Boca Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boca Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
62%
23873
15%
74533
13%
23826
65%
23826
16%
54555

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 10thNight
40%
758
15%
2459
10%
757
47%
757
13%
1820
January11th to 20thNight
49%
744
19%
2326
13%
744
55%
744
15%
1709
January21st to endNight
39%
792
16%
2376
10%
792
45%
792
13%
1852
February1st to 10thNight
45%
720
16%
2160
10%
720
50%
720
15%
1606
February11th to 20thNight
46%
700
14%
2098
6%
699
53%
699
14%
1593
February21st to endNight
48%
592
17%
1776
11%
592
53%
592
17%
1317
March1st to 10thNight
57%
720
18%
2116
13%
720
62%
720
20%
1497
March11th to 20thNight
56%
720
20%
1980
12%
720
61%
720
21%
1423
March21st to endNight
60%
792
20%
2178
13%
792
63%
792
23%
1540
April1st to 10thNight
59%
702
16%
1962
12%
702
63%
702
20%
1424
April11th to 20thNight
58%
533
19%
1775
18%
533
62%
533
17%
1241
April21st to endNight
68%
540
21%
1800
18%
540
74%
540
21%
1181
May1st to 10thNight
71%
540
20%
1625
17%
540
75%
540
23%
1106
May11th to 20thNight
71%
531
17%
1592
16%
531
72%
531
19%
1155
May21st to endNight
81%
582
18%
1744
17%
582
81%
582
22%
1207
June1st to 10thNight
71%
540
15%
1620
14%
540
71%
540
17%
1178
June11th to 20thNight
80%
540
13%
1620
13%
540
80%
540
20%
1155
June21st to endNight
79%
540
11%
1620
10%
540
79%
540
16%
1214
July1st to 10thNight
76%
525
6%
1575
6%
525
76%
525
12%
1254
July11th to 20thNight
76%
522
5%
1566
6%
522
76%
522
14%
1215
July21st to endNight
80%
591
8%
1718
7%
558
80%
558
16%
1276
August1st to 10thNight
81%
537
8%
1778
9%
534
82%
534
17%
1269
August11th to 20thNight
76%
534
7%
1776
8%
534
76%
534
13%
1351
August21st to endNight
71%
594
8%
1980
10%
594
71%
594
10%
1593
September1st to 10thNight
75%
708
10%
1968
9%
708
75%
708
16%
1549
September11th to 20thNight
68%
720
6%
1980
5%
720
68%
720
13%
1611
September21st to endNight
70%
720
16%
1980
13%
720
72%
720
17%
1507
October1st to 10thNight
65%
720
16%
1980
14%
720
68%
720
19%
1472
October11th to 20thNight
71%
720
24%
1980
22%
720
74%
720
22%
1422
October21st to endNight
61%
792
17%
2367
15%
792
64%
792
18%
1732
November1st to 10thNight
63%
740
22%
2300
21%
740
67%
740
21%
1576
November11th to 20thNight
57%
760
18%
2470
17%
760
61%
760
17%
1758
November21st to endNight
52%
760
15%
2470
13%
760
57%
760
14%
1843
December1st to 10thNight
52%
760
16%
2470
15%
760
56%
760
15%
1809
December11th to 20thNight
49%
759
17%
2923
12%
758
54%
758
11%
2073
December21st to endNight
46%
825
12%
4425
14%
817
52%
817
9%
3027

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
9%5%25%5%35%6%7%9%44%
74845
Night
9%5%25%5%35%5%6%9%47%
74971
TransparencyDay
23%39%10%14%10%4
74572
Night
23%38%9%13%12%5%
74764
SeeingDay
10%311%27%32%18%
13842
Night
11%315%27%31%13%
23892

By Month

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 10thDay
11%6%46%5%346%5%7%44%
1706
11th to 20thDay
9%5%35%435%449%49%
1760
21st to endDay
14%6%36%6%4445%6%42%
1980
February1st to 10thDay
14%7%35%5%345%47%43%
1800
11th to 20thDay
13%6%24424347%50%
1748
21st to endDay
14%7%26%5%3445%6%44%
1480
March1st to 10thDay
8%4245%3446%8%54%
1843
11th to 20thDay
8%42443445%7%53%
1980
21st to endDay
9%425%323447%56%
2178
April1st to 10thDay
10%5%245%3446%9%47%
2011
11th to 20thDay
10%5%25%5%3445%7%51%
2134
21st to endDay
6%32332445%10%59%
2160
May1st to 10thDay
6%21332345%9%62%
2332
11th to 20thDay
5%5%15%6%45%5%6%10%49%
2301
21st to endDay
5%425%5%35%5%7%11%49%
2531
June1st to 10thDay
9%5%26%6%46%8%9%13%33%
2340
11th to 20thDay
6%435%6%37%7%9%13%37%
2340
21st to endDay
7%5%26%7%5%7%8%9%12%33%
2340
July1st to 10thDay
8%5%36%7%37%7%10%12%29%
2340
11th to 20thDay
8%6%37%7%5%7%8%11%11%26%
2340
21st to endDay
45%26%8%5%8%8%9%15%29%
2493
August1st to 10thDay
7%436%6%5%7%9%10%13%30%
2148
11th to 20thDay
11%5%26%7%5%8%9%10%13%25%
2125
21st to endDay
8%6%38%6%47%8%10%11%30%
2368
September1st to 10thDay
7%6%27%7%47%8%11%13%30%
1980
11th to 20thDay
8%436%7%46%6%9%12%34%
1980
21st to endDay
9%5%25%435%6%6%10%44%
1980
October1st to 10thDay
9%5%25%5%35%45%7%49%
1980
11th to 20thDay
6%32332445%8%61%
1980
21st to endDay
8%426%444446%54%
1986
November1st to 10thDay
7%31443445%7%58%
1774
11th to 20thDay
9%424434347%56%
1710
21st to endDay
9%5%25%5%345%7%8%48%
1710
December1st to 10thDay
12%5%245%345%5%8%46%
1710
11th to 20thDay
13%7%36%6%35%45%7%43%
2153
21st to endDay
17%9%35%424446%42%
3124
January1st to 10thNight
13%8%35%5%35%5%5%6%43%
2459
11th to 20thNight
10%6%344345%5%7%50%
2326
21st to endNight
16%7%36%5%3445%6%41%
2376
February1st to 10thNight
15%6%35%42445%6%46%
2160
11th to 20thNight
13%7%35%434345%49%
2098
21st to endNight
14%7%35%5%2435%6%45%
1776
March1st to 10thNight
9%5%25%4245%5%8%53%
2116
11th to 20thNight
9%5%3442446%8%49%
1980
21st to endNight
8%424424447%56%
2178
April1st to 10thNight
9%5%244345%7%8%48%
1962
11th to 20thNight
9%5%26%5%3445%8%49%
1775
21st to endNight
442443445%8%57%
1800
May1st to 10thNight
432332445%8%62%
1625
11th to 20thNight
5%424435%5%7%8%53%
1592
21st to endNight
5%214345%47%11%54%
1744
June1st to 10thNight
6%6%25%5%35%6%7%11%42%
1620
11th to 20thNight
5%325%5%346%8%13%46%
1620
21st to endNight
6%4146%46%6%7%12%44%
1620
July1st to 10thNight
6%435%5%46%6%8%13%40%
1620
11th to 20thNight
5%425%5%46%7%10%14%38%
1620
21st to endNight
2435%5%45%7%8%14%43%
1819
August1st to 10thNight
5%415%435%7%10%15%41%
1790
11th to 20thNight
6%436%6%37%7%9%14%36%
1776
21st to endNight
9%436%6%36%6%9%11%36%
1980
September1st to 10thNight
6%5%26%6%5%6%8%10%13%34%
1968
11th to 20thNight
8%6%36%6%5%6%6%9%10%34%
1980
21st to endNight
7%5%25%6%346%7%11%44%
1980
October1st to 10thNight
5%426%6%35%5%6%9%49%
1980
11th to 20thNight
6%32432445%8%59%
1980
21st to endNight
8%435%5%35%5%5%7%51%
2367
November1st to 10thNight
6%4245%345%6%6%55%
2300
11th to 20thNight
9%5%3433445%7%53%
2470
21st to endNight
10%6%345%2346%7%50%
2470
December1st to 10thNight
12%5%25%5%345%5%8%47%
2470
11th to 20thNight
13%6%25%42445%7%47%
3042
21st to endNight
16%8%36%5%345%45%40%
4532

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 10thDay
24%40%6%11%12%7%
1707
11th to 20thDay
21%41%7%12%15%5%
1760
21st to endDay
30%37%8%7%13%6%
1980
February1st to 10thDay
28%37%6%10%14%6%
1800
11th to 20thDay
26%37%411%13%9%
1758
21st to endDay
26%38%7%12%14%4
1480
March1st to 10thDay
18%37%5%16%19%5%
1843
11th to 20thDay
18%37%11%16%12%6%
1980
21st to endDay
19%38%10%17%12%4
2178
April1st to 10thDay
21%38%9%14%12%7%
2011
11th to 20thDay
20%36%6%17%14%6%
2134
21st to endDay
14%37%9%21%14%5%
2160
May1st to 10thDay
14%37%10%23%14%2
2332
11th to 20thDay
18%41%13%15%12%1
2305
21st to endDay
17%38%10%20%13%1
2531
June1st to 10thDay
22%41%13%19%4
2340
11th to 20thDay
19%41%17%19%5%
2340
21st to endDay
27%39%14%13%5%1
2340
July1st to 10thDay
31%43%15%10%2
2275
11th to 20thDay
27%44%15%11%2
2271
21st to endDay
25%43%20%10%1
2354
August1st to 10thDay
23%42%18%14%2
2136
11th to 20thDay
28%42%18%11%2
2125
21st to endDay
32%42%12%9%41
2368
September1st to 10thDay
26%42%16%12%41
1980
11th to 20thDay
29%41%15%9%5%1
1980
21st to endDay
25%37%9%12%11%6%
1980
October1st to 10thDay
25%36%6%12%11%10%
1980
11th to 20thDay
17%37%6%16%17%7%
1980
21st to endDay
20%38%411%18%9%
1986
November1st to 10thDay
14%40%6%13%15%12%
1774
11th to 20thDay
17%40%5%13%19%6%
1710
21st to endDay
21%41%7%15%13%4
1710
December1st to 10thDay
24%41%6%13%11%4
1710
11th to 20thDay
32%33%7%9%13%7%
2150
21st to endDay
34%25%7%14%15%5%
3124
January1st to 10thNight
23%40%5%10%15%7%
2459
11th to 20thNight
21%40%413%16%6%
2326
21st to endNight
29%37%5%8%13%8%
2376
February1st to 10thNight
26%36%5%9%15%8%
2160
11th to 20thNight
27%37%5%10%11%11%
2099
21st to endNight
24%36%6%13%13%7%
1776
March1st to 10thNight
20%36%6%15%17%6%
2116
11th to 20thNight
18%37%7%17%13%7%
1980
21st to endNight
17%37%9%15%15%7%
2178
April1st to 10thNight
20%37%10%14%12%7%
1962
11th to 20thNight
22%36%7%14%15%6%
1775
21st to endNight
14%38%6%21%15%6%
1800
May1st to 10thNight
15%37%9%19%16%4
1625
11th to 20thNight
19%39%11%17%12%1
1593
21st to endNight
16%38%11%18%15%2
1745
June1st to 10thNight
20%40%12%21%7%
1620
11th to 20thNight
17%39%17%20%6%
1620
21st to endNight
23%40%17%13%8%
1620
July1st to 10thNight
28%42%18%11%2
1575
11th to 20thNight
23%43%21%9%4
1566
21st to endNight
20%42%22%14%11
1718
August1st to 10thNight
18%41%21%16%4
1778
11th to 20thNight
25%41%19%13%2
1776
21st to endNight
30%42%13%10%4
1980
September1st to 10thNight
25%41%16%14%41
1968
11th to 20thNight
30%40%13%10%6%
1980
21st to endNight
24%39%9%11%12%5%
1980
October1st to 10thNight
23%37%7%11%12%11%
1980
11th to 20thNight
19%36%5%14%18%8%
1980
21st to endNight
22%37%49%19%9%
2367
November1st to 10thNight
14%40%413%16%13%
2300
11th to 20thNight
19%39%5%11%16%9%
2470
21st to endNight
23%40%6%12%13%6%
2470
December1st to 10thNight
21%40%8%14%13%5%
2470
11th to 20thNight
27%33%6%12%15%8%
3044
21st to endNight
34%26%5%17%14%4
4532

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 10thDay
10%430%41%14%1
270
11th to 20thDay
10%5%23%39%21%3
257
21st to endDay
20%7%23%42%8%
264
February1st to 10thDay
15%7%20%39%18%1
240
11th to 20thDay
17%417%41%21%
240
21st to endDay
13%316%47%19%2
198
March1st to 10thDay
10%422%45%19%1
283
11th to 20thDay
12%420%38%24%3
420
21st to endDay
11%418%42%22%2
462
April1st to 10thDay
10%425%33%26%2
420
11th to 20thDay
13%317%35%27%3
412
21st to endDay
7%314%38%34%5%
420
May1st to 10thDay
4312%36%36%9%
423
11th to 20thDay
6%17%29%39%17%
447
21st to endDay
5%2419%44%26%
485
June1st to 10thDay
12%420%41%23%
450
11th to 20thDay
8%2416%40%30%
450
21st to endDay
8%2310%42%34%
450
July1st to 10thDay
10%237%29%49%
445
11th to 20thDay
8%126%32%51%
444
21st to endDay
41311%42%38%
488
August1st to 10thDay
10%119%35%43%
446
11th to 20thDay
10%137%32%47%
439
21st to endDay
10%3411%36%36%
495
September1st to 10thDay
9%26%13%36%34%
450
11th to 20thDay
7%27%19%40%24%
450
21st to endDay
10%26%18%42%23%
450
October1st to 10thDay
12%113%29%35%10%
450
11th to 20thDay
5%210%30%40%14%
450
21st to endDay
9%412%36%31%8%
495
November1st to 10thDay
10%113%33%35%8%
372
11th to 20thDay
11%313%42%27%4
270
21st to endDay
11%316%43%25%3
270
December1st to 10thDay
12%324%34%21%5%
270
11th to 20thDay
13%222%43%19%1
270
21st to endDay
17%7%12%38%22%4
297
January1st to 10thNight
16%9%28%32%14%1
760
11th to 20thNight
11%7%25%33%20%3
744
21st to endNight
19%7%28%33%12%1
792
February1st to 10thNight
18%6%25%31%19%1
720
11th to 20thNight
15%7%24%34%17%2
703
21st to endNight
18%421%39%18%1
592
March1st to 10thNight
11%323%40%22%1
720
11th to 20thNight
11%321%34%27%3
720
21st to endNight
9%421%34%30%3
792
April1st to 10thNight
11%419%35%28%3
702
11th to 20thNight
10%5%17%36%29%3
533
21st to endNight
6%316%35%34%6%
540
May1st to 10thNight
5%214%34%36%9%
540
11th to 20thNight
7%211%27%42%11%
531
21st to endNight
5%1421%53%16%
584
June1st to 10thNight
10%15%19%47%18%
540
11th to 20thNight
6%1314%46%30%
540
21st to endNight
7%1211%46%33%
540
July1st to 10thNight
5%237%42%40%
525
11th to 20thNight
6%12436%51%
522
21st to endNight
4127%46%40%
591
August1st to 10thNight
6%115%45%42%
537
11th to 20thNight
6%127%41%43%
534
21st to endNight
10%15%13%36%34%
594
September1st to 10thNight
8%2414%42%31%
708
11th to 20thNight
10%16%20%43%20%
720
21st to endNight
10%27%21%43%17%
720
October1st to 10thNight
9%214%31%35%10%
720
11th to 20thNight
7%213%29%39%11%
720
21st to endNight
10%316%31%32%7%
792
November1st to 10thNight
8%317%38%29%5%
740
11th to 20thNight
12%5%20%35%24%3
760
21st to endNight
13%423%35%21%4
760
December1st to 10thNight
14%424%30%23%5%
760
11th to 20thNight
16%5%23%33%20%3
760
21st to endNight
17%5%22%35%19%2
836
Page generated at 2024-01-13 19:28:33. Version ac07

Copyright 2024 Attilla Danko


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