Lac Chantier
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Chantier clear sky chart from 2005-11-06 to 2024-11-25.

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	16% 13% 5% 10% 6% 5% 4 4 5% 6% 25%	101779
	Night	15% 14% 5% 11% 6% 5% 5% 3 4 5% 25%	97689
Transparency	Day	59% 4 10% 18% 8% 1	105203
	Night	61% 3 10% 17% 8% 1	102341
Seeing	Day	27% 16% 32% 17% 6% 2	14469
	Night	25% 15% 31% 21% 7% 1	23437

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	11% 21% 8% 19% 9% 7% 5% 3 4 3 11%	2517
	11th to 20th	Day	10% 14% 7% 20% 11% 8% 3 3 4 3 16%	2520
	21st to end	Day	9% 13% 9% 19% 7% 6% 6% 4 6% 5% 16%	2772
February	1st to 10th	Day	8% 18% 8% 15% 9% 7% 5% 4 5% 5% 16%	1652
	11th to 20th	Day	10% 18% 6% 16% 7% 6% 5% 3 4 5% 19%	1703
	21st to end	Day	12% 19% 7% 12% 8% 6% 5% 3 5% 3 20%	1570
March	1st to 10th	Day	12% 20% 5% 11% 7% 4 4 3 3 4 25%	3116
	11th to 20th	Day	10% 20% 8% 14% 7% 5% 4 3 4 4 21%	3336
	21st to end	Day	10% 13% 5% 11% 6% 4 4 3 5% 6% 32%	4128
April	1st to 10th	Day	19% 19% 5% 9% 5% 4 3 3 4 5% 24%	2280
	11th to 20th	Day	21% 13% 6% 9% 4 3 3 3 4 5% 30%	2254
	21st to end	Day	19% 14% 5% 8% 6% 4 4 2 5% 4 29%	2485
May	1st to 10th	Day	20% 12% 4 8% 6% 5% 4 4 5% 6% 26%	4426
	11th to 20th	Day	18% 9% 3 7% 6% 5% 5% 4 7% 8% 28%	4398
	21st to end	Day	18% 9% 3 9% 5% 6% 5% 4 5% 7% 30%	4837
June	1st to 10th	Day	23% 11% 3 8% 6% 4 5% 3 6% 6% 24%	2660
	11th to 20th	Day	16% 9% 2 7% 6% 5% 5% 4 5% 9% 31%	2660
	21st to end	Day	23% 9% 3 9% 7% 6% 4 4 6% 6% 24%	2660
July	1st to 10th	Day	17% 10% 3 9% 6% 5% 5% 5% 6% 8% 26%	4440
	11th to 20th	Day	14% 10% 4 9% 6% 5% 5% 5% 6% 8% 29%	4440
	21st to end	Day	13% 8% 3 7% 4 5% 5% 5% 7% 7% 38%	4814
August	1st to 10th	Day	16% 8% 4 9% 6% 6% 6% 5% 6% 9% 26%	4423
	11th to 20th	Day	17% 10% 3 8% 5% 5% 5% 4 6% 7% 30%	4118
	21st to end	Day	15% 8% 4 8% 6% 5% 6% 4 6% 8% 31%	4180
September	1st to 10th	Day	19% 9% 2 7% 4 4 4 3 6% 6% 36%	2280
	11th to 20th	Day	17% 10% 3 7% 4 4 4 4 5% 6% 37%	2228
	21st to end	Day	23% 9% 3 7% 4 4 4 3 5% 6% 33%	2090
October	1st to 10th	Day	22% 15% 4 8% 5% 3 4 4 4 5% 26%	1914
	11th to 20th	Day	24% 18% 5% 10% 4 3 4 4 4 4 20%	1861
	21st to end	Day	25% 20% 6% 8% 4 4 3 2 4 6% 19%	1881
November	1st to 10th	Day	17% 20% 6% 9% 4 4 4 2 4 5% 26%	1761
	11th to 20th	Day	16% 20% 8% 15% 6% 4 3 3 4 4 17%	1625
	21st to end	Day	18% 22% 8% 16% 6% 4 3 2 3 4 14%	1552
December	1st to 10th	Day	19% 23% 7% 14% 7% 5% 4 3 4 4 12%	1520
	11th to 20th	Day	18% 20% 7% 14% 8% 4 4 3 5% 3 14%	1906
	21st to end	Day	17% 18% 8% 16% 8% 5% 3 2 4 4 14%	2772
January	1st to 10th	Night	12% 21% 9% 16% 8% 6% 5% 3 4 4 14%	4429
	11th to 20th	Night	9% 14% 6% 17% 13% 11% 7% 4 4 4 13%	4440
	21st to end	Night	8% 14% 9% 20% 8% 8% 7% 4 6% 5% 13%	4884
February	1st to 10th	Night	9% 14% 6% 13% 12% 7% 7% 4 5% 5% 17%	2527
	11th to 20th	Night	9% 17% 7% 15% 8% 7% 6% 4 4 5% 17%	2361
	21st to end	Night	10% 15% 6% 13% 9% 6% 5% 3 5% 5% 23%	1884
March	1st to 10th	Night	16% 18% 5% 10% 7% 5% 5% 3 4 4 23%	3724
	11th to 20th	Night	12% 21% 7% 14% 5% 4 4 3 4 5% 22%	3621
	21st to end	Night	12% 12% 5% 12% 5% 6% 5% 4 6% 6% 28%	3503
April	1st to 10th	Night	20% 16% 5% 10% 4 4 4 3 4 5% 25%	1900
	11th to 20th	Night	17% 13% 4 8% 4 5% 3 4 4 6% 32%	1875
	21st to end	Night	19% 13% 4 8% 4 4 3 3 4 6% 33%	1709
May	1st to 10th	Night	19% 11% 3 8% 4 5% 5% 4 5% 6% 30%	2514
	11th to 20th	Night	18% 10% 3 7% 6% 5% 5% 3 5% 7% 32%	2495
	21st to end	Night	20% 9% 3 7% 5% 5% 5% 4 6% 8% 30%	2738
June	1st to 10th	Night	20% 11% 3 6% 5% 5% 5% 4 7% 6% 29%	1520
	11th to 20th	Night	16% 9% 3 7% 5% 4 4 3 5% 8% 34%	1520
	21st to end	Night	20% 7% 3 7% 5% 4 5% 4 6% 7% 32%	1520
July	1st to 10th	Night	15% 10% 4 9% 6% 6% 5% 4 6% 7% 28%	2520
	11th to 20th	Night	14% 9% 3 7% 5% 5% 5% 4 6% 8% 35%	2520
	21st to end	Night	11% 6% 2 6% 4 4 4 4 7% 9% 44%	2739
August	1st to 10th	Night	12% 9% 4 8% 4 5% 5% 4 6% 8% 35%	2506
	11th to 20th	Night	18% 9% 3 8% 5% 3 4 3 5% 6% 35%	2662
	21st to end	Night	19% 9% 3 8% 5% 4 4 3 5% 7% 35%	3476
September	1st to 10th	Night	18% 9% 3 5% 4 5% 4 3 4 7% 39%	1900
	11th to 20th	Night	17% 9% 3 6% 4 4 3 2 5% 6% 42%	1952
	21st to end	Night	18% 11% 3 8% 4 3 3 3 4 5% 38%	2090
October	1st to 10th	Night	19% 11% 3 7% 5% 3 4 3 4 5% 34%	2262
	11th to 20th	Night	22% 18% 4 8% 5% 3 4 2 5% 4 23%	2318
	21st to end	Night	24% 18% 5% 10% 4 4 3 3 3 4 20%	2717
November	1st to 10th	Night	16% 18% 7% 11% 5% 5% 4 3 4 5% 23%	2537
	11th to 20th	Night	15% 16% 8% 13% 7% 6% 4 3 3 4 20%	2771
	21st to end	Night	19% 20% 9% 14% 8% 4 4 3 3 3 14%	2723
December	1st to 10th	Night	15% 22% 9% 16% 9% 6% 4 2 3 2 12%	2660
	11th to 20th	Night	18% 19% 6% 14% 8% 5% 4 3 4 3 15%	3288
	21st to end	Night	16% 21% 8% 17% 8% 5% 4 2 3 3 14%	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	79% 2 7% 9% 4	2518
	11th to 20th	Day	74% 2 3 15% 5% 1	2520
	21st to end	Day	69% 2 6% 14% 7% 1	2772
February	1st to 10th	Day	69% 3 5% 14% 8% 2	1652
	11th to 20th	Day	68% 3 6% 12% 10% 1	1712
	21st to end	Day	68% 2 6% 13% 8% 2	1570
March	1st to 10th	Day	64% 2 7% 12% 13% 2	3119
	11th to 20th	Day	68% 3 6% 11% 10% 3	3336
	21st to end	Day	52% 3 7% 20% 16% 2	4128
April	1st to 10th	Day	64% 3 8% 13% 10% 2	2280
	11th to 20th	Day	58% 3 6% 20% 11% 2	2254
	21st to end	Day	59% 3 8% 15% 13% 2	2485
May	1st to 10th	Day	58% 3 8% 19% 10% 1	4440
	11th to 20th	Day	54% 3 12% 22% 8% 1	4402
	21st to end	Day	54% 3 8% 19% 14% 1	4837
June	1st to 10th	Day	60% 4 7% 19% 9% 1	2660
	11th to 20th	Day	49% 4 12% 23% 11% 1	2660
	21st to end	Day	60% 3 11% 17% 8%	2660
July	1st to 10th	Day	54% 5% 12% 24% 5%	4370
	11th to 20th	Day	50% 5% 18% 22% 5%	4365
	21st to end	Day	43% 6% 18% 25% 8%	4661
August	1st to 10th	Day	53% 5% 15% 22% 5%	4409
	11th to 20th	Day	50% 5% 16% 24% 5%	4160
	21st to end	Day	49% 5% 12% 21% 11% 1	4180
September	1st to 10th	Day	48% 3 14% 25% 10% 1	2280
	11th to 20th	Day	48% 4 15% 25% 9%	2228
	21st to end	Day	52% 4 12% 23% 9%	2090
October	1st to 10th	Day	57% 5% 10% 23% 5%	3174
	11th to 20th	Day	61% 4 13% 18% 4	3064
	21st to end	Day	63% 4 15% 12% 4 1	3081
November	1st to 10th	Day	62% 3 9% 19% 7%	1761
	11th to 20th	Day	71% 3 7% 13% 7%	1625
	21st to end	Day	75% 3 7% 10% 5%	1552
December	1st to 10th	Day	77% 2 5% 10% 5%	1520
	11th to 20th	Day	74% 3 4 11% 7% 1	1906
	21st to end	Day	76% 2 4 13% 5%	2772
January	1st to 10th	Night	75% 2 9% 11% 3	4429
	11th to 20th	Night	75% 3 6% 12% 4 1	4440
	21st to end	Night	73% 3 6% 10% 8% 1	4884
February	1st to 10th	Night	67% 4 5% 15% 8% 1	2527
	11th to 20th	Night	68% 3 5% 14% 8% 1	2363
	21st to end	Night	63% 3 6% 16% 11% 2	1884
March	1st to 10th	Night	66% 2 9% 10% 10% 3	3734
	11th to 20th	Night	66% 2 5% 14% 12% 1	3622
	21st to end	Night	56% 3 8% 19% 11% 4	3503
April	1st to 10th	Night	61% 3 7% 16% 12% 2	1900
	11th to 20th	Night	53% 4 8% 21% 12% 2	1875
	21st to end	Night	54% 2 8% 21% 12% 2	1709
May	1st to 10th	Night	56% 2 13% 18% 8% 2	2520
	11th to 20th	Night	52% 3 13% 20% 11% 1	2496
	21st to end	Night	53% 3 10% 21% 12% 1	2739
June	1st to 10th	Night	53% 4 11% 22% 11% 1	1520
	11th to 20th	Night	48% 3 14% 22% 10% 3	1520
	21st to end	Night	50% 4 14% 22% 10% 1	1520
July	1st to 10th	Night	53% 7% 13% 20% 6%	2480
	11th to 20th	Night	45% 5% 21% 24% 5%	2472
	21st to end	Night	36% 5% 20% 28% 11%	2651
August	1st to 10th	Night	45% 5% 21% 21% 7%	2496
	11th to 20th	Night	49% 5% 20% 22% 5%	2686
	21st to end	Night	49% 4 15% 22% 8% 2	3476
September	1st to 10th	Night	46% 4 15% 24% 11%	1900
	11th to 20th	Night	44% 4 15% 29% 7% 1	1952
	21st to end	Night	49% 4 11% 27% 8%	2090
October	1st to 10th	Night	50% 5% 14% 21% 10% 1	3782
	11th to 20th	Night	60% 3 12% 18% 7%	3841
	21st to end	Night	60% 4 14% 14% 7% 1	4467
November	1st to 10th	Night	64% 3 10% 17% 5%	2537
	11th to 20th	Night	67% 4 7% 14% 6% 1	2771
	21st to end	Night	75% 4 6% 12% 4	2723
December	1st to 10th	Night	80% 2 5% 9% 4	2660
	11th to 20th	Night	73% 3 3 13% 7% 1	3288
	21st to end	Night	76% 3 5% 10% 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	23% 23% 41% 11% 2	180
	11th to 20th	Day	25% 19% 36% 16% 3 2	180
	21st to end	Day	20% 21% 34% 20% 4	198
February	1st to 10th	Day	32% 29% 33% 5% 1	243
	11th to 20th	Day	25% 34% 34% 7% 1	310
	21st to end	Day	29% 26% 32% 11% 1	382
March	1st to 10th	Day	25% 20% 37% 15% 3	460
	11th to 20th	Day	28% 22% 33% 13% 4	460
	21st to end	Day	29% 22% 32% 13% 4 2	506
April	1st to 10th	Day	33% 16% 34% 12% 5% 1	460
	11th to 20th	Day	36% 19% 24% 13% 6% 1	452
	21st to end	Day	34% 18% 33% 12% 3	460
May	1st to 10th	Day	28% 17% 32% 16% 6% 1	463
	11th to 20th	Day	28% 14% 32% 18% 5% 2	487
	21st to end	Day	29% 18% 31% 17% 4 1	529
June	1st to 10th	Day	30% 11% 39% 14% 4 1	490
	11th to 20th	Day	24% 16% 34% 17% 8% 1	490
	21st to end	Day	29% 12% 33% 18% 7% 1	490
July	1st to 10th	Day	21% 9% 37% 23% 8% 2	485
	11th to 20th	Day	20% 12% 36% 24% 7% 1	484
	21st to end	Day	18% 11% 33% 27% 10% 1	532
August	1st to 10th	Day	22% 8% 32% 28% 9% 2	486
	11th to 20th	Day	20% 8% 29% 27% 11% 5%	479
	21st to end	Day	23% 13% 28% 22% 8% 6%	539
September	1st to 10th	Day	25% 13% 30% 19% 9% 3	490
	11th to 20th	Day	22% 8% 31% 22% 13% 4	490
	21st to end	Day	26% 14% 26% 20% 11% 3	490
October	1st to 10th	Day	29% 14% 30% 16% 9% 2	490
	11th to 20th	Day	33% 17% 31% 13% 5% 1	469
	21st to end	Day	36% 14% 32% 15% 3	429
November	1st to 10th	Day	34% 21% 30% 11% 4	395
	11th to 20th	Day	31% 22% 34% 9% 4	225
	21st to end	Day	35% 23% 32% 7% 4	188
December	1st to 10th	Day	33% 18% 30% 13% 6%	180
	11th to 20th	Day	34% 26% 29% 7% 3 1	180
	21st to end	Day	34% 19% 33% 9% 4 2	198
January	1st to 10th	Night	27% 19% 38% 12% 3 1	760
	11th to 20th	Night	23% 23% 33% 15% 5%	760
	21st to end	Night	15% 19% 40% 20% 5% 1	836
February	1st to 10th	Night	19% 22% 37% 18% 5%	760
	11th to 20th	Night	21% 22% 38% 15% 3 1	743
	21st to end	Night	23% 20% 36% 18% 3	628
March	1st to 10th	Night	25% 19% 32% 19% 4	760
	11th to 20th	Night	26% 20% 31% 16% 5% 1	760
	21st to end	Night	23% 15% 34% 22% 5% 1	836
April	1st to 10th	Night	31% 15% 27% 24% 4	760
	11th to 20th	Night	26% 17% 30% 19% 8%	751
	21st to end	Night	28% 16% 30% 20% 6%	569
May	1st to 10th	Night	26% 10% 30% 24% 9% 1	380
	11th to 20th	Night	26% 8% 31% 27% 6% 1	374
	21st to end	Night	22% 11% 38% 23% 6%	411
June	1st to 10th	Night	26% 7% 33% 27% 7%	380
	11th to 20th	Night	20% 8% 29% 28% 13% 1	380
	21st to end	Night	24% 6% 26% 31% 11% 2	380
July	1st to 10th	Night	16% 7% 33% 36% 7% 1	370
	11th to 20th	Night	15% 5% 32% 33% 15% 1	368
	21st to end	Night	16% 6% 28% 38% 11% 2	416
August	1st to 10th	Night	15% 6% 25% 37% 16% 1	378
	11th to 20th	Night	17% 4 26% 34% 18% 2	490
	21st to end	Night	21% 9% 26% 26% 15% 3	836
September	1st to 10th	Night	24% 7% 27% 31% 10% 1	760
	11th to 20th	Night	22% 8% 26% 28% 15% 1	760
	21st to end	Night	25% 11% 27% 22% 13% 2	760
October	1st to 10th	Night	25% 13% 29% 22% 9% 2	760
	11th to 20th	Night	33% 13% 30% 17% 6% 1	760
	21st to end	Night	33% 17% 28% 16% 5%	836
November	1st to 10th	Night	28% 19% 30% 17% 5% 2	780
	11th to 20th	Night	26% 20% 30% 16% 8% 1	800
	21st to end	Night	31% 21% 27% 16% 3 1	779
December	1st to 10th	Night	28% 19% 32% 16% 4 1	760
	11th to 20th	Night	28% 20% 34% 13% 5% 1	760
	21st to end	Night	33% 21% 28% 14% 4 1	836

Page generated at 2024-11-22 08:02:28. Version ac07

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