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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 2017-10-16.

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
34%
15377
21%
47230
10%
15339
46%
15339
23%
29566

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%
717
23%
2413
10%
716
38%
716
18%
1492
January16th to endNight
20%
768
23%
2496
7%
768
40%
768
19%
1565
February1st to 15thNight
21%
702
20%
2287
6%
701
40%
701
18%
1392
February16th to endNight
16%
631
25%
1911
6%
631
39%
631
21%
1192
March1st to 15thNight
22%
720
22%
2007
9%
720
36%
720
22%
1296
March16th to endNight
22%
768
21%
2085
7%
768
33%
768
21%
1402
April1st to 15thNight
22%
718
19%
1796
5%
718
31%
718
25%
1179
April16th to endNight
31%
720
20%
1800
5%
720
39%
720
25%
1185
May1st to 15thNight
30%
571
18%
1651
7%
571
37%
571
19%
1115
May16th to endNight
44%
374
18%
1497
13%
374
53%
374
19%
888
June1st to 15thNight
46%
360
20%
1440
17%
360
56%
360
23%
818
June16th to endNight
46%
360
17%
1440
12%
360
57%
360
22%
826
July1st to 15thNight
49%
340
13%
1360
13%
340
54%
340
18%
857
July16th to endNight
60%
554
17%
1585
12%
521
68%
521
35%
907
August1st to 15thNight
58%
539
18%
1609
12%
536
61%
536
27%
1014
August16th to endNight
57%
762
18%
1908
10%
762
59%
762
30%
1260
September1st to 15thNight
54%
720
25%
1800
15%
720
58%
720
33%
1195
September16th to endNight
51%
717
24%
1973
16%
717
57%
717
27%
1289
October1st to 15thNight
44%
720
23%
2160
19%
720
52%
720
25%
1371
October16th to endNight
34%
708
29%
2123
15%
708
52%
708
28%
1256
November1st to 15thNight
32%
700
25%
2221
13%
700
48%
700
26%
1319
November16th to endNight
30%
720
22%
2460
10%
720
45%
720
20%
1449
December1st to 15thNight
25%
720
19%
2520
7%
720
40%
720
15%
1600
December16th to endNight
18%
768
22%
2688
7%
768
37%
768
15%
1699

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
13%5%2443445%7%42%
48174
Night
14%5%2442445%7%44%
47412
Cloud CoverDay
13%5%244345%5%7%42%
48184
Night
14%5%2442445%7%44%
47416
TransparencyDay
39%6%11%23%16%2
47874
Night
38%5%11%23%17%3
47230
SeeingDay
16%14%21%24%16%6%
5809
Night
14%21%24%25%12%1
15383

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%425%42335%7%42%
1522
16th to endDay
15%6%25%5%34346%42%
1728
February1st to 15thDay
14%7%245%3446%6%41%
1575
16th to endDay
14%7%35%5%245%36%42%
1560
March1st to 15thDay
15%5%25%424245%45%
1941
16th to endDay
16%6%345%24446%40%
2137
April1st to 15thDay
14%42443445%6%45%
2152
16th to endDay
17%5%14424445%45%
2160
May1st to 15thDay
16%6%2443446%8%37%
2307
16th to endDay
14%415%5%35%5%5%8%40%
2618
June1st to 15thDay
12%315%5%346%6%9%42%
2520
16th to endDay
8%324435%5%7%10%42%
2520
July1st to 15thDay
9%326%5%35%5%7%9%39%
2520
16th to endDay
7%325%5%37%6%7%11%39%
2473
August1st to 15thDay
11%5%26%6%36%6%7%8%36%
2328
16th to endDay
11%4246%346%7%8%41%
2292
September1st to 15thDay
13%314425%46%7%45%
2160
16th to endDay
14%6%2443445%7%41%
1983
October1st to 15thDay
18%414423445%45%
1800
16th to endDay
15%42432335%6%48%
1770
November1st to 15thDay
14%413424346%49%
1634
16th to endDay
16%423323446%46%
1498
December1st to 15thDay
15%415%425%45%7%43%
1440
16th to endDay
19%7%24324346%41%
1536
January1st to 15thNight
17%5%24323446%44%
2413
16th to endNight
16%7%24324336%44%
2496
February1st to 15thNight
15%5%24424346%45%
2285
16th to endNight
14%6%24324347%45%
1911
March1st to 15thNight
16%5%14424437%44%
1995
16th to endNight
15%6%25%5%24445%42%
2085
April1st to 15thNight
14%4245%245%5%6%44%
1796
16th to endNight
17%32432445%7%44%
1800
May1st to 15thNight
17%6%35%32446%6%39%
1651
16th to endNight
12%4245%245%7%9%41%
1495
June1st to 15thNight
9%414326%5%6%10%45%
1440
16th to endNight
8%425%435%5%6%9%43%
1440
July1st to 15thNight
7%5%36%5%36%5%6%9%38%
1440
16th to endNight
6%223436%5%9%12%44%
1692
August1st to 15thNight
9%415%5%346%6%8%43%
1620
16th to endNight
10%425%5%35%5%6%8%42%
1908
September1st to 15thNight
11%425%5%245%6%7%45%
1800
16th to endNight
12%6%25%5%3445%7%42%
1973
October1st to 15thNight
18%424433345%45%
2160
16th to endNight
14%313423346%52%
2123
November1st to 15thNight
13%5%2441323451%
2221
16th to endNight
15%41432345%7%45%
2460
December1st to 15thNight
16%5%25%425%45%6%40%
2520
16th to endNight
18%5%24424446%41%
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
17%425%42345%7%42%
1522
16th to endDay
15%6%25%5%24346%42%
1728
February1st to 15thDay
14%7%2443445%6%41%
1575
16th to endDay
14%6%35%5%33446%41%
1560
March1st to 15thDay
15%6%25%423345%45%
1952
16th to endDay
16%5%345%25%446%40%
2136
April1st to 15thDay
13%5%2443445%6%45%
2152
16th to endDay
17%6%1442345%5%45%
2160
May1st to 15thDay
16%6%25%4245%6%8%37%
2307
16th to endDay
14%4245%26%5%6%8%39%
2618
June1st to 15thDay
12%3145%345%6%9%42%
2520
16th to endDay
8%325%5%36%5%7%9%42%
2520
July1st to 15thDay
9%426%5%36%5%7%9%39%
2520
16th to endDay
6%425%5%37%6%8%11%39%
2473
August1st to 15thDay
11%5%25%6%36%6%7%7%36%
2328
16th to endDay
11%4145%35%6%6%9%39%
2292
September1st to 15thDay
12%41443446%8%45%
2160
16th to endDay
14%6%244245%5%8%40%
1983
October1st to 15thDay
17%5%14423446%45%
1800
16th to endDay
15%5%2432335%5%48%
1770
November1st to 15thDay
14%5%12324346%49%
1634
16th to endDay
15%5%2432445%7%46%
1498
December1st to 15thDay
15%415%425%35%6%44%
1440
16th to endDay
19%6%34424446%41%
1536
January1st to 15thNight
16%6%24323446%43%
2413
16th to endNight
16%6%24323347%43%
2496
February1st to 15thNight
14%5%245%2435%6%46%
2278
16th to endNight
14%6%25%323447%45%
1911
March1st to 15thNight
17%424423448%43%
2007
16th to endNight
15%6%25%5%24446%42%
2085
April1st to 15thNight
14%425%43445%6%44%
1796
16th to endNight
16%5%2432346%7%44%
1800
May1st to 15thNight
17%6%35%42446%7%38%
1650
16th to endNight
12%5%245%145%7%9%41%
1495
June1st to 15thNight
9%324325%6%6%10%44%
1440
16th to endNight
8%425%5%345%6%9%43%
1440
July1st to 15thNight
7%5%36%5%35%5%7%9%38%
1440
16th to endNight
6%214335%5%9%12%44%
1692
August1st to 15thNight
9%315%5%35%6%6%8%43%
1620
16th to endNight
10%425%5%35%46%8%42%
1908
September1st to 15thNight
11%5%25%325%45%8%44%
1800
16th to endNight
11%7%15%5%3446%7%42%
1973
October1st to 15thNight
17%5%24333345%45%
2160
16th to endNight
14%314323346%52%
2123
November1st to 15thNight
13%5%24423235%51%
2221
16th to endNight
15%4134235%5%7%45%
2460
December1st to 15thNight
16%6%25%425%45%6%40%
2520
16th to endNight
17%6%24424446%41%
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
41%413%22%13%4
1523
16th to endDay
43%310%24%13%3
1728
February1st to 15thDay
42%410%25%14%2
1577
16th to endDay
42%411%24%14%1
1560
March1st to 15thDay
41%410%23%15%3
1952
16th to endDay
44%410%19%17%3
2137
April1st to 15thDay
38%49%24%18%4
2152
16th to endDay
40%49%18%20%6%
2160
May1st to 15thDay
43%6%11%21%15%1
2307
16th to endDay
40%7%12%25%12%1
2622
June1st to 15thDay
36%8%13%26%14%1
2520
16th to endDay
34%8%14%22%17%2
2520
July1st to 15thDay
38%8%13%20%15%3
2371
16th to endDay
35%8%15%23%15%2
2317
August1st to 15thDay
42%8%11%21%14%1
2315
16th to endDay
38%8%13%21%15%2
2292
September1st to 15thDay
35%6%14%20%20%2
2160
16th to endDay
41%5%9%22%18%2
1983
October1st to 15thDay
39%49%25%17%3
1800
16th to endDay
36%38%26%21%2
1770
November1st to 15thDay
35%312%23%19%5%
1634
16th to endDay
38%49%26%18%3
1498
December1st to 15thDay
40%5%13%24%13%3
1440
16th to endDay
44%5%10%24%13%1
1536
January1st to 15thNight
41%410%20%18%4
2413
16th to endNight
41%39%25%17%1
2496
February1st to 15thNight
39%310%24%17%3
2287
16th to endNight
39%39%26%18%2
1911
March1st to 15thNight
39%5%11%26%14%2
2007
16th to endNight
41%5%10%21%17%3
2085
April1st to 15thNight
38%49%20%21%3
1796
16th to endNight
38%410%20%17%7%
1800
May1st to 15thNight
44%6%11%20%14%3
1651
16th to endNight
36%8%16%22%14%2
1497
June1st to 15thNight
33%8%12%28%15%1
1440
16th to endNight
35%7%15%20%18%2
1440
July1st to 15thNight
41%8%14%18%12%4
1360
16th to endNight
27%7%18%27%17%1
1585
August1st to 15thNight
35%8%13%22%18%1
1609
16th to endNight
37%7%13%23%15%2
1908
September1st to 15thNight
35%7%10%20%20%4
1800
16th to endNight
38%6%8%21%20%4
1973
October1st to 15thNight
41%39%23%18%3
2160
16th to endNight
33%5%7%27%22%3
2123
November1st to 15thNight
37%38%22%21%7%
2221
16th to endNight
37%410%23%19%4
2460
December1st to 15thNight
44%5%10%22%15%2
2520
16th to endNight
43%411%23%13%2
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
24%20%37%16%11
75
16th to endDay
21%27%28%19%3
96
February1st to 15thDay
27%21%37%10%3
90
16th to endDay
17%24%36%19%1
219
March1st to 15thDay
16%25%27%22%6%
270
16th to endDay
18%23%31%19%5%2
288
April1st to 15thDay
14%25%22%24%9%2
270
16th to endDay
20%18%21%21%12%5%
270
May1st to 15thDay
25%24%21%14%11%2
288
16th to endDay
19%12%18%25%19%5%
331
June1st to 15thDay
12%14%21%24%18%9%
315
16th to endDay
10%12%26%31%15%3
315
July1st to 15thDay
12%7%16%34%22%6%
305
16th to endDay
5%10%11%30%30%11%
326
August1st to 15thDay
15%6%13%26%28%9%
313
16th to endDay
9%5%12%28%28%16%
332
September1st to 15thDay
13%7%20%22%18%18%
315
16th to endDay
20%7%13%27%18%12%
314
October1st to 15thDay
22%7%17%22%22%6%
315
16th to endDay
14%15%27%25%14%1
276
November1st to 15thDay
17%17%23%21%15%4
244
16th to endDay
16%21%29%20%9%2
118
December1st to 15thDay
18%20%28%16%13%3
60
16th to endDay
37%10%28%20%11
64
January1st to 15thNight
17%29%28%20%4
720
16th to endNight
16%27%32%21%2
768
February1st to 15thNight
17%27%29%23%2
704
16th to endNight
17%29%33%19%1
631
March1st to 15thNight
18%24%31%21%2
720
16th to endNight
15%25%33%19%41
768
April1st to 15thNight
14%28%31%21%3
718
16th to endNight
15%23%24%24%10%
720
May1st to 15thNight
18%23%22%25%8%
571
16th to endNight
12%19%18%30%18%1
375
June1st to 15thNight
9%17%22%31%18%1
360
16th to endNight
7%19%19%40%13%
360
July1st to 15thNight
8%13%18%33%25%
340
16th to endNight
6%16%11%32%29%3
554
August1st to 15thNight
12%10%9%38%26%2
539
16th to endNight
11%9%13%30%29%3
762
September1st to 15thNight
11%9%18%29%27%3
720
16th to endNight
14%9%16%29%26%3
717
October1st to 15thNight
18%12%17%26%21%3
720
16th to endNight
13%18%29%23%14%
708
November1st to 15thNight
14%21%25%24%12%2
700
16th to endNight
14%27%25%22%8%
720
December1st to 15thNight
17%25%26%22%6%
720
16th to endNight
19%27%30%19%2
768
Page generated at 2017-10-17 16:35:22. Version ac04

Copyright 2017 A. Danko


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