UW-Whitewater Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the UW-Whitewater Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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% 9% 4 7% 6% 3 5% 5% 5% 7% 37%	74795
	Night	14% 9% 4 6% 5% 3 4 4 5% 7% 38%	74958
Transparency	Day	47% 5% 12% 23% 12% 1	74496
	Night	46% 5% 11% 22% 14% 2	74778
Seeing	Day	16% 10% 29% 26% 14% 5%	14703
	Night	18% 9% 31% 30% 11% 1	24689

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% 11% 7% 8% 7% 4 5% 5% 4 7% 30%	1517
	11th to 20th	Day	13% 15% 7% 12% 9% 3 4 5% 5% 6% 22%	1456
	21st to end	Day	13% 14% 7% 14% 7% 4 5% 4 4 8% 22%	1634
February	1st to 10th	Day	12% 13% 6% 9% 7% 4 5% 5% 4 6% 29%	1620
	11th to 20th	Day	14% 11% 4 6% 6% 4 5% 4 5% 5% 35%	1724
	21st to end	Day	12% 14% 5% 10% 8% 3 4 4 4 6% 30%	1480
March	1st to 10th	Day	13% 10% 5% 8% 7% 4 5% 5% 5% 7% 33%	1800
	11th to 20th	Day	12% 9% 4 7% 6% 3 4 3 5% 7% 39%	1872
	21st to end	Day	19% 10% 4 8% 7% 3 5% 4 5% 7% 29%	2371
April	1st to 10th	Day	17% 11% 5% 8% 6% 4 5% 4 5% 6% 30%	2160
	11th to 20th	Day	16% 9% 4 6% 6% 3 5% 5% 5% 8% 33%	2134
	21st to end	Day	19% 9% 3 6% 6% 3 4 4 5% 6% 33%	2246
May	1st to 10th	Day	17% 9% 3 6% 7% 4 5% 5% 7% 7% 31%	2366
	11th to 20th	Day	19% 7% 3 6% 6% 3 5% 4 5% 7% 35%	2479
	21st to end	Day	13% 7% 3 7% 5% 3 6% 5% 5% 7% 38%	2725
June	1st to 10th	Day	10% 5% 2 6% 5% 3 6% 5% 6% 9% 43%	2520
	11th to 20th	Day	11% 5% 2 5% 6% 2 6% 5% 7% 9% 43%	2520
	21st to end	Day	12% 5% 2 5% 5% 4 4 5% 7% 10% 39%	2520
July	1st to 10th	Day	7% 4 2 4 5% 3 5% 5% 7% 10% 47%	2520
	11th to 20th	Day	7% 4 2 5% 5% 5% 6% 6% 7% 9% 45%	2520
	21st to end	Day	7% 5% 2 4 4 3 6% 5% 7% 10% 46%	2743
August	1st to 10th	Day	7% 5% 2 5% 6% 4 5% 7% 7% 10% 43%	2507
	11th to 20th	Day	10% 6% 2 5% 6% 4 5% 4 6% 9% 43%	2141
	21st to end	Day	9% 6% 2 5% 5% 3 5% 5% 6% 8% 46%	2376
September	1st to 10th	Day	13% 6% 2 6% 5% 4 4 4 6% 8% 42%	2160
	11th to 20th	Day	12% 5% 2 4 3 2 4 4 5% 8% 51%	2075
	21st to end	Day	12% 7% 3 5% 6% 4 4 4 5% 7% 43%	1980
October	1st to 10th	Day	15% 7% 2 5% 4 2 4 4 5% 7% 45%	1882
	11th to 20th	Day	19% 11% 3 6% 5% 4 5% 4 4 7% 33%	1800
	21st to end	Day	19% 10% 3 6% 5% 3 4 3 5% 5% 36%	1786
November	1st to 10th	Day	12% 8% 3 7% 5% 3 4 4 3 6% 45%	1672
	11th to 20th	Day	13% 11% 5% 8% 7% 4 4 5% 5% 6% 32%	1710
	21st to end	Day	17% 11% 3 7% 6% 3 4 3 4 6% 36%	1558
December	1st to 10th	Day	14% 12% 4 8% 8% 4 5% 5% 4 6% 30%	1520
	11th to 20th	Day	12% 14% 6% 9% 7% 3 5% 5% 5% 7% 27%	1918
	21st to end	Day	18% 20% 10% 12% 7% 4 4 3 3 4 15%	2783
January	1st to 10th	Night	12% 13% 6% 9% 7% 3 4 4 4 5% 34%	2648
	11th to 20th	Night	15% 13% 7% 10% 6% 3 4 4 5% 5% 26%	2549
	21st to end	Night	13% 12% 7% 10% 6% 4 6% 4 6% 7% 25%	2722
February	1st to 10th	Night	13% 14% 6% 9% 6% 4 4 4 4 6% 32%	2340
	11th to 20th	Night	13% 10% 4 6% 6% 3 5% 5% 5% 5% 37%	2120
	21st to end	Night	17% 12% 4 7% 5% 2 3 4 5% 5% 36%	1776
March	1st to 10th	Night	16% 10% 4 5% 6% 3 4 4 5% 6% 35%	2160
	11th to 20th	Night	12% 8% 3 6% 5% 3 5% 4 6% 8% 41%	2105
	21st to end	Night	19% 10% 4 6% 5% 3 6% 5% 4 5% 33%	1984
April	1st to 10th	Night	16% 10% 4 5% 5% 4 5% 4 5% 7% 36%	1800
	11th to 20th	Night	18% 9% 3 6% 5% 2 5% 4 5% 5% 37%	1775
	21st to end	Night	19% 7% 3 6% 5% 3 4 5% 5% 6% 38%	1712
May	1st to 10th	Night	16% 8% 3 6% 6% 3 5% 5% 6% 9% 34%	1592
	11th to 20th	Night	16% 8% 3 6% 5% 3 4 4 6% 6% 38%	1416
	21st to end	Night	11% 7% 3 6% 5% 3 5% 5% 6% 10% 40%	1551
June	1st to 10th	Night	9% 4 2 4 5% 2 5% 5% 7% 9% 48%	1440
	11th to 20th	Night	11% 5% 2 5% 5% 3 4 5% 6% 9% 46%	1440
	21st to end	Night	8% 5% 3 6% 5% 2 4 4 5% 9% 49%	1440
July	1st to 10th	Night	7% 4 1 4 4 2 5% 5% 6% 12% 51%	1440
	11th to 20th	Night	7% 4 2 4 5% 2 4 4 5% 10% 52%	1440
	21st to end	Night	6% 3 2 5% 4 3 5% 7% 6% 8% 51%	1575
August	1st to 10th	Night	6% 3 2 5% 4 3 5% 6% 8% 9% 48%	1432
	11th to 20th	Night	8% 4 2 5% 5% 2 4 5% 5% 9% 51%	1754
	21st to end	Night	8% 5% 2 4 4 3 4 4 6% 8% 51%	1980
September	1st to 10th	Night	9% 5% 2 5% 5% 2 4 4 5% 7% 52%	1800
	11th to 20th	Night	12% 4 2 3 4 3 4 4 5% 6% 53%	1866
	21st to end	Night	13% 6% 3 6% 5% 2 4 3 4 7% 49%	1980
October	1st to 10th	Night	11% 7% 3 5% 5% 3 4 4 4 5% 49%	2075
	11th to 20th	Night	17% 8% 3 6% 4 3 3 4 4 6% 42%	2160
	21st to end	Night	20% 9% 2 5% 5% 3 4 4 5% 7% 36%	2569
November	1st to 10th	Night	11% 8% 2 5% 5% 3 3 4 5% 6% 47%	2406
	11th to 20th	Night	14% 11% 4 8% 6% 4 4 4 4 6% 35%	2470
	21st to end	Night	17% 10% 4 6% 5% 3 3 4 4 7% 36%	2618
December	1st to 10th	Night	15% 13% 4 8% 6% 3 5% 5% 5% 6% 30%	2660
	11th to 20th	Night	15% 14% 5% 9% 6% 3 5% 4 4 6% 29%	3279
	21st to end	Night	21% 17% 6% 10% 7% 3 4 4 4 5% 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	55% 5% 13% 18% 9%	1518
	11th to 20th	Day	63% 5% 11% 15% 7%	1456
	21st to end	Day	63% 5% 11% 13% 8%	1634
February	1st to 10th	Day	57% 4 12% 18% 8% 1	1620
	11th to 20th	Day	51% 4 10% 22% 10% 2	1734
	21st to end	Day	58% 3 9% 18% 11% 1	1480
March	1st to 10th	Day	51% 5% 13% 22% 7% 1	1800
	11th to 20th	Day	47% 4 12% 22% 14% 1	1872
	21st to end	Day	56% 5% 12% 19% 7% 1	2371
April	1st to 10th	Day	55% 5% 11% 19% 11%	2160
	11th to 20th	Day	51% 4 10% 21% 12% 2	2134
	21st to end	Day	51% 6% 12% 19% 11% 1	2246
May	1st to 10th	Day	51% 6% 13% 23% 7%	2366
	11th to 20th	Day	49% 5% 11% 23% 12%	2483
	21st to end	Day	45% 7% 12% 22% 13% 2	2725
June	1st to 10th	Day	37% 6% 13% 26% 16% 2	2520
	11th to 20th	Day	37% 6% 13% 25% 18% 2	2520
	21st to end	Day	40% 6% 14% 23% 16% 2	2520
July	1st to 10th	Day	32% 7% 13% 32% 14% 2	2451
	11th to 20th	Day	34% 7% 14% 26% 17% 2	2445
	21st to end	Day	32% 6% 17% 27% 16% 3	2591
August	1st to 10th	Day	34% 8% 15% 30% 12% 1	2492
	11th to 20th	Day	37% 7% 15% 28% 12% 1	2141
	21st to end	Day	35% 7% 11% 26% 19% 2	2376
September	1st to 10th	Day	39% 7% 10% 26% 17% 2	2160
	11th to 20th	Day	32% 6% 11% 33% 16% 2	2075
	21st to end	Day	40% 5% 10% 30% 14% 1	1980
October	1st to 10th	Day	40% 5% 9% 29% 15% 1	1882
	11th to 20th	Day	52% 4 11% 21% 12% 1	1800
	21st to end	Day	51% 4 10% 22% 12% 1	1786
November	1st to 10th	Day	42% 5% 13% 24% 15% 2	1672
	11th to 20th	Day	52% 5% 13% 20% 9% 1	1710
	21st to end	Day	51% 4 14% 24% 7% 1	1558
December	1st to 10th	Day	56% 5% 15% 16% 7% 1	1520
	11th to 20th	Day	56% 5% 14% 17% 6% 2	1915
	21st to end	Day	75% 4 7% 9% 5%	2783
January	1st to 10th	Night	53% 4 9% 21% 12% 1	2648
	11th to 20th	Night	61% 5% 12% 14% 8%	2549
	21st to end	Night	59% 5% 11% 15% 10% 1	2722
February	1st to 10th	Night	54% 5% 10% 19% 11% 1	2340
	11th to 20th	Night	48% 5% 12% 20% 14% 1	2121
	21st to end	Night	51% 4 10% 20% 11% 3	1776
March	1st to 10th	Night	50% 5% 13% 21% 10% 2	2160
	11th to 20th	Night	42% 4 13% 22% 16% 2	2105
	21st to end	Night	54% 5% 9% 20% 11% 2	1984
April	1st to 10th	Night	48% 6% 10% 20% 15% 1	1800
	11th to 20th	Night	49% 4 6% 21% 17% 3	1775
	21st to end	Night	46% 6% 10% 21% 14% 2	1712
May	1st to 10th	Night	46% 7% 12% 22% 12% 1	1592
	11th to 20th	Night	45% 7% 11% 23% 12% 2	1417
	21st to end	Night	39% 7% 13% 23% 15% 2	1552
June	1st to 10th	Night	32% 6% 13% 29% 19% 1	1440
	11th to 20th	Night	34% 7% 10% 25% 23% 3	1440
	21st to end	Night	33% 6% 15% 24% 18% 3	1440
July	1st to 10th	Night	26% 7% 15% 29% 19% 4	1400
	11th to 20th	Night	28% 6% 11% 31% 21% 3	1392
	21st to end	Night	28% 7% 14% 29% 17% 5%	1487
August	1st to 10th	Night	29% 8% 15% 31% 15% 3	1423
	11th to 20th	Night	30% 5% 15% 31% 18% 1	1754
	21st to end	Night	30% 7% 11% 28% 21% 3	1980
September	1st to 10th	Night	31% 5% 13% 25% 23% 3	1800
	11th to 20th	Night	32% 5% 10% 33% 18% 2	1866
	21st to end	Night	37% 5% 9% 31% 17% 1	1980
October	1st to 10th	Night	37% 5% 9% 29% 18% 2	2075
	11th to 20th	Night	44% 4 11% 22% 17% 1	2160
	21st to end	Night	49% 4 11% 24% 12% 1	2569
November	1st to 10th	Night	39% 4 10% 27% 18% 2	2406
	11th to 20th	Night	51% 4 12% 20% 11% 1	2470
	21st to end	Night	49% 4 14% 22% 10% 1	2618
December	1st to 10th	Night	55% 5% 11% 19% 8% 1	2660
	11th to 20th	Night	57% 5% 12% 17% 8% 1	3281
	21st to end	Night	68% 5% 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	18% 15% 33% 26% 7% 1	270
	11th to 20th	Day	21% 15% 33% 25% 5% 1	246
	21st to end	Day	21% 11% 42% 20% 5% 2	264
February	1st to 10th	Day	15% 19% 48% 14% 4	240
	11th to 20th	Day	21% 21% 35% 18% 5%	240
	21st to end	Day	22% 19% 43% 14% 2 1	198
March	1st to 10th	Day	17% 17% 46% 14% 6%	240
	11th to 20th	Day	20% 19% 33% 18% 9% 1	240
	21st to end	Day	27% 13% 29% 22% 7% 2	457
April	1st to 10th	Day	23% 15% 33% 24% 5%	420
	11th to 20th	Day	22% 19% 25% 23% 8% 3	412
	21st to end	Day	25% 12% 27% 24% 11% 2	420
May	1st to 10th	Day	21% 11% 30% 27% 8% 2	449
	11th to 20th	Day	23% 10% 27% 26% 11% 2	625
	21st to end	Day	16% 9% 28% 25% 15% 6%	679
June	1st to 10th	Day	9% 7% 29% 31% 17% 6%	630
	11th to 20th	Day	14% 7% 28% 31% 15% 5%	630
	21st to end	Day	14% 7% 28% 28% 18% 5%	630
July	1st to 10th	Day	8% 3 17% 32% 27% 13%	621
	11th to 20th	Day	9% 5% 27% 30% 21% 8%	618
	21st to end	Day	7% 3 25% 36% 20% 9%	684
August	1st to 10th	Day	8% 3 19% 35% 23% 12%	626
	11th to 20th	Day	11% 5% 16% 27% 25% 16%	453
	21st to end	Day	12% 3 20% 32% 23% 10%	495
September	1st to 10th	Day	14% 7% 22% 28% 21% 7%	450
	11th to 20th	Day	12% 3 22% 30% 22% 11%	450
	21st to end	Day	15% 12% 25% 22% 17% 9%	450
October	1st to 10th	Day	20% 9% 25% 25% 17% 5%	352
	11th to 20th	Day	23% 20% 30% 20% 7%	270
	21st to end	Day	29% 13% 33% 18% 5% 2	297
November	1st to 10th	Day	16% 16% 37% 20% 11% 1	270
	11th to 20th	Day	20% 16% 37% 17% 9%	270
	21st to end	Day	23% 12% 40% 21% 4	270
December	1st to 10th	Day	19% 16% 40% 18% 6% 1	270
	11th to 20th	Day	17% 18% 37% 19% 8% 1	270
	21st to end	Day	25% 16% 40% 16% 2	297
January	1st to 10th	Night	17% 14% 38% 24% 7% 1	950
	11th to 20th	Night	22% 11% 35% 25% 6% 1	911
	21st to end	Night	20% 10% 36% 27% 6%	990
February	1st to 10th	Night	21% 10% 38% 26% 5%	900
	11th to 20th	Night	20% 14% 36% 26% 4	725
	21st to end	Night	25% 12% 36% 23% 4	592
March	1st to 10th	Night	22% 10% 36% 25% 7% 1	720
	11th to 20th	Night	16% 11% 34% 31% 8%	665
	21st to end	Night	24% 9% 29% 30% 8% 1	594
April	1st to 10th	Night	21% 11% 38% 25% 5% 1	540
	11th to 20th	Night	23% 11% 30% 29% 7% 1	533
	21st to end	Night	23% 8% 31% 27% 9% 1	540
May	1st to 10th	Night	20% 7% 36% 29% 7% 1	540
	11th to 20th	Night	19% 5% 32% 32% 11%	531
	21st to end	Night	15% 5% 27% 35% 18%	584
June	1st to 10th	Night	11% 3 25% 45% 16% 1	540
	11th to 20th	Night	14% 3 31% 40% 12% 1	540
	21st to end	Night	11% 3 27% 40% 17% 1	540
July	1st to 10th	Night	9% 2 14% 41% 32% 3	525
	11th to 20th	Night	9% 1 20% 43% 24% 2	522
	21st to end	Night	8% 2 16% 49% 23% 1	591
August	1st to 10th	Night	7% 2 14% 45% 29% 3	537
	11th to 20th	Night	9% 3 13% 41% 29% 5%	534
	21st to end	Night	11% 2 16% 42% 26% 3	594
September	1st to 10th	Night	9% 4 23% 37% 23% 5%	540
	11th to 20th	Night	13% 3 22% 34% 24% 4	606
	21st to end	Night	16% 7% 26% 29% 20% 2	720
October	1st to 10th	Night	15% 6% 30% 31% 16% 2	720
	11th to 20th	Night	21% 12% 31% 28% 8%	720
	21st to end	Night	25% 10% 30% 27% 7%	792
November	1st to 10th	Night	15% 12% 38% 25% 10% 1	740
	11th to 20th	Night	21% 14% 36% 23% 6%	760
	21st to end	Night	22% 11% 38% 21% 7%	908
December	1st to 10th	Night	23% 12% 38% 20% 5%	950
	11th to 20th	Night	24% 11% 36% 23% 5% 1	950
	21st to end	Night	30% 12% 34% 22% 3	1045

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