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 2024-02-10.

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	15% 9% 4 6% 5% 3 5% 5% 5% 7% 36%	78632
	Night	15% 9% 4 6% 5% 3 4 4 5% 7% 38%	80345
Transparency	Day	47% 6% 10% 21% 14% 2	78355
	Night	45% 6% 10% 20% 15% 3	80141
Seeing	Day	19% 11% 24% 23% 16% 7%	13702
	Night	19% 9% 25% 28% 17% 2	23850

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% 9% 6% 3 4 4 6% 6% 24%	2836
	11th to 20th	Day	17% 15% 7% 14% 5% 4 4 3 3 4 24%	2840
	21st to end	Day	25% 13% 7% 6% 5% 2 4 3 4 5% 26%	3124
February	1st to 10th	Day	18% 13% 5% 8% 5% 2 4 4 5% 6% 31%	1856
	11th to 20th	Day	23% 9% 4 7% 6% 3 4 4 5% 5% 30%	1748
	21st to end	Day	21% 13% 3 7% 5% 2 5% 4 4 5% 30%	1480
March	1st to 10th	Day	19% 10% 3 5% 5% 3 4 4 5% 6% 37%	1822
	11th to 20th	Day	23% 9% 4 6% 5% 3 5% 4 5% 5% 31%	1980
	21st to end	Day	18% 10% 4 6% 6% 4 5% 4 4 6% 32%	2178
April	1st to 10th	Day	14% 7% 3 5% 5% 3 4 5% 6% 8% 40%	2096
	11th to 20th	Day	14% 9% 4 7% 5% 3 4 4 4 6% 41%	2155
	21st to end	Day	17% 6% 4 6% 5% 3 6% 5% 6% 7% 36%	2340
May	1st to 10th	Day	18% 7% 3 6% 5% 3 5% 4 6% 8% 34%	2340
	11th to 20th	Day	17% 8% 4 6% 6% 3 5% 5% 5% 6% 34%	2301
	21st to end	Day	9% 6% 3 6% 7% 4 6% 6% 6% 10% 37%	2531
June	1st to 10th	Day	11% 5% 3 6% 7% 4 5% 5% 6% 9% 38%	2340
	11th to 20th	Day	7% 5% 2 6% 6% 4 6% 6% 6% 9% 42%	2340
	21st to end	Day	9% 4 2 6% 5% 4 5% 6% 8% 11% 38%	2340
July	1st to 10th	Day	11% 6% 3 6% 7% 4 8% 6% 8% 9% 33%	2340
	11th to 20th	Day	10% 6% 3 6% 7% 4 7% 6% 7% 10% 35%	2340
	21st to end	Day	11% 6% 3 6% 6% 5% 5% 7% 6% 9% 36%	2547
August	1st to 10th	Day	11% 5% 3 6% 7% 4 6% 6% 9% 9% 36%	2327
	11th to 20th	Day	11% 7% 3 7% 7% 4 6% 5% 7% 8% 34%	2269
	21st to end	Day	9% 5% 2 6% 5% 3 7% 7% 8% 10% 38%	2376
September	1st to 10th	Day	14% 6% 3 5% 6% 3 6% 5% 5% 7% 38%	2030
	11th to 20th	Day	13% 6% 3 5% 5% 3 4 4 6% 9% 43%	1980
	21st to end	Day	15% 5% 2 4 4 3 4 5% 5% 6% 47%	1980
October	1st to 10th	Day	11% 4 2 4 4 2 4 4 5% 7% 51%	1980
	11th to 20th	Day	14% 6% 2 5% 5% 2 4 4 4 5% 49%	1847
	21st to end	Day	20% 7% 2 4 4 2 3 3 4 6% 43%	1890
November	1st to 10th	Day	12% 6% 2 3 4 3 3 3 4 7% 52%	1672
	11th to 20th	Day	16% 8% 2 5% 3 2 4 4 4 6% 44%	1710
	21st to end	Day	16% 9% 4 6% 4 2 4 4 4 6% 41%	1710
December	1st to 10th	Day	22% 14% 4 5% 5% 3 4 3 3 6% 30%	1710
	11th to 20th	Day	16% 14% 3 7% 5% 3 5% 5% 5% 6% 32%	2153
	21st to end	Day	18% 16% 4 7% 6% 3 5% 5% 5% 7% 23%	3124
January	1st to 10th	Night	16% 17% 6% 9% 6% 3 3 4 4 5% 26%	4109
	11th to 20th	Night	20% 14% 5% 8% 8% 3 3 2 3 4 30%	4120
	21st to end	Night	23% 13% 5% 6% 5% 2 3 3 4 5% 31%	4532
February	1st to 10th	Night	19% 10% 5% 8% 6% 3 5% 5% 4 5% 30%	2307
	11th to 20th	Night	22% 10% 4 7% 5% 3 4 4 4 5% 32%	2098
	21st to end	Night	24% 11% 4 8% 6% 3 4 4 3 4 29%	1776
March	1st to 10th	Night	17% 9% 4 6% 5% 3 5% 4 4 5% 38%	2136
	11th to 20th	Night	18% 8% 4 5% 6% 3 5% 4 5% 7% 35%	1980
	21st to end	Night	16% 11% 5% 7% 6% 3 5% 5% 4 6% 33%	2178
April	1st to 10th	Night	12% 8% 3 4 5% 3 4 5% 5% 7% 44%	1877
	11th to 20th	Night	15% 6% 3 5% 5% 3 4 4 5% 7% 43%	1753
	21st to end	Night	16% 7% 3 5% 5% 3 4 5% 6% 8% 38%	1620
May	1st to 10th	Night	16% 6% 3 7% 7% 4 5% 5% 5% 6% 37%	1620
	11th to 20th	Night	16% 6% 3 4 5% 4 6% 6% 6% 8% 37%	1592
	21st to end	Night	5% 5% 2 5% 6% 5% 7% 6% 7% 11% 41%	1744
June	1st to 10th	Night	8% 4 3 6% 5% 3 4 6% 8% 10% 44%	1620
	11th to 20th	Night	5% 3 2 5% 5% 3 6% 6% 7% 13% 46%	1620
	21st to end	Night	7% 5% 3 4 5% 3 6% 6% 8% 13% 40%	1620
July	1st to 10th	Night	9% 5% 2 6% 6% 4 5% 6% 6% 11% 40%	1620
	11th to 20th	Night	5% 4 3 5% 5% 3 6% 4 8% 11% 47%	1620
	21st to end	Night	9% 4 2 4 6% 5% 6% 6% 7% 11% 41%	1771
August	1st to 10th	Night	9% 4 2 5% 6% 3 5% 5% 6% 9% 46%	1611
	11th to 20th	Night	7% 6% 3 6% 5% 4 6% 5% 7% 10% 43%	1627
	21st to end	Night	7% 4 2 5% 5% 4 5% 5% 7% 10% 48%	1980
September	1st to 10th	Night	13% 5% 2 4 4 2 5% 4 7% 7% 46%	1912
	11th to 20th	Night	11% 6% 3 5% 4 2 5% 5% 5% 7% 47%	1980
	21st to end	Night	10% 6% 2 4 5% 2 4 3 4 6% 54%	1980
October	1st to 10th	Night	10% 5% 2 4 4 2 4 4 5% 6% 55%	1980
	11th to 20th	Night	16% 6% 2 4 5% 2 2 5% 5% 6% 47%	2111
	21st to end	Night	17% 8% 3 5% 4 2 4 3 4 6% 44%	2461
November	1st to 10th	Night	11% 6% 3 5% 4 2 3 4 4 5% 52%	2406
	11th to 20th	Night	15% 8% 3 5% 4 2 3 4 3 6% 47%	2470
	21st to end	Night	17% 9% 4 5% 4 3 4 4 4 6% 42%	2470
December	1st to 10th	Night	21% 12% 5% 7% 4 3 4 4 4 5% 30%	2470
	11th to 20th	Night	19% 10% 5% 9% 4 2 4 3 4 5% 35%	3042
	21st to end	Night	17% 15% 4 8% 8% 5% 6% 6% 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	1856
	11th to 20th	Day	56% 5% 7% 20% 10% 2	1758
	21st to end	Day	56% 4 9% 15% 11% 5%	1480
March	1st to 10th	Day	49% 4 8% 20% 17% 2	1822
	11th to 20th	Day	55% 5% 9% 17% 11% 2	1980
	21st to end	Day	52% 6% 10% 21% 10% 2	2178
April	1st to 10th	Day	42% 5% 11% 25% 14% 3	2096
	11th to 20th	Day	45% 4 9% 20% 18% 4	2155
	21st to end	Day	46% 6% 11% 23% 11% 2	2340
May	1st to 10th	Day	47% 6% 11% 25% 9% 1	2340
	11th to 20th	Day	50% 7% 12% 21% 10% 1	2305
	21st to end	Day	41% 9% 15% 22% 12% 2	2531
June	1st to 10th	Day	41% 8% 10% 24% 16% 1	2340
	11th to 20th	Day	37% 9% 13% 23% 17% 2	2340
	21st to end	Day	38% 9% 14% 19% 18% 3	2340
July	1st to 10th	Day	44% 10% 13% 18% 14% 2	2275
	11th to 20th	Day	42% 9% 16% 17% 13% 3	2271
	21st to end	Day	41% 9% 14% 21% 12% 2	2405
August	1st to 10th	Day	42% 10% 15% 21% 12% 1	2314
	11th to 20th	Day	43% 10% 12% 21% 13% 1	2269
	21st to end	Day	37% 10% 13% 23% 14% 3	2376
September	1st to 10th	Day	43% 8% 11% 18% 14% 5%	2030
	11th to 20th	Day	38% 6% 11% 22% 20% 2	1980
	21st to end	Day	36% 6% 10% 25% 21% 3	1980
October	1st to 10th	Day	32% 6% 10% 24% 25% 4	1980
	11th to 20th	Day	38% 4 8% 22% 24% 4	1847
	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	55% 4 10% 18% 11% 1	2307
	11th to 20th	Night	56% 4 7% 19% 12% 2	2099
	21st to end	Night	60% 4 8% 14% 11% 4	1776
March	1st to 10th	Night	48% 4 7% 17% 20% 3	2136
	11th to 20th	Night	49% 6% 9% 22% 12% 2	1980
	21st to end	Night	52% 6% 9% 22% 10% 2	2178
April	1st to 10th	Night	39% 6% 10% 23% 19% 4	1877
	11th to 20th	Night	41% 5% 10% 19% 19% 6%	1753
	21st to end	Night	44% 6% 11% 25% 13% 1	1620
May	1st to 10th	Night	47% 6% 10% 24% 10% 3	1620
	11th to 20th	Night	44% 10% 12% 20% 13% 1	1593
	21st to end	Night	35% 11% 16% 24% 13% 2	1745
June	1st to 10th	Night	33% 9% 14% 27% 15% 3	1620
	11th to 20th	Night	29% 10% 17% 24% 19% 2	1620
	21st to end	Night	33% 10% 15% 21% 15% 5%	1620
July	1st to 10th	Night	37% 10% 14% 22% 15% 2	1575
	11th to 20th	Night	31% 8% 18% 21% 17% 5%	1566
	21st to end	Night	35% 10% 15% 24% 15% 1	1672
August	1st to 10th	Night	34% 8% 15% 25% 16% 2	1600
	11th to 20th	Night	35% 10% 16% 24% 14% 2	1627
	21st to end	Night	29% 9% 14% 26% 18% 3	1980
September	1st to 10th	Night	34% 9% 14% 20% 17% 6%	1912
	11th to 20th	Night	35% 6% 11% 25% 21% 2	1980
	21st to end	Night	32% 4 9% 24% 27% 4	1980
October	1st to 10th	Night	29% 6% 10% 22% 26% 6%	1980
	11th to 20th	Night	37% 5% 9% 21% 24% 4	2111
	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	25% 20% 37% 14% 3	267
	11th to 20th	Day	42% 21% 29% 7% 1	240
	21st to end	Day	41% 19% 31% 8% 2	198
March	1st to 10th	Day	26% 24% 40% 9% 2	262
	11th to 20th	Day	25% 22% 32% 15% 5% 1	420
	21st to end	Day	28% 19% 29% 17% 7%	462
April	1st to 10th	Day	19% 20% 27% 23% 10% 1	420
	11th to 20th	Day	19% 18% 31% 19% 10% 3	412
	21st to end	Day	20% 17% 30% 21% 10% 3	420
May	1st to 10th	Day	20% 13% 32% 20% 11% 4	423
	11th to 20th	Day	18% 10% 26% 27% 13% 6%	447
	21st to end	Day	15% 7% 18% 28% 20% 12%	485
June	1st to 10th	Day	14% 5% 21% 27% 22% 11%	450
	11th to 20th	Day	10% 4 21% 29% 26% 10%	450
	21st to end	Day	12% 4 22% 30% 20% 12%	450
July	1st to 10th	Day	13% 3 13% 24% 24% 23%	445
	11th to 20th	Day	11% 5% 16% 25% 28% 16%	444
	21st to end	Day	13% 3 15% 29% 27% 14%	488
August	1st to 10th	Day	15% 2 14% 28% 27% 14%	446
	11th to 20th	Day	13% 2 17% 32% 25% 11%	439
	21st to end	Day	12% 2 11% 26% 31% 17%	495
September	1st to 10th	Day	14% 2 13% 22% 33% 15%	450
	11th to 20th	Day	12% 4 14% 24% 31% 14%	450
	21st to end	Day	16% 6% 17% 30% 22% 9%	450
October	1st to 10th	Day	14% 5% 21% 31% 22% 8%	450
	11th to 20th	Day	14% 13% 29% 28% 11% 5%	450
	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	759
	11th to 20th	Night	29% 18% 34% 17% 1	703
	21st to end	Night	32% 15% 37% 15% 2	592
March	1st to 10th	Night	23% 15% 33% 24% 5%	720
	11th to 20th	Night	25% 13% 34% 21% 7%	720
	21st to end	Night	22% 13% 29% 28% 8%	792
April	1st to 10th	Night	17% 12% 32% 28% 9%	617
	11th to 20th	Night	19% 9% 34% 26% 11% 1	533
	21st to end	Night	19% 8% 33% 29% 11%	540
May	1st to 10th	Night	19% 9% 27% 30% 13% 3	540
	11th to 20th	Night	17% 5% 22% 33% 20% 3	531
	21st to end	Night	7% 3 18% 35% 31% 6%	584
June	1st to 10th	Night	8% 3 16% 41% 28% 4	540
	11th to 20th	Night	7% 2 17% 40% 30% 5%	540
	21st to end	Night	9% 3 17% 40% 29% 3	540
July	1st to 10th	Night	12% 2 10% 34% 35% 8%	525
	11th to 20th	Night	7% 2 11% 30% 44% 6%	522
	21st to end	Night	10% 3 11% 32% 39% 5%	591
August	1st to 10th	Night	10% 1 10% 30% 43% 6%	537
	11th to 20th	Night	9% 2 10% 37% 36% 6%	534
	21st to end	Night	9% 1 7% 35% 40% 8%	594
September	1st to 10th	Night	13% 2 12% 31% 37% 5%	652
	11th to 20th	Night	14% 2 14% 28% 37% 6%	720
	21st to end	Night	14% 2 21% 30% 30% 4	720
October	1st to 10th	Night	13% 6% 18% 29% 30% 5%	720
	11th to 20th	Night	19% 8% 23% 31% 17% 2	720
	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

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