11th to 20th	Night	18% 8% 23% 31% 18% 2	760
	21st to end	Night	20% 8% 29% 28% 13% 2	836
November	1st to 10th	Night	15% 8% 24% 35% 16% 2	780
	11th to 20th	Night	20% 13% 29% 29% 9% 1	800
	21st to end	Night	24% 12% 25% 30% 9% 1	800
December	1st to 10th	Night	27% 14% 29% 25% 5%	800
	11th to 20th	Night	26% 11% 31% 25% 6% 1	800
	21st to end	Night	28% 16% 29% 25% 3	880

Page generated at 2025-03-09 08:08:45. Version ac07

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