ACME Planetary Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ACME Planetary Observatory clear sky chart from 2005-11-06 to 2024-03-18.

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% 5% 2 5% 5% 3 5% 5% 6% 8% 44%	79103
	Night	13% 6% 2 5% 5% 3 4 5% 5% 7% 45%	80692
Transparency	Day	39% 4 11% 22% 19% 5%	78825
	Night	39% 4 10% 20% 20% 6%	80489
Seeing	Day	16% 7% 22% 25% 20% 10%	14603
	Night	16% 6% 23% 33% 19% 2	24799

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 4 4 2 3 3 3 6% 51%	2836
	11th to 20th	Day	14% 5% 2 4 3 3 3 4 4 5% 54%	2840
	21st to end	Day	18% 8% 2 5% 5% 2 4 4 4 5% 42%	3124
February	1st to 10th	Day	16% 6% 3 5% 4 3 4 3 5% 8% 43%	1710
	11th to 20th	Day	20% 7% 3 4 3 3 3 3 4 5% 45%	1701
	21st to end	Day	19% 7% 2 5% 5% 3 4 3 5% 5% 41%	1725
March	1st to 10th	Day	16% 5% 2 4 4 2 3 3 4 5% 50%	2090
	11th to 20th	Day	14% 5% 3 5% 6% 3 4 5% 5% 7% 42%	2058
	21st to end	Day	15% 6% 3 6% 5% 3 5% 4 5% 6% 41%	2178
April	1st to 10th	Day	10% 4 2 3 4 3 4 4 5% 8% 53%	2060
	11th to 20th	Day	12% 4 2 4 5% 3 4 4 5% 7% 50%	2134
	21st to end	Day	12% 4 2 4 5% 3 5% 5% 5% 6% 50%	2160
May	1st to 10th	Day	8% 5% 2 6% 6% 3 4 5% 6% 9% 45%	2322
	11th to 20th	Day	13% 5% 3 5% 5% 5% 5% 5% 6% 7% 42%	2301
	21st to end	Day	10% 6% 2 5% 6% 4 6% 6% 7% 8% 40%	2531
June	1st to 10th	Day	10% 4 3 5% 6% 3 6% 7% 7% 10% 39%	2340
	11th to 20th	Day	9% 4 2 4 6% 3 6% 6% 8% 11% 41%	2340
	21st to end	Day	7% 5% 2 5% 5% 4 6% 7% 8% 11% 39%	2340
July	1st to 10th	Day	7% 5% 2 5% 7% 4 7% 7% 9% 11% 35%	2340
	11th to 20th	Day	9% 4 2 6% 7% 4 6% 8% 9% 12% 33%	2340
	21st to end	Day	5% 5% 3 6% 7% 4 7% 7% 9% 12% 36%	2547
August	1st to 10th	Day	11% 6% 3 6% 6% 4 6% 8% 8% 11% 30%	2327
	11th to 20th	Day	11% 7% 3 6% 7% 5% 6% 8% 7% 10% 29%	2241
	21st to end	Day	10% 6% 3 6% 5% 3 6% 7% 7% 10% 36%	2376
September	1st to 10th	Day	8% 4 2 6% 5% 4 6% 6% 8% 8% 44%	2160
	11th to 20th	Day	12% 6% 2 6% 5% 3 4 5% 6% 7% 44%	1989
	21st to end	Day	18% 6% 2 6% 5% 3 5% 4 5% 7% 40%	1965
October	1st to 10th	Day	15% 6% 3 4 3 2 3 4 4 6% 49%	1800
	11th to 20th	Day	11% 4 2 4 4 2 4 3 4 5% 56%	1800
	21st to end	Day	11% 5% 2 5% 3 2 2 3 3 5% 58%	1980
November	1st to 10th	Day	13% 5% 2 5% 3 1 2 3 4 5% 56%	1857
	11th to 20th	Day	14% 4 2 3 3 2 4 3 4 6% 54%	1894
	21st to end	Day	14% 5% 2 4 4 3 3 4 4 7% 50%	1710
December	1st to 10th	Day	17% 7% 3 4 5% 3 4 4 5% 7% 40%	1710
	11th to 20th	Day	17% 4 2 4 3 1 2 3 4 6% 54%	2153
	21st to end	Day	17% 6% 3 5% 5% 2 3 4 4 5% 45%	3124
January	1st to 10th	Night	15% 5% 2 4 4 2 3 4 5% 6% 48%	4109
	11th to 20th	Night	13% 6% 3 6% 5% 3 5% 4 5% 5% 45%	4120
	21st to end	Night	18% 7% 3 5% 4 2 3 3 4 5% 45%	4532
February	1st to 10th	Night	16% 5% 2 5% 5% 3 4 4 4 6% 46%	2470
	11th to 20th	Night	19% 6% 2 5% 4 3 4 4 4 6% 43%	2361
	21st to end	Night	15% 6% 3 5% 5% 2 4 4 4 7% 46%	1727
March	1st to 10th	Night	15% 5% 2 6% 4 2 4 3 5% 6% 48%	2090
	11th to 20th	Night	14% 5% 2 5% 6% 4 5% 5% 6% 7% 42%	2068
	21st to end	Night	16% 5% 2 5% 5% 3 5% 4 6% 6% 44%	2178
April	1st to 10th	Night	12% 5% 2 4 4 2 4 4 5% 7% 51%	1898
	11th to 20th	Night	12% 4 3 4 5% 2 4 5% 5% 6% 51%	1775
	21st to end	Night	11% 4 2 4 4 3 5% 5% 5% 7% 51%	1800
May	1st to 10th	Night	7% 6% 3 5% 5% 3 4 6% 6% 7% 47%	1652
	11th to 20th	Night	12% 6% 3 5% 5% 3 4 6% 6% 9% 41%	1592
	21st to end	Night	10% 5% 3 5% 6% 3 5% 7% 6% 9% 40%	1744
June	1st to 10th	Night	10% 5% 3 6% 6% 4 6% 6% 8% 10% 37%	1620
	11th to 20th	Night	11% 4 3 6% 6% 4 5% 6% 7% 10% 38%	1620
	21st to end	Night	8% 5% 3 6% 6% 4 5% 7% 8% 11% 38%	1620
July	1st to 10th	Night	7% 5% 3 7% 8% 5% 7% 6% 8% 9% 35%	1620
	11th to 20th	Night	6% 5% 3 6% 6% 4 7% 7% 9% 13% 34%	1620
	21st to end	Night	6% 5% 3 6% 7% 5% 5% 7% 8% 12% 36%	1771
August	1st to 10th	Night	9% 7% 3 5% 7% 4 5% 7% 8% 11% 34%	1611
	11th to 20th	Night	10% 7% 2 7% 6% 3 7% 6% 7% 10% 35%	1639
	21st to end	Night	10% 6% 3 7% 7% 4 5% 7% 8% 11% 33%	1980
September	1st to 10th	Night	9% 5% 3 5% 6% 4 4 6% 5% 10% 44%	1800
	11th to 20th	Night	12% 6% 3 6% 6% 4 5% 4 6% 7% 42%	1967
	21st to end	Night	18% 7% 3 6% 5% 3 5% 5% 4 7% 38%	1993
October	1st to 10th	Night	14% 5% 2 4 4 2 4 3 4 5% 51%	2160
	11th to 20th	Night	13% 5% 2 4 4 2 3 4 4 6% 54%	2160
	21st to end	Night	12% 5% 2 4 3 2 3 3 4 6% 56%	2376
November	1st to 10th	Night	12% 6% 2 5% 3 2 3 3 3 5% 55%	2221
	11th to 20th	Night	14% 6% 3 4 3 3 4 3 4 7% 50%	2284
	21st to end	Night	14% 5% 2 4 4 3 4 4 5% 6% 51%	2470
December	1st to 10th	Night	18% 7% 3 5% 3 2 4 5% 5% 6% 42%	2470
	11th to 20th	Night	18% 6% 2 5% 4 2 3 3 3 5% 50%	3042
	21st to end	Night	17% 6% 2 5% 4 3 4 4 4 6% 46%	4532

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% 2 4 25% 25% 6%	2837
	11th to 20th	Day	35% 2 5% 19% 30% 9%	2840
	21st to end	Day	46% 2 3 17% 23% 9%	3124
February	1st to 10th	Day	41% 2 9% 21% 21% 6%	1710
	11th to 20th	Day	42% 2 6% 18% 24% 7%	1710
	21st to end	Day	45% 3 7% 19% 20% 7%	1725
March	1st to 10th	Day	37% 2 8% 22% 23% 8%	2090
	11th to 20th	Day	42% 4 9% 21% 17% 7%	2058
	21st to end	Day	43% 4 10% 19% 20% 4	2178
April	1st to 10th	Day	30% 2 11% 24% 26% 7%	2060
	11th to 20th	Day	34% 3 10% 24% 21% 9%	2134
	21st to end	Day	36% 4 10% 26% 20% 5%	2160
May	1st to 10th	Day	36% 4 16% 22% 19% 3	2322
	11th to 20th	Day	42% 4 14% 24% 15% 1	2305
	21st to end	Day	40% 5% 15% 24% 15% 1	2531
June	1st to 10th	Day	39% 5% 16% 25% 14% 1	2340
	11th to 20th	Day	35% 7% 19% 24% 14% 2	2340
	21st to end	Day	36% 8% 17% 23% 14% 2	2340
July	1st to 10th	Day	38% 6% 22% 20% 11% 3	2275
	11th to 20th	Day	39% 8% 23% 21% 6% 2	2271
	21st to end	Day	36% 8% 21% 24% 10% 1	2405
August	1st to 10th	Day	45% 7% 18% 19% 10% 1	2314
	11th to 20th	Day	47% 7% 16% 19% 10% 1	2241
	21st to end	Day	41% 6% 17% 22% 10% 3	2376
September	1st to 10th	Day	35% 5% 18% 18% 18% 5%	2160
	11th to 20th	Day	39% 4 12% 18% 22% 5%	1989
	21st to end	Day	45% 4 8% 22% 16% 5%	1965
October	1st to 10th	Day	37% 3 9% 22% 25% 4	1800
	11th to 20th	Day	32% 2 8% 26% 25% 7%	1800
	21st to end	Day	31% 3 5% 24% 28% 10%	1980
November	1st to 10th	Day	32% 2 6% 20% 30% 9%	1857
	11th to 20th	Day	33% 2 7% 21% 28% 9%	1894
	21st to end	Day	36% 3 7% 23% 23% 9%	1710
December	1st to 10th	Day	44% 3 10% 21% 18% 4	1710
	11th to 20th	Day	35% 1 6% 22% 26% 10%	2150
	21st to end	Day	43% 1 7% 22% 24% 3	3124
January	1st to 10th	Night	38% 2 6% 20% 28% 6%	4109
	11th to 20th	Night	42% 2 6% 17% 26% 7%	4120
	21st to end	Night	43% 2 5% 16% 26% 8%	4532
February	1st to 10th	Night	42% 2 8% 21% 21% 7%	2470
	11th to 20th	Night	44% 2 7% 17% 22% 7%	2363
	21st to end	Night	40% 2 8% 20% 21% 8%	1727
March	1st to 10th	Night	38% 2 8% 19% 24% 9%	2090
	11th to 20th	Night	42% 4 9% 17% 21% 8%	2068
	21st to end	Night	41% 4 11% 20% 19% 5%	2178
April	1st to 10th	Night	34% 4 8% 21% 25% 8%	1898
	11th to 20th	Night	34% 3 9% 23% 22% 9%	1775
	21st to end	Night	33% 4 11% 26% 21% 5%	1800
May	1st to 10th	Night	35% 4 14% 24% 18% 4	1652
	11th to 20th	Night	41% 4 13% 23% 17% 1	1593
	21st to end	Night	40% 6% 14% 25% 13% 2	1745
June	1st to 10th	Night	39% 7% 17% 23% 11% 2	1620
	11th to 20th	Night	40% 8% 17% 21% 13% 2	1620
	21st to end	Night	38% 9% 18% 21% 12% 3	1620
July	1st to 10th	Night	43% 8% 18% 18% 11% 3	1575
	11th to 20th	Night	38% 9% 25% 19% 8% 1	1566
	21st to end	Night	38% 8% 22% 21% 10% 1	1672
August	1st to 10th	Night	42% 7% 21% 23% 6% 1	1600
	11th to 20th	Night	43% 7% 23% 18% 9% 1	1639
	21st to end	Night	43% 7% 18% 21% 9% 2	1980
September	1st to 10th	Night	37% 6% 14% 22% 15% 6%	1800
	11th to 20th	Night	41% 4 13% 17% 21% 3	1967
	21st to end	Night	48% 3 11% 18% 16% 5%	1993
October	1st to 10th	Night	37% 2 8% 22% 25% 5%	2160
	11th to 20th	Night	34% 3 7% 23% 24% 9%	2160
	21st to end	Night	31% 2 6% 23% 25% 12%	2376
November	1st to 10th	Night	34% 2 6% 18% 26% 14%	2221
	11th to 20th	Night	37% 2 6% 17% 26% 12%	2284
	21st to end	Night	35% 3 6% 21% 26% 9%	2470
December	1st to 10th	Night	43% 4 9% 18% 19% 6%	2470
	11th to 20th	Night	40% 2 6% 19% 23% 9%	3044
	21st to end	Night	42% 2 6% 22% 25% 3	4532

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	19% 17% 38% 23% 3	270
	11th to 20th	Day	20% 21% 35% 17% 7%	270
	21st to end	Day	20% 17% 41% 18% 5%	297
February	1st to 10th	Day	19% 16% 37% 21% 7%	270
	11th to 20th	Day	32% 14% 39% 14% 1	270
	21st to end	Day	24% 14% 35% 21% 5%	380
March	1st to 10th	Day	20% 14% 31% 27% 8%	460
	11th to 20th	Day	18% 14% 37% 22% 6% 1	449
	21st to end	Day	21% 12% 34% 24% 8% 2	462
April	1st to 10th	Day	17% 15% 31% 23% 13% 1	420
	11th to 20th	Day	13% 12% 31% 22% 16% 6%	412
	21st to end	Day	15% 8% 27% 28% 18% 3	420
May	1st to 10th	Day	12% 10% 34% 23% 16% 5%	423
	11th to 20th	Day	14% 4 17% 29% 26% 10%	447
	21st to end	Day	17% 2 13% 26% 25% 17%	485
June	1st to 10th	Day	14% 2 15% 30% 27% 12%	450
	11th to 20th	Day	11% 2 15% 28% 27% 16%	450
	21st to end	Day	9% 2 12% 28% 33% 16%	450
July	1st to 10th	Day	9% 2 4 25% 34% 25%	445
	11th to 20th	Day	10% 1 5% 26% 35% 23%	444
	21st to end	Day	7% 1 7% 30% 39% 17%	488
August	1st to 10th	Day	12% 2 8% 28% 28% 22%	446
	11th to 20th	Day	13% 2 5% 22% 34% 24%	439
	21st to end	Day	12% 2 8% 25% 27% 26%	495
September	1st to 10th	Day	9% 2 10% 25% 26% 28%	450
	11th to 20th	Day	15% 2 11% 27% 30% 16%	450
	21st to end	Day	20% 3 15% 30% 24% 8%	450
October	1st to 10th	Day	17% 3 21% 25% 24% 11%	450
	11th to 20th	Day	15% 7% 23% 26% 22% 7%	450
	21st to end	Day	11% 8% 25% 30% 21% 5%	495
November	1st to 10th	Day	20% 5% 25% 29% 16% 4	455
	11th to 20th	Day	17% 8% 33% 28% 11% 2	454
	21st to end	Day	15% 9% 31% 29% 11% 4	270
December	1st to 10th	Day	21% 10% 42% 20% 6%	270
	11th to 20th	Day	23% 10% 33% 22% 9% 2	270
	21st to end	Day	24% 13% 33% 21% 8% 2	297
January	1st to 10th	Night	20% 12% 34% 28% 7% 1	760
	11th to 20th	Night	17% 11% 33% 33% 6%	760
	21st to end	Night	20% 10% 36% 31% 3	836
February	1st to 10th	Night	19% 8% 38% 30% 5%	760
	11th to 20th	Night	24% 13% 39% 23% 1	743
	21st to end	Night	20% 11% 36% 28% 5%	628
March	1st to 10th	Night	19% 9% 34% 32% 5% 1	760
	11th to 20th	Night	18% 11% 35% 27% 8% 1	752
	21st to end	Night	18% 9% 34% 31% 7%	792
April	1st to 10th	Night	15% 13% 32% 32% 8%	720
	11th to 20th	Night	14% 9% 31% 33% 12% 1	711
	21st to end	Night	13% 6% 31% 39% 11%	720
May	1st to 10th	Night	11% 8% 30% 39% 11%	572
	11th to 20th	Night	15% 2 22% 41% 18% 1	531
	21st to end	Night	13% 2 11% 40% 32% 3	584
June	1st to 10th	Night	13% 1 14% 42% 27% 3	540
	11th to 20th	Night	12% 3 12% 34% 32% 7%	540
	21st to end	Night	10% 1 10% 40% 35% 4	540
July	1st to 10th	Night	9% 2 6% 38% 40% 5%	525
	11th to 20th	Night	7% 2 4 35% 45% 7%	522
	21st to end	Night	8% 3 7% 39% 39% 4	591
August	1st to 10th	Night	11% 2 5% 37% 39% 6%	537
	11th to 20th	Night	13% 2 5% 38% 35% 7%	575
	21st to end	Night	13% 1 7% 31% 41% 7%	792
September	1st to 10th	Night	11% 1 7% 33% 43% 6%	720
	11th to 20th	Night	16% 2 10% 31% 37% 4	720
	21st to end	Night	23% 3 14% 32% 26% 3	720
October	1st to 10th	Night	18% 3 16% 30% 28% 5%	720
	11th to 20th	Night	15% 5% 24% 31% 22% 3	720
	21st to end	Night	15% 6% 24% 34% 19% 3	792
November	1st to 10th	Night	16% 6% 22% 36% 15% 3	740
	11th to 20th	Night	17% 9% 28% 34% 13%	760
	21st to end	Night	16% 6% 29% 33% 16% 1	760
December	1st to 10th	Night	20% 8% 28% 36% 7%	760
	11th to 20th	Night	19% 8% 29% 34% 10%	760
	21st to end	Night	22% 8% 26% 35% 8% 1	836

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