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 2024-11-02.

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 5% 4 6% 8% 42%	101124
	Night	14% 6% 2 6% 4 4 4 4 5% 7% 43%	97819
Transparency	Day	40% 4 12% 21% 18% 5%	100936
	Night	41% 4 10% 20% 19% 6%	97677
Seeing	Day	16% 7% 22% 26% 20% 9%	15519
	Night	16% 6% 23% 34% 19% 2	25607

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% 4 3 3 2 3 5% 51%	2836
	11th to 20th	Day	14% 5% 2 5% 3 4 3 3 4 5% 54%	2840
	21st to end	Day	18% 9% 2 6% 4 4 4 3 4 4 42%	3124
February	1st to 10th	Day	16% 7% 3 6% 4 4 3 3 6% 7% 43%	1710
	11th to 20th	Day	20% 7% 3 5% 3 3 2 3 5% 5% 45%	1701
	21st to end	Day	19% 7% 2 6% 4 4 4 3 5% 5% 41%	1725
March	1st to 10th	Day	22% 8% 3 6% 4 4 3 3 5% 5% 37%	3435
	11th to 20th	Day	10% 4 2 5% 4 4 4 3 4 6% 54%	3480
	21st to end	Day	18% 8% 2 6% 4 3 3 3 4 5% 44%	3815
April	1st to 10th	Day	10% 4 1 4 4 4 3 3 5% 9% 53%	2175
	11th to 20th	Day	12% 4 2 5% 4 4 4 3 5% 7% 50%	2254
	21st to end	Day	11% 5% 2 5% 4 4 4 4 5% 6% 50%	2280
May	1st to 10th	Day	9% 7% 3 9% 6% 5% 5% 4 7% 10% 36%	4064
	11th to 20th	Day	16% 6% 3 7% 4 5% 5% 4 6% 7% 36%	4081
	21st to end	Day	6% 4 2 5% 5% 4 5% 4 7% 9% 48%	4476
June	1st to 10th	Day	10% 5% 3 6% 5% 5% 6% 5% 7% 10% 39%	2470
	11th to 20th	Day	8% 5% 2 4 6% 5% 5% 5% 8% 11% 41%	2470
	21st to end	Day	7% 5% 2 7% 5% 5% 6% 5% 8% 11% 38%	2470
July	1st to 10th	Day	7% 6% 3 8% 6% 6% 7% 6% 9% 11% 32%	4120
	11th to 20th	Day	9% 6% 2 9% 6% 6% 6% 6% 9% 12% 29%	4120
	21st to end	Day	9% 9% 3 9% 6% 5% 6% 5% 9% 10% 28%	4466
August	1st to 10th	Day	22% 9% 3 7% 6% 5% 5% 5% 7% 9% 21%	4104
	11th to 20th	Day	10% 6% 2 8% 6% 6% 6% 5% 7% 10% 34%	3926
	21st to end	Day	6% 4 2 5% 3 4 5% 5% 7% 11% 49%	4180
September	1st to 10th	Day	7% 5% 2 7% 5% 5% 6% 5% 7% 8% 44%	2280
	11th to 20th	Day	12% 6% 2 7% 5% 5% 4 4 6% 7% 42%	2099
	21st to end	Day	18% 6% 2 7% 4 4 4 3 5% 7% 39%	2074
October	1st to 10th	Day	14% 6% 2 4 3 3 3 3 5% 6% 49%	1900
	11th to 20th	Day	11% 4 2 5% 3 3 3 2 4 5% 58%	1900
	21st to end	Day	11% 4 2 5% 3 2 3 2 4 5% 59%	2090
November	1st to 10th	Day	13% 5% 2 6% 3 2 3 2 5% 5% 56%	1868
	11th to 20th	Day	14% 4 2 4 3 3 4 3 4 6% 54%	1894
	21st to end	Day	14% 5% 2 4 4 4 3 3 5% 6% 49%	1710
December	1st to 10th	Day	17% 7% 2 5% 4 4 3 4 5% 7% 40%	1710
	11th to 20th	Day	17% 4 2 4 3 2 3 2 4 6% 54%	2153
	21st to end	Day	17% 6% 3 6% 4 3 3 3 5% 5% 45%	3124
January	1st to 10th	Night	15% 6% 2 5% 4 3 3 3 5% 6% 48%	4109
	11th to 20th	Night	13% 6% 2 7% 5% 4 5% 4 5% 5% 45%	4120
	21st to end	Night	17% 7% 3 6% 3 3 3 3 4 5% 45%	4532
February	1st to 10th	Night	16% 6% 2 6% 4 4 3 3 4 6% 45%	2470
	11th to 20th	Night	19% 7% 2 6% 4 4 3 3 5% 5% 43%	2361
	21st to end	Night	15% 7% 2 6% 4 3 3 4 4 7% 46%	1727
March	1st to 10th	Night	24% 9% 3 8% 4 4 4 3 5% 5% 33%	3418
	11th to 20th	Night	12% 5% 1 5% 4 4 4 3 6% 6% 50%	3480
	21st to end	Night	18% 4 2 5% 4 4 3 3 5% 5% 47%	3817
April	1st to 10th	Night	12% 6% 2 5% 3 3 4 4 5% 6% 50%	2003
	11th to 20th	Night	11% 5% 2 5% 4 3 4 3 5% 6% 51%	1875
	21st to end	Night	10% 4 2 4 3 5% 5% 4 5% 6% 51%	1900
May	1st to 10th	Night	9% 8% 3 7% 5% 5% 4 4 6% 9% 40%	2859
	11th to 20th	Night	15% 9% 3 8% 4 4 4 4 5% 6% 38%	2812
	21st to end	Night	7% 4 3 6% 5% 5% 5% 5% 7% 9% 45%	3079
June	1st to 10th	Night	10% 6% 3 7% 6% 6% 4 5% 8% 10% 36%	1710
	11th to 20th	Night	11% 5% 2 7% 6% 5% 6% 4 7% 10% 39%	1710
	21st to end	Night	7% 5% 2 6% 5% 4 5% 6% 8% 11% 38%	1710
July	1st to 10th	Night	9% 7% 3 8% 6% 6% 7% 5% 8% 10% 31%	2840
	11th to 20th	Night	12% 8% 3 8% 5% 5% 7% 5% 8% 12% 28%	2840
	21st to end	Night	15% 11% 4 8% 7% 5% 5% 5% 7% 8% 25%	3087
August	1st to 10th	Night	22% 8% 3 7% 5% 5% 5% 5% 7% 9% 24%	2825
	11th to 20th	Night	9% 6% 2 7% 6% 6% 7% 5% 8% 11% 35%	2868
	21st to end	Night	6% 4 2 5% 5% 4 4 4 8% 11% 47%	3476
September	1st to 10th	Night	9% 5% 2 6% 5% 5% 4 4 5% 10% 44%	1900
	11th to 20th	Night	13% 7% 3 7% 5% 5% 4 3 6% 7% 41%	2077
	21st to end	Night	18% 7% 3 6% 5% 4 4 4 4 7% 38%	2104
October	1st to 10th	Night	14% 6% 2 5% 3 3 4 3 4 5% 51%	2280
	11th to 20th	Night	12% 5% 2 4 3 3 2 3 4 5% 56%	2280
	21st to end	Night	11% 5% 2 4 2 3 3 3 4 5% 57%	2508
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 54%	2244
	11th to 20th	Night	13% 7% 3 4 3 3 3 3 4 7% 49%	2284
	21st to end	Night	14% 5% 1 4 3 4 4 3 5% 6% 51%	2470
December	1st to 10th	Night	18% 7% 3 5% 3 3 4 4 5% 6% 42%	2470
	11th to 20th	Night	18% 6% 2 6% 3 3 3 3 3 4 49%	3042
	21st to end	Night	17% 6% 2 5% 3 4 4 3 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	50% 2 6% 19% 14% 9%	3435
	11th to 20th	Day	33% 2 8% 17% 27% 13%	3480
	21st to end	Day	45% 3 6% 22% 20% 5%	3815
April	1st to 10th	Day	30% 2 11% 24% 27% 7%	2175
	11th to 20th	Day	34% 3 10% 23% 22% 9%	2254
	21st to end	Day	36% 4 11% 26% 20% 5%	2280
May	1st to 10th	Day	45% 3 17% 20% 12% 2	4102
	11th to 20th	Day	48% 3 10% 23% 15% 1	4085
	21st to end	Day	32% 4 16% 23% 22% 3	4489
June	1st to 10th	Day	39% 5% 16% 25% 14% 1	2470
	11th to 20th	Day	34% 6% 18% 24% 15% 2	2470
	21st to end	Day	36% 8% 16% 23% 15% 2	2470
July	1st to 10th	Day	41% 8% 19% 20% 11% 2	4055
	11th to 20th	Day	44% 9% 26% 16% 4 1	4051
	21st to end	Day	47% 10% 16% 17% 10%	4324
August	1st to 10th	Day	58% 6% 17% 12% 6% 1	4091
	11th to 20th	Day	43% 7% 16% 23% 10% 1	3965
	21st to end	Day	29% 6% 14% 34% 16% 2	4180
September	1st to 10th	Day	36% 5% 17% 18% 19% 5%	2280
	11th to 20th	Day	41% 4 12% 17% 21% 4	2099
	21st to end	Day	45% 4 8% 22% 16% 5%	2074
October	1st to 10th	Day	37% 3 9% 22% 25% 4	1900
	11th to 20th	Day	31% 2 7% 25% 25% 10%	1900
	21st to end	Day	30% 3 5% 24% 27% 11%	2090
November	1st to 10th	Day	32% 3 7% 20% 30% 9%	1868
	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	56% 2 7% 14% 16% 6%	3418
	11th to 20th	Night	35% 3 6% 13% 25% 18%	3480
	21st to end	Night	41% 2 7% 20% 22% 7%	3817
April	1st to 10th	Night	34% 3 9% 20% 25% 9%	2003
	11th to 20th	Night	34% 3 8% 23% 22% 9%	1875
	21st to end	Night	33% 4 11% 26% 21% 5%	1900
May	1st to 10th	Night	42% 3 15% 24% 13% 2	2886
	11th to 20th	Night	48% 3 9% 22% 17% 1	2813
	21st to end	Night	35% 4 13% 27% 18% 2	3087
June	1st to 10th	Night	40% 7% 17% 23% 12% 2	1710
	11th to 20th	Night	39% 7% 16% 22% 14% 2	1710
	21st to end	Night	37% 9% 18% 21% 12% 3	1710
July	1st to 10th	Night	45% 10% 18% 16% 9% 1	2795
	11th to 20th	Night	47% 10% 25% 13% 5% 1	2786
	21st to end	Night	55% 7% 14% 16% 9%	2988
August	1st to 10th	Night	57% 5% 18% 16% 4 1	2814
	11th to 20th	Night	41% 8% 22% 21% 7% 1	2895
	21st to end	Night	31% 6% 13% 30% 18% 3	3476
September	1st to 10th	Night	37% 6% 13% 21% 16% 6%	1900
	11th to 20th	Night	43% 4 13% 17% 20% 3	2077
	21st to end	Night	47% 3 11% 18% 15% 5%	2104
October	1st to 10th	Night	37% 2 8% 22% 25% 6%	2280
	11th to 20th	Night	32% 3 7% 23% 24% 11%	2280
	21st to end	Night	31% 2 6% 23% 25% 13%	2508
November	1st to 10th	Night	34% 3 6% 18% 26% 14%	2244
	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% 39% 22% 6% 1	460
	21st to end	Day	22% 11% 35% 23% 7% 2	506
April	1st to 10th	Day	18% 15% 32% 22% 12% 1	460
	11th to 20th	Day	13% 12% 32% 23% 15% 5%	452
	21st to end	Day	15% 8% 27% 29% 17% 3	460
May	1st to 10th	Day	12% 10% 33% 24% 16% 5%	463
	11th to 20th	Day	15% 4 17% 29% 25% 9%	487
	21st to end	Day	16% 2 15% 26% 25% 16%	529
June	1st to 10th	Day	13% 2 15% 32% 27% 11%	490
	11th to 20th	Day	10% 2 15% 30% 28% 15%	490
	21st to end	Day	8% 3 11% 29% 34% 16%	490
July	1st to 10th	Day	9% 2 4 25% 35% 24%	485
	11th to 20th	Day	10% 2 5% 27% 34% 22%	484
	21st to end	Day	8% 2 8% 30% 38% 16%	532
August	1st to 10th	Day	14% 3 8% 27% 27% 21%	486
	11th to 20th	Day	13% 2 6% 24% 33% 22%	479
	21st to end	Day	11% 3 8% 26% 27% 25%	539
September	1st to 10th	Day	9% 2 13% 25% 25% 26%	490
	11th to 20th	Day	17% 2 11% 26% 29% 15%	490
	21st to end	Day	21% 3 16% 30% 23% 7%	490
October	1st to 10th	Day	16% 3 21% 25% 24% 10%	490
	11th to 20th	Day	13% 8% 23% 27% 21% 6%	490
	21st to end	Day	11% 8% 24% 31% 22% 5%	539
November	1st to 10th	Day	20% 5% 25% 30% 16% 4	460
	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	760
	21st to end	Night	19% 9% 35% 30% 7%	836
April	1st to 10th	Night	15% 13% 33% 31% 7%	760
	11th to 20th	Night	14% 10% 31% 33% 12% 1	751
	21st to end	Night	12% 6% 31% 39% 11%	760
May	1st to 10th	Night	11% 8% 29% 40% 11%	603
	11th to 20th	Night	15% 3 22% 42% 17% 1	561
	21st to end	Night	12% 2 12% 40% 32% 3	617
June	1st to 10th	Night	13% 1 14% 42% 26% 3	570
	11th to 20th	Night	12% 3 13% 34% 32% 7%	570
	21st to end	Night	10% 1 11% 40% 34% 4	570
July	1st to 10th	Night	8% 2 7% 39% 39% 5%	555
	11th to 20th	Night	8% 2 4 36% 43% 7%	552
	21st to end	Night	8% 4 7% 39% 38% 4	624
August	1st to 10th	Night	12% 2 5% 37% 39% 6%	567
	11th to 20th	Night	12% 2 6% 39% 34% 7%	608
	21st to end	Night	12% 1 7% 32% 41% 7%	836
September	1st to 10th	Night	11% 1 8% 32% 42% 6%	760
	11th to 20th	Night	17% 2 10% 31% 36% 4	760
	21st to end	Night	23% 3 15% 33% 25% 3	760
October	1st to 10th	Night	17% 3 16% 31% 28% 5%	760
	11th to 20th	Night	14% 5% 25% 32% 21% 3	760
	21st to end	Night	15% 5% 23% 33% 21% 3	836
November	1st to 10th	Night	16% 6% 22% 36% 15% 3	748
	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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