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 2024-11-08.

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% 11% 4 9% 6% 5% 4 4 5% 6% 28%	101609
	Night	17% 13% 4 9% 6% 5% 4 3 5% 6% 28%	97500
Transparency	Day	55% 5% 11% 19% 8% 1	105057
	Night	56% 5% 12% 18% 8% 1	102129
Seeing	Day	25% 16% 29% 19% 8% 3	14446
	Night	25% 12% 26% 26% 10% 1	23435

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	16% 20% 8% 17% 8% 6% 4 3 2 4 13%	2517
	11th to 20th	Day	13% 15% 9% 21% 9% 4 3 2 3 4 19%	2520
	21st to end	Day	11% 17% 9% 14% 6% 6% 6% 3 5% 4 17%	2772
February	1st to 10th	Day	10% 18% 7% 14% 10% 6% 3 3 5% 5% 20%	1703
	11th to 20th	Day	12% 20% 5% 13% 6% 6% 4 3 4 5% 23%	1686
	21st to end	Day	16% 17% 5% 10% 8% 5% 4 3 5% 5% 23%	1570
March	1st to 10th	Day	15% 19% 5% 11% 5% 5% 4 3 4 5% 25%	3116
	11th to 20th	Day	13% 18% 7% 13% 7% 5% 4 2 4 5% 23%	3400
	21st to end	Day	12% 9% 3 9% 6% 5% 4 4 6% 7% 35%	4088
April	1st to 10th	Day	21% 15% 4 9% 3 4 4 2 4 5% 29%	2280
	11th to 20th	Day	22% 11% 3 8% 5% 4 3 3 4 4 32%	2254
	21st to end	Day	20% 12% 4 8% 5% 4 3 4 4 5% 30%	2461
May	1st to 10th	Day	21% 10% 3 8% 6% 4 4 4 5% 6% 27%	4426
	11th to 20th	Day	19% 8% 3 7% 5% 5% 4 4 5% 8% 32%	4398
	21st to end	Day	16% 9% 3 7% 5% 5% 5% 4 5% 7% 33%	4837
June	1st to 10th	Day	23% 10% 3 8% 4 5% 4 4 5% 6% 28%	2660
	11th to 20th	Day	16% 6% 3 7% 5% 5% 5% 4 7% 8% 34%	2660
	21st to end	Day	21% 8% 3 8% 5% 5% 5% 4 6% 7% 28%	2660
July	1st to 10th	Day	14% 7% 3 8% 6% 5% 6% 5% 8% 8% 30%	4440
	11th to 20th	Day	16% 6% 3 7% 6% 5% 5% 4 7% 8% 33%	4440
	21st to end	Day	13% 7% 3 7% 4 4 4 4 6% 8% 42%	4814
August	1st to 10th	Day	15% 7% 3 9% 7% 6% 6% 5% 6% 8% 28%	4423
	11th to 20th	Day	16% 8% 3 7% 4 5% 5% 5% 7% 8% 32%	4037
	21st to end	Day	14% 6% 3 7% 5% 5% 5% 4 7% 9% 35%	4180
September	1st to 10th	Day	18% 6% 2 6% 5% 4 4 3 5% 7% 39%	2280
	11th to 20th	Day	15% 8% 3 6% 4 4 4 3 6% 7% 40%	2252
	21st to end	Day	22% 6% 2 6% 5% 3 4 3 5% 6% 37%	2071
October	1st to 10th	Day	22% 9% 3 7% 5% 5% 5% 4 5% 7% 30%	1900
	11th to 20th	Day	27% 14% 3 9% 4 4 4 3 4 6% 24%	1899
	21st to end	Day	25% 15% 4 9% 5% 4 4 2 4 6% 22%	1881
November	1st to 10th	Day	17% 14% 4 8% 5% 5% 4 4 5% 7% 28%	1734
	11th to 20th	Day	20% 18% 6% 11% 6% 4 4 4 4 4 19%	1532
	21st to end	Day	23% 17% 6% 12% 7% 5% 4 2 3 3 18%	1520
December	1st to 10th	Day	22% 22% 5% 12% 7% 5% 3 3 4 4 14%	1520
	11th to 20th	Day	20% 17% 7% 13% 6% 4 4 3 4 5% 16%	1906
	21st to end	Day	22% 20% 5% 13% 5% 5% 4 2 3 4 17%	2772
January	1st to 10th	Night	16% 20% 8% 13% 7% 5% 4 3 3 4 19%	4429
	11th to 20th	Night	13% 15% 5% 16% 10% 6% 4 3 5% 5% 18%	4440
	21st to end	Night	11% 16% 8% 16% 7% 7% 5% 3 4 5% 17%	4884
February	1st to 10th	Night	11% 16% 6% 13% 7% 6% 5% 4 4 4 22%	2475
	11th to 20th	Night	12% 16% 6% 14% 7% 5% 5% 4 5% 4 23%	2380
	21st to end	Night	14% 15% 6% 10% 6% 5% 5% 3 4 7% 25%	1884
March	1st to 10th	Night	18% 16% 4 9% 5% 5% 4 3 4 4 28%	3724
	11th to 20th	Night	16% 18% 5% 11% 5% 4 4 3 4 5% 25%	3557
	21st to end	Night	13% 9% 3 10% 7% 5% 4 4 5% 6% 35%	3543
April	1st to 10th	Night	22% 12% 4 7% 4 4 4 3 4 6% 29%	1900
	11th to 20th	Night	19% 9% 3 7% 4 4 3 3 6% 6% 36%	1875
	21st to end	Night	21% 10% 3 9% 4 4 4 2 5% 5% 34%	1732
May	1st to 10th	Night	20% 11% 3 7% 4 5% 5% 4 5% 7% 30%	2514
	11th to 20th	Night	19% 8% 3 6% 5% 4 4 4 5% 7% 34%	2495
	21st to end	Night	17% 8% 3 7% 5% 6% 4 4 6% 7% 33%	2738
June	1st to 10th	Night	19% 9% 3 7% 5% 5% 5% 4 6% 9% 30%	1520
	11th to 20th	Night	15% 7% 3 6% 5% 4 5% 4 6% 7% 38%	1520
	21st to end	Night	19% 7% 3 7% 4 5% 4 4 5% 7% 34%	1520
July	1st to 10th	Night	13% 8% 3 9% 6% 5% 5% 4 7% 7% 32%	2520
	11th to 20th	Night	15% 6% 4 6% 4 4 5% 4 6% 8% 37%	2520
	21st to end	Night	11% 5% 2 6% 4 4 5% 4 6% 7% 46%	2739
August	1st to 10th	Night	13% 7% 3 7% 6% 6% 5% 4 6% 7% 36%	2506
	11th to 20th	Night	18% 7% 2 6% 4 4 4 4 7% 7% 37%	2756
	21st to end	Night	20% 7% 3 7% 4 4 4 3 5% 8% 35%	3476
September	1st to 10th	Night	17% 5% 2 6% 4 4 4 3 5% 7% 43%	1900
	11th to 20th	Night	16% 6% 2 5% 4 4 4 3 5% 7% 45%	1928
	21st to end	Night	18% 9% 2 6% 3 4 4 3 5% 7% 39%	2106
October	1st to 10th	Night	20% 9% 3 5% 4 4 4 4 4 7% 36%	2280
	11th to 20th	Night	24% 12% 3 8% 5% 4 4 4 5% 5% 27%	2280
	21st to end	Night	24% 13% 3 9% 5% 5% 4 4 4 5% 24%	2717
November	1st to 10th	Night	20% 14% 4 8% 5% 5% 3 3 5% 6% 27%	2505
	11th to 20th	Night	19% 14% 5% 11% 6% 5% 4 3 4 5% 22%	2645
	21st to end	Night	22% 18% 5% 12% 6% 4 4 3 5% 4 16%	2660
December	1st to 10th	Night	20% 20% 8% 12% 6% 5% 4 3 4 4 15%	2660
	11th to 20th	Night	22% 16% 6% 12% 6% 4 3 3 3 4 21%	3288
	21st to end	Night	23% 23% 5% 11% 6% 4 3 2 3 3 17%	4884

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	78% 2 8% 9% 3	2518
	11th to 20th	Day	72% 2 6% 14% 6%	2520
	21st to end	Day	70% 4 9% 10% 6% 1	2772
February	1st to 10th	Day	68% 3 6% 15% 7% 1	1703
	11th to 20th	Day	65% 3 11% 11% 10% 1	1695
	21st to end	Day	65% 2 8% 14% 10% 1	1570
March	1st to 10th	Day	64% 3 8% 14% 11% 1	3119
	11th to 20th	Day	65% 3 9% 13% 9% 2	3400
	21st to end	Day	48% 4 8% 23% 16% 2	4088
April	1st to 10th	Day	59% 3 8% 17% 10% 3	2280
	11th to 20th	Day	55% 4 7% 20% 12% 2	2254
	21st to end	Day	57% 4 8% 16% 12% 3	2461
May	1st to 10th	Day	56% 6% 8% 21% 9% 1	4440
	11th to 20th	Day	50% 5% 14% 21% 9% 1	4402
	21st to end	Day	50% 5% 11% 18% 14% 1	4837
June	1st to 10th	Day	56% 6% 10% 17% 10% 1	2660
	11th to 20th	Day	46% 6% 12% 23% 11% 2	2660
	21st to end	Day	54% 6% 12% 18% 9%	2660
July	1st to 10th	Day	47% 7% 13% 26% 7%	4370
	11th to 20th	Day	45% 7% 17% 25% 6%	4365
	21st to end	Day	40% 7% 16% 28% 9%	4661
August	1st to 10th	Day	51% 8% 14% 21% 6%	4409
	11th to 20th	Day	46% 8% 17% 23% 5%	4078
	21st to end	Day	42% 8% 15% 21% 12% 1	4180
September	1st to 10th	Day	44% 5% 14% 24% 13%	2280
	11th to 20th	Day	42% 4 15% 27% 10% 1	2252
	21st to end	Day	47% 6% 14% 24% 9%	2071
October	1st to 10th	Day	54% 4 11% 25% 5%	3160
	11th to 20th	Day	57% 6% 11% 21% 5%	3127
	21st to end	Day	58% 5% 17% 13% 5% 1	3081
November	1st to 10th	Day	56% 4 13% 20% 6% 1	1734
	11th to 20th	Day	69% 4 11% 11% 6%	1532
	21st to end	Day	73% 4 9% 9% 5%	1520
December	1st to 10th	Day	74% 4 9% 10% 3	1520
	11th to 20th	Day	71% 4 8% 11% 5%	1906
	21st to end	Day	74% 3 7% 13% 4	2772
January	1st to 10th	Night	70% 3 14% 10% 3	4429
	11th to 20th	Night	69% 3 13% 10% 4 1	4440
	21st to end	Night	70% 4 10% 9% 7% 1	4884
February	1st to 10th	Night	65% 3 9% 15% 6% 1	2475
	11th to 20th	Night	64% 3 9% 15% 7% 1	2382
	21st to end	Night	61% 3 10% 16% 10% 1	1884
March	1st to 10th	Night	60% 3 11% 13% 10% 2	3734
	11th to 20th	Night	61% 4 9% 16% 9% 1	3558
	21st to end	Night	50% 4 8% 22% 13% 3	3543
April	1st to 10th	Night	56% 3 9% 16% 12% 3	1900
	11th to 20th	Night	49% 4 9% 22% 13% 2	1875
	21st to end	Night	54% 4 8% 18% 14% 3	1732
May	1st to 10th	Night	53% 6% 11% 19% 9% 2	2520
	11th to 20th	Night	47% 6% 15% 19% 11% 2	2496
	21st to end	Night	50% 4 10% 20% 13% 2	2739
June	1st to 10th	Night	50% 5% 13% 21% 11%	1520
	11th to 20th	Night	44% 6% 13% 23% 12% 3	1520
	21st to end	Night	48% 8% 13% 20% 11% 1	1520
July	1st to 10th	Night	48% 8% 16% 19% 8%	2480
	11th to 20th	Night	43% 7% 19% 24% 6% 1	2472
	21st to end	Night	35% 7% 19% 29% 10%	2651
August	1st to 10th	Night	45% 7% 15% 25% 7%	2496
	11th to 20th	Night	44% 8% 19% 24% 6%	2781
	21st to end	Night	46% 6% 14% 22% 10% 1	3476
September	1st to 10th	Night	40% 5% 15% 27% 13% 1	1900
	11th to 20th	Night	38% 4 17% 32% 9%	1928
	21st to end	Night	44% 6% 13% 28% 9%	2106
October	1st to 10th	Night	45% 7% 14% 24% 10%	3800
	11th to 20th	Night	51% 7% 14% 20% 7%	3779
	21st to end	Night	56% 6% 16% 12% 9% 1	4467
November	1st to 10th	Night	58% 5% 13% 18% 6%	2505
	11th to 20th	Night	64% 4 11% 14% 6% 2	2645
	21st to end	Night	71% 4 10% 11% 3	2660
December	1st to 10th	Night	73% 4 9% 10% 3	2660
	11th to 20th	Night	68% 3 9% 14% 6% 1	3288
	21st to end	Night	74% 3 6% 12% 5%	4884

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	21% 20% 39% 16% 4	180
	11th to 20th	Day	28% 16% 32% 19% 4 1	180
	21st to end	Day	23% 17% 32% 23% 5% 1	198
February	1st to 10th	Day	27% 25% 35% 10% 2 1	267
	11th to 20th	Day	24% 27% 39% 11% 1	293
	21st to end	Day	29% 25% 28% 15% 3	382
March	1st to 10th	Day	25% 18% 32% 19% 6%	460
	11th to 20th	Day	27% 20% 31% 17% 4 1	460
	21st to end	Day	30% 20% 26% 16% 6% 2	506
April	1st to 10th	Day	31% 17% 28% 14% 8% 1	460
	11th to 20th	Day	33% 17% 25% 15% 8% 3	452
	21st to end	Day	30% 18% 30% 18% 4 1	460
May	1st to 10th	Day	30% 17% 28% 15% 6% 2	463
	11th to 20th	Day	24% 16% 29% 19% 10% 2	487
	21st to end	Day	23% 17% 33% 19% 6% 2	529
June	1st to 10th	Day	27% 16% 30% 19% 6% 1	490
	11th to 20th	Day	19% 18% 30% 20% 10% 2	490
	21st to end	Day	26% 11% 32% 19% 9% 2	490
July	1st to 10th	Day	17% 10% 33% 28% 10% 3	485
	11th to 20th	Day	17% 11% 32% 29% 9% 2	484
	21st to end	Day	14% 11% 30% 31% 12% 2	532
August	1st to 10th	Day	20% 10% 24% 31% 12% 3	486
	11th to 20th	Day	19% 6% 26% 28% 15% 8%	479
	21st to end	Day	19% 13% 28% 20% 13% 7%	539
September	1st to 10th	Day	22% 12% 28% 21% 10% 8%	490
	11th to 20th	Day	16% 11% 23% 23% 18% 8%	490
	21st to end	Day	23% 13% 24% 21% 12% 7%	490
October	1st to 10th	Day	28% 16% 23% 17% 14% 2	490
	11th to 20th	Day	34% 17% 25% 16% 6% 2	489
	21st to end	Day	37% 13% 25% 18% 7%	429
November	1st to 10th	Day	32% 16% 27% 19% 5% 1	386
	11th to 20th	Day	29% 19% 35% 10% 6% 1	192
	21st to end	Day	33% 21% 30% 12% 3 1	180
December	1st to 10th	Day	35% 16% 28% 14% 7%	180
	11th to 20th	Day	33% 22% 29% 13% 2 1	180
	21st to end	Day	31% 19% 30% 13% 6% 2	198
January	1st to 10th	Night	28% 14% 34% 19% 5%	760
	11th to 20th	Night	30% 13% 27% 22% 7%	760
	21st to end	Night	17% 12% 32% 29% 8% 1	836
February	1st to 10th	Night	20% 16% 33% 24% 6%	760
	11th to 20th	Night	22% 16% 36% 22% 5% 1	743
	21st to end	Night	23% 18% 28% 27% 4	628
March	1st to 10th	Night	24% 15% 30% 26% 5%	760
	11th to 20th	Night	26% 17% 28% 23% 6% 1	760
	21st to end	Night	23% 13% 32% 24% 8%	836
April	1st to 10th	Night	29% 14% 24% 27% 6%	760
	11th to 20th	Night	25% 13% 29% 23% 9% 1	751
	21st to end	Night	29% 13% 25% 23% 9% 1	592
May	1st to 10th	Night	25% 9% 27% 27% 11% 1	380
	11th to 20th	Night	21% 11% 27% 32% 10%	374
	21st to end	Night	20% 6% 34% 31% 9%	411
June	1st to 10th	Night	22% 7% 31% 32% 8% 1	380
	11th to 20th	Night	18% 6% 26% 34% 13% 2	380
	21st to end	Night	23% 5% 18% 36% 18%	380
July	1st to 10th	Night	12% 7% 21% 47% 12% 1	370
	11th to 20th	Night	15% 4 19% 42% 19%	368
	21st to end	Night	14% 4 22% 41% 18% 2	416
August	1st to 10th	Night	15% 5% 18% 40% 22%	378
	11th to 20th	Night	16% 5% 16% 35% 26% 2	533
	21st to end	Night	20% 7% 21% 31% 19% 2	836
September	1st to 10th	Night	21% 5% 23% 33% 17% 2	760
	11th to 20th	Night	19% 6% 19% 31% 22% 3	760
	21st to end	Night	24% 8% 22% 25% 18% 2	760
October	1st to 10th	Night	25% 9% 25% 26% 14% 1	760
	11th to 20th	Night	32% 13% 23% 23% 9% 1	760
	21st to end	Night	32% 13% 24% 24% 6%	836
November	1st to 10th	Night	30% 14% 25% 23% 7% 1	771
	11th to 20th	Night	28% 16% 27% 19% 10% 1	760
	21st to end	Night	35% 16% 21% 21% 6% 1	760
December	1st to 10th	Night	32% 15% 25% 22% 5% 1	760
	11th to 20th	Night	30% 15% 28% 19% 6% 1	760
	21st to end	Night	34% 14% 25% 21% 4 1	836

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