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 2025-02-21.

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% 13% 4 10% 5% 4 4 3 5% 7% 30%	108669
	Night	15% 14% 5% 11% 5% 4 4 3 5% 6% 27%	109881
Transparency	Day	52% 7% 11% 19% 10% 1	112344
	Night	56% 7% 10% 16% 9% 1	114346
Seeing	Day	22% 15% 29% 21% 10% 3	14839
	Night	23% 15% 26% 24% 11% 1	24669

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% 22% 9% 26% 5% 3 2 2 3 3 11%	4056
	11th to 20th	Day	11% 25% 9% 20% 7% 6% 3 2 3 3 11%	4060
	21st to end	Day	19% 21% 10% 17% 7% 4 4 2 3 3 11%	4466
February	1st to 10th	Day	16% 21% 6% 16% 7% 4 3 3 3 3 18%	1800
	11th to 20th	Day	15% 17% 8% 15% 9% 5% 3 3 4 4 17%	1764
	21st to end	Day	17% 18% 4 13% 4 4 5% 3 5% 5% 22%	1570
March	1st to 10th	Day	19% 15% 7% 8% 4 3 3 3 5% 7% 26%	3391
	11th to 20th	Day	12% 17% 7% 10% 5% 4 3 3 4 5% 31%	3480
	21st to end	Day	20% 14% 5% 10% 4 3 4 2 4 5% 29%	3815
April	1st to 10th	Day	15% 16% 3 7% 5% 4 4 4 5% 7% 32%	2156
	11th to 20th	Day	19% 12% 3 6% 4 4 5% 4 4 6% 33%	2387
	21st to end	Day	19% 12% 4 8% 4 3 3 3 4 5% 35%	2470
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 4 4 5% 6% 31%	4082
	11th to 20th	Day	18% 10% 3 8% 5% 4 4 4 6% 7% 33%	4081
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 7% 41%	4715
June	1st to 10th	Day	15% 7% 2 6% 5% 4 5% 5% 6% 9% 37%	2660
	11th to 20th	Day	12% 6% 3 6% 5% 4 5% 4 7% 9% 39%	2660
	21st to end	Day	12% 5% 2 5% 5% 4 5% 4 7% 10% 40%	2660
July	1st to 10th	Day	8% 5% 2 7% 4 5% 5% 4 6% 11% 42%	4295
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 6% 10% 44%	4120
	21st to end	Day	9% 5% 2 7% 6% 5% 5% 5% 6% 9% 42%	4466
August	1st to 10th	Day	13% 6% 3 6% 5% 5% 5% 4 7% 9% 38%	4104
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 5% 7% 9% 34%	4044
	21st to end	Day	11% 5% 2 7% 4 4 5% 5% 6% 9% 42%	4422
September	1st to 10th	Day	15% 7% 3 6% 3 4 5% 3 5% 8% 41%	2224
	11th to 20th	Day	12% 7% 2 5% 4 4 5% 4 6% 9% 43%	2090
	21st to end	Day	18% 9% 2 7% 5% 4 4 3 5% 6% 36%	2090
October	1st to 10th	Day	16% 6% 3 8% 5% 5% 4 4 6% 7% 37%	1938
	11th to 20th	Day	21% 10% 3 8% 5% 4 4 3 5% 6% 30%	1900
	21st to end	Day	24% 13% 4 8% 5% 5% 4 3 4 6% 24%	2090
November	1st to 10th	Day	14% 13% 4 8% 5% 5% 4 3 4 6% 32%	1773
	11th to 20th	Day	16% 22% 3 9% 6% 4 5% 4 4 6% 23%	1690
	21st to end	Day	18% 25% 7% 8% 6% 4 4 2 5% 6% 15%	1600
December	1st to 10th	Day	17% 24% 11% 14% 6% 5% 4 3 4 3 11%	2600
	11th to 20th	Day	20% 24% 8% 14% 7% 4 3 3 4 4 10%	2990
	21st to end	Day	21% 25% 6% 17% 6% 4 3 3 3 3 8%	3960
January	1st to 10th	Night	12% 22% 12% 25% 5% 3 2 2 3 3 9%	5889
	11th to 20th	Night	9% 21% 12% 22% 8% 4 3 3 4 4 10%	5900
	21st to end	Night	19% 21% 8% 15% 6% 4 4 2 3 4 14%	6490
February	1st to 10th	Night	18% 18% 6% 13% 8% 5% 4 3 4 4 17%	2600
	11th to 20th	Night	16% 17% 6% 14% 7% 5% 4 3 3 4 20%	2518
	21st to end	Night	18% 15% 5% 13% 6% 5% 5% 4 4 5% 21%	1885
March	1st to 10th	Night	20% 16% 4 7% 5% 4 3 3 4 5% 31%	3462
	11th to 20th	Night	15% 14% 5% 10% 4 4 4 3 4 5% 33%	3480
	21st to end	Night	16% 15% 6% 9% 5% 3 3 3 4 4 33%	3817
April	1st to 10th	Night	16% 16% 3 8% 5% 4 3 3 5% 5% 31%	2024
	11th to 20th	Night	17% 13% 3 5% 4 4 5% 5% 6% 6% 34%	1758
	21st to end	Night	15% 10% 3 7% 5% 5% 4 4 5% 8% 34%	1710
May	1st to 10th	Night	21% 11% 3 7% 5% 4 4 3 6% 7% 30%	2813
	11th to 20th	Night	13% 10% 3 7% 4 5% 4 5% 6% 8% 35%	2812
	21st to end	Night	12% 5% 2 4 3 4 4 4 6% 10% 45%	2836
June	1st to 10th	Night	10% 7% 2 8% 5% 4 5% 5% 6% 7% 41%	1520
	11th to 20th	Night	8% 5% 3 8% 5% 5% 5% 4 6% 7% 44%	1520
	21st to end	Night	10% 5% 2 7% 5% 5% 4 3 7% 10% 41%	1520
July	1st to 10th	Night	9% 6% 2 6% 4 4 4 3 6% 9% 47%	2646
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 7% 9% 47%	2840
	21st to end	Night	7% 6% 2 7% 4 4 5% 5% 6% 8% 45%	3087
August	1st to 10th	Night	11% 7% 3 8% 4 5% 5% 4 6% 8% 40%	2825
	11th to 20th	Night	14% 6% 4 8% 6% 5% 5% 3 5% 6% 39%	2785
	21st to end	Night	8% 6% 3 7% 5% 5% 5% 4 6% 8% 43%	3188
September	1st to 10th	Night	13% 5% 2 6% 4 4 4 4 6% 8% 45%	1952
	11th to 20th	Night	12% 5% 2 5% 4 4 5% 4 5% 6% 50%	2090
	21st to end	Night	17% 7% 3 7% 6% 5% 5% 3 5% 7% 36%	2090
October	1st to 10th	Night	16% 7% 2 6% 5% 4 4 3 6% 7% 41%	2242
	11th to 20th	Night	20% 9% 3 8% 6% 5% 4 4 5% 6% 31%	2280
	21st to end	Night	26% 10% 3 8% 5% 4 4 3 5% 5% 26%	2508
November	1st to 10th	Night	16% 14% 4 7% 5% 4 4 3 4 6% 33%	2522
	11th to 20th	Night	17% 19% 5% 10% 6% 5% 4 3 5% 5% 22%	2707
	21st to end	Night	20% 22% 6% 9% 5% 4 4 2 4 5% 18%	2800
December	1st to 10th	Night	14% 23% 12% 12% 5% 4 4 3 4 5% 13%	4580
	11th to 20th	Night	18% 25% 8% 12% 5% 5% 4 2 3 4 14%	5205
	21st to end	Night	19% 23% 6% 14% 6% 5% 4 3 4 5% 11%	6980

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	81% 6% 6% 5% 2	4057
	11th to 20th	Day	80% 4 8% 6% 2	4060
	21st to end	Day	79% 4 6% 8% 3	4466
February	1st to 10th	Day	72% 5% 8% 11% 4	1800
	11th to 20th	Day	71% 5% 7% 11% 5%	1773
	21st to end	Day	62% 7% 11% 13% 6% 2	1570
March	1st to 10th	Day	57% 7% 10% 23% 3	3391
	11th to 20th	Day	53% 8% 16% 17% 5% 1	3480
	21st to end	Day	55% 8% 9% 17% 10% 1	3815
April	1st to 10th	Day	51% 6% 13% 17% 12%	2156
	11th to 20th	Day	50% 6% 11% 18% 12% 2	2387
	21st to end	Day	51% 6% 11% 19% 10% 3	2470
May	1st to 10th	Day	51% 7% 9% 22% 9% 1	4120
	11th to 20th	Day	47% 9% 12% 21% 9% 2	4085
	21st to end	Day	36% 10% 13% 21% 14% 5%	4729
June	1st to 10th	Day	41% 8% 13% 24% 13% 1	2660
	11th to 20th	Day	39% 9% 15% 22% 14% 1	2660
	21st to end	Day	38% 8% 13% 25% 14% 2	2660
July	1st to 10th	Day	34% 7% 15% 24% 16% 3	4229
	11th to 20th	Day	33% 7% 14% 27% 18% 1	4051
	21st to end	Day	36% 9% 16% 21% 17% 1	4324
August	1st to 10th	Day	41% 8% 15% 24% 12%	4091
	11th to 20th	Day	41% 9% 14% 29% 6% 1	4083
	21st to end	Day	36% 8% 15% 28% 13% 1	4422
September	1st to 10th	Day	40% 7% 15% 21% 14% 2	2224
	11th to 20th	Day	37% 8% 13% 25% 16% 1	2090
	21st to end	Day	48% 6% 11% 22% 12% 1	2090
October	1st to 10th	Day	35% 7% 15% 24% 18%	3224
	11th to 20th	Day	48% 6% 12% 19% 14% 1	3140
	21st to end	Day	45% 6% 14% 26% 9%	3428
November	1st to 10th	Day	52% 7% 11% 18% 11% 1	1773
	11th to 20th	Day	63% 6% 10% 12% 7% 2	1690
	21st to end	Day	70% 6% 9% 11% 4	1600
December	1st to 10th	Day	79% 7% 8% 5% 1	2600
	11th to 20th	Day	78% 6% 7% 9% 2	2986
	21st to end	Day	81% 6% 6% 6% 1	3960
January	1st to 10th	Night	82% 5% 4 7% 3	5889
	11th to 20th	Night	79% 6% 7% 6% 1	5900
	21st to end	Night	76% 4 8% 7% 4	6490
February	1st to 10th	Night	70% 7% 9% 11% 3	2600
	11th to 20th	Night	69% 5% 9% 13% 4	2520
	21st to end	Night	65% 7% 8% 13% 7% 1	1885
March	1st to 10th	Night	56% 6% 12% 18% 8%	3462
	11th to 20th	Night	52% 7% 15% 17% 8% 1	3480
	21st to end	Night	52% 6% 12% 17% 11% 1	3817
April	1st to 10th	Night	54% 7% 11% 16% 11% 2	2024
	11th to 20th	Night	48% 7% 12% 19% 11% 3	1758
	21st to end	Night	48% 7% 11% 20% 11% 3	1710
May	1st to 10th	Night	51% 7% 11% 18% 10% 3	2840
	11th to 20th	Night	44% 9% 11% 23% 10% 2	2813
	21st to end	Night	31% 8% 15% 26% 17% 2	2843
June	1st to 10th	Night	39% 7% 11% 25% 14% 3	1520
	11th to 20th	Night	38% 7% 13% 20% 19% 3	1520
	21st to end	Night	37% 9% 13% 24% 17% 1	1520
July	1st to 10th	Night	34% 7% 13% 23% 19% 4	2603
	11th to 20th	Night	31% 8% 12% 27% 18% 3	2786
	21st to end	Night	34% 8% 14% 21% 21% 1	2988
August	1st to 10th	Night	41% 8% 11% 26% 14% 1	2814
	11th to 20th	Night	43% 7% 11% 27% 11% 1	2812
	21st to end	Night	36% 8% 13% 27% 14% 2	3188
September	1st to 10th	Night	36% 7% 14% 24% 15% 3	1952
	11th to 20th	Night	34% 7% 13% 24% 20% 2	2090
	21st to end	Night	47% 7% 12% 19% 15%	2090
October	1st to 10th	Night	35% 7% 9% 25% 22% 1	3736
	11th to 20th	Night	50% 6% 9% 18% 15% 2	3779
	21st to end	Night	45% 5% 14% 21% 13% 1	4120
November	1st to 10th	Night	51% 7% 11% 18% 10% 2	2522
	11th to 20th	Night	64% 6% 9% 12% 5% 3	2707
	21st to end	Night	69% 6% 9% 12% 4	2800
December	1st to 10th	Night	75% 6% 11% 6% 2	4580
	11th to 20th	Night	75% 6% 9% 9% 1	5208
	21st to end	Night	75% 8% 8% 8% 1	6980

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	30% 30% 28% 9% 3	300
	11th to 20th	Day	34% 29% 25% 8% 2 1	300
	21st to end	Day	28% 31% 31% 8% 2	330
February	1st to 10th	Day	32% 25% 34% 9%	300
	11th to 20th	Day	35% 27% 28% 9%	300
	21st to end	Day	34% 28% 30% 8%	225
March	1st to 10th	Day	27% 20% 35% 13% 4	427
	11th to 20th	Day	26% 20% 35% 16% 3 1	460
	21st to end	Day	34% 19% 26% 16% 4	506
April	1st to 10th	Day	24% 21% 32% 16% 6%	460
	11th to 20th	Day	31% 16% 29% 16% 6% 2	452
	21st to end	Day	25% 18% 33% 18% 5% 1	460
May	1st to 10th	Day	25% 16% 31% 20% 6% 2	463
	11th to 20th	Day	18% 10% 32% 27% 9% 3	487
	21st to end	Day	14% 7% 31% 29% 14% 5%	529
June	1st to 10th	Day	18% 9% 34% 27% 10% 2	490
	11th to 20th	Day	15% 10% 29% 31% 13% 2	490
	21st to end	Day	15% 8% 31% 30% 13% 2	490
July	1st to 10th	Day	10% 8% 26% 29% 19% 8%	485
	11th to 20th	Day	14% 6% 29% 28% 16% 7%	484
	21st to end	Day	10% 5% 33% 30% 17% 5%	532
August	1st to 10th	Day	12% 8% 23% 31% 19% 7%	486
	11th to 20th	Day	13% 7% 25% 30% 18% 7%	479
	21st to end	Day	13% 7% 23% 32% 19% 6%	539
September	1st to 10th	Day	17% 9% 22% 27% 20% 6%	490
	11th to 20th	Day	11% 5% 21% 31% 22% 10%	490
	21st to end	Day	20% 12% 29% 22% 11% 6%	490
October	1st to 10th	Day	17% 12% 26% 25% 17% 4	490
	11th to 20th	Day	26% 19% 31% 17% 7% 2	490
	21st to end	Day	35% 16% 28% 18% 3	539
November	1st to 10th	Day	23% 24% 27% 16% 8% 1	311
	11th to 20th	Day	35% 25% 25% 10% 4 1	245
	21st to end	Day	33% 26% 31% 11%	200
December	1st to 10th	Day	32% 29% 27% 9% 3 1	200
	11th to 20th	Day	27% 28% 33% 12% 1	200
	21st to end	Day	32% 27% 30% 9% 2	220
January	1st to 10th	Night	29% 27% 30% 11% 3	800
	11th to 20th	Night	34% 23% 27% 15% 2	800
	21st to end	Night	29% 22% 31% 15% 3	880
February	1st to 10th	Night	30% 21% 28% 18% 3	800
	11th to 20th	Night	28% 21% 33% 16% 2	783
	21st to end	Night	31% 21% 31% 16% 1	629
March	1st to 10th	Night	25% 17% 34% 21% 3	760
	11th to 20th	Night	24% 20% 31% 20% 5% 1	760
	21st to end	Night	24% 15% 30% 23% 7%	836
April	1st to 10th	Night	25% 15% 29% 26% 6%	760
	11th to 20th	Night	24% 11% 32% 24% 8% 1	634
	21st to end	Night	18% 11% 33% 31% 7% 1	570
May	1st to 10th	Night	21% 11% 24% 31% 12% 1	570
	11th to 20th	Night	17% 7% 26% 37% 11% 2	561
	21st to end	Night	12% 5% 23% 36% 21% 3	477
June	1st to 10th	Night	13% 5% 28% 37% 14% 1	380
	11th to 20th	Night	13% 7% 23% 39% 18% 1	380
	21st to end	Night	11% 8% 24% 39% 19%	380
July	1st to 10th	Night	7% 5% 18% 40% 25% 5%	441
	11th to 20th	Night	9% 4 20% 36% 25% 5%	552
	21st to end	Night	11% 4 20% 38% 25% 3	624
August	1st to 10th	Night	10% 4 19% 38% 25% 5%	567
	11th to 20th	Night	13% 3 14% 35% 30% 4	564
	21st to end	Night	13% 6% 20% 30% 28% 3	665
September	1st to 10th	Night	15% 7% 18% 31% 24% 5%	760
	11th to 20th	Night	13% 5% 16% 34% 28% 5%	760
	21st to end	Night	20% 9% 23% 26% 17% 4	760
October	1st to 10th	Night	19% 10% 24% 26% 18% 3	760
	11th to 20th	Night	26% 16% 25% 24% 8% 1	760
	21st to end	Night	31% 19% 27% 20% 3	836
November	1st to 10th	Night	26% 16% 28% 22% 8% 1	780
	11th to 20th	Night	31% 21% 28% 14% 5% 1	800
	21st to end	Night	35% 21% 26% 13% 4	800
December	1st to 10th	Night	36% 22% 28% 11% 4	800
	11th to 20th	Night	32% 27% 27% 13% 2	800
	21st to end	Night	33% 21% 32% 13% 1	880

Page generated at 2025-02-18 03:26:26. Version ac07

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