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 2025-05-26.

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% 8% 3 6% 4 4 4 3 5% 6% 51%	118784
	Night	8% 9% 3 6% 4 4 4 4 5% 6% 48%	119409
Transparency	Day	34% 5% 10% 21% 19% 13%	118542
	Night	36% 5% 11% 22% 16% 10%	119240
Seeing	Day	11% 5% 20% 32% 24% 8%	15947
	Night	13% 2 13% 44% 25% 3	25781

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	9% 18% 5% 11% 6% 5% 5% 4 4 5% 27%	4098
	11th to 20th	Day	7% 14% 5% 10% 7% 6% 5% 4 4 5% 31%	4100
	21st to end	Day	9% 13% 4 9% 5% 4 4 3 4 6% 38%	4510
February	1st to 10th	Day	14% 15% 4 9% 4 3 4 4 5% 6% 33%	1800
	11th to 20th	Day	11% 15% 4 10% 5% 4 3 4 5% 7% 32%	1820
	21st to end	Day	6% 15% 4 9% 5% 5% 5% 4 6% 6% 34%	1650
March	1st to 10th	Day	7% 15% 4 9% 6% 3 4 3 4 5% 40%	4774
	11th to 20th	Day	6% 10% 3 8% 5% 4 4 4 6% 6% 45%	5000
	21st to end	Day	10% 14% 5% 10% 6% 5% 5% 4 5% 6% 30%	5486
April	1st to 10th	Day	10% 10% 3 7% 5% 5% 4 4 6% 7% 40%	2220
	11th to 20th	Day	9% 9% 3 6% 4 4 4 4 5% 8% 43%	2567
	21st to end	Day	8% 8% 2 6% 5% 4 5% 3 6% 7% 44%	2600
May	1st to 10th	Day	9% 9% 3 6% 5% 4 5% 5% 6% 8% 41%	4240
	11th to 20th	Day	6% 4 2 4 3 3 4 4 6% 8% 56%	4201
	21st to end	Day	6% 5% 2 6% 4 5% 5% 4 6% 7% 51%	4544
June	1st to 10th	Day	5% 4 1 3 4 3 4 5% 6% 9% 56%	2650
	11th to 20th	Day	5% 3 2 5% 3 4 3 3 6% 7% 58%	2799
	21st to end	Day	2 2 1 3 2 3 3 3 4 6% 72%	2796
July	1st to 10th	Day	2 1 1 2 1 2 2 2 3 5% 80%	4420
	11th to 20th	Day	2 2 1 3 3 3 4 4 6% 8% 65%	4151
	21st to end	Day	4 2 1 2 2 2 3 3 5% 7% 68%	4454
August	1st to 10th	Day	3 2 1 4 3 3 3 3 4 7% 68%	4092
	11th to 20th	Day	3 2 1 3 3 3 3 3 4 6% 68%	4028
	21st to end	Day	2 2 1 2 2 2 2 3 4 7% 73%	4521
September	1st to 10th	Day	3 3 1 3 3 2 3 3 4 5% 70%	2149
	11th to 20th	Day	4 2 1 4 2 3 4 3 5% 6% 66%	2090
	21st to end	Day	7% 3 1 2 2 2 3 3 4 5% 69%	2090
October	1st to 10th	Day	6% 4 1 3 2 3 3 3 4 4 67%	3340
	11th to 20th	Day	6% 5% 2 4 2 3 3 3 5% 7% 60%	3150
	21st to end	Day	6% 6% 2 5% 3 3 3 3 5% 6% 58%	3348
November	1st to 10th	Day	10% 10% 2 6% 6% 4 4 3 5% 6% 45%	1764
	11th to 20th	Day	11% 8% 2 5% 3 4 3 3 6% 8% 47%	1800
	21st to end	Day	10% 11% 3 6% 5% 3 4 3 5% 7% 43%	1606
December	1st to 10th	Day	6% 8% 3 8% 4 4 3 3 4 6% 51%	2620
	11th to 20th	Day	11% 13% 4 10% 5% 5% 6% 4 6% 8% 29%	3026
	21st to end	Day	10% 16% 5% 12% 6% 6% 5% 4 5% 5% 26%	4280
January	1st to 10th	Night	9% 15% 4 8% 5% 4 5% 4 5% 7% 32%	5867
	11th to 20th	Night	11% 15% 6% 10% 5% 4 4 3 5% 7% 29%	5880
	21st to end	Night	11% 13% 4 11% 7% 4 3 3 3 5% 36%	6468
February	1st to 10th	Night	13% 16% 4 9% 5% 4 4 4 5% 6% 31%	2600
	11th to 20th	Night	11% 13% 3 7% 5% 4 4 4 4 5% 39%	2463
	21st to end	Night	7% 14% 4 8% 6% 5% 4 4 5% 7% 37%	1980
March	1st to 10th	Night	11% 14% 3 6% 4 4 5% 4 5% 6% 37%	5119
	11th to 20th	Night	6% 9% 3 7% 4 4 5% 5% 6% 7% 43%	5000
	21st to end	Night	10% 10% 3 8% 5% 5% 5% 4 6% 7% 38%	5489
April	1st to 10th	Night	9% 9% 3 7% 4 4 4 3 5% 7% 44%	2176
	11th to 20th	Night	8% 9% 2 8% 5% 4 5% 3 5% 5% 45%	1781
	21st to end	Night	11% 7% 2 6% 4 4 3 4 5% 6% 49%	1800
May	1st to 10th	Night	9% 8% 2 7% 5% 4 4 3 6% 7% 45%	2950
	11th to 20th	Night	6% 4 1 4 3 4 3 3 5% 6% 59%	2924
	21st to end	Night	9% 5% 2 5% 4 4 4 3 5% 7% 51%	3159
June	1st to 10th	Night	5% 3 1 5% 3 3 4 4 7% 8% 55%	1525
	11th to 20th	Night	6% 3 1 5% 3 3 3 3 6% 8% 59%	1374
	21st to end	Night	2 2 1 3 2 2 3 3 5% 7% 69%	1377
July	1st to 10th	Night	2 2 1 3 2 3 3 3 4 5% 74%	2540
	11th to 20th	Night	2 3 1 5% 4 4 4 4 6% 7% 60%	2814
	21st to end	Night	2 4 2 4 3 3 3 4 5% 6% 66%	3109
August	1st to 10th	Night	3 3 1 4 3 4 4 4 6% 8% 61%	2847
	11th to 20th	Night	3 3 1 6% 4 4 4 3 5% 6% 61%	2811
	21st to end	Night	2 2 1 3 2 3 3 3 4 5% 71%	3146
September	1st to 10th	Night	3 2 1 3 3 3 3 2 4 6% 68%	2028
	11th to 20th	Night	5% 3 1 4 3 2 3 3 4 6% 66%	2090
	21st to end	Night	6% 3 1 3 2 2 3 2 3 4 70%	2090
October	1st to 10th	Night	4 3 1 3 2 2 2 2 4 5% 72%	3635
	11th to 20th	Night	8% 6% 2 5% 3 3 3 3 3 5% 58%	3778
	21st to end	Night	7% 7% 2 5% 3 3 5% 3 5% 7% 53%	4207
November	1st to 10th	Night	10% 7% 2 5% 4 4 4 3 5% 7% 49%	2535
	11th to 20th	Night	10% 7% 3 5% 4 4 4 3 5% 6% 49%	2600
	21st to end	Night	8% 9% 3 6% 4 4 5% 4 6% 6% 45%	2770
December	1st to 10th	Night	7% 7% 3 6% 3 3 4 3 4 5% 56%	4570
	11th to 20th	Night	11% 12% 4 8% 4 6% 6% 4 5% 6% 35%	5181
	21st to end	Night	13% 14% 4 10% 6% 5% 5% 4 6% 7% 26%	6726

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	57% 7% 15% 14% 6%	4099
	11th to 20th	Day	55% 6% 15% 15% 5% 3	4100
	21st to end	Day	46% 10% 11% 20% 13%	4510
February	1st to 10th	Day	53% 7% 18% 16% 6% 1	1800
	11th to 20th	Day	52% 6% 14% 20% 6% 1	1829
	21st to end	Day	50% 6% 15% 20% 7% 2	1650
March	1st to 10th	Day	48% 4 10% 26% 8% 4	4774
	11th to 20th	Day	38% 4 10% 33% 14%	5000
	21st to end	Day	54% 4 17% 19% 5%	5486
April	1st to 10th	Day	43% 5% 14% 24% 12% 3	2220
	11th to 20th	Day	40% 4 10% 25% 18% 2	2570
	21st to end	Day	38% 4 11% 26% 19% 2	2600
May	1st to 10th	Day	39% 4 8% 25% 19% 5%	4240
	11th to 20th	Day	24% 5% 7% 32% 23% 9%	4204
	21st to end	Day	30% 5% 8% 26% 28% 3	4544
June	1st to 10th	Day	23% 6% 11% 25% 29% 6%	2650
	11th to 20th	Day	24% 4 8% 17% 28% 18%	2799
	21st to end	Day	14% 3 3 14% 31% 35%	2796
July	1st to 10th	Day	10% 2 2 9% 16% 61%	4351
	11th to 20th	Day	16% 3 2 9% 25% 45%	4080
	21st to end	Day	16% 3 3 10% 30% 39%	4314
August	1st to 10th	Day	18% 3 3 14% 30% 33%	4078
	11th to 20th	Day	18% 2 3 15% 37% 26%	4067
	21st to end	Day	13% 3 3 15% 34% 32%	4520
September	1st to 10th	Day	17% 3 4 15% 31% 29%	2149
	11th to 20th	Day	20% 4 6% 19% 31% 20%	2090
	21st to end	Day	19% 3 7% 22% 37% 13%	2090
October	1st to 10th	Day	22% 3 5% 18% 30% 23%	3340
	11th to 20th	Day	26% 3 8% 30% 26% 8%	3150
	21st to end	Day	29% 3 12% 38% 18% 1	3348
November	1st to 10th	Day	42% 4 15% 24% 14% 1	1764
	11th to 20th	Day	36% 5% 20% 27% 11% 1	1800
	21st to end	Day	41% 5% 18% 26% 9% 1	1606
December	1st to 10th	Day	36% 5% 19% 31% 8% 1	2620
	11th to 20th	Day	52% 7% 18% 22% 1	3024
	21st to end	Day	57% 8% 12% 17% 6%	4280
January	1st to 10th	Night	50% 7% 15% 24% 4	5867
	11th to 20th	Night	56% 6% 14% 19% 4 1	5880
	21st to end	Night	45% 12% 11% 21% 10%	6468
February	1st to 10th	Night	54% 7% 14% 18% 6% 1	2600
	11th to 20th	Night	46% 6% 13% 23% 12% 1	2464
	21st to end	Night	46% 5% 12% 25% 10% 2	1980
March	1st to 10th	Night	47% 5% 7% 26% 10% 5%	5119
	11th to 20th	Night	38% 5% 11% 29% 17% 1	5000
	21st to end	Night	45% 5% 19% 22% 9% 1	5489
April	1st to 10th	Night	41% 5% 13% 23% 12% 6%	2176
	11th to 20th	Night	40% 4 8% 23% 21% 3	1781
	21st to end	Night	36% 4 9% 27% 20% 3	1800
May	1st to 10th	Night	36% 6% 9% 22% 22% 5%	2950
	11th to 20th	Night	24% 5% 6% 31% 25% 8%	2925
	21st to end	Night	31% 5% 9% 26% 27% 2	3159
June	1st to 10th	Night	23% 5% 13% 23% 29% 7%	1525
	11th to 20th	Night	23% 4 7% 20% 29% 17%	1374
	21st to end	Night	15% 4 3 14% 29% 36%	1377
July	1st to 10th	Night	14% 3 3 8% 16% 57%	2500
	11th to 20th	Night	22% 3 2 8% 25% 41%	2762
	21st to end	Night	19% 3 3 9% 29% 37%	3011
August	1st to 10th	Night	21% 3 4 11% 27% 33%	2838
	11th to 20th	Night	25% 2 3 13% 29% 27%	2838
	21st to end	Night	15% 3 3 10% 29% 39%	3146
September	1st to 10th	Night	18% 3 4 14% 25% 35%	2028
	11th to 20th	Night	20% 3 6% 16% 31% 23%	2090
	21st to end	Night	20% 3 5% 19% 34% 20%	2090
October	1st to 10th	Night	17% 2 6% 15% 39% 22%	3635
	11th to 20th	Night	31% 2 4 26% 28% 9%	3778
	21st to end	Night	31% 3 8% 35% 19% 3	4207
November	1st to 10th	Night	35% 5% 13% 27% 17% 3	2535
	11th to 20th	Night	36% 4 16% 29% 14% 1	2600
	21st to end	Night	39% 5% 15% 29% 11% 1	2770
December	1st to 10th	Night	32% 4 17% 37% 8% 1	4570
	11th to 20th	Night	49% 7% 22% 20% 2	5182
	21st to end	Night	56% 7% 15% 18% 5%	6726

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	25% 2 18% 34% 15% 6%	300
	11th to 20th	Day	17% 5% 19% 34% 20% 5%	300
	21st to end	Day	17% 5% 18% 36% 19% 6%	330
February	1st to 10th	Day	26% 3 27% 29% 13% 3	300
	11th to 20th	Day	20% 6% 27% 31% 12% 4	365
	21st to end	Day	11% 8% 35% 28% 14% 4	414
March	1st to 10th	Day	16% 8% 23% 36% 14% 3	500
	11th to 20th	Day	12% 7% 30% 31% 18% 3	500
	21st to end	Day	18% 9% 27% 32% 10% 3	550
April	1st to 10th	Day	15% 10% 25% 28% 18% 4	500
	11th to 20th	Day	12% 14% 29% 28% 14% 3	492
	21st to end	Day	14% 8% 25% 30% 17% 5%	500
May	1st to 10th	Day	7% 11% 26% 31% 23% 3	503
	11th to 20th	Day	13% 7% 22% 28% 23% 7%	528
	21st to end	Day	9% 5% 21% 29% 25% 11%	550
June	1st to 10th	Day	6% 4 17% 32% 32% 9%	670
	11th to 20th	Day	9% 5% 20% 36% 24% 6%	680
	21st to end	Day	3 2 20% 39% 29% 7%	626
July	1st to 10th	Day	2 3 19% 37% 30% 8%	486
	11th to 20th	Day	4 2 17% 39% 31% 8%	484
	21st to end	Day	5% 1 10% 37% 37% 9%	531
August	1st to 10th	Day	6% 1 15% 37% 32% 9%	487
	11th to 20th	Day	3 2 14% 31% 38% 11%	477
	21st to end	Day	5% 4 13% 30% 36% 12%	539
September	1st to 10th	Day	3 5% 12% 31% 33% 16%	490
	11th to 20th	Day	6% 2 21% 29% 29% 12%	490
	21st to end	Day	8% 3 19% 26% 33% 12%	490
October	1st to 10th	Day	11% 3 17% 25% 27% 17%	405
	11th to 20th	Day	8% 3 21% 25% 24% 18%	300
	21st to end	Day	9% 3 23% 34% 25% 6%	330
November	1st to 10th	Day	21% 2 17% 32% 17% 11%	300
	11th to 20th	Day	13% 3 22% 33% 22% 8%	300
	21st to end	Day	17% 3 12% 35% 25% 8%	300
December	1st to 10th	Day	15% 2 16% 32% 24% 11%	300
	11th to 20th	Day	18% 5% 12% 42% 20% 3	300
	21st to end	Day	22% 3 18% 36% 15% 5%	330
January	1st to 10th	Night	21% 1 11% 41% 21% 4	800
	11th to 20th	Night	20% 3 12% 39% 21% 5%	800
	21st to end	Night	22% 3 12% 39% 21% 4	880
February	1st to 10th	Night	21% 2 16% 43% 17% 2	800
	11th to 20th	Night	20% 1 14% 46% 18% 2	784
	21st to end	Night	14% 3 17% 48% 15% 3	660
March	1st to 10th	Night	19% 2 14% 47% 15% 3	800
	11th to 20th	Night	13% 3 14% 49% 19% 2	800
	21st to end	Night	18% 3 15% 45% 18% 1	880
April	1st to 10th	Night	14% 4 17% 43% 20% 1	783
	11th to 20th	Night	13% 3 19% 45% 18% 2	593
	21st to end	Night	14% 2 17% 42% 22% 2	600
May	1st to 10th	Night	12% 4 16% 46% 22% 2	600
	11th to 20th	Night	11% 3 14% 38% 31% 3	591
	21st to end	Night	14% 4 13% 35% 30% 4	634
June	1st to 10th	Night	6% 5% 12% 40% 35% 2	570
	11th to 20th	Night	8% 2 19% 45% 23% 3	424
	21st to end	Night	3 1 14% 48% 31% 4	380
July	1st to 10th	Night	4 1 10% 44% 39% 3	370
	11th to 20th	Night	4 2 10% 48% 34% 1	521
	21st to end	Night	3 1 5% 47% 41% 4	624
August	1st to 10th	Night	6% 1 8% 48% 35% 2	567
	11th to 20th	Night	5% 1 11% 46% 35% 2	564
	21st to end	Night	5% 1 11% 43% 36% 4	627
September	1st to 10th	Night	5% 1 8% 44% 38% 5%	708
	11th to 20th	Night	7% 1 8% 43% 36% 6%	760
	21st to end	Night	8% 1 11% 41% 31% 8%	760
October	1st to 10th	Night	9% 1 11% 45% 30% 4	760
	11th to 20th	Night	12% 1 12% 41% 32% 4	760
	21st to end	Night	10% 2 13% 45% 25% 4	836
November	1st to 10th	Night	15% 2 11% 44% 26% 3	780
	11th to 20th	Night	15% 1 13% 49% 19% 3	800
	21st to end	Night	13% 2 14% 44% 23% 4	970
December	1st to 10th	Night	17% 3 14% 43% 22% 2	1000
	11th to 20th	Night	22% 2 11% 45% 18% 2	1000
	21st to end	Night	24% 3 14% 41% 16% 1	995

Page generated at 2025-05-23 07:20:59. Version ac07

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