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 2024-02-15.

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	13% 5% 2 5% 5% 3 4 5% 6% 8% 44%	78402
	Night	14% 6% 2 5% 5% 3 4 4 5% 7% 44%	80679
Transparency	Day	37% 7% 13% 24% 16% 3	78114
	Night	39% 6% 11% 23% 17% 4	80487
Seeing	Day	16% 6% 20% 32% 22% 6%	14167
	Night	17% 6% 24% 33% 18% 3	23865

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	16% 4 1 4 3 3 3 3 3 6% 52%	2645
	11th to 20th	Day	12% 7% 3 5% 5% 3 4 4 4 6% 47%	2840
	21st to end	Day	15% 8% 4 7% 5% 3 4 4 4 6% 40%	3124
February	1st to 10th	Day	12% 7% 3 6% 5% 3 5% 5% 6% 7% 41%	1710
	11th to 20th	Day	21% 6% 2 4 3 2 4 3 4 5% 46%	1736
	21st to end	Day	16% 9% 2 5% 5% 4 5% 5% 7% 6% 37%	1480
March	1st to 10th	Day	13% 7% 1 5% 4 2 3 4 4 6% 51%	1908
	11th to 20th	Day	17% 4 3 5% 4 3 5% 4 5% 6% 45%	1980
	21st to end	Day	16% 5% 3 5% 6% 4 4 5% 5% 7% 42%	2240
April	1st to 10th	Day	12% 5% 2 4 4 2 4 4 5% 7% 51%	2160
	11th to 20th	Day	10% 4 3 5% 5% 3 4 5% 6% 7% 49%	2134
	21st to end	Day	14% 5% 3 4 4 3 4 4 5% 8% 44%	2160
May	1st to 10th	Day	13% 6% 3 5% 5% 2 5% 5% 5% 8% 43%	2169
	11th to 20th	Day	15% 5% 3 5% 5% 3 4 5% 6% 8% 41%	2396
	21st to end	Day	13% 5% 2 4 4 3 4 5% 6% 9% 45%	2725
June	1st to 10th	Day	10% 4 2 4 4 3 5% 6% 7% 11% 43%	2520
	11th to 20th	Day	11% 4 2 4 6% 3 6% 5% 7% 10% 42%	2520
	21st to end	Day	6% 4 3 5% 5% 4 6% 5% 7% 11% 43%	2520
July	1st to 10th	Day	8% 4 2 4 5% 3 5% 6% 8% 12% 42%	2520
	11th to 20th	Day	6% 4 2 4 4 3 7% 7% 9% 11% 42%	2412
	21st to end	Day	6% 4 2 5% 5% 4 6% 8% 9% 12% 39%	2547
August	1st to 10th	Day	10% 5% 2 5% 6% 4 5% 7% 8% 11% 37%	2326
	11th to 20th	Day	12% 5% 2 6% 6% 4 6% 6% 6% 9% 37%	2126
	21st to end	Day	10% 5% 3 5% 5% 3 5% 5% 7% 11% 42%	2376
September	1st to 10th	Day	14% 4 3 5% 4 3 5% 5% 6% 8% 44%	2160
	11th to 20th	Day	12% 5% 2 6% 6% 2 5% 4 6% 7% 44%	2160
	21st to end	Day	18% 7% 2 6% 5% 3 5% 4 6% 7% 38%	1925
October	1st to 10th	Day	16% 6% 2 5% 4 3 3 5% 4 6% 46%	1800
	11th to 20th	Day	15% 6% 2 4 5% 3 3 4 5% 6% 50%	1800
	21st to end	Day	12% 4 2 5% 5% 3 3 3 5% 6% 50%	1980
November	1st to 10th	Day	13% 5% 2 4 4 2 3 4 4 7% 50%	1761
	11th to 20th	Day	14% 7% 2 4 4 3 4 3 4 6% 51%	1710
	21st to end	Day	14% 4 2 4 4 2 3 5% 4 6% 51%	1630
December	1st to 10th	Day	16% 7% 2 4 5% 2 4 4 5% 7% 43%	1520
	11th to 20th	Day	15% 6% 2 5% 4 3 3 3 3 5% 52%	1910
	21st to end	Day	15% 7% 3 5% 4 2 3 5% 4 6% 45%	2772
January	1st to 10th	Night	13% 6% 3 5% 5% 3 4 5% 4 6% 46%	4298
	11th to 20th	Night	15% 7% 3 6% 5% 3 4 3 5% 6% 44%	4120
	21st to end	Night	17% 9% 3 6% 4 2 3 3 4 5% 43%	4532
February	1st to 10th	Night	16% 7% 3 5% 4 3 4 5% 5% 7% 42%	2470
	11th to 20th	Night	20% 7% 3 5% 4 2 4 3 5% 6% 41%	2202
	21st to end	Night	18% 8% 2 5% 4 2 3 3 4 6% 46%	1776
March	1st to 10th	Night	14% 5% 2 4 4 3 4 3 4 6% 50%	2048
	11th to 20th	Night	19% 6% 2 4 5% 3 5% 5% 5% 7% 39%	1980
	21st to end	Night	15% 6% 3 6% 6% 3 5% 4 5% 6% 41%	2116
April	1st to 10th	Night	15% 6% 2 4 5% 3 4 4 6% 7% 42%	1800
	11th to 20th	Night	12% 6% 2 4 4 3 3 3 5% 8% 50%	1775
	21st to end	Night	16% 5% 3 4 5% 3 4 5% 5% 7% 44%	1800
May	1st to 10th	Night	13% 7% 3 5% 7% 3 4 5% 6% 9% 38%	1800
	11th to 20th	Night	15% 6% 3 5% 5% 3 5% 6% 5% 8% 38%	1502
	21st to end	Night	14% 6% 1 5% 4 3 4 4 6% 10% 43%	1550
June	1st to 10th	Night	13% 4 2 5% 6% 3 4 6% 6% 11% 40%	1440
	11th to 20th	Night	11% 4 2 5% 5% 3 6% 7% 7% 10% 40%	1440
	21st to end	Night	8% 5% 2 6% 7% 5% 6% 5% 6% 9% 41%	1440
July	1st to 10th	Night	8% 5% 2 5% 7% 4 6% 6% 5% 10% 42%	1440
	11th to 20th	Night	5% 5% 2 4 4 4 6% 7% 8% 11% 44%	1544
	21st to end	Night	7% 5% 3 5% 6% 3 6% 6% 9% 11% 39%	1771
August	1st to 10th	Night	8% 4 3 6% 7% 5% 7% 6% 7% 11% 36%	1611
	11th to 20th	Night	10% 6% 3 6% 6% 4 5% 5% 7% 9% 38%	1757
	21st to end	Night	9% 5% 2 6% 6% 3 5% 6% 7% 11% 38%	1980
September	1st to 10th	Night	13% 4 2 5% 4 3 5% 6% 6% 8% 44%	1800
	11th to 20th	Night	11% 6% 2 5% 5% 3 5% 4 5% 7% 47%	1800
	21st to end	Night	20% 7% 3 5% 5% 3 4 4 5% 6% 37%	2030
October	1st to 10th	Night	16% 6% 2 4 5% 3 3 4 5% 7% 45%	2160
	11th to 20th	Night	16% 5% 2 4 4 2 3 4 4 6% 49%	2160
	21st to end	Night	15% 5% 2 4 4 3 4 4 4 5% 50%	2376
November	1st to 10th	Night	15% 5% 2 5% 4 3 4 4 4 5% 49%	2316
	11th to 20th	Night	16% 5% 2 5% 4 3 4 4 4 6% 49%	2470
	21st to end	Night	12% 4 2 4 4 3 4 5% 5% 6% 51%	2546
December	1st to 10th	Night	17% 7% 3 6% 5% 3 5% 4 4 6% 41%	2660
	11th to 20th	Night	17% 6% 2 4 4 2 3 4 5% 6% 46%	3285
	21st to end	Night	13% 7% 3 5% 5% 2 4 5% 5% 7% 43%	4884

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	34% 5% 7% 32% 20% 3	2646
	11th to 20th	Day	39% 4 8% 21% 24% 5%	2840
	21st to end	Day	45% 5% 9% 22% 16% 3	3124
February	1st to 10th	Day	42% 5% 10% 26% 14% 3	1710
	11th to 20th	Day	41% 3 8% 22% 19% 6%	1745
	21st to end	Day	46% 6% 11% 18% 14% 5%	1480
March	1st to 10th	Day	36% 4 11% 24% 22% 3	1908
	11th to 20th	Day	40% 5% 11% 20% 18% 6%	1980
	21st to end	Day	42% 7% 11% 19% 18% 3	2240
April	1st to 10th	Day	33% 5% 11% 23% 21% 6%	2160
	11th to 20th	Day	33% 5% 13% 23% 20% 5%	2134
	21st to end	Day	38% 5% 12% 23% 15% 5%	2160
May	1st to 10th	Day	38% 7% 16% 21% 15% 3	2169
	11th to 20th	Day	40% 8% 15% 24% 11% 2	2400
	21st to end	Day	36% 8% 16% 26% 14% 1	2725
June	1st to 10th	Day	33% 9% 18% 27% 12% 1	2520
	11th to 20th	Day	35% 8% 18% 23% 14% 2	2520
	21st to end	Day	33% 9% 18% 23% 16% 1	2520
July	1st to 10th	Day	33% 10% 17% 23% 14% 2	2450
	11th to 20th	Day	31% 11% 21% 26% 10% 1	2339
	21st to end	Day	33% 11% 21% 20% 14% 1	2405
August	1st to 10th	Day	37% 10% 17% 27% 8% 1	2313
	11th to 20th	Day	42% 8% 16% 22% 12% 1	2126
	21st to end	Day	34% 10% 16% 23% 14% 3	2376
September	1st to 10th	Day	37% 9% 16% 18% 16% 4	2160
	11th to 20th	Day	38% 7% 11% 22% 19% 2	2160
	21st to end	Day	45% 6% 10% 21% 16% 2	1925
October	1st to 10th	Day	39% 5% 10% 24% 19% 3	1800
	11th to 20th	Day	36% 5% 9% 25% 21% 4	1800
	21st to end	Day	36% 4 7% 24% 23% 6%	1980
November	1st to 10th	Day	35% 5% 8% 27% 21% 4	1761
	11th to 20th	Day	36% 4 11% 20% 23% 6%	1710
	21st to end	Day	34% 5% 9% 27% 21% 4	1630
December	1st to 10th	Day	41% 4 12% 24% 16% 3	1520
	11th to 20th	Day	37% 4 6% 28% 18% 6%	1906
	21st to end	Day	41% 6% 10% 28% 15% 1	2772
January	1st to 10th	Night	39% 4 8% 25% 20% 5%	4298
	11th to 20th	Night	43% 5% 7% 22% 21% 3	4120
	21st to end	Night	45% 5% 6% 22% 18% 4	4532
February	1st to 10th	Night	42% 4 11% 23% 16% 3	2470
	11th to 20th	Night	45% 4 6% 22% 18% 6%	2204
	21st to end	Night	41% 4 9% 22% 19% 6%	1776
March	1st to 10th	Night	37% 5% 9% 25% 21% 3	2048
	11th to 20th	Night	44% 6% 9% 20% 17% 4	1980
	21st to end	Night	44% 5% 9% 21% 16% 5%	2116
April	1st to 10th	Night	40% 6% 10% 17% 23% 5%	1800
	11th to 20th	Night	34% 4 11% 24% 21% 6%	1775
	21st to end	Night	40% 5% 11% 23% 17% 4	1800
May	1st to 10th	Night	42% 8% 13% 21% 14% 3	1800
	11th to 20th	Night	42% 9% 14% 21% 13% 2	1503
	21st to end	Night	39% 8% 15% 25% 12% 1	1551
June	1st to 10th	Night	38% 9% 16% 22% 14% 1	1440
	11th to 20th	Night	37% 10% 18% 21% 13% 2	1440
	21st to end	Night	37% 9% 14% 23% 14% 3	1440
July	1st to 10th	Night	37% 10% 15% 22% 12% 3	1400
	11th to 20th	Night	29% 12% 19% 29% 9% 1	1495
	21st to end	Night	34% 11% 17% 25% 12%	1672
August	1st to 10th	Night	40% 11% 19% 22% 9%	1600
	11th to 20th	Night	40% 10% 16% 20% 14%	1757
	21st to end	Night	38% 9% 17% 22% 12% 2	1980
September	1st to 10th	Night	36% 8% 16% 20% 16% 4	1800
	11th to 20th	Night	38% 5% 10% 24% 21% 2	1800
	21st to end	Night	48% 6% 10% 16% 17% 2	2030
October	1st to 10th	Night	39% 6% 9% 24% 19% 3	2160
	11th to 20th	Night	37% 5% 8% 24% 22% 4	2160
	21st to end	Night	36% 4 8% 24% 22% 5%	2376
November	1st to 10th	Night	38% 5% 10% 22% 22% 4	2316
	11th to 20th	Night	38% 5% 9% 20% 19% 9%	2470
	21st to end	Night	34% 4 9% 26% 22% 4	2546
December	1st to 10th	Night	45% 5% 10% 21% 15% 3	2660
	11th to 20th	Night	39% 4 11% 22% 20% 5%	3288
	21st to end	Night	39% 6% 12% 26% 15% 2	4884

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	21% 9% 31% 32% 7%	216
	11th to 20th	Day	18% 14% 37% 27% 4	270
	21st to end	Day	18% 8% 33% 34% 6%	297
February	1st to 10th	Day	16% 10% 30% 37% 6% 1	270
	11th to 20th	Day	26% 8% 39% 23% 3	380
	21st to end	Day	22% 12% 34% 28% 4	346
March	1st to 10th	Day	15% 11% 35% 33% 5% 1	420
	11th to 20th	Day	19% 10% 36% 28% 8% 1	420
	21st to end	Day	16% 8% 31% 35% 9% 1	462
April	1st to 10th	Day	14% 13% 30% 32% 11% 1	420
	11th to 20th	Day	11% 5% 28% 35% 17% 4	412
	21st to end	Day	17% 7% 23% 35% 15% 2	420
May	1st to 10th	Day	15% 7% 23% 39% 13% 2	423
	11th to 20th	Day	19% 2 19% 35% 21% 4	447
	21st to end	Day	20% 2 11% 30% 28% 8%	485
June	1st to 10th	Day	12% 3 10% 38% 29% 8%	450
	11th to 20th	Day	14% 3 11% 34% 31% 8%	450
	21st to end	Day	8% 2 11% 36% 36% 7%	450
July	1st to 10th	Day	10% 4 4 32% 38% 12%	445
	11th to 20th	Day	8% 2 4 27% 47% 13%	444
	21st to end	Day	9% 2 5% 36% 38% 10%	488
August	1st to 10th	Day	11% 2 7% 33% 35% 13%	446
	11th to 20th	Day	16% 2 6% 27% 36% 13%	439
	21st to end	Day	11% 3 7% 27% 35% 17%	495
September	1st to 10th	Day	15% 2 8% 27% 32% 16%	450
	11th to 20th	Day	14% 3 10% 29% 33% 11%	450
	21st to end	Day	24% 4 16% 31% 21% 5%	450
October	1st to 10th	Day	21% 4 13% 25% 26% 11%	450
	11th to 20th	Day	15% 5% 20% 33% 25% 3	450
	21st to end	Day	14% 7% 24% 34% 17% 4	495
November	1st to 10th	Day	17% 6% 21% 32% 19% 6%	409
	11th to 20th	Day	17% 11% 28% 29% 14% 1	370
	21st to end	Day	17% 10% 23% 30% 18% 2	290
December	1st to 10th	Day	24% 4 31% 32% 9%	180
	11th to 20th	Day	20% 6% 29% 33% 12% 1	180
	21st to end	Day	23% 6% 29% 27% 15%	198
January	1st to 10th	Night	17% 12% 37% 28% 6%	760
	11th to 20th	Night	18% 11% 34% 29% 8%	760
	21st to end	Night	21% 9% 36% 32% 3	836
February	1st to 10th	Night	20% 6% 37% 32% 5%	760
	11th to 20th	Night	24% 10% 42% 21% 4	722
	21st to end	Night	21% 9% 35% 31% 4	592
March	1st to 10th	Night	16% 8% 35% 33% 7%	720
	11th to 20th	Night	23% 6% 34% 27% 8% 1	720
	21st to end	Night	17% 7% 33% 35% 8% 1	792
April	1st to 10th	Night	18% 7% 36% 31% 8%	720
	11th to 20th	Night	14% 5% 29% 38% 13% 1	711
	21st to end	Night	16% 5% 26% 39% 13% 1	720
May	1st to 10th	Night	17% 4 27% 40% 11% 1	720
	11th to 20th	Night	15% 3 21% 40% 18% 2	441
	21st to end	Night	17% 1 11% 34% 31% 5%	389
June	1st to 10th	Night	12% 4 9% 39% 30% 5%	360
	11th to 20th	Night	11% 2 11% 44% 27% 5%	360
	21st to end	Night	7% 3 12% 40% 33% 5%	360
July	1st to 10th	Night	11% 3 7% 38% 36% 5%	350
	11th to 20th	Night	5% 2 4 35% 48% 6%	451
	21st to end	Night	8% 3 7% 41% 37% 4	591
August	1st to 10th	Night	12% 3 6% 38% 37% 5%	537
	11th to 20th	Night	13% 3 7% 35% 37% 6%	693
	21st to end	Night	11% 2 9% 30% 39% 10%	792
September	1st to 10th	Night	15% 1 8% 32% 35% 9%	720
	11th to 20th	Night	14% 2 10% 30% 37% 7%	720
	21st to end	Night	24% 3 12% 33% 25% 3	720
October	1st to 10th	Night	20% 3 14% 29% 27% 7%	720
	11th to 20th	Night	18% 5% 21% 33% 19% 3	720
	21st to end	Night	17% 8% 25% 29% 18% 3	792
November	1st to 10th	Night	17% 6% 22% 33% 17% 4	740
	11th to 20th	Night	18% 8% 29% 31% 14% 1	760
	21st to end	Night	14% 9% 28% 32% 15% 2	760
December	1st to 10th	Night	21% 6% 33% 27% 10% 2	760
	11th to 20th	Night	18% 7% 37% 29% 9%	760
	21st to end	Night	19% 7% 32% 33% 9% 1	836

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