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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 2020-10-22.

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%
19269
21%
59212
11%
19231
46%
19231
23%
37317

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%
897
23%
3020
9%
896
39%
896
19%
1860
January16th to endNight
22%
960
25%
3120
9%
960
42%
960
20%
1927
February1st to 15thNight
22%
882
19%
2872
7%
881
39%
881
17%
1812
February16th to endNight
16%
791
25%
2396
6%
791
38%
791
20%
1530
March1st to 15thNight
22%
900
22%
2508
8%
900
36%
900
22%
1635
March16th to endNight
22%
960
21%
2608
8%
960
34%
960
21%
1761
April1st to 15thNight
22%
898
20%
2246
5%
898
31%
898
24%
1489
April16th to endNight
30%
891
20%
2227
5%
891
37%
891
25%
1498
May1st to 15thNight
31%
717
17%
2067
7%
717
38%
717
21%
1381
May16th to endNight
44%
470
16%
1881
12%
470
51%
470
18%
1155
June1st to 15thNight
44%
450
19%
1800
16%
450
55%
450
22%
1053
June16th to endNight
47%
450
17%
1800
14%
450
56%
450
21%
1053
July1st to 15thNight
54%
430
15%
1720
16%
430
59%
430
21%
1035
July16th to endNight
62%
695
17%
2014
13%
662
68%
662
32%
1193
August1st to 15thNight
57%
665
16%
1985
11%
662
60%
662
24%
1306
August16th to endNight
57%
952
18%
2386
10%
952
59%
952
31%
1576
September1st to 15thNight
53%
900
23%
2250
14%
900
57%
900
31%
1525
September16th to endNight
49%
897
24%
2465
16%
897
55%
897
28%
1609
October1st to 15thNight
43%
900
22%
2700
18%
900
51%
900
26%
1704
October16th to endNight
35%
924
29%
2771
16%
924
52%
924
29%
1629
November1st to 15thNight
33%
880
24%
2791
14%
880
47%
880
25%
1683
November16th to endNight
30%
900
24%
3075
11%
900
47%
900
21%
1780
December1st to 15thNight
25%
900
18%
3150
7%
900
40%
900
16%
2028
December16th to endNight
22%
960
22%
3360
9%
960
38%
960
17%
2095

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%
60297
Night
14%5%2442445%7%43%
59394
Cloud CoverDay
13%5%244345%5%7%41%
60307
Night
14%5%25%42445%7%43%
59398
TransparencyDay
39%6%11%22%16%2
59997
Night
39%5%11%22%17%3
59212
SeeingDay
17%13%24%24%14%5%
9732
Night
15%18%25%26%12%1
19275

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
16%5%25%5%2445%6%42%
1904
16th to endDay
14%6%25%5%34346%43%
2160
February1st to 15thDay
17%7%245%3445%7%39%
1980
16th to endDay
16%7%35%424436%40%
1955
March1st to 15thDay
14%6%25%425%346%44%
2429
16th to endDay
16%6%35%5%34446%39%
2671
April1st to 15thDay
14%42443445%6%44%
2692
16th to endDay
17%6%14424446%43%
2668
May1st to 15thDay
15%6%244245%6%8%37%
2886
16th to endDay
15%4245%35%5%5%8%39%
3290
June1st to 15thDay
12%315%4346%6%8%42%
3150
16th to endDay
8%4245%45%6%7%10%40%
3150
July1st to 15thDay
8%325%5%35%47%10%43%
3150
16th to endDay
8%425%5%36%6%7%10%40%
3100
August1st to 15thDay
11%5%26%6%36%6%7%8%34%
2863
16th to endDay
10%3245%35%6%8%8%40%
2868
September1st to 15thDay
14%41442445%7%43%
2700
16th to endDay
15%6%2432445%7%42%
2480
October1st to 15thDay
17%414323446%46%
2250
16th to endDay
14%424313346%49%
2304
November1st to 15thDay
15%5%13424346%47%
2054
16th to endDay
14%424324446%48%
1873
December1st to 15thDay
16%5%25%425%35%6%42%
1800
16th to endDay
19%6%24324446%40%
1920
January1st to 15thNight
17%5%24323446%43%
3020
16th to endNight
15%7%24423336%45%
3120
February1st to 15thNight
17%5%24434346%42%
2870
16th to endNight
16%7%34423347%43%
2396
March1st to 15thNight
16%5%14424447%43%
2496
16th to endNight
15%6%26%5%23445%42%
2608
April1st to 15thNight
14%5%245%245%5%7%43%
2246
16th to endNight
18%414424447%43%
2227
May1st to 15thNight
17%5%25%32446%7%39%
2067
16th to endNight
13%5%245%245%7%10%38%
1879
June1st to 15thNight
10%414336%5%6%9%43%
1800
16th to endNight
9%425%435%47%9%42%
1800
July1st to 15thNight
6%5%35%5%36%5%6%9%41%
1800
16th to endNight
7%323436%6%8%11%42%
2121
August1st to 15thNight
9%426%6%446%6%8%41%
1996
16th to endNight
10%425%5%35%46%9%42%
2386
September1st to 15thNight
12%5%25%5%2446%8%42%
2250
16th to endNight
13%6%25%5%2435%7%43%
2465
October1st to 15thNight
18%424433345%45%
2700
16th to endNight
14%413413346%52%
2771
November1st to 15thNight
15%5%24423335%50%
2791
16th to endNight
14%41442345%7%47%
3075
December1st to 15thNight
17%6%26%42445%6%38%
3150
16th to endNight
17%5%24424447%41%
3360

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%245%2345%6%41%
1904
16th to endDay
14%6%25%5%24346%43%
2160
February1st to 15thDay
17%7%2443445%6%38%
1980
16th to endDay
16%7%35%433446%39%
1955
March1st to 15thDay
14%6%25%434346%44%
2440
16th to endDay
17%5%35%5%35%446%39%
2670
April1st to 15thDay
13%5%24435%45%6%43%
2692
16th to endDay
16%6%14424446%43%
2668
May1st to 15thDay
15%6%25%4245%6%8%37%
2886
16th to endDay
15%4245%35%5%5%8%38%
3290
June1st to 15thDay
12%3145%346%6%9%42%
3150
16th to endDay
8%425%436%6%8%9%40%
3150
July1st to 15thDay
8%325%5%35%5%7%9%42%
3150
16th to endDay
7%415%5%37%6%7%11%39%
3100
August1st to 15thDay
11%5%25%6%46%6%7%8%35%
2863
16th to endDay
10%415%5%45%6%7%10%38%
2868
September1st to 15thDay
13%5%2443346%8%43%
2700
16th to endDay
14%6%2442445%7%41%
2480
October1st to 15thDay
16%5%14423446%46%
2250
16th to endDay
14%5%2432335%6%49%
2304
November1st to 15thDay
15%5%13323347%47%
2054
16th to endDay
14%42432435%7%48%
1873
December1st to 15thDay
16%5%25%42435%6%42%
1800
16th to endDay
19%6%34323446%41%
1920
January1st to 15thNight
16%6%24423446%44%
3020
16th to endNight
15%6%24323346%45%
3120
February1st to 15thNight
16%6%245%2435%6%42%
2863
16th to endNight
16%7%25%323346%43%
2396
March1st to 15thNight
16%5%25%423447%42%
2508
16th to endNight
15%6%26%5%24346%42%
2608
April1st to 15thNight
14%425%43445%7%43%
2246
16th to endNight
17%5%15%32345%6%43%
2227
May1st to 15thNight
16%6%3442446%8%39%
2066
16th to endNight
13%5%25%5%245%7%9%38%
1879
June1st to 15thNight
10%424335%6%7%9%42%
1800
16th to endNight
9%425%5%345%7%9%41%
1800
July1st to 15thNight
6%5%36%5%35%5%7%9%41%
1800
16th to endNight
7%314436%5%8%11%42%
2121
August1st to 15thNight
9%426%5%45%6%7%8%40%
1996
16th to endNight
9%425%435%46%8%42%
2386
September1st to 15thNight
12%6%26%33445%8%42%
2250
16th to endNight
13%6%25%42435%7%43%
2465
October1st to 15thNight
17%5%24433346%45%
2700
16th to endNight
14%413323346%51%
2771
November1st to 15thNight
15%5%24413335%49%
2791
16th to endNight
13%4144235%5%7%47%
3075
December1st to 15thNight
16%6%36%42445%6%38%
3150
16th to endNight
17%6%14434447%41%
3360

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
42%412%21%14%4
1905
16th to endDay
42%310%24%15%3
2160
February1st to 15thDay
44%5%10%23%13%2
1982
16th to endDay
44%410%22%14%2
1955
March1st to 15thDay
41%410%22%17%3
2440
16th to endDay
44%5%10%18%17%3
2671
April1st to 15thDay
39%5%9%22%18%4
2692
16th to endDay
41%49%18%19%5%
2668
May1st to 15thDay
42%7%12%21%14%2
2886
16th to endDay
41%8%12%24%11%1
3294
June1st to 15thDay
36%8%13%25%15%1
3150
16th to endDay
35%9%15%20%17%1
3150
July1st to 15thDay
35%7%13%21%17%3
3001
16th to endDay
36%8%15%22%16%1
2944
August1st to 15thDay
42%8%12%21%13%1
2850
16th to endDay
38%8%13%22%14%3
2868
September1st to 15thDay
38%6%13%19%19%2
2700
16th to endDay
40%5%9%23%18%2
2480
October1st to 15thDay
39%49%26%17%3
2250
16th to endDay
35%38%26%22%2
2304
November1st to 15thDay
37%312%23%18%4
2054
16th to endDay
36%39%28%18%2
1873
December1st to 15thDay
41%5%12%25%12%3
1800
16th to endDay
43%5%10%25%13%1
1920
January1st to 15thNight
41%49%20%19%5%
3020
16th to endNight
40%39%25%19%1
3120
February1st to 15thNight
42%410%23%16%3
2872
16th to endNight
41%39%24%17%4
2396
March1st to 15thNight
40%5%10%24%16%2
2508
16th to endNight
42%5%9%20%17%3
2608
April1st to 15thNight
39%5%10%20%20%4
2246
16th to endNight
40%5%10%20%16%6%
2227
May1st to 15thNight
42%6%12%20%14%3
2067
16th to endNight
39%8%15%21%12%2
1881
June1st to 15thNight
35%8%12%26%15%1
1800
16th to endNight
35%8%15%20%17%2
1800
July1st to 15thNight
37%8%15%19%15%3
1720
16th to endNight
30%8%16%27%15%1
2014
August1st to 15thNight
38%9%14%20%15%1
1985
16th to endNight
36%7%14%23%14%3
2386
September1st to 15thNight
38%7%10%21%18%3
2250
16th to endNight
39%6%8%22%19%4
2465
October1st to 15thNight
40%39%23%18%3
2700
16th to endNight
33%5%7%27%22%4
2771
November1st to 15thNight
37%49%22%19%6%
2791
16th to endNight
36%410%25%19%3
3075
December1st to 15thNight
45%5%11%22%13%2
3150
16th to endNight
42%411%24%13%2
3360

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%32%15%4
187
16th to endDay
22%24%27%20%5%
240
February1st to 15thDay
30%18%36%8%4
225
16th to endDay
24%21%33%17%2
374
March1st to 15thDay
18%28%30%18%4
450
16th to endDay
20%20%30%22%41
480
April1st to 15thDay
16%26%26%21%7%2
450
16th to endDay
22%19%26%19%8%3
439
May1st to 15thDay
22%21%21%20%11%1
468
16th to endDay
19%11%22%24%17%4
523
June1st to 15thDay
12%12%25%25%16%7%
495
16th to endDay
10%9%26%30%17%4
495
July1st to 15thDay
9%414%35%24%10%
485
16th to endDay
9%6%11%32%30%9%
518
August1st to 15thDay
15%415%28%26%9%
478
16th to endDay
8%417%28%26%14%
524
September1st to 15thDay
18%6%18%24%16%15%
495
16th to endDay
21%7%18%28%15%8%
494
October1st to 15thDay
21%8%24%23%16%5%
495
16th to endDay
15%14%29%23%13%2
490
November1st to 15thDay
19%16%26%22%11%2
394
16th to endDay
15%20%32%21%8%2
223
December1st to 15thDay
24%18%30%16%10%2
150
16th to endDay
29%11%33%22%21
160
January1st to 15thNight
18%26%29%21%4
900
16th to endNight
17%24%31%23%3
960
February1st to 15thNight
19%24%29%23%2
884
16th to endNight
20%26%34%17%2
791
March1st to 15thNight
19%23%33%21%2
900
16th to endNight
16%23%33%20%41
960
April1st to 15thNight
15%26%32%21%4
898
16th to endNight
18%20%27%24%9%
891
May1st to 15thNight
18%20%25%26%8%
717
16th to endNight
14%15%20%30%17%1
471
June1st to 15thNight
10%14%25%29%18%1
450
16th to endNight
9%15%19%40%14%
450
July1st to 15thNight
7%10%17%33%29%1
430
16th to endNight
7%13%11%33%29%4
695
August1st to 15thNight
12%8%10%37%28%2
665
16th to endNight
11%8%15%31%29%3
952
September1st to 15thNight
13%7%17%31%25%4
900
16th to endNight
16%8%17%31%24%2
897
October1st to 15thNight
18%10%20%28%19%2
900
16th to endNight
14%16%30%24%13%
924
November1st to 15thNight
16%18%26%26%10%1
880
16th to endNight
14%24%28%24%8%
900
December1st to 15thNight
18%22%27%24%7%
900
16th to endNight
19%22%30%23%3
960
Page generated at 2020-10-23 15:21:05. Version ac04

Copyright 2020 A. Danko


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