Blue Braille Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Braille Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
28%
14915
11%
46964
7%
14877
33%
14877
13%
35272

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
8%
716
5%
2461
2%
716
12%
716
3%
2173
January16th to endNight
9%
768
5%
2496
2%
768
14%
768
4%
2199
February1st to 15thNight
11%
704
4%
2287
2%
701
15%
701
5%
1991
February16th to endNight
16%
631
7%
2001
2%
631
22%
631
8%
1650
March1st to 15thNight
20%
720
11%
1980
5%
720
24%
720
10%
1598
March16th to endNight
23%
768
17%
2112
7%
768
31%
768
16%
1537
April1st to 15thNight
23%
718
13%
1814
5%
718
27%
718
17%
1380
April16th to endNight
32%
591
18%
1671
6%
591
41%
591
21%
1112
May1st to 15thNight
34%
500
15%
1580
9%
500
41%
500
14%
1098
May16th to endNight
39%
374
17%
1497
13%
374
50%
374
18%
902
June1st to 15thNight
38%
360
13%
1440
10%
360
49%
360
16%
923
June16th to endNight
39%
360
11%
1440
12%
360
47%
360
16%
914
July1st to 15thNight
50%
340
16%
1360
21%
340
55%
340
23%
763
July16th to endNight
47%
502
14%
1534
12%
470
56%
470
25%
927
August1st to 15thNight
55%
539
16%
1609
12%
536
60%
536
28%
978
August16th to endNight
57%
643
19%
1789
11%
643
61%
643
31%
1109
September1st to 15thNight
51%
720
19%
1800
11%
720
54%
720
28%
1244
September16th to endNight
50%
689
21%
1929
15%
689
53%
689
25%
1293
October1st to 15thNight
34%
660
15%
1980
14%
660
38%
660
18%
1399
October16th to endNight
18%
704
8%
2112
4%
704
23%
704
9%
1710
November1st to 15thNight
29%
700
16%
2344
15%
700
34%
700
15%
1675
November16th to endNight
15%
720
8%
2520
5%
720
21%
720
7%
2050
December1st to 15thNight
10%
720
3%
2520
2%
720
12%
720
3%
2230
December16th to endNight
8%
768
3%
2688
1%
768
11%
768
3%
2417

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
15%9%36%5%3445%7%32%
47934
Night
17%10%46%5%3445%6%31%
47145
Cloud CoverDay
15%9%46%5%3445%7%32%
47944
Night
17%10%46%5%3445%6%31%
47149
TransparencyDay
51%7%12%18%9%
47634
Night
56%6%10%16%9%1
46964
SeeingDay
17%18%23%22%13%4
5417
Night
20%24%22%21%10%1
14920

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
19%18%6%10%8%44345%14%
1476
16th to endDay
15%17%7%12%9%45%45%411%
1728
February1st to 15thDay
17%18%6%13%7%35%44414%
1575
16th to endDay
17%14%6%12%8%35%345%17%
1467
March1st to 15thDay
17%13%7%9%6%44445%21%
1969
16th to endDay
16%12%5%6%5%335%5%5%31%
2112
April1st to 15thDay
21%11%35%5%34345%31%
2134
16th to endDay
18%8%345%23345%39%
2298
May1st to 15thDay
16%6%245%45%5%5%7%36%
2370
16th to endDay
11%7%25%43445%9%42%
2618
June1st to 15thDay
15%6%3443446%7%38%
2520
16th to endDay
13%4144245%7%8%42%
2520
July1st to 15thDay
8%4245%25%5%5%9%45%
2520
16th to endDay
10%425%5%37%5%7%10%37%
2525
August1st to 15thDay
8%4245%35%5%8%10%40%
2340
16th to endDay
10%5%244335%6%9%44%
2399
September1st to 15thDay
15%5%25%5%3445%8%41%
2160
16th to endDay
14%425%4345%5%8%40%
1864
October1st to 15thDay
20%7%26%5%345%46%33%
1650
16th to endDay
23%10%48%6%35%445%22%
1760
November1st to 15thDay
13%9%35%6%45%5%47%33%
1513
16th to endDay
21%12%46%7%34346%24%
1440
December1st to 15thDay
19%20%7%8%6%24436%16%
1440
16th to endDay
21%20%8%9%6%3435%412%
1536
January1st to 15thNight
22%17%5%9%7%3434416%
2461
16th to endNight
17%18%6%11%7%34435%17%
2496
February1st to 15thNight
18%17%6%11%7%3434318%
2285
16th to endNight
17%14%5%10%8%35%445%18%
2001
March1st to 15thNight
21%11%47%7%34445%25%
1968
16th to endNight
16%10%36%324445%36%
2112
April1st to 15thNight
22%9%35%43445%431%
1814
16th to endNight
12%7%25%5%35%45%5%42%
1671
May1st to 15thNight
16%5%26%5%35%5%7%6%34%
1580
16th to endNight
12%425%5%35%5%6%7%42%
1495
June1st to 15thNight
14%5%26%5%35%46%7%38%
1440
16th to endNight
11%5%246%46%5%6%7%40%
1440
July1st to 15thNight
7%425%43346%8%49%
1440
16th to endNight
8%3245%446%6%8%45%
1640
August1st to 15thNight
7%5%144346%6%8%45%
1620
16th to endNight
8%424425%46%8%49%
1789
September1st to 15thNight
15%5%2442445%6%45%
1800
16th to endNight
14%5%1443345%5%46%
1929
October1st to 15thNight
20%6%35%334446%38%
1980
16th to endNight
25%7%36%5%3445%7%25%
2112
November1st to 15thNight
16%8%35%423447%38%
2344
16th to endNight
19%11%47%6%35%45%7%24%
2520
December1st to 15thNight
22%18%7%7%5%24445%17%
2520
16th to endNight
22%16%7%9%8%35%345%13%
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
19%17%7%10%8%45%345%14%
1476
16th to endDay
15%16%8%12%9%35%5%5%411%
1728
February1st to 15thDay
17%18%6%13%6%35%44414%
1575
16th to endDay
18%13%6%11%9%26%34418%
1467
March1st to 15thDay
18%13%6%9%7%35%445%21%
1980
16th to endDay
16%12%46%43445%5%31%
2111
April1st to 15thDay
21%11%35%5%33345%31%
2134
16th to endDay
18%8%345%24345%39%
2298
May1st to 15thDay
16%6%25%5%45%5%5%7%36%
2370
16th to endDay
11%6%2443445%8%42%
2618
June1st to 15thDay
15%6%345%335%6%8%37%
2520
16th to endDay
13%4244345%7%8%42%
2520
July1st to 15thDay
8%4245%25%5%6%9%45%
2520
16th to endDay
10%415%5%36%5%7%10%37%
2525
August1st to 15thDay
8%4245%445%7%10%40%
2340
16th to endDay
11%5%2443446%9%44%
2399
September1st to 15thDay
15%5%25%5%34448%41%
2160
16th to endDay
14%5%35%4345%5%7%40%
1864
October1st to 15thDay
20%7%36%4345%46%33%
1650
16th to endDay
24%10%48%6%35%445%22%
1760
November1st to 15thDay
12%10%46%7%45%447%33%
1513
16th to endDay
21%12%46%6%34446%24%
1440
December1st to 15thDay
20%19%6%9%5%24445%16%
1440
16th to endDay
22%19%8%9%7%34445%12%
1536
January1st to 15thNight
23%17%5%9%6%3434416%
2461
16th to endNight
17%18%6%11%7%34435%17%
2496
February1st to 15thNight
18%16%7%11%7%3433319%
2278
16th to endNight
17%14%5%10%8%35%445%19%
2001
March1st to 15thNight
21%12%37%6%3444425%
1980
16th to endNight
16%10%46%434445%35%
2112
April1st to 15thNight
23%9%45%43444431%
1814
16th to endNight
13%6%25%5%35%45%5%42%
1671
May1st to 15thNight
17%5%26%5%25%5%7%6%34%
1579
16th to endNight
12%5%25%5%35%5%5%7%42%
1495
June1st to 15thNight
14%5%25%6%45%45%7%38%
1440
16th to endNight
11%5%245%46%5%6%7%39%
1440
July1st to 15thNight
7%42443346%7%49%
1440
16th to endNight
8%4145%345%7%9%45%
1640
August1st to 15thNight
7%5%24435%5%6%8%46%
1620
16th to endNight
8%424435%46%8%49%
1789
September1st to 15thNight
15%5%2442345%6%45%
1800
16th to endNight
15%42442345%5%46%
1929
October1st to 15thNight
20%7%25%424445%38%
1980
16th to endNight
25%8%36%5%3445%6%25%
2112
November1st to 15thNight
17%8%36%42345%6%38%
2344
16th to endNight
20%11%47%6%35%45%6%24%
2520
December1st to 15thNight
22%19%7%7%5%24445%16%
2520
16th to endNight
23%16%7%9%8%34345%12%
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
76%5%8%7%1
1477
16th to endDay
79%48%6%1
1728
February1st to 15thDay
75%8%6%8%
1577
16th to endDay
67%6%11%11%3
1467
March1st to 15thDay
63%6%11%14%4
1980
16th to endDay
54%5%9%20%8%1
2112
April1st to 15thDay
53%5%11%18%10%
2134
16th to endDay
46%49%19%16%2
2298
May1st to 15thDay
45%7%12%22%11%
2370
16th to endDay
38%7%15%23%12%1
2622
June1st to 15thDay
42%7%13%23%11%1
2520
16th to endDay
36%8%16%24%12%
2520
July1st to 15thDay
32%8%13%25%18%1
2371
16th to endDay
38%9%17%21%11%1
2369
August1st to 15thDay
34%10%17%23%12%1
2327
16th to endDay
34%8%14%27%13%1
2399
September1st to 15thDay
42%7%12%23%11%1
2160
16th to endDay
41%7%12%24%12%
1864
October1st to 15thDay
52%7%11%15%11%
1650
16th to endDay
66%6%12%9%3
1760
November1st to 15thDay
55%6%14%14%7%1
1513
16th to endDay
66%7%10%10%4
1440
December1st to 15thDay
78%5%9%6%
1440
16th to endDay
80%7%7%4
1536
January1st to 15thNight
77%5%7%6%2
2461
16th to endNight
77%5%6%7%2
2496
February1st to 15thNight
74%6%7%9%1
2287
16th to endNight
67%6%9%12%3
2001
March1st to 15thNight
64%5%9%15%4
1980
16th to endNight
52%5%9%18%13%1
2112
April1st to 15thNight
54%5%9%18%11%
1814
16th to endNight
42%5%11%20%16%3
1671
May1st to 15thNight
47%7%9%22%11%1
1580
16th to endNight
40%6%12%21%16%2
1497
June1st to 15thNight
44%7%10%21%15%
1440
16th to endNight
43%6%12%20%13%1
1440
July1st to 15thNight
34%6%11%23%20%3
1360
16th to endNight
35%7%15%23%14%3
1534
August1st to 15thNight
33%7%16%27%13%1
1609
16th to endNight
33%7%14%28%14%1
1789
September1st to 15thNight
42%6%12%22%14%2
1800
16th to endNight
42%6%9%24%16%1
1929
October1st to 15thNight
50%5%10%18%14%
1980
16th to endNight
63%7%11%12%3
2112
November1st to 15thNight
52%6%11%17%10%2
2344
16th to endNight
66%6%9%12%3
2520
December1st to 15thNight
77%6%8%5%1
2520
16th to endNight
79%5%7%5%
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
28%34%19%8%7%1
67
16th to endDay
31%17%33%14%3
96
February1st to 15thDay
22%35%34%7%
90
16th to endDay
22%23%37%15%1
108
March1st to 15thDay
24%26%24%18%41
270
16th to endDay
22%21%27%20%6%1
288
April1st to 15thDay
22%24%25%17%8%1
270
16th to endDay
16%23%22%21%9%5%
270
May1st to 15thDay
25%20%19%19%11%3
288
16th to endDay
13%17%26%25%11%4
331
June1st to 15thDay
20%18%20%27%13%
315
16th to endDay
15%18%26%27%11%1
315
July1st to 15thDay
9%13%21%31%20%4
305
16th to endDay
11%14%23%28%17%4
326
August1st to 15thDay
11%9%20%26%21%10%
313
16th to endDay
12%10%18%25%21%12%
332
September1st to 15thDay
11%8%21%26%24%8%
315
16th to endDay
15%10%14%19%26%13%
283
October1st to 15thDay
16%15%24%20%16%6%
255
16th to endDay
28%22%25%19%4
272
November1st to 15thDay
14%16%31%25%8%4
124
16th to endDay
26%25%16%30%1
60
December1st to 15thDay
31%33%13%15%6%
60
16th to endDay
29%42%25%3
64
January1st to 15thNight
25%35%22%13%3
720
16th to endNight
24%30%27%13%3
768
February1st to 15thNight
22%32%25%16%3
704
16th to endNight
22%28%25%21%2
631
March1st to 15thNight
25%27%23%19%5%
720
16th to endNight
20%23%28%19%7%
768
April1st to 15thNight
22%27%22%22%4
718
16th to endNight
14%24%24%24%10%1
591
May1st to 15thNight
19%22%16%28%11%1
500
16th to endNight
11%20%23%28%14%1
375
June1st to 15thNight
15%18%23%29%13%
360
16th to endNight
13%20%21%31%11%
360
July1st to 15thNight
7%13%20%37%20%
340
16th to endNight
8%17%20%28%21%2
502
August1st to 15thNight
9%12%15%36%21%3
539
16th to endNight
10%10%17%30%27%3
643
September1st to 15thNight
14%12%16%28%24%3
720
16th to endNight
15%13%15%24%24%7%
689
October1st to 15thNight
22%16%20%23%15%2
660
16th to endNight
28%24%25%16%4
704
November1st to 15thNight
19%23%25%20%9%1
700
16th to endNight
22%35%22%13%6%
720
December1st to 15thNight
33%32%18%12%2
720
16th to endNight
28%32%23%12%2
768
Page generated at 2017-09-24 09:15:52. Version ac04

Copyright 2017 A. Danko


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