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 2026-10-14.

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	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	149041
	Night	13% 6% 2 6% 4 4 4 4 5% 7% 44%	142729
Transparency	Day	39% 5% 12% 21% 18% 6%	152647
	Night	40% 4 10% 19% 20% 7%	147195
Seeing	Day	16% 8% 23% 26% 19% 9%	18176
	Night	16% 7% 24% 33% 18% 2	28232

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	13% 5% 2 5% 3 3 3 2 3 5% 54%	5258
	11th to 20th	Day	13% 5% 1 4 2 3 2 2 3 4 61%	5280
	21st to end	Day	17% 7% 3 7% 4 4 4 3 5% 5% 40%	5780
February	1st to 10th	Day	15% 7% 3 6% 4 4 3 3 6% 7% 43%	1890
	11th to 20th	Day	21% 7% 2 5% 3 4 3 3 4 5% 44%	1885
	21st to end	Day	19% 8% 2 6% 4 4 3 3 5% 5% 41%	1901
March	1st to 10th	Day	20% 7% 2 6% 4 4 4 3 5% 5% 40%	5045
	11th to 20th	Day	10% 5% 2 5% 4 3 4 3 4 7% 53%	5090
	21st to end	Day	14% 6% 2 6% 4 4 4 3 4 5% 49%	5586
April	1st to 10th	Day	10% 4 1 4 4 4 3 4 6% 9% 52%	2405
	11th to 20th	Day	11% 4 2 5% 4 4 4 3 6% 7% 52%	2494
	21st to end	Day	11% 5% 2 5% 4 4 4 4 5% 6% 49%	2520
May	1st to 10th	Day	12% 6% 3 8% 5% 5% 5% 4 6% 9% 37%	7570
	11th to 20th	Day	14% 5% 2 6% 4 5% 5% 4 6% 8% 41%	7626
	21st to end	Day	12% 6% 3 7% 5% 6% 6% 5% 6% 9% 36%	8391
June	1st to 10th	Day	9% 5% 3 6% 5% 5% 6% 5% 7% 10% 39%	2730
	11th to 20th	Day	8% 5% 2 5% 6% 5% 6% 5% 8% 11% 40%	2730
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 5% 8% 12% 40%	2730
July	1st to 10th	Day	7% 5% 2 7% 5% 6% 6% 6% 9% 11% 36%	7680
	11th to 20th	Day	8% 6% 2 8% 6% 6% 7% 5% 9% 13% 30%	7680
	21st to end	Day	10% 7% 3 8% 5% 5% 6% 5% 8% 11% 32%	8340
August	1st to 10th	Day	18% 8% 4 9% 6% 5% 6% 6% 8% 11% 18%	6014
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 12% 39%	5788
	21st to end	Day	8% 5% 2 5% 4 4 6% 4 6% 10% 45%	6080
September	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 4 7% 8% 46%	2520
	11th to 20th	Day	11% 6% 2 7% 5% 5% 4 4 6% 7% 43%	2319
	21st to end	Day	18% 6% 2 6% 4 4 4 3 5% 7% 40%	2292
October	1st to 10th	Day	15% 6% 2 5% 3 3 3 3 5% 6% 49%	2100
	11th to 20th	Day	11% 4 2 5% 3 3 3 2 4 5% 58%	2030
	21st to end	Day	11% 5% 2 5% 3 3 3 2 3 5% 58%	2200
November	1st to 10th	Day	12% 4 2 6% 3 2 3 3 5% 5% 56%	2057
	11th to 20th	Day	14% 4 2 3 3 3 4 2 4 6% 55%	2092
	21st to end	Day	13% 5% 2 4 4 3 3 3 5% 7% 50%	1890
December	1st to 10th	Day	12% 6% 2 6% 4 4 3 3 4 6% 51%	3020
	11th to 20th	Day	17% 4 2 6% 4 3 4 3 5% 7% 46%	3463
	21st to end	Day	17% 6% 2 6% 4 3 3 3 4 5% 46%	4565
January	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 4 5% 56%	7635
	11th to 20th	Night	12% 5% 2 5% 4 3 3 3 4 5% 55%	7680
	21st to end	Night	17% 8% 3 6% 3 3 3 3 4 5% 44%	8401
February	1st to 10th	Night	16% 6% 2 5% 4 4 3 3 4 6% 46%	2730
	11th to 20th	Night	19% 7% 2 5% 4 4 3 3 5% 5% 42%	2616
	21st to end	Night	15% 7% 2 5% 4 3 3 3 4 7% 46%	1903
March	1st to 10th	Night	19% 8% 2 7% 4 4 3 3 5% 5% 41%	5028
	11th to 20th	Night	11% 5% 1 4 3 3 4 3 5% 7% 53%	5090
	21st to end	Night	14% 4 2 6% 4 4 3 3 5% 6% 49%	5588
April	1st to 10th	Night	12% 6% 2 5% 3 3 4 4 5% 7% 50%	2213
	11th to 20th	Night	10% 5% 2 4 4 3 4 3 5% 7% 52%	2075
	21st to end	Night	10% 4 2 5% 4 5% 6% 4 5% 6% 50%	2100
May	1st to 10th	Night	11% 8% 3 7% 4 5% 4 4 6% 9% 38%	5325
	11th to 20th	Night	14% 7% 2 6% 4 4 4 4 5% 7% 44%	5234
	21st to end	Night	16% 7% 3 7% 5% 5% 5% 4 6% 8% 34%	5761
June	1st to 10th	Night	10% 6% 2 7% 6% 6% 4 5% 9% 10% 36%	1890
	11th to 20th	Night	11% 5% 2 7% 5% 5% 6% 4 7% 10% 38%	1890
	21st to end	Night	7% 5% 2 6% 5% 4 5% 6% 8% 12% 39%	1890
July	1st to 10th	Night	9% 7% 3 8% 6% 6% 6% 5% 8% 11% 32%	5278
	11th to 20th	Night	12% 8% 3 8% 6% 6% 6% 5% 8% 13% 25%	5277
	21st to end	Night	12% 9% 3 9% 6% 6% 6% 5% 7% 11% 25%	5736
August	1st to 10th	Night	19% 8% 3 8% 5% 5% 5% 5% 7% 11% 23%	4135
	11th to 20th	Night	7% 5% 2 6% 5% 5% 6% 6% 8% 13% 37%	4209
	21st to end	Night	9% 5% 3 6% 5% 4 4 4 7% 9% 43%	5045
September	1st to 10th	Night	9% 5% 2 6% 5% 4 4 4 5% 9% 46%	2100
	11th to 20th	Night	12% 7% 2 7% 5% 5% 4 3 6% 7% 41%	2296
	21st to end	Night	18% 7% 3 6% 5% 4 4 3 4 7% 39%	2326
October	1st to 10th	Night	14% 6% 2 5% 4 3 4 3 4 6% 50%	2520
	11th to 20th	Night	13% 5% 2 4 3 3 2 3 4 5% 55%	2437
	21st to end	Night	12% 5% 2 4 2 3 3 3 4 5% 56%	2640
November	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 5% 54%	2461
	11th to 20th	Night	13% 6% 3 4 3 3 3 3 4 7% 51%	2525
	21st to end	Night	13% 5% 2 4 3 4 3 3 5% 6% 52%	2730
December	1st to 10th	Night	13% 7% 2 4 3 3 3 3 4 5% 53%	4380
	11th to 20th	Night	16% 8% 3 8% 4 4 4 3 4 5% 42%	4952
	21st to end	Night	16% 6% 2 6% 3 4 3 3 4 6% 47%	6633

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	35% 2 7% 22% 27% 7%	5259
	11th to 20th	Day	31% 2 3 14% 35% 15%	5280
	21st to end	Day	47% 2 3 18% 20% 10%	5780
February	1st to 10th	Day	41% 2 9% 21% 20% 6%	1890
	11th to 20th	Day	44% 2 6% 18% 23% 7%	1894
	21st to end	Day	45% 3 6% 19% 20% 7%	1901
March	1st to 10th	Day	47% 2 5% 16% 19% 11%	5045
	11th to 20th	Day	33% 3 7% 16% 27% 15%	5090
	21st to end	Day	39% 3 8% 23% 20% 7%	5586
April	1st to 10th	Day	30% 2 11% 24% 25% 6%	2405
	11th to 20th	Day	33% 3 10% 25% 22% 8%	2494
	21st to end	Day	36% 4 11% 25% 20% 4	2520
May	1st to 10th	Day	44% 4 15% 24% 11% 2	7605
	11th to 20th	Day	42% 4 12% 24% 16% 2	7630
	21st to end	Day	44% 6% 13% 19% 16% 2	8405
June	1st to 10th	Day	38% 5% 15% 25% 15% 1	2730
	11th to 20th	Day	34% 7% 19% 24% 14% 2	2730
	21st to end	Day	34% 8% 17% 25% 14% 2	2730
July	1st to 10th	Day	38% 8% 20% 26% 7% 1	7615
	11th to 20th	Day	42% 11% 26% 14% 6% 1	7611
	21st to end	Day	43% 9% 16% 19% 12% 1	8156
August	1st to 10th	Day	56% 10% 20% 10% 4	6001
	11th to 20th	Day	35% 7% 22% 28% 7%	5827
	21st to end	Day	33% 6% 14% 32% 14% 1	6080
September	1st to 10th	Day	34% 5% 17% 21% 20% 4	2520
	11th to 20th	Day	39% 5% 12% 19% 21% 4	2319
	21st to end	Day	44% 4 8% 23% 16% 5%	2292
October	1st to 10th	Day	34% 3 6% 21% 27% 8%	3360
	11th to 20th	Day	20% 2 4 20% 26% 27%	3270
	21st to end	Day	25% 2 4 25% 26% 18%	3538
November	1st to 10th	Day	32% 3 7% 20% 30% 9%	2057
	11th to 20th	Day	32% 2 7% 22% 28% 8%	2092
	21st to end	Day	34% 3 7% 24% 24% 9%	1890
December	1st to 10th	Day	36% 3 7% 18% 25% 11%	3020
	11th to 20th	Day	40% 3 11% 18% 21% 6%	3460
	21st to end	Day	42% 2 8% 24% 23% 2	4565
January	1st to 10th	Night	32% 2 8% 22% 30% 6%	7636
	11th to 20th	Night	35% 2 4 14% 34% 11%	7680
	21st to end	Night	45% 2 3 17% 24% 9%	8401
February	1st to 10th	Night	42% 2 8% 21% 21% 7%	2730
	11th to 20th	Night	44% 2 8% 17% 22% 7%	2618
	21st to end	Night	39% 2 8% 19% 23% 9%	1903
March	1st to 10th	Night	47% 2 5% 13% 25% 7%	5028
	11th to 20th	Night	33% 2 6% 14% 27% 19%	5090
	21st to end	Night	38% 2 8% 22% 23% 7%	5588
April	1st to 10th	Night	35% 3 9% 22% 23% 8%	2213
	11th to 20th	Night	33% 3 9% 24% 23% 9%	2075
	21st to end	Night	34% 4 11% 26% 20% 5%	2100
May	1st to 10th	Night	42% 4 17% 22% 13% 2	5352
	11th to 20th	Night	41% 4 14% 22% 18% 1	5235
	21st to end	Night	48% 5% 11% 21% 13% 2	5771
June	1st to 10th	Night	40% 7% 16% 22% 12% 2	1890
	11th to 20th	Night	39% 8% 16% 22% 13% 1	1890
	21st to end	Night	36% 9% 18% 23% 11% 3	1890
July	1st to 10th	Night	43% 9% 20% 20% 7% 1	5235
	11th to 20th	Night	49% 12% 23% 10% 6% 1	5226
	21st to end	Night	49% 9% 16% 16% 8% 1	5606
August	1st to 10th	Night	55% 10% 20% 13% 3	4124
	11th to 20th	Night	36% 9% 26% 24% 5%	4236
	21st to end	Night	37% 6% 12% 28% 15% 2	5045
September	1st to 10th	Night	35% 6% 13% 24% 16% 6%	2100
	11th to 20th	Night	42% 4 13% 18% 20% 3	2296
	21st to end	Night	46% 3 12% 19% 15% 5%	2326
October	1st to 10th	Night	37% 3 6% 21% 25% 7%	4040
	11th to 20th	Night	23% 2 4 18% 29% 24%	3936
	21st to end	Night	27% 2 5% 24% 25% 17%	4252
November	1st to 10th	Night	33% 3 6% 20% 26% 13%	2461
	11th to 20th	Night	35% 2 6% 17% 27% 12%	2525
	21st to end	Night	34% 3 6% 22% 26% 9%	2730
December	1st to 10th	Night	35% 2 6% 18% 29% 10%	4380
	11th to 20th	Night	46% 4 8% 16% 17% 9%	4954
	21st to end	Night	40% 2 8% 24% 23% 2	6633

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	18% 20% 38% 22% 3	330
	11th to 20th	Day	20% 22% 36% 15% 6%	330
	21st to end	Day	20% 20% 41% 16% 4	363
February	1st to 10th	Day	19% 16% 40% 19% 6%	330
	11th to 20th	Day	35% 15% 37% 12% 1	330
	21st to end	Day	25% 14% 34% 21% 5%	444
March	1st to 10th	Day	20% 15% 31% 26% 8%	540
	11th to 20th	Day	18% 15% 39% 21% 6% 1	540
	21st to end	Day	19% 12% 35% 25% 7% 2	594
April	1st to 10th	Day	17% 14% 32% 24% 12% 2	540
	11th to 20th	Day	12% 12% 33% 24% 14% 5%	532
	21st to end	Day	14% 7% 27% 30% 19% 3	540
May	1st to 10th	Day	13% 10% 35% 23% 14% 4	543
	11th to 20th	Day	16% 4 19% 29% 25% 8%	567
	21st to end	Day	18% 3 16% 26% 22% 14%	617
June	1st to 10th	Day	12% 3 17% 31% 26% 11%	570
	11th to 20th	Day	9% 3 16% 32% 26% 14%	570
	21st to end	Day	7% 3 10% 32% 32% 15%	570
July	1st to 10th	Day	9% 2 5% 26% 36% 22%	565
	11th to 20th	Day	9% 2 5% 28% 35% 22%	564
	21st to end	Day	9% 2 9% 28% 36% 16%	620
August	1st to 10th	Day	16% 3 9% 27% 27% 18%	566
	11th to 20th	Day	12% 2 6% 27% 32% 21%	559
	21st to end	Day	11% 4 10% 28% 25% 22%	627
September	1st to 10th	Day	8% 2 14% 26% 26% 24%	570
	11th to 20th	Day	15% 2 12% 26% 29% 15%	570
	21st to end	Day	21% 4 16% 29% 22% 8%	570
October	1st to 10th	Day	17% 4 21% 25% 23% 9%	570
	11th to 20th	Day	14% 8% 25% 26% 21% 6%	542
	21st to end	Day	12% 8% 26% 29% 21% 5%	583
November	1st to 10th	Day	18% 7% 26% 31% 14% 4	535
	11th to 20th	Day	17% 10% 34% 27% 10% 2	532
	21st to end	Day	15% 12% 32% 27% 10% 3	330
December	1st to 10th	Day	22% 12% 41% 19% 5%	330
	11th to 20th	Day	22% 11% 35% 22% 8% 2	330
	21st to end	Day	23% 14% 34% 20% 7% 1	363
January	1st to 10th	Night	19% 13% 35% 27% 6% 1	840
	11th to 20th	Night	17% 12% 34% 32% 6%	840
	21st to end	Night	20% 10% 37% 30% 2	924
February	1st to 10th	Night	20% 8% 38% 30% 5%	840
	11th to 20th	Night	24% 13% 39% 22% 1	823
	21st to end	Night	21% 12% 36% 27% 5%	692
March	1st to 10th	Night	18% 10% 33% 33% 5%	840
	11th to 20th	Night	17% 12% 35% 27% 8% 1	840
	21st to end	Night	18% 10% 37% 29% 6%	924
April	1st to 10th	Night	15% 13% 33% 32% 7%	840
	11th to 20th	Night	13% 10% 33% 32% 11% 1	831
	21st to end	Night	12% 6% 31% 40% 11%	840
May	1st to 10th	Night	12% 8% 30% 39% 10%	666
	11th to 20th	Night	14% 4 23% 41% 17% 1	621
	21st to end	Night	14% 3 13% 38% 29% 3	683
June	1st to 10th	Night	13% 2 16% 42% 25% 2	630
	11th to 20th	Night	12% 3 14% 34% 30% 6%	630
	21st to end	Night	9% 1 11% 41% 35% 3	630
July	1st to 10th	Night	8% 2 8% 39% 39% 5%	615
	11th to 20th	Night	9% 2 4 35% 42% 7%	612
	21st to end	Night	9% 4 8% 38% 37% 4	690
August	1st to 10th	Night	13% 3 5% 36% 37% 5%	627
	11th to 20th	Night	11% 3 5% 37% 36% 7%	673
	21st to end	Night	12% 2 8% 33% 40% 6%	924
September	1st to 10th	Night	11% 1 9% 33% 40% 5%	840
	11th to 20th	Night	16% 2 10% 33% 35% 4	840
	21st to end	Night	23% 3 15% 32% 24% 3	840
October	1st to 10th	Night	17% 3 16% 32% 27% 5%	840
	11th to 20th	Night	16% 6% 24% 32% 20% 2	813
	21st to end	Night	16% 6% 24% 32% 20% 3	880
November	1st to 10th	Night	16% 6% 24% 36% 14% 3	820
	11th to 20th	Night	16% 10% 29% 33% 12%	840
	21st to end	Night	15% 7% 31% 33% 15% 1	840
December	1st to 10th	Night	20% 9% 28% 35% 7%	840
	11th to 20th	Night	19% 8% 29% 33% 9%	840
	21st to end	Night	21% 9% 27% 35% 8% 1	924

Page generated at 2026-10-11 05:06:30. Version ac07

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