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 2024-02-10.

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	17% 9% 4 7% 6% 3 5% 5% 5% 7% 33%	77844
	Night	17% 11% 4 8% 6% 4 5% 5% 5% 6% 29%	81111
Transparency	Day	52% 6% 14% 19% 8% 1	77544
	Night	56% 6% 11% 18% 8% 1	80946
Seeing	Day	24% 14% 30% 22% 8% 2	14410
	Night	24% 13% 30% 25% 8% 1	22924

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	12% 15% 5% 9% 8% 4 6% 6% 6% 7% 23%	2436
	11th to 20th	Day	13% 11% 5% 10% 7% 4 5% 5% 5% 6% 30%	2520
	21st to end	Day	9% 9% 4 9% 9% 4 5% 5% 5% 7% 34%	2772
February	1st to 10th	Day	10% 13% 5% 8% 8% 5% 6% 5% 7% 7% 27%	1549
	11th to 20th	Day	14% 13% 5% 10% 8% 5% 4 5% 5% 6% 26%	1687
	21st to end	Day	12% 12% 5% 8% 8% 3 5% 5% 5% 7% 32%	1480
March	1st to 10th	Day	15% 11% 5% 8% 5% 4 6% 5% 5% 6% 32%	1797
	11th to 20th	Day	16% 11% 5% 8% 7% 3 5% 5% 4 6% 31%	1920
	21st to end	Day	15% 12% 4 7% 6% 3 4 5% 5% 6% 33%	2263
April	1st to 10th	Day	22% 11% 4 7% 6% 3 4 4 5% 6% 28%	2160
	11th to 20th	Day	19% 9% 3 6% 4 3 3 3 4 6% 40%	2261
	21st to end	Day	23% 10% 3 5% 5% 3 4 4 4 6% 32%	2340
May	1st to 10th	Day	20% 9% 3 5% 5% 3 5% 5% 5% 6% 35%	2352
	11th to 20th	Day	18% 7% 3 7% 6% 3 5% 4 5% 6% 36%	2478
	21st to end	Day	19% 6% 3 5% 6% 3 6% 5% 5% 7% 35%	2857
June	1st to 10th	Day	19% 6% 3 5% 6% 3 5% 6% 7% 8% 31%	2700
	11th to 20th	Day	19% 6% 3 5% 4 3 5% 5% 6% 7% 37%	2700
	21st to end	Day	18% 8% 3 6% 7% 4 5% 5% 6% 9% 30%	2700
July	1st to 10th	Day	13% 6% 3 6% 5% 3 6% 5% 6% 10% 36%	2676
	11th to 20th	Day	13% 5% 3 5% 6% 4 5% 5% 7% 10% 37%	2520
	21st to end	Day	15% 7% 3 5% 5% 4 5% 5% 7% 9% 36%	2744
August	1st to 10th	Day	14% 5% 3 6% 6% 4 6% 7% 7% 10% 33%	2463
	11th to 20th	Day	12% 6% 3 6% 4 3 5% 5% 6% 9% 40%	2304
	21st to end	Day	14% 6% 2 5% 5% 3 5% 5% 6% 8% 42%	2525
September	1st to 10th	Day	16% 5% 2 4 4 4 4 4 5% 8% 42%	2149
	11th to 20th	Day	18% 5% 2 5% 3 2 3 4 4 5% 48%	1980
	21st to end	Day	19% 7% 2 5% 4 2 3 4 4 7% 42%	1980
October	1st to 10th	Day	18% 7% 3 5% 6% 3 4 4 5% 7% 37%	1969
	11th to 20th	Day	21% 11% 4 7% 6% 4 5% 4 4 6% 28%	1661
	21st to end	Day	25% 13% 3 7% 5% 4 4 4 4 5% 26%	1782
November	1st to 10th	Day	17% 10% 4 8% 8% 3 5% 5% 4 6% 30%	1671
	11th to 20th	Day	19% 13% 5% 8% 7% 4 4 5% 5% 6% 26%	1649
	21st to end	Day	18% 15% 6% 8% 8% 4 5% 5% 5% 5% 23%	1370
December	1st to 10th	Day	21% 13% 8% 11% 7% 3 4 4 4 4 21%	1330
	11th to 20th	Day	19% 13% 5% 9% 7% 5% 4 4 4 6% 24%	1668
	21st to end	Day	21% 13% 5% 8% 6% 3 5% 4 4 6% 26%	2431
January	1st to 10th	Night	13% 16% 7% 11% 9% 5% 6% 5% 5% 6% 18%	4497
	11th to 20th	Night	12% 14% 6% 10% 8% 5% 7% 5% 5% 5% 23%	4440
	21st to end	Night	9% 12% 5% 9% 7% 5% 5% 5% 6% 7% 28%	4884
February	1st to 10th	Night	10% 13% 5% 10% 8% 4 5% 5% 5% 7% 28%	2616
	11th to 20th	Night	13% 15% 6% 9% 9% 5% 5% 4 5% 5% 24%	2155
	21st to end	Night	13% 13% 5% 9% 7% 3 5% 4 4 6% 30%	1776
March	1st to 10th	Night	15% 13% 5% 8% 5% 4 5% 4 5% 6% 29%	2150
	11th to 20th	Night	17% 11% 5% 8% 6% 3 5% 5% 5% 5% 30%	2038
	21st to end	Night	16% 15% 4 7% 5% 2 5% 4 4 6% 30%	2089
April	1st to 10th	Night	24% 14% 4 9% 5% 2 3 4 5% 4 28%	1800
	11th to 20th	Night	20% 9% 3 6% 6% 3 5% 4 5% 7% 34%	1647
	21st to end	Night	25% 11% 4 6% 5% 3 4 3 3 5% 32%	1620
May	1st to 10th	Night	24% 8% 4 7% 4 2 4 5% 5% 5% 32%	1620
	11th to 20th	Night	22% 6% 3 5% 7% 3 5% 4 4 6% 35%	1418
	21st to end	Night	21% 8% 3 5% 6% 3 3 5% 4 6% 36%	1416
June	1st to 10th	Night	22% 7% 3 7% 6% 5% 5% 5% 6% 6% 29%	1260
	11th to 20th	Night	17% 6% 3 6% 5% 3 4 5% 6% 6% 38%	1260
	21st to end	Night	21% 8% 4 7% 6% 3 4 4 4 7% 31%	1260
July	1st to 10th	Night	17% 8% 3 5% 6% 2 4 5% 6% 7% 37%	1280
	11th to 20th	Night	14% 5% 3 6% 7% 3 6% 6% 6% 9% 34%	1440
	21st to end	Night	14% 6% 3 6% 6% 4 6% 5% 6% 8% 35%	1574
August	1st to 10th	Night	14% 5% 3 5% 5% 3 4 5% 6% 9% 41%	1458
	11th to 20th	Night	15% 6% 3 7% 6% 4 6% 6% 6% 9% 32%	1596
	21st to end	Night	15% 7% 2 6% 6% 3 4 5% 5% 7% 40%	1827
September	1st to 10th	Night	18% 6% 3 5% 5% 3 4 5% 6% 6% 39%	1810
	11th to 20th	Night	20% 7% 3 5% 4 3 4 4 4 5% 42%	1980
	21st to end	Night	19% 7% 3 6% 4 3 4 4 4 6% 41%	1980
October	1st to 10th	Night	18% 8% 3 6% 4 3 4 3 5% 6% 39%	1990
	11th to 20th	Night	26% 10% 3 6% 6% 4 4 3 4 5% 29%	2295
	21st to end	Night	23% 10% 4 7% 6% 3 3 4 5% 6% 28%	2574
November	1st to 10th	Night	19% 11% 3 7% 6% 5% 4 5% 4 6% 30%	2407
	11th to 20th	Night	18% 12% 4 8% 6% 4 4 5% 4 5% 29%	2530
	21st to end	Night	18% 14% 6% 9% 7% 3 5% 5% 4 6% 24%	2807
December	1st to 10th	Night	19% 16% 6% 11% 8% 4 5% 4 4 6% 18%	2850
	11th to 20th	Night	18% 14% 5% 8% 8% 4 5% 4 5% 5% 22%	3531
	21st to end	Night	20% 16% 6% 8% 6% 3 4 4 3 4 26%	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	60% 8% 14% 14% 4	2437
	11th to 20th	Day	56% 6% 13% 19% 5% 1	2520
	21st to end	Day	49% 10% 12% 20% 9%	2772
February	1st to 10th	Day	57% 5% 13% 15% 8% 1	1549
	11th to 20th	Day	61% 4 13% 13% 8% 1	1695
	21st to end	Day	54% 4 10% 21% 9% 2	1480
March	1st to 10th	Day	55% 5% 11% 15% 11% 2	1800
	11th to 20th	Day	55% 5% 10% 17% 10% 1	1920
	21st to end	Day	53% 5% 12% 18% 9% 3	2263
April	1st to 10th	Day	59% 4 11% 14% 10% 2	2160
	11th to 20th	Day	49% 3 12% 21% 12% 2	2261
	21st to end	Day	54% 5% 10% 16% 12% 3	2340
May	1st to 10th	Day	51% 6% 12% 17% 13% 2	2352
	11th to 20th	Day	50% 5% 11% 22% 11% 1	2482
	21st to end	Day	50% 7% 11% 21% 9% 1	2857
June	1st to 10th	Day	50% 8% 13% 19% 8% 1	2700
	11th to 20th	Day	48% 6% 14% 21% 10% 1	2700
	21st to end	Day	54% 6% 14% 16% 9%	2700
July	1st to 10th	Day	45% 8% 19% 21% 7%	2602
	11th to 20th	Day	43% 9% 17% 24% 7% 1	2445
	21st to end	Day	47% 8% 18% 20% 6% 1	2591
August	1st to 10th	Day	47% 8% 22% 20% 3	2449
	11th to 20th	Day	42% 7% 22% 21% 8%	2304
	21st to end	Day	42% 7% 18% 24% 9%	2525
September	1st to 10th	Day	42% 6% 17% 23% 11% 1	2149
	11th to 20th	Day	39% 6% 15% 27% 12%	1980
	21st to end	Day	43% 5% 15% 25% 12%	1980
October	1st to 10th	Day	47% 5% 12% 26% 9%	1969
	11th to 20th	Day	60% 6% 15% 16% 4	1661
	21st to end	Day	63% 5% 12% 16% 5%	1782
November	1st to 10th	Day	55% 7% 13% 18% 7%	1671
	11th to 20th	Day	60% 5% 12% 17% 5% 1	1649
	21st to end	Day	65% 6% 13% 13% 3	1370
December	1st to 10th	Day	67% 5% 10% 14% 5%	1330
	11th to 20th	Day	63% 4 8% 18% 7%	1668
	21st to end	Day	62% 6% 12% 13% 6% 1	2431
January	1st to 10th	Night	64% 8% 10% 12% 6% 1	4497
	11th to 20th	Night	62% 6% 11% 14% 6% 1	4440
	21st to end	Night	54% 8% 10% 16% 11% 1	4884
February	1st to 10th	Night	56% 5% 11% 17% 10% 1	2616
	11th to 20th	Night	63% 4 9% 14% 9% 1	2158
	21st to end	Night	57% 4 8% 17% 12% 1	1776
March	1st to 10th	Night	57% 5% 8% 18% 11% 1	2160
	11th to 20th	Night	55% 5% 10% 17% 11% 2	2039
	21st to end	Night	56% 4 10% 18% 9% 3	2089
April	1st to 10th	Night	60% 4 7% 15% 12% 2	1800
	11th to 20th	Night	50% 7% 9% 21% 13% 1	1647
	21st to end	Night	56% 4 7% 17% 13% 2	1620
May	1st to 10th	Night	54% 5% 10% 17% 13% 2	1620
	11th to 20th	Night	51% 5% 10% 19% 14% 1	1419
	21st to end	Night	50% 6% 10% 19% 14% 1	1417
June	1st to 10th	Night	54% 6% 13% 19% 7%	1260
	11th to 20th	Night	45% 7% 12% 23% 11% 3	1260
	21st to end	Night	54% 6% 14% 16% 10%	1260
July	1st to 10th	Night	45% 8% 17% 23% 7%	1244
	11th to 20th	Night	44% 9% 16% 24% 6% 1	1392
	21st to end	Night	45% 11% 17% 20% 7%	1486
August	1st to 10th	Night	40% 7% 22% 28% 3	1448
	11th to 20th	Night	47% 9% 19% 18% 7%	1596
	21st to end	Night	42% 8% 13% 28% 8%	1827
September	1st to 10th	Night	44% 7% 14% 23% 11% 1	1810
	11th to 20th	Night	45% 6% 16% 23% 10%	1980
	21st to end	Night	43% 7% 11% 26% 11%	1980
October	1st to 10th	Night	47% 5% 11% 27% 9% 1	1990
	11th to 20th	Night	58% 5% 13% 19% 4	2295
	21st to end	Night	58% 6% 13% 16% 7%	2574
November	1st to 10th	Night	56% 6% 12% 18% 6%	2407
	11th to 20th	Night	58% 5% 12% 16% 8% 1	2530
	21st to end	Night	64% 5% 11% 14% 5%	2807
December	1st to 10th	Night	68% 6% 10% 11% 4	2850
	11th to 20th	Night	64% 6% 8% 14% 8%	3532
	21st to end	Night	63% 6% 10% 14% 7% 1	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	27% 24% 31% 14% 3 1	180
	11th to 20th	Day	30% 20% 34% 9% 6% 1	180
	21st to end	Day	16% 23% 34% 18% 8% 1	198
February	1st to 10th	Day	23% 21% 34% 15% 5%	215
	11th to 20th	Day	22% 23% 35% 16% 2	388
	21st to end	Day	23% 24% 28% 20% 5%	346
March	1st to 10th	Day	24% 17% 32% 22% 4 1	420
	11th to 20th	Day	26% 16% 30% 20% 7% 2	420
	21st to end	Day	24% 13% 30% 21% 10% 2	462
April	1st to 10th	Day	32% 15% 29% 15% 8% 1	420
	11th to 20th	Day	28% 17% 26% 21% 5% 2	412
	21st to end	Day	27% 15% 33% 17% 5% 2	420
May	1st to 10th	Day	28% 11% 34% 19% 6% 1	423
	11th to 20th	Day	23% 11% 30% 27% 7% 2	447
	21st to end	Day	25% 12% 35% 21% 6% 1	617
June	1st to 10th	Day	24% 11% 33% 23% 7% 1	630
	11th to 20th	Day	23% 11% 26% 25% 13% 1	630
	21st to end	Day	22% 10% 28% 27% 12% 1	630
July	1st to 10th	Day	19% 9% 32% 28% 11% 2	597
	11th to 20th	Day	17% 10% 33% 29% 9% 2	444
	21st to end	Day	19% 7% 36% 27% 10% 1	488
August	1st to 10th	Day	16% 10% 31% 27% 13% 2	446
	11th to 20th	Day	16% 8% 26% 31% 16% 2	439
	21st to end	Day	21% 14% 22% 25% 14% 5%	495
September	1st to 10th	Day	25% 8% 26% 28% 9% 5%	450
	11th to 20th	Day	23% 11% 30% 21% 13% 2	450
	21st to end	Day	20% 15% 28% 23% 10% 4	450
October	1st to 10th	Day	21% 15% 29% 23% 9% 2	444
	11th to 20th	Day	34% 12% 24% 20% 9% 1	360
	21st to end	Day	35% 15% 29% 16% 4 1	396
November	1st to 10th	Day	31% 17% 30% 18% 4 1	365
	11th to 20th	Day	28% 19% 24% 22% 7% 1	370
	21st to end	Day	30% 20% 33% 16%	220
December	1st to 10th	Day	27% 17% 31% 18% 6% 1	180
	11th to 20th	Day	31% 24% 29% 11% 4 2	180
	21st to end	Day	34% 22% 27% 14% 3	198
January	1st to 10th	Night	26% 20% 31% 19% 4	780
	11th to 20th	Night	22% 20% 34% 19% 4	760
	21st to end	Night	17% 16% 36% 24% 6% 1	836
February	1st to 10th	Night	18% 17% 38% 21% 5% 1	759
	11th to 20th	Night	22% 19% 35% 18% 4	703
	21st to end	Night	20% 16% 34% 24% 4 1	592
March	1st to 10th	Night	22% 14% 36% 23% 5%	720
	11th to 20th	Night	23% 13% 36% 19% 7% 2	720
	21st to end	Night	22% 13% 31% 25% 8% 1	792
April	1st to 10th	Night	31% 12% 28% 22% 7%	720
	11th to 20th	Night	27% 10% 30% 25% 9%	583
	21st to end	Night	30% 11% 26% 24% 8% 1	540
May	1st to 10th	Night	29% 9% 25% 28% 8%	540
	11th to 20th	Night	27% 7% 25% 32% 9% 1	357
	21st to end	Night	27% 7% 31% 28% 6%	389
June	1st to 10th	Night	26% 7% 25% 34% 8% 1	360
	11th to 20th	Night	18% 5% 24% 38% 14%	360
	21st to end	Night	21% 11% 24% 33% 11%	360
July	1st to 10th	Night	20% 6% 31% 32% 10% 1	350
	11th to 20th	Night	17% 4 30% 35% 12% 1	348
	21st to end	Night	15% 6% 28% 40% 11%	394
August	1st to 10th	Night	15% 4 26% 37% 18% 1	384
	11th to 20th	Night	18% 6% 25% 36% 15% 1	532
	21st to end	Night	17% 7% 30% 30% 15% 2	639
September	1st to 10th	Night	20% 7% 29% 32% 11% 2	720
	11th to 20th	Night	24% 7% 29% 27% 11% 1	720
	21st to end	Night	23% 7% 29% 30% 10% 1	720
October	1st to 10th	Night	25% 12% 30% 25% 7% 1	720
	11th to 20th	Night	31% 12% 24% 23% 9% 1	720
	21st to end	Night	30% 13% 31% 20% 6%	792
November	1st to 10th	Night	29% 17% 28% 22% 5%	740
	11th to 20th	Night	25% 19% 28% 21% 6% 1	789
	21st to end	Night	27% 17% 31% 19% 5% 1	850
December	1st to 10th	Night	30% 16% 30% 20% 4	850
	11th to 20th	Night	27% 19% 30% 18% 5%	850
	21st to end	Night	30% 19% 27% 19% 4 1	935

Page generated at 2024-02-07 06:11:59. Version ac07

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