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 2024-03-28.

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% 4 7% 6% 3 5% 5% 6% 8% 36%	78653
	Night	14% 10% 4 6% 5% 3 4 5% 5% 7% 36%	81388
Transparency	Day	45% 6% 13% 23% 11% 1	78354
	Night	47% 5% 11% 22% 12% 2	81208
Seeing	Day	16% 6% 27% 31% 16% 4	14937
	Night	19% 8% 27% 29% 15% 3	25007

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% 12% 7% 9% 7% 3 5% 5% 5% 7% 27%	2527
	11th to 20th	Day	12% 11% 6% 11% 7% 3 5% 8% 9% 9% 19%	2530
	21st to end	Day	16% 18% 9% 9% 6% 3 4 4 4 6% 21%	2783
February	1st to 10th	Day	11% 12% 6% 9% 6% 3 5% 6% 6% 9% 27%	1722
	11th to 20th	Day	13% 10% 3 6% 7% 3 5% 5% 6% 7% 35%	1848
	21st to end	Day	11% 12% 6% 8% 8% 4 5% 5% 5% 7% 30%	1570
March	1st to 10th	Day	13% 8% 4 8% 7% 4 5% 5% 6% 6% 34%	1900
	11th to 20th	Day	11% 8% 4 6% 6% 4 6% 5% 6% 7% 38%	1952
	21st to end	Day	17% 10% 5% 7% 6% 4 5% 5% 5% 7% 29%	2460
April	1st to 10th	Day	17% 9% 5% 7% 6% 3 4 6% 6% 7% 30%	2160
	11th to 20th	Day	16% 7% 3 6% 6% 4 5% 5% 6% 7% 34%	2134
	21st to end	Day	17% 9% 3 6% 6% 3 5% 5% 5% 7% 34%	2290
May	1st to 10th	Day	15% 8% 4 7% 6% 4 5% 6% 7% 8% 32%	2340
	11th to 20th	Day	16% 7% 4 6% 5% 2 5% 5% 5% 8% 37%	2457
	21st to end	Day	12% 6% 3 5% 6% 4 4 5% 7% 8% 40%	2725
June	1st to 10th	Day	9% 5% 2 5% 5% 4 5% 5% 6% 8% 45%	2520
	11th to 20th	Day	11% 5% 2 5% 5% 3 4 5% 6% 9% 46%	2520
	21st to end	Day	8% 5% 3 6% 6% 3 5% 6% 7% 9% 43%	2520
July	1st to 10th	Day	6% 5% 2 5% 4 2 4 6% 6% 9% 51%	2520
	11th to 20th	Day	7% 3 2 5% 5% 3 5% 5% 7% 11% 47%	2520
	21st to end	Day	5% 3 3 4 4 3 6% 6% 7% 10% 48%	2743
August	1st to 10th	Day	7% 4 2 5% 5% 4 5% 6% 7% 11% 45%	2485
	11th to 20th	Day	9% 5% 2 5% 5% 4 5% 4 6% 10% 45%	2189
	21st to end	Day	8% 5% 2 5% 5% 3 5% 5% 6% 9% 47%	2376
September	1st to 10th	Day	11% 6% 2 5% 4 3 5% 5% 6% 8% 44%	2160
	11th to 20th	Day	12% 5% 2 4 4 2 4 5% 5% 9% 48%	2044
	21st to end	Day	12% 6% 3 6% 5% 3 6% 5% 6% 9% 41%	1980
October	1st to 10th	Day	14% 5% 3 6% 4 4 3 4 6% 7% 44%	1931
	11th to 20th	Day	18% 9% 3 7% 7% 4 4 5% 6% 7% 31%	1761
	21st to end	Day	17% 8% 4 6% 6% 3 5% 5% 5% 6% 35%	1782
November	1st to 10th	Day	12% 8% 2 6% 6% 3 6% 4 5% 7% 41%	1672
	11th to 20th	Day	12% 9% 4 8% 8% 3 6% 5% 6% 8% 30%	1710
	21st to end	Day	18% 10% 3 6% 5% 3 5% 3 4 6% 37%	1601
December	1st to 10th	Day	16% 11% 5% 8% 7% 4 5% 5% 6% 9% 25%	1520
	11th to 20th	Day	13% 12% 5% 7% 6% 3 7% 6% 7% 8% 26%	1918
	21st to end	Day	18% 22% 7% 11% 7% 3 4 4 4 5% 15%	2783
January	1st to 10th	Night	15% 14% 7% 8% 6% 3 4 4 4 6% 29%	4428
	11th to 20th	Night	14% 14% 6% 11% 7% 4 5% 7% 7% 6% 17%	4440
	21st to end	Night	18% 17% 7% 9% 5% 3 4 3 4 7% 22%	4884
February	1st to 10th	Night	12% 14% 6% 7% 6% 4 4 4 5% 7% 31%	2451
	11th to 20th	Night	13% 9% 4 6% 5% 2 5% 6% 5% 7% 39%	2218
	21st to end	Night	19% 11% 3 6% 4 3 4 4 5% 6% 35%	1884
March	1st to 10th	Night	15% 9% 4 7% 6% 4 5% 5% 5% 6% 34%	2280
	11th to 20th	Night	12% 6% 3 4 5% 3 4 5% 6% 8% 43%	2242
	21st to end	Night	19% 9% 5% 7% 6% 4 5% 5% 4 6% 31%	2050
April	1st to 10th	Night	16% 8% 3 5% 5% 3 5% 5% 5% 8% 35%	1800
	11th to 20th	Night	20% 8% 4 6% 5% 2 5% 4 5% 5% 37%	1775
	21st to end	Night	18% 8% 3 4 4 3 5% 4 5% 7% 38%	1668
May	1st to 10th	Night	15% 8% 3 6% 6% 4 5% 4 6% 9% 33%	1620
	11th to 20th	Night	18% 7% 3 5% 4 3 4 4 5% 8% 38%	1434
	21st to end	Night	13% 6% 3 6% 5% 4 4 4 5% 8% 42%	1551
June	1st to 10th	Night	10% 4 2 5% 5% 3 4 5% 7% 8% 47%	1440
	11th to 20th	Night	11% 7% 2 4 5% 3 5% 4 6% 8% 44%	1440
	21st to end	Night	9% 7% 3 5% 5% 3 4 5% 5% 8% 46%	1440
July	1st to 10th	Night	8% 3 2 4 4 2 4 5% 6% 10% 52%	1440
	11th to 20th	Night	7% 4 1 4 4 3 4 5% 7% 9% 52%	1440
	21st to end	Night	6% 4 2 3 4 3 5% 4 7% 9% 51%	1575
August	1st to 10th	Night	5% 4 3 4 5% 3 6% 4 7% 10% 50%	1453
	11th to 20th	Night	8% 4 2 4 4 3 5% 5% 6% 9% 51%	1709
	21st to end	Night	9% 4 2 4 4 3 4 4 6% 8% 52%	1980
September	1st to 10th	Night	9% 4 2 6% 5% 3 5% 5% 5% 7% 50%	1800
	11th to 20th	Night	11% 5% 2 4 4 3 3 4 4 7% 54%	1898
	21st to end	Night	14% 6% 3 6% 5% 3 4 4 4 7% 46%	1980
October	1st to 10th	Night	14% 5% 2 5% 4 3 4 5% 6% 7% 45%	2024
	11th to 20th	Night	17% 8% 3 5% 5% 3 4 4 5% 6% 41%	2197
	21st to end	Night	20% 9% 3 5% 6% 3 4 5% 5% 7% 34%	2574
November	1st to 10th	Night	12% 7% 3 5% 5% 3 4 4 4 7% 46%	2406
	11th to 20th	Night	14% 8% 3 8% 7% 4 5% 4 4 7% 35%	2470
	21st to end	Night	17% 8% 3 6% 5% 3 4 4 6% 7% 37%	2574
December	1st to 10th	Night	15% 12% 3 8% 6% 4 5% 5% 6% 6% 29%	2660
	11th to 20th	Night	15% 13% 5% 8% 6% 3 5% 6% 5% 6% 28%	3279
	21st to end	Night	21% 18% 5% 9% 6% 3 4 4 5% 6% 19%	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	57% 6% 14% 17% 6%	2528
	11th to 20th	Day	59% 6% 13% 19% 4	2530
	21st to end	Day	65% 4 8% 17% 5%	2783
February	1st to 10th	Day	54% 5% 12% 18% 9% 1	1722
	11th to 20th	Day	48% 4 11% 24% 11% 2	1858
	21st to end	Day	53% 5% 12% 18% 10% 2	1570
March	1st to 10th	Day	49% 5% 14% 22% 8% 2	1900
	11th to 20th	Day	45% 5% 12% 22% 13% 2	1952
	21st to end	Day	53% 6% 14% 19% 7% 1	2460
April	1st to 10th	Day	52% 6% 13% 18% 10% 1	2160
	11th to 20th	Day	48% 6% 10% 21% 12% 3	2134
	21st to end	Day	49% 6% 13% 18% 12% 2	2290
May	1st to 10th	Day	47% 6% 13% 24% 9% 1	2340
	11th to 20th	Day	45% 6% 12% 24% 12% 2	2461
	21st to end	Day	41% 7% 14% 23% 14% 1	2725
June	1st to 10th	Day	35% 7% 13% 26% 16% 3	2520
	11th to 20th	Day	34% 6% 14% 25% 18% 2	2520
	21st to end	Day	35% 7% 15% 25% 16% 2	2520
July	1st to 10th	Day	28% 7% 14% 33% 15% 3	2451
	11th to 20th	Day	29% 8% 15% 30% 17% 2	2445
	21st to end	Day	27% 8% 17% 28% 16% 4	2591
August	1st to 10th	Day	30% 8% 18% 29% 13% 2	2470
	11th to 20th	Day	33% 5% 18% 30% 13% 1	2189
	21st to end	Day	33% 7% 13% 27% 18% 2	2376
September	1st to 10th	Day	36% 7% 13% 27% 15% 2	2160
	11th to 20th	Day	33% 5% 13% 33% 14% 2	2044
	21st to end	Day	39% 5% 12% 31% 12% 1	1980
October	1st to 10th	Day	38% 6% 10% 31% 14% 1	1931
	11th to 20th	Day	51% 6% 12% 19% 12% 1	1761
	21st to end	Day	49% 5% 11% 23% 11% 1	1782
November	1st to 10th	Day	43% 3 12% 26% 13% 2	1672
	11th to 20th	Day	52% 5% 14% 20% 8%	1710
	21st to end	Day	49% 4 15% 25% 7%	1601
December	1st to 10th	Day	57% 4 15% 15% 7% 1	1520
	11th to 20th	Day	54% 6% 15% 18% 7% 2	1915
	21st to end	Day	72% 4 7% 12% 4	2783
January	1st to 10th	Night	56% 6% 9% 19% 9% 1	4428
	11th to 20th	Night	65% 5% 10% 13% 6%	4440
	21st to end	Night	63% 5% 10% 17% 5%	4884
February	1st to 10th	Night	53% 4 11% 19% 11% 1	2451
	11th to 20th	Night	45% 6% 10% 24% 14% 1	2219
	21st to end	Night	50% 5% 11% 20% 13% 3	1884
March	1st to 10th	Night	50% 5% 13% 21% 9% 2	2280
	11th to 20th	Night	38% 5% 14% 25% 16% 3	2242
	21st to end	Night	54% 5% 10% 20% 10% 1	2050
April	1st to 10th	Night	47% 6% 9% 21% 16% 1	1800
	11th to 20th	Night	49% 3 7% 19% 17% 4	1775
	21st to end	Night	45% 4 13% 22% 14% 2	1668
May	1st to 10th	Night	47% 5% 11% 24% 11% 1	1620
	11th to 20th	Night	45% 5% 11% 22% 14% 2	1435
	21st to end	Night	41% 5% 12% 24% 15% 2	1552
June	1st to 10th	Night	34% 7% 12% 28% 18% 2	1440
	11th to 20th	Night	37% 5% 9% 25% 21% 3	1440
	21st to end	Night	36% 6% 14% 25% 17% 2	1440
July	1st to 10th	Night	27% 8% 14% 29% 18% 4	1400
	11th to 20th	Night	27% 6% 13% 30% 19% 4	1392
	21st to end	Night	27% 7% 16% 26% 20% 5%	1487
August	1st to 10th	Night	28% 6% 17% 31% 15% 3	1444
	11th to 20th	Night	28% 6% 17% 32% 16% 1	1709
	21st to end	Night	30% 5% 12% 29% 21% 3	1980
September	1st to 10th	Night	33% 5% 11% 26% 22% 2	1800
	11th to 20th	Night	31% 5% 9% 37% 16% 2	1898
	21st to end	Night	40% 4 8% 32% 14% 1	1980
October	1st to 10th	Night	38% 5% 9% 29% 16% 1	2024
	11th to 20th	Night	44% 5% 13% 21% 16% 1	2197
	21st to end	Night	49% 5% 12% 23% 11% 1	2574
November	1st to 10th	Night	40% 4 9% 27% 17% 2	2406
	11th to 20th	Night	49% 5% 12% 23% 11% 1	2470
	21st to end	Night	48% 5% 15% 23% 9% 1	2574
December	1st to 10th	Night	56% 5% 10% 20% 8% 1	2660
	11th to 20th	Night	56% 6% 11% 17% 9% 1	3281
	21st to end	Night	67% 4 9% 14% 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% 11% 32% 28% 9% 1	270
	11th to 20th	Day	20% 10% 34% 24% 11% 1	270
	21st to end	Day	22% 5% 32% 32% 8% 1	297
February	1st to 10th	Day	13% 13% 42% 24% 8% 1	270
	11th to 20th	Day	15% 18% 34% 25% 7%	270
	21st to end	Day	19% 12% 44% 20% 4	225
March	1st to 10th	Day	15% 13% 45% 22% 4	270
	11th to 20th	Day	17% 13% 36% 24% 9% 2	302
	21st to end	Day	27% 9% 31% 24% 8% 2	490
April	1st to 10th	Day	22% 9% 36% 25% 8%	420
	11th to 20th	Day	18% 10% 33% 25% 9% 4	412
	21st to end	Day	24% 6% 29% 25% 15% 2	420
May	1st to 10th	Day	22% 5% 34% 31% 7% 2	423
	11th to 20th	Day	19% 5% 29% 32% 14% 2	603
	21st to end	Day	16% 2 25% 30% 22% 6%	679
June	1st to 10th	Day	10% 2 25% 40% 19% 4	630
	11th to 20th	Day	14% 3 22% 38% 19% 4	630
	21st to end	Day	12% 2 23% 39% 20% 4	630
July	1st to 10th	Day	8% 2 14% 36% 31% 10%	621
	11th to 20th	Day	9% 1 22% 37% 24% 7%	618
	21st to end	Day	5% 1 20% 44% 25% 4	684
August	1st to 10th	Day	9% 2 13% 41% 27% 8%	604
	11th to 20th	Day	10% 3 15% 33% 28% 12%	439
	21st to end	Day	9% 2 17% 36% 27% 8%	495
September	1st to 10th	Day	13% 3 19% 34% 23% 7%	450
	11th to 20th	Day	13% 2 15% 32% 27% 11%	450
	21st to end	Day	16% 7% 24% 26% 20% 7%	450
October	1st to 10th	Day	20% 5% 24% 26% 20% 5%	401
	11th to 20th	Day	22% 10% 30% 26% 10% 1	270
	21st to end	Day	21% 8% 36% 27% 6% 1	297
November	1st to 10th	Day	14% 13% 31% 27% 13% 3	270
	11th to 20th	Day	14% 17% 34% 24% 10%	270
	21st to end	Day	25% 8% 36% 24% 7%	270
December	1st to 10th	Day	20% 12% 37% 22% 8%	270
	11th to 20th	Day	24% 11% 37% 18% 8% 1	270
	21st to end	Day	25% 15% 36% 20% 3 1	297
January	1st to 10th	Night	20% 14% 36% 23% 6%	950
	11th to 20th	Night	23% 11% 35% 23% 7% 1	950
	21st to end	Night	21% 10% 36% 26% 7%	1045
February	1st to 10th	Night	20% 11% 35% 27% 7% 1	931
	11th to 20th	Night	18% 13% 34% 28% 6%	743
	21st to end	Night	26% 11% 35% 23% 5%	628
March	1st to 10th	Night	20% 8% 33% 29% 11% 1	760
	11th to 20th	Night	14% 9% 35% 31% 9% 1	755
	21st to end	Night	23% 6% 25% 34% 11% 2	615
April	1st to 10th	Night	20% 8% 29% 32% 10% 1	540
	11th to 20th	Night	28% 5% 26% 27% 12% 3	533
	21st to end	Night	22% 4 22% 34% 16% 2	540
May	1st to 10th	Night	17% 5% 22% 39% 14% 2	540
	11th to 20th	Night	21% 3 22% 31% 21% 2	531
	21st to end	Night	14% 1 18% 34% 25% 8%	584
June	1st to 10th	Night	13% 1 16% 40% 26% 4	540
	11th to 20th	Night	16% 2 19% 35% 25% 4	540
	21st to end	Night	10% 2 17% 38% 30% 2	540
July	1st to 10th	Night	10% 1 7% 32% 39% 10%	525
	11th to 20th	Night	8% 1 14% 37% 32% 8%	522
	21st to end	Night	8% 1 15% 41% 32% 3	591
August	1st to 10th	Night	7% 1 10% 39% 36% 7%	537
	11th to 20th	Night	11% 2 11% 33% 32% 11%	534
	21st to end	Night	12% 2 14% 33% 34% 5%	594
September	1st to 10th	Night	11% 3 15% 35% 28% 9%	540
	11th to 20th	Night	13% 3 16% 31% 28% 9%	638
	21st to end	Night	17% 7% 20% 24% 23% 9%	720
October	1st to 10th	Night	18% 5% 23% 27% 23% 4	720
	11th to 20th	Night	21% 9% 32% 26% 11% 1	720
	21st to end	Night	27% 8% 28% 27% 9% 2	792
November	1st to 10th	Night	16% 10% 35% 26% 11% 2	740
	11th to 20th	Night	19% 15% 34% 23% 8% 1	760
	21st to end	Night	22% 13% 34% 24% 8%	864
December	1st to 10th	Night	23% 14% 35% 22% 6%	950
	11th to 20th	Night	24% 12% 34% 22% 7%	950
	21st to end	Night	29% 13% 33% 21% 4	1045

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