Nocturne Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nocturne Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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	6% 7% 2 6% 4 4 4 3 5% 7% 53%	158570
	Night	7% 8% 3 6% 4 4 4 4 5% 6% 49%	150427
Transparency	Day	32% 4 9% 21% 21% 14%	153287
	Night	35% 4 10% 22% 18% 11%	146717
Seeing	Day	11% 5% 21% 33% 24% 8%	17829
	Night	13% 2 14% 44% 24% 3	27470

By Month

Percentage Cloud Cover SW (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	11% 19% 6% 11% 6% 5% 4 3 4 5% 27%	5318
	11th to 20th	Day	6% 11% 4 8% 5% 5% 4 3 4 6% 44%	5340
	21st to end	Day	8% 12% 4 9% 5% 4 4 3 4 6% 42%	5844
February	1st to 10th	Day	13% 14% 4 8% 4 3 4 4 5% 6% 34%	1890
	11th to 20th	Day	11% 15% 4 10% 6% 4 4 4 6% 7% 31%	1913
	21st to end	Day	6% 15% 4 9% 5% 4 5% 4 6% 6% 35%	1730
March	1st to 10th	Day	7% 15% 4 9% 6% 3 4 3 4 5% 40%	4880
	11th to 20th	Day	6% 10% 3 8% 5% 4 4 4 5% 6% 46%	5110
	21st to end	Day	9% 14% 5% 10% 6% 5% 5% 4 5% 7% 31%	5607
April	1st to 10th	Day	10% 10% 3 7% 5% 5% 4 4 6% 7% 41%	2331
	11th to 20th	Day	9% 9% 3 6% 5% 4 4 5% 5% 7% 42%	2697
	21st to end	Day	9% 9% 3 6% 5% 4 5% 4 6% 7% 44%	2730
May	1st to 10th	Day	6% 5% 2 5% 4 3 4 4 5% 7% 56%	7626
	11th to 20th	Day	7% 6% 3 7% 4 4 4 4 6% 7% 49%	7596
	21st to end	Day	5% 5% 2 5% 3 4 4 4 6% 8% 55%	8370
June	1st to 10th	Day	4 4 1 3 3 3 4 5% 6% 8% 57%	2929
	11th to 20th	Day	5% 3 1 4 3 4 3 3 6% 7% 60%	3094
	21st to end	Day	2 2 1 3 2 3 3 3 4 6% 71%	3090
July	1st to 10th	Day	2 2 1 2 2 3 3 3 5% 7% 72%	8219
	11th to 20th	Day	2 2 1 3 3 3 4 3 6% 8% 67%	7730
	21st to end	Day	3 2 1 3 2 3 3 3 5% 7% 69%	8304
August	1st to 10th	Day	3 2 1 3 2 2 2 2 3 5% 74%	7549
	11th to 20th	Day	3 2 1 4 3 3 4 3 5% 7% 65%	7565
	21st to end	Day	5% 3 1 4 3 3 3 4 6% 9% 60%	8374
September	1st to 10th	Day	3 3 1 3 2 2 3 3 5% 5% 70%	2375
	11th to 20th	Day	4 3 1 4 3 3 4 3 5% 6% 65%	2310
	21st to end	Day	7% 3 1 3 2 2 3 3 4 5% 68%	2289
October	1st to 10th	Day	6% 3 1 3 2 3 3 3 4 4 67%	3445
	11th to 20th	Day	6% 5% 2 4 2 3 3 3 5% 7% 60%	3250
	21st to end	Day	6% 6% 2 5% 3 3 3 3 5% 6% 58%	3455
November	1st to 10th	Day	9% 9% 2 6% 6% 4 4 3 5% 6% 46%	1854
	11th to 20th	Day	11% 8% 2 5% 3 4 3 3 6% 8% 46%	1890
	21st to end	Day	9% 11% 3 6% 5% 3 4 3 5% 7% 43%	1686
December	1st to 10th	Day	6% 8% 3 9% 4 4 3 2 4 6% 51%	2700
	11th to 20th	Day	11% 13% 4 10% 5% 5% 6% 4 6% 8% 30%	3106
	21st to end	Day	10% 15% 5% 12% 6% 6% 5% 4 5% 5% 26%	4374
January	1st to 10th	Night	12% 15% 4 8% 5% 4 5% 4 5% 7% 31%	7605
	11th to 20th	Night	8% 12% 5% 8% 4 3 4 3 5% 7% 42%	7650
	21st to end	Night	9% 11% 3 10% 6% 4 4 3 4 6% 41%	8370
February	1st to 10th	Night	13% 15% 4 9% 5% 4 4 4 5% 6% 32%	2730
	11th to 20th	Night	11% 13% 3 7% 5% 4 4 4 4 6% 38%	2589
	21st to end	Night	7% 14% 4 8% 5% 5% 4 4 5% 7% 38%	2076
March	1st to 10th	Night	11% 14% 4 6% 4 4 5% 4 5% 6% 37%	5233
	11th to 20th	Night	6% 9% 3 7% 4 4 5% 5% 6% 7% 43%	5110
	21st to end	Night	10% 10% 3 8% 5% 5% 5% 4 6% 7% 38%	5610
April	1st to 10th	Night	9% 9% 3 7% 4 4 4 3 5% 7% 44%	2285
	11th to 20th	Night	9% 9% 2 8% 5% 4 5% 3 5% 6% 45%	1871
	21st to end	Night	10% 7% 2 6% 4 4 3 4 5% 6% 48%	1890
May	1st to 10th	Night	6% 5% 2 4 4 4 4 4 5% 7% 55%	5321
	11th to 20th	Night	7% 5% 2 5% 3 4 3 3 4 7% 58%	5296
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 8% 52%	5837
June	1st to 10th	Night	5% 3 1 6% 4 3 4 4 7% 8% 56%	1685
	11th to 20th	Night	6% 3 1 5% 3 3 3 3 5% 8% 61%	1518
	21st to end	Night	3 3 1 3 2 2 3 3 5% 7% 68%	1523
July	1st to 10th	Night	3 3 2 5% 3 4 4 3 5% 6% 63%	4740
	11th to 20th	Night	2 3 1 5% 4 5% 4 4 6% 8% 59%	5238
	21st to end	Night	3 4 2 5% 4 4 4 4 6% 8% 58%	5805
August	1st to 10th	Night	3 2 1 3 2 3 3 3 5% 7% 69%	5273
	11th to 20th	Night	3 4 2 7% 4 5% 5% 4 5% 7% 55%	5291
	21st to end	Night	5% 5% 2 6% 5% 5% 5% 4 5% 7% 52%	5842
September	1st to 10th	Night	3 3 1 3 3 3 3 2 4 6% 68%	2241
	11th to 20th	Night	5% 3 1 4 3 2 3 3 4 7% 64%	2310
	21st to end	Night	6% 3 1 3 2 3 3 3 3 4 68%	2288
October	1st to 10th	Night	5% 3 1 3 2 2 2 3 4 4 72%	3750
	11th to 20th	Night	9% 6% 2 5% 3 3 3 3 3 5% 58%	3898
	21st to end	Night	7% 7% 2 5% 3 3 5% 3 5% 7% 54%	4342
November	1st to 10th	Night	10% 7% 2 5% 4 4 4 3 5% 7% 49%	2665
	11th to 20th	Night	10% 7% 3 6% 4 4 4 3 5% 7% 48%	2730
	21st to end	Night	8% 9% 3 6% 5% 4 5% 4 6% 6% 45%	2909
December	1st to 10th	Night	7% 8% 3 6% 3 3 4 3 4 5% 55%	4710
	11th to 20th	Night	11% 11% 3 8% 4 6% 6% 4 5% 6% 35%	5321
	21st to end	Night	13% 14% 4 11% 6% 5% 5% 4 6% 7% 26%	6875

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	59% 6% 18% 11% 5%	5321
	11th to 20th	Day	44% 5% 18% 23% 8% 3	5340
	21st to end	Day	43% 8% 13% 23% 13% 1	5844
February	1st to 10th	Day	52% 7% 18% 17% 6% 1	1890
	11th to 20th	Day	52% 6% 14% 20% 7% 1	1922
	21st to end	Day	49% 6% 15% 21% 8% 2	1730
March	1st to 10th	Day	48% 4 10% 26% 8% 4	4880
	11th to 20th	Day	38% 4 11% 33% 14% 1	5110
	21st to end	Day	54% 4 17% 19% 6% 1	5607
April	1st to 10th	Day	43% 5% 13% 25% 12% 3	2331
	11th to 20th	Day	41% 4 10% 25% 18% 2	2700
	21st to end	Day	39% 4 10% 26% 19% 2	2730
May	1st to 10th	Day	28% 3 8% 27% 29% 6%	7626
	11th to 20th	Day	33% 4 5% 24% 27% 7%	7599
	21st to end	Day	27% 4 5% 29% 31% 4	8371
June	1st to 10th	Day	23% 5% 10% 24% 31% 6%	2929
	11th to 20th	Day	22% 4 8% 17% 30% 19%	3094
	21st to end	Day	14% 3 3 14% 32% 33%	3090
July	1st to 10th	Day	14% 2 1 9% 22% 51%	8151
	11th to 20th	Day	16% 2 2 13% 29% 38%	7659
	21st to end	Day	16% 2 4 12% 28% 38%	8120
August	1st to 10th	Day	15% 2 2 12% 26% 43%	5978
	11th to 20th	Day	24% 2 5% 21% 30% 18%	5964
	21st to end	Day	17% 2 6% 26% 27% 22%	6569
September	1st to 10th	Day	17% 3 5% 16% 32% 28%	2375
	11th to 20th	Day	21% 4 6% 19% 32% 19%	2310
	21st to end	Day	19% 3 6% 23% 37% 12%	2289
October	1st to 10th	Day	22% 3 5% 18% 30% 22%	3445
	11th to 20th	Day	26% 3 8% 31% 25% 8%	3250
	21st to end	Day	28% 3 12% 38% 17% 1	3455
November	1st to 10th	Day	40% 4 15% 25% 15% 1	1854
	11th to 20th	Day	37% 4 21% 26% 11% 1	1890
	21st to end	Day	41% 5% 18% 27% 9% 1	1686
December	1st to 10th	Day	37% 5% 19% 30% 8% 1	2700
	11th to 20th	Day	52% 7% 18% 22% 2	3104
	21st to end	Day	57% 8% 12% 18% 6%	4374
January	1st to 10th	Night	52% 6% 17% 22% 3	7605
	11th to 20th	Night	43% 5% 17% 27% 6% 1	7650
	21st to end	Night	41% 9% 12% 24% 12% 1	8370
February	1st to 10th	Night	53% 7% 15% 19% 6%	2730
	11th to 20th	Night	47% 5% 13% 22% 11% 1	2590
	21st to end	Night	45% 5% 12% 26% 10% 2	2076
March	1st to 10th	Night	47% 5% 7% 26% 9% 5%	5233
	11th to 20th	Night	38% 4 11% 28% 17% 1	5110
	21st to end	Night	44% 5% 19% 22% 9% 1	5610
April	1st to 10th	Night	41% 4 12% 24% 12% 6%	2285
	11th to 20th	Night	40% 4 8% 23% 22% 3	1871
	21st to end	Night	36% 4 9% 27% 21% 3	1890
May	1st to 10th	Night	28% 4 8% 24% 31% 6%	5319
	11th to 20th	Night	27% 3 4 24% 31% 11%	5297
	21st to end	Night	30% 3 5% 25% 32% 4	5838
June	1st to 10th	Night	23% 5% 12% 21% 30% 9%	1685
	11th to 20th	Night	22% 4 6% 19% 29% 20%	1518
	21st to end	Night	17% 3 2 15% 29% 34%	1523
July	1st to 10th	Night	23% 2 2 8% 21% 44%	4700
	11th to 20th	Night	24% 2 3 10% 23% 38%	5186
	21st to end	Night	24% 3 3 11% 24% 35%	5677
August	1st to 10th	Night	17% 2 2 10% 25% 44%	4168
	11th to 20th	Night	32% 3 5% 17% 24% 19%	4168
	21st to end	Night	28% 3 4 15% 24% 27%	4578
September	1st to 10th	Night	18% 3 4 14% 26% 35%	2241
	11th to 20th	Night	22% 3 6% 16% 32% 22%	2310
	21st to end	Night	22% 3 5% 19% 34% 18%	2288
October	1st to 10th	Night	17% 2 6% 15% 39% 21%	3750
	11th to 20th	Night	31% 2 4 26% 27% 9%	3898
	21st to end	Night	31% 3 8% 35% 20% 3	4342
November	1st to 10th	Night	35% 4 13% 28% 17% 3	2665
	11th to 20th	Night	37% 4 16% 29% 13% 1	2730
	21st to end	Night	39% 5% 15% 29% 10% 1	2909
December	1st to 10th	Night	34% 4 17% 37% 8% 1	4710
	11th to 20th	Night	48% 7% 22% 20% 2	5322
	21st to end	Night	56% 7% 14% 18% 5%	6875

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	26% 3 18% 34% 14% 6%	330
	11th to 20th	Day	15% 4 18% 35% 22% 6%	330
	21st to end	Day	16% 4 17% 38% 19% 5%	363
February	1st to 10th	Day	24% 3 27% 29% 14% 4	330
	11th to 20th	Day	19% 6% 27% 32% 12% 4	398
	21st to end	Day	12% 7% 36% 28% 13% 4	446
March	1st to 10th	Day	16% 8% 24% 35% 14% 3	540
	11th to 20th	Day	11% 8% 31% 30% 17% 3	540
	21st to end	Day	18% 9% 29% 31% 11% 3	594
April	1st to 10th	Day	15% 10% 25% 27% 19% 5%	540
	11th to 20th	Day	12% 14% 29% 28% 14% 3	532
	21st to end	Day	15% 8% 25% 29% 17% 5%	540
May	1st to 10th	Day	7% 10% 26% 30% 24% 3	543
	11th to 20th	Day	14% 7% 23% 27% 22% 7%	568
	21st to end	Day	8% 5% 21% 29% 25% 10%	617
June	1st to 10th	Day	6% 4 18% 33% 31% 9%	769
	11th to 20th	Day	7% 5% 21% 37% 23% 6%	780
	21st to end	Day	3 3 22% 39% 27% 6%	720
July	1st to 10th	Day	2 3 19% 38% 30% 8%	566
	11th to 20th	Day	4 2 16% 37% 32% 9%	564
	21st to end	Day	4 2 13% 38% 35% 9%	619
August	1st to 10th	Day	5% 2 14% 38% 31% 9%	567
	11th to 20th	Day	4 2 13% 34% 36% 11%	557
	21st to end	Day	7% 4 13% 31% 34% 12%	627
September	1st to 10th	Day	3 5% 14% 31% 32% 15%	570
	11th to 20th	Day	6% 3 21% 30% 28% 12%	570
	21st to end	Day	8% 3 18% 26% 33% 12%	563
October	1st to 10th	Day	11% 3 18% 27% 26% 16%	440
	11th to 20th	Day	9% 4 22% 26% 22% 17%	330
	21st to end	Day	9% 3 22% 34% 25% 7%	363
November	1st to 10th	Day	19% 2 17% 34% 17% 11%	330
	11th to 20th	Day	14% 3 21% 34% 22% 7%	330
	21st to end	Day	16% 3 14% 35% 25% 8%	330
December	1st to 10th	Day	16% 2 19% 31% 22% 10%	330
	11th to 20th	Day	18% 5% 12% 41% 20% 4	330
	21st to end	Day	21% 4 19% 34% 15% 6%	363
January	1st to 10th	Night	22% 1 11% 42% 20% 4	840
	11th to 20th	Night	19% 3 13% 39% 21% 5%	840
	21st to end	Night	21% 2 12% 40% 20% 4	924
February	1st to 10th	Night	20% 2 16% 43% 18% 2	840
	11th to 20th	Night	20% 1 14% 45% 17% 2	824
	21st to end	Night	14% 3 18% 47% 15% 3	692
March	1st to 10th	Night	19% 3 15% 47% 15% 3	840
	11th to 20th	Night	13% 3 15% 49% 18% 2	840
	21st to end	Night	17% 3 17% 45% 17% 1	924
April	1st to 10th	Night	14% 4 17% 44% 20% 1	822
	11th to 20th	Night	13% 3 20% 45% 17% 2	623
	21st to end	Night	14% 2 18% 42% 22% 2	630
May	1st to 10th	Night	11% 3 16% 47% 21% 2	630
	11th to 20th	Night	11% 3 15% 38% 30% 3	621
	21st to end	Night	13% 4 14% 37% 28% 4	683
June	1st to 10th	Night	7% 4 14% 40% 33% 1	630
	11th to 20th	Night	8% 3 20% 44% 22% 3	468
	21st to end	Night	4 1 15% 48% 29% 3	420
July	1st to 10th	Night	4 1 11% 44% 36% 3	410
	11th to 20th	Night	4 2 10% 50% 33% 1	577
	21st to end	Night	3 1 6% 48% 38% 3	690
August	1st to 10th	Night	6% 1 9% 50% 33% 1	627
	11th to 20th	Night	6% 1 11% 47% 33% 1	624
	21st to end	Night	5% 1 11% 46% 33% 3	693
September	1st to 10th	Night	4 1 11% 43% 36% 4	782
	11th to 20th	Night	7% 2 9% 44% 33% 5%	840
	21st to end	Night	7% 1 12% 42% 31% 8%	832
October	1st to 10th	Night	9% 1 11% 46% 29% 4	800
	11th to 20th	Night	12% 1 12% 41% 30% 4	800
	21st to end	Night	11% 2 13% 45% 25% 4	880
November	1st to 10th	Night	14% 2 11% 44% 25% 3	820
	11th to 20th	Night	15% 2 13% 49% 19% 3	840
	21st to end	Night	12% 2 14% 44% 22% 4	1019
December	1st to 10th	Night	18% 2 15% 43% 21% 2	1050
	11th to 20th	Night	22% 2 12% 45% 17% 2	1050
	21st to end	Night	24% 3 15% 40% 16% 1	1045

Page generated at 2026-09-26 02:18:42. Version ac07

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