Anstruther Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Anstruther Lake Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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 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
29%
14691
14%
46811
8%
14660
36%
14660
17%
32988

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
14%
719
7%
2506
2%
716
20%
716
6%
2017
January16th to endNight
19%
768
12%
2542
6%
768
26%
768
10%
1968
February1st to 15thNight
15%
703
10%
2287
3%
701
24%
701
11%
1753
February16th to endNight
20%
631
13%
2012
4%
631
31%
631
13%
1478
March1st to 15thNight
18%
720
13%
2010
6%
720
24%
720
15%
1487
March16th to endNight
29%
768
20%
2097
9%
768
38%
768
24%
1419
April1st to 15thNight
23%
718
15%
1796
5%
718
29%
718
19%
1340
April16th to endNight
29%
597
19%
1677
8%
597
38%
597
24%
1137
May1st to 15thNight
36%
417
17%
1497
11%
417
45%
417
19%
957
May16th to endNight
40%
374
15%
1497
12%
374
52%
374
22%
876
June1st to 15thNight
37%
360
10%
1440
8%
360
48%
360
18%
891
June16th to endNight
46%
360
10%
1440
12%
360
51%
360
21%
890
July1st to 15thNight
52%
340
15%
1360
20%
340
58%
340
30%
715
July16th to endNight
51%
397
15%
1438
14%
374
57%
374
29%
797
August1st to 15thNight
57%
539
15%
1609
11%
536
61%
536
33%
980
August16th to endNight
54%
651
21%
1797
10%
651
60%
651
36%
1088
September1st to 15thNight
44%
700
17%
1750
8%
700
47%
700
30%
1162
September16th to endNight
48%
657
21%
1825
14%
657
52%
657
29%
1176
October1st to 15thNight
32%
660
16%
1980
11%
660
40%
660
19%
1409
October16th to endNight
18%
704
10%
2123
4%
704
26%
704
12%
1658
November1st to 15thNight
30%
700
17%
2400
15%
700
37%
700
17%
1639
November16th to endNight
20%
720
11%
2520
6%
720
27%
720
11%
1924
December1st to 15thNight
13%
720
5%
2520
1%
720
17%
720
7%
2038
December16th to endNight
12%
768
8%
2688
3%
768
18%
768
7%
2189

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
17%9%36%5%3445%6%31%
47820
Night
16%9%46%5%3445%6%32%
46983
Cloud CoverDay
18%9%36%5%3445%6%31%
47830
Night
16%9%36%5%3445%6%33%
46988
TransparencyDay
53%5%11%19%10%1
47510
Night
51%5%12%19%10%
46811
SeeingDay
23%11%30%20%9%4
5347
Night
21%12%30%24%10%1
14694

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
19%17%5%8%7%3423423%
1432
16th to endDay
13%16%8%11%7%35%335%21%
1680
February1st to 15thDay
13%15%7%13%9%35%44320%
1575
16th to endDay
16%15%5%9%6%35%43425%
1461
March1st to 15thDay
16%12%5%8%6%35%45%5%27%
1937
16th to endDay
14%10%46%433445%37%
2127
April1st to 15thDay
23%11%26%433345%31%
2152
16th to endDay
21%8%25%423345%38%
2292
May1st to 15thDay
19%9%36%5%3445%6%33%
2453
16th to endDay
14%6%25%5%345%5%7%38%
2618
June1st to 15thDay
21%7%35%5%35%448%29%
2520
16th to endDay
16%6%35%445%5%6%10%31%
2520
July1st to 15thDay
12%425%6%36%5%6%8%37%
2520
16th to endDay
11%5%36%6%46%7%6%8%33%
2631
August1st to 15thDay
12%6%26%6%36%6%6%7%34%
2340
16th to endDay
12%6%26%5%345%6%8%37%
2393
September1st to 15thDay
17%6%25%5%24447%38%
2098
16th to endDay
16%6%36%433447%40%
1801
October1st to 15thDay
23%8%35%5%3445%6%29%
1650
16th to endDay
29%11%37%5%33345%21%
1748
November1st to 15thDay
18%8%35%5%34447%32%
1456
16th to endDay
23%15%5%6%5%245%45%20%
1440
December1st to 15thDay
19%20%7%9%6%23335%16%
1440
16th to endDay
21%19%7%8%6%2423319%
1536
January1st to 15thNight
20%17%5%9%6%3434418%
2506
16th to endNight
14%15%7%9%8%34445%23%
2542
February1st to 15thNight
13%13%6%10%7%35%45%5%23%
2285
16th to endNight
15%13%46%6%35%45%6%27%
2012
March1st to 15thNight
18%11%46%6%3434430%
1998
16th to endNight
15%6%36%5%34435%41%
2097
April1st to 15thNight
20%8%46%5%34445%32%
1796
16th to endNight
15%8%25%43445%6%38%
1677
May1st to 15thNight
17%6%26%5%34446%38%
1497
16th to endNight
11%5%24445%5%5%8%42%
1495
June1st to 15thNight
16%6%24435%36%8%37%
1440
16th to endNight
11%5%26%5%45%45%8%39%
1440
July1st to 15thNight
8%315%5%2445%8%50%
1440
16th to endNight
8%42343446%8%47%
1535
August1st to 15thNight
9%3145%245%6%9%47%
1620
16th to endNight
7%4135%345%5%8%48%
1797
September1st to 15thNight
14%425%42446%7%42%
1750
16th to endNight
18%5%14324345%46%
1825
October1st to 15thNight
19%7%36%5%34446%33%
1980
16th to endNight
23%10%37%6%345%45%24%
2123
November1st to 15thNight
18%7%35%5%3445%6%34%
2400
16th to endNight
23%11%37%5%35%35%6%24%
2520
December1st to 15thNight
21%17%6%9%5%33445%18%
2520
16th to endNight
21%16%7%10%5%2433417%
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
19%17%5%8%5%3433324%
1432
16th to endDay
14%16%7%11%7%34335%22%
1680
February1st to 15thDay
13%15%7%13%8%3444420%
1575
16th to endDay
16%15%6%9%6%35%43425%
1461
March1st to 15thDay
16%12%47%7%35%445%27%
1948
16th to endDay
15%10%36%434345%38%
2126
April1st to 15thDay
23%11%35%5%33345%31%
2152
16th to endDay
21%8%25%423346%37%
2292
May1st to 15thDay
19%8%35%5%3435%6%33%
2453
16th to endDay
16%5%245%35%45%7%38%
2618
June1st to 15thDay
22%6%35%5%35%45%7%29%
2520
16th to endDay
17%5%25%5%36%5%6%9%32%
2520
July1st to 15thDay
12%5%25%5%45%5%6%8%37%
2520
16th to endDay
11%5%26%7%46%6%6%8%33%
2631
August1st to 15thDay
12%6%36%6%35%7%6%7%34%
2340
16th to endDay
13%6%25%6%345%6%7%38%
2393
September1st to 15thDay
17%5%25%5%3345%7%39%
2098
16th to endDay
16%5%26%5%23446%40%
1801
October1st to 15thDay
23%7%35%6%24446%29%
1650
16th to endDay
30%10%36%5%34345%21%
1748
November1st to 15thDay
18%8%36%5%345%46%33%
1456
16th to endDay
23%15%5%7%5%34445%21%
1440
December1st to 15thDay
20%20%7%9%6%2334417%
1440
16th to endDay
21%19%7%8%5%2323319%
1536
January1st to 15thNight
20%16%6%9%7%2434419%
2506
16th to endNight
14%15%6%9%6%44445%23%
2542
February1st to 15thNight
13%14%5%10%7%35%446%23%
2278
16th to endNight
15%13%37%5%45%45%6%28%
2012
March1st to 15thNight
18%11%37%5%4434431%
2010
16th to endNight
15%6%36%5%34445%41%
2097
April1st to 15thNight
20%7%37%5%3445%5%32%
1796
16th to endNight
16%7%25%5%2445%5%39%
1677
May1st to 15thNight
18%5%25%5%2445%5%39%
1497
16th to endNight
12%4235%35%5%5%7%43%
1495
June1st to 15thNight
16%6%24425%45%9%37%
1440
16th to endNight
12%5%25%446%46%7%40%
1440
July1st to 15thNight
8%3144245%47%51%
1440
16th to endNight
9%424335%5%6%9%47%
1535
August1st to 15thNight
9%4145%2445%9%47%
1620
16th to endNight
8%3245%345%5%7%49%
1797
September1st to 15thNight
13%5%26%42346%7%43%
1750
16th to endNight
17%5%13334345%46%
1825
October1st to 15thNight
20%7%27%5%34446%33%
1980
16th to endNight
24%9%46%6%345%45%24%
2123
November1st to 15thNight
18%7%35%5%3446%6%35%
2400
16th to endNight
23%10%45%6%3445%6%24%
2520
December1st to 15thNight
21%17%6%8%5%33446%19%
2520
16th to endNight
22%16%6%10%6%2434418%
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
65%311%12%6%
1433
16th to endDay
66%38%10%8%1
1680
February1st to 15thDay
68%48%13%4
1577
16th to endDay
62%38%12%11%
1461
March1st to 15thDay
58%414%15%6%1
1948
16th to endDay
48%48%19%15%3
2127
April1st to 15thDay
55%37%17%12%1
2152
16th to endDay
48%38%22%15%2
2292
May1st to 15thDay
51%49%18%13%1
2453
16th to endDay
44%6%12%21%13%1
2622
June1st to 15thDay
53%5%11%20%9%
2520
16th to endDay
47%6%12%21%11%1
2520
July1st to 15thDay
40%6%12%27%12%
2371
16th to endDay
45%7%13%23%9%
2465
August1st to 15thDay
45%7%14%20%10%
2327
16th to endDay
42%6%13%26%10%1
2393
September1st to 15thDay
44%5%12%25%10%
2098
16th to endDay
44%5%11%28%9%
1801
October1st to 15thDay
54%410%19%10%
1650
16th to endDay
64%412%13%5%
1748
November1st to 15thDay
52%5%14%17%9%1
1456
16th to endDay
64%5%10%11%5%1
1440
December1st to 15thDay
71%411%8%2
1440
16th to endDay
71%37%11%5%
1536
January1st to 15thNight
69%39%10%5%
2506
16th to endNight
63%47%15%8%
2542
February1st to 15thNight
62%412%15%6%
2287
16th to endNight
56%411%19%8%
2012
March1st to 15thNight
55%412%18%8%
2010
16th to endNight
44%410%21%16%2
2097
April1st to 15thNight
53%47%19%13%1
1796
16th to endNight
44%410%21%17%2
1677
May1st to 15thNight
45%5%10%19%15%3
1497
16th to endNight
38%6%12%24%15%2
1497
June1st to 15thNight
44%5%13%21%14%
1440
16th to endNight
41%7%14%23%13%
1440
July1st to 15thNight
30%5%11%31%19%
1360
16th to endNight
33%5%16%30%13%
1438
August1st to 15thNight
32%8%18%27%13%
1609
16th to endNight
31%6%15%31%13%1
1797
September1st to 15thNight
39%5%16%26%10%
1750
16th to endNight
40%411%32%10%
1825
October1st to 15thNight
51%5%10%21%11%
1980
16th to endNight
61%5%11%14%7%
2123
November1st to 15thNight
48%6%13%20%9%1
2400
16th to endNight
60%6%12%15%4
2520
December1st to 15thNight
67%5%12%10%3
2520
16th to endNight
70%49%10%6%
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
28%23%30%11%6%
60
16th to endDay
37%15%31%11%3
88
February1st to 15thDay
35%24%36%3
90
16th to endDay
35%15%36%10%2
120
March1st to 15thDay
25%13%36%18%5%
270
16th to endDay
25%14%34%14%8%2
288
April1st to 15thDay
27%18%27%17%7%1
270
16th to endDay
25%16%27%17%11%1
270
May1st to 15thDay
31%10%26%16%7%7%
288
16th to endDay
21%11%36%18%8%3
331
June1st to 15thDay
26%9%32%22%8%1
315
16th to endDay
19%8%34%24%10%2
315
July1st to 15thDay
14%7%30%26%12%7%
305
16th to endDay
12%10%32%24%13%6%
326
August1st to 15thDay
14%328%30%14%8%
313
16th to endDay
18%424%27%15%10%
332
September1st to 15thDay
17%9%28%20%15%9%
294
16th to endDay
20%9%22%25%13%9%
254
October1st to 15thDay
19%13%30%19%12%3
255
16th to endDay
36%14%26%17%4
269
November1st to 15thDay
21%10%34%20%10%2
110
16th to endDay
41%10%35%11%1
60
December1st to 15thDay
35%20%26%15%3
60
16th to endDay
39%31%25%31
64
January1st to 15thNight
30%18%29%15%4
720
16th to endNight
21%15%34%22%5%1
768
February1st to 15thNight
21%18%37%19%2
704
16th to endNight
22%17%34%19%6%
631
March1st to 15thNight
26%17%33%18%3
720
16th to endNight
19%13%32%23%9%1
768
April1st to 15thNight
25%15%31%22%5%
718
16th to endNight
20%12%33%22%10%1
597
May1st to 15thNight
23%6%29%24%13%1
417
16th to endNight
14%6%33%35%9%
375
June1st to 15thNight
19%7%30%30%11%
360
16th to endNight
12%5%29%41%10%
360
July1st to 15thNight
6%429%40%17%2
340
16th to endNight
10%229%38%18%
397
August1st to 15thNight
11%321%36%23%3
539
16th to endNight
10%325%31%25%2
651
September1st to 15thNight
14%5%29%27%18%3
700
16th to endNight
20%6%21%28%19%3
657
October1st to 15thNight
23%11%27%22%12%1
660
16th to endNight
29%15%31%17%5%
704
November1st to 15thNight
21%12%30%24%9%1
700
16th to endNight
31%12%29%19%5%
720
December1st to 15thNight
31%18%31%14%3
720
16th to endNight
31%13%33%16%3
768
Page generated at 2017-09-11 19:35:21. Version ac04

Copyright 2017 A. Danko


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