WWIN Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the WWIN Observatory clear sky chart from 2005-11-06 to 2024-08-30.

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% 6% 2 6% 4 4 4 4 5% 7% 44%	95185
	Night	13% 6% 2 5% 4 3 4 3 5% 6% 49%	93867
Transparency	Day	38% 6% 10% 23% 18% 4	94958
	Night	35% 5% 10% 23% 22% 5%	93701
Seeing	Day	14% 7% 21% 26% 23% 11%	15129
	Night	15% 5% 24% 33% 20% 2	24881

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	17% 9% 3 6% 4 3 3 2 3 4 46%	2847
	11th to 20th	Day	14% 10% 2 5% 3 3 3 2 3 5% 48%	2850
	21st to end	Day	25% 7% 2 4 3 2 2 2 3 4 46%	3135
February	1st to 10th	Day	21% 7% 2 6% 4 3 2 3 4 6% 41%	1710
	11th to 20th	Day	17% 9% 3 6% 4 4 3 4 3 5% 43%	1824
	21st to end	Day	23% 8% 3 7% 4 3 3 3 3 6% 37%	1575
March	1st to 10th	Day	19% 10% 3 8% 4 4 4 3 3 4 38%	3436
	11th to 20th	Day	13% 7% 3 6% 4 4 4 3 5% 6% 45%	3480
	21st to end	Day	16% 8% 3 7% 4 4 3 3 3 5% 43%	3864
April	1st to 10th	Day	14% 6% 2 6% 3 4 4 4 6% 6% 46%	2280
	11th to 20th	Day	15% 6% 2 6% 4 4 4 3 4 6% 45%	2254
	21st to end	Day	15% 6% 2 6% 5% 5% 5% 3 5% 7% 42%	2280
May	1st to 10th	Day	15% 7% 2 7% 5% 5% 5% 4 6% 7% 38%	3765
	11th to 20th	Day	11% 5% 2 7% 5% 4 5% 4 7% 8% 42%	3954
	21st to end	Day	11% 6% 3 8% 6% 6% 6% 4 7% 8% 35%	4594
June	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 4 7% 9% 43%	2660
	11th to 20th	Day	5% 4 2 5% 5% 5% 5% 5% 7% 9% 48%	2660
	21st to end	Day	4 4 2 5% 5% 4 4 6% 7% 10% 50%	2616
July	1st to 10th	Day	7% 5% 2 6% 6% 6% 6% 5% 7% 10% 40%	4120
	11th to 20th	Day	6% 4 2 4 4 4 5% 4 6% 9% 51%	4120
	21st to end	Day	13% 7% 3 8% 6% 5% 6% 5% 5% 8% 34%	4465
August	1st to 10th	Day	5% 5% 1 6% 5% 5% 6% 5% 8% 10% 43%	2437
	11th to 20th	Day	9% 5% 2 6% 4 6% 5% 5% 6% 8% 42%	2245
	21st to end	Day	7% 4 2 5% 5% 5% 5% 4 8% 9% 45%	2485
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 4 3 6% 7% 47%	2160
	11th to 20th	Day	13% 5% 2 4 3 4 5% 4 5% 7% 48%	2160
	21st to end	Day	10% 4 1 5% 4 3 3 3 4 7% 56%	1905
October	1st to 10th	Day	8% 3 2 5% 3 3 4 3 6% 6% 58%	1800
	11th to 20th	Day	14% 5% 1 4 2 3 3 2 4 6% 56%	1800
	21st to end	Day	19% 5% 2 5% 3 2 3 2 4 5% 52%	1980
November	1st to 10th	Day	12% 5% 2 4 3 3 2 2 4 5% 58%	1858
	11th to 20th	Day	11% 5% 2 6% 3 3 3 3 4 7% 55%	1771
	21st to end	Day	20% 8% 2 5% 3 3 4 3 3 5% 45%	1710
December	1st to 10th	Day	19% 6% 2 5% 4 3 4 3 4 5% 45%	1520
	11th to 20th	Day	15% 8% 3 6% 5% 4 3 4 4 5% 44%	1918
	21st to end	Day	14% 8% 3 7% 5% 4 4 4 5% 6% 39%	2947
January	1st to 10th	Night	17% 6% 2 6% 4 4 4 2 4 5% 45%	4108
	11th to 20th	Night	18% 5% 2 4 3 3 3 3 3 4 53%	4120
	21st to end	Night	24% 6% 2 4 3 3 3 2 3 4 47%	4532
February	1st to 10th	Night	21% 8% 3 5% 4 3 3 3 4 5% 43%	2470
	11th to 20th	Night	19% 8% 2 6% 4 3 3 3 4 4 46%	2240
	21st to end	Night	20% 6% 3 5% 3 3 2 2 4 5% 46%	1884
March	1st to 10th	Night	19% 8% 2 6% 3 3 4 3 5% 5% 42%	3429
	11th to 20th	Night	13% 6% 3 6% 3 3 4 3 4 6% 49%	3480
	21st to end	Night	12% 6% 2 7% 5% 3 4 3 6% 6% 44%	3765
April	1st to 10th	Night	12% 5% 2 6% 3 3 3 3 5% 7% 50%	1900
	11th to 20th	Night	13% 4 1 4 4 3 4 4 5% 8% 50%	1875
	21st to end	Night	13% 5% 2 5% 5% 3 4 4 5% 8% 47%	1900
May	1st to 10th	Night	16% 8% 3 7% 4 4 4 4 5% 7% 39%	3130
	11th to 20th	Night	14% 7% 3 7% 3 3 3 3 5% 6% 45%	2930
	21st to end	Night	12% 7% 2 7% 5% 5% 5% 4 6% 8% 40%	2963
June	1st to 10th	Night	5% 4 2 5% 4 4 4 5% 8% 9% 52%	1520
	11th to 20th	Night	2 3 1 5% 4 4 4 3 6% 8% 60%	1520
	21st to end	Night	2 3 2 3 4 3 4 3 6% 8% 61%	1555
July	1st to 10th	Night	6% 4 2 5% 4 4 5% 5% 6% 11% 48%	2850
	11th to 20th	Night	5% 3 1 4 4 3 4 4 6% 11% 54%	2850
	21st to end	Night	11% 7% 3 7% 4 4 4 4 5% 8% 42%	3098
August	1st to 10th	Night	3 2 1 4 4 4 5% 4 7% 11% 54%	1719
	11th to 20th	Night	5% 3 2 6% 4 4 4 4 7% 11% 50%	1876
	21st to end	Night	5% 4 2 5% 4 5% 5% 4 6% 9% 51%	2080
September	1st to 10th	Night	7% 4 2 4 3 4 3 4 5% 8% 55%	1800
	11th to 20th	Night	10% 4 2 5% 3 4 4 3 5% 6% 54%	1800
	21st to end	Night	8% 4 1 4 3 3 3 3 5% 6% 59%	2031
October	1st to 10th	Night	9% 4 2 4 2 3 4 3 4 5% 62%	2160
	11th to 20th	Night	11% 4 2 4 3 3 3 2 4 5% 59%	2160
	21st to end	Night	17% 5% 1 4 3 4 3 2 3 3 55%	2376
November	1st to 10th	Night	11% 4 2 5% 3 2 3 2 5% 6% 58%	2220
	11th to 20th	Night	11% 5% 2 4 3 3 3 3 5% 6% 56%	2405
	21st to end	Night	15% 6% 2 5% 4 4 3 3 4 5% 50%	2470
December	1st to 10th	Night	18% 7% 2 5% 3 4 3 4 3 4 46%	2657
	11th to 20th	Night	16% 7% 2 6% 4 3 3 2 4 4 49%	3279
	21st to end	Night	15% 7% 3 7% 5% 4 4 3 4 5% 43%	4715

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	44% 3 6% 25% 20% 3	2848
	11th to 20th	Day	40% 3 8% 24% 21% 3	2850
	21st to end	Day	44% 3 7% 18% 25% 4	3135
February	1st to 10th	Day	46% 4 10% 21% 16% 3	1710
	11th to 20th	Day	45% 3 7% 20% 18% 6%	1834
	21st to end	Day	50% 4 7% 17% 16% 8%	1575
March	1st to 10th	Day	49% 5% 7% 12% 18% 9%	3436
	11th to 20th	Day	40% 5% 8% 24% 19% 5%	3480
	21st to end	Day	44% 4 8% 22% 20% 2	3864
April	1st to 10th	Day	38% 6% 9% 23% 20% 4	2280
	11th to 20th	Day	40% 4 9% 21% 18% 7%	2254
	21st to end	Day	41% 6% 10% 22% 19% 2	2280
May	1st to 10th	Day	43% 8% 10% 21% 15% 2	3800
	11th to 20th	Day	37% 9% 13% 27% 14% 1	3958
	21st to end	Day	42% 9% 12% 24% 12% 2	4607
June	1st to 10th	Day	35% 8% 12% 27% 17% 2	2660
	11th to 20th	Day	29% 7% 13% 29% 19% 3	2660
	21st to end	Day	27% 7% 14% 27% 20% 5%	2616
July	1st to 10th	Day	35% 8% 16% 28% 12% 1	4056
	11th to 20th	Day	27% 6% 10% 33% 20% 3	4051
	21st to end	Day	46% 7% 14% 24% 8%	4325
August	1st to 10th	Day	31% 9% 17% 29% 13% 1	2423
	11th to 20th	Day	36% 9% 13% 26% 15% 3	2245
	21st to end	Day	32% 9% 14% 25% 16% 4	2485
September	1st to 10th	Day	36% 7% 10% 21% 20% 6%	2160
	11th to 20th	Day	34% 6% 10% 18% 24% 6%	2160
	21st to end	Day	30% 4 9% 21% 27% 9%	1905
October	1st to 10th	Day	27% 4 10% 25% 27% 8%	1800
	11th to 20th	Day	31% 3 7% 20% 29% 10%	1800
	21st to end	Day	36% 4 5% 23% 22% 10%	1980
November	1st to 10th	Day	30% 3 7% 26% 25% 8%	1858
	11th to 20th	Day	31% 4 8% 20% 28% 9%	1771
	21st to end	Day	43% 3 6% 19% 23% 6%	1710
December	1st to 10th	Day	42% 6% 6% 24% 17% 5%	1520
	11th to 20th	Day	43% 4 7% 21% 21% 5%	1915
	21st to end	Day	44% 5% 11% 19% 16% 5%	2947
January	1st to 10th	Night	42% 3 7% 19% 27% 3	4108
	11th to 20th	Night	37% 4 9% 21% 25% 4	4120
	21st to end	Night	42% 3 10% 19% 22% 4	4532
February	1st to 10th	Night	44% 4 8% 20% 19% 6%	2470
	11th to 20th	Night	43% 3 7% 21% 19% 6%	2241
	21st to end	Night	41% 4 8% 17% 21% 9%	1884
March	1st to 10th	Night	44% 5% 9% 14% 18% 11%	3429
	11th to 20th	Night	37% 4 8% 26% 19% 6%	3480
	21st to end	Night	39% 4 9% 24% 22% 2	3765
April	1st to 10th	Night	34% 5% 10% 23% 21% 8%	1900
	11th to 20th	Night	32% 5% 7% 24% 22% 10%	1875
	21st to end	Night	35% 5% 10% 23% 23% 3	1900
May	1st to 10th	Night	44% 6% 11% 21% 14% 3	3160
	11th to 20th	Night	38% 6% 13% 23% 18% 1	2931
	21st to end	Night	41% 8% 13% 22% 14% 2	2971
June	1st to 10th	Night	26% 8% 13% 29% 21% 3	1520
	11th to 20th	Night	20% 6% 14% 30% 26% 5%	1520
	21st to end	Night	21% 5% 13% 30% 24% 7%	1555
July	1st to 10th	Night	28% 7% 18% 28% 17% 2	2805
	11th to 20th	Night	22% 6% 12% 33% 22% 4	2796
	21st to end	Night	40% 7% 11% 27% 15%	2999
August	1st to 10th	Night	20% 8% 21% 33% 16% 1	1709
	11th to 20th	Night	26% 8% 15% 29% 18% 3	1876
	21st to end	Night	28% 8% 13% 27% 20% 4	2080
September	1st to 10th	Night	26% 7% 12% 24% 23% 8%	1800
	11th to 20th	Night	30% 6% 10% 20% 26% 8%	1800
	21st to end	Night	26% 4 9% 21% 30% 10%	2031
October	1st to 10th	Night	25% 5% 10% 24% 25% 12%	2160
	11th to 20th	Night	29% 3 6% 19% 32% 11%	2160
	21st to end	Night	36% 3 5% 18% 28% 10%	2376
November	1st to 10th	Night	29% 3 7% 23% 28% 10%	2220
	11th to 20th	Night	29% 3 6% 24% 27% 10%	2405
	21st to end	Night	37% 4 6% 20% 28% 5%	2470
December	1st to 10th	Night	42% 4 7% 20% 21% 7%	2657
	11th to 20th	Night	40% 3 6% 21% 25% 5%	3281
	21st to end	Night	43% 4 9% 19% 20% 4	4715

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	26% 11% 34% 20% 7% 2	270
	11th to 20th	Day	26% 12% 39% 20% 3 1	270
	21st to end	Day	20% 12% 43% 20% 6%	297
February	1st to 10th	Day	27% 10% 37% 17% 7% 1	270
	11th to 20th	Day	26% 19% 35% 16% 4	270
	21st to end	Day	36% 16% 31% 12% 5%	225
March	1st to 10th	Day	25% 13% 31% 22% 7% 1	270
	11th to 20th	Day	22% 19% 34% 23% 2	270
	21st to end	Day	23% 14% 37% 17% 8% 1	322
April	1st to 10th	Day	17% 13% 33% 25% 11% 1	460
	11th to 20th	Day	23% 11% 31% 23% 11% 1	452
	21st to end	Day	18% 9% 32% 25% 12% 3	460
May	1st to 10th	Day	17% 10% 28% 31% 13% 2	463
	11th to 20th	Day	14% 4 23% 29% 23% 8%	599
	21st to end	Day	9% 4 20% 33% 24% 10%	734
June	1st to 10th	Day	10% 4 12% 27% 31% 16%	680
	11th to 20th	Day	5% 2 12% 29% 37% 14%	680
	21st to end	Day	5% 3 11% 37% 27% 17%	680
July	1st to 10th	Day	5% 2 8% 28% 37% 19%	671
	11th to 20th	Day	5% 2 6% 28% 35% 23%	668
	21st to end	Day	8% 1 7% 26% 37% 21%	739
August	1st to 10th	Day	5% 2 8% 31% 37% 17%	655
	11th to 20th	Day	12% 3 6% 26% 35% 18%	479
	21st to end	Day	9% 2 5% 19% 38% 27%	532
September	1st to 10th	Day	9% 2 5% 24% 39% 21%	450
	11th to 20th	Day	10% 2 11% 20% 36% 22%	450
	21st to end	Day	11% 3 14% 30% 26% 16%	329
October	1st to 10th	Day	10% 2 22% 26% 30% 10%	270
	11th to 20th	Day	13% 9% 32% 25% 16% 6%	270
	21st to end	Day	25% 10% 28% 23% 11% 5%	297
November	1st to 10th	Day	14% 8% 31% 26% 17% 4	270
	11th to 20th	Day	9% 7% 38% 33% 12% 2	270
	21st to end	Day	26% 13% 28% 19% 11% 3	270
December	1st to 10th	Day	20% 14% 34% 20% 11% 3	270
	11th to 20th	Day	27% 8% 34% 19% 12%	270
	21st to end	Day	25% 13% 37% 21% 3 1	297
January	1st to 10th	Night	22% 8% 33% 30% 6%	950
	11th to 20th	Night	22% 9% 37% 27% 5% 1	950
	21st to end	Night	21% 7% 38% 30% 4	1045
February	1st to 10th	Night	25% 8% 33% 28% 6%	950
	11th to 20th	Night	22% 10% 38% 26% 3	765
	21st to end	Night	24% 14% 36% 25% 2	628
March	1st to 10th	Night	20% 8% 33% 34% 5%	580
	11th to 20th	Night	19% 9% 37% 30% 5% 1	570
	21st to end	Night	18% 7% 37% 29% 8%	627
April	1st to 10th	Night	16% 8% 35% 31% 9% 1	570
	11th to 20th	Night	15% 7% 34% 31% 12% 1	563
	21st to end	Night	16% 6% 35% 32% 10% 2	570
May	1st to 10th	Night	15% 5% 21% 46% 13% 1	570
	11th to 20th	Night	15% 4 25% 36% 18% 2	561
	21st to end	Night	9% 3 18% 39% 27% 5%	617
June	1st to 10th	Night	5% 2 10% 38% 40% 4	570
	11th to 20th	Night	2 2 7% 44% 41% 4	570
	21st to end	Night	3 1 9% 41% 41% 6%	570
July	1st to 10th	Night	4 1 6% 34% 45% 9%	555
	11th to 20th	Night	4 1 5% 30% 50% 10%	552
	21st to end	Night	6% 6% 34% 43% 10%	624
August	1st to 10th	Night	4 4 36% 48% 8%	567
	11th to 20th	Night	6% 1 5% 36% 45% 6%	564
	21st to end	Night	7% 1 6% 27% 50% 9%	624
September	1st to 10th	Night	8% 1 7% 32% 47% 5%	540
	11th to 20th	Night	11% 1 8% 33% 42% 5%	540
	21st to end	Night	10% 2 12% 37% 35% 4	655
October	1st to 10th	Night	9% 3 16% 38% 30% 5%	720
	11th to 20th	Night	13% 3 25% 40% 18% 2	720
	21st to end	Night	18% 5% 27% 31% 17% 1	792
November	1st to 10th	Night	13% 4 25% 38% 18% 2	740
	11th to 20th	Night	13% 5% 32% 37% 13%	760
	21st to end	Night	17% 8% 30% 31% 14%	760
December	1st to 10th	Night	21% 7% 29% 36% 7%	947
	11th to 20th	Night	23% 7% 29% 34% 7%	950
	21st to end	Night	22% 9% 33% 31% 5%	1045

Page generated at 2024-08-27 08:49:40. Version ac07

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