Waning Moon II Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Waning Moon II Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 40%	126491
	Night	12% 6% 2 5% 4 4 4 4 6% 8% 45%	124175
Transparency	Day	35% 9% 14% 19% 16% 7%	130217
	Night	34% 7% 14% 19% 17% 8%	128523
Seeing	Day	12% 6% 18% 27% 26% 11%	16003
	Night	12% 5% 19% 30% 26% 8%	25391

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% 5% 2 5% 3 3 4 3 5% 6% 45%	4516
	11th to 20th	Day	14% 7% 2 5% 3 3 3 3 4 4 50%	4520
	21st to end	Day	22% 7% 3 6% 4 4 4 3 5% 6% 36%	4972
February	1st to 10th	Day	16% 8% 3 8% 4 4 4 3 6% 4 40%	2000
	11th to 20th	Day	17% 7% 2 6% 3 3 3 3 5% 7% 43%	1948
	21st to end	Day	16% 7% 2 9% 5% 5% 3 4 4 7% 37%	1650
March	1st to 10th	Day	19% 9% 3 7% 4 4 4 4 5% 7% 36%	4607
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 7% 45%	4980
	21st to end	Day	13% 7% 3 7% 4 5% 5% 4 6% 6% 41%	5783
April	1st to 10th	Day	11% 6% 2 7% 5% 6% 5% 5% 7% 7% 39%	2400
	11th to 20th	Day	13% 7% 2 6% 5% 4 4 4 6% 7% 41%	2374
	21st to end	Day	9% 5% 1 5% 5% 4 5% 5% 6% 9% 46%	2400
May	1st to 10th	Day	15% 7% 3 7% 5% 5% 5% 4 7% 9% 34%	5405
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 7% 9% 46%	5404
	21st to end	Day	6% 4 2 6% 5% 4 5% 5% 8% 13% 42%	5932
June	1st to 10th	Day	9% 6% 2 7% 5% 7% 7% 6% 9% 10% 32%	2530
	11th to 20th	Day	4 5% 2 7% 6% 7% 8% 6% 10% 12% 33%	2589
	21st to end	Day	6% 7% 2 7% 7% 8% 8% 7% 11% 11% 27%	2600
July	1st to 10th	Day	5% 5% 2 8% 6% 7% 8% 7% 9% 13% 30%	5900
	11th to 20th	Day	4 4 2 7% 6% 6% 8% 6% 9% 13% 33%	5588
	21st to end	Day	5% 5% 2 7% 7% 7% 7% 6% 11% 15% 28%	5922
August	1st to 10th	Day	3 3 1 5% 4 5% 6% 5% 9% 11% 48%	3905
	11th to 20th	Day	6% 4 2 6% 5% 6% 7% 6% 9% 13% 36%	3849
	21st to end	Day	7% 6% 3 10% 7% 7% 7% 6% 7% 9% 32%	4312
September	1st to 10th	Day	9% 7% 2 8% 5% 6% 7% 6% 8% 9% 34%	2400
	11th to 20th	Day	10% 6% 3 7% 5% 5% 6% 5% 7% 9% 38%	2314
	21st to end	Day	7% 5% 2 5% 4 4 6% 4 6% 8% 47%	2200
October	1st to 10th	Day	6% 4 2 5% 4 4 4 5% 6% 7% 54%	2165
	11th to 20th	Day	5% 4 2 5% 4 4 4 3 4 9% 58%	2000
	21st to end	Day	9% 4 1 5% 4 3 3 3 5% 7% 57%	2200
November	1st to 10th	Day	9% 5% 2 4 3 3 4 4 6% 6% 55%	2058
	11th to 20th	Day	11% 4 2 4 3 4 3 3 4 6% 56%	1949
	21st to end	Day	11% 7% 2 6% 4 4 4 4 6% 7% 45%	1890
December	1st to 10th	Day	17% 7% 2 6% 4 4 4 3 5% 5% 42%	2948
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 6% 7% 47%	3373
	21st to end	Day	18% 7% 2 6% 4 4 4 3 4 5% 43%	4908
January	1st to 10th	Night	17% 7% 2 5% 3 3 3 2 5% 6% 47%	5429
	11th to 20th	Night	20% 7% 2 5% 3 3 2 2 4 5% 48%	5440
	21st to end	Night	22% 7% 2 6% 3 3 4 3 5% 7% 38%	5984
February	1st to 10th	Night	17% 7% 3 6% 4 4 3 4 5% 6% 43%	2400
	11th to 20th	Night	19% 8% 3 5% 4 3 3 3 5% 6% 41%	2338
	21st to end	Night	19% 9% 3 5% 4 4 4 4 5% 6% 38%	1980
March	1st to 10th	Night	20% 9% 3 6% 4 4 4 3 5% 6% 37%	5286
	11th to 20th	Night	14% 7% 2 4 4 3 4 3 4 6% 48%	4980
	21st to end	Night	15% 6% 2 5% 4 4 4 3 5% 6% 46%	5130
April	1st to 10th	Night	15% 7% 2 6% 4 3 4 4 5% 6% 45%	2000
	11th to 20th	Night	12% 6% 2 6% 5% 4 3 4 6% 6% 46%	1975
	21st to end	Night	7% 4 1 5% 3 4 4 3 6% 8% 55%	2000
May	1st to 10th	Night	15% 7% 3 7% 5% 5% 4 4 5% 9% 38%	4490
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 6% 8% 46%	4489
	21st to end	Night	6% 5% 2 5% 4 4 5% 4 7% 13% 45%	4922
June	1st to 10th	Night	7% 6% 1 5% 4 5% 6% 5% 8% 11% 43%	1853
	11th to 20th	Night	3 4 2 5% 4 5% 6% 6% 8% 13% 45%	1781
	21st to end	Night	6% 4 3 6% 6% 5% 5% 4 9% 11% 40%	1800
July	1st to 10th	Night	3 4 2 6% 5% 5% 7% 7% 8% 13% 40%	4078
	11th to 20th	Night	3 3 1 5% 4 4 6% 5% 8% 12% 47%	4358
	21st to end	Night	4 4 2 7% 6% 6% 6% 6% 10% 15% 35%	4929
August	1st to 10th	Night	1 2 1 4 3 4 5% 5% 8% 12% 56%	3244
	11th to 20th	Night	3 3 1 5% 4 5% 6% 4 10% 14% 45%	3200
	21st to end	Night	5% 4 2 7% 6% 5% 6% 5% 8% 10% 41%	3586
September	1st to 10th	Night	7% 6% 2 7% 4 6% 6% 5% 8% 11% 40%	2000
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 7% 10% 45%	2065
	21st to end	Night	7% 5% 2 5% 4 5% 4 3 6% 8% 52%	2200
October	1st to 10th	Night	7% 4 2 5% 3 3 3 3 5% 7% 57%	2230
	11th to 20th	Night	5% 4 1 4 3 3 3 3 5% 6% 62%	2400
	21st to end	Night	10% 4 1 5% 4 3 3 3 4 6% 57%	2640
November	1st to 10th	Night	9% 6% 2 5% 3 3 3 2 4 5% 57%	2460
	11th to 20th	Night	12% 4 1 4 3 3 3 2 5% 5% 57%	2666
	21st to end	Night	10% 6% 2 6% 5% 4 4 3 5% 7% 49%	2730
December	1st to 10th	Night	14% 7% 2 7% 5% 4 4 3 5% 6% 43%	4277
	11th to 20th	Night	12% 6% 2 5% 5% 3 4 4 4 6% 50%	4822
	21st to end	Night	19% 10% 3 6% 4 3 3 2 4 4 43%	6013

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	38% 6% 7% 18% 24% 8%	4517
	11th to 20th	Day	37% 4 6% 14% 29% 9%	4520
	21st to end	Day	48% 6% 7% 14% 15% 10%	4972
February	1st to 10th	Day	45% 6% 9% 13% 19% 10%	2000
	11th to 20th	Day	39% 7% 9% 17% 18% 10%	1958
	21st to end	Day	45% 7% 9% 14% 18% 7%	1650
March	1st to 10th	Day	46% 6% 8% 18% 13% 9%	4607
	11th to 20th	Day	35% 7% 9% 15% 19% 15%	4980
	21st to end	Day	40% 8% 12% 17% 16% 8%	5785
April	1st to 10th	Day	37% 9% 12% 17% 17% 9%	2400
	11th to 20th	Day	37% 7% 10% 19% 19% 8%	2374
	21st to end	Day	29% 7% 15% 23% 21% 6%	2400
May	1st to 10th	Day	40% 9% 17% 22% 9% 3	5440
	11th to 20th	Day	29% 8% 18% 26% 17% 1	5408
	21st to end	Day	28% 9% 19% 31% 11% 1	5945
June	1st to 10th	Day	37% 11% 17% 24% 11% 1	2530
	11th to 20th	Day	33% 13% 19% 24% 11% 1	2589
	21st to end	Day	40% 14% 21% 17% 8%	2600
July	1st to 10th	Day	37% 14% 28% 18% 3	5836
	11th to 20th	Day	34% 15% 39% 10% 1	5521
	21st to end	Day	38% 15% 23% 22% 2	5752
August	1st to 10th	Day	22% 11% 18% 28% 22%	3893
	11th to 20th	Day	31% 13% 22% 27% 7% 1	3885
	21st to end	Day	44% 12% 14% 16% 13% 1	4311
September	1st to 10th	Day	39% 12% 18% 17% 11% 4	2400
	11th to 20th	Day	34% 10% 16% 19% 15% 5%	2314
	21st to end	Day	29% 9% 13% 23% 17% 9%	2200
October	1st to 10th	Day	25% 5% 9% 14% 20% 27%	3529
	11th to 20th	Day	14% 3 6% 23% 26% 28%	3240
	21st to end	Day	19% 4 6% 13% 42% 17%	3538
November	1st to 10th	Day	27% 6% 9% 20% 26% 12%	2058
	11th to 20th	Day	30% 5% 6% 19% 28% 12%	1949
	21st to end	Day	36% 6% 9% 19% 20% 11%	1890
December	1st to 10th	Day	43% 6% 7% 15% 23% 6%	2948
	11th to 20th	Day	35% 5% 11% 18% 21% 10%	3370
	21st to end	Day	42% 6% 7% 16% 24% 5%	4908
January	1st to 10th	Night	38% 5% 7% 17% 24% 9%	5429
	11th to 20th	Night	40% 3 6% 15% 28% 8%	5440
	21st to end	Night	46% 4 7% 13% 19% 10%	5984
February	1st to 10th	Night	43% 4 8% 16% 20% 9%	2400
	11th to 20th	Night	43% 6% 7% 15% 19% 11%	2339
	21st to end	Night	43% 6% 10% 15% 14% 11%	1980
March	1st to 10th	Night	44% 6% 10% 13% 17% 9%	5286
	11th to 20th	Night	34% 7% 9% 14% 20% 15%	4980
	21st to end	Night	36% 6% 11% 20% 18% 8%	5130
April	1st to 10th	Night	38% 8% 11% 16% 16% 11%	2000
	11th to 20th	Night	37% 6% 9% 21% 17% 10%	1975
	21st to end	Night	25% 5% 14% 24% 24% 7%	2000
May	1st to 10th	Night	41% 8% 14% 21% 13% 3	4520
	11th to 20th	Night	34% 8% 16% 26% 15% 1	4490
	21st to end	Night	29% 8% 20% 32% 10% 1	4931
June	1st to 10th	Night	32% 9% 21% 26% 12%	1853
	11th to 20th	Night	27% 11% 23% 28% 11% 1	1781
	21st to end	Night	32% 13% 24% 22% 9%	1800
July	1st to 10th	Night	31% 14% 33% 19% 4	4035
	11th to 20th	Night	27% 15% 46% 10% 1	4305
	21st to end	Night	33% 18% 22% 25% 2	4785
August	1st to 10th	Night	18% 10% 22% 29% 21% 1	3232
	11th to 20th	Night	23% 13% 30% 27% 6%	3230
	21st to end	Night	36% 12% 19% 19% 11% 3	3586
September	1st to 10th	Night	35% 12% 20% 17% 12% 5%	2000
	11th to 20th	Night	33% 9% 16% 19% 15% 7%	2065
	21st to end	Night	29% 7% 13% 26% 15% 10%	2200
October	1st to 10th	Night	28% 5% 8% 14% 22% 23%	3646
	11th to 20th	Night	16% 4 5% 20% 28% 27%	3899
	21st to end	Night	19% 3 6% 10% 39% 23%	4252
November	1st to 10th	Night	30% 3 8% 20% 26% 13%	2460
	11th to 20th	Night	30% 4 7% 18% 27% 15%	2666
	21st to end	Night	34% 6% 9% 19% 21% 12%	2730
December	1st to 10th	Night	42% 4 7% 17% 22% 8%	4277
	11th to 20th	Night	34% 5% 12% 19% 19% 11%	4824
	21st to end	Night	45% 5% 7% 15% 21% 7%	6013

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	20% 13% 40% 22% 6%	300
	11th to 20th	Day	17% 16% 32% 28% 7% 1	300
	21st to end	Day	20% 17% 38% 22% 3	330
February	1st to 10th	Day	24% 15% 32% 24% 5% 1	300
	11th to 20th	Day	22% 17% 32% 22% 7%	300
	21st to end	Day	14% 19% 42% 20% 4	249
March	1st to 10th	Day	15% 16% 40% 26% 4	300
	11th to 20th	Day	17% 19% 32% 26% 6%	300
	21st to end	Day	14% 11% 34% 27% 13%	470
April	1st to 10th	Day	16% 12% 31% 30% 10% 1	500
	11th to 20th	Day	14% 13% 32% 28% 12% 2	492
	21st to end	Day	9% 6% 26% 36% 20% 3	500
May	1st to 10th	Day	12% 6% 23% 36% 19% 4	503
	11th to 20th	Day	10% 5% 20% 29% 28% 7%	527
	21st to end	Day	5% 2 14% 36% 30% 12%	573
June	1st to 10th	Day	10% 3 9% 31% 31% 15%	530
	11th to 20th	Day	8% 2 9% 26% 38% 17%	580
	21st to end	Day	7% 2 8% 26% 37% 19%	730
July	1st to 10th	Day	7% 3 5% 22% 39% 24%	721
	11th to 20th	Day	7% 2 3 12% 45% 31%	590
	21st to end	Day	8% 1 3 18% 44% 26%	576
August	1st to 10th	Day	6% 1 3 19% 41% 31%	526
	11th to 20th	Day	7% 1 3 12% 42% 35%	519
	21st to end	Day	10% 2 7% 19% 38% 24%	583
September	1st to 10th	Day	9% 1 7% 23% 41% 19%	530
	11th to 20th	Day	11% 2 9% 22% 39% 16%	530
	21st to end	Day	9% 2 11% 27% 40% 11%	530
October	1st to 10th	Day	7% 2 14% 39% 32% 6%	495
	11th to 20th	Day	5% 4 17% 42% 26% 6%	330
	21st to end	Day	15% 8% 16% 38% 20% 4	363
November	1st to 10th	Day	14% 5% 19% 36% 24% 2	330
	11th to 20th	Day	15% 7% 25% 35% 16% 2	330
	21st to end	Day	13% 7% 36% 32% 10% 2	330
December	1st to 10th	Day	19% 9% 30% 28% 13% 1	306
	11th to 20th	Day	19% 10% 32% 30% 9%	300
	21st to end	Day	23% 9% 31% 26% 10% 1	330
January	1st to 10th	Night	18% 9% 32% 33% 7% 1	800
	11th to 20th	Night	19% 9% 28% 35% 9%	800
	21st to end	Night	22% 8% 31% 32% 6%	880
February	1st to 10th	Night	19% 8% 33% 33% 8%	800
	11th to 20th	Night	22% 11% 30% 29% 8%	783
	21st to end	Night	21% 11% 33% 30% 5%	660
March	1st to 10th	Night	17% 10% 33% 31% 9%	765
	11th to 20th	Night	15% 7% 28% 35% 14% 1	600
	21st to end	Night	14% 7% 28% 35% 15% 1	660
April	1st to 10th	Night	15% 12% 25% 34% 15% 1	600
	11th to 20th	Night	13% 7% 30% 31% 18% 1	593
	21st to end	Night	9% 6% 20% 42% 22% 2	600
May	1st to 10th	Night	10% 3 19% 42% 25% 1	600
	11th to 20th	Night	7% 4 15% 42% 29% 5%	591
	21st to end	Night	6% 2 10% 33% 41% 8%	650
June	1st to 10th	Night	9% 1 8% 32% 41% 10%	600
	11th to 20th	Night	3 2 5% 25% 54% 12%	600
	21st to end	Night	7% 1 7% 22% 44% 20%	600
July	1st to 10th	Night	5% 1 4 15% 51% 24%	585
	11th to 20th	Night	4 1 2 8% 48% 37%	582
	21st to end	Night	4 3 14% 53% 26%	657
August	1st to 10th	Night	2 1 2 14% 48% 34%	597
	11th to 20th	Night	5% 2 11% 49% 33%	594
	21st to end	Night	9% 1 5% 15% 44% 26%	660
September	1st to 10th	Night	10% 1 4 17% 47% 21%	600
	11th to 20th	Night	9% 3 7% 24% 47% 10%	665
	21st to end	Night	9% 2 8% 32% 42% 8%	800
October	1st to 10th	Night	7% 2 13% 36% 35% 7%	800
	11th to 20th	Night	7% 4 17% 37% 29% 6%	800
	21st to end	Night	11% 5% 18% 36% 27% 3	880
November	1st to 10th	Night	11% 5% 16% 41% 23% 3	820
	11th to 20th	Night	13% 6% 22% 38% 18% 2	840
	21st to end	Night	12% 7% 28% 35% 18% 1	840
December	1st to 10th	Night	16% 7% 26% 32% 16% 2	809
	11th to 20th	Night	19% 5% 25% 39% 11% 1	800
	21st to end	Night	24% 9% 27% 30% 10%	880

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