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 2024-01-16.

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	13% 8% 4 7% 6% 3 5% 5% 5% 7% 37%	74800
	Night	14% 9% 4 6% 5% 3 4 4 5% 7% 39%	75027
Transparency	Day	46% 6% 12% 22% 12% 1	74500
	Night	46% 5% 11% 22% 14% 2	74847
Seeing	Day	16% 10% 29% 26% 14% 5%	14727
	Night	18% 9% 31% 30% 11% 1	24734

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	12% 11% 6% 9% 6% 3 5% 5% 5% 7% 30%	1517
	11th to 20th	Day	12% 15% 6% 12% 8% 4 5% 4 5% 6% 22%	1480
	21st to end	Day	12% 14% 7% 12% 7% 4 5% 4 5% 8% 22%	1660
February	1st to 10th	Day	12% 12% 8% 9% 5% 4 5% 5% 5% 6% 31%	1620
	11th to 20th	Day	14% 10% 4 7% 7% 4 5% 4 4 6% 35%	1686
	21st to end	Day	13% 11% 6% 10% 7% 4 4 4 5% 5% 31%	1480
March	1st to 10th	Day	13% 9% 6% 7% 5% 3 4 5% 5% 7% 34%	1800
	11th to 20th	Day	13% 7% 4 6% 6% 4 4 5% 4 7% 39%	1909
	21st to end	Day	19% 11% 4 7% 5% 4 4 4 4 8% 30%	2344
April	1st to 10th	Day	17% 11% 5% 7% 6% 3 4 5% 5% 6% 31%	2160
	11th to 20th	Day	17% 10% 3 6% 6% 3 5% 5% 5% 7% 34%	2134
	21st to end	Day	19% 9% 4 6% 6% 3 5% 4 4 6% 33%	2219
May	1st to 10th	Day	17% 8% 3 7% 7% 4 5% 6% 7% 8% 30%	2417
	11th to 20th	Day	18% 7% 3 6% 6% 3 5% 5% 5% 6% 36%	2479
	21st to end	Day	15% 7% 3 5% 5% 4 6% 5% 6% 8% 38%	2725
June	1st to 10th	Day	10% 4 3 5% 5% 3 5% 4 7% 9% 44%	2520
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 5% 6% 10% 43%	2520
	21st to end	Day	11% 5% 3 5% 6% 3 5% 6% 6% 10% 41%	2520
July	1st to 10th	Day	8% 4 2 4 5% 3 4 5% 7% 10% 48%	2520
	11th to 20th	Day	7% 4 2 5% 5% 3 6% 6% 8% 9% 45%	2520
	21st to end	Day	7% 4 2 4 5% 3 5% 5% 6% 10% 47%	2743
August	1st to 10th	Day	7% 4 2 5% 6% 3 5% 6% 8% 11% 43%	2475
	11th to 20th	Day	11% 4 2 5% 6% 3 6% 5% 6% 8% 44%	2176
	21st to end	Day	10% 4 3 5% 4 3 4 5% 7% 7% 47%	2376
September	1st to 10th	Day	13% 5% 2 5% 5% 3 5% 4 6% 7% 44%	2160
	11th to 20th	Day	14% 5% 2 4 4 2 4 4 4 8% 50%	2102
	21st to end	Day	13% 6% 3 6% 5% 3 4 4 5% 7% 44%	1980
October	1st to 10th	Day	14% 6% 3 6% 4 3 3 4 5% 6% 46%	1836
	11th to 20th	Day	19% 9% 4 7% 6% 2 4 4 5% 8% 34%	1800
	21st to end	Day	18% 10% 3 5% 5% 3 3 3 4 6% 38%	1813
November	1st to 10th	Day	12% 8% 3 5% 5% 3 4 4 4 7% 45%	1672
	11th to 20th	Day	14% 11% 4 8% 6% 4 5% 4 5% 6% 33%	1696
	21st to end	Day	15% 11% 4 8% 6% 3 4 3 3 6% 36%	1520
December	1st to 10th	Day	14% 13% 5% 7% 7% 4 6% 3 4 7% 29%	1520
	11th to 20th	Day	13% 13% 6% 10% 6% 3 5% 5% 5% 7% 28%	1918
	21st to end	Day	21% 20% 9% 11% 6% 3 4 4 4 4 15%	2783
January	1st to 10th	Night	12% 11% 6% 8% 7% 2 4 4 5% 6% 35%	2648
	11th to 20th	Night	15% 13% 6% 10% 7% 3 5% 4 5% 6% 26%	2603
	21st to end	Night	13% 13% 7% 11% 7% 4 5% 4 5% 6% 26%	2694
February	1st to 10th	Night	10% 15% 5% 8% 6% 4 5% 4 4 6% 33%	2340
	11th to 20th	Night	12% 9% 4 7% 6% 4 4 5% 4 6% 38%	2160
	21st to end	Night	17% 11% 4 8% 4 3 5% 3 4 6% 35%	1776
March	1st to 10th	Night	17% 8% 4 6% 5% 3 4 5% 6% 6% 36%	2160
	11th to 20th	Night	12% 8% 3 5% 5% 4 5% 5% 5% 8% 41%	2066
	21st to end	Night	20% 10% 3 6% 5% 4 5% 4 4 7% 32%	2010
April	1st to 10th	Night	17% 9% 3 6% 4 3 5% 5% 5% 6% 36%	1800
	11th to 20th	Night	19% 7% 3 6% 5% 2 4 4 5% 6% 37%	1775
	21st to end	Night	17% 8% 3 5% 5% 3 4 4 6% 8% 38%	1739
May	1st to 10th	Night	17% 7% 3 7% 5% 3 4 6% 6% 7% 35%	1540
	11th to 20th	Night	17% 7% 3 5% 6% 2 5% 5% 5% 8% 37%	1416
	21st to end	Night	12% 6% 2 4 5% 3 4 5% 5% 10% 42%	1551
June	1st to 10th	Night	9% 5% 2 5% 5% 3 5% 5% 6% 10% 46%	1440
	11th to 20th	Night	13% 6% 2 4 4 2 4 4 6% 9% 47%	1440
	21st to end	Night	9% 4 3 5% 5% 3 3 4 5% 8% 52%	1440
July	1st to 10th	Night	7% 3 1 4 3 3 4 5% 6% 8% 56%	1440
	11th to 20th	Night	7% 3 3 4 5% 3 4 4 5% 8% 55%	1440
	21st to end	Night	6% 3 1 3 5% 3 5% 5% 7% 10% 53%	1575
August	1st to 10th	Night	5% 4 2 5% 6% 3 4 6% 8% 7% 49%	1461
	11th to 20th	Night	9% 5% 2 4 5% 2 4 4 5% 8% 52%	1724
	21st to end	Night	9% 4 2 4 4 2 5% 4 4 7% 54%	1980
September	1st to 10th	Night	10% 4 3 4 4 2 3 4 6% 7% 53%	1800
	11th to 20th	Night	12% 4 1 4 4 3 3 4 4 5% 54%	1840
	21st to end	Night	11% 5% 2 5% 5% 3 4 4 5% 7% 49%	1980
October	1st to 10th	Night	12% 7% 2 5% 4 3 3 3 5% 7% 50%	2119
	11th to 20th	Night	17% 8% 2 6% 5% 2 4 4 4 6% 42%	2160
	21st to end	Night	18% 9% 3 6% 6% 3 4 5% 6% 7% 36%	2542
November	1st to 10th	Night	12% 7% 3 5% 5% 2 4 4 4 6% 47%	2406
	11th to 20th	Night	14% 10% 4 7% 6% 4 6% 4 4 5% 34%	2479
	21st to end	Night	17% 10% 4 5% 5% 2 4 4 5% 6% 38%	2660
December	1st to 10th	Night	15% 12% 5% 8% 7% 3 5% 4 5% 6% 31%	2660
	11th to 20th	Night	15% 13% 6% 9% 6% 3 5% 5% 4 5% 29%	3279
	21st to end	Night	22% 17% 5% 9% 6% 4 4 5% 4 5% 20%	4884

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	53% 5% 14% 17% 10%	1518
	11th to 20th	Day	63% 5% 11% 14% 7%	1480
	21st to end	Day	61% 5% 12% 13% 8%	1660
February	1st to 10th	Day	55% 4 13% 19% 9% 1	1620
	11th to 20th	Day	51% 4 12% 21% 10% 2	1695
	21st to end	Day	56% 4 9% 18% 11% 2	1480
March	1st to 10th	Day	50% 6% 13% 21% 9% 1	1800
	11th to 20th	Day	45% 5% 13% 22% 13% 1	1909
	21st to end	Day	55% 5% 12% 21% 7% 1	2344
April	1st to 10th	Day	53% 5% 11% 20% 10% 1	2160
	11th to 20th	Day	51% 5% 10% 20% 12% 2	2134
	21st to end	Day	52% 6% 10% 19% 11% 2	2219
May	1st to 10th	Day	50% 6% 14% 22% 8% 1	2417
	11th to 20th	Day	49% 6% 12% 21% 12%	2483
	21st to end	Day	44% 8% 12% 20% 14% 2	2725
June	1st to 10th	Day	36% 7% 13% 26% 16% 1	2520
	11th to 20th	Day	38% 6% 12% 24% 18% 2	2520
	21st to end	Day	38% 8% 15% 23% 14% 1	2520
July	1st to 10th	Day	32% 7% 14% 30% 15% 2	2451
	11th to 20th	Day	33% 9% 14% 24% 17% 2	2445
	21st to end	Day	31% 7% 17% 27% 16% 3	2591
August	1st to 10th	Day	33% 9% 16% 29% 12% 1	2460
	11th to 20th	Day	38% 6% 14% 27% 13% 1	2176
	21st to end	Day	34% 7% 12% 27% 18% 2	2376
September	1st to 10th	Day	39% 6% 11% 25% 18% 2	2160
	11th to 20th	Day	33% 5% 13% 32% 16% 2	2102
	21st to end	Day	40% 5% 10% 30% 13% 1	1980
October	1st to 10th	Day	39% 6% 9% 29% 16% 1	1836
	11th to 20th	Day	50% 4 11% 23% 12% 1	1800
	21st to end	Day	49% 5% 10% 23% 13% 1	1813
November	1st to 10th	Day	40% 5% 15% 25% 14% 2	1672
	11th to 20th	Day	51% 5% 12% 21% 10% 1	1696
	21st to end	Day	51% 4 15% 22% 7% 1	1520
December	1st to 10th	Day	56% 4 15% 16% 8% 1	1520
	11th to 20th	Day	56% 3 15% 16% 7% 3	1915
	21st to end	Day	72% 6% 7% 9% 5%	2783
January	1st to 10th	Night	51% 4 11% 21% 12% 1	2648
	11th to 20th	Night	60% 5% 12% 15% 8%	2603
	21st to end	Night	59% 5% 11% 15% 9% 1	2694
February	1st to 10th	Night	54% 4 10% 19% 11% 2	2340
	11th to 20th	Night	48% 5% 11% 21% 14% 1	2161
	21st to end	Night	52% 4 11% 20% 11% 3	1776
March	1st to 10th	Night	49% 5% 13% 21% 9% 3	2160
	11th to 20th	Night	41% 5% 13% 22% 17% 2	2066
	21st to end	Night	55% 4 9% 20% 11% 2	2010
April	1st to 10th	Night	48% 6% 10% 20% 15% 1	1800
	11th to 20th	Night	48% 4 7% 20% 17% 3	1775
	21st to end	Night	45% 6% 11% 24% 12% 2	1739
May	1st to 10th	Night	47% 7% 12% 21% 13% 1	1540
	11th to 20th	Night	45% 6% 12% 22% 13% 1	1417
	21st to end	Night	38% 7% 13% 24% 15% 2	1552
June	1st to 10th	Night	33% 7% 12% 28% 20% 1	1440
	11th to 20th	Night	34% 6% 10% 24% 24% 2	1440
	21st to end	Night	32% 6% 16% 24% 18% 3	1440
July	1st to 10th	Night	25% 7% 13% 32% 19% 4	1400
	11th to 20th	Night	28% 7% 11% 30% 21% 3	1392
	21st to end	Night	26% 8% 16% 29% 17% 5%	1487
August	1st to 10th	Night	31% 8% 15% 28% 16% 3	1452
	11th to 20th	Night	31% 6% 14% 31% 18% 1	1724
	21st to end	Night	31% 6% 11% 27% 21% 3	1980
September	1st to 10th	Night	30% 7% 11% 27% 23% 2	1800
	11th to 20th	Night	32% 6% 10% 32% 18% 2	1840
	21st to end	Night	35% 5% 10% 29% 19% 1	1980
October	1st to 10th	Night	36% 5% 9% 29% 19% 2	2119
	11th to 20th	Night	43% 4 11% 24% 17% 1	2160
	21st to end	Night	48% 5% 11% 23% 12% 1	2542
November	1st to 10th	Night	39% 4 11% 26% 17% 2	2406
	11th to 20th	Night	51% 5% 12% 19% 12% 1	2479
	21st to end	Night	48% 4 14% 23% 10% 1	2660
December	1st to 10th	Night	54% 5% 12% 20% 8% 1	2660
	11th to 20th	Night	58% 4 12% 18% 8% 1	3281
	21st to end	Night	67% 5% 8% 15% 5%	4884

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	19% 13% 33% 26% 9% 1	270
	11th to 20th	Day	18% 16% 34% 23% 7% 1	255
	21st to end	Day	21% 11% 35% 27% 6%	264
February	1st to 10th	Day	13% 16% 45% 20% 5%	240
	11th to 20th	Day	21% 21% 31% 21% 5%	240
	21st to end	Day	23% 16% 43% 15% 2	198
March	1st to 10th	Day	16% 18% 43% 19% 5%	240
	11th to 20th	Day	20% 16% 33% 20% 7% 3	240
	21st to end	Day	28% 12% 32% 20% 7% 2	430
April	1st to 10th	Day	24% 13% 35% 23% 5%	420
	11th to 20th	Day	24% 16% 26% 21% 10% 2	412
	21st to end	Day	25% 12% 28% 21% 11% 2	420
May	1st to 10th	Day	21% 11% 31% 26% 8% 2	500
	11th to 20th	Day	24% 10% 28% 25% 12% 2	625
	21st to end	Day	18% 9% 27% 24% 18% 5%	679
June	1st to 10th	Day	9% 7% 29% 32% 19% 5%	630
	11th to 20th	Day	14% 6% 30% 30% 14% 5%	630
	21st to end	Day	12% 7% 31% 29% 17% 5%	630
July	1st to 10th	Day	9% 4 17% 30% 28% 13%	621
	11th to 20th	Day	10% 4 26% 31% 20% 9%	618
	21st to end	Day	7% 2 26% 35% 23% 7%	684
August	1st to 10th	Day	8% 3 18% 34% 26% 11%	626
	11th to 20th	Day	12% 4 16% 27% 24% 15%	490
	21st to end	Day	11% 6% 20% 31% 23% 10%	495
September	1st to 10th	Day	16% 6% 23% 26% 20% 8%	450
	11th to 20th	Day	15% 3 20% 30% 22% 10%	450
	21st to end	Day	14% 12% 26% 23% 18% 6%	450
October	1st to 10th	Day	17% 11% 25% 25% 18% 5%	306
	11th to 20th	Day	23% 17% 34% 18% 7%	270
	21st to end	Day	28% 14% 32% 20% 5% 1	297
November	1st to 10th	Day	14% 17% 37% 23% 6% 3	270
	11th to 20th	Day	19% 18% 36% 18% 9%	270
	21st to end	Day	23% 11% 42% 19% 5%	270
December	1st to 10th	Day	18% 20% 38% 16% 7% 1	270
	11th to 20th	Day	19% 13% 37% 21% 9% 1	270
	21st to end	Day	23% 18% 40% 16% 2	297
January	1st to 10th	Night	17% 15% 37% 22% 8% 1	950
	11th to 20th	Night	21% 11% 38% 24% 5% 1	930
	21st to end	Night	19% 12% 37% 26% 5% 1	990
February	1st to 10th	Night	20% 10% 41% 24% 6%	900
	11th to 20th	Night	18% 14% 37% 26% 4	765
	21st to end	Night	24% 14% 38% 21% 4 1	592
March	1st to 10th	Night	21% 11% 35% 25% 7% 1	720
	11th to 20th	Night	17% 11% 35% 29% 8%	626
	21st to end	Night	23% 8% 32% 29% 7% 1	594
April	1st to 10th	Night	21% 12% 39% 24% 4	540
	11th to 20th	Night	25% 13% 26% 28% 7%	533
	21st to end	Night	21% 7% 34% 27% 9% 1	540
May	1st to 10th	Night	20% 9% 32% 30% 8% 1	540
	11th to 20th	Night	20% 6% 30% 33% 10% 1	531
	21st to end	Night	15% 4 26% 38% 16% 1	584
June	1st to 10th	Night	11% 3 26% 43% 16% 1	540
	11th to 20th	Night	16% 4 28% 38% 14% 1	540
	21st to end	Night	10% 3 27% 42% 18%	540
July	1st to 10th	Night	9% 2 14% 38% 34% 4	525
	11th to 20th	Night	7% 2 22% 43% 23% 2	522
	21st to end	Night	6% 1 19% 49% 22% 2	591
August	1st to 10th	Night	5% 2 16% 48% 26% 3	537
	11th to 20th	Night	10% 2 13% 41% 28% 5%	534
	21st to end	Night	11% 2 18% 42% 25% 3	594
September	1st to 10th	Night	11% 4 23% 34% 23% 5%	540
	11th to 20th	Night	13% 3 22% 35% 24% 3	580
	21st to end	Night	12% 8% 26% 32% 19% 2	720
October	1st to 10th	Night	16% 5% 28% 32% 17% 1	720
	11th to 20th	Night	19% 13% 32% 27% 8%	720
	21st to end	Night	22% 11% 31% 28% 7% 1	792
November	1st to 10th	Night	15% 11% 38% 25% 10% 1	740
	11th to 20th	Night	19% 14% 39% 21% 6%	769
	21st to end	Night	22% 12% 35% 23% 7%	950
December	1st to 10th	Night	21% 13% 38% 21% 6%	950
	11th to 20th	Night	24% 11% 35% 24% 5% 1	950
	21st to end	Night	29% 13% 34% 22% 3	1045

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