Appleton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Appleton clear sky chart from 2005-11-06 to 2026-03-03.

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 8% 5% 4 5% 4 6% 8% 38%	131085
	Night	12% 10% 4 8% 5% 4 4 3 5% 6% 38%	130399
Transparency	Day	44% 4 12% 26% 13% 1	134560
	Night	46% 3 12% 24% 14% 2	134986
Seeing	Day	17% 11% 31% 25% 13% 4	17711
	Night	18% 10% 32% 29% 10% 1	27738

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% 5% 14% 7% 5% 5% 4 5% 5% 29%	4691
	11th to 20th	Day	7% 12% 5% 11% 5% 5% 6% 5% 6% 7% 30%	4710
	21st to end	Day	9% 11% 4 11% 6% 5% 4 4 5% 6% 35%	5156
February	1st to 10th	Day	10% 11% 5% 10% 6% 5% 5% 4 6% 7% 31%	1873
	11th to 20th	Day	11% 10% 3 8% 4 5% 5% 4 5% 7% 38%	2001
	21st to end	Day	12% 12% 4 9% 6% 5% 5% 4 5% 6% 33%	1730
March	1st to 10th	Day	13% 7% 2 5% 4 3 4 3 4 8% 46%	4500
	11th to 20th	Day	11% 7% 2 7% 4 4 4 4 6% 8% 42%	4689
	21st to end	Day	24% 12% 3 10% 4 3 4 3 4 5% 28%	5967
April	1st to 10th	Day	14% 14% 4 8% 4 5% 5% 4 5% 6% 30%	2400
	11th to 20th	Day	19% 9% 3 7% 5% 5% 4 3 5% 6% 35%	2374
	21st to end	Day	17% 9% 4 8% 5% 5% 5% 4 5% 6% 32%	2550
May	1st to 10th	Day	13% 6% 3 6% 4 4 4 4 5% 7% 44%	6035
	11th to 20th	Day	11% 6% 2 7% 4 4 4 4 6% 8% 42%	6319
	21st to end	Day	14% 7% 2 6% 4 4 5% 4 6% 8% 39%	6935
June	1st to 10th	Day	11% 6% 2 7% 5% 4 4 4 6% 8% 44%	2800
	11th to 20th	Day	13% 7% 2 6% 4 5% 5% 4 6% 9% 40%	2800
	21st to end	Day	10% 6% 3 5% 5% 5% 5% 4 7% 10% 41%	2800
July	1st to 10th	Day	11% 6% 2 6% 4 4 5% 5% 7% 10% 40%	6360
	11th to 20th	Day	6% 4 1 5% 3 4 5% 5% 7% 11% 48%	6360
	21st to end	Day	8% 5% 2 6% 5% 5% 5% 5% 6% 9% 45%	6924
August	1st to 10th	Day	8% 5% 2 7% 5% 5% 6% 4 6% 9% 43%	4563
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 3 6% 9% 46%	4038
	21st to end	Day	10% 7% 2 6% 4 5% 4 4 6% 9% 42%	4312
September	1st to 10th	Day	10% 7% 2 7% 4 3 5% 4 6% 8% 44%	2400
	11th to 20th	Day	11% 4 2 5% 4 4 4 4 5% 9% 48%	2296
	21st to end	Day	11% 7% 3 8% 4 4 5% 4 5% 9% 40%	2200
October	1st to 10th	Day	13% 7% 3 6% 4 4 4 3 4 6% 46%	2096
	11th to 20th	Day	18% 10% 3 8% 5% 5% 5% 4 5% 8% 31%	1961
	21st to end	Day	16% 10% 2 8% 5% 5% 4 3 5% 6% 37%	1980
November	1st to 10th	Day	12% 9% 3 5% 6% 4 4 4 5% 7% 41%	1852
	11th to 20th	Day	11% 11% 4 9% 7% 5% 5% 4 6% 7% 31%	1885
	21st to end	Day	16% 11% 3 9% 5% 4 5% 5% 5% 5% 33%	1680
December	1st to 10th	Day	8% 12% 5% 9% 8% 5% 5% 5% 7% 7% 29%	2690
	11th to 20th	Day	11% 18% 5% 11% 5% 5% 4 4 4 5% 28%	3088
	21st to end	Day	19% 19% 6% 13% 6% 5% 4 3 3 4 17%	4070
January	1st to 10th	Night	12% 13% 5% 11% 5% 3 3 3 4 4 36%	8232
	11th to 20th	Night	9% 14% 6% 13% 6% 5% 7% 5% 5% 6% 25%	8280
	21st to end	Night	8% 13% 5% 11% 6% 6% 5% 3 5% 5% 33%	9058
February	1st to 10th	Night	10% 13% 5% 10% 6% 5% 4 4 5% 5% 33%	2746
	11th to 20th	Night	10% 9% 4 10% 6% 5% 4 3 5% 5% 39%	2505
	21st to end	Night	14% 12% 4 7% 5% 4 4 3 5% 6% 35%	2076
March	1st to 10th	Night	14% 7% 2 6% 3 4 4 3 5% 6% 46%	5398
	11th to 20th	Night	9% 9% 3 7% 5% 4 5% 4 5% 8% 40%	5313
	21st to end	Night	20% 10% 4 9% 4 4 4 3 5% 5% 31%	4962
April	1st to 10th	Night	18% 11% 3 7% 4 5% 4 3 5% 6% 35%	2000
	11th to 20th	Night	20% 8% 2 6% 5% 3 4 3 6% 7% 36%	1975
	21st to end	Night	17% 8% 3 7% 4 4 4 4 5% 5% 39%	1850
May	1st to 10th	Night	14% 8% 3 7% 4 4 4 3 5% 7% 42%	3866
	11th to 20th	Night	9% 5% 2 6% 5% 4 5% 4 7% 9% 43%	3596
	21st to end	Night	18% 8% 3 7% 4 4 4 4 5% 6% 37%	3942
June	1st to 10th	Night	9% 5% 1 7% 4 4 5% 4 6% 7% 48%	1600
	11th to 20th	Night	12% 8% 2 6% 4 4 4 4 6% 9% 42%	1600
	21st to end	Night	8% 5% 2 4 5% 4 5% 4 7% 9% 46%	1600
July	1st to 10th	Night	12% 6% 2 5% 3 4 5% 4 6% 8% 45%	3618
	11th to 20th	Night	7% 4 2 5% 4 3 4 3 5% 9% 53%	3617
	21st to end	Night	5% 4 3 6% 3 4 5% 4 6% 8% 51%	3947
August	1st to 10th	Night	11% 5% 2 6% 3 3 4 4 6% 8% 48%	2597
	11th to 20th	Night	11% 7% 3 6% 3 5% 4 3 6% 7% 46%	3007
	21st to end	Night	8% 6% 2 6% 4 4 5% 4 6% 8% 49%	3586
September	1st to 10th	Night	10% 5% 2 5% 3 3 4 3 5% 7% 53%	2000
	11th to 20th	Night	12% 4 2 5% 3 3 4 3 4 7% 53%	2083
	21st to end	Night	11% 7% 2 6% 4 4 4 3 5% 7% 47%	2200
October	1st to 10th	Night	12% 6% 2 5% 3 3 4 4 5% 6% 49%	2300
	11th to 20th	Night	15% 8% 3 7% 5% 4 5% 3 6% 7% 38%	2437
	21st to end	Night	17% 10% 2 7% 5% 4 4 3 5% 7% 35%	2860
November	1st to 10th	Night	12% 8% 2 6% 5% 4 4 3 4 6% 44%	2666
	11th to 20th	Night	13% 12% 4 9% 6% 5% 5% 4 5% 6% 34%	2733
	21st to end	Night	14% 12% 3 8% 6% 4 4 3 4 6% 36%	2940
December	1st to 10th	Night	9% 11% 4 9% 5% 4 4 4 5% 8% 37%	4720
	11th to 20th	Night	13% 18% 7% 10% 5% 4 3 3 4 4 28%	5339
	21st to end	Night	20% 17% 5% 11% 6% 4 4 3 3 5% 21%	7150

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	56% 2 16% 18% 8% 1	4692
	11th to 20th	Day	51% 4 10% 22% 12% 1	4710
	21st to end	Day	51% 2 10% 22% 14%	5156
February	1st to 10th	Day	51% 4 11% 22% 11% 1	1873
	11th to 20th	Day	46% 4 11% 26% 12% 1	2011
	21st to end	Day	50% 4 12% 21% 10% 2	1730
March	1st to 10th	Day	38% 3 15% 23% 16% 6%	4500
	11th to 20th	Day	40% 4 15% 24% 15% 1	4689
	21st to end	Day	60% 3 8% 18% 10%	5969
April	1st to 10th	Day	53% 5% 11% 20% 10%	2400
	11th to 20th	Day	51% 4 8% 23% 13% 2	2374
	21st to end	Day	51% 5% 10% 21% 11% 2	2550
May	1st to 10th	Day	40% 3 12% 27% 16% 2	6070
	11th to 20th	Day	38% 5% 11% 29% 16% 1	6323
	21st to end	Day	42% 5% 10% 26% 15% 2	6949
June	1st to 10th	Day	39% 4 12% 29% 15% 2	2800
	11th to 20th	Day	40% 5% 14% 26% 14% 1	2800
	21st to end	Day	38% 6% 14% 26% 15% 1	2800
July	1st to 10th	Day	39% 5% 13% 33% 9% 1	6291
	11th to 20th	Day	28% 5% 17% 34% 15% 1	6285
	21st to end	Day	35% 5% 14% 26% 18% 2	6728
August	1st to 10th	Day	37% 5% 16% 28% 13% 1	4548
	11th to 20th	Day	34% 5% 12% 36% 12% 1	4078
	21st to end	Day	39% 4 15% 26% 16% 1	4311
September	1st to 10th	Day	38% 5% 14% 28% 15% 1	2400
	11th to 20th	Day	34% 4 17% 32% 12% 1	2296
	21st to end	Day	41% 4 12% 31% 11%	2200
October	1st to 10th	Day	25% 3 9% 37% 24% 1	3408
	11th to 20th	Day	44% 4 9% 27% 15% 1	3177
	21st to end	Day	42% 4 14% 28% 11%	3180
November	1st to 10th	Day	43% 4 13% 24% 15% 1	1852
	11th to 20th	Day	51% 4 14% 21% 9% 1	1885
	21st to end	Day	52% 3 16% 21% 7% 1	1680
December	1st to 10th	Day	51% 6% 16% 23% 4	2690
	11th to 20th	Day	59% 3 10% 18% 10% 1	3085
	21st to end	Day	72% 2 6% 13% 7%	4070
January	1st to 10th	Night	53% 2 10% 24% 10% 1	8233
	11th to 20th	Night	59% 3 9% 14% 14% 1	8280
	21st to end	Night	54% 2 11% 19% 14%	9058
February	1st to 10th	Night	52% 3 10% 22% 11% 2	2746
	11th to 20th	Night	47% 4 9% 25% 13% 2	2506
	21st to end	Night	51% 3 12% 22% 11% 2	2076
March	1st to 10th	Night	38% 3 15% 27% 13% 4	5398
	11th to 20th	Night	43% 3 16% 23% 13% 2	5313
	21st to end	Night	56% 3 9% 18% 12% 1	4962
April	1st to 10th	Night	51% 4 7% 19% 18% 1	2000
	11th to 20th	Night	47% 3 9% 23% 15% 3	1975
	21st to end	Night	47% 3 11% 22% 14% 2	1850
May	1st to 10th	Night	42% 4 12% 20% 20% 2	3893
	11th to 20th	Night	36% 6% 15% 24% 17% 2	3597
	21st to end	Night	47% 4 10% 24% 13% 3	3950
June	1st to 10th	Night	34% 5% 13% 31% 16% 1	1600
	11th to 20th	Night	39% 5% 10% 26% 17% 2	1600
	21st to end	Night	33% 6% 17% 26% 14% 4	1600
July	1st to 10th	Night	36% 4 15% 32% 9% 4	3580
	11th to 20th	Night	28% 4 16% 34% 16% 2	3572
	21st to end	Night	30% 5% 15% 26% 22% 2	3832
August	1st to 10th	Night	34% 4 14% 28% 19% 1	2588
	11th to 20th	Night	37% 4 13% 30% 15% 1	3033
	21st to end	Night	34% 4 14% 26% 19% 3	3586
September	1st to 10th	Night	31% 5% 12% 29% 22% 1	2000
	11th to 20th	Night	33% 3 13% 35% 16% 1	2083
	21st to end	Night	36% 4 12% 31% 16% 1	2200
October	1st to 10th	Night	28% 3 8% 38% 21% 2	3755
	11th to 20th	Night	35% 4 11% 31% 16% 2	3960
	21st to end	Night	45% 3 10% 24% 16%	4610
November	1st to 10th	Night	41% 4 12% 26% 16% 2	2666
	11th to 20th	Night	50% 4 12% 20% 11% 2	2733
	21st to end	Night	49% 4 14% 24% 8% 1	2940
December	1st to 10th	Night	45% 4 20% 23% 6% 2	4720
	11th to 20th	Night	61% 3 10% 15% 12% 1	5341
	21st to end	Night	66% 3 8% 15% 7%	7150

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	17% 13% 35% 25% 8% 2	330
	11th to 20th	Day	19% 18% 34% 22% 5%	330
	21st to end	Day	22% 12% 34% 25% 6% 1	363
February	1st to 10th	Day	15% 16% 40% 22% 6% 1	330
	11th to 20th	Day	16% 19% 41% 17% 7%	330
	21st to end	Day	19% 16% 47% 16% 2	273
March	1st to 10th	Day	19% 16% 39% 19% 6%	306
	11th to 20th	Day	25% 16% 31% 19% 7% 2	310
	21st to end	Day	29% 11% 27% 24% 7% 1	550
April	1st to 10th	Day	27% 14% 34% 20% 5% 1	500
	11th to 20th	Day	28% 16% 27% 19% 8% 2	492
	21st to end	Day	24% 12% 29% 23% 10% 2	500
May	1st to 10th	Day	19% 11% 34% 26% 9% 2	572
	11th to 20th	Day	19% 10% 33% 26% 9% 4	725
	21st to end	Day	17% 10% 30% 25% 14% 5%	789
June	1st to 10th	Day	13% 10% 32% 29% 12% 4	730
	11th to 20th	Day	17% 8% 33% 27% 12% 3	730
	21st to end	Day	15% 8% 30% 29% 14% 3	730
July	1st to 10th	Day	10% 4 22% 33% 23% 7%	721
	11th to 20th	Day	9% 7% 26% 31% 19% 7%	718
	21st to end	Day	8% 4 27% 32% 21% 7%	794
August	1st to 10th	Day	9% 5% 26% 30% 22% 8%	726
	11th to 20th	Day	13% 4 20% 30% 24% 10%	557
	21st to end	Day	15% 7% 24% 26% 19% 8%	583
September	1st to 10th	Day	15% 7% 23% 29% 18% 7%	530
	11th to 20th	Day	12% 4 23% 33% 22% 7%	530
	21st to end	Day	17% 10% 26% 24% 18% 5%	530
October	1st to 10th	Day	18% 12% 25% 27% 17% 2	426
	11th to 20th	Day	18% 19% 35% 20% 7%	330
	21st to end	Day	22% 15% 37% 20% 5% 1	363
November	1st to 10th	Day	17% 17% 38% 21% 7% 1	330
	11th to 20th	Day	18% 20% 37% 15% 9% 1	330
	21st to end	Day	25% 15% 42% 13% 5%	330
December	1st to 10th	Day	19% 17% 41% 18% 5%	330
	11th to 20th	Day	24% 18% 36% 17% 5% 1	330
	21st to end	Day	26% 18% 36% 16% 4 1	363
January	1st to 10th	Night	17% 14% 37% 25% 6%	1050
	11th to 20th	Night	20% 14% 38% 22% 6% 1	1050
	21st to end	Night	19% 12% 37% 25% 6%	1155
February	1st to 10th	Night	17% 13% 37% 27% 6% 1	1050
	11th to 20th	Night	16% 16% 37% 23% 7%	870
	21st to end	Night	21% 14% 35% 25% 4	692
March	1st to 10th	Night	19% 11% 33% 28% 8% 1	809
	11th to 20th	Night	18% 12% 37% 27% 5% 1	762
	21st to end	Night	23% 8% 31% 29% 9% 1	660
April	1st to 10th	Night	25% 10% 37% 24% 5%	600
	11th to 20th	Night	23% 13% 29% 27% 7% 1	593
	21st to end	Night	20% 8% 36% 29% 7% 1	600
May	1st to 10th	Night	21% 10% 32% 30% 8%	600
	11th to 20th	Night	18% 9% 33% 32% 8% 1	591
	21st to end	Night	15% 7% 27% 36% 15% 1	650
June	1st to 10th	Night	11% 6% 32% 38% 13% 1	600
	11th to 20th	Night	17% 5% 30% 36% 11% 1	600
	21st to end	Night	11% 4 29% 42% 13% 1	600
July	1st to 10th	Night	10% 2 20% 46% 22% 1	585
	11th to 20th	Night	10% 4 23% 40% 21% 1	582
	21st to end	Night	6% 2 23% 45% 23% 1	657
August	1st to 10th	Night	9% 2 18% 45% 24% 2	597
	11th to 20th	Night	11% 3 21% 36% 27% 3	594
	21st to end	Night	11% 3 23% 38% 23% 2	660
September	1st to 10th	Night	11% 5% 25% 37% 18% 5%	600
	11th to 20th	Night	13% 4 24% 33% 23% 3	683
	21st to end	Night	13% 8% 25% 33% 19% 2	800
October	1st to 10th	Night	17% 8% 27% 29% 17% 1	800
	11th to 20th	Night	21% 13% 34% 25% 7%	800
	21st to end	Night	23% 12% 29% 26% 9% 1	880
November	1st to 10th	Night	17% 11% 39% 25% 7% 1	820
	11th to 20th	Night	20% 18% 35% 22% 5%	843
	21st to end	Night	21% 15% 36% 22% 6%	1050
December	1st to 10th	Night	22% 14% 39% 20% 5%	1050
	11th to 20th	Night	23% 13% 34% 23% 5% 1	1050
	21st to end	Night	29% 12% 33% 22% 4	1155

Page generated at 2026-02-28 00:40:20. Version ac07

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