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 2025-02-25.

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% 10% 3 8% 5% 5% 5% 4 5% 7% 32%	108172
	Night	16% 12% 4 10% 6% 5% 5% 4 5% 6% 28%	110550
Transparency	Day	52% 6% 14% 19% 8% 1	111670
	Night	56% 6% 12% 18% 8% 1	115217
Seeing	Day	24% 14% 30% 22% 8% 2	15770
	Night	24% 13% 30% 25% 7% 1	24267

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	14% 19% 6% 11% 7% 5% 4 3 4 5% 21%	3490
	11th to 20th	Day	10% 14% 5% 15% 6% 5% 5% 4 5% 5% 24%	3570
	21st to end	Day	7% 8% 4 14% 8% 5% 5% 4 5% 6% 34%	3960
February	1st to 10th	Day	10% 13% 4 10% 7% 7% 5% 4 7% 6% 27%	1640
	11th to 20th	Day	13% 13% 5% 12% 7% 6% 4 4 5% 5% 26%	1880
	21st to end	Day	11% 12% 5% 8% 6% 5% 5% 4 5% 6% 32%	1610
March	1st to 10th	Day	19% 11% 4 9% 5% 5% 5% 3 5% 6% 28%	3116
	11th to 20th	Day	15% 19% 4 9% 6% 4 4 3 4 5% 25%	3378
	21st to end	Day	13% 16% 4 8% 4 4 3 3 4 5% 35%	3969
April	1st to 10th	Day	22% 12% 3 7% 5% 4 3 4 5% 6% 29%	2280
	11th to 20th	Day	19% 10% 3 7% 3 3 3 3 4 6% 39%	2389
	21st to end	Day	23% 10% 2 6% 4 5% 3 3 5% 6% 33%	2470
May	1st to 10th	Day	17% 9% 3 7% 5% 4 5% 4 5% 6% 35%	4132
	11th to 20th	Day	18% 8% 3 7% 5% 5% 5% 4 6% 7% 33%	4398
	21st to end	Day	16% 7% 3 7% 6% 5% 6% 5% 6% 7% 33%	5081
June	1st to 10th	Day	19% 6% 3 6% 5% 5% 5% 5% 7% 7% 31%	2850
	11th to 20th	Day	18% 7% 2 5% 4 5% 4 4 6% 7% 37%	2850
	21st to end	Day	19% 9% 3 7% 6% 5% 5% 4 6% 8% 29%	2850
July	1st to 10th	Day	13% 7% 3 7% 5% 6% 6% 4 7% 8% 34%	4708
	11th to 20th	Day	12% 6% 3 7% 5% 5% 5% 4 7% 9% 38%	4440
	21st to end	Day	12% 6% 2 6% 4 5% 5% 4 6% 8% 41%	4814
August	1st to 10th	Day	13% 6% 2 7% 5% 5% 6% 5% 8% 9% 33%	4339
	11th to 20th	Day	16% 7% 3 8% 5% 6% 5% 4 6% 9% 32%	4045
	21st to end	Day	17% 7% 2 6% 4 4 4 3 5% 6% 41%	4441
September	1st to 10th	Day	16% 5% 2 5% 4 5% 4 3 6% 8% 42%	2268
	11th to 20th	Day	17% 5% 2 5% 3 3 3 3 5% 6% 49%	2090
	21st to end	Day	19% 8% 2 6% 4 3 4 3 4 7% 41%	2090
October	1st to 10th	Day	18% 8% 3 7% 5% 4 4 4 6% 6% 37%	2078
	11th to 20th	Day	21% 12% 3 8% 5% 5% 5% 3 5% 6% 28%	1753
	21st to end	Day	24% 13% 3 8% 5% 4 4 3 4 5% 27%	1881
November	1st to 10th	Day	16% 11% 4 9% 7% 4 5% 4 5% 6% 30%	1761
	11th to 20th	Day	18% 14% 4 9% 5% 4 4 4 5% 5% 26%	1735
	21st to end	Day	18% 17% 5% 10% 6% 5% 4 3 5% 4 22%	1442
December	1st to 10th	Day	17% 15% 6% 12% 5% 5% 4 4 4 6% 21%	2280
	11th to 20th	Day	18% 11% 4 11% 8% 6% 5% 3 5% 7% 22%	2618
	21st to end	Day	18% 13% 5% 11% 6% 4 5% 3 5% 7% 23%	3476
January	1st to 10th	Night	13% 20% 6% 13% 7% 6% 6% 4 5% 5% 16%	6445
	11th to 20th	Night	10% 17% 7% 17% 7% 6% 5% 4 5% 4 18%	6315
	21st to end	Night	6% 10% 5% 13% 7% 5% 5% 4 6% 7% 32%	6996
February	1st to 10th	Night	9% 14% 5% 11% 7% 5% 4 4 5% 7% 28%	2760
	11th to 20th	Night	12% 16% 5% 11% 8% 5% 5% 3 5% 5% 25%	2402
	21st to end	Night	13% 13% 4 11% 7% 5% 5% 3 4 6% 30%	1939
March	1st to 10th	Night	21% 13% 4 9% 4 4 6% 3 4 5% 26%	3724
	11th to 20th	Night	15% 19% 4 11% 6% 6% 5% 3 5% 5% 22%	3580
	21st to end	Night	19% 16% 5% 9% 4 4 3 3 4 5% 30%	3659
April	1st to 10th	Night	23% 14% 3 9% 4 3 3 3 4 4 30%	1900
	11th to 20th	Night	20% 9% 3 6% 5% 4 4 2 5% 7% 33%	1739
	21st to end	Night	24% 11% 3 7% 4 4 3 3 3 5% 33%	1710
May	1st to 10th	Night	22% 8% 3 7% 3 4 5% 4 6% 5% 34%	2834
	11th to 20th	Night	19% 9% 3 8% 6% 6% 5% 3 5% 6% 30%	2498
	21st to end	Night	17% 7% 2 6% 5% 4 5% 5% 7% 8% 34%	2500
June	1st to 10th	Night	22% 8% 3 7% 5% 6% 4 5% 6% 5% 30%	1330
	11th to 20th	Night	16% 7% 2 7% 5% 4 4 5% 6% 6% 38%	1330
	21st to end	Night	21% 9% 4 8% 5% 4 5% 3 4 7% 30%	1330
July	1st to 10th	Night	12% 9% 3 8% 6% 4 6% 5% 7% 8% 34%	2256
	11th to 20th	Night	17% 7% 3 6% 6% 4 5% 5% 6% 9% 33%	2520
	21st to end	Night	11% 6% 3 6% 5% 5% 4 4 5% 8% 42%	2739
August	1st to 10th	Night	17% 8% 3 8% 4 4 5% 4 6% 7% 35%	2560
	11th to 20th	Night	17% 7% 3 9% 6% 6% 6% 5% 6% 8% 28%	2782
	21st to end	Night	15% 8% 2 8% 4 5% 4 4 5% 6% 38%	3211
September	1st to 10th	Night	17% 7% 2 6% 4 4 4 4 6% 6% 39%	1911
	11th to 20th	Night	19% 7% 3 5% 3 4 4 3 5% 5% 43%	2090
	21st to end	Night	18% 7% 3 7% 4 4 3 3 5% 6% 40%	2090
October	1st to 10th	Night	17% 9% 3 7% 3 4 4 3 5% 6% 38%	2101
	11th to 20th	Night	25% 11% 3 7% 5% 5% 4 2 4 5% 30%	2423
	21st to end	Night	22% 11% 4 9% 5% 4 4 3 5% 6% 28%	2717
November	1st to 10th	Night	19% 12% 3 8% 6% 5% 4 4 5% 5% 30%	2537
	11th to 20th	Night	18% 13% 4 10% 5% 5% 4 3 4 5% 28%	2664
	21st to end	Night	18% 16% 6% 10% 6% 5% 5% 4 4 5% 22%	2955
December	1st to 10th	Night	14% 16% 7% 15% 8% 6% 5% 3 5% 5% 16%	4910
	11th to 20th	Night	19% 13% 5% 11% 6% 5% 5% 3 4 5% 23%	5591
	21st to end	Night	16% 16% 6% 10% 6% 5% 5% 3 4 5% 25%	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	66% 6% 10% 13% 6%	3491
	11th to 20th	Day	64% 4 12% 15% 4 1	3600
	21st to end	Day	51% 7% 9% 18% 15%	3960
February	1st to 10th	Day	57% 5% 13% 15% 9% 2	1640
	11th to 20th	Day	60% 5% 13% 14% 8% 1	1888
	21st to end	Day	53% 5% 10% 21% 9% 2	1610
March	1st to 10th	Day	56% 9% 11% 14% 9% 2	3119
	11th to 20th	Day	61% 7% 13% 13% 6% 1	3378
	21st to end	Day	53% 4 9% 19% 12% 4	3969
April	1st to 10th	Day	58% 4 11% 15% 10% 2	2280
	11th to 20th	Day	49% 4 12% 21% 12% 2	2389
	21st to end	Day	53% 5% 10% 17% 13% 3	2470
May	1st to 10th	Day	48% 9% 12% 19% 12% 1	4146
	11th to 20th	Day	49% 8% 18% 18% 7% 1	4402
	21st to end	Day	47% 9% 11% 21% 11%	5081
June	1st to 10th	Day	50% 8% 13% 20% 8% 1	2850
	11th to 20th	Day	47% 6% 15% 21% 10% 1	2850
	21st to end	Day	55% 6% 14% 17% 9%	2850
July	1st to 10th	Day	49% 5% 16% 22% 7%	4634
	11th to 20th	Day	44% 6% 22% 24% 4 1	4365
	21st to end	Day	42% 6% 21% 24% 8%	4661
August	1st to 10th	Day	47% 6% 22% 21% 4	4325
	11th to 20th	Day	50% 6% 23% 17% 4	4084
	21st to end	Day	45% 6% 19% 18% 12%	4441
September	1st to 10th	Day	42% 6% 17% 24% 11% 1	2268
	11th to 20th	Day	38% 5% 15% 28% 12%	2090
	21st to end	Day	44% 5% 14% 25% 11%	2090
October	1st to 10th	Day	54% 5% 11% 25% 5%	3455
	11th to 20th	Day	53% 4 16% 24% 3	2891
	21st to end	Day	52% 4 16% 21% 7%	3081
November	1st to 10th	Day	55% 6% 13% 19% 7%	1761
	11th to 20th	Day	60% 5% 11% 18% 6% 1	1735
	21st to end	Day	66% 6% 12% 13% 3	1442
December	1st to 10th	Day	64% 4 12% 12% 8%	2280
	11th to 20th	Day	64% 3 8% 18% 6%	2618
	21st to end	Day	61% 5% 11% 11% 11% 1	3476
January	1st to 10th	Night	69% 6% 9% 12% 4	6445
	11th to 20th	Night	70% 5% 10% 11% 4	6360
	21st to end	Night	52% 6% 8% 19% 15%	6996
February	1st to 10th	Night	56% 5% 11% 17% 10% 1	2760
	11th to 20th	Night	62% 4 10% 14% 10% 1	2405
	21st to end	Night	56% 5% 8% 18% 12% 1	1939
March	1st to 10th	Night	59% 7% 9% 16% 8% 1	3734
	11th to 20th	Night	61% 8% 11% 13% 6% 1	3581
	21st to end	Night	57% 4 8% 21% 8% 2	3659
April	1st to 10th	Night	58% 4 7% 16% 13% 2	1900
	11th to 20th	Night	51% 6% 9% 21% 12% 1	1739
	21st to end	Night	55% 4 7% 18% 13% 2	1710
May	1st to 10th	Night	48% 8% 12% 20% 12% 1	2840
	11th to 20th	Night	51% 11% 11% 17% 10%	2499
	21st to end	Night	43% 10% 14% 20% 12% 1	2501
June	1st to 10th	Night	54% 7% 12% 20% 7%	1330
	11th to 20th	Night	44% 7% 13% 22% 11% 3	1330
	21st to end	Night	55% 6% 13% 16% 9%	1330
July	1st to 10th	Night	47% 6% 20% 24% 4	2220
	11th to 20th	Night	48% 6% 20% 21% 3 1	2472
	21st to end	Night	39% 7% 25% 21% 9%	2651
August	1st to 10th	Night	50% 5% 18% 24% 4	2550
	11th to 20th	Night	52% 7% 19% 16% 5%	2809
	21st to end	Night	47% 6% 13% 22% 12%	3211
September	1st to 10th	Night	44% 7% 14% 23% 11% 1	1911
	11th to 20th	Night	44% 6% 16% 24% 9%	2090
	21st to end	Night	44% 7% 11% 26% 11%	2090
October	1st to 10th	Night	50% 4 11% 29% 5% 1	3504
	11th to 20th	Night	57% 3 13% 24% 3	4024
	21st to end	Night	53% 4 18% 18% 7%	4467
November	1st to 10th	Night	57% 6% 12% 19% 6%	2537
	11th to 20th	Night	58% 5% 12% 16% 8% 1	2664
	21st to end	Night	65% 5% 11% 13% 5%	2955
December	1st to 10th	Night	71% 4 11% 11% 3	4910
	11th to 20th	Night	65% 4 6% 19% 6%	5592
	21st to end	Night	63% 4 9% 15% 8%	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	29% 24% 30% 14% 3 1	200
	11th to 20th	Day	29% 20% 34% 11% 6% 1	200
	21st to end	Day	17% 24% 35% 16% 7%	220
February	1st to 10th	Day	23% 23% 34% 15% 5%	240
	11th to 20th	Day	22% 24% 35% 16% 2	461
	21st to end	Day	21% 24% 30% 21% 5%	398
March	1st to 10th	Day	25% 17% 31% 23% 4 1	460
	11th to 20th	Day	26% 16% 30% 20% 7% 2	460
	21st to end	Day	26% 13% 31% 20% 9% 1	506
April	1st to 10th	Day	32% 15% 30% 15% 7% 1	460
	11th to 20th	Day	29% 17% 27% 21% 5% 2	452
	21st to end	Day	26% 19% 32% 17% 5% 2	460
May	1st to 10th	Day	28% 12% 33% 19% 7% 1	463
	11th to 20th	Day	22% 12% 29% 26% 8% 2	487
	21st to end	Day	24% 13% 35% 21% 6% 1	669
June	1st to 10th	Day	24% 11% 32% 23% 8% 1	680
	11th to 20th	Day	23% 11% 27% 25% 13% 1	680
	21st to end	Day	24% 11% 27% 26% 11% 1	680
July	1st to 10th	Day	19% 9% 33% 27% 10% 2	645
	11th to 20th	Day	19% 11% 33% 27% 8% 1	484
	21st to end	Day	18% 7% 35% 27% 11% 1	532
August	1st to 10th	Day	17% 11% 31% 26% 13% 2	486
	11th to 20th	Day	18% 7% 26% 31% 16% 2	479
	21st to end	Day	21% 13% 21% 26% 14% 5%	539
September	1st to 10th	Day	24% 8% 28% 27% 8% 4	490
	11th to 20th	Day	21% 10% 31% 23% 12% 2	490
	21st to end	Day	20% 14% 27% 24% 11% 5%	490
October	1st to 10th	Day	22% 14% 29% 22% 10% 2	483
	11th to 20th	Day	34% 13% 24% 19% 9% 1	390
	21st to end	Day	35% 15% 29% 15% 5%	429
November	1st to 10th	Day	33% 17% 29% 17% 3 1	395
	11th to 20th	Day	28% 19% 25% 21% 7% 1	400
	21st to end	Day	34% 20% 31% 15%	242
December	1st to 10th	Day	29% 18% 30% 17% 6% 1	200
	11th to 20th	Day	32% 24% 29% 11% 4 2	200
	21st to end	Day	34% 21% 27% 15% 3	220
January	1st to 10th	Night	27% 20% 30% 19% 3	822
	11th to 20th	Night	22% 20% 33% 20% 5%	800
	21st to end	Night	17% 16% 37% 24% 5% 1	880
February	1st to 10th	Night	18% 18% 38% 21% 5% 1	800
	11th to 20th	Night	21% 20% 37% 18% 4	783
	21st to end	Night	20% 15% 35% 25% 4	647
March	1st to 10th	Night	23% 14% 35% 23% 5%	760
	11th to 20th	Night	23% 14% 35% 20% 7% 2	760
	21st to end	Night	23% 13% 31% 25% 8%	836
April	1st to 10th	Night	30% 12% 28% 23% 7%	760
	11th to 20th	Night	27% 10% 30% 24% 8%	615
	21st to end	Night	30% 11% 26% 24% 8% 1	570
May	1st to 10th	Night	29% 10% 26% 27% 8%	570
	11th to 20th	Night	25% 7% 24% 32% 11% 1	377
	21st to end	Night	27% 8% 31% 28% 7%	411
June	1st to 10th	Night	25% 7% 25% 34% 8% 1	380
	11th to 20th	Night	18% 5% 24% 38% 14%	380
	21st to end	Night	22% 10% 24% 32% 11%	380
July	1st to 10th	Night	20% 6% 32% 32% 10% 1	370
	11th to 20th	Night	18% 5% 32% 33% 11% 1	368
	21st to end	Night	16% 6% 28% 39% 11%	416
August	1st to 10th	Night	16% 4 27% 36% 17% 1	406
	11th to 20th	Night	18% 6% 24% 36% 15% 1	562
	21st to end	Night	17% 7% 29% 30% 15% 2	675
September	1st to 10th	Night	21% 7% 30% 31% 11% 1	760
	11th to 20th	Night	23% 6% 29% 28% 12% 1	760
	21st to end	Night	23% 6% 29% 30% 11% 1	760
October	1st to 10th	Night	25% 12% 29% 25% 8% 1	760
	11th to 20th	Night	32% 12% 25% 22% 8% 1	760
	21st to end	Night	30% 13% 31% 19% 6%	836
November	1st to 10th	Night	29% 16% 28% 22% 5%	780
	11th to 20th	Night	25% 18% 29% 21% 6% 1	833
	21st to end	Night	29% 17% 30% 19% 5% 1	900
December	1st to 10th	Night	29% 16% 30% 20% 4	900
	11th to 20th	Night	28% 19% 30% 18% 5%	900
	21st to end	Night	30% 19% 27% 20% 4 1	990

Page generated at 2025-02-22 06:51:36. Version ac07

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