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 2005-11-05 to 2017-12-04.

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 TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(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

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
46%
15726
21%
47862
14%
15690
54%
15690
27%
30254

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
32%
716
23%
2396
11%
716
48%
716
23%
1456
January16th to endNight
26%
768
22%
2496
9%
768
42%
768
24%
1576
February1st to 15thNight
27%
701
20%
2262
10%
701
42%
701
26%
1370
February16th to endNight
28%
631
27%
1893
13%
631
45%
631
28%
1144
March1st to 15thNight
35%
720
21%
2025
12%
720
47%
720
28%
1302
March16th to endNight
35%
768
20%
2070
11%
768
43%
768
26%
1420
April1st to 15thNight
38%
718
21%
1796
7%
718
46%
718
33%
1189
April16th to endNight
50%
720
20%
1800
11%
720
52%
720
32%
1188
May1st to 15thNight
44%
657
14%
1737
8%
657
47%
657
26%
1207
May16th to endNight
62%
374
18%
1497
18%
374
66%
374
23%
863
June1st to 15thNight
66%
360
16%
1440
20%
360
69%
360
24%
843
June16th to endNight
64%
360
15%
1440
18%
360
67%
360
22%
860
July1st to 15thNight
68%
349
13%
1369
15%
349
68%
349
20%
849
July16th to endNight
73%
564
17%
1595
14%
531
76%
531
32%
986
August1st to 15thNight
67%
587
13%
1657
10%
584
67%
584
25%
1115
August16th to endNight
64%
764
19%
1910
12%
764
65%
764
31%
1301
September1st to 15thNight
65%
720
23%
1800
16%
720
67%
720
33%
1210
September16th to endNight
54%
717
20%
1955
17%
717
56%
717
25%
1358
October1st to 15thNight
51%
720
23%
2160
21%
720
57%
720
27%
1382
October16th to endNight
45%
768
32%
2304
24%
768
57%
768
32%
1361
November1st to 15thNight
43%
760
22%
2411
15%
760
54%
760
27%
1493
November16th to endNight
43%
780
25%
2587
19%
780
54%
780
27%
1533
December1st to 15thNight
34%
736
19%
2574
11%
736
47%
736
21%
1600
December16th to endNight
29%
768
23%
2688
14%
768
44%
768
23%
1648

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 ForecastData
Points
Cloud CoverDay
12%5%2442445%7%43%
48620
Night
13%5%2442445%7%43%
48046
Cloud CoverDay
12%5%2442445%8%44%
48630
Night
14%5%2442445%7%44%
48050
TransparencyDay
37%6%13%23%16%3
48323
Night
39%5%11%22%17%3
47862
SeeingDay
16%418%30%23%6%
6086
Night
16%5%24%32%18%2
15734

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
15%6%34423446%44%
1540
16th to endDay
15%6%3442335%5%44%
1728
February1st to 15thDay
13%7%26%425%445%44%
1598
16th to endDay
12%6%24425%46%7%43%
1580
March1st to 15thDay
14%5%23414346%47%
1921
16th to endDay
17%5%25%5%23436%44%
2154
April1st to 15thDay
11%5%24323346%50%
2152
16th to endDay
13%6%2443435%7%45%
2160
May1st to 15thDay
13%5%26%5%2345%7%42%
2223
16th to endDay
10%4244235%6%9%45%
2618
June1st to 15thDay
10%313425%6%8%10%42%
2520
16th to endDay
6%425%5%35%6%7%11%41%
2520
July1st to 15thDay
7%415%5%37%6%7%11%39%
2508
16th to endDay
5%4245%46%6%8%12%39%
2465
August1st to 15thDay
10%5%36%5%35%6%7%8%37%
2279
16th to endDay
11%414445%5%7%10%39%
2292
September1st to 15thDay
13%425%5%245%6%7%42%
2160
16th to endDay
17%6%26%6%25%45%7%34%
2002
October1st to 15thDay
17%7%1442345%444%
1800
16th to endDay
12%414423345%54%
1920
November1st to 15thDay
16%5%24324336%46%
1776
16th to endDay
12%413323435%54%
1700
December1st to 15thDay
13%5%244235%47%45%
1468
16th to endDay
20%7%25%41343443%
1536
January1st to 15thNight
14%5%2442445%7%43%
2396
16th to endNight
16%6%35%423346%43%
2496
February1st to 15thNight
15%6%2431345%6%45%
2261
16th to endNight
14%6%2432335%6%48%
1893
March1st to 15thNight
14%5%24425%45%5%45%
2013
16th to endNight
17%6%25%434445%41%
2070
April1st to 15thNight
12%6%2443345%7%44%
1796
16th to endNight
16%5%24413446%45%
1800
May1st to 15thNight
14%7%35%5%345%5%8%36%
1737
16th to endNight
11%414435%45%9%46%
1495
June1st to 15thNight
11%324435%5%7%10%43%
1440
16th to endNight
7%426%6%46%5%6%8%41%
1440
July1st to 15thNight
6%5%25%6%46%6%7%9%39%
1449
16th to endNight
5%4245%26%6%8%11%41%
1703
August1st to 15thNight
8%436%6%45%5%7%10%36%
1668
16th to endNight
10%5%35%6%3446%10%39%
1910
September1st to 15thNight
13%4145%35%5%5%7%44%
1800
16th to endNight
17%6%26%42445%6%38%
1955
October1st to 15thNight
16%6%24433346%44%
2160
16th to endNight
14%413323346%52%
2304
November1st to 15thNight
16%5%15%424345%47%
2411
16th to endNight
13%424424445%48%
2587
December1st to 15thNight
14%6%25%425%435%43%
2574
16th to endNight
17%6%25%323346%44%
2688

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
15%5%35%423436%44%
1540
16th to endDay
14%7%2443345%5%44%
1728
February1st to 15thDay
13%7%25%424445%45%
1598
16th to endDay
12%6%24335%46%7%44%
1580
March1st to 15thDay
14%5%24323446%47%
1932
16th to endDay
17%425%5%23435%44%
2153
April1st to 15thDay
11%5%3442335%5%50%
2152
16th to endDay
13%424434347%46%
2160
May1st to 15thDay
14%5%25%5%2445%7%42%
2223
16th to endDay
11%31442346%10%46%
2618
June1st to 15thDay
10%313325%6%7%11%43%
2520
16th to endDay
6%4246%36%5%6%11%42%
2520
July1st to 15thDay
8%315%5%35%6%8%10%40%
2508
16th to endDay
5%424446%7%8%12%40%
2465
August1st to 15thDay
11%5%25%5%35%6%6%9%38%
2279
16th to endDay
11%4245%345%7%10%40%
2292
September1st to 15thDay
13%425%42445%7%43%
2160
16th to endDay
17%6%26%6%25%46%7%34%
2002
October1st to 15thDay
18%6%13433445%44%
1800
16th to endDay
12%314433345%53%
1920
November1st to 15thDay
16%6%24323436%46%
1776
16th to endDay
12%313423435%54%
1700
December1st to 15thDay
13%5%245%2445%7%45%
1468
16th to endDay
20%6%25%41342443%
1536
January1st to 15thNight
14%5%2442445%7%43%
2396
16th to endNight
16%6%25%423346%43%
2496
February1st to 15thNight
15%5%2432345%6%45%
2254
16th to endNight
13%6%24323346%48%
1893
March1st to 15thNight
15%5%24424346%45%
2025
16th to endNight
17%6%25%425%445%40%
2070
April1st to 15thNight
13%5%2443345%8%44%
1796
16th to endNight
16%424423446%46%
1800
May1st to 15thNight
14%6%26%5%245%5%8%36%
1736
16th to endNight
11%41443445%9%46%
1495
June1st to 15thNight
11%3145%246%6%10%43%
1440
16th to endNight
7%5%25%6%36%5%6%8%41%
1440
July1st to 15thNight
7%4246%46%7%6%9%40%
1449
16th to endNight
6%4245%26%7%8%11%41%
1703
August1st to 15thNight
8%426%6%45%6%6%10%36%
1668
16th to endNight
10%5%26%5%35%5%6%10%39%
1910
September1st to 15thNight
13%3245%345%5%7%44%
1800
16th to endNight
17%6%25%434446%38%
1955
October1st to 15thNight
16%6%145%23346%44%
2160
16th to endNight
14%313323345%52%
2304
November1st to 15thNight
16%415%334345%46%
2411
16th to endNight
13%414424445%49%
2587
December1st to 15thNight
14%6%25%425%445%43%
2574
16th to endNight
17%6%24323346%44%
2688

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
40%410%21%18%3
1541
16th to endDay
40%310%23%17%4
1728
February1st to 15thDay
41%37%26%17%4
1601
16th to endDay
38%411%24%16%3
1580
March1st to 15thDay
37%412%22%19%3
1932
16th to endDay
42%5%9%20%19%3
2154
April1st to 15thDay
35%310%26%18%5%
2152
16th to endDay
37%411%20%18%7%
2160
May1st to 15thDay
40%6%15%22%13%1
2223
16th to endDay
33%7%16%25%15%1
2622
June1st to 15thDay
32%7%18%26%12%1
2520
16th to endDay
34%8%17%22%14%2
2520
July1st to 15thDay
35%10%18%21%11%2
2360
16th to endDay
32%9%18%22%14%1
2310
August1st to 15thDay
39%8%14%23%11%1
2266
16th to endDay
36%7%16%22%14%2
2292
September1st to 15thDay
38%7%13%19%17%3
2160
16th to endDay
46%6%10%17%17%
2002
October1st to 15thDay
41%48%24%19%2
1800
16th to endDay
32%38%27%22%5%
1920
November1st to 15thDay
40%39%22%19%4
1776
16th to endDay
32%410%26%21%4
1700
December1st to 15thDay
38%410%24%17%4
1468
16th to endDay
46%38%22%15%2
1536
January1st to 15thNight
39%410%20%19%5%
2396
16th to endNight
42%39%22%16%4
2496
February1st to 15thNight
39%38%25%19%4
2262
16th to endNight
37%39%25%19%4
1893
March1st to 15thNight
40%49%25%16%3
2025
16th to endNight
45%47%22%16%4
2070
April1st to 15thNight
37%5%10%21%20%4
1796
16th to endNight
39%410%20%19%5%
1800
May1st to 15thNight
43%7%13%21%12%1
1737
16th to endNight
35%8%16%24%13%1
1497
June1st to 15thNight
35%8%17%22%14%1
1440
16th to endNight
38%7%15%19%15%2
1440
July1st to 15thNight
38%11%15%21%11%1
1369
16th to endNight
31%10%17%27%12%1
1595
August1st to 15thNight
40%9%16%19%13%
1657
16th to endNight
38%7%15%23%13%1
1910
September1st to 15thNight
38%6%13%20%17%3
1800
16th to endNight
45%5%10%16%19%1
1955
October1st to 15thNight
40%5%9%23%18%2
2160
16th to endNight
33%47%25%23%4
2304
November1st to 15thNight
39%410%19%20%5%
2411
16th to endNight
37%47%23%20%6%
2587
December1st to 15thNight
42%411%21%16%3
2574
16th to endNight
41%311%22%16%4
2688

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
21%8%38%30%
78
16th to endDay
21%12%32%30%3
96
February1st to 15thDay
18%9%39%29%3
115
16th to endDay
14%7%38%35%3
239
March1st to 15thDay
14%8%34%33%7%
270
16th to endDay
18%7%28%33%10%1
288
April1st to 15thDay
14%9%26%29%18%1
270
16th to endDay
17%419%31%21%5%
270
May1st to 15thDay
20%426%32%14%2
288
16th to endDay
18%114%26%26%11%
331
June1st to 15thDay
13%312%31%28%10%
315
16th to endDay
8%113%38%33%4
315
July1st to 15thDay
10%2436%40%4
305
16th to endDay
9%15%30%40%12%
326
August1st to 15thDay
15%19%24%35%13%
313
16th to endDay
12%15%27%38%13%
332
September1st to 15thDay
18%110%29%26%13%
315
16th to endDay
23%312%27%24%8%
314
October1st to 15thDay
25%312%28%22%8%
315
16th to endDay
10%5%25%31%19%6%
336
November1st to 15thDay
22%423%26%19%3
294
16th to endDay
15%11%25%26%18%2
230
December1st to 15thDay
13%5%29%35%14%
67
16th to endDay
43%320%29%3
64
January1st to 15thNight
16%10%35%29%8%
720
16th to endNight
20%8%40%27%3
768
February1st to 15thNight
19%7%40%29%2
704
16th to endNight
16%9%41%28%4
631
March1st to 15thNight
17%6%34%31%8%
720
16th to endNight
21%5%31%30%10%1
768
April1st to 15thNight
14%6%35%32%10%
718
16th to endNight
17%420%40%14%1
720
May1st to 15thNight
17%226%37%12%2
657
16th to endNight
13%114%36%29%4
375
June1st to 15thNight
10%39%38%33%5%
360
16th to endNight
7%113%41%31%4
360
July1st to 15thNight
9%28%40%34%4
349
16th to endNight
7%17%37%39%6%
564
August1st to 15thNight
10%26%39%36%4
587
16th to endNight
14%17%31%38%7%
764
September1st to 15thNight
15%8%34%34%6%
720
16th to endNight
21%212%29%30%4
717
October1st to 15thNight
20%314%32%24%5%
720
16th to endNight
17%8%25%26%18%3
768
November1st to 15thNight
18%5%24%32%15%3
760
16th to endNight
15%8%27%30%16%1
780
December1st to 15thNight
19%5%32%26%13%2
736
16th to endNight
21%6%36%29%5%
768
Page generated at 2017-12-05 10:18:58. Version ac04

Copyright 2017 A. Danko


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