Yonderplace Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Yonderplace Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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 6% 8% 43%	126766
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 45%	125214
Transparency	Day	37% 6% 13% 22% 17% 5%	130371
	Night	38% 6% 10% 21% 20% 6%	129678
Seeing	Day	18% 11% 25% 24% 16% 6%	16786
	Night	17% 9% 26% 30% 16% 2	27051

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	16% 5% 2 4 3 2 3 2 3 4 56%	4146
	11th to 20th	Day	13% 6% 2 4 2 2 3 2 4 4 58%	4150
	21st to end	Day	16% 7% 3 6% 4 4 3 3 4 4 47%	4565
February	1st to 10th	Day	13% 6% 2 5% 5% 4 5% 4 6% 7% 43%	1800
	11th to 20th	Day	22% 6% 1 5% 4 4 4 3 4 5% 43%	1753
	21st to end	Day	19% 6% 2 6% 4 4 5% 2 5% 7% 40%	1777
March	1st to 10th	Day	17% 8% 3 6% 4 3 4 3 5% 7% 40%	4935
	11th to 20th	Day	11% 5% 2 5% 3 3 3 4 5% 7% 52%	4980
	21st to end	Day	17% 5% 2 5% 5% 4 4 3 5% 5% 44%	5465
April	1st to 10th	Day	11% 4 1 5% 3 4 4 3 6% 8% 51%	2330
	11th to 20th	Day	11% 5% 2 6% 4 4 3 3 5% 7% 49%	2374
	21st to end	Day	14% 6% 2 6% 5% 5% 4 4 6% 6% 43%	2413
May	1st to 10th	Day	10% 7% 2 6% 5% 5% 6% 5% 9% 10% 34%	5862
	11th to 20th	Day	19% 8% 3 7% 5% 5% 5% 5% 6% 8% 29%	5861
	21st to end	Day	13% 5% 2 5% 4 4 5% 4 6% 9% 42%	6433
June	1st to 10th	Day	9% 4 2 5% 5% 5% 6% 5% 8% 10% 43%	2644
	11th to 20th	Day	9% 5% 2 6% 4 5% 4 4 8% 10% 43%	2737
	21st to end	Day	7% 4 2 6% 5% 5% 5% 5% 8% 12% 41%	2600
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 10% 40%	5900
	11th to 20th	Day	8% 5% 2 6% 5% 6% 7% 6% 9% 15% 31%	5900
	21st to end	Day	8% 6% 3 6% 5% 6% 6% 5% 8% 11% 36%	6424
August	1st to 10th	Day	17% 7% 3 7% 5% 5% 6% 5% 7% 11% 27%	4234
	11th to 20th	Day	9% 5% 2 7% 4 5% 6% 5% 8% 11% 37%	4080
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 10% 51%	4312
September	1st to 10th	Day	11% 4 2 5% 4 5% 4 4 6% 8% 48%	2400
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 6% 7% 42%	2267
	21st to end	Day	21% 7% 2 5% 4 4 4 3 5% 7% 37%	2155
October	1st to 10th	Day	15% 6% 2 5% 3 3 2 2 4 5% 53%	2000
	11th to 20th	Day	15% 4 1 4 3 3 3 3 4 4 56%	2000
	21st to end	Day	12% 5% 2 6% 4 3 3 2 3 5% 55%	2200
November	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 4 6% 55%	2057
	11th to 20th	Day	13% 5% 2 4 3 3 3 3 5% 6% 52%	2046
	21st to end	Day	14% 5% 2 5% 3 3 4 4 5% 6% 50%	1680
December	1st to 10th	Day	14% 5% 2 4 3 3 4 3 4 6% 53%	2680
	11th to 20th	Day	18% 5% 2 5% 3 3 4 3 4 5% 48%	3070
	21st to end	Day	16% 6% 2 5% 3 4 4 4 6% 7% 43%	4536
January	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 5% 55%	6019
	11th to 20th	Night	13% 6% 2 4 3 3 2 2 3 5% 57%	6030
	21st to end	Night	16% 7% 2 5% 3 3 3 2 4 5% 50%	6633
February	1st to 10th	Night	16% 6% 2 5% 4 3 4 4 5% 6% 44%	2601
	11th to 20th	Night	20% 8% 2 5% 2 3 3 4 5% 6% 43%	2533
	21st to end	Night	14% 7% 2 5% 3 4 4 3 5% 5% 47%	1846
March	1st to 10th	Night	17% 6% 2 6% 4 4 4 3 4 5% 44%	4918
	11th to 20th	Night	11% 4 2 4 3 3 3 3 5% 6% 55%	4980
	21st to end	Night	14% 5% 2 6% 4 4 3 3 5% 6% 47%	5467
April	1st to 10th	Night	14% 6% 3 6% 4 3 4 3 5% 7% 45%	2070
	11th to 20th	Night	12% 5% 2 4 3 4 4 4 6% 7% 51%	1975
	21st to end	Night	13% 5% 2 5% 4 4 4 4 5% 8% 47%	2000
May	1st to 10th	Night	13% 7% 3 8% 5% 5% 5% 4 7% 9% 35%	4036
	11th to 20th	Night	22% 7% 3 7% 4 4 4 3 5% 7% 33%	4032
	21st to end	Night	15% 5% 2 5% 4 3 4 4 6% 9% 43%	4421
June	1st to 10th	Night	10% 5% 2 5% 5% 4 4 4 7% 10% 43%	1736
	11th to 20th	Night	9% 4 2 6% 3 5% 5% 5% 9% 11% 41%	1641
	21st to end	Night	7% 4 2 5% 5% 5% 6% 4 8% 12% 41%	1800
July	1st to 10th	Night	10% 6% 3 8% 6% 6% 6% 5% 8% 9% 34%	4058
	11th to 20th	Night	11% 7% 3 9% 6% 7% 7% 6% 9% 10% 26%	4057
	21st to end	Night	11% 7% 3 7% 5% 5% 6% 5% 8% 9% 33%	4427
August	1st to 10th	Night	18% 7% 3 7% 5% 5% 5% 4 8% 10% 28%	2915
	11th to 20th	Night	6% 5% 2 7% 4 5% 5% 5% 8% 11% 42%	2933
	21st to end	Night	8% 4 2 6% 4 5% 4 4 7% 9% 46%	3586
September	1st to 10th	Night	11% 6% 2 5% 4 4 4 3 6% 7% 47%	2000
	11th to 20th	Night	15% 6% 2 5% 5% 4 5% 4 5% 5% 44%	2129
	21st to end	Night	23% 8% 2 6% 5% 4 4 3 5% 4 37%	2244
October	1st to 10th	Night	15% 6% 2 5% 4 4 4 3 4 6% 47%	2400
	11th to 20th	Night	13% 6% 2 5% 3 3 3 2 4 5% 54%	2400
	21st to end	Night	14% 4 1 4 3 3 4 4 4 5% 55%	2640
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 6% 52%	2461
	11th to 20th	Night	14% 5% 2 4 3 3 4 4 4 6% 51%	2569
	21st to end	Night	13% 4 2 5% 4 4 3 3 4 6% 52%	2936
December	1st to 10th	Night	11% 5% 2 4 4 4 4 3 4 5% 53%	4720
	11th to 20th	Night	18% 8% 3 7% 4 4 4 3 4 4 41%	5345
	21st to end	Night	17% 6% 2 5% 3 4 4 3 5% 6% 46%	6656

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	34% 3 5% 22% 29% 8%	4147
	11th to 20th	Day	31% 4 4 21% 31% 10%	4150
	21st to end	Day	41% 3 6% 25% 20% 4	4565
February	1st to 10th	Day	39% 5% 12% 22% 18% 4	1800
	11th to 20th	Day	44% 3 7% 21% 20% 5%	1762
	21st to end	Day	44% 4 11% 16% 19% 6%	1777
March	1st to 10th	Day	43% 4 7% 20% 15% 10%	4935
	11th to 20th	Day	31% 5% 8% 19% 24% 13%	4980
	21st to end	Day	42% 5% 9% 19% 19% 7%	5465
April	1st to 10th	Day	30% 5% 11% 24% 21% 9%	2330
	11th to 20th	Day	35% 5% 11% 22% 20% 6%	2374
	21st to end	Day	40% 6% 11% 23% 16% 4	2413
May	1st to 10th	Day	41% 8% 18% 22% 10% 1	5897
	11th to 20th	Day	51% 7% 11% 20% 9% 2	5865
	21st to end	Day	37% 7% 14% 22% 17% 2	6447
June	1st to 10th	Day	34% 7% 15% 28% 15% 1	2644
	11th to 20th	Day	34% 8% 18% 23% 16% 2	2737
	21st to end	Day	32% 11% 17% 24% 15% 2	2600
July	1st to 10th	Day	35% 10% 19% 19% 13% 3	5835
	11th to 20th	Day	38% 13% 26% 18% 5% 1	5831
	21st to end	Day	38% 10% 17% 24% 12%	6240
August	1st to 10th	Day	48% 8% 18% 22% 5%	4221
	11th to 20th	Day	37% 9% 23% 22% 9% 1	4119
	21st to end	Day	28% 6% 18% 31% 16% 2	4312
September	1st to 10th	Day	33% 7% 16% 18% 21% 4	2400
	11th to 20th	Day	40% 6% 10% 22% 19% 3	2267
	21st to end	Day	47% 6% 11% 18% 16% 3	2155
October	1st to 10th	Day	33% 4 8% 20% 28% 7%	3260
	11th to 20th	Day	22% 2 5% 23% 30% 17%	3240
	21st to end	Day	24% 3 9% 26% 26% 12%	3538
November	1st to 10th	Day	32% 4 8% 24% 27% 6%	2057
	11th to 20th	Day	33% 3 10% 23% 23% 8%	2046
	21st to end	Day	34% 4 9% 24% 25% 5%	1680
December	1st to 10th	Day	34% 4 7% 27% 22% 7%	2680
	11th to 20th	Day	39% 4 11% 19% 21% 5%	3066
	21st to end	Day	39% 5% 13% 25% 17% 1	4536
January	1st to 10th	Night	32% 4 5% 19% 28% 11%	6019
	11th to 20th	Night	32% 3 5% 18% 35% 7%	6030
	21st to end	Night	38% 2 5% 27% 22% 6%	6633
February	1st to 10th	Night	40% 5% 10% 23% 19% 4	2601
	11th to 20th	Night	42% 3 9% 19% 20% 6%	2535
	21st to end	Night	39% 4 8% 22% 19% 8%	1846
March	1st to 10th	Night	42% 4 6% 17% 21% 9%	4918
	11th to 20th	Night	30% 5% 7% 16% 28% 14%	4980
	21st to end	Night	37% 4 8% 23% 22% 6%	5467
April	1st to 10th	Night	38% 6% 10% 18% 22% 6%	2070
	11th to 20th	Night	32% 5% 11% 24% 21% 7%	1975
	21st to end	Night	35% 6% 12% 24% 19% 4	2000
May	1st to 10th	Night	44% 7% 16% 20% 11% 2	4063
	11th to 20th	Night	50% 6% 11% 18% 12% 2	4033
	21st to end	Night	37% 7% 14% 25% 14% 2	4429
June	1st to 10th	Night	34% 8% 16% 24% 16% 1	1736
	11th to 20th	Night	34% 9% 19% 21% 15% 2	1641
	21st to end	Night	34% 10% 15% 23% 16% 3	1800
July	1st to 10th	Night	43% 11% 15% 17% 11% 2	4015
	11th to 20th	Night	48% 13% 20% 14% 4 1	4006
	21st to end	Night	44% 9% 16% 21% 10%	4297
August	1st to 10th	Night	49% 9% 18% 17% 7%	2904
	11th to 20th	Night	33% 9% 20% 27% 9% 1	2960
	21st to end	Night	32% 8% 12% 29% 17% 2	3586
September	1st to 10th	Night	36% 7% 13% 22% 18% 5%	2000
	11th to 20th	Night	40% 7% 10% 19% 21% 2	2129
	21st to end	Night	50% 5% 9% 16% 15% 4	2244
October	1st to 10th	Night	38% 5% 9% 19% 24% 6%	3920
	11th to 20th	Night	26% 3 6% 23% 28% 15%	3899
	21st to end	Night	23% 3 6% 28% 26% 14%	4252
November	1st to 10th	Night	34% 4 9% 21% 26% 7%	2461
	11th to 20th	Night	34% 4 8% 18% 25% 10%	2569
	21st to end	Night	33% 4 8% 23% 26% 7%	2936
December	1st to 10th	Night	34% 4 7% 25% 26% 4	4720
	11th to 20th	Night	47% 4 8% 18% 16% 7%	5348
	21st to end	Night	38% 4 12% 26% 18% 2	6656

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	31% 23% 29% 12% 5%	330
	11th to 20th	Day	28% 23% 38% 9% 2	330
	21st to end	Day	27% 21% 38% 12% 2	363
February	1st to 10th	Day	22% 21% 40% 15% 3	300
	11th to 20th	Day	40% 23% 27% 7% 2	300
	21st to end	Day	27% 20% 33% 18% 2	406
March	1st to 10th	Day	24% 18% 32% 20% 6%	500
	11th to 20th	Day	23% 20% 33% 18% 5% 1	500
	21st to end	Day	25% 14% 39% 18% 4 1	550
April	1st to 10th	Day	19% 20% 33% 20% 7% 1	500
	11th to 20th	Day	19% 14% 34% 20% 10% 4	492
	21st to end	Day	19% 12% 32% 24% 10% 2	500
May	1st to 10th	Day	17% 13% 34% 23% 9% 3	503
	11th to 20th	Day	18% 10% 25% 27% 16% 4	527
	21st to end	Day	18% 6% 23% 26% 20% 7%	573
June	1st to 10th	Day	10% 5% 26% 30% 22% 8%	530
	11th to 20th	Day	9% 5% 20% 35% 22% 9%	530
	21st to end	Day	10% 3 20% 32% 26% 9%	530
July	1st to 10th	Day	9% 2 12% 34% 31% 12%	525
	11th to 20th	Day	4 2 12% 34% 33% 15%	524
	21st to end	Day	8% 2 16% 32% 28% 13%	576
August	1st to 10th	Day	17% 4 17% 25% 25% 12%	526
	11th to 20th	Day	12% 3 13% 30% 30% 12%	519
	21st to end	Day	8% 3 15% 29% 30% 16%	583
September	1st to 10th	Day	13% 5% 16% 26% 26% 15%	530
	11th to 20th	Day	17% 5% 13% 28% 25% 11%	530
	21st to end	Day	26% 7% 22% 26% 14% 5%	530
October	1st to 10th	Day	19% 6% 19% 25% 21% 9%	530
	11th to 20th	Day	14% 11% 26% 26% 19% 5%	530
	21st to end	Day	17% 11% 26% 29% 13% 4	583
November	1st to 10th	Day	16% 9% 31% 27% 12% 5%	535
	11th to 20th	Day	19% 14% 30% 24% 13% 1	486
	21st to end	Day	18% 22% 24% 24% 10% 2	220
December	1st to 10th	Day	22% 20% 35% 16% 5% 2	220
	11th to 20th	Day	23% 16% 31% 24% 5% 1	220
	21st to end	Day	25% 16% 34% 13% 8% 3	355
January	1st to 10th	Night	20% 18% 35% 23% 4	840
	11th to 20th	Night	20% 16% 35% 25% 4	840
	21st to end	Night	19% 17% 37% 25% 3	924
February	1st to 10th	Night	20% 15% 36% 25% 4	801
	11th to 20th	Night	26% 18% 37% 18% 1	783
	21st to end	Night	20% 15% 38% 24% 3	660
March	1st to 10th	Night	19% 16% 33% 27% 4	800
	11th to 20th	Night	19% 16% 34% 24% 7% 1	800
	21st to end	Night	19% 13% 40% 22% 5%	880
April	1st to 10th	Night	18% 17% 35% 24% 6%	800
	11th to 20th	Night	15% 12% 35% 26% 11%	791
	21st to end	Night	15% 7% 38% 31% 8%	800
May	1st to 10th	Night	15% 8% 34% 29% 13%	603
	11th to 20th	Night	19% 6% 26% 31% 18% 1	591
	21st to end	Night	16% 3 14% 36% 29% 2	650
June	1st to 10th	Night	10% 3 20% 40% 26% 1	536
	11th to 20th	Night	10% 2 16% 39% 29% 4	441
	21st to end	Night	9% 3 13% 42% 31% 3	600
July	1st to 10th	Night	10% 1 10% 39% 35% 5%	585
	11th to 20th	Night	5% 2 9% 37% 41% 7%	582
	21st to end	Night	9% 3 12% 38% 33% 6%	657
August	1st to 10th	Night	14% 2 9% 40% 30% 5%	597
	11th to 20th	Night	12% 3 9% 36% 37% 3	626
	21st to end	Night	10% 2 12% 34% 35% 6%	880
September	1st to 10th	Night	15% 2 10% 34% 34% 5%	800
	11th to 20th	Night	18% 3 12% 30% 33% 5%	800
	21st to end	Night	26% 4 16% 32% 21% 2	800
October	1st to 10th	Night	17% 3 19% 29% 26% 6%	800
	11th to 20th	Night	16% 8% 25% 32% 18% 1	800
	21st to end	Night	16% 9% 24% 33% 16% 2	880
November	1st to 10th	Night	14% 9% 27% 34% 15% 2	820
	11th to 20th	Night	16% 12% 30% 32% 11%	840
	21st to end	Night	13% 12% 32% 31% 10% 1	840
December	1st to 10th	Night	20% 13% 34% 26% 6%	840
	11th to 20th	Night	18% 11% 35% 30% 6%	840
	21st to end	Night	22% 12% 28% 33% 5%	924

Page generated at 2026-01-29 01:21:41. Version ac07

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