Milwaukee
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Milwaukee clear sky chart from 2005-11-06 to 2025-09-04.

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	12% 8% 3 7% 5% 4 5% 4 6% 8% 38%	126139
	Night	13% 10% 3 7% 4 4 4 3 5% 7% 38%	122836
Transparency	Day	42% 6% 12% 25% 13% 1	129639
	Night	45% 5% 11% 23% 14% 2	127410
Seeing	Day	15% 6% 26% 31% 17% 4	17054
	Night	18% 8% 27% 29% 16% 3	26846

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	9% 10% 7% 12% 6% 5% 6% 4 6% 8% 27%	3617
	11th to 20th	Day	9% 9% 4 10% 6% 5% 6% 5% 8% 7% 30%	3620
	21st to end	Day	12% 16% 7% 8% 4 3 4 3 5% 7% 31%	3982
February	1st to 10th	Day	11% 14% 5% 10% 5% 4 5% 4 7% 8% 27%	1813
	11th to 20th	Day	12% 11% 3 8% 6% 4 5% 4 6% 6% 35%	1948
	21st to end	Day	11% 13% 5% 10% 6% 5% 5% 4 6% 6% 30%	1650
March	1st to 10th	Day	13% 8% 3 7% 4 4 4 3 5% 6% 43%	4480
	11th to 20th	Day	10% 6% 3 7% 6% 5% 5% 4 6% 7% 42%	4666
	21st to end	Day	19% 11% 4 10% 6% 5% 4 3 5% 5% 26%	5967
April	1st to 10th	Day	17% 11% 3 7% 5% 4 4 5% 6% 6% 30%	2400
	11th to 20th	Day	15% 8% 2 7% 6% 5% 5% 4 6% 7% 35%	2374
	21st to end	Day	16% 9% 3 7% 5% 4 5% 4 5% 7% 34%	2546
May	1st to 10th	Day	15% 8% 3 7% 5% 4 5% 4 6% 6% 38%	5862
	11th to 20th	Day	13% 7% 3 6% 4 4 7% 6% 6% 7% 36%	6269
	21st to end	Day	15% 6% 2 5% 4 4 4 4 6% 9% 41%	6935
June	1st to 10th	Day	9% 6% 2 6% 4 5% 5% 4 7% 8% 44%	2800
	11th to 20th	Day	11% 6% 2 6% 5% 4 4 4 7% 8% 44%	2800
	21st to end	Day	8% 6% 2 7% 5% 4 5% 4 7% 8% 42%	2800
July	1st to 10th	Day	10% 7% 2 7% 5% 4 5% 5% 7% 10% 40%	6360
	11th to 20th	Day	6% 4 2 6% 4 5% 5% 4 8% 10% 46%	6360
	21st to end	Day	7% 6% 2 6% 5% 5% 5% 4 7% 9% 45%	6924
August	1st to 10th	Day	10% 5% 2 5% 4 5% 5% 4 7% 9% 43%	4512
	11th to 20th	Day	10% 4 2 6% 4 4 5% 3 6% 9% 47%	3955
	21st to end	Day	8% 5% 2 6% 5% 4 5% 3 6% 9% 46%	4312
September	1st to 10th	Day	10% 6% 2 6% 3 5% 4 4 6% 8% 46%	2316
	11th to 20th	Day	11% 5% 2 5% 3 3 4 4 5% 9% 49%	2157
	21st to end	Day	12% 6% 2 7% 4 4 5% 4 6% 9% 41%	2090
October	1st to 10th	Day	13% 5% 3 7% 3 4 3 3 6% 7% 45%	2038
	11th to 20th	Day	17% 9% 3 8% 6% 5% 5% 4 6% 7% 32%	1858
	21st to end	Day	16% 9% 3 7% 4 5% 5% 4 5% 6% 36%	1881
November	1st to 10th	Day	12% 8% 2 7% 5% 4 5% 3 5% 7% 41%	1762
	11th to 20th	Day	12% 11% 4 10% 7% 5% 6% 4 7% 7% 29%	1800
	21st to end	Day	17% 11% 3 7% 5% 4 4 2 4 6% 36%	1685
December	1st to 10th	Day	10% 9% 4 8% 6% 5% 5% 4 6% 9% 35%	2610
	11th to 20th	Day	12% 14% 4 9% 5% 5% 6% 5% 8% 7% 22%	3008
	21st to end	Day	22% 20% 7% 11% 6% 4 4 3 4 4 15%	3982
January	1st to 10th	Night	11% 12% 6% 12% 5% 4 4 4 4 6% 32%	6348
	11th to 20th	Night	12% 13% 5% 12% 7% 5% 6% 5% 6% 6% 23%	6360
	21st to end	Night	13% 15% 5% 9% 4 4 3 3 5% 7% 31%	6996
February	1st to 10th	Night	12% 15% 4 8% 6% 5% 4 3 6% 6% 31%	2580
	11th to 20th	Night	12% 11% 3 7% 4 4 5% 4 5% 6% 39%	2338
	21st to end	Night	18% 12% 3 7% 3 3 4 3 5% 6% 35%	1980
March	1st to 10th	Night	16% 8% 2 6% 4 4 4 3 4 5% 42%	5373
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 6% 9% 46%	5335
	21st to end	Night	18% 12% 5% 10% 5% 5% 4 3 4 4 29%	4962
April	1st to 10th	Night	16% 9% 3 6% 4 4 5% 3 6% 8% 36%	2000
	11th to 20th	Night	19% 9% 3 7% 4 4 4 3 5% 5% 38%	1975
	21st to end	Night	17% 8% 3 5% 3 4 5% 3 5% 7% 39%	1852
May	1st to 10th	Night	16% 8% 3 7% 4 4 4 3 5% 7% 37%	4033
	11th to 20th	Night	12% 8% 5% 7% 4 4 4 4 6% 7% 39%	3640
	21st to end	Night	17% 7% 3 6% 4 4 3 3 4 6% 42%	3942
June	1st to 10th	Night	10% 4 2 6% 5% 4 5% 4 7% 8% 46%	1600
	11th to 20th	Night	11% 7% 2 5% 4 4 4 3 6% 9% 43%	1600
	21st to end	Night	9% 8% 3 6% 4 5% 4 3 5% 8% 45%	1600
July	1st to 10th	Night	10% 6% 2 7% 4 5% 5% 4 6% 8% 43%	3618
	11th to 20th	Night	6% 5% 2 5% 4 4 4 4 6% 8% 52%	3617
	21st to end	Night	7% 4 2 6% 4 5% 5% 4 6% 9% 49%	3947
August	1st to 10th	Night	9% 4 2 4 3 4 4 3 6% 9% 49%	2645
	11th to 20th	Night	10% 5% 2 6% 4 3 4 3 5% 8% 48%	3090
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 6% 9% 50%	3586
September	1st to 10th	Night	8% 5% 2 6% 4 4 4 3 5% 7% 52%	1930
	11th to 20th	Night	10% 5% 1 4 3 3 4 4 5% 7% 53%	2004
	21st to end	Night	14% 6% 3 7% 4 3 4 3 4 7% 46%	2090
October	1st to 10th	Night	13% 5% 2 5% 4 4 4 3 6% 7% 47%	2137
	11th to 20th	Night	17% 8% 3 6% 4 4 3 3 5% 6% 42%	2320
	21st to end	Night	19% 9% 2 6% 5% 4 4 4 6% 7% 34%	2717
November	1st to 10th	Night	12% 8% 2 6% 4 4 4 3 4 7% 45%	2536
	11th to 20th	Night	14% 9% 3 9% 6% 5% 5% 3 5% 7% 35%	2600
	21st to end	Night	17% 10% 3 7% 5% 4 4 4 6% 6% 35%	2710
December	1st to 10th	Night	11% 10% 3 7% 4 4 4 4 5% 6% 41%	4580
	11th to 20th	Night	16% 17% 5% 9% 5% 4 4 3 5% 5% 27%	5199
	21st to end	Night	20% 19% 5% 10% 5% 4 4 3 5% 5% 18%	6996

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	54% 6% 13% 19% 7%	3618
	11th to 20th	Day	50% 6% 12% 16% 16% 1	3620
	21st to end	Day	53% 4 9% 21% 13%	3982
February	1st to 10th	Day	54% 5% 12% 18% 9% 1	1813
	11th to 20th	Day	48% 4 11% 24% 10% 2	1958
	21st to end	Day	53% 5% 12% 18% 11% 2	1650
March	1st to 10th	Day	41% 4 12% 25% 12% 5%	4480
	11th to 20th	Day	41% 5% 15% 25% 13% 2	4666
	21st to end	Day	57% 6% 12% 15% 9% 1	5969
April	1st to 10th	Day	52% 6% 12% 19% 10% 1	2400
	11th to 20th	Day	47% 6% 10% 21% 12% 3	2374
	21st to end	Day	48% 6% 14% 19% 12% 2	2546
May	1st to 10th	Day	42% 7% 10% 24% 14% 2	5897
	11th to 20th	Day	41% 10% 10% 24% 13% 1	6273
	21st to end	Day	38% 6% 12% 27% 14% 3	6949
June	1st to 10th	Day	35% 7% 13% 26% 17% 3	2800
	11th to 20th	Day	36% 6% 14% 25% 17% 1	2800
	21st to end	Day	36% 7% 15% 25% 16% 2	2800
July	1st to 10th	Day	37% 8% 12% 31% 11% 1	6291
	11th to 20th	Day	29% 8% 16% 33% 13% 1	6285
	21st to end	Day	32% 9% 16% 24% 17% 2	6728
August	1st to 10th	Day	34% 8% 15% 30% 12% 1	4497
	11th to 20th	Day	32% 6% 15% 35% 11% 1	3994
	21st to end	Day	33% 7% 14% 25% 19% 2	4311
September	1st to 10th	Day	34% 7% 13% 29% 15% 2	2316
	11th to 20th	Day	32% 5% 13% 33% 16% 1	2157
	21st to end	Day	39% 5% 12% 31% 13% 1	2090
October	1st to 10th	Day	23% 4 6% 43% 22% 1	3389
	11th to 20th	Day	35% 8% 10% 27% 19%	3061
	21st to end	Day	41% 5% 10% 30% 13% 2	3081
November	1st to 10th	Day	44% 3 13% 26% 13% 2	1762
	11th to 20th	Day	53% 5% 14% 20% 8%	1800
	21st to end	Day	50% 4 14% 25% 6%	1685
December	1st to 10th	Day	47% 5% 21% 21% 6%	2610
	11th to 20th	Day	56% 8% 12% 15% 7% 1	3005
	21st to end	Day	72% 4 6% 13% 5%	3982
January	1st to 10th	Night	53% 5% 7% 22% 11%	6348
	11th to 20th	Night	60% 6% 9% 11% 15% 1	6360
	21st to end	Night	53% 5% 13% 18% 11%	6996
February	1st to 10th	Night	53% 4 11% 18% 12% 1	2580
	11th to 20th	Night	46% 6% 9% 24% 13% 1	2339
	21st to end	Night	49% 4 11% 21% 12% 2	1980
March	1st to 10th	Night	43% 4 13% 25% 12% 3	5373
	11th to 20th	Night	34% 5% 13% 29% 15% 3	5335
	21st to end	Night	58% 5% 9% 15% 12% 1	4962
April	1st to 10th	Night	46% 6% 9% 22% 17% 1	2000
	11th to 20th	Night	49% 3 7% 21% 17% 4	1975
	21st to end	Night	44% 4 13% 23% 15% 2	1852
May	1st to 10th	Night	45% 6% 11% 19% 17% 2	4060
	11th to 20th	Night	43% 7% 12% 21% 16% 2	3641
	21st to end	Night	43% 5% 9% 23% 14% 6%	3950
June	1st to 10th	Night	35% 7% 12% 27% 18% 2	1600
	11th to 20th	Night	38% 5% 10% 24% 20% 3	1600
	21st to end	Night	38% 6% 14% 24% 17% 3	1600
July	1st to 10th	Night	36% 6% 14% 29% 11% 3	3580
	11th to 20th	Night	28% 6% 14% 31% 19% 2	3572
	21st to end	Night	30% 6% 15% 24% 23% 2	3832
August	1st to 10th	Night	31% 6% 15% 27% 19% 2	2636
	11th to 20th	Night	32% 5% 13% 33% 15% 1	3117
	21st to end	Night	29% 6% 13% 28% 21% 3	3586
September	1st to 10th	Night	32% 5% 12% 27% 23% 2	1930
	11th to 20th	Night	30% 5% 9% 36% 18% 2	2004
	21st to end	Night	40% 4 8% 31% 15% 1	2090
October	1st to 10th	Night	26% 4 7% 39% 24% 1	3566
	11th to 20th	Night	36% 4 13% 25% 21% 1	3856
	21st to end	Night	43% 4 9% 26% 17% 1	4467
November	1st to 10th	Night	40% 4 10% 27% 17% 2	2536
	11th to 20th	Night	49% 5% 12% 22% 11% 2	2600
	21st to end	Night	49% 5% 14% 23% 8% 1	2710
December	1st to 10th	Night	43% 5% 17% 26% 6% 3	4580
	11th to 20th	Night	59% 5% 10% 14% 10% 1	5201
	21st to end	Night	68% 4 8% 14% 5%	6996

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% 11% 32% 29% 8% 1	300
	11th to 20th	Day	19% 9% 37% 24% 10% 1	300
	21st to end	Day	21% 6% 34% 31% 7% 1	330
February	1st to 10th	Day	14% 13% 40% 25% 7% 1	300
	11th to 20th	Day	15% 17% 35% 24% 8%	300
	21st to end	Day	18% 13% 43% 21% 4	249
March	1st to 10th	Day	16% 12% 42% 25% 4	300
	11th to 20th	Day	16% 13% 36% 24% 8% 1	334
	21st to end	Day	27% 9% 31% 25% 7% 2	550
April	1st to 10th	Day	22% 9% 37% 25% 7%	500
	11th to 20th	Day	17% 13% 34% 25% 9% 3	492
	21st to end	Day	22% 8% 28% 28% 13% 1	500
May	1st to 10th	Day	20% 5% 35% 31% 7% 2	503
	11th to 20th	Day	18% 5% 28% 32% 15% 3	701
	21st to end	Day	17% 2 25% 32% 19% 6%	789
June	1st to 10th	Day	9% 3 25% 40% 18% 4	730
	11th to 20th	Day	14% 3 20% 41% 19% 4	730
	21st to end	Day	12% 2 22% 41% 20% 4	730
July	1st to 10th	Day	8% 2 13% 37% 31% 8%	721
	11th to 20th	Day	9% 2 20% 37% 25% 8%	718
	21st to end	Day	5% 1 19% 42% 28% 5%	794
August	1st to 10th	Day	8% 2 13% 40% 28% 9%	701
	11th to 20th	Day	11% 3 14% 33% 28% 11%	519
	21st to end	Day	9% 3 16% 35% 28% 9%	583
September	1st to 10th	Day	12% 3 18% 34% 24% 9%	502
	11th to 20th	Day	12% 2 14% 32% 29% 12%	490
	21st to end	Day	16% 7% 23% 28% 19% 7%	490
October	1st to 10th	Day	18% 5% 24% 27% 21% 5%	438
	11th to 20th	Day	20% 11% 29% 26% 12% 2	300
	21st to end	Day	20% 9% 34% 28% 8% 1	330
November	1st to 10th	Day	14% 13% 31% 29% 12% 2	300
	11th to 20th	Day	16% 17% 34% 23% 9%	300
	21st to end	Day	26% 8% 35% 25% 7%	300
December	1st to 10th	Day	19% 11% 38% 23% 8% 1	300
	11th to 20th	Day	23% 12% 37% 18% 8% 1	300
	21st to end	Day	26% 14% 35% 20% 3 2	330
January	1st to 10th	Night	20% 13% 37% 24% 6%	1000
	11th to 20th	Night	22% 11% 36% 23% 6% 1	1000
	21st to end	Night	20% 10% 37% 26% 6%	1100
February	1st to 10th	Night	21% 11% 35% 26% 6% 1	980
	11th to 20th	Night	19% 13% 35% 27% 6%	783
	21st to end	Night	26% 10% 34% 25% 5%	660
March	1st to 10th	Night	20% 8% 33% 29% 10% 1	800
	11th to 20th	Night	14% 9% 35% 31% 9% 1	795
	21st to end	Night	22% 7% 25% 35% 10% 2	660
April	1st to 10th	Night	20% 8% 30% 31% 10% 1	600
	11th to 20th	Night	26% 5% 26% 27% 12% 3	593
	21st to end	Night	22% 4 22% 34% 16% 2	600
May	1st to 10th	Night	17% 5% 22% 39% 15% 2	600
	11th to 20th	Night	20% 3 22% 31% 21% 2	591
	21st to end	Night	15% 2 17% 35% 24% 7%	650
June	1st to 10th	Night	13% 1 16% 40% 26% 4	600
	11th to 20th	Night	15% 2 17% 37% 25% 4	600
	21st to end	Night	11% 3 16% 39% 29% 2	600
July	1st to 10th	Night	10% 1 8% 33% 39% 9%	585
	11th to 20th	Night	8% 2 13% 37% 31% 9%	582
	21st to end	Night	7% 1 14% 39% 35% 4	657
August	1st to 10th	Night	7% 1 11% 38% 36% 7%	597
	11th to 20th	Night	11% 2 11% 33% 33% 10%	594
	21st to end	Night	11% 2 13% 34% 34% 6%	660
September	1st to 10th	Night	10% 3 14% 34% 28% 10%	579
	11th to 20th	Night	12% 3 16% 30% 29% 10%	674
	21st to end	Night	16% 7% 20% 25% 23% 8%	760
October	1st to 10th	Night	17% 5% 24% 28% 23% 4	760
	11th to 20th	Night	21% 9% 31% 26% 12% 1	760
	21st to end	Night	26% 8% 28% 27% 9% 2	836
November	1st to 10th	Night	16% 10% 35% 27% 11% 2	780
	11th to 20th	Night	20% 15% 34% 23% 8% 1	800
	21st to end	Night	22% 12% 35% 24% 7%	910
December	1st to 10th	Night	22% 14% 36% 23% 6%	1000
	11th to 20th	Night	24% 12% 35% 22% 7%	1000
	21st to end	Night	29% 12% 33% 21% 4	1100

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