Lac des Ilets
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac des Ilets clear sky chart from 2005-11-06 to 2025-01-07.

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% 12% 4 10% 6% 6% 5% 4 5% 6% 25%	104798
	Night	15% 14% 5% 11% 7% 6% 5% 4 5% 5% 23%	104270
Transparency	Day	58% 9% 11% 15% 6% 1	108241
	Night	61% 9% 10% 13% 5%	108917
Seeing	Day	25% 21% 30% 17% 6% 1	15518
	Night	24% 19% 31% 20% 6% 1	23955

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	10% 15% 7% 19% 9% 6% 5% 3 5% 6% 14%	2452
	11th to 20th	Day	8% 11% 6% 18% 12% 12% 9% 4 6% 3 10%	2520
	21st to end	Day	7% 12% 7% 18% 8% 7% 7% 4 7% 5% 19%	2772
February	1st to 10th	Day	6% 12% 5% 13% 11% 12% 10% 6% 5% 5% 16%	1520
	11th to 20th	Day	10% 16% 6% 16% 9% 9% 7% 5% 5% 4 14%	1760
	21st to end	Day	6% 17% 5% 13% 8% 7% 6% 5% 6% 5% 22%	1570
March	1st to 10th	Day	12% 15% 4 10% 6% 5% 6% 4 4 6% 30%	3116
	11th to 20th	Day	12% 21% 7% 15% 6% 6% 4 3 3 5% 18%	3315
	21st to end	Day	11% 17% 6% 12% 4 5% 4 3 5% 6% 28%	4060
April	1st to 10th	Day	18% 20% 5% 10% 6% 4 4 3 4 5% 21%	2280
	11th to 20th	Day	17% 16% 3 8% 5% 3 5% 3 4 5% 30%	2370
	21st to end	Day	18% 15% 3 8% 5% 4 4 4 5% 6% 28%	2470
May	1st to 10th	Day	20% 13% 3 8% 5% 5% 5% 3 5% 6% 28%	4293
	11th to 20th	Day	17% 10% 3 8% 5% 5% 5% 4 5% 7% 31%	4398
	21st to end	Day	18% 9% 2 7% 5% 5% 6% 4 6% 8% 29%	5091
June	1st to 10th	Day	23% 9% 2 7% 5% 4 4 4 6% 7% 28%	2850
	11th to 20th	Day	20% 8% 3 7% 5% 5% 5% 3 6% 7% 30%	2850
	21st to end	Day	23% 9% 2 7% 5% 5% 5% 5% 5% 6% 26%	2850
July	1st to 10th	Day	19% 9% 3 8% 6% 5% 5% 4 7% 8% 27%	4741
	11th to 20th	Day	15% 7% 4 9% 6% 5% 6% 5% 7% 8% 26%	4440
	21st to end	Day	15% 7% 2 8% 5% 6% 5% 4 6% 8% 33%	4814
August	1st to 10th	Day	17% 7% 3 8% 6% 6% 7% 5% 8% 9% 24%	4423
	11th to 20th	Day	21% 7% 2 8% 5% 6% 6% 5% 8% 9% 24%	4083
	21st to end	Day	19% 9% 3 8% 5% 4 5% 3 5% 7% 31%	4388
September	1st to 10th	Day	19% 8% 3 8% 5% 5% 5% 4 5% 6% 32%	2280
	11th to 20th	Day	20% 9% 3 6% 4 5% 4 3 4 7% 36%	2119
	21st to end	Day	24% 10% 3 6% 4 4 5% 4 5% 5% 30%	2090
October	1st to 10th	Day	20% 13% 3 8% 5% 5% 4 3 5% 7% 26%	2071
	11th to 20th	Day	23% 20% 5% 9% 4 5% 4 3 4 5% 18%	1720
	21st to end	Day	22% 24% 6% 8% 4 4 4 2 4 4 19%	1881
November	1st to 10th	Day	15% 22% 8% 10% 5% 5% 4 2 3 5% 21%	1761
	11th to 20th	Day	15% 21% 7% 14% 6% 5% 5% 3 4 4 16%	1676
	21st to end	Day	15% 20% 6% 16% 8% 5% 3 3 4 5% 14%	1400
December	1st to 10th	Day	12% 17% 7% 17% 15% 8% 4 3 4 4 10%	2280
	11th to 20th	Day	13% 16% 5% 15% 8% 10% 6% 4 4 4 15%	2618
	21st to end	Day	12% 14% 7% 13% 10% 8% 6% 4 4 5% 17%	3476
January	1st to 10th	Night	9% 17% 7% 16% 11% 11% 8% 4 4 4 8%	4612
	11th to 20th	Night	8% 13% 5% 18% 13% 8% 8% 4 6% 4 13%	4440
	21st to end	Night	6% 13% 6% 15% 9% 10% 7% 5% 6% 5% 19%	4884
February	1st to 10th	Night	7% 13% 5% 13% 9% 9% 8% 5% 6% 6% 19%	2660
	11th to 20th	Night	9% 17% 6% 16% 8% 8% 7% 4 5% 4 16%	2301
	21st to end	Night	9% 17% 5% 11% 8% 6% 6% 4 6% 6% 22%	1884
March	1st to 10th	Night	15% 16% 4 10% 6% 5% 7% 5% 5% 5% 23%	3724
	11th to 20th	Night	12% 22% 8% 14% 7% 5% 5% 3 4 4 16%	3644
	21st to end	Night	12% 17% 6% 13% 5% 5% 4 3 4 6% 27%	3568
April	1st to 10th	Night	20% 17% 5% 10% 6% 4 4 2 3 3 24%	1900
	11th to 20th	Night	18% 17% 3 7% 5% 4 4 3 5% 6% 28%	1758
	21st to end	Night	20% 14% 3 6% 5% 5% 3 2 4 5% 31%	1710
May	1st to 10th	Night	20% 13% 4 7% 5% 4 5% 3 5% 5% 28%	2676
	11th to 20th	Night	15% 10% 3 7% 4 4 4 4 6% 9% 35%	2495
	21st to end	Night	22% 9% 3 7% 4 5% 5% 3 5% 7% 30%	2476
June	1st to 10th	Night	21% 8% 4 7% 5% 4 5% 5% 5% 6% 29%	1330
	11th to 20th	Night	18% 7% 3 5% 6% 5% 5% 4 7% 8% 34%	1330
	21st to end	Night	21% 8% 3 8% 7% 5% 5% 3 5% 8% 28%	1330
July	1st to 10th	Night	17% 8% 3 7% 6% 5% 5% 5% 7% 8% 28%	2225
	11th to 20th	Night	13% 6% 3 8% 6% 6% 5% 5% 8% 8% 31%	2520
	21st to end	Night	14% 6% 2 7% 5% 6% 5% 4 6% 8% 37%	2739
August	1st to 10th	Night	15% 7% 3 7% 6% 6% 6% 5% 7% 9% 29%	2506
	11th to 20th	Night	17% 7% 3 8% 6% 5% 6% 4 6% 7% 30%	2713
	21st to end	Night	18% 7% 3 7% 5% 5% 5% 4 5% 8% 33%	3252
September	1st to 10th	Night	19% 7% 3 7% 4 4 4 4 6% 6% 36%	1900
	11th to 20th	Night	21% 10% 2 7% 5% 4 5% 3 5% 5% 34%	2061
	21st to end	Night	21% 9% 3 7% 5% 4 5% 4 5% 5% 33%	2090
October	1st to 10th	Night	19% 13% 3 7% 4 4 4 4 5% 6% 31%	2107
	11th to 20th	Night	26% 17% 3 8% 5% 4 4 2 5% 5% 21%	2458
	21st to end	Night	23% 19% 5% 8% 5% 4 4 3 5% 5% 20%	2717
November	1st to 10th	Night	18% 18% 7% 10% 5% 4 5% 3 3 5% 21%	2537
	11th to 20th	Night	15% 18% 5% 14% 7% 5% 4 3 5% 5% 18%	2720
	21st to end	Night	15% 21% 7% 16% 8% 6% 4 3 4 4 13%	3000
December	1st to 10th	Night	10% 14% 8% 20% 13% 8% 5% 3 4 4 11%	4910
	11th to 20th	Night	13% 15% 5% 16% 12% 8% 6% 3 4 3 13%	5591
	21st to end	Night	12% 16% 7% 14% 8% 8% 5% 4 4 4 19%	7502

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	72% 8% 10% 9% 1	2453
	11th to 20th	Day	75% 8% 6% 6% 4	2520
	21st to end	Day	61% 9% 8% 10% 11% 1	2772
February	1st to 10th	Day	66% 9% 9% 9% 6% 1	1520
	11th to 20th	Day	70% 9% 8% 7% 6% 1	1769
	21st to end	Day	62% 9% 8% 16% 5% 2	1570
March	1st to 10th	Day	53% 9% 12% 16% 8% 3	3119
	11th to 20th	Day	69% 9% 7% 11% 5%	3315
	21st to end	Day	56% 8% 8% 16% 10% 2	4060
April	1st to 10th	Day	67% 6% 8% 11% 6% 3	2280
	11th to 20th	Day	56% 6% 9% 18% 9% 1	2370
	21st to end	Day	57% 8% 10% 11% 12% 1	2470
May	1st to 10th	Day	52% 13% 12% 14% 8% 1	4307
	11th to 20th	Day	49% 12% 12% 20% 7%	4402
	21st to end	Day	50% 12% 8% 18% 10% 1	5091
June	1st to 10th	Day	55% 8% 9% 18% 8% 1	2850
	11th to 20th	Day	52% 9% 11% 18% 9% 1	2850
	21st to end	Day	58% 9% 11% 15% 7%	2850
July	1st to 10th	Day	51% 9% 12% 24% 3	4666
	11th to 20th	Day	51% 11% 18% 16% 3	4365
	21st to end	Day	48% 10% 16% 20% 6%	4661
August	1st to 10th	Day	52% 12% 16% 18% 2	4409
	11th to 20th	Day	54% 11% 19% 13% 2	4123
	21st to end	Day	51% 9% 15% 16% 8% 1	4388
September	1st to 10th	Day	51% 9% 14% 19% 6%	2280
	11th to 20th	Day	49% 9% 16% 21% 6%	2119
	21st to end	Day	56% 9% 10% 18% 7%	2090
October	1st to 10th	Day	57% 8% 12% 19% 4	3448
	11th to 20th	Day	66% 7% 11% 14% 1	2832
	21st to end	Day	63% 9% 12% 12% 3	3081
November	1st to 10th	Day	68% 8% 10% 12% 2	1761
	11th to 20th	Day	72% 8% 8% 9% 3 1	1676
	21st to end	Day	75% 9% 9% 5% 1	1400
December	1st to 10th	Day	77% 7% 8% 7% 1	2280
	11th to 20th	Day	68% 9% 8% 11% 4	2618
	21st to end	Day	66% 9% 9% 9% 7%	3476
January	1st to 10th	Night	78% 9% 6% 5% 1	4612
	11th to 20th	Night	72% 9% 7% 8% 3 1	4440
	21st to end	Night	63% 9% 8% 9% 10% 1	4884
February	1st to 10th	Night	63% 9% 8% 12% 6%	2660
	11th to 20th	Night	71% 8% 7% 10% 4	2303
	21st to end	Night	61% 10% 8% 14% 7%	1884
March	1st to 10th	Night	62% 11% 8% 13% 6%	3734
	11th to 20th	Night	71% 9% 7% 9% 3 1	3645
	21st to end	Night	59% 7% 8% 19% 7% 1	3568
April	1st to 10th	Night	66% 5% 7% 13% 8% 2	1900
	11th to 20th	Night	56% 7% 9% 18% 9% 1	1758
	21st to end	Night	56% 7% 8% 18% 10% 1	1710
May	1st to 10th	Night	53% 11% 10% 16% 10% 1	2682
	11th to 20th	Night	43% 12% 15% 21% 9%	2496
	21st to end	Night	52% 10% 10% 17% 11% 1	2477
June	1st to 10th	Night	55% 9% 12% 18% 5% 1	1330
	11th to 20th	Night	47% 10% 13% 18% 10% 3	1330
	21st to end	Night	54% 10% 13% 16% 7%	1330
July	1st to 10th	Night	49% 11% 15% 22% 3	2190
	11th to 20th	Night	46% 11% 20% 19% 4	2472
	21st to end	Night	44% 10% 19% 19% 8%	2651
August	1st to 10th	Night	48% 12% 18% 17% 4	2496
	11th to 20th	Night	51% 10% 21% 15% 3	2739
	21st to end	Night	48% 10% 12% 22% 7%	3252
September	1st to 10th	Night	48% 11% 14% 20% 8%	1900
	11th to 20th	Night	52% 9% 14% 19% 6%	2061
	21st to end	Night	52% 9% 12% 19% 7% 1	2090
October	1st to 10th	Night	53% 7% 13% 22% 4 1	3510
	11th to 20th	Night	64% 7% 11% 14% 5%	4085
	21st to end	Night	60% 11% 14% 12% 3 1	4467
November	1st to 10th	Night	67% 9% 10% 11% 3	2537
	11th to 20th	Night	69% 9% 8% 9% 4	2720
	21st to end	Night	77% 8% 8% 6% 2	3000
December	1st to 10th	Night	76% 9% 7% 7% 1	4910
	11th to 20th	Night	72% 9% 6% 9% 4	5592
	21st to end	Night	69% 8% 7% 10% 6%	7502

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	19% 27% 38% 14% 3	192
	11th to 20th	Day	21% 22% 33% 21% 3	180
	21st to end	Day	16% 23% 36% 20% 4 2	198
February	1st to 10th	Day	18% 29% 41% 9% 2 1	180
	11th to 20th	Day	22% 26% 37% 12% 4	395
	21st to end	Day	21% 27% 32% 16% 3	382
March	1st to 10th	Day	24% 22% 34% 16% 3	460
	11th to 20th	Day	23% 25% 31% 13% 7% 1	460
	21st to end	Day	26% 25% 31% 14% 4 1	506
April	1st to 10th	Day	30% 23% 27% 16% 3 1	460
	11th to 20th	Day	30% 23% 27% 14% 5% 1	452
	21st to end	Day	27% 22% 34% 13% 3 1	460
May	1st to 10th	Day	29% 22% 29% 14% 5% 1	463
	11th to 20th	Day	22% 18% 33% 20% 5% 1	487
	21st to end	Day	26% 23% 30% 15% 4 1	679
June	1st to 10th	Day	28% 18% 28% 20% 5% 1	680
	11th to 20th	Day	23% 18% 29% 20% 8% 1	680
	21st to end	Day	24% 15% 33% 20% 7% 1	680
July	1st to 10th	Day	23% 15% 32% 23% 6% 1	664
	11th to 20th	Day	19% 17% 35% 20% 8%	484
	21st to end	Day	18% 15% 34% 23% 9%	532
August	1st to 10th	Day	22% 15% 29% 24% 7% 2	486
	11th to 20th	Day	19% 13% 27% 28% 11% 2	479
	21st to end	Day	23% 18% 26% 18% 11% 4	539
September	1st to 10th	Day	23% 18% 30% 19% 7% 2	490
	11th to 20th	Day	23% 16% 31% 21% 7% 2	490
	21st to end	Day	29% 18% 24% 17% 9% 3	490
October	1st to 10th	Day	25% 20% 27% 17% 8% 2	490
	11th to 20th	Day	30% 28% 25% 10% 6% 1	395
	21st to end	Day	35% 23% 26% 13% 3	429
November	1st to 10th	Day	34% 27% 27% 9% 2 1	395
	11th to 20th	Day	26% 24% 30% 15% 4 1	341
	21st to end	Day	29% 30% 32% 8% 2	200
December	1st to 10th	Day	20% 22% 36% 18% 6%	200
	11th to 20th	Day	28% 28% 33% 7% 5% 2	200
	21st to end	Day	24% 30% 25% 14% 6% 1	220
January	1st to 10th	Night	20% 24% 36% 16% 4	815
	11th to 20th	Night	20% 24% 31% 19% 4 1	760
	21st to end	Night	12% 21% 39% 22% 6% 1	836
February	1st to 10th	Night	14% 21% 40% 20% 3 1	760
	11th to 20th	Night	22% 20% 36% 16% 6%	743
	21st to end	Night	20% 20% 39% 16% 5% 1	628
March	1st to 10th	Night	23% 19% 36% 19% 3	760
	11th to 20th	Night	23% 22% 32% 15% 8% 1	760
	21st to end	Night	21% 24% 30% 21% 4	836
April	1st to 10th	Night	29% 17% 31% 19% 4 1	760
	11th to 20th	Night	27% 20% 28% 21% 4	634
	21st to end	Night	31% 15% 31% 19% 4	570
May	1st to 10th	Night	33% 11% 30% 21% 5%	477
	11th to 20th	Night	21% 13% 33% 26% 7%	374
	21st to end	Night	29% 15% 34% 18% 4	411
June	1st to 10th	Night	23% 10% 33% 29% 5%	380
	11th to 20th	Night	19% 12% 28% 30% 10% 1	380
	21st to end	Night	22% 13% 30% 27% 7% 1	380
July	1st to 10th	Night	22% 10% 35% 26% 6%	370
	11th to 20th	Night	13% 14% 33% 31% 9%	368
	21st to end	Night	19% 9% 33% 28% 9% 1	416
August	1st to 10th	Night	17% 11% 31% 32% 9% 1	378
	11th to 20th	Night	20% 10% 28% 30% 11% 1	517
	21st to end	Night	23% 11% 29% 25% 10% 1	703
September	1st to 10th	Night	22% 16% 29% 24% 8% 1	760
	11th to 20th	Night	25% 13% 30% 22% 8% 2	760
	21st to end	Night	24% 15% 27% 24% 8% 1	760
October	1st to 10th	Night	28% 16% 27% 21% 7% 1	760
	11th to 20th	Night	34% 21% 24% 14% 6% 1	760
	21st to end	Night	35% 19% 26% 15% 4	836
November	1st to 10th	Night	32% 21% 28% 13% 5% 1	780
	11th to 20th	Night	23% 29% 28% 14% 5% 1	833
	21st to end	Night	26% 26% 31% 14% 4	900
December	1st to 10th	Night	24% 23% 28% 19% 6%	900
	11th to 20th	Night	24% 22% 30% 18% 6% 1	900
	21st to end	Night	23% 23% 30% 18% 5% 1	990

Page generated at 2025-01-04 03:24:02. Version ac07

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