L'Islet
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the L'Islet clear sky chart from 2005-11-06 to 2026-07-01.

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% 10% 3 8% 5% 5% 5% 4 5% 7% 32%	137672
	Night	16% 12% 4 10% 6% 5% 5% 4 5% 6% 28%	134757
Transparency	Day	53% 5% 14% 20% 8% 1	141124
	Night	57% 5% 11% 18% 8% 1	139395
Seeing	Day	25% 15% 30% 21% 8% 1	17612
	Night	24% 13% 30% 24% 7% 1	25918

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	13% 17% 5% 10% 6% 5% 4 4 5% 5% 27%	4530
	11th to 20th	Day	11% 15% 6% 15% 7% 6% 5% 4 5% 5% 22%	4650
	21st to end	Day	5% 8% 4 13% 8% 5% 6% 5% 6% 7% 35%	5124
February	1st to 10th	Day	9% 12% 4 11% 7% 7% 5% 4 7% 6% 28%	1722
	11th to 20th	Day	12% 13% 5% 12% 7% 6% 4 4 5% 5% 27%	1977
	21st to end	Day	11% 12% 5% 9% 6% 5% 5% 4 5% 6% 31%	1730
March	1st to 10th	Day	18% 14% 5% 11% 6% 5% 4 3 4 5% 26%	4576
	11th to 20th	Day	14% 15% 4 8% 5% 5% 5% 4 5% 6% 28%	4943
	21st to end	Day	15% 16% 5% 10% 4 4 4 3 4 5% 31%	5815
April	1st to 10th	Day	22% 12% 3 8% 5% 4 3 4 4 6% 29%	2520
	11th to 20th	Day	19% 11% 3 7% 3 3 3 3 4 6% 37%	2643
	21st to end	Day	22% 10% 2 6% 4 5% 4 3 5% 7% 33%	2730
May	1st to 10th	Day	20% 10% 3 8% 5% 4 5% 4 5% 6% 29%	7692
	11th to 20th	Day	19% 9% 3 7% 5% 5% 5% 4 5% 6% 32%	8221
	21st to end	Day	17% 9% 3 8% 5% 5% 6% 4 6% 7% 31%	9514
June	1st to 10th	Day	19% 6% 3 6% 5% 5% 5% 5% 7% 8% 31%	3150
	11th to 20th	Day	19% 7% 2 5% 4 4 4 4 6% 7% 37%	3150
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 4 6% 8% 29%	3150
July	1st to 10th	Day	15% 7% 3 8% 5% 5% 6% 4 7% 8% 31%	6740
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 4 6% 8% 37%	6360
	21st to end	Day	11% 5% 2 6% 4 5% 5% 4 7% 9% 42%	6926
August	1st to 10th	Day	13% 6% 2 7% 5% 5% 6% 5% 8% 9% 34%	4476
	11th to 20th	Day	16% 7% 3 7% 5% 6% 5% 4 6% 9% 33%	4175
	21st to end	Day	17% 7% 3 6% 4 4 4 3 5% 6% 41%	4581
September	1st to 10th	Day	15% 5% 2 5% 4 5% 4 4 6% 8% 42%	2387
	11th to 20th	Day	16% 5% 2 5% 3 3 3 3 4 6% 50%	2200
	21st to end	Day	18% 7% 2 6% 4 3 4 3 5% 7% 42%	2200
October	1st to 10th	Day	17% 7% 3 6% 5% 4 4 3 6% 7% 38%	2187
	11th to 20th	Day	20% 11% 3 8% 5% 5% 5% 4 5% 6% 29%	1845
	21st to end	Day	24% 13% 3 8% 5% 4 5% 3 4 6% 27%	1980
November	1st to 10th	Day	17% 11% 4 9% 7% 4 5% 4 4 6% 29%	1851
	11th to 20th	Day	18% 14% 5% 9% 5% 4 5% 4 5% 5% 26%	1822
	21st to end	Day	18% 17% 5% 10% 6% 5% 4 3 5% 4 22%	1514
December	1st to 10th	Day	17% 14% 6% 12% 5% 5% 5% 4 4 6% 21%	2350
	11th to 20th	Day	18% 11% 4 11% 8% 6% 5% 3 5% 7% 22%	2688
	21st to end	Day	18% 13% 5% 11% 6% 4 5% 4 5% 7% 23%	3553
January	1st to 10th	Night	12% 17% 6% 13% 7% 5% 6% 4 5% 6% 19%	8356
	11th to 20th	Night	10% 19% 7% 16% 7% 6% 6% 4 4 4 16%	8235
	21st to end	Night	5% 10% 5% 15% 7% 6% 6% 4 6% 6% 31%	9057
February	1st to 10th	Night	9% 14% 5% 11% 7% 5% 4 4 5% 7% 30%	2898
	11th to 20th	Night	12% 16% 5% 10% 8% 5% 5% 3 5% 5% 26%	2525
	21st to end	Night	12% 14% 4 10% 6% 4 5% 3 4 6% 30%	2076
March	1st to 10th	Night	20% 13% 4 11% 6% 4 6% 3 4 5% 25%	5484
	11th to 20th	Night	14% 15% 4 10% 6% 6% 6% 5% 7% 6% 21%	5235
	21st to end	Night	18% 16% 5% 9% 4 4 3 3 4 5% 29%	5355
April	1st to 10th	Night	23% 14% 3 9% 4 3 3 3 4 4 29%	2100
	11th to 20th	Night	20% 10% 3 7% 5% 5% 5% 3 5% 6% 32%	1925
	21st to end	Night	23% 11% 3 7% 5% 4 3 3 3 5% 33%	1890
May	1st to 10th	Night	23% 10% 3 7% 4 5% 4 3 6% 6% 29%	5259
	11th to 20th	Night	21% 9% 3 8% 6% 5% 5% 3 5% 6% 30%	4642
	21st to end	Night	17% 7% 3 7% 5% 4 5% 4 6% 7% 35%	4668
June	1st to 10th	Night	21% 8% 3 7% 5% 6% 5% 5% 6% 5% 30%	1470
	11th to 20th	Night	17% 7% 2 6% 5% 4 4 4 6% 6% 37%	1470
	21st to end	Night	21% 9% 4 8% 6% 4 5% 3 4 7% 30%	1470
July	1st to 10th	Night	13% 8% 2 7% 5% 5% 6% 5% 7% 10% 32%	3219
	11th to 20th	Night	18% 7% 3 6% 5% 4 5% 4 6% 8% 34%	3600
	21st to end	Night	10% 6% 3 7% 5% 5% 5% 4 5% 8% 42%	3926
August	1st to 10th	Night	16% 8% 3 8% 4 4 5% 4 6% 7% 36%	2642
	11th to 20th	Night	16% 7% 3 9% 6% 6% 6% 4 6% 8% 29%	2872
	21st to end	Night	15% 8% 2 8% 5% 5% 4 4 5% 6% 38%	3313
September	1st to 10th	Night	17% 6% 2 6% 4 4 4 4 6% 6% 41%	2012
	11th to 20th	Night	18% 7% 3 5% 3 4 4 3 4 5% 43%	2200
	21st to end	Night	18% 7% 3 6% 4 4 3 4 5% 6% 40%	2200
October	1st to 10th	Night	17% 8% 3 7% 3 4 4 3 6% 7% 39%	2212
	11th to 20th	Night	25% 11% 3 7% 5% 5% 4 2 4 5% 31%	2551
	21st to end	Night	22% 11% 4 9% 5% 4 4 3 5% 6% 28%	2860
November	1st to 10th	Night	19% 12% 3 8% 6% 5% 4 4 4 5% 29%	2667
	11th to 20th	Night	18% 13% 4 10% 5% 5% 4 3 4 5% 28%	2797
	21st to end	Night	18% 16% 6% 10% 6% 5% 5% 3 4 5% 22%	3103
December	1st to 10th	Night	13% 16% 7% 15% 8% 6% 6% 3 5% 5% 16%	5060
	11th to 20th	Night	19% 13% 5% 11% 7% 5% 5% 3 5% 5% 23%	5741
	21st to end	Night	16% 16% 6% 10% 6% 5% 5% 3 4 5% 25%	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	59% 5% 10% 19% 7%	4531
	11th to 20th	Day	67% 3 10% 15% 4	4680
	21st to end	Day	49% 6% 10% 20% 14%	5124
February	1st to 10th	Day	56% 4 13% 17% 9% 2	1722
	11th to 20th	Day	59% 5% 12% 16% 8% 1	1985
	21st to end	Day	54% 5% 10% 22% 9% 2	1730
March	1st to 10th	Day	61% 6% 8% 11% 11% 3	4579
	11th to 20th	Day	56% 6% 16% 15% 7%	4943
	21st to end	Day	57% 3 7% 17% 12% 3	5815
April	1st to 10th	Day	58% 4 10% 16% 10% 2	2520
	11th to 20th	Day	51% 3 12% 21% 12% 2	2643
	21st to end	Day	53% 4 10% 18% 12% 2	2730
May	1st to 10th	Day	56% 6% 9% 19% 10% 1	7704
	11th to 20th	Day	52% 5% 13% 20% 6% 2	8225
	21st to end	Day	53% 6% 12% 18% 11%	9515
June	1st to 10th	Day	50% 7% 13% 21% 8% 1	3150
	11th to 20th	Day	47% 6% 14% 22% 10% 1	3150
	21st to end	Day	55% 5% 15% 16% 8%	3150
July	1st to 10th	Day	52% 4 15% 22% 7%	6666
	11th to 20th	Day	45% 5% 21% 25% 4	6285
	21st to end	Day	39% 5% 19% 29% 7%	6728
August	1st to 10th	Day	45% 6% 23% 21% 5%	4462
	11th to 20th	Day	49% 6% 23% 18% 5%	4214
	21st to end	Day	45% 6% 19% 18% 12%	4581
September	1st to 10th	Day	42% 5% 17% 25% 10% 1	2387
	11th to 20th	Day	37% 5% 15% 30% 12%	2200
	21st to end	Day	43% 5% 14% 26% 12%	2200
October	1st to 10th	Day	52% 5% 12% 26% 6%	3564
	11th to 20th	Day	53% 4 16% 24% 3	2983
	21st to end	Day	53% 4 16% 21% 7%	3180
November	1st to 10th	Day	56% 6% 13% 18% 7%	1851
	11th to 20th	Day	60% 5% 11% 18% 6%	1822
	21st to end	Day	66% 5% 12% 13% 3	1514
December	1st to 10th	Day	64% 4 12% 12% 8%	2350
	11th to 20th	Day	64% 3 8% 18% 6%	2688
	21st to end	Day	61% 5% 11% 12% 11% 1	3553
January	1st to 10th	Night	65% 5% 9% 14% 6%	8356
	11th to 20th	Night	72% 4 8% 11% 5%	8280
	21st to end	Night	54% 5% 9% 18% 15%	9057
February	1st to 10th	Night	55% 5% 10% 19% 10% 1	2898
	11th to 20th	Night	61% 4 9% 15% 10% 1	2528
	21st to end	Night	55% 5% 8% 18% 13% 1	2076
March	1st to 10th	Night	62% 5% 7% 13% 12% 1	5494
	11th to 20th	Night	60% 7% 13% 14% 6% 1	5236
	21st to end	Night	59% 3 6% 21% 10% 1	5355
April	1st to 10th	Night	59% 4 6% 16% 13% 2	2100
	11th to 20th	Night	53% 6% 9% 20% 12% 1	1925
	21st to end	Night	55% 4 7% 19% 13% 2	1890
May	1st to 10th	Night	55% 5% 10% 18% 11% 1	5265
	11th to 20th	Night	54% 7% 9% 20% 9%	4643
	21st to end	Night	47% 6% 12% 19% 14% 2	4669
June	1st to 10th	Night	53% 6% 12% 21% 8%	1470
	11th to 20th	Night	46% 6% 13% 22% 10% 3	1470
	21st to end	Night	55% 6% 14% 16% 9%	1470
July	1st to 10th	Night	48% 5% 21% 22% 5%	3183
	11th to 20th	Night	49% 5% 20% 24% 3	3552
	21st to end	Night	40% 6% 22% 23% 8%	3809
August	1st to 10th	Night	49% 5% 18% 24% 4	2632
	11th to 20th	Night	51% 7% 19% 17% 5%	2899
	21st to end	Night	47% 6% 13% 22% 12%	3313
September	1st to 10th	Night	42% 6% 14% 25% 10% 1	2012
	11th to 20th	Night	43% 6% 16% 25% 9%	2200
	21st to end	Night	44% 7% 11% 27% 12%	2200
October	1st to 10th	Night	49% 4 12% 29% 6% 1	3615
	11th to 20th	Night	56% 3 13% 24% 3	4152
	21st to end	Night	54% 4 17% 18% 7%	4610
November	1st to 10th	Night	58% 6% 12% 18% 6%	2667
	11th to 20th	Night	58% 5% 12% 16% 8% 1	2797
	21st to end	Night	66% 5% 11% 13% 5%	3103
December	1st to 10th	Night	71% 4 11% 11% 3	5060
	11th to 20th	Night	65% 4 6% 19% 5%	5742
	21st to end	Night	63% 4 9% 15% 9%	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	29% 25% 30% 13% 3 1	220
	11th to 20th	Day	30% 20% 33% 10% 5%	220
	21st to end	Day	17% 24% 36% 15% 7%	242
February	1st to 10th	Day	21% 22% 33% 18% 5%	262
	11th to 20th	Day	21% 24% 35% 17% 3	498
	21st to end	Day	21% 23% 32% 20% 4	446
March	1st to 10th	Day	27% 20% 29% 20% 4 1	540
	11th to 20th	Day	28% 17% 30% 18% 6% 1	540
	21st to end	Day	28% 15% 30% 18% 8% 1	594
April	1st to 10th	Day	34% 16% 30% 14% 6% 1	540
	11th to 20th	Day	31% 17% 27% 19% 5% 1	532
	21st to end	Day	26% 19% 31% 17% 5% 2	540
May	1st to 10th	Day	31% 13% 32% 17% 6% 1	543
	11th to 20th	Day	25% 12% 30% 24% 7% 2	567
	21st to end	Day	26% 13% 34% 21% 6% 1	772
June	1st to 10th	Day	24% 12% 32% 23% 8% 1	780
	11th to 20th	Day	25% 11% 27% 25% 11% 1	780
	21st to end	Day	24% 11% 28% 26% 11% 1	780
July	1st to 10th	Day	20% 10% 32% 27% 9% 1	693
	11th to 20th	Day	19% 11% 33% 26% 8% 2	524
	21st to end	Day	18% 9% 36% 26% 10% 1	576
August	1st to 10th	Day	16% 10% 32% 27% 13% 2	526
	11th to 20th	Day	18% 7% 26% 31% 16% 2	519
	21st to end	Day	22% 13% 22% 26% 13% 4	583
September	1st to 10th	Day	24% 9% 28% 27% 8% 4	530
	11th to 20th	Day	20% 10% 32% 22% 13% 3	530
	21st to end	Day	20% 14% 27% 23% 11% 5%	530
October	1st to 10th	Day	22% 15% 31% 21% 9% 2	522
	11th to 20th	Day	32% 13% 25% 19% 10% 1	420
	21st to end	Day	35% 15% 31% 14% 5%	462
November	1st to 10th	Day	35% 17% 29% 16% 3	425
	11th to 20th	Day	29% 19% 24% 21% 7%	430
	21st to end	Day	35% 20% 31% 14%	264
December	1st to 10th	Day	28% 20% 30% 15% 5% 1	220
	11th to 20th	Day	34% 24% 27% 10% 3 1	220
	21st to end	Day	32% 21% 28% 15% 3	242
January	1st to 10th	Night	27% 20% 31% 19% 3	864
	11th to 20th	Night	22% 20% 33% 19% 5%	840
	21st to end	Night	17% 17% 36% 23% 5% 1	924
February	1st to 10th	Night	17% 17% 37% 22% 6% 1	840
	11th to 20th	Night	21% 19% 37% 19% 4	823
	21st to end	Night	20% 15% 36% 24% 4	692
March	1st to 10th	Night	25% 15% 34% 21% 5%	840
	11th to 20th	Night	24% 14% 36% 18% 6% 2	840
	21st to end	Night	23% 14% 32% 23% 7%	924
April	1st to 10th	Night	32% 12% 28% 22% 6%	840
	11th to 20th	Night	28% 10% 31% 23% 7%	681
	21st to end	Night	30% 11% 27% 24% 8%	630
May	1st to 10th	Night	29% 11% 27% 26% 7%	630
	11th to 20th	Night	26% 7% 25% 32% 10%	417
	21st to end	Night	26% 9% 30% 28% 7%	455
June	1st to 10th	Night	25% 6% 26% 34% 8% 1	420
	11th to 20th	Night	19% 6% 25% 37% 13%	420
	21st to end	Night	22% 10% 25% 32% 10%	420
July	1st to 10th	Night	20% 6% 32% 32% 9% 1	390
	11th to 20th	Night	18% 6% 31% 33% 11% 1	388
	21st to end	Night	15% 6% 29% 39% 11%	438
August	1st to 10th	Night	15% 4 27% 36% 17% 1	428
	11th to 20th	Night	17% 6% 25% 38% 14% 1	592
	21st to end	Night	17% 7% 29% 31% 14% 2	711
September	1st to 10th	Night	20% 7% 29% 32% 11% 1	800
	11th to 20th	Night	22% 7% 29% 29% 12% 1	800
	21st to end	Night	22% 7% 30% 29% 12% 1	800
October	1st to 10th	Night	24% 12% 31% 25% 8% 1	800
	11th to 20th	Night	31% 12% 25% 23% 9% 1	800
	21st to end	Night	31% 13% 31% 20% 6%	880
November	1st to 10th	Night	31% 16% 28% 21% 5%	820
	11th to 20th	Night	25% 18% 29% 21% 6% 1	876
	21st to end	Night	30% 17% 30% 18% 5% 1	950
December	1st to 10th	Night	29% 16% 31% 20% 4	950
	11th to 20th	Night	28% 20% 30% 17% 5%	950
	21st to end	Night	30% 18% 28% 19% 4 1	1045

Page generated at 2026-06-28 02:10:42. Version ac07

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