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 2024-01-17.

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	18% 12% 5% 9% 7% 4 6% 5% 5% 6% 24%	74576
	Night	16% 13% 5% 9% 8% 4 6% 5% 5% 5% 22%	75248
Transparency	Day	60% 9% 10% 14% 6% 1	74276
	Night	63% 9% 10% 13% 5% 1	75083
Seeing	Day	25% 21% 30% 17% 6% 1	14240
	Night	24% 19% 31% 20% 6% 1	22721

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% 17% 7% 14% 9% 5% 8% 5% 5% 6% 13%	1455
	11th to 20th	Day	9% 13% 9% 15% 9% 5% 7% 6% 7% 5% 15%	1488
	21st to end	Day	7% 9% 6% 13% 10% 6% 9% 9% 9% 5% 18%	1584
February	1st to 10th	Day	6% 10% 6% 11% 12% 10% 11% 8% 5% 5% 15%	1440
	11th to 20th	Day	11% 16% 6% 15% 9% 6% 8% 6% 5% 4 15%	1665
	21st to end	Day	5% 16% 6% 13% 10% 5% 7% 6% 6% 5% 22%	1480
March	1st to 10th	Day	13% 17% 6% 12% 7% 4 7% 6% 4 4 20%	1797
	11th to 20th	Day	12% 15% 7% 10% 10% 6% 5% 4 4 5% 22%	1885
	21st to end	Day	14% 16% 7% 11% 5% 3 5% 4 5% 5% 25%	2312
April	1st to 10th	Day	19% 18% 6% 9% 7% 3 5% 4 4 5% 19%	2160
	11th to 20th	Day	18% 15% 3 7% 6% 2 4 4 4 5% 31%	2243
	21st to end	Day	19% 14% 4 7% 6% 3 4 4 5% 7% 27%	2340
May	1st to 10th	Day	22% 11% 4 6% 4 3 6% 4 5% 6% 30%	2443
	11th to 20th	Day	18% 10% 3 7% 6% 3 4 4 5% 5% 34%	2478
	21st to end	Day	21% 8% 3 6% 6% 4 6% 5% 5% 7% 30%	2867
June	1st to 10th	Day	23% 8% 3 7% 6% 3 4 6% 5% 8% 28%	2700
	11th to 20th	Day	21% 7% 3 6% 6% 4 5% 5% 5% 7% 31%	2700
	21st to end	Day	23% 8% 3 6% 6% 3 6% 6% 5% 6% 26%	2700
July	1st to 10th	Day	22% 7% 2 7% 6% 4 4 5% 7% 9% 27%	2695
	11th to 20th	Day	18% 6% 3 8% 8% 4 6% 6% 7% 8% 25%	2520
	21st to end	Day	18% 7% 3 7% 6% 5% 6% 6% 6% 9% 27%	2744
August	1st to 10th	Day	22% 8% 3 7% 7% 4 6% 5% 7% 8% 22%	2506
	11th to 20th	Day	21% 7% 3 6% 6% 4 5% 5% 7% 9% 27%	2329
	21st to end	Day	22% 8% 3 6% 6% 3 5% 5% 6% 7% 28%	2500
September	1st to 10th	Day	20% 8% 3 7% 6% 4 5% 5% 5% 6% 32%	2160
	11th to 20th	Day	21% 9% 4 5% 5% 4 4 4 4 7% 34%	2008
	21st to end	Day	24% 9% 3 5% 5% 3 4 5% 5% 5% 31%	1980
October	1st to 10th	Day	21% 13% 3 6% 6% 4 5% 4 5% 7% 27%	1962
	11th to 20th	Day	24% 19% 5% 8% 5% 3 5% 4 4 5% 17%	1630
	21st to end	Day	23% 24% 5% 7% 5% 3 4 3 4 4 19%	1782
November	1st to 10th	Day	16% 20% 8% 9% 6% 3 5% 3 3 5% 21%	1671
	11th to 20th	Day	15% 20% 8% 13% 8% 4 5% 4 4 4 15%	1593
	21st to end	Day	16% 18% 7% 15% 10% 4 3 4 4 5% 15%	1330
December	1st to 10th	Day	16% 19% 7% 12% 13% 5% 6% 4 4 4 10%	1330
	11th to 20th	Day	17% 17% 6% 13% 7% 4 6% 5% 3 3 18%	1668
	21st to end	Day	16% 16% 7% 10% 12% 6% 6% 5% 4 4 15%	2431
January	1st to 10th	Night	10% 17% 7% 15% 12% 7% 7% 6% 5% 5% 10%	2705
	11th to 20th	Night	11% 14% 6% 13% 10% 5% 8% 8% 8% 4 13%	2616
	21st to end	Night	7% 10% 6% 11% 11% 8% 10% 8% 6% 5% 17%	2772
February	1st to 10th	Night	8% 11% 6% 11% 10% 7% 10% 7% 6% 6% 18%	2520
	11th to 20th	Night	9% 17% 7% 13% 9% 6% 9% 5% 5% 4 17%	2176
	21st to end	Night	9% 16% 6% 11% 9% 4 6% 5% 6% 7% 22%	1776
March	1st to 10th	Night	12% 16% 6% 11% 9% 4 7% 6% 4 5% 20%	2150
	11th to 20th	Night	13% 16% 5% 8% 10% 5% 7% 5% 5% 4 22%	2074
	21st to end	Night	13% 16% 8% 10% 7% 4 5% 3 3 5% 26%	2040
April	1st to 10th	Night	21% 15% 6% 10% 7% 4 5% 4 3 3 22%	1800
	11th to 20th	Night	19% 16% 3 6% 5% 3 4 4 5% 6% 29%	1665
	21st to end	Night	21% 13% 4 5% 6% 3 4 3 4 5% 32%	1620
May	1st to 10th	Night	25% 13% 4 4 6% 3 5% 4 4 4 28%	1532
	11th to 20th	Night	19% 9% 4 6% 4 3 4 5% 5% 8% 33%	1415
	21st to end	Night	24% 10% 4 6% 5% 3 5% 4 5% 5% 30%	1405
June	1st to 10th	Night	22% 8% 4 6% 6% 3 6% 6% 6% 6% 28%	1260
	11th to 20th	Night	18% 7% 3 5% 6% 3 5% 5% 6% 8% 34%	1260
	21st to end	Night	21% 7% 3 7% 7% 4 5% 5% 5% 8% 28%	1260
July	1st to 10th	Night	20% 7% 3 5% 6% 3 5% 7% 7% 9% 28%	1262
	11th to 20th	Night	15% 6% 3 6% 7% 4 6% 5% 8% 9% 31%	1440
	21st to end	Night	18% 7% 3 7% 6% 4 6% 6% 7% 8% 28%	1574
August	1st to 10th	Night	16% 6% 3 6% 7% 3 5% 6% 8% 9% 31%	1432
	11th to 20th	Night	19% 7% 3 7% 5% 5% 6% 5% 5% 7% 32%	1553
	21st to end	Night	22% 8% 3 6% 6% 4 5% 5% 6% 8% 28%	1854
September	1st to 10th	Night	19% 7% 3 6% 5% 3 4 5% 5% 6% 36%	1800
	11th to 20th	Night	22% 10% 3 6% 6% 3 5% 4 4 5% 33%	1952
	21st to end	Night	21% 8% 3 6% 5% 3 5% 4 5% 5% 34%	1980
October	1st to 10th	Night	20% 12% 3 6% 5% 3 4 5% 5% 5% 32%	1996
	11th to 20th	Night	27% 16% 4 6% 6% 3 4 3 5% 5% 21%	2328
	21st to end	Night	24% 18% 5% 7% 5% 3 4 4 5% 6% 20%	2574
November	1st to 10th	Night	18% 17% 8% 9% 6% 3 5% 4 3 6% 21%	2407
	11th to 20th	Night	16% 16% 6% 13% 8% 4 5% 4 5% 5% 18%	2583
	21st to end	Night	15% 18% 8% 15% 10% 5% 5% 4 4 5% 14%	2850
December	1st to 10th	Night	16% 17% 7% 12% 11% 6% 6% 4 4 4 13%	2850
	11th to 20th	Night	14% 16% 7% 15% 12% 5% 6% 5% 4 3 13%	3531
	21st to end	Night	14% 17% 7% 11% 11% 6% 6% 5% 3 3 16%	5236

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	73% 8% 9% 8% 2	1456
	11th to 20th	Day	68% 8% 8% 10% 6% 1	1488
	21st to end	Day	59% 10% 8% 13% 9% 1	1584
February	1st to 10th	Day	67% 9% 9% 8% 5% 1	1440
	11th to 20th	Day	70% 9% 8% 6% 6% 1	1674
	21st to end	Day	63% 8% 7% 16% 5% 2	1480
March	1st to 10th	Day	66% 6% 7% 11% 8% 2	1800
	11th to 20th	Day	65% 6% 7% 13% 8%	1885
	21st to end	Day	62% 7% 7% 15% 8% 1	2312
April	1st to 10th	Day	69% 6% 8% 10% 6% 2	2160
	11th to 20th	Day	56% 6% 9% 18% 9% 2	2243
	21st to end	Day	58% 8% 10% 11% 11% 1	2340
May	1st to 10th	Day	54% 8% 11% 14% 11% 2	2443
	11th to 20th	Day	52% 8% 10% 19% 11% 1	2482
	21st to end	Day	54% 9% 7% 18% 10% 1	2867
June	1st to 10th	Day	56% 8% 9% 17% 8% 1	2700
	11th to 20th	Day	53% 8% 11% 18% 9% 1	2700
	21st to end	Day	58% 9% 11% 14% 7%	2700
July	1st to 10th	Day	53% 10% 14% 18% 4	2620
	11th to 20th	Day	55% 11% 13% 15% 5%	2445
	21st to end	Day	55% 12% 13% 17% 4	2591
August	1st to 10th	Day	60% 12% 13% 13% 2	2492
	11th to 20th	Day	54% 12% 16% 14% 4	2329
	21st to end	Day	55% 10% 14% 17% 4	2500
September	1st to 10th	Day	52% 9% 14% 19% 6%	2160
	11th to 20th	Day	51% 8% 15% 20% 6%	2008
	21st to end	Day	56% 9% 11% 17% 7%	1980
October	1st to 10th	Day	59% 8% 10% 15% 7%	1962
	11th to 20th	Day	70% 8% 10% 10% 1	1630
	21st to end	Day	71% 6% 8% 10% 3 1	1782
November	1st to 10th	Day	68% 8% 10% 12% 2	1671
	11th to 20th	Day	72% 8% 8% 8% 3 1	1593
	21st to end	Day	74% 9% 9% 5% 1	1330
December	1st to 10th	Day	78% 7% 7% 6% 2	1330
	11th to 20th	Day	72% 7% 6% 11% 5%	1668
	21st to end	Day	69% 10% 10% 6% 5%	2431
January	1st to 10th	Night	77% 7% 7% 7% 2	2705
	11th to 20th	Night	68% 10% 9% 8% 4 1	2616
	21st to end	Night	64% 9% 8% 12% 6%	2772
February	1st to 10th	Night	64% 9% 9% 12% 6%	2520
	11th to 20th	Night	70% 8% 7% 10% 5%	2178
	21st to end	Night	62% 9% 8% 14% 7%	1776
March	1st to 10th	Night	66% 8% 7% 13% 6% 1	2160
	11th to 20th	Night	65% 7% 8% 13% 6% 1	2075
	21st to end	Night	62% 6% 9% 15% 6% 2	2040
April	1st to 10th	Night	68% 5% 7% 12% 7% 2	1800
	11th to 20th	Night	55% 7% 9% 19% 10% 1	1665
	21st to end	Night	56% 7% 8% 18% 11% 1	1620
May	1st to 10th	Night	59% 6% 9% 13% 11% 2	1532
	11th to 20th	Night	50% 8% 11% 20% 11% 1	1416
	21st to end	Night	56% 7% 9% 17% 10% 1	1406
June	1st to 10th	Night	56% 9% 12% 16% 6% 1	1260
	11th to 20th	Night	48% 9% 12% 18% 10% 3	1260
	21st to end	Night	53% 10% 13% 16% 7%	1260
July	1st to 10th	Night	49% 12% 16% 19% 4	1227
	11th to 20th	Night	48% 12% 16% 18% 6%	1392
	21st to end	Night	54% 12% 13% 17% 4	1486
August	1st to 10th	Night	47% 15% 19% 18% 2	1422
	11th to 20th	Night	52% 10% 17% 17% 4	1553
	21st to end	Night	53% 11% 13% 20% 3	1854
September	1st to 10th	Night	48% 10% 14% 20% 8%	1800
	11th to 20th	Night	54% 9% 14% 18% 5%	1952
	21st to end	Night	52% 9% 12% 19% 7% 1	1980
October	1st to 10th	Night	55% 9% 11% 17% 7% 1	1996
	11th to 20th	Night	67% 9% 8% 12% 3	2328
	21st to end	Night	67% 8% 10% 10% 4 1	2574
November	1st to 10th	Night	66% 9% 10% 11% 3	2407
	11th to 20th	Night	69% 9% 9% 9% 4	2583
	21st to end	Night	76% 8% 8% 6% 2	2850
December	1st to 10th	Night	76% 8% 7% 6% 2	2850
	11th to 20th	Night	75% 8% 6% 7% 4	3532
	21st to end	Night	74% 8% 7% 8% 3	5236

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% 27% 39% 13% 3	180
	11th to 20th	Day	21% 22% 33% 21% 3	172
	21st to end	Day	15% 24% 34% 21% 4 2	176
February	1st to 10th	Day	19% 32% 40% 8% 1 1	160
	11th to 20th	Day	24% 26% 37% 10% 4	360
	21st to end	Day	21% 26% 32% 17% 4	346
March	1st to 10th	Day	24% 22% 34% 17% 3	420
	11th to 20th	Day	24% 25% 30% 13% 7%	420
	21st to end	Day	25% 23% 31% 15% 4 1	462
April	1st to 10th	Day	29% 24% 27% 15% 3 1	420
	11th to 20th	Day	31% 22% 27% 14% 5% 1	412
	21st to end	Day	26% 22% 34% 13% 3 1	420
May	1st to 10th	Day	30% 21% 29% 15% 5% 1	423
	11th to 20th	Day	23% 18% 35% 19% 5% 1	447
	21st to end	Day	26% 22% 31% 15% 5% 1	627
June	1st to 10th	Day	28% 19% 29% 19% 5% 1	630
	11th to 20th	Day	23% 18% 29% 21% 8% 1	630
	21st to end	Day	23% 14% 32% 22% 8% 1	630
July	1st to 10th	Day	23% 15% 31% 24% 7% 1	615
	11th to 20th	Day	19% 17% 34% 21% 8%	444
	21st to end	Day	18% 15% 34% 23% 10%	488
August	1st to 10th	Day	23% 13% 29% 24% 8% 2	446
	11th to 20th	Day	19% 13% 28% 27% 11% 2	439
	21st to end	Day	23% 18% 28% 16% 11% 4	495
September	1st to 10th	Day	24% 18% 27% 20% 8% 2	450
	11th to 20th	Day	25% 17% 30% 20% 6% 2	450
	21st to end	Day	30% 17% 25% 16% 9% 3	450
October	1st to 10th	Day	25% 22% 26% 18% 8% 2	450
	11th to 20th	Day	29% 28% 25% 10% 6% 1	365
	21st to end	Day	35% 23% 26% 14% 3	396
November	1st to 10th	Day	33% 28% 27% 9% 2 1	365
	11th to 20th	Day	25% 24% 31% 15% 4 1	314
	21st to end	Day	29% 29% 32% 8% 2	180
December	1st to 10th	Day	21% 22% 34% 17% 6%	180
	11th to 20th	Day	28% 28% 33% 6% 4 1	180
	21st to end	Day	26% 31% 24% 13% 5% 1	198
January	1st to 10th	Night	20% 24% 37% 16% 4	787
	11th to 20th	Night	20% 24% 31% 20% 5% 1	748
	21st to end	Night	12% 21% 39% 21% 6% 1	792
February	1st to 10th	Night	14% 22% 41% 19% 3 1	720
	11th to 20th	Night	23% 20% 35% 16% 6%	703
	21st to end	Night	19% 20% 39% 16% 5% 1	592
March	1st to 10th	Night	23% 19% 36% 18% 3	720
	11th to 20th	Night	24% 22% 32% 14% 7% 1	720
	21st to end	Night	22% 23% 29% 22% 4 1	792
April	1st to 10th	Night	29% 18% 30% 19% 4 1	720
	11th to 20th	Night	27% 20% 27% 22% 4	601
	21st to end	Night	30% 16% 31% 20% 4	540
May	1st to 10th	Night	34% 10% 29% 22% 5%	452
	11th to 20th	Night	22% 12% 33% 25% 7%	354
	21st to end	Night	29% 16% 33% 18% 4	389
June	1st to 10th	Night	24% 10% 33% 29% 4	360
	11th to 20th	Night	19% 13% 28% 31% 10% 1	360
	21st to end	Night	21% 13% 31% 28% 7% 1	360
July	1st to 10th	Night	23% 10% 35% 26% 7%	350
	11th to 20th	Night	14% 14% 31% 31% 10%	348
	21st to end	Night	19% 9% 33% 29% 9% 1	394
August	1st to 10th	Night	17% 10% 30% 33% 8% 1	358
	11th to 20th	Night	20% 11% 28% 28% 12% 1	489
	21st to end	Night	24% 11% 29% 25% 10% 1	666
September	1st to 10th	Night	22% 15% 29% 25% 8% 1	720
	11th to 20th	Night	27% 13% 30% 21% 8% 2	720
	21st to end	Night	25% 16% 28% 23% 7% 1	720
October	1st to 10th	Night	28% 16% 27% 22% 7% 1	720
	11th to 20th	Night	34% 22% 24% 14% 6% 1	720
	21st to end	Night	35% 19% 26% 15% 5%	792
November	1st to 10th	Night	32% 21% 28% 13% 5% 1	740
	11th to 20th	Night	23% 30% 29% 13% 5% 1	789
	21st to end	Night	26% 25% 30% 14% 4	850
December	1st to 10th	Night	25% 23% 28% 18% 6%	850
	11th to 20th	Night	24% 22% 30% 18% 6% 1	850
	21st to end	Night	24% 24% 29% 18% 5% 1	935

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