Madison
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Madison clear sky chart from 2005-11-06 to 2026-04-02.

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	13% 8% 3 8% 5% 4 4 4 6% 7% 38%	131572
	Night	13% 9% 4 8% 5% 4 4 3 5% 6% 39%	130557
Transparency	Day	44% 5% 12% 25% 13% 1	135054
	Night	45% 5% 11% 23% 14% 2	135149
Seeing	Day	17% 11% 30% 25% 13% 4	17748
	Night	18% 10% 31% 29% 11% 1	27768

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	10% 11% 6% 15% 7% 6% 5% 3 5% 6% 25%	4691
	11th to 20th	Day	6% 10% 6% 12% 5% 4 5% 7% 7% 6% 31%	4710
	21st to end	Day	10% 11% 6% 10% 5% 4 5% 3 4 5% 37%	5414
February	1st to 10th	Day	11% 12% 7% 10% 5% 5% 4 4 5% 6% 31%	1890
	11th to 20th	Day	12% 11% 3 8% 5% 5% 5% 3 5% 6% 36%	1976
	21st to end	Day	12% 11% 5% 11% 6% 4 4 3 6% 5% 32%	1730
March	1st to 10th	Day	15% 7% 3 5% 3 3 3 3 5% 7% 46%	4580
	11th to 20th	Day	12% 6% 2 8% 4 5% 4 4 5% 7% 44%	4917
	21st to end	Day	23% 11% 3 10% 5% 4 3 3 4 5% 30%	6037
April	1st to 10th	Day	18% 13% 3 8% 5% 4 3 4 5% 6% 31%	2412
	11th to 20th	Day	17% 10% 3 7% 5% 4 5% 4 5% 7% 34%	2374
	21st to end	Day	19% 9% 3 7% 5% 5% 4 3 5% 6% 34%	2467
May	1st to 10th	Day	15% 7% 2 6% 5% 4 4 4 6% 7% 41%	6079
	11th to 20th	Day	15% 5% 2 7% 4 4 5% 4 5% 7% 42%	6319
	21st to end	Day	16% 7% 2 5% 4 4 5% 4 6% 9% 40%	6935
June	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 3 7% 9% 44%	2800
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	2800
	21st to end	Day	12% 6% 3 5% 5% 4 5% 4 7% 9% 41%	2800
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 7% 10% 41%	6360
	11th to 20th	Day	8% 5% 1 6% 4 5% 5% 5% 6% 8% 48%	6360
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 4 6% 9% 41%	6924
August	1st to 10th	Day	10% 5% 2 7% 5% 4 4 4 7% 9% 42%	4501
	11th to 20th	Day	12% 4 2 5% 4 4 5% 4 5% 8% 48%	3942
	21st to end	Day	10% 5% 2 6% 4 4 4 4 7% 9% 45%	4312
September	1st to 10th	Day	12% 5% 2 6% 4 5% 4 4 6% 7% 45%	2400
	11th to 20th	Day	12% 5% 2 5% 3 3 4 3 5% 8% 50%	2335
	21st to end	Day	12% 6% 3 7% 4 4 4 3 5% 6% 46%	2200
October	1st to 10th	Day	13% 6% 2 6% 4 4 3 3 5% 6% 48%	2040
	11th to 20th	Day	18% 9% 3 8% 5% 3 4 3 4 7% 35%	2000
	21st to end	Day	17% 11% 3 6% 5% 4 3 2 4 6% 40%	2013
November	1st to 10th	Day	12% 9% 3 6% 4 4 4 4 4 7% 44%	1852
	11th to 20th	Day	13% 12% 3 9% 5% 5% 4 3 5% 6% 33%	1874
	21st to end	Day	14% 13% 4 11% 5% 4 3 3 3 6% 34%	1680
December	1st to 10th	Day	8% 10% 5% 8% 6% 7% 5% 3 5% 7% 37%	2690
	11th to 20th	Day	12% 14% 5% 12% 6% 4 5% 4 5% 7% 25%	3088
	21st to end	Day	21% 21% 8% 12% 5% 4 4 3 4 5% 14%	4070
January	1st to 10th	Night	10% 11% 6% 13% 7% 3 4 3 4 5% 32%	8232
	11th to 20th	Night	9% 12% 6% 14% 6% 5% 6% 5% 7% 6% 23%	8280
	21st to end	Night	9% 13% 7% 9% 6% 5% 4 4 5% 6% 33%	8785
February	1st to 10th	Night	10% 14% 4 9% 5% 5% 4 4 5% 5% 34%	2730
	11th to 20th	Night	12% 10% 3 8% 5% 4 5% 4 4 6% 40%	2530
	21st to end	Night	16% 11% 4 8% 4 4 4 3 4 6% 36%	2076
March	1st to 10th	Night	16% 7% 3 7% 4 4 4 3 4 5% 43%	5493
	11th to 20th	Night	10% 7% 2 5% 4 4 4 4 5% 8% 47%	5307
	21st to end	Night	22% 12% 4 9% 4 4 3 2 4 5% 29%	5132
April	1st to 10th	Night	17% 9% 3 7% 4 4 5% 4 5% 6% 37%	2010
	11th to 20th	Night	19% 8% 3 7% 5% 3 4 3 5% 5% 38%	1975
	21st to end	Night	17% 8% 2 6% 4 4 4 4 5% 8% 38%	1931
May	1st to 10th	Night	18% 6% 2 6% 4 4 4 3 5% 7% 41%	3823
	11th to 20th	Night	11% 5% 2 5% 4 4 5% 4 5% 8% 47%	3596
	21st to end	Night	16% 8% 2 6% 5% 4 4 4 5% 7% 39%	3942
June	1st to 10th	Night	8% 5% 2 6% 5% 5% 4 5% 7% 9% 46%	1600
	11th to 20th	Night	13% 6% 2 5% 4 3 4 4 6% 9% 45%	1600
	21st to end	Night	10% 5% 3 6% 4 4 3 3 5% 8% 50%	1600
July	1st to 10th	Night	14% 5% 2 6% 3 4 4 3 6% 8% 45%	3618
	11th to 20th	Night	6% 5% 2 5% 4 4 4 3 5% 8% 54%	3617
	21st to end	Night	8% 4 1 5% 4 4 5% 4 6% 7% 51%	3947
August	1st to 10th	Night	11% 4 2 5% 4 3 4 3 6% 7% 50%	2656
	11th to 20th	Night	11% 7% 2 5% 4 3 4 3 5% 8% 49%	3109
	21st to end	Night	10% 4 2 5% 4 4 5% 4 5% 8% 50%	3586
September	1st to 10th	Night	9% 4 2 5% 3 3 3 3 6% 7% 55%	2000
	11th to 20th	Night	11% 4 1 5% 3 4 5% 3 5% 6% 53%	2045
	21st to end	Night	10% 5% 2 5% 4 4 4 4 5% 6% 50%	2200
October	1st to 10th	Night	11% 7% 2 6% 3 3 3 2 5% 7% 51%	2355
	11th to 20th	Night	17% 8% 2 6% 4 4 4 2 5% 6% 43%	2400
	21st to end	Night	17% 9% 3 7% 4 4 4 3 6% 7% 37%	2826
November	1st to 10th	Night	12% 8% 3 6% 5% 3 4 3 4 6% 46%	2666
	11th to 20th	Night	14% 11% 4 8% 5% 5% 4 4 4 5% 35%	2741
	21st to end	Night	16% 12% 4 7% 5% 3 4 3 5% 6% 36%	2940
December	1st to 10th	Night	9% 8% 3 8% 5% 5% 4 3 6% 7% 42%	4720
	11th to 20th	Night	16% 17% 6% 9% 5% 5% 4 4 4 4 26%	5339
	21st to end	Night	20% 19% 6% 11% 5% 4 4 3 4 5% 18%	7150

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% 4 14% 15% 6%	4692
	11th to 20th	Day	51% 4 10% 17% 17% 1	4710
	21st to end	Day	50% 4 11% 24% 11%	5414
February	1st to 10th	Day	54% 4 13% 18% 11% 1	1890
	11th to 20th	Day	49% 4 11% 23% 10% 3	1985
	21st to end	Day	54% 4 9% 20% 11% 2	1730
March	1st to 10th	Day	39% 5% 12% 29% 12% 4	4580
	11th to 20th	Day	40% 4 13% 28% 14% 1	4917
	21st to end	Day	58% 4 11% 16% 10% 2	6039
April	1st to 10th	Day	53% 5% 10% 20% 11%	2412
	11th to 20th	Day	50% 5% 11% 20% 12% 2	2374
	21st to end	Day	52% 6% 11% 19% 11% 1	2467
May	1st to 10th	Day	42% 5% 10% 24% 17% 2	6114
	11th to 20th	Day	40% 7% 10% 26% 16% 1	6323
	21st to end	Day	40% 6% 11% 27% 13% 2	6949
June	1st to 10th	Day	36% 7% 13% 27% 16% 1	2800
	11th to 20th	Day	39% 6% 13% 24% 17% 1	2800
	21st to end	Day	39% 8% 14% 23% 14% 2	2800
July	1st to 10th	Day	37% 7% 15% 30% 10% 1	6291
	11th to 20th	Day	33% 7% 13% 31% 15% 1	6285
	21st to end	Day	38% 8% 15% 22% 16% 1	6728
August	1st to 10th	Day	37% 7% 15% 29% 12% 1	4486
	11th to 20th	Day	34% 6% 14% 33% 13% 1	3980
	21st to end	Day	34% 6% 13% 29% 16% 1	4311
September	1st to 10th	Day	37% 6% 11% 26% 18% 1	2400
	11th to 20th	Day	32% 5% 13% 32% 17% 2	2335
	21st to end	Day	39% 5% 10% 29% 16% 1	2200
October	1st to 10th	Day	24% 4 5% 40% 26% 1	3326
	11th to 20th	Day	36% 4 8% 28% 22% 2	3240
	21st to end	Day	42% 4 10% 29% 14% 2	3225
November	1st to 10th	Day	40% 5% 15% 25% 13% 2	1852
	11th to 20th	Day	52% 5% 11% 21% 10% 1	1874
	21st to end	Day	54% 4 14% 22% 6% 1	1680
December	1st to 10th	Day	46% 4 20% 22% 7% 1	2690
	11th to 20th	Day	58% 3 12% 18% 6% 2	3085
	21st to end	Day	73% 5% 7% 9% 6%	4070
January	1st to 10th	Night	54% 4 12% 21% 9%	8233
	11th to 20th	Night	59% 4 9% 12% 14% 1	8280
	21st to end	Night	52% 4 11% 21% 11%	8785
February	1st to 10th	Night	53% 4 10% 20% 11% 2	2730
	11th to 20th	Night	46% 5% 10% 24% 14% 1	2531
	21st to end	Night	50% 3 11% 21% 12% 3	2076
March	1st to 10th	Night	45% 4 12% 23% 10% 7%	5493
	11th to 20th	Night	35% 4 12% 32% 13% 4	5307
	21st to end	Night	60% 4 8% 16% 12% 1	5132
April	1st to 10th	Night	47% 6% 10% 21% 15% 1	2010
	11th to 20th	Night	47% 4 7% 21% 17% 3	1975
	21st to end	Night	44% 6% 11% 25% 12% 2	1931
May	1st to 10th	Night	43% 6% 11% 18% 20% 2	3850
	11th to 20th	Night	35% 8% 15% 23% 17% 2	3597
	21st to end	Night	43% 6% 10% 23% 14% 3	3950
June	1st to 10th	Night	33% 7% 12% 28% 20% 1	1600
	11th to 20th	Night	35% 6% 10% 24% 22% 2	1600
	21st to end	Night	34% 6% 15% 22% 19% 3	1600
July	1st to 10th	Night	37% 6% 13% 29% 13% 2	3580
	11th to 20th	Night	29% 6% 13% 32% 19% 2	3572
	21st to end	Night	30% 8% 15% 24% 21% 3	3832
August	1st to 10th	Night	33% 6% 14% 26% 20% 2	2647
	11th to 20th	Night	34% 6% 13% 32% 15% 1	3137
	21st to end	Night	32% 6% 12% 27% 19% 3	3586
September	1st to 10th	Night	29% 6% 11% 29% 23% 2	2000
	11th to 20th	Night	32% 6% 10% 32% 18% 2	2045
	21st to end	Night	34% 5% 10% 30% 21% 1	2200
October	1st to 10th	Night	25% 3 6% 37% 27% 2	3849
	11th to 20th	Night	34% 3 10% 28% 22% 2	3899
	21st to end	Night	43% 4 9% 27% 15% 1	4564
November	1st to 10th	Night	41% 4 10% 26% 16% 2	2666
	11th to 20th	Night	51% 5% 12% 20% 11% 2	2741
	21st to end	Night	50% 4 13% 22% 9% 1	2940
December	1st to 10th	Night	42% 4 17% 27% 9% 1	4720
	11th to 20th	Night	61% 4 10% 15% 9% 1	5341
	21st to end	Night	70% 4 7% 13% 5%	7150

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	18% 15% 34% 24% 8% 1	330
	11th to 20th	Day	18% 19% 35% 22% 5% 1	330
	21st to end	Day	23% 15% 34% 24% 4	363
February	1st to 10th	Day	14% 18% 42% 21% 5% 1	330
	11th to 20th	Day	20% 20% 35% 20% 5%	330
	21st to end	Day	22% 16% 47% 13% 2	273
March	1st to 10th	Day	18% 19% 42% 17% 4	330
	11th to 20th	Day	23% 18% 34% 18% 5% 2	330
	21st to end	Day	28% 15% 32% 18% 6% 2	558
April	1st to 10th	Day	26% 14% 34% 21% 4	504
	11th to 20th	Day	26% 17% 25% 20% 10% 2	492
	21st to end	Day	25% 14% 28% 21% 10% 2	500
May	1st to 10th	Day	20% 11% 31% 27% 9% 2	590
	11th to 20th	Day	22% 10% 27% 25% 13% 2	725
	21st to end	Day	17% 8% 29% 24% 16% 5%	789
June	1st to 10th	Day	10% 8% 30% 31% 17% 4	730
	11th to 20th	Day	13% 7% 33% 28% 14% 5%	730
	21st to end	Day	13% 8% 33% 27% 15% 4	730
July	1st to 10th	Day	8% 5% 19% 31% 25% 11%	721
	11th to 20th	Day	10% 5% 26% 30% 19% 9%	718
	21st to end	Day	7% 3 26% 35% 21% 7%	794
August	1st to 10th	Day	8% 4 20% 33% 25% 10%	726
	11th to 20th	Day	13% 5% 18% 27% 24% 13%	576
	21st to end	Day	10% 7% 21% 31% 22% 9%	583
September	1st to 10th	Day	15% 7% 24% 26% 19% 9%	530
	11th to 20th	Day	13% 3 20% 32% 23% 10%	530
	21st to end	Day	13% 11% 27% 24% 18% 6%	530
October	1st to 10th	Day	15% 12% 28% 25% 16% 4	370
	11th to 20th	Day	22% 16% 36% 19% 6%	330
	21st to end	Day	25% 15% 34% 19% 5% 1	363
November	1st to 10th	Day	16% 20% 36% 20% 5% 2	330
	11th to 20th	Day	22% 20% 33% 17% 8%	330
	21st to end	Day	23% 14% 42% 16% 4	330
December	1st to 10th	Day	16% 21% 39% 16% 7% 1	330
	11th to 20th	Day	19% 17% 36% 19% 7% 1	330
	21st to end	Day	25% 18% 39% 15% 3	363
January	1st to 10th	Night	17% 16% 37% 22% 7% 1	1050
	11th to 20th	Night	20% 14% 39% 22% 5% 1	1050
	21st to end	Night	19% 13% 37% 25% 4 1	1155
February	1st to 10th	Night	19% 11% 40% 23% 6%	1050
	11th to 20th	Night	17% 16% 37% 26% 4	895
	21st to end	Night	22% 15% 38% 21% 3	692
March	1st to 10th	Night	21% 11% 36% 24% 6% 1	840
	11th to 20th	Night	18% 13% 36% 27% 7%	730
	21st to end	Night	24% 10% 33% 27% 6% 1	693
April	1st to 10th	Night	22% 13% 38% 24% 4	603
	11th to 20th	Night	24% 14% 28% 27% 7%	593
	21st to end	Night	21% 8% 34% 28% 8% 1	600
May	1st to 10th	Night	19% 10% 32% 30% 8% 1	600
	11th to 20th	Night	19% 7% 30% 34% 10% 1	591
	21st to end	Night	15% 5% 26% 38% 15% 1	650
June	1st to 10th	Night	11% 4 27% 43% 15% 1	600
	11th to 20th	Night	16% 5% 30% 37% 13% 1	600
	21st to end	Night	11% 5% 27% 40% 17%	600
July	1st to 10th	Night	10% 2 15% 38% 32% 3	585
	11th to 20th	Night	8% 3 22% 42% 23% 2	582
	21st to end	Night	7% 2 19% 48% 22% 2	657
August	1st to 10th	Night	6% 3 17% 47% 25% 3	597
	11th to 20th	Night	11% 3 15% 41% 27% 5%	594
	21st to end	Night	11% 2 17% 43% 24% 3	660
September	1st to 10th	Night	10% 5% 24% 33% 23% 6%	600
	11th to 20th	Night	12% 3 22% 36% 24% 3	645
	21st to end	Night	12% 8% 26% 32% 20% 2	800
October	1st to 10th	Night	15% 6% 30% 32% 17% 1	800
	11th to 20th	Night	19% 13% 33% 26% 8%	800
	21st to end	Night	21% 12% 32% 28% 6% 1	880
November	1st to 10th	Night	16% 12% 37% 25% 9% 1	820
	11th to 20th	Night	20% 15% 39% 20% 6%	851
	21st to end	Night	23% 14% 34% 22% 7%	1050
December	1st to 10th	Night	21% 14% 38% 20% 6%	1050
	11th to 20th	Night	24% 13% 34% 24% 5%	1050
	21st to end	Night	29% 13% 34% 21% 3	1155

Page generated at 2026-03-30 01:18:46. Version ac07

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