Brodhead
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brodhead clear sky chart from 2005-11-05 to 2024-10-14.

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 5% 4 6% 7% 37%	100790
	Night	14% 9% 3 7% 4 4 4 3 5% 7% 39%	97731
Transparency	Day	45% 6% 11% 22% 14% 2	100603
	Night	44% 5% 10% 22% 15% 3	97592
Seeing	Day	19% 12% 25% 23% 15% 7%	14662
	Night	19% 9% 25% 28% 17% 2	24686

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% 16% 7% 10% 4 4 4 4 6% 6% 24%	2836
	11th to 20th	Day	17% 16% 7% 15% 4 6% 2 2 3 4 24%	2840
	21st to end	Day	25% 14% 7% 7% 4 3 3 2 4 5% 26%	3124
February	1st to 10th	Day	18% 14% 4 8% 4 2 4 3 6% 5% 31%	1866
	11th to 20th	Day	22% 9% 3 9% 5% 4 4 3 5% 5% 31%	1848
	21st to end	Day	21% 14% 3 8% 5% 4 4 4 5% 5% 30%	1570
March	1st to 10th	Day	23% 13% 3 7% 4 3 4 3 4 5% 30%	3170
	11th to 20th	Day	15% 6% 3 6% 4 4 4 3 4 6% 45%	3480
	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% 50%	1879
	21st to end	Day	20% 8% 2 4 4 2 3 3 4 6% 43%	1890
November	1st to 10th	Day	12% 6% 2 4 4 3 3 3 4 7% 52%	1672
	11th to 20th	Day	16% 9% 2 6% 3 3 4 3 4 7% 44%	1710
	21st to end	Day	16% 10% 4 7% 3 3 4 3 4 6% 40%	1710
December	1st to 10th	Day	22% 14% 4 6% 5% 5% 3 3 3 5% 30%	1710
	11th to 20th	Day	16% 14% 3 8% 4 4 4 4 5% 5% 32%	2153
	21st to end	Day	18% 16% 4 8% 4 4 5% 4 5% 7% 23%	3124
January	1st to 10th	Night	16% 18% 6% 10% 5% 4 3 3 4 5% 26%	4109
	11th to 20th	Night	19% 15% 4 10% 6% 4 3 2 3 4 30%	4120
	21st to end	Night	23% 14% 5% 7% 4 3 3 3 4 5% 30%	4532
February	1st to 10th	Night	19% 11% 4 9% 5% 4 4 4 4 5% 30%	2312
	11th to 20th	Night	22% 11% 4 7% 4 4 4 3 4 5% 33%	2218
	21st to end	Night	24% 12% 3 9% 5% 4 4 3 3 4 30%	1884
March	1st to 10th	Night	19% 15% 3 7% 4 4 4 3 4 5% 31%	3681
	11th to 20th	Night	13% 7% 2 5% 4 4 4 3 4 6% 48%	3480
	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% 48%	2152
	21st to end	Night	17% 8% 2 6% 3 3 4 2 4 6% 44%	2461
November	1st to 10th	Night	11% 7% 3 5% 4 3 3 3 4 5% 52%	2406
	11th to 20th	Night	15% 8% 3 6% 3 3 3 3 3 6% 46%	2470
	21st to end	Night	17% 10% 3 5% 4 4 4 3 4 5% 41%	2470
December	1st to 10th	Night	21% 13% 4 8% 4 4 3 3 5% 5% 30%	2470
	11th to 20th	Night	18% 11% 5% 10% 3 4 3 2 4 5% 34%	3042
	21st to end	Night	16% 15% 4 10% 6% 7% 6% 4 5% 6% 21%	4532

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	59% 4 9% 17% 10% 1	2837
	11th to 20th	Day	66% 3 7% 17% 7%	2840
	21st to end	Day	62% 4 6% 21% 7% 1	3124
February	1st to 10th	Day	55% 5% 8% 18% 13% 2	1866
	11th to 20th	Day	55% 4 7% 20% 11% 2	1858
	21st to end	Day	55% 4 9% 16% 12% 4	1570
March	1st to 10th	Day	56% 4 7% 17% 12% 4	3170
	11th to 20th	Day	40% 4 11% 24% 19% 2	3480
	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	30% 6% 9% 24% 27% 4	2090
	11th to 20th	Day	37% 4 8% 22% 24% 4	1880
	21st to end	Day	42% 4 7% 25% 18% 4	1890
November	1st to 10th	Day	34% 4 8% 25% 25% 5%	1672
	11th to 20th	Day	41% 4 7% 24% 19% 5%	1710
	21st to end	Day	46% 4 9% 21% 18% 3	1710
December	1st to 10th	Day	57% 4 7% 21% 9% 1	1710
	11th to 20th	Day	52% 4 10% 17% 14% 2	2150
	21st to end	Day	58% 6% 10% 19% 6% 1	3124
January	1st to 10th	Night	61% 3 8% 16% 11% 1	4109
	11th to 20th	Night	60% 3 6% 16% 12% 3	4120
	21st to end	Night	58% 3 8% 19% 11% 1	4532
February	1st to 10th	Night	56% 4 10% 17% 11% 1	2312
	11th to 20th	Night	55% 4 7% 19% 13% 3	2219
	21st to end	Night	59% 4 8% 14% 11% 4	1884
March	1st to 10th	Night	55% 4 8% 18% 13% 2	3681
	11th to 20th	Night	36% 5% 9% 30% 13% 6%	3480
	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	29% 6% 10% 22% 28% 5%	2090
	11th to 20th	Night	37% 4 9% 21% 24% 4	2156
	21st to end	Night	41% 4 8% 21% 22% 5%	2461
November	1st to 10th	Night	35% 4 6% 26% 23% 5%	2406
	11th to 20th	Night	41% 4 7% 18% 24% 6%	2470
	21st to end	Night	45% 4 7% 24% 18% 3	2470
December	1st to 10th	Night	56% 4 9% 18% 11% 2	2470
	11th to 20th	Night	53% 3 7% 21% 14% 2	3044
	21st to end	Night	62% 6% 11% 13% 8%	4532

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% 21% 36% 13% 4	270
	11th to 20th	Day	30% 26% 31% 11% 2	270
	21st to end	Day	26% 26% 35% 12% 2	297
February	1st to 10th	Day	26% 20% 37% 14% 4	270
	11th to 20th	Day	39% 22% 30% 7% 1 1	270
	21st to end	Day	41% 20% 30% 8% 1	225
March	1st to 10th	Day	28% 22% 36% 9% 4	294
	11th to 20th	Day	23% 22% 33% 16% 4 1	460
	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% 29% 28% 12% 5%	462
	21st to end	Day	24% 11% 29% 24% 11% 1	405
November	1st to 10th	Day	18% 11% 33% 26% 10% 3	270
	11th to 20th	Day	21% 16% 36% 22% 5% 1	270
	21st to end	Day	22% 16% 33% 21% 8% 1	270
December	1st to 10th	Day	27% 23% 28% 16% 5%	270
	11th to 20th	Day	24% 19% 30% 19% 7%	270
	21st to end	Day	28% 21% 35% 11% 5%	297
January	1st to 10th	Night	25% 18% 33% 19% 4	760
	11th to 20th	Night	31% 18% 29% 19% 3	760
	21st to end	Night	24% 16% 37% 21% 2	836
February	1st to 10th	Night	24% 15% 36% 22% 3	760
	11th to 20th	Night	29% 18% 34% 17% 2	743
	21st to end	Night	31% 14% 38% 15% 1	628
March	1st to 10th	Night	24% 15% 33% 24% 5%	760
	11th to 20th	Night	24% 14% 34% 22% 6%	760
	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	19% 8% 23% 31% 17% 2	735
	21st to end	Night	21% 8% 29% 27% 13% 2	792
November	1st to 10th	Night	15% 8% 24% 36% 16% 2	740
	11th to 20th	Night	20% 13% 29% 28% 9% 1	760
	21st to end	Night	23% 11% 25% 31% 9% 1	760
December	1st to 10th	Night	27% 14% 28% 25% 5%	760
	11th to 20th	Night	25% 11% 31% 26% 6% 1	760
	21st to end	Night	28% 16% 28% 25% 3	836

Page generated at 2024-10-11 10:50:00. Version ac07

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