Boca Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boca Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
54%
15584
23%
47187
17%
15545
61%
15545
28%
28125

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
33%
717
22%
2327
11%
716
47%
716
21%
1415
January16th to endNight
38%
768
25%
2304
15%
768
48%
768
23%
1499
February1st to 15thNight
40%
701
26%
2106
15%
699
51%
699
27%
1252
February16th to endNight
39%
631
24%
1893
11%
631
50%
631
27%
1141
March1st to 15thNight
46%
720
27%
2070
14%
720
56%
720
31%
1196
March16th to endNight
50%
768
28%
2112
16%
768
57%
768
34%
1209
April1st to 15thNight
51%
647
26%
1905
18%
647
59%
647
30%
1091
April16th to endNight
57%
540
31%
1800
24%
540
67%
540
34%
898
May1st to 15thNight
60%
539
27%
1622
21%
539
67%
539
36%
877
May16th to endNight
64%
561
26%
1682
18%
561
71%
561
36%
884
June1st to 15thNight
63%
540
18%
1620
14%
540
66%
540
28%
952
June16th to endNight
67%
540
18%
1620
14%
540
70%
540
29%
951
July1st to 15thNight
71%
510
11%
1530
11%
510
72%
510
27%
944
July16th to endNight
66%
564
11%
1626
11%
531
71%
531
26%
1017
August1st to 15thNight
71%
539
10%
1788
12%
536
71%
536
21%
1160
August16th to endNight
67%
573
14%
1910
17%
573
67%
573
23%
1240
September1st to 15thNight
66%
713
12%
1973
11%
713
67%
713
24%
1364
September16th to endNight
64%
717
21%
1980
16%
717
67%
717
26%
1306
October1st to 15thNight
60%
684
28%
1881
23%
684
65%
684
36%
1108
October16th to endNight
59%
704
30%
2051
25%
704
66%
704
35%
1196
November1st to 15thNight
53%
700
31%
2211
26%
700
61%
700
32%
1185
November16th to endNight
46%
720
28%
2340
20%
720
60%
720
29%
1301
December1st to 15thNight
45%
720
26%
2340
22%
720
54%
720
27%
1360
December16th to endNight
41%
768
22%
2496
16%
768
51%
768
20%
1579

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
8%425%5%35%5%6%9%43%
47993
Night
8%42442446%9%47%
47396
TransparencyDay
33%7%16%20%15%6%
47698
Night
33%6%14%20%17%7%
47196
SeeingDay
9%8%8%22%29%21%
5497
Night
9%16%12%21%27%11%
15593

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 15thDay
10%5%36%4345%47%44%
1611
16th to endDay
12%5%35%5%34446%45%
1919
February1st to 15thDay
14%5%24323436%49%
1750
16th to endDay
13%6%15%323336%51%
1580
March1st to 15thDay
6%224435%45%7%53%
1889
16th to endDay
8%424223346%57%
2111
April1st to 15thDay
10%31342446%8%50%
2052
16th to endDay
6%313313448%58%
2160
May1st to 15thDay
6%31432345%9%53%
2327
16th to endDay
431442446%11%50%
2431
June1st to 15thDay
7%426%5%36%7%9%13%33%
2340
16th to endDay
6%325%6%46%7%8%12%34%
2340
July1st to 15thDay
7%435%7%47%8%11%12%27%
2340
16th to endDay
7%5%26%8%5%7%8%9%13%25%
2429
August1st to 15thDay
10%427%6%5%8%10%9%12%21%
2160
16th to endDay
10%426%5%47%7%9%10%30%
2286
September1st to 15thDay
8%5%26%7%36%7%10%12%28%
1980
16th to endDay
8%425%5%45%6%7%10%39%
1980
October1st to 15thDay
7%41343435%7%54%
1877
16th to endDay
8%324323345%57%
1818
November1st to 15thDay
7%213424447%56%
1645
16th to endDay
8%42433335%6%55%
1620
December1st to 15thDay
13%5%23423347%49%
1620
16th to endDay
12%7%35%435%5%5%7%37%
1728
January1st to 15thNight
12%6%25%425%446%45%
2327
16th to endNight
13%6%35%424446%42%
2304
February1st to 15thNight
14%424323345%51%
2103
16th to endNight
13%6%24434235%50%
1893
March1st to 15thNight
8%42442445%7%51%
2070
16th to endNight
9%314223346%56%
2112
April1st to 15thNight
8%42432446%7%50%
1905
16th to endNight
431442435%9%56%
1800
May1st to 15thNight
5%22322435%8%57%
1622
16th to endNight
3213335%36%10%56%
1682
June1st to 15thNight
6%4245%246%7%12%44%
1620
16th to endNight
5%3135%345%7%12%46%
1620
July1st to 15thNight
5%323435%6%10%15%40%
1620
16th to endNight
3325%5%45%6%9%14%37%
1736
August1st to 15thNight
6%425%5%36%7%10%14%33%
1800
16th to endNight
9%325%6%25%6%8%12%37%
1910
September1st to 15thNight
9%425%5%45%7%9%12%32%
1973
16th to endNight
7%5%245%35%6%7%11%38%
1980
October1st to 15thNight
4315%5%2446%9%52%
1881
16th to endNight
8%324424435%55%
2051
November1st to 15thNight
5%423423446%56%
2211
16th to endNight
9%423323346%55%
2340
December1st to 15thNight
11%5%2442435%9%47%
2340
16th to endNight
13%5%35%425%5%5%5%43%
2496

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
37%5%12%16%19%8%
1612
16th to endDay
40%49%15%21%8%
1919
February1st to 15thDay
37%28%17%21%12%
1752
16th to endDay
34%5%9%18%22%9%
1580
March1st to 15thDay
28%5%11%23%23%7%
1889
16th to endDay
27%412%24%19%9%
2112
April1st to 15thDay
29%6%10%21%21%8%
2052
16th to endDay
24%413%29%20%7%
2160
May1st to 15thDay
25%6%14%25%20%8%
2327
16th to endDay
24%6%19%28%17%3
2435
June1st to 15thDay
34%11%23%25%4
2340
16th to endDay
35%9%24%23%6%
2340
July1st to 15thDay
40%13%27%17%1
2201
16th to endDay
38%12%28%16%2
2277
August1st to 15thDay
42%16%23%14%2
2148
16th to endDay
38%12%26%16%5%
2286
September1st to 15thDay
39%14%23%14%6%1
1980
16th to endDay
36%8%19%17%11%5%
1980
October1st to 15thDay
28%411%21%21%12%
1877
16th to endDay
30%37%17%27%14%
1818
November1st to 15thDay
27%411%21%23%11%
1645
16th to endDay
28%49%22%22%11%
1620
December1st to 15thDay
35%413%22%18%6%
1620
16th to endDay
44%5%10%19%13%6%
1728
January1st to 15thNight
39%48%16%21%8%
2327
16th to endNight
42%45%14%22%10%
2304
February1st to 15thNight
35%37%16%24%13%
2112
16th to endNight
36%39%17%19%12%
1893
March1st to 15thNight
31%410%24%21%8%
2070
16th to endNight
28%49%23%21%12%
2112
April1st to 15thNight
30%410%19%23%11%
1905
16th to endNight
23%5%10%30%21%8%
1800
May1st to 15thNight
25%412%24%22%10%
1623
16th to endNight
23%5%18%28%20%3
1684
June1st to 15thNight
29%8%22%30%8%
1620
16th to endNight
29%8%25%25%11%
1620
July1st to 15thNight
31%10%31%23%2
1530
16th to endNight
32%12%31%19%3
1626
August1st to 15thNight
36%13%29%18%2
1788
16th to endNight
38%11%24%20%5%
1910
September1st to 15thNight
39%11%23%16%7%1
1973
16th to endNight
37%8%18%17%14%3
1980
October1st to 15thNight
29%5%11%18%21%13%
1881
16th to endNight
31%45%14%26%17%
2051
November1st to 15thNight
29%37%22%25%12%
2211
16th to endNight
31%49%18%20%16%
2340
December1st to 15thNight
35%310%25%19%6%
2340
16th to endNight
40%5%9%22%13%7%
2496

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
10%227%34%17%7%
90
16th to endDay
13%13%18%43%10%
96
February1st to 15thDay
7%5%28%26%30%1
90
16th to endDay
9%416%50%18%
81
March1st to 15thDay
9%9%20%41%17%1
179
16th to endDay
12%13%15%30%25%2
288
April1st to 15thDay
8%12%21%30%25%2
270
16th to endDay
7%12%11%27%35%6%
270
May1st to 15thDay
5%13%8%33%29%10%
288
16th to endDay
411%316%37%25%
331
June1st to 15thDay
9%9%214%36%27%
315
16th to endDay
11%10%16%33%36%
315
July1st to 15thDay
6%6%326%56%
305
16th to endDay
7%9%27%33%40%
326
August1st to 15thDay
15%5%18%30%37%
313
16th to endDay
11%5%38%28%43%
332
September1st to 15thDay
12%5%7%17%29%27%
315
16th to endDay
10%5%5%17%38%23%
314
October1st to 15thDay
11%5%12%25%35%8%
278
16th to endDay
8%8%10%36%26%8%
272
November1st to 15thDay
10%6%13%34%25%9%
153
16th to endDay
3115%45%24%10%
90
December1st to 15thDay
5%215%46%27%2
90
16th to endDay
19%412%37%19%6%
96
January1st to 15thNight
13%23%23%25%11%2
720
16th to endNight
12%22%21%27%15%1
768
February1st to 15thNight
14%21%20%25%15%2
704
16th to endNight
14%20%19%30%14%
631
March1st to 15thNight
9%19%19%30%18%1
720
16th to endNight
10%19%15%25%25%3
768
April1st to 15thNight
9%18%14%27%26%3
647
16th to endNight
6%17%13%24%32%5%
540
May1st to 15thNight
7%18%9%28%30%6%
540
16th to endNight
417%6%13%44%12%
563
June1st to 15thNight
7%16%112%41%19%
540
16th to endNight
6%16%9%37%29%
540
July1st to 15thNight
5%12%2433%42%
510
16th to endNight
417%1436%35%
564
August1st to 15thNight
6%9%1442%34%
539
16th to endNight
10%8%38%33%35%
573
September1st to 15thNight
9%9%312%37%26%
713
16th to endNight
11%9%421%41%12%
717
October1st to 15thNight
8%9%14%25%34%8%
684
16th to endNight
8%11%13%26%31%7%
704
November1st to 15thNight
8%17%13%31%24%4
700
16th to endNight
10%19%18%28%17%4
720
December1st to 15thNight
10%19%19%24%22%3
720
16th to endNight
13%20%16%30%16%1
768
Page generated at 2017-10-07 14:07:49. Version ac04

Copyright 2017 A. Danko


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