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 2026-06-16.

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	15% 12% 4 10% 5% 4 4 3 5% 7% 30%	137421
	Night	15% 14% 5% 11% 5% 4 4 3 5% 6% 28%	134554
Transparency	Day	52% 7% 11% 19% 10% 1	141052
	Night	56% 6% 10% 17% 10% 1	138994
Seeing	Day	23% 16% 29% 21% 9% 3	16580
	Night	23% 15% 26% 24% 10% 1	26323

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% 8% 28% 5% 3 2 2 3 3 9%	5258
	11th to 20th	Day	9% 23% 9% 22% 9% 7% 4 2 3 3 10%	5280
	21st to end	Day	16% 19% 8% 17% 8% 6% 4 3 3 3 12%	5780
February	1st to 10th	Day	15% 20% 6% 16% 8% 5% 3 3 3 3 19%	1890
	11th to 20th	Day	15% 17% 8% 15% 8% 5% 3 3 4 4 17%	1855
	21st to end	Day	16% 19% 4 13% 4 4 5% 3 5% 5% 21%	1730
March	1st to 10th	Day	15% 13% 8% 12% 4 3 3 3 5% 6% 27%	4971
	11th to 20th	Day	12% 14% 6% 10% 5% 4 4 3 4 6% 33%	5090
	21st to end	Day	18% 15% 6% 11% 5% 4 4 2 4 5% 27%	5586
April	1st to 10th	Day	16% 15% 3 7% 5% 4 4 4 5% 7% 31%	2383
	11th to 20th	Day	18% 12% 3 6% 4 4 5% 3 4 6% 33%	2641
	21st to end	Day	18% 12% 4 7% 4 3 3 3 4 5% 35%	2730
May	1st to 10th	Day	19% 9% 3 9% 5% 5% 4 4 5% 6% 31%	7616
	11th to 20th	Day	16% 9% 3 8% 4 4 5% 4 6% 8% 34%	7626
	21st to end	Day	15% 8% 3 7% 5% 4 5% 4 5% 6% 39%	8826
June	1st to 10th	Day	15% 7% 2 5% 4 4 5% 5% 6% 9% 39%	2940
	11th to 20th	Day	13% 6% 3 6% 5% 4 5% 4 6% 9% 38%	2870
	21st to end	Day	12% 5% 2 5% 5% 4 5% 4 7% 10% 41%	2800
July	1st to 10th	Day	8% 6% 2 7% 4 4 4 4 6% 10% 44%	6159
	11th to 20th	Day	10% 6% 3 6% 4 5% 5% 4 7% 10% 40%	5900
	21st to end	Day	11% 5% 2 6% 5% 5% 4 4 5% 8% 45%	6424
August	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 4 7% 9% 38%	4234
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 5% 7% 9% 34%	4174
	21st to end	Day	11% 5% 2 7% 4 4 5% 5% 6% 9% 41%	4562
September	1st to 10th	Day	15% 6% 2 6% 4 4 5% 3 5% 8% 42%	2341
	11th to 20th	Day	11% 6% 2 5% 4 4 4 4 6% 9% 45%	2200
	21st to end	Day	18% 9% 2 7% 5% 4 5% 3 5% 6% 36%	2200
October	1st to 10th	Day	15% 6% 2 8% 5% 4 4 4 6% 7% 39%	2040
	11th to 20th	Day	21% 10% 3 8% 5% 4 4 3 6% 7% 31%	2000
	21st to end	Day	23% 12% 4 8% 5% 5% 4 3 5% 6% 25%	2200
November	1st to 10th	Day	15% 13% 4 8% 5% 5% 4 3 5% 6% 32%	1863
	11th to 20th	Day	16% 22% 3 9% 6% 4 5% 3 4 5% 22%	1774
	21st to end	Day	18% 25% 7% 8% 6% 4 4 3 5% 6% 14%	1680
December	1st to 10th	Day	16% 24% 11% 14% 6% 5% 4 3 4 3 11%	2680
	11th to 20th	Day	20% 24% 8% 14% 7% 4 3 3 4 4 10%	3070
	21st to end	Day	21% 25% 6% 17% 6% 4 3 3 3 3 8%	4048
January	1st to 10th	Night	13% 22% 11% 26% 5% 3 3 2 3 3 9%	7635
	11th to 20th	Night	8% 20% 11% 22% 9% 5% 3 3 4 4 11%	7680
	21st to end	Night	16% 19% 7% 14% 7% 5% 4 3 3 4 17%	8401
February	1st to 10th	Night	17% 18% 6% 13% 8% 5% 4 3 4 4 18%	2730
	11th to 20th	Night	16% 17% 6% 15% 7% 5% 4 3 3 4 19%	2647
	21st to end	Night	17% 15% 5% 14% 5% 5% 5% 4 4 5% 21%	2076
March	1st to 10th	Night	17% 16% 4 8% 5% 4 3 3 4 5% 30%	5102
	11th to 20th	Night	11% 12% 5% 9% 4 4 4 3 4 7% 37%	5090
	21st to end	Night	15% 15% 6% 10% 5% 4 4 3 4 4 30%	5588
April	1st to 10th	Night	17% 16% 4 9% 5% 4 3 3 5% 5% 29%	2237
	11th to 20th	Night	16% 13% 3 6% 5% 4 5% 5% 6% 6% 33%	1946
	21st to end	Night	14% 10% 3 7% 5% 5% 4 4 5% 7% 35%	1890
May	1st to 10th	Night	21% 10% 3 8% 5% 4 5% 4 6% 6% 29%	5237
	11th to 20th	Night	14% 9% 3 7% 4 4 4 4 5% 8% 37%	5234
	21st to end	Night	20% 8% 2 5% 3 4 4 4 6% 8% 37%	5310
June	1st to 10th	Night	10% 7% 3 8% 5% 5% 4 5% 6% 7% 42%	1680
	11th to 20th	Night	9% 5% 3 8% 5% 5% 5% 4 6% 8% 42%	1640
	21st to end	Night	10% 5% 2 7% 5% 5% 4 3 7% 10% 42%	1600
July	1st to 10th	Night	8% 6% 2 6% 4 5% 5% 4 6% 10% 44%	3780
	11th to 20th	Night	9% 6% 2 6% 4 5% 5% 4 7% 8% 43%	4057
	21st to end	Night	8% 5% 2 7% 4 4 4 4 5% 7% 49%	4427
August	1st to 10th	Night	10% 7% 3 7% 4 5% 5% 4 6% 8% 41%	2915
	11th to 20th	Night	14% 6% 4 7% 6% 4 4 3 5% 6% 40%	2875
	21st to end	Night	8% 6% 3 7% 5% 5% 5% 4 6% 8% 42%	3289
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 6% 8% 45%	2055
	11th to 20th	Night	11% 5% 2 5% 4 4 5% 4 5% 6% 51%	2200
	21st to end	Night	17% 7% 3 7% 6% 5% 5% 3 5% 7% 36%	2200
October	1st to 10th	Night	15% 7% 2 6% 5% 4 4 3 6% 6% 42%	2360
	11th to 20th	Night	20% 9% 3 8% 5% 5% 4 3 5% 6% 32%	2400
	21st to end	Night	26% 10% 3 8% 5% 4 4 3 5% 5% 27%	2640
November	1st to 10th	Night	15% 13% 4 7% 5% 4 4 3 5% 6% 33%	2651
	11th to 20th	Night	16% 18% 5% 10% 6% 5% 4 3 5% 5% 22%	2843
	21st to end	Night	20% 22% 6% 10% 5% 4 4 2 4 5% 18%	2940
December	1st to 10th	Night	14% 23% 12% 12% 5% 4 4 3 4 5% 13%	4720
	11th to 20th	Night	18% 25% 8% 13% 6% 5% 4 2 3 4 14%	5345
	21st to end	Night	19% 23% 6% 14% 6% 5% 4 3 4 5% 11%	7134

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	82% 5% 7% 4 2	5259
	11th to 20th	Day	81% 4 7% 5% 3	5280
	21st to end	Day	77% 4 6% 9% 4	5780
February	1st to 10th	Day	71% 5% 8% 11% 4	1890
	11th to 20th	Day	71% 5% 8% 12% 4	1864
	21st to end	Day	62% 7% 11% 13% 5% 2	1730
March	1st to 10th	Day	56% 6% 12% 20% 5%	4971
	11th to 20th	Day	51% 7% 15% 20% 6% 1	5090
	21st to end	Day	58% 6% 7% 18% 10% 1	5586
April	1st to 10th	Day	52% 5% 13% 17% 12% 1	2383
	11th to 20th	Day	51% 6% 11% 18% 12% 2	2641
	21st to end	Day	50% 6% 11% 21% 10% 3	2730
May	1st to 10th	Day	51% 7% 9% 21% 9% 3	7651
	11th to 20th	Day	46% 8% 11% 22% 11% 1	7630
	21st to end	Day	43% 7% 11% 19% 17% 3	8841
June	1st to 10th	Day	40% 8% 12% 25% 14% 1	2940
	11th to 20th	Day	40% 8% 15% 21% 14% 1	2870
	21st to end	Day	37% 8% 13% 25% 15% 2	2800
July	1st to 10th	Day	34% 7% 13% 27% 18% 2	6093
	11th to 20th	Day	37% 7% 14% 25% 16% 1	5831
	21st to end	Day	35% 7% 13% 24% 19% 1	6240
August	1st to 10th	Day	40% 8% 15% 24% 13%	4221
	11th to 20th	Day	41% 9% 13% 29% 7% 1	4213
	21st to end	Day	36% 8% 15% 28% 13% 1	4562
September	1st to 10th	Day	39% 7% 15% 23% 14% 2	2341
	11th to 20th	Day	35% 8% 13% 27% 16% 1	2200
	21st to end	Day	48% 7% 11% 21% 12% 1	2200
October	1st to 10th	Day	34% 7% 15% 25% 19% 1	3326
	11th to 20th	Day	47% 6% 12% 20% 15% 1	3240
	21st to end	Day	45% 6% 13% 25% 10% 1	3538
November	1st to 10th	Day	52% 7% 11% 18% 11% 1	1863
	11th to 20th	Day	63% 7% 10% 12% 7% 2	1774
	21st to end	Day	70% 6% 9% 11% 4	1680
December	1st to 10th	Day	79% 7% 8% 5% 1	2680
	11th to 20th	Day	78% 6% 7% 8% 2	3066
	21st to end	Day	81% 6% 6% 6% 1	4048
January	1st to 10th	Night	83% 4 4 6% 2	7636
	11th to 20th	Night	78% 6% 7% 6% 2	7680
	21st to end	Night	71% 4 8% 12% 5%	8401
February	1st to 10th	Night	69% 6% 8% 12% 4	2730
	11th to 20th	Night	69% 5% 9% 13% 4	2649
	21st to end	Night	65% 7% 8% 13% 7% 1	2076
March	1st to 10th	Night	56% 6% 13% 16% 9% 1	5102
	11th to 20th	Night	47% 6% 13% 24% 10% 1	5090
	21st to end	Night	55% 6% 11% 15% 12% 1	5588
April	1st to 10th	Night	56% 6% 10% 16% 10% 2	2237
	11th to 20th	Night	49% 7% 11% 19% 11% 2	1946
	21st to end	Night	47% 7% 11% 21% 11% 3	1890
May	1st to 10th	Night	54% 7% 9% 15% 11% 5%	5264
	11th to 20th	Night	45% 8% 11% 24% 11% 1	5235
	21st to end	Night	44% 6% 12% 21% 15% 1	5317
June	1st to 10th	Night	39% 7% 11% 24% 16% 4	1680
	11th to 20th	Night	39% 8% 13% 20% 18% 2	1640
	21st to end	Night	36% 9% 13% 24% 17% 1	1600
July	1st to 10th	Night	34% 7% 13% 23% 19% 3	3739
	11th to 20th	Night	35% 8% 12% 25% 16% 3	4006
	21st to end	Night	32% 7% 12% 21% 25% 2	4297
August	1st to 10th	Night	40% 8% 11% 26% 14% 1	2904
	11th to 20th	Night	43% 7% 11% 27% 11% 1	2902
	21st to end	Night	36% 8% 13% 27% 14% 2	3289
September	1st to 10th	Night	36% 7% 14% 26% 15% 3	2055
	11th to 20th	Night	33% 7% 13% 26% 20% 1	2200
	21st to end	Night	47% 7% 12% 19% 15% 1	2200
October	1st to 10th	Night	35% 7% 9% 26% 23% 1	3854
	11th to 20th	Night	49% 6% 9% 18% 16% 1	3899
	21st to end	Night	46% 5% 14% 21% 14% 1	4252
November	1st to 10th	Night	51% 7% 11% 19% 10% 2	2651
	11th to 20th	Night	64% 6% 10% 12% 5% 2	2843
	21st to end	Night	70% 6% 9% 12% 4	2940
December	1st to 10th	Night	75% 6% 11% 6% 2	4720
	11th to 20th	Night	75% 6% 9% 9% 1	5348
	21st to end	Night	75% 8% 8% 8% 1	7134

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	32% 30% 27% 8% 3	330
	11th to 20th	Day	37% 30% 24% 7% 2 1	330
	21st to end	Day	30% 31% 29% 8% 1	363
February	1st to 10th	Day	31% 24% 34% 10% 1	330
	11th to 20th	Day	35% 27% 28% 9% 1	330
	21st to end	Day	34% 30% 30% 7%	273
March	1st to 10th	Day	28% 22% 35% 11% 3	503
	11th to 20th	Day	31% 20% 32% 14% 2 1	540
	21st to end	Day	35% 19% 27% 14% 3	594
April	1st to 10th	Day	27% 21% 31% 15% 5%	540
	11th to 20th	Day	32% 17% 28% 16% 5% 2	532
	21st to end	Day	25% 18% 34% 18% 4 1	540
May	1st to 10th	Day	26% 18% 31% 18% 5% 2	543
	11th to 20th	Day	20% 11% 33% 26% 8% 2	567
	21st to end	Day	18% 10% 30% 26% 12% 4	617
June	1st to 10th	Day	18% 11% 34% 26% 10% 2	570
	11th to 20th	Day	17% 11% 29% 29% 11% 2	550
	21st to end	Day	14% 8% 32% 31% 13% 2	530
July	1st to 10th	Day	10% 9% 25% 30% 19% 7%	525
	11th to 20th	Day	15% 7% 29% 27% 16% 6%	524
	21st to end	Day	10% 5% 33% 30% 17% 6%	576
August	1st to 10th	Day	11% 8% 24% 32% 19% 6%	526
	11th to 20th	Day	13% 7% 24% 30% 18% 7%	519
	21st to end	Day	13% 8% 24% 31% 18% 6%	583
September	1st to 10th	Day	17% 10% 22% 26% 20% 6%	530
	11th to 20th	Day	11% 5% 21% 32% 22% 11%	530
	21st to end	Day	19% 12% 29% 23% 11% 5%	530
October	1st to 10th	Day	16% 12% 25% 26% 17% 3	530
	11th to 20th	Day	25% 19% 31% 17% 6% 2	530
	21st to end	Day	35% 17% 28% 17% 2	583
November	1st to 10th	Day	26% 25% 26% 15% 7% 1	341
	11th to 20th	Day	38% 23% 25% 10% 4 1	269
	21st to end	Day	35% 25% 30% 10%	220
December	1st to 10th	Day	33% 29% 27% 9% 2 1	220
	11th to 20th	Day	29% 27% 31% 12% 1	220
	21st to end	Day	35% 26% 28% 9% 2	242
January	1st to 10th	Night	30% 27% 29% 11% 3	840
	11th to 20th	Night	34% 24% 26% 14% 2	840
	21st to end	Night	29% 23% 30% 15% 3	924
February	1st to 10th	Night	29% 21% 28% 19% 3	840
	11th to 20th	Night	28% 21% 32% 17% 2	823
	21st to end	Night	31% 21% 32% 16% 1	692
March	1st to 10th	Night	26% 18% 33% 20% 3	840
	11th to 20th	Night	25% 20% 30% 19% 5% 1	840
	21st to end	Night	24% 16% 31% 22% 6%	924
April	1st to 10th	Night	27% 16% 28% 24% 5%	840
	11th to 20th	Night	24% 13% 32% 23% 7% 1	702
	21st to end	Night	18% 11% 33% 30% 7% 1	630
May	1st to 10th	Night	22% 12% 24% 31% 11%	630
	11th to 20th	Night	17% 9% 28% 35% 10% 1	621
	21st to end	Night	15% 6% 23% 34% 19% 2	528
June	1st to 10th	Night	13% 6% 28% 37% 15% 1	420
	11th to 20th	Night	13% 7% 24% 38% 17%	410
	21st to end	Night	11% 8% 24% 39% 19%	400
July	1st to 10th	Night	7% 5% 18% 41% 24% 5%	465
	11th to 20th	Night	9% 3 20% 38% 25% 5%	582
	21st to end	Night	11% 4 20% 38% 25% 2	657
August	1st to 10th	Night	9% 4 19% 38% 25% 4	597
	11th to 20th	Night	13% 3 14% 36% 30% 4	594
	21st to end	Night	13% 6% 20% 31% 27% 3	700
September	1st to 10th	Night	15% 7% 18% 31% 24% 5%	800
	11th to 20th	Night	12% 4 15% 34% 29% 5%	800
	21st to end	Night	20% 9% 23% 27% 17% 4	800
October	1st to 10th	Night	19% 10% 23% 27% 19% 3	800
	11th to 20th	Night	25% 16% 27% 24% 8% 1	800
	21st to end	Night	31% 18% 27% 20% 3	880
November	1st to 10th	Night	26% 16% 28% 22% 8% 1	820
	11th to 20th	Night	31% 21% 28% 15% 4 1	840
	21st to end	Night	36% 22% 25% 13% 4	840
December	1st to 10th	Night	35% 22% 28% 11% 4	840
	11th to 20th	Night	32% 27% 27% 12% 2	840
	21st to end	Night	33% 21% 31% 13% 1	924

Page generated at 2026-06-13 02:31:41. Version ac07

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