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 2024-09-14.

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	15% 12% 4 9% 5% 4 4 4 5% 7% 31%	100606
	Night	16% 14% 5% 10% 5% 4 4 3 5% 6% 29%	97213
Transparency	Day	51% 7% 12% 19% 10% 1	100417
	Night	55% 7% 11% 17% 9% 1	97073
Seeing	Day	22% 15% 29% 22% 10% 3	14359
	Night	23% 14% 26% 24% 11% 1	24032

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% 25% 10% 15% 5% 3 3 2 4 4 13%	2836
	11th to 20th	Day	12% 27% 8% 17% 6% 4 3 2 3 4 14%	2840
	21st to end	Day	23% 23% 11% 17% 6% 4 3 2 2 2 7%	3124
February	1st to 10th	Day	16% 21% 6% 16% 8% 4 3 3 3 3 18%	1710
	11th to 20th	Day	15% 17% 8% 15% 8% 5% 3 3 4 4 17%	1673
	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 6% 4 4 5% 4 6% 9% 42%	2014
	21st to end	Day	17% 8% 2 7% 5% 4 4 3 5% 6% 38%	1980
October	1st to 10th	Day	16% 6% 3 8% 5% 5% 4 4 6% 8% 35%	1836
	11th to 20th	Day	22% 10% 3 8% 6% 4 4 3 5% 7% 28%	1800
	21st to end	Day	25% 13% 4 8% 5% 5% 4 3 4 6% 23%	1980
November	1st to 10th	Day	14% 14% 4 8% 5% 5% 4 3 4 6% 32%	1683
	11th to 20th	Day	16% 22% 3 9% 6% 3 5% 3 4 5% 23%	1606
	21st to end	Day	18% 24% 7% 8% 6% 5% 4 3 5% 6% 15%	1520
December	1st to 10th	Day	16% 28% 9% 10% 5% 4 4 3 4 4 13%	1520
	11th to 20th	Day	16% 23% 9% 14% 5% 4 4 3 5% 5% 12%	1910
	21st to end	Day	22% 26% 7% 13% 6% 4 3 2 3 3 10%	2772
January	1st to 10th	Night	14% 26% 13% 17% 5% 4 3 2 3 4 9%	4109
	11th to 20th	Night	12% 21% 11% 20% 6% 4 3 3 4 4 12%	4120
	21st to end	Night	23% 24% 7% 16% 5% 3 3 2 2 3 11%	4532
February	1st to 10th	Night	18% 18% 5% 13% 8% 5% 4 3 4 4 18%	2470
	11th to 20th	Night	16% 18% 6% 14% 7% 5% 4 3 3 4 20%	2389
	21st to end	Night	18% 15% 5% 13% 6% 5% 5% 4 4 5% 21%	1884
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 3 5% 4 5% 6% 49%	2024
	21st to end	Night	16% 6% 3 7% 6% 5% 5% 3 5% 7% 37%	1980
October	1st to 10th	Night	16% 7% 2 6% 5% 4 4 3 6% 7% 40%	2124
	11th to 20th	Night	20% 9% 3 8% 6% 5% 4 4 5% 6% 30%	2160
	21st to end	Night	27% 11% 3 8% 5% 4 4 3 5% 5% 25%	2376
November	1st to 10th	Night	16% 14% 4 7% 4 4 4 3 4 6% 33%	2392
	11th to 20th	Night	16% 18% 5% 10% 6% 5% 4 3 5% 5% 22%	2571
	21st to end	Night	20% 21% 6% 9% 5% 4 4 2 4 5% 19%	2660
December	1st to 10th	Night	20% 26% 8% 9% 5% 4 4 3 3 4 14%	2660
	11th to 20th	Night	17% 23% 7% 12% 6% 5% 4 3 3 4 16%	3285
	21st to end	Night	21% 24% 6% 11% 7% 5% 4 3 4 5% 9%	4882

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	76% 8% 8% 6% 1	2837
	11th to 20th	Day	76% 5% 9% 8% 2	2840
	21st to end	Day	85% 5% 5% 5% 1	3124
February	1st to 10th	Day	72% 5% 8% 11% 4	1710
	11th to 20th	Day	71% 5% 7% 11% 5%	1682
	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% 26% 15% 1	2014
	21st to end	Day	46% 7% 11% 23% 12% 1	1980
October	1st to 10th	Day	45% 9% 14% 18% 13% 1	1836
	11th to 20th	Day	55% 7% 13% 18% 7% 1	1800
	21st to end	Day	63% 7% 11% 13% 6% 1	1980
November	1st to 10th	Day	52% 7% 11% 17% 11% 1	1683
	11th to 20th	Day	63% 7% 10% 12% 7% 2	1606
	21st to end	Day	69% 6% 9% 11% 4	1520
December	1st to 10th	Day	76% 6% 8% 8% 2	1520
	11th to 20th	Day	75% 6% 8% 9% 2	1906
	21st to end	Day	80% 6% 7% 6% 1	2772
January	1st to 10th	Night	80% 6% 5% 6% 2	4109
	11th to 20th	Night	77% 8% 8% 6% 1	4120
	21st to end	Night	81% 4 7% 6% 2	4532
February	1st to 10th	Night	70% 7% 9% 11% 3	2470
	11th to 20th	Night	69% 5% 8% 13% 5%	2391
	21st to end	Night	65% 7% 8% 13% 7% 1	1884
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	35% 7% 13% 24% 19% 1	2024
	21st to end	Night	45% 7% 12% 20% 15% 1	1980
October	1st to 10th	Night	43% 8% 11% 20% 17% 1	2124
	11th to 20th	Night	53% 7% 12% 18% 10% 1	2160
	21st to end	Night	61% 6% 11% 13% 7% 1	2376
November	1st to 10th	Night	52% 7% 12% 17% 10% 2	2392
	11th to 20th	Night	64% 6% 9% 13% 5% 2	2571
	21st to end	Night	69% 6% 9% 12% 4	2660
December	1st to 10th	Night	76% 6% 8% 7% 3	2660
	11th to 20th	Night	73% 7% 10% 8% 2	3288
	21st to end	Night	78% 8% 8% 5% 1	4882

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% 27% 29% 10% 3	270
	11th to 20th	Day	33% 28% 27% 9% 3 1	270
	21st to end	Day	28% 30% 31% 9% 2	297
February	1st to 10th	Day	32% 23% 35% 10%	270
	11th to 20th	Day	33% 28% 29% 10%	270
	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	12% 5% 21% 30% 23% 10%	463
	21st to end	Day	18% 12% 29% 23% 12% 6%	450
October	1st to 10th	Day	17% 12% 25% 24% 17% 4	450
	11th to 20th	Day	26% 18% 32% 17% 5% 1	450
	21st to end	Day	37% 14% 29% 17% 3	495
November	1st to 10th	Day	23% 24% 26% 17% 9% 1	281
	11th to 20th	Day	36% 24% 24% 11% 4 1	221
	21st to end	Day	30% 27% 31% 12%	180
December	1st to 10th	Day	33% 28% 26% 10% 3 1	180
	11th to 20th	Day	24% 30% 33% 12% 1	180
	21st to end	Day	32% 27% 29% 10% 1	198
January	1st to 10th	Night	29% 27% 30% 11% 3	760
	11th to 20th	Night	33% 22% 27% 16% 2	760
	21st to end	Night	28% 22% 32% 16% 3	836
February	1st to 10th	Night	29% 21% 28% 19% 3	760
	11th to 20th	Night	27% 21% 33% 17% 2	743
	21st to end	Night	31% 21% 31% 16% 1	628
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% 35% 27% 5%	736
	21st to end	Night	19% 9% 23% 26% 18% 4	720
October	1st to 10th	Night	20% 10% 23% 26% 18% 3	720
	11th to 20th	Night	26% 16% 26% 25% 7% 1	720
	21st to end	Night	32% 19% 26% 19% 3	792
November	1st to 10th	Night	26% 15% 28% 23% 8% 1	740
	11th to 20th	Night	30% 21% 28% 15% 5% 1	760
	21st to end	Night	34% 21% 27% 14% 4	760
December	1st to 10th	Night	36% 22% 27% 11% 4	760
	11th to 20th	Night	31% 26% 27% 13% 2	760
	21st to end	Night	33% 21% 32% 13% 1	836

Page generated at 2024-09-11 10:00:03. Version ac07

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