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 2026-07-16.

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 8% 5% 4 5% 4 6% 7% 36%	137759
	Night	14% 9% 3 8% 4 4 4 3 5% 7% 38%	134934
Transparency	Day	46% 5% 10% 22% 14% 2	141459
	Night	45% 5% 10% 22% 16% 3	139305
Seeing	Day	19% 12% 25% 22% 15% 6%	16954
	Night	19% 9% 25% 28% 17% 2	26988

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	17% 15% 8% 11% 4 3 4 3 5% 5% 25%	5258
	11th to 20th	Day	13% 12% 6% 15% 4 4 2 2 3 4 35%	5280
	21st to end	Day	20% 10% 5% 7% 6% 4 4 3 5% 5% 30%	5780
February	1st to 10th	Day	18% 14% 4 8% 4 2 4 2 5% 5% 32%	2063
	11th to 20th	Day	22% 9% 4 9% 5% 4 4 3 4 5% 30%	2048
	21st to end	Day	19% 13% 3 8% 4 4 4 3 5% 5% 31%	1730
March	1st to 10th	Day	18% 13% 4 7% 4 4 4 3 4 5% 34%	4645
	11th to 20th	Day	13% 8% 3 6% 4 4 4 3 5% 6% 43%	5090
	21st to end	Day	14% 9% 3 7% 5% 5% 5% 4 5% 7% 38%	5586
April	1st to 10th	Day	13% 8% 3 6% 4 4 5% 4 6% 7% 39%	2446
	11th to 20th	Day	13% 9% 3 7% 4 4 3 4 5% 6% 41%	2519
	21st to end	Day	16% 7% 3 6% 5% 4 5% 4 7% 6% 37%	2730
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 5% 7% 8% 30%	7616
	11th to 20th	Day	14% 9% 3 8% 6% 5% 5% 4 6% 7% 35%	7626
	21st to end	Day	18% 8% 3 8% 6% 5% 5% 4 6% 9% 26%	8391
June	1st to 10th	Day	10% 6% 3 7% 6% 6% 5% 4 7% 9% 38%	2730
	11th to 20th	Day	7% 6% 2 7% 5% 5% 5% 5% 7% 9% 41%	2730
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 5% 8% 12% 38%	2730
July	1st to 10th	Day	8% 5% 2 8% 5% 5% 6% 4 7% 9% 40%	6030
	11th to 20th	Day	9% 6% 3 7% 6% 6% 6% 5% 8% 11% 32%	5965
	21st to end	Day	14% 9% 3 9% 6% 6% 6% 5% 7% 9% 27%	6424
August	1st to 10th	Day	8% 4 2 7% 5% 5% 6% 5% 8% 9% 41%	4234
	11th to 20th	Day	9% 7% 2 7% 5% 6% 6% 4 8% 10% 36%	4110
	21st to end	Day	5% 3 1 5% 3 4 5% 4 7% 9% 53%	4312
September	1st to 10th	Day	13% 7% 3 6% 4 5% 6% 4 6% 7% 40%	2255
	11th to 20th	Day	12% 6% 3 6% 4 4 4 3 6% 8% 45%	2200
	21st to end	Day	16% 6% 2 5% 4 4 4 4 5% 7% 44%	2200
October	1st to 10th	Day	11% 4 2 5% 3 3 4 3 5% 7% 53%	2200
	11th to 20th	Day	13% 6% 2 5% 4 3 4 3 4 5% 52%	2051
	21st to end	Day	20% 7% 2 4 4 3 3 3 5% 6% 44%	2100
November	1st to 10th	Day	12% 7% 2 5% 4 3 3 3 5% 7% 50%	1852
	11th to 20th	Day	15% 9% 2 6% 3 3 4 3 4 7% 43%	1890
	21st to end	Day	16% 10% 4 8% 3 3 4 3 4 6% 39%	1890
December	1st to 10th	Day	18% 12% 3 7% 5% 4 3 3 4 5% 36%	3020
	11th to 20th	Day	21% 14% 5% 8% 4 4 4 3 5% 5% 27%	3463
	21st to end	Day	18% 15% 5% 11% 5% 5% 5% 3 4 6% 23%	4565
January	1st to 10th	Night	15% 15% 6% 13% 4 3 3 3 4 5% 29%	7635
	11th to 20th	Night	16% 12% 5% 9% 5% 4 3 2 4 4 35%	7680
	21st to end	Night	19% 11% 4 9% 4 3 3 3 4 4 36%	8401
February	1st to 10th	Night	19% 11% 5% 9% 5% 5% 4 4 5% 5% 29%	2554
	11th to 20th	Night	23% 11% 4 8% 4 4 4 2 4 5% 32%	2458
	21st to end	Night	23% 11% 3 10% 5% 4 4 3 3 3 31%	2076
March	1st to 10th	Night	17% 14% 3 7% 4 4 4 3 4 5% 35%	5412
	11th to 20th	Night	12% 7% 2 5% 4 4 4 3 5% 7% 48%	5090
	21st to end	Night	14% 9% 3 8% 5% 6% 5% 4 5% 6% 34%	5588
April	1st to 10th	Night	13% 9% 3 5% 4 4 4 4 5% 7% 42%	2189
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 7% 43%	2049
	21st to end	Night	15% 8% 2 7% 4 4 4 4 6% 8% 38%	1890
May	1st to 10th	Night	17% 9% 3 9% 6% 5% 5% 4 6% 7% 29%	5237
	11th to 20th	Night	13% 8% 3 8% 5% 5% 5% 4 6% 8% 35%	5234
	21st to end	Night	16% 10% 4 8% 5% 5% 5% 3 5% 7% 31%	5761
June	1st to 10th	Night	9% 5% 2 7% 4 4 4 5% 8% 9% 43%	1890
	11th to 20th	Night	7% 4 2 6% 4 4 6% 4 7% 13% 44%	1890
	21st to end	Night	7% 6% 2 5% 4 4 6% 5% 9% 11% 40%	1890
July	1st to 10th	Night	7% 5% 2 7% 4 5% 5% 5% 6% 9% 43%	4148
	11th to 20th	Night	8% 5% 2 7% 4 4 5% 4 8% 12% 39%	4102
	21st to end	Night	11% 8% 3 7% 5% 7% 6% 5% 8% 11% 30%	4427
August	1st to 10th	Night	7% 5% 2 6% 5% 4 5% 4 7% 9% 46%	2915
	11th to 20th	Night	8% 7% 3 7% 4 5% 5% 4 7% 10% 41%	2934
	21st to end	Night	4 3 1 4 3 3 4 3 6% 9% 61%	3586
September	1st to 10th	Night	12% 6% 2 5% 4 4 5% 3 7% 7% 48%	2125
	11th to 20th	Night	11% 6% 3 6% 4 4 5% 4 5% 7% 47%	2200
	21st to end	Night	12% 7% 2 5% 4 3 3 3 4 6% 51%	2200
October	1st to 10th	Night	10% 5% 2 4 3 3 3 3 5% 6% 56%	2200
	11th to 20th	Night	14% 6% 2 5% 4 3 3 4 5% 6% 50%	2347
	21st to end	Night	17% 8% 2 6% 3 3 4 2 4 6% 45%	2735
November	1st to 10th	Night	12% 7% 3 6% 4 3 3 3 4 5% 50%	2666
	11th to 20th	Night	15% 9% 3 6% 3 3 3 3 3 6% 46%	2730
	21st to end	Night	17% 11% 3 5% 4 3 3 3 4 5% 41%	2730
December	1st to 10th	Night	18% 13% 4 9% 4 3 3 2 3 4 36%	4380
	11th to 20th	Night	22% 12% 4 9% 3 3 3 2 4 5% 33%	4952
	21st to end	Night	16% 15% 5% 10% 6% 7% 5% 4 5% 6% 21%	6633

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	62% 3 8% 18% 8% 1	5259
	11th to 20th	Day	55% 2 4 20% 16% 2	5280
	21st to end	Day	57% 3 7% 22% 10% 1	5780
February	1st to 10th	Day	55% 4 8% 19% 13% 2	2063
	11th to 20th	Day	57% 4 7% 20% 11% 2	2058
	21st to end	Day	54% 4 8% 18% 12% 4	1730
March	1st to 10th	Day	53% 3 6% 15% 18% 6%	4645
	11th to 20th	Day	42% 3 9% 22% 21% 3	5090
	21st to end	Day	45% 5% 10% 28% 12% 1	5586
April	1st to 10th	Day	42% 5% 12% 24% 14% 3	2446
	11th to 20th	Day	44% 4 10% 22% 18% 3	2519
	21st to end	Day	45% 6% 11% 24% 12% 2	2730
May	1st to 10th	Day	51% 5% 12% 21% 10% 1	7651
	11th to 20th	Day	48% 5% 12% 21% 13% 1	7630
	21st to end	Day	53% 6% 12% 15% 12% 2	8405
June	1st to 10th	Day	41% 8% 11% 23% 16% 2	2730
	11th to 20th	Day	37% 8% 13% 23% 16% 2	2730
	21st to end	Day	37% 9% 15% 20% 17% 3	2730
July	1st to 10th	Day	40% 6% 16% 22% 15% 1	5965
	11th to 20th	Day	43% 7% 18% 24% 6% 1	5896
	21st to end	Day	53% 6% 14% 20% 8% 1	6240
August	1st to 10th	Day	37% 7% 15% 29% 12%	4221
	11th to 20th	Day	40% 7% 12% 27% 13% 2	4149
	21st to end	Day	26% 7% 11% 39% 15% 2	4311
September	1st to 10th	Day	42% 7% 11% 18% 17% 5%	2255
	11th to 20th	Day	36% 6% 11% 23% 21% 2	2200
	21st to end	Day	39% 6% 10% 24% 20% 3	2200
October	1st to 10th	Day	23% 4 7% 23% 40% 3	3590
	11th to 20th	Day	25% 3 9% 27% 31% 5%	3317
	21st to end	Day	32% 3 8% 28% 19% 10%	3376
November	1st to 10th	Day	36% 4 8% 24% 24% 4	1852
	11th to 20th	Day	41% 4 7% 24% 19% 5%	1890
	21st to end	Day	48% 3 8% 21% 17% 3	1890
December	1st to 10th	Day	52% 3 6% 21% 17% 1	3020
	11th to 20th	Day	59% 3 8% 16% 12% 2	3460
	21st to end	Day	61% 5% 10% 17% 6% 1	4565
January	1st to 10th	Night	58% 3 10% 20% 8% 1	7636
	11th to 20th	Night	54% 3 4 19% 17% 4	7680
	21st to end	Night	53% 2 7% 20% 15% 3	8401
February	1st to 10th	Night	56% 4 10% 17% 11% 1	2554
	11th to 20th	Night	56% 3 7% 19% 12% 2	2459
	21st to end	Night	58% 3 7% 16% 12% 3	2076
March	1st to 10th	Night	52% 3 7% 20% 14% 4	5412
	11th to 20th	Night	37% 4 7% 28% 19% 5%	5090
	21st to end	Night	50% 5% 10% 23% 12% 1	5588
April	1st to 10th	Night	41% 6% 10% 22% 18% 3	2189
	11th to 20th	Night	40% 5% 11% 21% 18% 5%	2049
	21st to end	Night	43% 5% 11% 26% 13% 1	1890
May	1st to 10th	Night	53% 5% 10% 21% 11% 1	5264
	11th to 20th	Night	46% 6% 14% 21% 12%	5235
	21st to end	Night	51% 6% 11% 19% 11% 1	5771
June	1st to 10th	Night	34% 8% 13% 26% 16% 3	1890
	11th to 20th	Night	31% 9% 16% 23% 19% 2	1890
	21st to end	Night	34% 9% 15% 21% 16% 4	1890
July	1st to 10th	Night	36% 7% 13% 26% 17% 1	4105
	11th to 20th	Night	36% 8% 21% 25% 9% 2	4051
	21st to end	Night	47% 7% 16% 21% 9%	4297
August	1st to 10th	Night	34% 6% 14% 30% 16% 1	2904
	11th to 20th	Night	37% 7% 13% 29% 13% 1	2961
	21st to end	Night	20% 6% 13% 36% 22% 3	3586
September	1st to 10th	Night	34% 8% 14% 19% 19% 6%	2125
	11th to 20th	Night	36% 5% 11% 25% 22% 2	2200
	21st to end	Night	35% 4 10% 22% 25% 4	2200
October	1st to 10th	Night	25% 4 6% 22% 39% 4	3590
	11th to 20th	Night	25% 3 7% 24% 32% 9%	3820
	21st to end	Night	29% 3 9% 22% 29% 10%	4409
November	1st to 10th	Night	36% 4 7% 25% 23% 5%	2666
	11th to 20th	Night	41% 4 7% 20% 23% 6%	2730
	21st to end	Night	46% 4 7% 24% 17% 2	2730
December	1st to 10th	Night	55% 2 7% 20% 15% 1	4380
	11th to 20th	Night	55% 3 7% 20% 13% 1	4954
	21st to end	Night	62% 5% 10% 14% 8%	6633

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% 21% 35% 13% 5%	330
	11th to 20th	Day	31% 26% 31% 11% 2	330
	21st to end	Day	26% 28% 34% 11% 1	363
February	1st to 10th	Day	27% 20% 37% 13% 3	330
	11th to 20th	Day	38% 24% 29% 7% 1 1	330
	21st to end	Day	37% 20% 32% 10% 1	273
March	1st to 10th	Day	30% 22% 33% 10% 4	356
	11th to 20th	Day	25% 23% 34% 15% 4 1	540
	21st to end	Day	26% 21% 32% 15% 5%	594
April	1st to 10th	Day	21% 20% 30% 20% 8% 1	540
	11th to 20th	Day	19% 19% 33% 19% 8% 2	532
	21st to end	Day	20% 16% 31% 21% 9% 3	540
May	1st to 10th	Day	21% 16% 32% 20% 9% 3	543
	11th to 20th	Day	18% 12% 28% 25% 11% 5%	567
	21st to end	Day	19% 9% 20% 26% 17% 9%	617
June	1st to 10th	Day	14% 6% 24% 27% 20% 9%	570
	11th to 20th	Day	11% 5% 23% 30% 23% 8%	570
	21st to end	Day	11% 4 22% 29% 21% 12%	570
July	1st to 10th	Day	11% 3 16% 26% 23% 21%	565
	11th to 20th	Day	12% 4 17% 26% 27% 14%	544
	21st to end	Day	14% 3 15% 29% 26% 13%	576
August	1st to 10th	Day	15% 3 15% 28% 26% 13%	526
	11th to 20th	Day	13% 3 18% 32% 24% 11%	519
	21st to end	Day	10% 2 11% 27% 32% 17%	583
September	1st to 10th	Day	14% 3 15% 23% 31% 14%	530
	11th to 20th	Day	12% 4 15% 25% 30% 14%	530
	21st to end	Day	19% 6% 17% 29% 21% 8%	530
October	1st to 10th	Day	13% 5% 20% 32% 23% 8%	530
	11th to 20th	Day	13% 12% 28% 28% 13% 6%	530
	21st to end	Day	24% 10% 30% 24% 10% 1	483
November	1st to 10th	Day	19% 13% 34% 24% 8% 2	330
	11th to 20th	Day	22% 18% 34% 21% 5% 1	330
	21st to end	Day	25% 16% 34% 18% 7% 1	330
December	1st to 10th	Day	29% 22% 30% 14% 4	330
	11th to 20th	Day	27% 18% 32% 17% 6%	330
	21st to end	Day	29% 20% 35% 12% 4	363
January	1st to 10th	Night	25% 19% 32% 20% 4	840
	11th to 20th	Night	30% 18% 30% 19% 3	840
	21st to end	Night	23% 16% 38% 21% 2	924
February	1st to 10th	Night	24% 15% 36% 22% 3	840
	11th to 20th	Night	30% 18% 33% 17% 2	823
	21st to end	Night	30% 14% 38% 17% 1	692
March	1st to 10th	Night	24% 15% 33% 24% 5%	840
	11th to 20th	Night	23% 14% 34% 22% 6%	840
	21st to end	Night	21% 14% 31% 27% 7%	924
April	1st to 10th	Night	19% 12% 33% 27% 8%	719
	11th to 20th	Night	18% 11% 34% 26% 10% 1	623
	21st to end	Night	19% 8% 34% 29% 10%	630
May	1st to 10th	Night	18% 8% 28% 31% 12% 2	630
	11th to 20th	Night	17% 6% 22% 34% 18% 2	621
	21st to end	Night	11% 4 19% 34% 28% 5%	683
June	1st to 10th	Night	9% 3 16% 43% 26% 4	630
	11th to 20th	Night	8% 3 17% 41% 28% 4	630
	21st to end	Night	9% 3 16% 39% 30% 4	630
July	1st to 10th	Night	12% 2 9% 34% 36% 8%	615
	11th to 20th	Night	8% 2 11% 31% 43% 6%	597
	21st to end	Night	12% 3 10% 32% 38% 5%	657
August	1st to 10th	Night	11% 1 10% 30% 42% 6%	597
	11th to 20th	Night	8% 3 11% 37% 35% 5%	594
	21st to end	Night	8% 1 8% 35% 41% 8%	660
September	1st to 10th	Night	13% 2 12% 33% 35% 5%	725
	11th to 20th	Night	14% 2 13% 28% 37% 6%	800
	21st to end	Night	16% 2 21% 30% 28% 3	800
October	1st to 10th	Night	12% 5% 16% 31% 31% 5%	800
	11th to 20th	Night	17% 8% 22% 32% 18% 2	800
	21st to end	Night	21% 8% 29% 27% 13% 2	880
November	1st to 10th	Night	15% 8% 25% 35% 15% 2	820
	11th to 20th	Night	21% 13% 29% 28% 8% 1	840
	21st to end	Night	24% 12% 25% 30% 9% 1	840
December	1st to 10th	Night	27% 14% 29% 25% 5%	840
	11th to 20th	Night	26% 11% 32% 25% 6% 1	840
	21st to end	Night	28% 16% 29% 24% 3	924

Page generated at 2026-07-13 03:14:48. Version ac07

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