Land's End
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Land's End clear sky chart from 2005-11-06 to 2026-07-31.

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	12% 6% 2 6% 4 4 4 4 6% 8% 44%	137931
	Night	13% 6% 2 6% 4 4 4 3 5% 7% 44%	135071
Transparency	Day	37% 6% 13% 23% 17% 4	141523
	Night	38% 6% 11% 23% 18% 4	139551
Seeing	Day	15% 6% 21% 31% 20% 5%	17473
	Night	16% 6% 25% 33% 17% 3	27001

By Month

Percentage Cloud Cover SE (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% 4 1 5% 3 3 3 3 4 6% 55%	4901
	11th to 20th	Day	12% 6% 2 5% 3 3 3 3 4 5% 55%	5280
	21st to end	Day	13% 7% 3 8% 4 4 4 3 4 5% 44%	5780
February	1st to 10th	Day	12% 7% 3 6% 5% 4 5% 4 6% 7% 42%	1890
	11th to 20th	Day	20% 7% 2 5% 3 3 4 3 4 6% 44%	1992
	21st to end	Day	15% 8% 3 7% 4 5% 4 4 6% 6% 39%	1730
March	1st to 10th	Day	17% 7% 2 7% 5% 4 3 4 5% 7% 39%	4861
	11th to 20th	Day	10% 6% 3 6% 3 3 4 3 5% 7% 52%	5090
	21st to end	Day	14% 7% 2 6% 4 3 4 3 5% 7% 45%	5762
April	1st to 10th	Day	11% 6% 2 5% 4 3 4 3 5% 7% 50%	2520
	11th to 20th	Day	9% 5% 3 5% 4 4 4 4 6% 7% 49%	2494
	21st to end	Day	13% 6% 3 5% 4 4 4 3 6% 8% 44%	2520
May	1st to 10th	Day	14% 6% 3 6% 4 4 5% 4 6% 8% 39%	7071
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 8% 42%	7959
	21st to end	Day	18% 6% 2 6% 4 4 4 4 5% 8% 40%	9045
June	1st to 10th	Day	9% 5% 2 5% 4 4 5% 5% 8% 10% 43%	2940
	11th to 20th	Day	10% 4 1 5% 5% 4 5% 4 8% 10% 43%	2940
	21st to end	Day	6% 4 2 5% 5% 5% 5% 4 7% 11% 44%	2940
July	1st to 10th	Day	6% 4 2 5% 4 5% 5% 5% 8% 12% 42%	6500
	11th to 20th	Day	11% 7% 3 7% 5% 6% 6% 6% 9% 11% 30%	6204
	21st to end	Day	6% 5% 2 6% 5% 6% 6% 6% 9% 12% 38%	6554
August	1st to 10th	Day	14% 8% 3 7% 5% 5% 6% 6% 8% 10% 29%	4220
	11th to 20th	Day	10% 6% 2 8% 6% 6% 6% 5% 6% 9% 36%	3850
	21st to end	Day	8% 4 2 5% 3 3 4 4 7% 12% 47%	4312
September	1st to 10th	Day	14% 5% 2 5% 3 4 5% 3 6% 8% 44%	2400
	11th to 20th	Day	13% 6% 2 7% 5% 3 6% 3 5% 7% 43%	2400
	21st to end	Day	19% 8% 2 6% 4 4 4 4 6% 7% 36%	2137
October	1st to 10th	Day	15% 6% 2 5% 4 4 4 3 5% 6% 46%	2000
	11th to 20th	Day	14% 6% 2 5% 4 3 3 3 4 6% 51%	2000
	21st to end	Day	12% 4 2 6% 4 4 3 3 5% 6% 52%	2200
November	1st to 10th	Day	13% 5% 2 5% 3 3 3 3 4 7% 50%	1950
	11th to 20th	Day	13% 7% 2 4 4 3 3 3 4 7% 51%	1890
	21st to end	Day	13% 5% 1 5% 4 3 3 4 4 6% 51%	1801
December	1st to 10th	Day	11% 6% 2 5% 3 3 3 3 4 6% 54%	2680
	11th to 20th	Day	16% 8% 2 6% 3 4 2 3 4 5% 47%	3070
	21st to end	Day	11% 6% 2 5% 3 3 3 4 5% 6% 50%	4048
January	1st to 10th	Night	11% 6% 2 5% 4 4 5% 4 4 7% 49%	7976
	11th to 20th	Night	12% 6% 2 6% 3 3 3 2 4 5% 54%	7680
	21st to end	Night	15% 7% 2 6% 3 3 3 3 4 5% 48%	8401
February	1st to 10th	Night	16% 7% 2 6% 3 4 4 4 5% 6% 42%	2730
	11th to 20th	Night	20% 7% 2 5% 4 3 4 3 5% 6% 41%	2511
	21st to end	Night	16% 8% 2 6% 3 3 3 2 5% 5% 46%	2076
March	1st to 10th	Night	17% 7% 2 6% 4 4 3 3 4 6% 44%	5194
	11th to 20th	Night	13% 6% 3 6% 4 3 4 3 5% 6% 49%	5090
	21st to end	Night	13% 7% 2 7% 4 4 4 3 4 6% 46%	5412
April	1st to 10th	Night	14% 7% 2 4 5% 4 4 3 6% 7% 43%	2100
	11th to 20th	Night	11% 6% 2 5% 3 3 4 2 5% 8% 49%	2075
	21st to end	Night	14% 5% 2 5% 4 4 4 4 5% 7% 45%	2100
May	1st to 10th	Night	13% 6% 3 7% 5% 5% 5% 4 7% 10% 35%	5833
	11th to 20th	Night	16% 7% 2 6% 4 3 5% 4 5% 8% 40%	4906
	21st to end	Night	21% 8% 2 7% 4 5% 4 3 5% 8% 35%	5108
June	1st to 10th	Night	11% 4 2 7% 5% 4 5% 4 7% 10% 40%	1680
	11th to 20th	Night	11% 4 2 6% 5% 5% 5% 5% 7% 9% 41%	1680
	21st to end	Night	7% 5% 2 6% 5% 6% 6% 4 7% 9% 43%	1680
July	1st to 10th	Night	9% 6% 2 6% 6% 5% 7% 5% 7% 10% 38%	3678
	11th to 20th	Night	9% 7% 3 7% 5% 5% 7% 6% 8% 13% 30%	3955
	21st to end	Night	9% 7% 3 7% 6% 6% 6% 5% 7% 10% 35%	4517
August	1st to 10th	Night	16% 8% 3 8% 5% 5% 5% 4 6% 10% 29%	2915
	11th to 20th	Night	9% 6% 3 8% 5% 4 4 4 7% 10% 39%	3166
	21st to end	Night	9% 5% 2 6% 4 4 4 3 6% 10% 46%	3586
September	1st to 10th	Night	13% 4 2 5% 4 4 5% 4 6% 9% 45%	2000
	11th to 20th	Night	12% 6% 2 6% 4 4 5% 3 5% 7% 45%	2000
	21st to end	Night	21% 8% 3 7% 4 4 4 3 5% 6% 35%	2257
October	1st to 10th	Night	15% 6% 2 6% 4 3 3 3 5% 7% 46%	2400
	11th to 20th	Night	16% 6% 2 5% 3 3 3 3 4 6% 50%	2400
	21st to end	Night	14% 5% 2 5% 3 4 4 3 4 5% 52%	2640
November	1st to 10th	Night	14% 5% 2 6% 3 4 4 3 4 6% 49%	2566
	11th to 20th	Night	15% 6% 2 6% 3 3 4 3 5% 6% 47%	2730
	21st to end	Night	11% 5% 2 5% 4 4 4 4 5% 6% 51%	2814
December	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 4 6% 54%	4720
	11th to 20th	Night	17% 8% 3 6% 5% 4 4 4 5% 6% 40%	5345
	21st to end	Night	11% 6% 3 6% 4 3 4 4 6% 8% 46%	7150

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	31% 4 10% 27% 19% 9%	4902
	11th to 20th	Day	33% 3 5% 19% 30% 10%	5280
	21st to end	Day	42% 4 7% 28% 17% 2	5780
February	1st to 10th	Day	41% 5% 11% 26% 14% 3	1890
	11th to 20th	Day	42% 4 9% 22% 19% 5%	2001
	21st to end	Day	45% 5% 11% 19% 16% 4	1730
March	1st to 10th	Day	43% 6% 9% 18% 19% 6%	4861
	11th to 20th	Day	32% 5% 10% 21% 24% 8%	5090
	21st to end	Day	38% 6% 13% 18% 19% 6%	5762
April	1st to 10th	Day	34% 5% 12% 23% 21% 6%	2520
	11th to 20th	Day	33% 5% 13% 25% 19% 5%	2494
	21st to end	Day	38% 6% 13% 24% 15% 5%	2520
May	1st to 10th	Day	40% 9% 14% 21% 15% 1	7103
	11th to 20th	Day	39% 7% 15% 25% 14% 1	7963
	21st to end	Day	41% 7% 12% 21% 16% 2	9061
June	1st to 10th	Day	33% 9% 17% 26% 14% 2	2940
	11th to 20th	Day	34% 8% 18% 25% 14% 1	2940
	21st to end	Day	32% 8% 17% 26% 15% 1	2940
July	1st to 10th	Day	32% 10% 22% 21% 12% 2	6430
	11th to 20th	Day	44% 11% 24% 16% 4	6131
	21st to end	Day	35% 10% 17% 21% 16% 1	6370
August	1st to 10th	Day	47% 8% 17% 23% 5% 1	4207
	11th to 20th	Day	41% 8% 14% 24% 12%	3886
	21st to end	Day	28% 7% 16% 29% 19% 2	4312
September	1st to 10th	Day	37% 9% 16% 18% 17% 4	2400
	11th to 20th	Day	40% 7% 11% 22% 18% 2	2400
	21st to end	Day	47% 6% 10% 20% 15% 2	2137
October	1st to 10th	Day	31% 5% 10% 26% 25% 3	3260
	11th to 20th	Day	25% 3 7% 21% 36% 8%	3240
	21st to end	Day	23% 3 9% 28% 25% 12%	3538
November	1st to 10th	Day	35% 5% 8% 29% 20% 4	1950
	11th to 20th	Day	35% 4 11% 22% 23% 6%	1890
	21st to end	Day	34% 4 10% 27% 21% 4	1801
December	1st to 10th	Day	33% 4 9% 29% 20% 5%	2680
	11th to 20th	Day	42% 4 12% 21% 17% 5%	3066
	21st to end	Day	34% 5% 13% 30% 16% 1	4048
January	1st to 10th	Night	36% 3 11% 23% 21% 7%	7977
	11th to 20th	Night	34% 3 4 23% 27% 8%	7680
	21st to end	Night	39% 4 6% 28% 19% 5%	8401
February	1st to 10th	Night	42% 4 11% 22% 17% 3	2730
	11th to 20th	Night	45% 3 7% 22% 18% 5%	2513
	21st to end	Night	41% 4 8% 22% 18% 7%	2076
March	1st to 10th	Night	41% 5% 8% 20% 18% 8%	5194
	11th to 20th	Night	37% 4 7% 20% 22% 9%	5090
	21st to end	Night	40% 5% 8% 24% 17% 7%	5412
April	1st to 10th	Night	39% 6% 11% 17% 23% 4	2100
	11th to 20th	Night	33% 5% 12% 24% 21% 6%	2075
	21st to end	Night	38% 6% 11% 24% 18% 4	2100
May	1st to 10th	Night	43% 8% 15% 23% 11% 1	5863
	11th to 20th	Night	41% 8% 13% 26% 13% 1	4907
	21st to end	Night	48% 7% 10% 20% 14% 2	5115
June	1st to 10th	Night	37% 9% 15% 21% 16% 1	1680
	11th to 20th	Night	37% 9% 17% 23% 13% 2	1680
	21st to end	Night	35% 9% 13% 25% 15% 3	1680
July	1st to 10th	Night	39% 12% 16% 21% 11% 1	3640
	11th to 20th	Night	43% 13% 22% 18% 4 1	3909
	21st to end	Night	42% 8% 13% 23% 14%	4387
August	1st to 10th	Night	50% 8% 17% 21% 5%	2904
	11th to 20th	Night	38% 8% 16% 24% 13%	3196
	21st to end	Night	33% 6% 11% 26% 23% 1	3586
September	1st to 10th	Night	36% 8% 15% 21% 16% 4	2000
	11th to 20th	Night	38% 5% 11% 23% 21% 2	2000
	21st to end	Night	50% 6% 11% 15% 16% 2	2257
October	1st to 10th	Night	36% 5% 10% 22% 23% 4	3920
	11th to 20th	Night	27% 4 7% 22% 31% 9%	3899
	21st to end	Night	23% 3 6% 32% 25% 11%	4252
November	1st to 10th	Night	37% 4 10% 22% 23% 4	2566
	11th to 20th	Night	38% 5% 9% 21% 19% 9%	2730
	21st to end	Night	34% 4 9% 26% 22% 4	2814
December	1st to 10th	Night	33% 4 8% 27% 24% 4	4720
	11th to 20th	Night	45% 4 12% 18% 14% 6%	5348
	21st to end	Night	35% 5% 13% 29% 15% 1	7150

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	20% 12% 34% 28% 6%	264
	11th to 20th	Day	17% 15% 39% 25% 4	330
	21st to end	Day	16% 9% 38% 31% 5%	363
February	1st to 10th	Day	17% 12% 32% 32% 5% 1	330
	11th to 20th	Day	26% 8% 40% 22% 3	480
	21st to end	Day	20% 12% 34% 29% 5%	446
March	1st to 10th	Day	15% 11% 34% 32% 6% 1	540
	11th to 20th	Day	17% 11% 37% 27% 7% 1	540
	21st to end	Day	15% 10% 34% 33% 7% 1	594
April	1st to 10th	Day	13% 13% 31% 32% 10% 1	540
	11th to 20th	Day	11% 6% 30% 34% 15% 3	532
	21st to end	Day	15% 7% 25% 34% 16% 2	540
May	1st to 10th	Day	16% 8% 25% 36% 14% 2	543
	11th to 20th	Day	18% 3 21% 35% 19% 4	567
	21st to end	Day	21% 5% 14% 30% 24% 7%	617
June	1st to 10th	Day	11% 3 10% 41% 27% 8%	570
	11th to 20th	Day	13% 3 14% 35% 29% 7%	570
	21st to end	Day	9% 2 11% 38% 34% 7%	570
July	1st to 10th	Day	9% 4 5% 33% 38% 12%	565
	11th to 20th	Day	9% 2 6% 28% 44% 11%	564
	21st to end	Day	10% 2 7% 34% 36% 10%	616
August	1st to 10th	Day	13% 3 9% 33% 32% 11%	526
	11th to 20th	Day	15% 2 7% 29% 34% 12%	519
	21st to end	Day	10% 3 9% 30% 33% 15%	583
September	1st to 10th	Day	15% 2 10% 29% 29% 14%	530
	11th to 20th	Day	16% 4 11% 28% 31% 10%	530
	21st to end	Day	25% 4 17% 30% 20% 4	530
October	1st to 10th	Day	19% 4 13% 26% 26% 12%	530
	11th to 20th	Day	15% 7% 22% 30% 23% 3	530
	21st to end	Day	14% 7% 26% 31% 17% 5%	583
November	1st to 10th	Day	16% 6% 23% 32% 18% 5%	478
	11th to 20th	Day	16% 11% 29% 30% 13% 1	430
	21st to end	Day	16% 10% 27% 30% 16% 2	341
December	1st to 10th	Day	24% 5% 32% 31% 9%	220
	11th to 20th	Day	20% 7% 30% 33% 10%	220
	21st to end	Day	19% 8% 35% 26% 12%	242
January	1st to 10th	Night	16% 13% 38% 27% 6%	840
	11th to 20th	Night	17% 12% 36% 27% 7%	840
	21st to end	Night	20% 10% 37% 30% 3	924
February	1st to 10th	Night	21% 6% 37% 30% 5%	840
	11th to 20th	Night	24% 10% 42% 21% 4	823
	21st to end	Night	20% 10% 35% 31% 5%	692
March	1st to 10th	Night	17% 9% 34% 31% 8%	840
	11th to 20th	Night	21% 8% 35% 28% 8% 1	840
	21st to end	Night	17% 8% 35% 33% 7%	924
April	1st to 10th	Night	17% 8% 36% 31% 7%	840
	11th to 20th	Night	14% 6% 31% 38% 11% 1	831
	21st to end	Night	15% 6% 26% 40% 12% 1	840
May	1st to 10th	Night	16% 5% 28% 38% 11% 1	840
	11th to 20th	Night	15% 3 24% 39% 17% 2	514
	21st to end	Night	18% 2 13% 35% 28% 5%	455
June	1st to 10th	Night	11% 4 10% 40% 29% 5%	420
	11th to 20th	Night	11% 2 13% 45% 25% 5%	420
	21st to end	Night	7% 3 13% 40% 32% 5%	420
July	1st to 10th	Night	10% 3 7% 39% 35% 5%	410
	11th to 20th	Night	6% 2 5% 36% 44% 6%	529
	21st to end	Night	8% 3 9% 39% 36% 5%	687
August	1st to 10th	Night	13% 3 7% 38% 35% 5%	597
	11th to 20th	Night	12% 3 8% 35% 36% 6%	771
	21st to end	Night	11% 3 9% 32% 37% 9%	880
September	1st to 10th	Night	15% 1 11% 33% 33% 8%	800
	11th to 20th	Night	14% 2 12% 30% 35% 7%	800
	21st to end	Night	24% 4 12% 33% 24% 3	800
October	1st to 10th	Night	19% 3 14% 29% 27% 8%	800
	11th to 20th	Night	19% 6% 23% 32% 18% 3	800
	21st to end	Night	17% 8% 24% 29% 18% 3	880
November	1st to 10th	Night	17% 6% 23% 33% 17% 4	820
	11th to 20th	Night	18% 8% 30% 31% 13% 1	840
	21st to end	Night	14% 9% 29% 32% 14% 2	840
December	1st to 10th	Night	20% 8% 33% 27% 10% 2	840
	11th to 20th	Night	18% 8% 36% 29% 9%	840
	21st to end	Night	18% 8% 32% 33% 9% 1	924

Page generated at 2026-07-28 03:25:23. Version ac07

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