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Beacon Field Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beacon Field Observatory clear sky chart from 2005-11-05 to 2019-09-17.

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
35%
17828
21%
54801
11%
17790
46%
17790
23%
34447

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
21%
837
24%
2817
10%
836
39%
836
19%
1725
January16th to endNight
22%
896
23%
2912
8%
896
40%
896
19%
1812
February1st to 15thNight
23%
822
20%
2677
8%
821
40%
821
18%
1663
February16th to endNight
16%
735
24%
2226
5%
735
38%
735
20%
1415
March1st to 15thNight
22%
840
22%
2341
9%
840
36%
840
21%
1529
March16th to endNight
23%
896
21%
2433
8%
896
35%
896
22%
1625
April1st to 15thNight
22%
838
20%
2096
5%
838
31%
838
24%
1391
April16th to endNight
30%
831
19%
2077
5%
831
38%
831
25%
1389
May1st to 15thNight
32%
667
17%
1927
8%
667
39%
667
20%
1294
May16th to endNight
45%
438
16%
1753
12%
438
53%
438
19%
1051
June1st to 15thNight
45%
420
19%
1680
16%
420
56%
420
21%
988
June16th to endNight
48%
420
17%
1680
14%
420
58%
420
23%
962
July1st to 15thNight
53%
400
16%
1600
16%
400
58%
400
20%
973
July16th to endNight
62%
648
17%
1871
13%
615
69%
615
33%
1091
August1st to 15thNight
58%
620
16%
1850
11%
617
61%
617
26%
1197
August16th to endNight
58%
890
18%
2228
10%
890
60%
890
31%
1463
September1st to 15thNight
54%
840
24%
2100
14%
840
57%
840
31%
1416
September16th to endNight
49%
782
23%
2150
16%
782
55%
782
27%
1415
October1st to 15thNight
44%
780
23%
2340
19%
780
52%
780
25%
1491
October16th to endNight
34%
832
29%
2496
16%
832
52%
832
30%
1463
November1st to 15thNight
32%
820
24%
2601
14%
820
46%
820
24%
1592
November16th to endNight
31%
840
23%
2870
11%
840
47%
840
22%
1655
December1st to 15thNight
26%
840
19%
2940
7%
840
41%
840
16%
1883
December16th to endNight
20%
896
21%
3136
7%
896
37%
896
16%
1964

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
14%5%2443445%7%42%
55872
Night
14%5%2442445%7%43%
54983
Cloud CoverDay
13%5%244345%5%7%41%
55882
Night
14%5%25%42445%7%43%
54987
TransparencyDay
39%6%11%22%16%2
55572
Night
39%5%11%23%17%3
54801
SeeingDay
17%14%22%24%15%6%
8279
Night
15%19%25%26%12%1
17834

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
17%5%25%42445%6%42%
1777
16th to endDay
15%6%25%5%34346%43%
2016
February1st to 15thDay
16%6%245%3445%7%39%
1845
16th to endDay
16%7%35%424436%41%
1817
March1st to 15thDay
15%5%25%425%346%44%
2266
16th to endDay
15%6%35%5%34446%40%
2493
April1st to 15thDay
14%42443445%6%44%
2512
16th to endDay
16%5%145%24446%44%
2488
May1st to 15thDay
16%6%244345%6%8%37%
2692
16th to endDay
15%4145%35%5%5%8%40%
3066
June1st to 15thDay
12%415%5%346%6%8%42%
2940
16th to endDay
8%3245%45%6%7%10%41%
2940
July1st to 15thDay
8%325%5%35%5%7%9%42%
2940
16th to endDay
8%425%5%37%6%7%10%40%
2891
August1st to 15thDay
10%5%26%6%36%6%7%8%35%
2668
16th to endDay
10%3246%35%6%7%8%41%
2676
September1st to 15thDay
15%414425%45%7%43%
2520
16th to endDay
15%7%2443445%7%40%
2161
October1st to 15thDay
18%414423446%44%
1950
16th to endDay
13%424323346%50%
2080
November1st to 15thDay
15%5%13424346%47%
1914
16th to endDay
14%423324446%49%
1748
December1st to 15thDay
15%5%25%425%45%6%42%
1680
16th to endDay
18%6%24324446%41%
1792
January1st to 15thNight
17%5%24313446%44%
2817
16th to endNight
16%6%24423336%44%
2912
February1st to 15thNight
15%5%24424346%44%
2675
16th to endNight
16%6%24423347%44%
2226
March1st to 15thNight
17%5%14424447%43%
2329
16th to endNight
15%6%26%5%24345%43%
2433
April1st to 15thNight
13%5%245%245%5%6%43%
2096
16th to endNight
17%31442445%7%43%
2077
May1st to 15thNight
17%5%35%32446%7%39%
1927
16th to endNight
13%5%244245%7%10%40%
1751
June1st to 15thNight
11%414336%5%6%9%43%
1680
16th to endNight
8%325%5%35%5%7%9%43%
1680
July1st to 15thNight
7%5%36%5%36%5%6%9%41%
1680
16th to endNight
7%223436%5%8%11%43%
1978
August1st to 15thNight
9%415%6%446%6%8%42%
1861
16th to endNight
10%425%5%35%5%6%8%43%
2228
September1st to 15thNight
12%5%25%5%2446%8%43%
2100
16th to endNight
13%6%25%5%2445%8%41%
2150
October1st to 15thNight
18%424433245%44%
2340
16th to endNight
13%313413346%53%
2496
November1st to 15thNight
15%5%2442333449%
2601
16th to endNight
14%41442345%7%47%
2870
December1st to 15thNight
16%6%25%42445%6%39%
2940
16th to endNight
17%5%245%2445%6%41%
3136

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
16%5%2442345%7%41%
1777
16th to endDay
15%6%25%5%24346%42%
2016
February1st to 15thDay
15%6%2443445%6%39%
1845
16th to endDay
16%7%35%433446%40%
1817
March1st to 15thDay
15%5%25%424346%44%
2277
16th to endDay
16%5%35%5%34446%40%
2492
April1st to 15thDay
14%5%24435%45%6%44%
2512
16th to endDay
15%6%14424446%44%
2488
May1st to 15thDay
15%6%25%4245%6%8%36%
2692
16th to endDay
15%4245%25%5%5%8%39%
3066
June1st to 15thDay
12%4145%345%6%9%41%
2940
16th to endDay
8%325%436%6%8%9%40%
2940
July1st to 15thDay
9%325%5%35%5%7%9%41%
2940
16th to endDay
8%415%5%37%6%7%10%39%
2891
August1st to 15thDay
10%5%25%6%46%6%7%8%36%
2668
16th to endDay
10%4145%45%6%7%10%39%
2676
September1st to 15thDay
14%42443446%7%43%
2520
16th to endDay
15%7%244245%5%8%39%
2161
October1st to 15thDay
17%5%14423446%44%
1950
16th to endDay
13%42432435%5%50%
2080
November1st to 15thDay
15%6%13323346%47%
1914
16th to endDay
14%423324346%49%
1748
December1st to 15thDay
15%5%25%425%45%6%43%
1680
16th to endDay
18%6%34424446%41%
1792
January1st to 15thNight
16%6%24323446%44%
2817
16th to endNight
16%6%24323346%44%
2912
February1st to 15thNight
15%5%2442435%6%44%
2668
16th to endNight
16%7%25%323346%44%
2226
March1st to 15thNight
17%5%25%423447%42%
2341
16th to endNight
15%6%26%5%24446%43%
2433
April1st to 15thNight
13%5%25%43445%7%43%
2096
16th to endNight
16%5%15%32345%7%43%
2077
May1st to 15thNight
16%6%35%42446%8%38%
1926
16th to endNight
13%5%245%145%7%10%40%
1751
June1st to 15thNight
10%424335%6%7%9%42%
1680
16th to endNight
8%315%5%345%7%10%43%
1680
July1st to 15thNight
6%5%36%5%35%5%6%9%41%
1680
16th to endNight
7%214435%5%8%12%43%
1978
August1st to 15thNight
8%325%5%45%6%7%8%42%
1861
16th to endNight
9%425%435%46%8%42%
2228
September1st to 15thNight
12%5%25%33445%8%42%
2100
16th to endNight
12%6%25%5%3446%7%42%
2150
October1st to 15thNight
17%5%24333346%44%
2340
16th to endNight
13%313323346%52%
2496
November1st to 15thNight
16%5%2441333448%
2601
16th to endNight
14%4134235%47%47%
2870
December1st to 15thNight
16%6%26%425%45%7%39%
2940
16th to endNight
17%6%14424447%41%
3136

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
41%413%21%14%4
1778
16th to endDay
43%310%24%14%4
2016
February1st to 15thDay
43%5%10%24%13%2
1847
16th to endDay
44%411%23%14%1
1817
March1st to 15thDay
41%410%22%17%3
2277
16th to endDay
44%49%19%18%3
2493
April1st to 15thDay
39%5%9%22%18%4
2512
16th to endDay
40%5%9%19%19%6%
2488
May1st to 15thDay
43%7%12%21%14%1
2692
16th to endDay
40%8%12%25%11%1
3070
June1st to 15thDay
37%7%13%25%15%1
2940
16th to endDay
35%8%15%21%17%2
2940
July1st to 15thDay
36%8%13%20%17%3
2791
16th to endDay
36%8%15%22%15%1
2735
August1st to 15thDay
41%8%12%21%14%1
2655
16th to endDay
37%8%13%21%14%3
2676
September1st to 15thDay
38%6%14%19%18%2
2520
16th to endDay
42%5%10%22%17%1
2161
October1st to 15thDay
40%410%25%15%3
1950
16th to endDay
34%38%27%23%2
2080
November1st to 15thDay
38%312%22%18%4
1914
16th to endDay
36%39%28%18%3
1748
December1st to 15thDay
41%5%13%24%12%2
1680
16th to endDay
43%5%10%25%13%1
1792
January1st to 15thNight
40%49%21%18%5%
2817
16th to endNight
41%39%25%18%1
2912
February1st to 15thNight
40%411%24%16%3
2677
16th to endNight
41%39%25%17%3
2226
March1st to 15thNight
40%5%10%24%15%2
2341
16th to endNight
41%5%10%20%18%3
2433
April1st to 15thNight
39%5%10%20%20%3
2096
16th to endNight
40%410%21%16%6%
2077
May1st to 15thNight
42%7%12%20%13%3
1927
16th to endNight
37%8%15%22%13%2
1753
June1st to 15thNight
35%8%12%26%15%1
1680
16th to endNight
33%8%15%21%18%2
1680
July1st to 15thNight
38%8%14%18%15%4
1600
16th to endNight
29%8%17%27%15%1
1871
August1st to 15thNight
36%9%14%21%16%1
1850
16th to endNight
36%7%14%22%15%3
2228
September1st to 15thNight
37%7%10%21%18%4
2100
16th to endNight
39%6%8%22%19%3
2150
October1st to 15thNight
41%410%23%17%3
2340
16th to endNight
32%5%7%27%22%3
2496
November1st to 15thNight
39%48%22%19%6%
2601
16th to endNight
35%411%24%19%3
2870
December1st to 15thNight
44%5%10%22%13%2
2940
16th to endNight
43%412%25%12%2
3136

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
22%24%31%16%5%
150
16th to endDay
22%25%26%21%4
192
February1st to 15thDay
26%20%37%9%5%1
180
16th to endDay
24%21%34%18%2
320
March1st to 15thDay
17%27%29%20%4
390
16th to endDay
18%20%29%23%5%2
416
April1st to 15thDay
16%26%25%21%7%2
390
16th to endDay
18%19%27%20%10%4
379
May1st to 15thDay
23%18%22%20%12%2
408
16th to endDay
19%11%18%26%18%4
459
June1st to 15thDay
13%13%22%23%17%8%
435
16th to endDay
10%10%25%30%18%4
435
July1st to 15thDay
11%5%14%33%24%10%
425
16th to endDay
9%7%12%31%29%9%
454
August1st to 15thDay
14%5%15%29%25%9%
418
16th to endDay
8%414%27%28%16%
460
September1st to 15thDay
18%6%17%22%17%17%
435
16th to endDay
22%6%14%27%17%10%
378
October1st to 15thDay
21%8%17%23%21%7%
375
16th to endDay
12%15%31%23%14%2
400
November1st to 15thDay
20%16%22%23%13%3
344
16th to endDay
13%21%30%22%9%2
188
December1st to 15thDay
19%17%30%18%11%2
120
16th to endDay
28%13%35%19%2
128
January1st to 15thNight
18%26%28%20%5%
840
16th to endNight
17%25%31%22%3
896
February1st to 15thNight
18%24%29%24%2
824
16th to endNight
19%27%33%18%1
735
March1st to 15thNight
19%23%32%21%2
840
16th to endNight
15%24%32%21%41
896
April1st to 15thNight
14%26%32%21%4
838
16th to endNight
16%21%27%24%9%
831
May1st to 15thNight
18%20%23%27%9%
667
16th to endNight
14%16%19%31%17%
439
June1st to 15thNight
10%15%24%29%19%1
420
16th to endNight
8%16%19%40%14%
420
July1st to 15thNight
7%11%17%33%28%1
400
16th to endNight
7%14%10%33%29%4
648
August1st to 15thNight
11%9%10%38%27%2
620
16th to endNight
11%8%14%31%30%4
890
September1st to 15thNight
12%8%17%30%26%5%
840
16th to endNight
15%8%16%29%26%3
782
October1st to 15thNight
18%12%17%27%21%3
780
16th to endNight
13%17%31%22%14%
832
November1st to 15thNight
17%18%25%25%11%2
820
16th to endNight
13%25%27%24%9%
840
December1st to 15thNight
18%22%26%24%7%
840
16th to endNight
19%23%31%22%3
896
Page generated at 2019-09-17 21:12:14. Version ac04

Copyright 2019 A. Danko


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