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 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	7% 7% 2 6% 4 4 4 3 5% 7% 51%	101704
	Night	8% 8% 3 6% 4 4 4 4 5% 6% 47%	97494
Transparency	Day	32% 5% 9% 20% 19% 14%	101462
	Night	36% 6% 11% 20% 17% 11%	97325
Seeing	Day	11% 5% 20% 32% 24% 8%	15233
	Night	13% 2 12% 44% 25% 3	24971

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% 6% 12% 7% 6% 5% 3 4 4 27%	2858
	11th to 20th	Day	10% 18% 6% 10% 5% 5% 4 4 4 5% 28%	2860
	21st to end	Day	13% 17% 5% 12% 6% 5% 4 3 4 5% 24%	3146
February	1st to 10th	Day	14% 15% 4 8% 4 3 4 4 5% 6% 34%	1710
	11th to 20th	Day	11% 14% 3 10% 5% 3 3 4 6% 7% 33%	1726
	21st to end	Day	6% 16% 4 9% 5% 5% 5% 4 6% 6% 33%	1570
March	1st to 10th	Day	7% 14% 4 10% 6% 3 4 3 5% 6% 38%	3316
	11th to 20th	Day	7% 8% 2 6% 4 3 4 3 5% 6% 51%	3490
	21st to end	Day	11% 15% 5% 10% 7% 5% 5% 4 5% 7% 26%	3825
April	1st to 10th	Day	10% 10% 3 7% 5% 5% 4 4 6% 6% 40%	2109
	11th to 20th	Day	9% 9% 3 6% 5% 4 4 4 5% 8% 42%	2437
	21st to end	Day	9% 8% 3 6% 5% 4 5% 3 6% 7% 44%	2470
May	1st to 10th	Day	9% 9% 3 6% 5% 4 5% 5% 6% 8% 40%	4110
	11th to 20th	Day	6% 4 2 4 3 3 4 3 6% 8% 58%	4071
	21st to end	Day	6% 5% 2 6% 4 5% 5% 4 6% 7% 51%	4477
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	10% 5% 2 4 3 3 4 3 5% 5% 55%	2005
	11th to 20th	Day	7% 5% 2 4 3 3 2 3 5% 7% 59%	1900
	21st to end	Day	6% 6% 2 5% 3 3 4 3 5% 7% 56%	2033
November	1st to 10th	Day	10% 10% 3 6% 6% 4 4 3 5% 6% 44%	1683
	11th to 20th	Day	11% 8% 2 5% 3 4 3 3 6% 8% 48%	1710
	21st to end	Day	10% 11% 3 6% 5% 3 4 3 5% 7% 43%	1526
December	1st to 10th	Day	11% 13% 5% 10% 6% 5% 4 3 4 6% 34%	1520
	11th to 20th	Day	13% 14% 3 11% 6% 5% 6% 4 6% 7% 26%	1926
	21st to end	Day	8% 13% 5% 11% 6% 5% 5% 4 6% 6% 31%	2986
January	1st to 10th	Night	11% 16% 5% 9% 5% 4 6% 5% 5% 7% 28%	4097
	11th to 20th	Night	14% 17% 6% 10% 5% 4 4 3 4 6% 26%	4110
	21st to end	Night	16% 18% 5% 14% 9% 4 3 3 3 5% 20%	4521
February	1st to 10th	Night	13% 16% 4 8% 5% 4 4 4 5% 6% 31%	2470
	11th to 20th	Night	11% 12% 3 7% 5% 4 4 4 4 6% 40%	2337
	21st to end	Night	7% 14% 4 8% 6% 5% 4 4 5% 7% 36%	1884
March	1st to 10th	Night	11% 13% 4 7% 5% 5% 5% 4 6% 6% 34%	3557
	11th to 20th	Night	5% 7% 2 5% 4 4 4 4 5% 7% 51%	3490
	21st to end	Night	11% 12% 3 9% 5% 5% 5% 4 6% 6% 34%	3828
April	1st to 10th	Night	10% 9% 3 7% 4 4 4 3 5% 7% 43%	2068
	11th to 20th	Night	8% 9% 3 8% 5% 4 5% 3 5% 5% 45%	1691
	21st to end	Night	10% 7% 2 5% 4 4 3 4 5% 6% 50%	1710
May	1st to 10th	Night	9% 8% 2 7% 5% 4 4 3 6% 7% 44%	2860
	11th to 20th	Night	6% 4 2 4 3 3 3 3 5% 6% 60%	2834
	21st to end	Night	9% 5% 2 5% 4 4 4 3 5% 7% 51%	3110
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	7% 4 1 4 3 3 3 3 5% 6% 59%	2175
	11th to 20th	Night	8% 5% 2 5% 3 3 3 3 4 5% 60%	2280
	21st to end	Night	7% 5% 2 4 3 3 5% 3 5% 7% 56%	2562
November	1st to 10th	Night	11% 8% 2 5% 4 4 4 3 5% 7% 49%	2418
	11th to 20th	Night	10% 7% 3 5% 3 4 4 3 5% 6% 49%	2470
	21st to end	Night	8% 9% 3 5% 4 4 5% 4 6% 6% 46%	2631
December	1st to 10th	Night	12% 12% 4 9% 4 4 5% 3 4 6% 38%	2660
	11th to 20th	Night	13% 12% 4 10% 5% 7% 6% 5% 5% 6% 27%	3271
	21st to end	Night	11% 13% 4 10% 6% 5% 5% 4 5% 7% 30%	4709

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% 11% 15% 15% 2	2859
	11th to 20th	Day	58% 8% 17% 13% 3 1	2860
	21st to end	Day	58% 13% 12% 11% 5%	3146
February	1st to 10th	Day	52% 7% 19% 16% 5% 1	1710
	11th to 20th	Day	49% 7% 15% 21% 7% 1	1735
	21st to end	Day	51% 6% 15% 20% 6% 1	1570
March	1st to 10th	Day	48% 6% 12% 25% 9% 1	3316
	11th to 20th	Day	32% 5% 13% 34% 16% 1	3490
	21st to end	Day	57% 6% 16% 16% 4 1	3825
April	1st to 10th	Day	44% 5% 14% 23% 12% 3	2109
	11th to 20th	Day	41% 4 10% 25% 18% 2	2440
	21st to end	Day	38% 4 11% 26% 20% 2	2470
May	1st to 10th	Day	40% 4 8% 24% 18% 5%	4110
	11th to 20th	Day	23% 5% 7% 32% 24% 9%	4074
	21st to end	Day	30% 5% 8% 26% 28% 3	4477
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	31% 5% 9% 24% 23% 9%	2005
	11th to 20th	Day	26% 4 12% 30% 23% 4	1900
	21st to end	Day	29% 4 16% 34% 17% 1	2033
November	1st to 10th	Day	42% 5% 14% 24% 14% 1	1683
	11th to 20th	Day	35% 5% 20% 27% 11% 1	1710
	21st to end	Day	41% 5% 18% 25% 10% 1	1526
December	1st to 10th	Day	51% 8% 14% 17% 8% 1	1520
	11th to 20th	Day	54% 10% 18% 17% 2	1924
	21st to end	Day	48% 11% 14% 20% 6%	2986
January	1st to 10th	Night	51% 9% 15% 21% 3 1	4097
	11th to 20th	Night	60% 8% 16% 13% 3 1	4110
	21st to end	Night	57% 17% 12% 9% 4 1	4521
February	1st to 10th	Night	54% 7% 15% 19% 5%	2470
	11th to 20th	Night	45% 6% 13% 24% 11% 1	2338
	21st to end	Night	47% 5% 13% 25% 9% 1	1884
March	1st to 10th	Night	48% 7% 10% 24% 11% 1	3557
	11th to 20th	Night	30% 6% 15% 33% 15% 1	3490
	21st to end	Night	49% 7% 15% 23% 6% 1	3828
April	1st to 10th	Night	42% 5% 13% 23% 11% 6%	2068
	11th to 20th	Night	40% 4 9% 24% 20% 2	1691
	21st to end	Night	35% 5% 9% 28% 21% 3	1710
May	1st to 10th	Night	37% 6% 9% 22% 22% 5%	2860
	11th to 20th	Night	24% 5% 6% 31% 25% 9%	2835
	21st to end	Night	31% 5% 9% 26% 27% 2	3110
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	25% 3 9% 22% 31% 9%	2175
	11th to 20th	Night	28% 3 6% 31% 25% 6%	2280
	21st to end	Night	28% 4 11% 33% 21% 3	2562
November	1st to 10th	Night	35% 5% 13% 27% 16% 3	2418
	11th to 20th	Night	35% 5% 16% 29% 14% 1	2470
	21st to end	Night	39% 5% 16% 29% 11% 1	2631
December	1st to 10th	Night	48% 6% 19% 18% 8% 2	2660
	11th to 20th	Night	53% 9% 17% 19% 2	3272
	21st to end	Night	50% 9% 16% 18% 6%	4709

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% 3 15% 34% 16% 7%	270
	11th to 20th	Day	19% 5% 16% 35% 20% 5%	270
	21st to end	Day	18% 4 15% 35% 21% 6%	297
February	1st to 10th	Day	25% 3 26% 30% 14% 3	270
	11th to 20th	Day	18% 6% 26% 31% 14% 5%	331
	21st to end	Day	12% 8% 36% 29% 13% 3	382
March	1st to 10th	Day	16% 8% 23% 37% 13% 3	460
	11th to 20th	Day	12% 6% 29% 31% 19% 3	460
	21st to end	Day	19% 9% 27% 32% 10% 2	506
April	1st to 10th	Day	16% 11% 25% 27% 18% 3	460
	11th to 20th	Day	13% 15% 28% 28% 14% 3	452
	21st to end	Day	14% 8% 25% 30% 17% 6%	460
May	1st to 10th	Day	7% 11% 27% 31% 21% 2	463
	11th to 20th	Day	12% 7% 21% 28% 24% 8%	488
	21st to end	Day	9% 6% 20% 29% 26% 11%	529
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	22% 2 15% 33% 16% 11%	273
	11th to 20th	Day	13% 3 20% 32% 23% 9%	270
	21st to end	Day	18% 3 10% 35% 26% 8%	270
December	1st to 10th	Day	17% 2 16% 34% 23% 8%	270
	11th to 20th	Day	19% 5% 10% 43% 21% 3	270
	21st to end	Day	20% 3 17% 38% 16% 6%	297
January	1st to 10th	Night	21% 1 9% 42% 22% 4	760
	11th to 20th	Night	21% 3 11% 38% 21% 5%	760
	21st to end	Night	23% 3 9% 38% 22% 4	836
February	1st to 10th	Night	20% 1 15% 44% 18% 2	760
	11th to 20th	Night	18% 1 14% 46% 18% 3	744
	21st to end	Night	14% 4 17% 47% 15% 3	628
March	1st to 10th	Night	19% 3 13% 48% 15% 3	760
	11th to 20th	Night	13% 3 14% 49% 19% 2	760
	21st to end	Night	18% 3 15% 44% 19% 1	836
April	1st to 10th	Night	14% 4 17% 43% 20% 1	744
	11th to 20th	Night	13% 3 18% 46% 18% 2	563
	21st to end	Night	14% 2 15% 42% 23% 2	570
May	1st to 10th	Night	12% 4 16% 46% 21% 2	570
	11th to 20th	Night	11% 2 13% 37% 33% 3	561
	21st to end	Night	14% 4 12% 36% 30% 4	617
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 9% 44% 26% 3	744
	11th to 20th	Night	15% 1 11% 50% 20% 3	760
	21st to end	Night	12% 2 13% 44% 24% 5%	921
December	1st to 10th	Night	18% 3 14% 44% 21% 1	950
	11th to 20th	Night	23% 2 10% 44% 18% 2	950
	21st to end	Night	23% 3 14% 42% 16% 1	946

Page generated at 2024-10-29 23:23:00. Version ac07

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