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 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	11% 6% 3 6% 6% 4 6% 6% 7% 8% 39%	75009
	Night	11% 5% 2 5% 5% 3 4 5% 6% 8% 46%	74665
Transparency	Day	25% 40% 8% 12% 11% 4	74747
	Night	23% 39% 9% 12% 12% 6%	74447
Seeing	Day	12% 6% 17% 26% 27% 12%	13485
	Night	12% 5% 18% 30% 27% 8%	23016

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% 6% 2 5% 5% 2 5% 4 6% 6% 43%	1896
	11th to 20th	Day	15% 7% 3 5% 4 3 4 4 5% 5% 46%	1820
	21st to end	Day	19% 6% 3 5% 5% 2 4 4 4 4 44%	1980
February	1st to 10th	Day	17% 7% 3 7% 5% 3 4 3 5% 5% 40%	1800
	11th to 20th	Day	17% 7% 2 5% 4 2 3 4 5% 7% 44%	1748
	21st to end	Day	17% 7% 2 8% 6% 4 4 5% 4 7% 36%	1480
March	1st to 10th	Day	14% 6% 2 5% 5% 3 4 5% 5% 8% 43%	1843
	11th to 20th	Day	14% 7% 4 5% 6% 3 5% 5% 6% 7% 38%	1980
	21st to end	Day	11% 5% 3 5% 4 3 5% 5% 6% 9% 46%	2304
April	1st to 10th	Day	10% 5% 3 6% 5% 4 5% 6% 7% 8% 41%	2160
	11th to 20th	Day	14% 6% 3 6% 5% 3 4 5% 6% 8% 40%	2134
	21st to end	Day	9% 4 1 4 6% 3 4 5% 6% 9% 47%	2160
May	1st to 10th	Day	11% 4 2 4 4 3 5% 5% 6% 8% 46%	2160
	11th to 20th	Day	9% 5% 2 6% 6% 4 5% 6% 7% 8% 42%	2124
	21st to end	Day	7% 5% 2 6% 7% 4 6% 7% 9% 10% 37%	2337
June	1st to 10th	Day	9% 5% 3 6% 7% 4 8% 8% 8% 11% 30%	2276
	11th to 20th	Day	4 4 3 6% 7% 5% 8% 8% 9% 13% 33%	2330
	21st to end	Day	7% 6% 3 6% 8% 6% 9% 9% 10% 11% 26%	2340
July	1st to 10th	Day	8% 7% 3 9% 8% 6% 8% 8% 8% 11% 24%	2340
	11th to 20th	Day	8% 5% 3 8% 9% 6% 9% 9% 9% 11% 24%	2224
	21st to end	Day	7% 6% 3 6% 8% 5% 9% 7% 9% 11% 28%	2350
August	1st to 10th	Day	5% 5% 3 7% 8% 5% 9% 9% 10% 13% 29%	2148
	11th to 20th	Day	10% 6% 3 8% 9% 5% 7% 9% 8% 11% 24%	2125
	21st to end	Day	10% 6% 2 8% 7% 5% 7% 8% 8% 10% 30%	2376
September	1st to 10th	Day	8% 6% 3 7% 7% 4 8% 8% 8% 9% 33%	2160
	11th to 20th	Day	10% 7% 3 6% 6% 4 7% 6% 6% 9% 38%	2084
	21st to end	Day	8% 5% 3 5% 5% 3 6% 5% 7% 8% 45%	1980
October	1st to 10th	Day	5% 3 2 4 5% 3 4 5% 6% 7% 55%	1949
	11th to 20th	Day	5% 4 2 5% 4 3 4 4 4 10% 55%	1800
	21st to end	Day	10% 4 1 4 4 2 3 4 4 8% 55%	1980
November	1st to 10th	Day	9% 4 2 3 3 2 4 4 6% 6% 56%	1858
	11th to 20th	Day	11% 4 2 4 4 3 4 4 4 6% 55%	1764
	21st to end	Day	12% 6% 2 5% 5% 3 4 4 5% 8% 45%	1710
December	1st to 10th	Day	14% 6% 3 5% 5% 3 4 4 5% 7% 44%	1710
	11th to 20th	Day	14% 8% 3 6% 6% 3 4 5% 5% 6% 39%	2153
	21st to end	Day	17% 8% 2 6% 5% 3 5% 5% 5% 6% 38%	3426
January	1st to 10th	Night	16% 6% 2 5% 4 3 3 3 5% 7% 46%	2269
	11th to 20th	Night	16% 6% 2 5% 4 3 4 4 4 5% 48%	2185
	21st to end	Night	18% 7% 2 5% 4 2 4 4 5% 5% 44%	2376
February	1st to 10th	Night	18% 6% 3 5% 5% 3 3 4 5% 5% 44%	2160
	11th to 20th	Night	17% 7% 3 5% 4 2 4 4 5% 7% 43%	2098
	21st to end	Night	20% 8% 4 4 4 3 4 5% 5% 7% 37%	1776
March	1st to 10th	Night	14% 5% 3 5% 5% 3 5% 4 5% 8% 44%	2129
	11th to 20th	Night	13% 6% 3 5% 6% 3 4 5% 5% 8% 41%	1980
	21st to end	Night	13% 4 2 4 4 2 4 3 5% 7% 52%	2050
April	1st to 10th	Night	14% 5% 3 5% 4 2 3 5% 5% 6% 46%	1800
	11th to 20th	Night	12% 6% 2 5% 6% 3 4 5% 6% 7% 45%	1775
	21st to end	Night	7% 4 1 4 3 3 4 4 6% 8% 56%	1800
May	1st to 10th	Night	9% 3 2 3 3 2 4 4 5% 10% 54%	1800
	11th to 20th	Night	6% 4 2 6% 5% 3 5% 6% 7% 9% 48%	1769
	21st to end	Night	5% 3 3 4 5% 4 5% 6% 7% 12% 46%	1938
June	1st to 10th	Night	7% 5% 2 5% 4 4 5% 6% 8% 11% 42%	1668
	11th to 20th	Night	3 3 2 4 4 4 5% 7% 8% 14% 46%	1603
	21st to end	Night	7% 4 3 5% 6% 4 5% 6% 8% 11% 40%	1620
July	1st to 10th	Night	4 5% 3 5% 6% 3 5% 8% 7% 13% 41%	1620
	11th to 20th	Night	5% 4 2 6% 5% 3 7% 7% 9% 14% 39%	1732
	21st to end	Night	5% 3 2 5% 7% 4 6% 6% 9% 15% 39%	1968
August	1st to 10th	Night	2 3 2 4 4 3 5% 7% 9% 12% 48%	1790
	11th to 20th	Night	5% 4 2 5% 6% 5% 6% 6% 10% 15% 36%	1776
	21st to end	Night	7% 4 2 5% 6% 3 6% 6% 9% 12% 39%	1980
September	1st to 10th	Night	6% 5% 2 6% 6% 4 7% 6% 7% 11% 41%	1800
	11th to 20th	Night	8% 5% 2 5% 5% 3 5% 5% 7% 10% 45%	1858
	21st to end	Night	7% 5% 2 4 4 4 5% 4 6% 7% 52%	1980
October	1st to 10th	Night	6% 4 2 4 4 2 4 4 4 7% 59%	2006
	11th to 20th	Night	6% 4 2 4 3 2 4 3 6% 6% 61%	2160
	21st to end	Night	11% 4 2 4 4 2 3 3 4 5% 56%	2376
November	1st to 10th	Night	10% 5% 2 4 4 2 3 3 3 6% 59%	2220
	11th to 20th	Night	12% 4 1 4 4 2 4 3 5% 6% 56%	2412
	21st to end	Night	11% 5% 3 5% 6% 3 4 4 5% 7% 48%	2470
December	1st to 10th	Night	14% 6% 3 6% 5% 2 4 4 4 8% 45%	2470
	11th to 20th	Night	14% 7% 2 5% 6% 3 4 5% 5% 6% 43%	3042
	21st to end	Night	18% 10% 3 6% 5% 3 4 4 4 5% 40%	4209

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	23% 40% 5% 11% 15% 6%	1897
	11th to 20th	Day	23% 42% 5% 9% 14% 6%	1820
	21st to end	Day	29% 37% 4 11% 11% 7%	1980
February	1st to 10th	Day	29% 37% 6% 9% 13% 6%	1800
	11th to 20th	Day	26% 37% 6% 10% 12% 9%	1758
	21st to end	Day	31% 37% 6% 12% 9% 5%	1480
March	1st to 10th	Day	23% 38% 6% 14% 14% 5%	1843
	11th to 20th	Day	25% 38% 8% 9% 13% 6%	1980
	21st to end	Day	23% 38% 9% 13% 14% 4	2304
April	1st to 10th	Day	25% 40% 9% 11% 9% 6%	2160
	11th to 20th	Day	25% 38% 6% 13% 13% 5%	2134
	21st to end	Day	19% 39% 8% 15% 15% 3	2160
May	1st to 10th	Day	24% 38% 8% 17% 10% 2	2160
	11th to 20th	Day	22% 42% 9% 14% 12% 1	2128
	21st to end	Day	22% 42% 10% 16% 10% 1	2337
June	1st to 10th	Day	27% 43% 9% 15% 6% 1	2276
	11th to 20th	Day	21% 41% 11% 18% 8% 2	2330
	21st to end	Day	27% 43% 12% 12% 7%	2340
July	1st to 10th	Day	36% 44% 10% 8% 2	2276
	11th to 20th	Day	30% 45% 12% 10% 2 1	2157
	21st to end	Day	28% 46% 15% 9% 2	2219
August	1st to 10th	Day	25% 43% 13% 12% 6%	2136
	11th to 20th	Day	32% 42% 11% 11% 2 1	2125
	21st to end	Day	30% 42% 10% 11% 6% 1	2376
September	1st to 10th	Day	27% 42% 10% 10% 8% 2	2160
	11th to 20th	Day	28% 39% 9% 11% 7% 5%	2084
	21st to end	Day	21% 39% 8% 11% 13% 7%	1980
October	1st to 10th	Day	18% 38% 5% 12% 14% 13%	1949
	11th to 20th	Day	17% 38% 6% 13% 17% 10%	1800
	21st to end	Day	17% 37% 5% 13% 20% 9%	1980
November	1st to 10th	Day	13% 40% 5% 11% 21% 10%	1858
	11th to 20th	Day	17% 40% 3 11% 20% 8%	1764
	21st to end	Day	24% 39% 5% 12% 13% 7%	1710
December	1st to 10th	Day	23% 41% 7% 12% 12% 5%	1710
	11th to 20th	Day	31% 33% 6% 8% 18% 4	2150
	21st to end	Day	30% 27% 8% 13% 20% 3	3426
January	1st to 10th	Night	23% 40% 5% 9% 16% 6%	2269
	11th to 20th	Night	23% 41% 4 10% 14% 7%	2185
	21st to end	Night	29% 37% 5% 7% 14% 8%	2376
February	1st to 10th	Night	28% 36% 5% 11% 13% 7%	2160
	11th to 20th	Night	28% 38% 4 8% 12% 10%	2099
	21st to end	Night	29% 38% 6% 10% 9% 8%	1776
March	1st to 10th	Night	22% 37% 6% 11% 16% 8%	2129
	11th to 20th	Night	24% 38% 9% 10% 13% 5%	1980
	21st to end	Night	22% 37% 8% 13% 15% 5%	2050
April	1st to 10th	Night	24% 38% 9% 12% 10% 7%	1800
	11th to 20th	Night	24% 36% 6% 15% 11% 7%	1775
	21st to end	Night	15% 37% 9% 17% 16% 6%	1800
May	1st to 10th	Night	21% 37% 8% 20% 12% 2	1800
	11th to 20th	Night	21% 40% 11% 15% 11% 2	1770
	21st to end	Night	19% 40% 11% 19% 10% 1	1939
June	1st to 10th	Night	21% 41% 15% 16% 6%	1668
	11th to 20th	Night	14% 40% 17% 19% 9% 1	1603
	21st to end	Night	21% 42% 15% 15% 7%	1620
July	1st to 10th	Night	27% 44% 18% 8% 3	1575
	11th to 20th	Night	20% 45% 21% 12% 2	1676
	21st to end	Night	23% 46% 17% 11% 2	1858
August	1st to 10th	Night	13% 42% 21% 17% 7%	1778
	11th to 20th	Night	20% 44% 19% 13% 3 1	1776
	21st to end	Night	24% 43% 14% 11% 6% 2	1980
September	1st to 10th	Night	24% 43% 11% 12% 8% 3	1800
	11th to 20th	Night	24% 40% 10% 11% 9% 6%	1858
	21st to end	Night	19% 38% 8% 15% 11% 8%	1980
October	1st to 10th	Night	18% 36% 4 13% 15% 14%	2006
	11th to 20th	Night	17% 37% 5% 13% 17% 10%	2160
	21st to end	Night	16% 36% 5% 12% 19% 11%	2376
November	1st to 10th	Night	14% 40% 2 13% 19% 12%	2220
	11th to 20th	Night	18% 39% 5% 10% 18% 10%	2412
	21st to end	Night	24% 40% 5% 12% 12% 8%	2470
December	1st to 10th	Night	23% 40% 6% 12% 15% 4	2470
	11th to 20th	Night	28% 34% 7% 8% 14% 9%	3044
	21st to end	Night	32% 27% 6% 13% 17% 6%	4209

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% 12% 37% 25% 6%	270
	11th to 20th	Day	17% 13% 30% 30% 8% 1	246
	21st to end	Day	20% 17% 40% 20% 3	264
February	1st to 10th	Day	25% 14% 31% 24% 5%	240
	11th to 20th	Day	22% 16% 31% 24% 7%	240
	21st to end	Day	15% 19% 43% 21% 3	198
March	1st to 10th	Day	11% 15% 40% 30% 4	240
	11th to 20th	Day	17% 17% 33% 26% 6%	240
	21st to end	Day	13% 10% 33% 28% 15% 1	390
April	1st to 10th	Day	14% 9% 32% 33% 12% 1	420
	11th to 20th	Day	16% 13% 29% 27% 13% 2	412
	21st to end	Day	10% 6% 25% 38% 19% 3	420
May	1st to 10th	Day	10% 6% 22% 37% 21% 4	423
	11th to 20th	Day	10% 3 17% 29% 32% 8%	447
	21st to end	Day	5% 2 11% 34% 34% 14%	485
June	1st to 10th	Day	12% 2 7% 31% 30% 18%	450
	11th to 20th	Day	9% 1 7% 25% 41% 17%	494
	21st to end	Day	8% 2 8% 24% 37% 20%	630
July	1st to 10th	Day	8% 3 5% 21% 38% 26%	621
	11th to 20th	Day	8% 2 3 11% 45% 31%	504
	21st to end	Day	9% 1 4 17% 42% 27%	488
August	1st to 10th	Day	6% 1 3 16% 41% 32%	446
	11th to 20th	Day	8% 1 3 11% 42% 35%	439
	21st to end	Day	10% 2 6% 16% 39% 26%	495
September	1st to 10th	Day	7% 1 6% 19% 45% 22%	450
	11th to 20th	Day	12% 2 8% 22% 41% 16%	450
	21st to end	Day	11% 2 9% 26% 41% 12%	450
October	1st to 10th	Day	5% 2 13% 39% 34% 7%	419
	11th to 20th	Day	6% 4 13% 42% 29% 7%	270
	21st to end	Day	17% 7% 14% 36% 21% 5%	297
November	1st to 10th	Day	14% 3 15% 36% 28% 3	270
	11th to 20th	Day	16% 8% 25% 34% 16% 1	270
	21st to end	Day	14% 6% 32% 35% 10% 3	270
December	1st to 10th	Day	17% 7% 30% 29% 15% 1	270
	11th to 20th	Day	21% 11% 31% 30% 8%	270
	21st to end	Day	23% 9% 30% 27% 10% 1	297
January	1st to 10th	Night	19% 9% 31% 34% 7% 1	760
	11th to 20th	Night	18% 7% 28% 36% 10%	729
	21st to end	Night	21% 8% 31% 33% 7%	792
February	1st to 10th	Night	19% 8% 33% 32% 8%	720
	11th to 20th	Night	20% 11% 30% 30% 9%	703
	21st to end	Night	22% 10% 32% 31% 4	592
March	1st to 10th	Night	17% 8% 33% 32% 10%	689
	11th to 20th	Night	16% 6% 27% 36% 15% 1	540
	21st to end	Night	13% 6% 28% 35% 16% 1	594
April	1st to 10th	Night	13% 10% 26% 34% 16% 1	540
	11th to 20th	Night	14% 7% 29% 30% 19% 1	533
	21st to end	Night	8% 5% 20% 44% 21% 2	540
May	1st to 10th	Night	10% 2 18% 43% 26% 1	540
	11th to 20th	Night	6% 3 13% 42% 31% 5%	531
	21st to end	Night	5% 2 9% 32% 43% 9%	584
June	1st to 10th	Night	9% 1 7% 29% 43% 11%	540
	11th to 20th	Night	3 2 4 25% 54% 13%	540
	21st to end	Night	7% 1 6% 22% 43% 21%	540
July	1st to 10th	Night	5% 1 4 14% 52% 24%	525
	11th to 20th	Night	4 1 2 9% 48% 36%	522
	21st to end	Night	5% 3 14% 51% 26%	591
August	1st to 10th	Night	2 1 14% 47% 35%	537
	11th to 20th	Night	6% 2 10% 50% 32%	534
	21st to end	Night	9% 1 5% 15% 43% 27%	594
September	1st to 10th	Night	8% 1 4 16% 48% 24%	540
	11th to 20th	Night	9% 3 7% 23% 47% 11%	598
	21st to end	Night	10% 1 7% 31% 43% 8%	720
October	1st to 10th	Night	6% 2 12% 36% 37% 7%	720
	11th to 20th	Night	8% 4 16% 36% 30% 6%	720
	21st to end	Night	12% 5% 19% 34% 27% 3	792
November	1st to 10th	Night	12% 5% 14% 42% 24% 3	740
	11th to 20th	Night	12% 6% 23% 38% 18% 2	760
	21st to end	Night	13% 7% 26% 35% 18% 1	760
December	1st to 10th	Night	16% 7% 26% 32% 17% 2	760
	11th to 20th	Night	19% 5% 25% 38% 11% 1	760
	21st to end	Night	24% 9% 27% 30% 10%	836

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