Racine
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Racine 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	13% 8% 3 7% 5% 4 5% 4 6% 7% 38%	126088
	Night	14% 10% 3 7% 5% 4 4 4 5% 6% 38%	122876
Transparency	Day	44% 5% 12% 24% 13% 1	129588
	Night	46% 5% 11% 23% 14% 2	127437
Seeing	Day	15% 4 19% 34% 22% 6%	17028
	Night	18% 6% 25% 30% 17% 3	26821

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	11% 12% 7% 11% 5% 5% 5% 5% 6% 6% 27%	3617
	11th to 20th	Day	10% 11% 6% 10% 4 4 7% 7% 7% 5% 29%	3620
	21st to end	Day	15% 16% 5% 7% 3 4 4 3 5% 6% 32%	3982
February	1st to 10th	Day	12% 14% 5% 9% 5% 6% 5% 5% 7% 6% 26%	1835
	11th to 20th	Day	12% 12% 3 7% 5% 5% 5% 4 6% 7% 33%	1948
	21st to end	Day	13% 11% 4 11% 5% 5% 5% 5% 6% 6% 29%	1650
March	1st to 10th	Day	13% 9% 3 7% 4 4 3 3 4 6% 43%	4480
	11th to 20th	Day	11% 5% 3 7% 6% 5% 5% 4 5% 7% 42%	4651
	21st to end	Day	19% 11% 5% 9% 6% 5% 5% 4 5% 6% 25%	5967
April	1st to 10th	Day	16% 11% 3 8% 6% 4 5% 4 5% 7% 31%	2400
	11th to 20th	Day	15% 8% 3 7% 5% 5% 5% 4 5% 6% 37%	2374
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 5% 6% 36%	2545
May	1st to 10th	Day	15% 7% 3 8% 5% 4 4 4 6% 7% 38%	5862
	11th to 20th	Day	14% 8% 4 8% 4 4 5% 4 6% 6% 38%	6219
	21st to end	Day	15% 6% 2 5% 4 4 4 3 6% 9% 43%	6935
June	1st to 10th	Day	10% 5% 2 6% 5% 4 4 4 6% 8% 45%	2800
	11th to 20th	Day	10% 5% 2 6% 5% 4 4 4 6% 9% 45%	2800
	21st to end	Day	9% 5% 3 7% 6% 5% 4 5% 7% 9% 42%	2800
July	1st to 10th	Day	11% 5% 2 7% 5% 4 5% 4 7% 9% 40%	6360
	11th to 20th	Day	8% 4 2 5% 4 4 5% 5% 7% 9% 47%	6360
	21st to end	Day	9% 5% 2 7% 5% 5% 5% 4 6% 8% 44%	6924
August	1st to 10th	Day	11% 4 2 5% 4 4 4 4 7% 9% 46%	4479
	11th to 20th	Day	10% 3 2 5% 4 4 4 4 6% 7% 51%	3953
	21st to end	Day	8% 5% 2 7% 4 4 4 4 6% 8% 49%	4312
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 6% 8% 48%	2316
	11th to 20th	Day	11% 5% 1 4 3 3 4 4 5% 7% 53%	2149
	21st to end	Day	12% 6% 2 7% 4 4 5% 4 6% 8% 42%	2090
October	1st to 10th	Day	13% 6% 2 6% 4 4 4 2 5% 7% 46%	2050
	11th to 20th	Day	18% 8% 3 7% 5% 4 6% 4 5% 6% 33%	1857
	21st to end	Day	19% 9% 3 6% 5% 5% 5% 3 5% 6% 36%	1881
November	1st to 10th	Day	11% 10% 2 7% 4 4 4 4 6% 6% 41%	1762
	11th to 20th	Day	14% 12% 4 9% 6% 5% 4 4 6% 7% 28%	1800
	21st to end	Day	20% 11% 4 7% 5% 4 4 3 4 6% 35%	1710
December	1st to 10th	Day	10% 10% 3 7% 6% 6% 5% 5% 6% 7% 34%	2610
	11th to 20th	Day	13% 14% 4 11% 6% 6% 5% 4 6% 7% 22%	3008
	21st to end	Day	23% 22% 7% 11% 5% 4 4 3 3 4 14%	3982
January	1st to 10th	Night	12% 13% 7% 11% 5% 4 4 3 4 6% 31%	6348
	11th to 20th	Night	14% 14% 5% 12% 6% 5% 7% 6% 5% 5% 22%	6360
	21st to end	Night	16% 15% 5% 8% 5% 3 3 3 4 5% 32%	6979
February	1st to 10th	Night	13% 15% 4 9% 6% 5% 4 4 4 6% 30%	2564
	11th to 20th	Night	14% 11% 3 7% 5% 5% 4 3 5% 6% 37%	2338
	21st to end	Night	19% 11% 3 6% 4 4 3 3 4 5% 36%	1980
March	1st to 10th	Night	15% 9% 3 6% 4 4 4 3 4 5% 43%	5373
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 5% 9% 46%	5348
	21st to end	Night	18% 13% 6% 9% 5% 5% 4 3 4 5% 29%	4966
April	1st to 10th	Night	16% 9% 2 5% 5% 5% 5% 4 6% 6% 37%	2000
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 4 4 5% 39%	1975
	21st to end	Night	19% 7% 3 7% 3 4 4 3 5% 6% 40%	1853
May	1st to 10th	Night	19% 7% 2 7% 5% 4 4 3 6% 7% 37%	4033
	11th to 20th	Night	13% 7% 5% 7% 4 4 4 3 5% 7% 39%	3689
	21st to end	Night	17% 7% 2 7% 4 4 3 3 5% 6% 43%	3942
June	1st to 10th	Night	9% 6% 1 6% 4 5% 5% 4 5% 8% 47%	1600
	11th to 20th	Night	11% 6% 2 7% 4 4 4 4 6% 9% 43%	1600
	21st to end	Night	9% 6% 2 7% 5% 5% 5% 4 6% 8% 44%	1600
July	1st to 10th	Night	10% 5% 2 6% 6% 5% 5% 5% 6% 8% 43%	3618
	11th to 20th	Night	7% 4 2 5% 4 4 4 4 6% 9% 51%	3617
	21st to end	Night	8% 4 2 6% 4 4 5% 4 6% 8% 49%	3947
August	1st to 10th	Night	10% 4 1 5% 4 3 4 3 5% 8% 52%	2675
	11th to 20th	Night	11% 3 2 6% 3 3 4 3 5% 8% 51%	3092
	21st to end	Night	8% 4 2 5% 4 4 4 3 6% 9% 52%	3586
September	1st to 10th	Night	9% 4 2 6% 4 4 5% 3 5% 7% 52%	1930
	11th to 20th	Night	11% 4 1 4 3 4 4 3 6% 7% 53%	2011
	21st to end	Night	14% 6% 2 7% 4 3 4 3 5% 6% 45%	2090
October	1st to 10th	Night	13% 6% 2 5% 4 3 5% 4 5% 6% 48%	2127
	11th to 20th	Night	17% 8% 3 6% 4 4 4 3 4 6% 41%	2322
	21st to end	Night	21% 7% 2 6% 5% 3 4 4 5% 8% 35%	2717
November	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 5% 6% 45%	2536
	11th to 20th	Night	15% 12% 3 8% 5% 5% 5% 3 5% 6% 34%	2600
	21st to end	Night	17% 10% 4 7% 5% 5% 4 3 4 6% 34%	2685
December	1st to 10th	Night	11% 11% 3 7% 5% 5% 4 4 5% 5% 38%	4580
	11th to 20th	Night	17% 15% 4 8% 5% 5% 4 4 6% 5% 25%	5199
	21st to end	Night	23% 19% 5% 9% 5% 4 5% 3 4 5% 17%	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	58% 6% 13% 18% 6%	3618
	11th to 20th	Day	52% 9% 11% 17% 11% 1	3620
	21st to end	Day	54% 4 9% 21% 11%	3982
February	1st to 10th	Day	55% 7% 12% 16% 10% 1	1835
	11th to 20th	Day	49% 7% 11% 23% 9% 2	1958
	21st to end	Day	54% 7% 10% 17% 10% 2	1650
March	1st to 10th	Day	43% 4 12% 24% 12% 4	4480
	11th to 20th	Day	41% 6% 14% 26% 12% 1	4651
	21st to end	Day	60% 5% 12% 14% 8% 1	5969
April	1st to 10th	Day	52% 5% 11% 19% 11% 1	2400
	11th to 20th	Day	46% 7% 11% 21% 12% 3	2374
	21st to end	Day	48% 5% 15% 19% 12% 2	2545
May	1st to 10th	Day	45% 5% 13% 22% 13% 3	5897
	11th to 20th	Day	45% 6% 11% 24% 14% 1	6223
	21st to end	Day	37% 5% 11% 29% 14% 3	6949
June	1st to 10th	Day	36% 6% 12% 26% 17% 3	2800
	11th to 20th	Day	35% 5% 15% 23% 19% 2	2800
	21st to end	Day	37% 7% 14% 24% 16% 2	2800
July	1st to 10th	Day	40% 4 12% 29% 12% 2	6291
	11th to 20th	Day	33% 4 15% 33% 14% 1	6285
	21st to end	Day	37% 4 16% 23% 17% 2	6728
August	1st to 10th	Day	34% 5% 16% 30% 14% 1	4464
	11th to 20th	Day	32% 4 15% 36% 13% 1	3992
	21st to end	Day	33% 5% 14% 26% 20% 2	4311
September	1st to 10th	Day	34% 5% 15% 28% 16% 2	2316
	11th to 20th	Day	30% 6% 13% 32% 17% 2	2149
	21st to end	Day	38% 6% 12% 28% 14% 1	2090
October	1st to 10th	Day	25% 3 7% 42% 21% 1	3401
	11th to 20th	Day	39% 4 10% 29% 17% 1	3060
	21st to end	Day	44% 4 9% 29% 12% 3	3081
November	1st to 10th	Day	42% 7% 13% 23% 14% 1	1762
	11th to 20th	Day	53% 7% 13% 19% 8% 1	1800
	21st to end	Day	53% 6% 11% 23% 7%	1710
December	1st to 10th	Day	48% 6% 18% 22% 5%	2610
	11th to 20th	Day	61% 5% 12% 15% 7%	3005
	21st to end	Day	75% 4 5% 12% 3	3982
January	1st to 10th	Night	55% 6% 8% 21% 8%	6348
	11th to 20th	Night	63% 7% 8% 12% 10%	6360
	21st to end	Night	56% 4 13% 18% 9%	6979
February	1st to 10th	Night	55% 6% 10% 17% 11% 1	2564
	11th to 20th	Night	48% 6% 11% 21% 12% 1	2339
	21st to end	Night	51% 4 10% 20% 11% 3	1980
March	1st to 10th	Night	44% 3 12% 25% 13% 3	5373
	11th to 20th	Night	35% 5% 14% 30% 14% 3	5348
	21st to end	Night	59% 4 9% 15% 12% 1	4966
April	1st to 10th	Night	46% 6% 10% 21% 15% 1	2000
	11th to 20th	Night	48% 5% 8% 18% 17% 4	1975
	21st to end	Night	45% 4 13% 20% 16% 2	1853
May	1st to 10th	Night	47% 5% 12% 17% 15% 3	4060
	11th to 20th	Night	43% 6% 12% 20% 15% 3	3690
	21st to end	Night	44% 5% 8% 24% 15% 5%	3950
June	1st to 10th	Night	34% 7% 10% 29% 17% 3	1600
	11th to 20th	Night	37% 6% 10% 24% 20% 3	1600
	21st to end	Night	37% 7% 13% 24% 16% 3	1600
July	1st to 10th	Night	40% 3 13% 30% 11% 4	3580
	11th to 20th	Night	31% 3 14% 31% 18% 2	3572
	21st to end	Night	34% 4 14% 24% 23% 2	3832
August	1st to 10th	Night	31% 5% 15% 28% 19% 2	2666
	11th to 20th	Night	33% 4 11% 35% 17% 1	3119
	21st to end	Night	30% 4 12% 30% 21% 3	3586
September	1st to 10th	Night	32% 6% 11% 26% 22% 2	1930
	11th to 20th	Night	30% 6% 8% 34% 19% 2	2011
	21st to end	Night	40% 5% 8% 30% 16% 2	2090
October	1st to 10th	Night	26% 4 7% 38% 24% 1	3543
	11th to 20th	Night	38% 5% 10% 23% 23% 1	3858
	21st to end	Night	42% 4 10% 25% 17% 2	4467
November	1st to 10th	Night	40% 7% 9% 25% 17% 3	2536
	11th to 20th	Night	51% 7% 11% 19% 11% 1	2600
	21st to end	Night	52% 6% 13% 20% 8%	2685
December	1st to 10th	Night	47% 5% 15% 24% 7% 3	4580
	11th to 20th	Night	60% 6% 10% 15% 8% 1	5201
	21st to end	Night	70% 5% 9% 12% 4	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	19% 8% 28% 34% 10% 2	300
	11th to 20th	Day	19% 8% 30% 32% 10%	300
	21st to end	Day	20% 5% 34% 29% 11% 1	330
February	1st to 10th	Day	16% 7% 38% 30% 8% 2	300
	11th to 20th	Day	17% 8% 34% 29% 11%	300
	21st to end	Day	16% 6% 35% 36% 5%	249
March	1st to 10th	Day	15% 4 36% 37% 8%	300
	11th to 20th	Day	21% 6% 28% 33% 12% 1	340
	21st to end	Day	24% 5% 28% 32% 9% 2	550
April	1st to 10th	Day	21% 6% 24% 38% 11%	500
	11th to 20th	Day	19% 5% 28% 32% 12% 4	492
	21st to end	Day	19% 4 25% 33% 16% 3	500
May	1st to 10th	Day	18% 3 20% 41% 17% 2	503
	11th to 20th	Day	18% 3 14% 39% 23% 4	677
	21st to end	Day	14% 2 13% 37% 24% 10%	789
June	1st to 10th	Day	10% 3 12% 41% 27% 7%	730
	11th to 20th	Day	12% 1 11% 40% 27% 8%	730
	21st to end	Day	10% 2 11% 42% 31% 5%	730
July	1st to 10th	Day	8% 1 6% 31% 40% 14%	721
	11th to 20th	Day	9% 2 9% 35% 35% 10%	718
	21st to end	Day	8% 1 7% 40% 36% 8%	794
August	1st to 10th	Day	6% 2 8% 35% 37% 12%	681
	11th to 20th	Day	11% 3 8% 30% 35% 13%	519
	21st to end	Day	8% 2 9% 32% 36% 12%	583
September	1st to 10th	Day	13% 3 14% 27% 30% 13%	502
	11th to 20th	Day	10% 2 10% 29% 34% 15%	490
	21st to end	Day	15% 4 18% 28% 24% 11%	490
October	1st to 10th	Day	16% 4 19% 29% 24% 8%	450
	11th to 20th	Day	21% 6% 24% 30% 17% 2	300
	21st to end	Day	26% 8% 24% 30% 12% 1	330
November	1st to 10th	Day	13% 6% 30% 29% 20% 2	300
	11th to 20th	Day	19% 12% 33% 24% 12%	300
	21st to end	Day	25% 5% 29% 35% 6%	300
December	1st to 10th	Day	18% 9% 35% 26% 11% 1	300
	11th to 20th	Day	18% 11% 34% 28% 8% 1	300
	21st to end	Day	25% 9% 35% 22% 7% 1	330
January	1st to 10th	Night	19% 12% 37% 25% 7%	1000
	11th to 20th	Night	21% 11% 35% 25% 7% 1	1000
	21st to end	Night	20% 10% 36% 27% 7%	1100
February	1st to 10th	Night	20% 8% 37% 27% 7% 1	964
	11th to 20th	Night	19% 10% 36% 27% 8%	783
	21st to end	Night	25% 6% 36% 28% 5%	660
March	1st to 10th	Night	19% 5% 33% 32% 11% 1	800
	11th to 20th	Night	15% 6% 31% 35% 11% 2	800
	21st to end	Night	22% 5% 26% 34% 12% 1	664
April	1st to 10th	Night	20% 6% 29% 34% 10% 1	600
	11th to 20th	Night	22% 3 26% 33% 14% 2	593
	21st to end	Night	21% 4 19% 38% 17% 1	600
May	1st to 10th	Night	19% 4 15% 44% 18% 2	600
	11th to 20th	Night	19% 2 17% 34% 24% 5%	591
	21st to end	Night	17% 2 13% 31% 30% 8%	650
June	1st to 10th	Night	11% 2 10% 43% 29% 6%	600
	11th to 20th	Night	15% 1 13% 38% 29% 5%	600
	21st to end	Night	10% 2 12% 40% 32% 5%	600
July	1st to 10th	Night	10% 2 4 33% 37% 13%	585
	11th to 20th	Night	9% 2 9% 37% 34% 10%	582
	21st to end	Night	8% 1 8% 37% 41% 5%	657
August	1st to 10th	Night	8% 2 7% 37% 38% 8%	597
	11th to 20th	Night	10% 2 10% 32% 37% 10%	594
	21st to end	Night	8% 2 11% 32% 41% 7%	660
September	1st to 10th	Night	10% 3 13% 32% 30% 11%	579
	11th to 20th	Night	11% 3 11% 30% 33% 11%	681
	21st to end	Night	14% 6% 20% 27% 24% 9%	760
October	1st to 10th	Night	15% 4 22% 32% 21% 6%	760
	11th to 20th	Night	22% 8% 28% 27% 14% 1	760
	21st to end	Night	24% 8% 28% 28% 10% 2	836
November	1st to 10th	Night	17% 8% 32% 27% 14% 2	780
	11th to 20th	Night	21% 15% 33% 23% 7% 1	800
	21st to end	Night	22% 10% 35% 25% 7%	885
December	1st to 10th	Night	21% 14% 35% 24% 6%	1000
	11th to 20th	Night	22% 11% 37% 23% 7%	1000
	21st to end	Night	30% 10% 33% 24% 3	1100

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