Lac Nominingue
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Nominingue clear sky chart from 2005-11-06 to 2025-11-18.

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	17% 12% 4 10% 6% 5% 4 4 5% 6% 28%	127207
	Night	16% 13% 5% 10% 6% 5% 4 3 5% 6% 27%	123159
Transparency	Day	56% 5% 11% 19% 9% 1	130637
	Night	58% 5% 11% 17% 8% 1	127804
Seeing	Day	25% 16% 29% 19% 8% 3	15726
	Night	25% 12% 26% 27% 10% 1	24708

By Month

Percentage Cloud Cover NE (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	12% 19% 8% 22% 8% 7% 5% 3 3 3 10%	3597
	11th to 20th	Day	11% 17% 8% 20% 10% 4 3 2 4 4 17%	3570
	21st to end	Day	8% 15% 10% 16% 6% 5% 6% 4 5% 6% 20%	3960
February	1st to 10th	Day	10% 18% 7% 15% 11% 5% 3 3 5% 5% 20%	1793
	11th to 20th	Day	11% 20% 5% 13% 7% 6% 3 3 4 5% 22%	1778
	21st to end	Day	16% 17% 5% 10% 8% 5% 4 2 5% 4 23%	1650
March	1st to 10th	Day	16% 18% 6% 13% 6% 4 4 2 4 5% 21%	4476
	11th to 20th	Day	14% 15% 5% 11% 6% 5% 5% 3 4 6% 26%	4858
	21st to end	Day	16% 14% 4 9% 5% 4 4 3 5% 5% 32%	5864
April	1st to 10th	Day	21% 15% 4 9% 3 3 4 3 4 5% 29%	2400
	11th to 20th	Day	22% 11% 3 7% 4 4 3 3 4 4 33%	2374
	21st to end	Day	20% 12% 4 8% 5% 5% 4 4 4 5% 30%	2591
May	1st to 10th	Day	23% 11% 4 8% 5% 5% 4 4 5% 6% 24%	6346
	11th to 20th	Day	19% 10% 3 8% 5% 4 4 4 5% 7% 31%	6318
	21st to end	Day	21% 10% 3 8% 5% 5% 4 3 5% 6% 30%	6949
June	1st to 10th	Day	23% 9% 3 8% 5% 5% 4 4 5% 6% 28%	2800
	11th to 20th	Day	16% 6% 3 7% 6% 5% 5% 4 7% 8% 34%	2800
	21st to end	Day	21% 7% 3 8% 5% 5% 5% 4 6% 7% 28%	2800
July	1st to 10th	Day	16% 7% 3 8% 6% 5% 6% 5% 8% 8% 28%	6360
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 7% 9% 37%	6360
	21st to end	Day	10% 5% 2 7% 4 4 5% 4 7% 10% 41%	6926
August	1st to 10th	Day	15% 7% 3 9% 7% 6% 6% 5% 6% 8% 29%	4563
	11th to 20th	Day	16% 8% 3 7% 4 5% 5% 4 7% 8% 33%	4168
	21st to end	Day	14% 6% 3 7% 5% 5% 5% 4 7% 9% 35%	4312
September	1st to 10th	Day	17% 6% 2 6% 5% 4 4 4 5% 7% 39%	2400
	11th to 20th	Day	14% 7% 3 6% 4 4 4 3 6% 7% 41%	2370
	21st to end	Day	22% 6% 2 6% 4 3 4 3 5% 6% 37%	2180
October	1st to 10th	Day	21% 9% 3 7% 5% 5% 5% 4 5% 7% 32%	2000
	11th to 20th	Day	26% 14% 3 8% 4 4 4 3 4 6% 25%	1999
	21st to end	Day	25% 15% 4 9% 5% 4 4 2 4 6% 22%	1980
November	1st to 10th	Day	17% 15% 4 8% 5% 5% 4 3 4 6% 27%	1851
	11th to 20th	Day	20% 18% 6% 10% 6% 4 5% 4 4 3 20%	1668
	21st to end	Day	23% 18% 7% 12% 7% 5% 4 2 3 3 17%	1600
December	1st to 10th	Day	19% 22% 9% 14% 8% 5% 4 3 4 4 10%	2600
	11th to 20th	Day	17% 18% 7% 14% 8% 5% 4 3 4 4 17%	2986
	21st to end	Day	19% 18% 5% 13% 6% 6% 5% 3 4 4 18%	3960
January	1st to 10th	Night	12% 22% 9% 17% 7% 5% 3 3 3 3 15%	6349
	11th to 20th	Night	11% 16% 6% 19% 11% 6% 4 3 4 5% 15%	6315
	21st to end	Night	8% 15% 8% 17% 8% 7% 6% 3 4 5% 19%	6996
February	1st to 10th	Night	11% 16% 6% 14% 7% 6% 5% 4 4 4 23%	2605
	11th to 20th	Night	12% 16% 6% 15% 8% 5% 5% 4 5% 4 22%	2508
	21st to end	Night	14% 15% 6% 11% 6% 5% 5% 3 4 7% 25%	1980
March	1st to 10th	Night	19% 18% 4 11% 5% 4 4 3 4 4 24%	5364
	11th to 20th	Night	12% 14% 5% 11% 7% 5% 4 4 5% 6% 27%	5099
	21st to end	Night	16% 12% 4 11% 7% 5% 4 3 5% 5% 29%	5067
April	1st to 10th	Night	22% 12% 4 7% 4 4 4 3 4 6% 29%	2000
	11th to 20th	Night	19% 10% 4 7% 4 4 3 3 6% 5% 36%	1975
	21st to end	Night	22% 10% 3 8% 4 4 4 2 5% 5% 34%	1823
May	1st to 10th	Night	21% 12% 4 8% 4 4 5% 4 6% 7% 26%	3594
	11th to 20th	Night	18% 10% 3 8% 5% 4 4 4 5% 7% 32%	3575
	21st to end	Night	20% 10% 3 8% 5% 5% 4 4 5% 7% 29%	3926
June	1st to 10th	Night	19% 9% 3 7% 5% 5% 5% 4 6% 9% 31%	1600
	11th to 20th	Night	15% 7% 3 6% 6% 4 5% 4 6% 7% 38%	1600
	21st to end	Night	19% 7% 3 7% 4 5% 4 4 5% 7% 34%	1600
July	1st to 10th	Night	14% 7% 3 8% 6% 6% 6% 5% 8% 9% 29%	3600
	11th to 20th	Night	12% 7% 3 6% 4 4 5% 4 6% 8% 40%	3600
	21st to end	Night	10% 5% 2 6% 4 4 5% 4 6% 7% 46%	3926
August	1st to 10th	Night	13% 7% 3 7% 6% 5% 5% 4 6% 7% 37%	2586
	11th to 20th	Night	18% 7% 2 6% 4 4 4 3 7% 7% 37%	2844
	21st to end	Night	20% 7% 3 7% 4 4 4 4 5% 8% 35%	3586
September	1st to 10th	Night	16% 5% 2 6% 4 4 4 3 5% 8% 43%	2000
	11th to 20th	Night	15% 6% 2 5% 4 4 4 4 5% 7% 46%	2030
	21st to end	Night	18% 9% 2 6% 3 4 4 4 5% 7% 40%	2217
October	1st to 10th	Night	19% 8% 3 5% 4 4 4 4 5% 7% 38%	2400
	11th to 20th	Night	23% 12% 3 8% 4 4 5% 4 5% 5% 27%	2400
	21st to end	Night	24% 13% 3 9% 6% 5% 4 4 4 5% 24%	2860
November	1st to 10th	Night	20% 13% 4 9% 5% 5% 3 3 5% 5% 27%	2667
	11th to 20th	Night	19% 14% 6% 11% 6% 5% 5% 3 4 5% 22%	2883
	21st to end	Night	22% 19% 5% 13% 7% 4 4 2 5% 4 16%	2800
December	1st to 10th	Night	18% 18% 7% 14% 9% 7% 5% 4 4 4 11%	4580
	11th to 20th	Night	23% 14% 5% 13% 7% 5% 3 3 3 5% 20%	5208
	21st to end	Night	21% 21% 5% 10% 6% 4 4 3 4 5% 17%	6996

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	80% 2 6% 9% 3	3598
	11th to 20th	Day	72% 2 5% 12% 7%	3600
	21st to end	Day	65% 4 9% 12% 10% 1	3960
February	1st to 10th	Day	68% 3 6% 14% 7% 1	1793
	11th to 20th	Day	66% 3 10% 11% 9% 1	1787
	21st to end	Day	65% 2 8% 14% 10% 1	1650
March	1st to 10th	Day	67% 3 6% 10% 12% 2	4479
	11th to 20th	Day	60% 4 14% 12% 10% 1	4858
	21st to end	Day	55% 3 6% 19% 16% 2	5864
April	1st to 10th	Day	59% 3 8% 17% 10% 3	2400
	11th to 20th	Day	55% 4 7% 20% 12% 2	2374
	21st to end	Day	58% 4 8% 15% 12% 3	2591
May	1st to 10th	Day	59% 5% 7% 19% 8% 1	6357
	11th to 20th	Day	52% 5% 13% 20% 9% 1	6322
	21st to end	Day	55% 5% 9% 16% 13% 1	6949
June	1st to 10th	Day	56% 6% 9% 17% 11% 1	2800
	11th to 20th	Day	46% 6% 12% 23% 11% 2	2800
	21st to end	Day	53% 6% 13% 18% 9%	2800
July	1st to 10th	Day	48% 8% 13% 25% 6%	6290
	11th to 20th	Day	41% 7% 17% 29% 7%	6285
	21st to end	Day	37% 7% 17% 31% 8%	6728
August	1st to 10th	Day	50% 8% 15% 22% 6%	4549
	11th to 20th	Day	46% 8% 17% 24% 5%	4209
	21st to end	Day	43% 8% 15% 21% 12% 1	4312
September	1st to 10th	Day	43% 5% 14% 25% 12%	2400
	11th to 20th	Day	41% 4 15% 28% 11% 1	2370
	21st to end	Day	47% 6% 13% 24% 10%	2180
October	1st to 10th	Day	53% 4 11% 26% 6%	3260
	11th to 20th	Day	56% 6% 11% 21% 6%	3227
	21st to end	Day	59% 5% 17% 13% 5% 1	3180
November	1st to 10th	Day	58% 4 13% 19% 6% 1	1851
	11th to 20th	Day	69% 4 10% 10% 7%	1668
	21st to end	Day	74% 4 9% 8% 5%	1600
December	1st to 10th	Day	79% 4 7% 9% 2	2600
	11th to 20th	Day	71% 4 6% 13% 6%	2986
	21st to end	Day	70% 3 7% 16% 4	3960
January	1st to 10th	Night	75% 3 10% 10% 2	6349
	11th to 20th	Night	73% 3 11% 9% 4	6360
	21st to end	Night	67% 4 8% 10% 11%	6996
February	1st to 10th	Night	64% 3 9% 15% 7% 1	2605
	11th to 20th	Night	65% 3 9% 15% 7% 1	2510
	21st to end	Night	61% 3 10% 16% 9% 1	1980
March	1st to 10th	Night	65% 3 8% 10% 12% 2	5374
	11th to 20th	Night	56% 6% 12% 16% 8% 2	5100
	21st to end	Night	56% 4 7% 22% 10% 2	5067
April	1st to 10th	Night	56% 3 9% 16% 12% 3	2000
	11th to 20th	Night	50% 4 9% 22% 14% 2	1975
	21st to end	Night	54% 4 8% 18% 14% 3	1823
May	1st to 10th	Night	56% 6% 10% 18% 9% 2	3600
	11th to 20th	Night	50% 7% 13% 18% 10% 2	3576
	21st to end	Night	55% 5% 10% 17% 12% 1	3927
June	1st to 10th	Night	50% 5% 12% 22% 11%	1600
	11th to 20th	Night	44% 6% 13% 23% 12% 3	1600
	21st to end	Night	48% 7% 13% 20% 11% 1	1600
July	1st to 10th	Night	48% 9% 18% 19% 6%	3560
	11th to 20th	Night	40% 7% 18% 29% 5%	3552
	21st to end	Night	35% 7% 17% 31% 10%	3809
August	1st to 10th	Night	44% 7% 16% 25% 7%	2576
	11th to 20th	Night	44% 8% 18% 24% 6%	2869
	21st to end	Night	47% 6% 14% 22% 10% 1	3586
September	1st to 10th	Night	39% 5% 16% 27% 12% 1	2000
	11th to 20th	Night	37% 4 17% 32% 9%	2030
	21st to end	Night	43% 6% 13% 28% 10%	2217
October	1st to 10th	Night	44% 7% 14% 24% 10%	3920
	11th to 20th	Night	51% 7% 14% 20% 8%	3899
	21st to end	Night	56% 6% 16% 13% 9% 1	4610
November	1st to 10th	Night	59% 5% 13% 18% 6%	2667
	11th to 20th	Night	64% 4 11% 13% 7% 1	2883
	21st to end	Night	72% 4 10% 11% 3	2800
December	1st to 10th	Night	75% 6% 9% 7% 2	4580
	11th to 20th	Night	69% 3 7% 13% 8% 1	5208
	21st to end	Night	70% 3 6% 12% 9%	6996

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	20% 20% 42% 15% 4	200
	11th to 20th	Day	28% 16% 34% 18% 5% 1	200
	21st to end	Day	21% 20% 32% 22% 5%	220
February	1st to 10th	Day	27% 26% 34% 10% 2 1	297
	11th to 20th	Day	24% 27% 38% 10% 1	325
	21st to end	Day	28% 24% 30% 14% 3	414
March	1st to 10th	Day	25% 19% 32% 18% 6%	500
	11th to 20th	Day	27% 22% 30% 17% 4 1	500
	21st to end	Day	30% 20% 26% 15% 6% 2	550
April	1st to 10th	Day	32% 17% 27% 14% 8% 1	500
	11th to 20th	Day	34% 17% 24% 14% 8% 3	492
	21st to end	Day	30% 17% 31% 17% 4 1	500
May	1st to 10th	Day	30% 18% 29% 15% 6% 2	503
	11th to 20th	Day	25% 17% 28% 18% 10% 2	527
	21st to end	Day	25% 18% 31% 18% 6% 2	573
June	1st to 10th	Day	27% 16% 30% 19% 6% 1	530
	11th to 20th	Day	20% 18% 30% 19% 10% 2	530
	21st to end	Day	25% 11% 33% 19% 9% 2	530
July	1st to 10th	Day	18% 10% 33% 27% 10% 2	525
	11th to 20th	Day	16% 11% 32% 29% 9% 2	524
	21st to end	Day	13% 12% 32% 29% 12% 2	576
August	1st to 10th	Day	18% 9% 24% 32% 13% 4	526
	11th to 20th	Day	18% 6% 25% 29% 15% 7%	519
	21st to end	Day	20% 13% 28% 20% 13% 7%	583
September	1st to 10th	Day	21% 12% 28% 21% 11% 8%	530
	11th to 20th	Day	15% 11% 22% 23% 19% 10%	530
	21st to end	Day	23% 14% 24% 21% 12% 7%	530
October	1st to 10th	Day	27% 15% 24% 18% 15% 3	530
	11th to 20th	Day	32% 17% 25% 17% 6% 3	529
	21st to end	Day	37% 13% 24% 19% 7%	462
November	1st to 10th	Day	32% 16% 28% 18% 5% 1	425
	11th to 20th	Day	30% 19% 31% 11% 8% 1	226
	21st to end	Day	34% 21% 31% 11% 3 1	200
December	1st to 10th	Day	36% 15% 26% 18% 6%	200
	11th to 20th	Day	34% 22% 28% 13% 4 1	200
	21st to end	Day	29% 19% 31% 13% 7% 2	220
January	1st to 10th	Night	27% 14% 35% 18% 5%	800
	11th to 20th	Night	30% 13% 27% 22% 7%	800
	21st to end	Night	17% 12% 32% 29% 8% 1	880
February	1st to 10th	Night	19% 17% 33% 24% 6%	800
	11th to 20th	Night	22% 16% 36% 21% 5% 1	783
	21st to end	Night	23% 17% 28% 27% 5%	660
March	1st to 10th	Night	25% 15% 29% 26% 5%	800
	11th to 20th	Night	25% 17% 29% 23% 6% 1	800
	21st to end	Night	23% 14% 31% 24% 8%	880
April	1st to 10th	Night	30% 14% 24% 27% 6%	800
	11th to 20th	Night	25% 14% 28% 23% 9% 1	791
	21st to end	Night	30% 13% 25% 23% 9%	623
May	1st to 10th	Night	25% 10% 27% 28% 11% 1	400
	11th to 20th	Night	21% 11% 26% 31% 10%	394
	21st to end	Night	21% 6% 33% 30% 9%	433
June	1st to 10th	Night	22% 7% 30% 33% 8% 1	400
	11th to 20th	Night	18% 7% 26% 35% 13% 2	400
	21st to end	Night	23% 5% 20% 35% 18%	400
July	1st to 10th	Night	12% 7% 20% 48% 12% 1	390
	11th to 20th	Night	15% 4 19% 42% 19%	388
	21st to end	Night	13% 4 23% 41% 17% 2	438
August	1st to 10th	Night	14% 5% 18% 41% 22% 1	398
	11th to 20th	Night	15% 5% 16% 36% 25% 2	561
	21st to end	Night	20% 7% 20% 32% 19% 2	880
September	1st to 10th	Night	20% 5% 23% 33% 17% 2	800
	11th to 20th	Night	18% 6% 19% 32% 23% 3	800
	21st to end	Night	24% 8% 22% 26% 19% 2	800
October	1st to 10th	Night	24% 8% 26% 26% 14% 1	800
	11th to 20th	Night	30% 13% 24% 24% 9% 1	800
	21st to end	Night	32% 12% 24% 26% 6%	880
November	1st to 10th	Night	30% 14% 26% 22% 7% 1	820
	11th to 20th	Night	27% 16% 27% 19% 10% 1	829
	21st to end	Night	35% 17% 21% 21% 6% 1	800
December	1st to 10th	Night	32% 14% 25% 22% 6% 1	800
	11th to 20th	Night	30% 15% 28% 19% 7% 1	800
	21st to end	Night	34% 14% 25% 21% 6% 1	880

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