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 2026-05-02.

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	16% 12% 4 11% 6% 6% 5% 4 5% 6% 24%	131511
	Night	13% 13% 5% 12% 8% 6% 6% 4 5% 5% 22%	131026
Transparency	Day	58% 9% 11% 15% 6% 1	134936
	Night	61% 9% 10% 14% 6%	135689
Seeing	Day	25% 21% 31% 17% 6% 1	17200
	Night	24% 19% 31% 20% 6% 1	25671

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% 18% 7% 19% 8% 6% 7% 4 4 4 13%	4475
	11th to 20th	Day	6% 12% 7% 20% 13% 10% 8% 5% 5% 4 10%	4650
	21st to end	Day	4 7% 5% 19% 11% 9% 10% 6% 7% 4 17%	5124
February	1st to 10th	Day	5% 11% 5% 13% 11% 11% 11% 6% 5% 5% 17%	1680
	11th to 20th	Day	10% 16% 6% 16% 8% 9% 6% 4 5% 4 16%	1953
	21st to end	Day	5% 16% 5% 13% 9% 7% 6% 5% 6% 6% 22%	1730
March	1st to 10th	Day	11% 18% 6% 13% 6% 4 5% 3 4 5% 25%	4576
	11th to 20th	Day	11% 18% 7% 15% 6% 6% 5% 3 5% 5% 18%	4850
	21st to end	Day	11% 18% 6% 11% 5% 7% 4 3 5% 5% 26%	5950
April	1st to 10th	Day	18% 20% 5% 11% 6% 4 4 3 4 5% 21%	2520
	11th to 20th	Day	17% 16% 4 9% 5% 3 5% 3 4 5% 29%	2622
	21st to end	Day	18% 15% 4 8% 5% 4 4 4 5% 6% 27%	2730
May	1st to 10th	Day	23% 14% 4 8% 4 4 4 3 4 5% 27%	6170
	11th to 20th	Day	23% 10% 3 8% 5% 5% 4 3 5% 5% 28%	6318
	21st to end	Day	19% 10% 2 7% 4 5% 6% 4 6% 8% 29%	7315
June	1st to 10th	Day	23% 8% 2 7% 5% 4 4 5% 6% 7% 28%	3000
	11th to 20th	Day	20% 8% 3 7% 5% 5% 5% 3 6% 6% 30%	3000
	21st to end	Day	23% 9% 2 7% 5% 5% 5% 5% 5% 6% 26%	3000
July	1st to 10th	Day	19% 9% 3 8% 6% 6% 5% 4 7% 8% 25%	6787
	11th to 20th	Day	15% 7% 3 8% 6% 5% 6% 5% 8% 9% 27%	6360
	21st to end	Day	13% 7% 2 8% 5% 6% 5% 4 7% 8% 35%	6926
August	1st to 10th	Day	16% 7% 3 8% 6% 6% 7% 5% 8% 9% 25%	4563
	11th to 20th	Day	21% 7% 2 7% 5% 6% 6% 5% 7% 9% 25%	4214
	21st to end	Day	18% 9% 3 8% 5% 4 4 4 5% 7% 31%	4527
September	1st to 10th	Day	18% 8% 3 8% 4 5% 5% 4 6% 6% 33%	2400
	11th to 20th	Day	19% 9% 3 6% 4 5% 4 3 5% 7% 35%	2230
	21st to end	Day	23% 10% 3 6% 4 4 5% 4 5% 5% 31%	2200
October	1st to 10th	Day	19% 13% 3 8% 5% 5% 4 3 5% 7% 27%	2180
	11th to 20th	Day	22% 20% 5% 9% 4 5% 4 3 4 5% 19%	1810
	21st to end	Day	22% 24% 5% 8% 4 4 4 2 4 4 19%	1980
November	1st to 10th	Day	15% 23% 8% 10% 5% 5% 4 2 3 5% 20%	1851
	11th to 20th	Day	15% 22% 7% 15% 6% 5% 5% 3 4 4 16%	1759
	21st to end	Day	15% 20% 7% 16% 8% 5% 3 3 4 4 13%	1470
December	1st to 10th	Day	12% 17% 7% 17% 15% 8% 4 3 4 4 10%	2350
	11th to 20th	Day	13% 16% 5% 15% 8% 10% 6% 4 5% 4 14%	2688
	21st to end	Day	12% 14% 7% 14% 10% 8% 6% 4 4 5% 17%	3553
January	1st to 10th	Night	7% 19% 8% 17% 10% 10% 9% 6% 4 4 8%	8411
	11th to 20th	Night	5% 15% 7% 24% 12% 8% 6% 4 5% 3 10%	8235
	21st to end	Night	3 7% 4 16% 11% 10% 9% 8% 9% 6% 17%	9057
February	1st to 10th	Night	7% 12% 4 13% 10% 9% 8% 6% 6% 5% 20%	2940
	11th to 20th	Night	8% 18% 6% 16% 7% 8% 7% 4 5% 4 17%	2548
	21st to end	Night	8% 16% 5% 11% 9% 6% 6% 3 6% 6% 24%	2076
March	1st to 10th	Night	13% 16% 5% 13% 8% 5% 7% 6% 5% 5% 18%	5484
	11th to 20th	Night	10% 18% 6% 13% 8% 6% 7% 5% 6% 6% 16%	5329
	21st to end	Night	12% 17% 6% 13% 5% 5% 4 2 4 5% 28%	5219
April	1st to 10th	Night	20% 17% 5% 10% 6% 4 4 2 4 3 24%	2100
	11th to 20th	Night	18% 17% 3 8% 5% 3 4 3 5% 6% 28%	1946
	21st to end	Night	20% 15% 3 7% 5% 5% 3 2 4 5% 31%	1890
May	1st to 10th	Night	20% 13% 3 7% 5% 4 4 4 5% 6% 30%	3836
	11th to 20th	Night	21% 10% 3 7% 4 4 4 3 5% 8% 30%	3575
	21st to end	Night	19% 9% 3 8% 5% 5% 4 3 5% 6% 32%	3560
June	1st to 10th	Night	21% 8% 4 7% 5% 4 5% 5% 6% 6% 29%	1400
	11th to 20th	Night	18% 7% 3 5% 6% 5% 5% 4 7% 8% 34%	1400
	21st to end	Night	21% 8% 3 8% 6% 5% 4 3 5% 8% 28%	1400
July	1st to 10th	Night	15% 8% 3 8% 6% 6% 5% 6% 8% 8% 27%	3175
	11th to 20th	Night	15% 7% 3 7% 6% 6% 5% 5% 8% 9% 29%	3600
	21st to end	Night	15% 8% 2 8% 5% 5% 5% 4 6% 8% 35%	3926
August	1st to 10th	Night	15% 7% 3 7% 6% 6% 5% 5% 7% 9% 30%	2586
	11th to 20th	Night	17% 7% 3 8% 6% 5% 6% 4 6% 7% 30%	2801
	21st to end	Night	18% 7% 3 7% 5% 5% 5% 4 5% 8% 33%	3355
September	1st to 10th	Night	18% 7% 2 6% 4 4 4 4 6% 6% 37%	2000
	11th to 20th	Night	20% 10% 2 7% 5% 4 5% 3 5% 5% 34%	2170
	21st to end	Night	20% 9% 3 7% 5% 4 5% 4 5% 5% 35%	2200
October	1st to 10th	Night	19% 13% 3 7% 4 4 4 4 5% 6% 32%	2218
	11th to 20th	Night	25% 16% 3 8% 5% 4 4 2 5% 5% 22%	2588
	21st to end	Night	23% 19% 5% 8% 5% 4 4 3 5% 5% 20%	2860
November	1st to 10th	Night	18% 19% 7% 10% 5% 4 5% 3 3 5% 20%	2667
	11th to 20th	Night	15% 18% 5% 14% 7% 5% 4 3 5% 5% 18%	2856
	21st to end	Night	14% 20% 7% 16% 9% 6% 4 3 4 4 13%	3150
December	1st to 10th	Night	10% 14% 8% 20% 13% 8% 5% 3 4 4 11%	5060
	11th to 20th	Night	13% 15% 6% 17% 12% 8% 6% 3 4 3 13%	5741
	21st to end	Night	12% 16% 7% 14% 8% 8% 5% 4 4 4 19%	7667

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	74% 7% 9% 10% 1	4476
	11th to 20th	Day	72% 10% 7% 6% 5%	4680
	21st to end	Day	61% 8% 7% 14% 10%	5124
February	1st to 10th	Day	65% 9% 9% 11% 6% 1	1680
	11th to 20th	Day	69% 8% 8% 8% 6% 1	1962
	21st to end	Day	61% 8% 8% 17% 5% 2	1730
March	1st to 10th	Day	59% 8% 9% 12% 9% 4	4579
	11th to 20th	Day	65% 9% 9% 10% 7%	4850
	21st to end	Day	59% 7% 6% 14% 12% 2	5950
April	1st to 10th	Day	67% 5% 8% 11% 6% 3	2520
	11th to 20th	Day	57% 7% 9% 18% 8% 1	2622
	21st to end	Day	58% 8% 10% 12% 11% 1	2730
May	1st to 10th	Day	57% 10% 10% 14% 9% 1	6181
	11th to 20th	Day	54% 10% 10% 17% 8% 1	6322
	21st to end	Day	51% 11% 9% 17% 11% 1	7315
June	1st to 10th	Day	55% 8% 9% 19% 8% 1	3000
	11th to 20th	Day	53% 9% 11% 18% 9% 1	3000
	21st to end	Day	58% 9% 11% 15% 8%	3000
July	1st to 10th	Day	54% 9% 13% 22% 3	6712
	11th to 20th	Day	48% 12% 20% 17% 3	6285
	21st to end	Day	45% 10% 15% 23% 6%	6728
August	1st to 10th	Day	51% 12% 17% 18% 2	4549
	11th to 20th	Day	54% 11% 19% 14% 3	4254
	21st to end	Day	51% 9% 15% 16% 8% 1	4527
September	1st to 10th	Day	50% 9% 15% 20% 6%	2400
	11th to 20th	Day	48% 9% 16% 21% 6%	2230
	21st to end	Day	55% 9% 10% 19% 7%	2200
October	1st to 10th	Day	57% 8% 12% 19% 4	3557
	11th to 20th	Day	66% 7% 11% 14% 2	2922
	21st to end	Day	63% 8% 12% 12% 3	3180
November	1st to 10th	Day	69% 7% 10% 11% 2	1851
	11th to 20th	Day	72% 8% 8% 9% 3 1	1759
	21st to end	Day	75% 9% 9% 5% 1	1470
December	1st to 10th	Day	76% 7% 8% 7% 1	2350
	11th to 20th	Day	68% 9% 8% 11% 4	2688
	21st to end	Day	66% 9% 8% 9% 7%	3553
January	1st to 10th	Night	77% 9% 8% 6% 1	8411
	11th to 20th	Night	75% 8% 6% 7% 3	8280
	21st to end	Night	58% 9% 8% 14% 10% 1	9057
February	1st to 10th	Night	62% 8% 9% 13% 7%	2940
	11th to 20th	Night	70% 8% 7% 10% 5%	2550
	21st to end	Night	60% 9% 8% 14% 8%	2076
March	1st to 10th	Night	65% 10% 7% 11% 7%	5494
	11th to 20th	Night	65% 11% 11% 9% 4	5330
	21st to end	Night	59% 6% 6% 19% 10% 1	5219
April	1st to 10th	Night	65% 5% 7% 13% 8% 2	2100
	11th to 20th	Night	56% 6% 8% 18% 10% 1	1946
	21st to end	Night	57% 7% 8% 18% 10% 1	1890
May	1st to 10th	Night	51% 10% 9% 17% 11% 1	3842
	11th to 20th	Night	50% 9% 13% 20% 8%	3576
	21st to end	Night	50% 10% 11% 15% 12% 1	3561
June	1st to 10th	Night	54% 9% 12% 18% 6% 1	1400
	11th to 20th	Night	47% 10% 13% 18% 10% 3	1400
	21st to end	Night	53% 10% 13% 17% 7%	1400
July	1st to 10th	Night	49% 11% 16% 20% 4	3140
	11th to 20th	Night	47% 11% 21% 19% 3	3552
	21st to end	Night	46% 10% 17% 21% 6%	3809
August	1st to 10th	Night	47% 12% 18% 18% 4	2576
	11th to 20th	Night	50% 10% 20% 16% 3	2827
	21st to end	Night	48% 10% 12% 22% 7%	3355
September	1st to 10th	Night	46% 10% 15% 21% 8%	2000
	11th to 20th	Night	52% 9% 13% 20% 6%	2170
	21st to end	Night	51% 9% 12% 20% 8% 1	2200
October	1st to 10th	Night	52% 7% 13% 23% 4	3621
	11th to 20th	Night	63% 7% 10% 15% 5%	4215
	21st to end	Night	60% 11% 14% 12% 3 1	4610
November	1st to 10th	Night	67% 9% 10% 11% 3	2667
	11th to 20th	Night	69% 9% 8% 9% 4	2856
	21st to end	Night	77% 8% 7% 6% 2	3150
December	1st to 10th	Night	75% 9% 7% 8% 1	5060
	11th to 20th	Night	72% 9% 6% 9% 4	5742
	21st to end	Night	69% 8% 7% 10% 6%	7667

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	18% 28% 38% 13% 3	220
	11th to 20th	Day	20% 22% 33% 20% 5%	220
	21st to end	Day	16% 25% 36% 18% 4 2	242
February	1st to 10th	Day	16% 26% 42% 11% 3 1	220
	11th to 20th	Day	22% 26% 36% 13% 3	468
	21st to end	Day	19% 27% 35% 16% 3	446
March	1st to 10th	Day	26% 22% 34% 15% 3	540
	11th to 20th	Day	26% 25% 31% 12% 6% 1	540
	21st to end	Day	27% 25% 30% 14% 3 1	594
April	1st to 10th	Day	31% 24% 27% 14% 3 1	540
	11th to 20th	Day	30% 23% 28% 14% 5% 1	532
	21st to end	Day	28% 22% 33% 13% 3 1	540
May	1st to 10th	Day	30% 21% 28% 15% 5% 1	507
	11th to 20th	Day	24% 17% 33% 20% 5% 1	527
	21st to end	Day	26% 22% 31% 16% 5% 1	731
June	1st to 10th	Day	28% 18% 28% 20% 5% 1	730
	11th to 20th	Day	24% 19% 30% 19% 8% 1	730
	21st to end	Day	25% 15% 32% 20% 7% 1	730
July	1st to 10th	Day	23% 16% 32% 23% 6% 1	713
	11th to 20th	Day	19% 19% 35% 19% 8%	524
	21st to end	Day	18% 17% 34% 22% 9%	576
August	1st to 10th	Day	21% 14% 30% 25% 8% 2	526
	11th to 20th	Day	18% 13% 29% 27% 11% 2	519
	21st to end	Day	24% 18% 26% 18% 10% 4	583
September	1st to 10th	Day	23% 17% 31% 18% 8% 2	530
	11th to 20th	Day	23% 16% 30% 21% 8% 2	530
	21st to end	Day	29% 18% 24% 17% 9% 3	530
October	1st to 10th	Day	25% 21% 28% 17% 8% 2	530
	11th to 20th	Day	29% 27% 25% 10% 7% 1	425
	21st to end	Day	35% 23% 26% 14% 3	462
November	1st to 10th	Day	34% 28% 27% 9% 2 1	425
	11th to 20th	Day	25% 25% 30% 15% 5% 1	368
	21st to end	Day	29% 30% 31% 8% 1	220
December	1st to 10th	Day	18% 24% 36% 17% 5%	220
	11th to 20th	Day	28% 27% 32% 7% 4 1	220
	21st to end	Day	23% 28% 28% 14% 5% 1	242
January	1st to 10th	Night	19% 23% 37% 16% 4	873
	11th to 20th	Night	20% 24% 30% 20% 5% 1	840
	21st to end	Night	12% 21% 39% 22% 6% 1	924
February	1st to 10th	Night	13% 21% 40% 20% 4 1	840
	11th to 20th	Night	21% 21% 36% 16% 5%	823
	21st to end	Night	19% 19% 39% 17% 4 1	692
March	1st to 10th	Night	23% 20% 35% 18% 3	840
	11th to 20th	Night	25% 22% 32% 14% 7%	840
	21st to end	Night	21% 23% 30% 21% 4	924
April	1st to 10th	Night	30% 18% 31% 17% 3	840
	11th to 20th	Night	28% 21% 27% 21% 3	702
	21st to end	Night	31% 16% 30% 19% 3	630
May	1st to 10th	Night	34% 11% 31% 20% 4	506
	11th to 20th	Night	22% 12% 33% 25% 7%	394
	21st to end	Night	28% 15% 34% 19% 4	433
June	1st to 10th	Night	23% 11% 33% 29% 5%	400
	11th to 20th	Night	20% 13% 28% 29% 10% 1	400
	21st to end	Night	23% 13% 31% 26% 7% 1	400
July	1st to 10th	Night	22% 9% 35% 27% 6%	390
	11th to 20th	Night	13% 14% 33% 31% 9%	388
	21st to end	Night	19% 9% 34% 28% 9% 1	438
August	1st to 10th	Night	16% 11% 31% 32% 9% 1	398
	11th to 20th	Night	20% 10% 28% 30% 11% 1	545
	21st to end	Night	23% 11% 28% 26% 10% 1	740
September	1st to 10th	Night	22% 16% 29% 25% 7% 1	800
	11th to 20th	Night	25% 13% 29% 23% 8% 2	800
	21st to end	Night	24% 16% 27% 24% 8% 1	800
October	1st to 10th	Night	27% 16% 28% 21% 7% 1	800
	11th to 20th	Night	33% 21% 24% 15% 6% 1	800
	21st to end	Night	35% 19% 26% 16% 4	880
November	1st to 10th	Night	33% 21% 28% 12% 5% 1	820
	11th to 20th	Night	23% 29% 28% 14% 5% 1	876
	21st to end	Night	26% 26% 31% 14% 4	950
December	1st to 10th	Night	23% 24% 29% 18% 6%	950
	11th to 20th	Night	24% 22% 30% 17% 5% 1	950
	21st to end	Night	23% 22% 30% 18% 5% 1	1045

Page generated at 2026-04-29 02:21:46. Version ac07

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