Baetsen Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Baetsen Observatory clear sky chart from 2005-11-05 to 2017-09-21.

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
37%
14804
14%
46936
9%
14770
42%
14770
19%
32705

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
15%
719
8%
2506
3%
716
20%
716
8%
1989
January16th to endNight
20%
768
10%
2505
4%
768
27%
768
10%
1948
February1st to 15thNight
16%
702
9%
2287
3%
701
23%
701
11%
1771
February16th to endNight
23%
631
12%
2017
5%
631
33%
631
14%
1463
March1st to 15thNight
24%
720
13%
1989
6%
720
31%
720
17%
1493
March16th to endNight
34%
768
20%
2111
10%
768
43%
768
26%
1405
April1st to 15thNight
33%
718
15%
1796
6%
718
38%
718
24%
1307
April16th to endNight
41%
594
19%
1674
9%
594
47%
594
28%
1098
May1st to 15thNight
50%
450
15%
1530
13%
450
55%
450
21%
1012
May16th to endNight
53%
374
17%
1497
18%
374
61%
374
25%
836
June1st to 15thNight
49%
360
11%
1440
12%
360
56%
360
20%
898
June16th to endNight
54%
360
11%
1440
15%
360
59%
360
22%
840
July1st to 15thNight
68%
340
16%
1360
25%
340
70%
340
32%
693
July16th to endNight
66%
441
16%
1478
18%
414
69%
414
31%
835
August1st to 15thNight
67%
539
16%
1609
13%
536
70%
536
34%
953
August16th to endNight
62%
647
22%
1793
13%
647
65%
647
36%
1084
September1st to 15thNight
56%
720
20%
1800
10%
720
60%
720
34%
1184
September16th to endNight
56%
681
21%
1898
16%
681
59%
681
30%
1217
October1st to 15thNight
38%
660
16%
1980
13%
660
43%
660
21%
1375
October16th to endNight
27%
704
11%
2112
7%
704
33%
704
15%
1612
November1st to 15thNight
37%
700
18%
2386
15%
700
43%
700
19%
1615
November16th to endNight
25%
720
10%
2520
7%
720
31%
720
11%
1907
December1st to 15thNight
16%
720
5%
2520
2%
720
19%
720
9%
1993
December16th to endNight
14%
768
6%
2688
2%
768
20%
768
8%
2177

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%8%36%5%35%45%7%34%
47932
Night
16%8%36%5%3445%6%35%
47112
Cloud CoverDay
14%7%36%5%35%5%5%7%35%
47942
Night
16%8%36%5%3445%6%35%
47117
TransparencyDay
47%8%13%19%10%1
47626
Night
48%7%13%19%10%1
46936
SeeingDay
18%5%25%27%16%5%
5398
Night
19%7%28%28%13%1
14808

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
18%14%5%7%7%2345%5%24%
1432
16th to endDay
13%15%6%10%8%45%5%45%20%
1719
February1st to 15thDay
14%12%5%13%8%36%345%21%
1575
16th to endDay
17%12%6%6%6%25%445%27%
1455
March1st to 15thDay
16%9%38%6%35%447%28%
1960
16th to endDay
16%9%35%5%23345%38%
2112
April1st to 15thDay
20%8%46%6%2445%6%30%
2152
16th to endDay
17%7%25%5%23445%39%
2295
May1st to 15thDay
14%7%36%5%35%45%6%35%
2418
16th to endDay
12%5%25%5%35%46%8%40%
2618
June1st to 15thDay
17%6%25%435%46%8%35%
2520
16th to endDay
12%5%245%25%5%6%10%38%
2520
July1st to 15thDay
8%424426%5%6%10%43%
2520
16th to endDay
8%425%6%35%6%7%8%39%
2588
August1st to 15thDay
8%6%246%36%5%6%7%41%
2340
16th to endDay
10%5%244245%6%8%43%
2396
September1st to 15thDay
15%4235%35%5%5%7%42%
2160
16th to endDay
12%5%25%435%35%7%43%
1854
October1st to 15thDay
18%9%26%5%345%45%33%
1650
16th to endDay
23%10%46%6%34445%26%
1760
November1st to 15thDay
16%8%37%5%35%45%6%32%
1472
16th to endDay
19%12%46%6%35%45%6%24%
1440
December1st to 15thDay
18%13%6%9%6%35%45%5%21%
1440
16th to endDay
21%13%5%9%6%36%436%19%
1536
January1st to 15thNight
21%13%6%7%7%3443423%
2506
16th to endNight
15%13%6%9%6%45%445%24%
2505
February1st to 15thNight
14%14%6%8%7%35%445%25%
2285
16th to endNight
16%9%48%6%3445%6%30%
2017
March1st to 15thNight
19%9%47%5%3433432%
1977
16th to endNight
14%6%35%5%34235%43%
2111
April1st to 15thNight
19%7%35%435%347%35%
1796
16th to endNight
13%7%25%325%446%44%
1674
May1st to 15thNight
15%5%25%5%35%46%7%38%
1530
16th to endNight
12%32342446%7%47%
1495
June1st to 15thNight
13%4245%25%5%6%7%40%
1440
16th to endNight
11%5%25%5%3445%9%42%
1440
July1st to 15thNight
6%32342445%8%55%
1440
16th to endNight
9%3134335%6%9%48%
1579
August1st to 15thNight
8%3145%245%7%8%49%
1620
16th to endNight
7%425%434446%52%
1793
September1st to 15thNight
13%5%1342445%6%48%
1800
16th to endNight
14%5%2342445%6%47%
1898
October1st to 15thNight
18%6%27%5%33347%37%
1980
16th to endNight
21%8%36%5%35%5%46%28%
2112
November1st to 15thNight
16%7%35%43445%7%35%
2386
16th to endNight
22%9%45%5%35%5%5%7%25%
2520
December1st to 15thNight
20%13%48%5%25%45%6%22%
2520
16th to endNight
22%11%5%7%7%35%45%6%19%
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
18%13%6%7%6%35%5%37%22%
1432
16th to endDay
13%14%5%10%9%46%5%45%18%
1719
February1st to 15thDay
14%11%5%12%8%46%45%6%20%
1575
16th to endDay
17%11%6%7%6%34446%27%
1455
March1st to 15thDay
16%8%49%5%36%45%5%28%
1971
16th to endDay
16%8%35%423446%38%
2111
April1st to 15thDay
19%7%36%6%35%45%7%30%
2152
16th to endDay
17%5%35%5%24446%39%
2295
May1st to 15thDay
13%5%35%6%36%5%5%7%36%
2418
16th to endDay
11%5%25%435%46%8%41%
2618
June1st to 15thDay
16%5%35%435%5%6%9%36%
2520
16th to endDay
11%5%14435%5%6%10%40%
2520
July1st to 15thDay
7%423436%5%6%10%46%
2520
16th to endDay
8%425%5%36%6%7%9%41%
2588
August1st to 15thDay
6%5%25%5%26%6%6%7%43%
2340
16th to endDay
8%5%234245%7%9%45%
2396
September1st to 15thDay
14%414435%5%47%43%
2160
16th to endDay
12%5%25%4245%47%44%
1854
October1st to 15thDay
19%7%346%36%446%34%
1650
16th to endDay
21%9%46%7%3445%5%28%
1760
November1st to 15thDay
14%8%47%6%35%46%7%31%
1472
16th to endDay
19%11%5%7%6%25%45%6%24%
1440
December1st to 15thDay
18%12%5%9%6%345%5%7%19%
1440
16th to endDay
21%13%6%8%8%345%5%6%18%
1536
January1st to 15thNight
22%12%6%8%6%34345%21%
2506
16th to endNight
15%13%6%9%6%36%5%46%22%
2505
February1st to 15thNight
14%14%5%9%7%36%446%24%
2278
16th to endNight
16%10%47%6%35%45%5%29%
2017
March1st to 15thNight
20%9%46%6%34335%31%
1989
16th to endNight
15%6%35%434345%44%
2111
April1st to 15thNight
19%6%45%425%35%6%35%
1796
16th to endNight
13%7%24424446%44%
1674
May1st to 15thNight
15%425%6%35%5%5%8%37%
1530
16th to endNight
12%4244335%5%7%47%
1495
June1st to 15thNight
12%5%245%25%6%6%7%39%
1440
16th to endNight
11%5%25%5%2446%9%42%
1440
July1st to 15thNight
5%41442445%8%55%
1440
16th to endNight
8%323435%5%6%9%48%
1579
August1st to 15thNight
8%4143345%6%9%48%
1620
16th to endNight
7%4345%245%45%52%
1793
September1st to 15thNight
14%5%233245%46%48%
1800
16th to endNight
14%5%24433446%46%
1898
October1st to 15thNight
18%5%37%5%3345%5%37%
1980
16th to endNight
21%7%36%6%345%5%6%28%
2112
November1st to 15thNight
16%6%35%5%35%5%5%7%35%
2386
16th to endNight
22%9%45%5%26%5%5%8%24%
2520
December1st to 15thNight
20%13%48%5%35%45%6%21%
2520
16th to endNight
22%11%5%7%6%45%45%6%18%
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
59%8%13%13%4
1433
16th to endDay
65%7%10%10%5%
1719
February1st to 15thDay
65%6%11%13%3
1577
16th to endDay
57%7%12%14%7%
1455
March1st to 15thDay
54%7%13%16%7%
1971
16th to endDay
46%5%9%18%16%2
2112
April1st to 15thDay
51%6%11%17%11%1
2152
16th to endDay
45%5%10%21%14%2
2295
May1st to 15thDay
46%7%11%19%13%1
2418
16th to endDay
39%8%15%22%12%1
2622
June1st to 15thDay
44%8%14%21%10%
2520
16th to endDay
38%8%17%21%12%
2520
July1st to 15thDay
32%8%15%26%16%1
2371
16th to endDay
38%10%15%24%9%1
2426
August1st to 15thDay
37%9%17%20%12%1
2327
16th to endDay
34%8%18%27%10%1
2396
September1st to 15thDay
39%8%14%25%10%
2160
16th to endDay
39%7%14%26%11%
1854
October1st to 15thDay
50%8%11%19%9%1
1650
16th to endDay
57%8%15%13%4
1760
November1st to 15thDay
50%9%15%15%8%1
1472
16th to endDay
58%8%13%14%4
1440
December1st to 15thDay
62%9%15%10%1
1440
16th to endDay
66%8%11%11%2
1536
January1st to 15thNight
63%7%11%12%31
2506
16th to endNight
60%7%11%13%5%
2505
February1st to 15thNight
60%6%12%15%4
2287
16th to endNight
54%5%14%18%6%
2017
March1st to 15thNight
55%5%12%19%6%
1989
16th to endNight
43%410%21%17%2
2111
April1st to 15thNight
48%5%10%18%15%1
1796
16th to endNight
40%5%11%19%19%2
1674
May1st to 15thNight
43%8%12%18%14%2
1530
16th to endNight
33%7%14%25%16%2
1497
June1st to 15thNight
40%9%11%21%15%1
1440
16th to endNight
38%6%14%23%15%1
1440
July1st to 15thNight
25%8%14%26%23%1
1360
16th to endNight
31%6%15%26%17%2
1478
August1st to 15thNight
29%8%19%26%13%1
1609
16th to endNight
31%7%14%30%15%1
1793
September1st to 15thNight
36%6%15%26%13%1
1800
16th to endNight
37%6%11%29%14%
1898
October1st to 15thNight
47%6%13%20%11%
1980
16th to endNight
54%9%13%14%7%
2112
November1st to 15thNight
46%7%14%18%12%1
2386
16th to endNight
56%9%15%13%4
2520
December1st to 15thNight
61%9%15%10%2
2520
16th to endNight
64%9%12%10%3
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
21%20%35%13%8%1
60
16th to endDay
30%15%28%22%3
95
February1st to 15thDay
22%27%38%11%
90
16th to endDay
26%13%35%21%3
114
March1st to 15thDay
25%11%33%23%5%
270
16th to endDay
25%435%23%9%2
288
April1st to 15thDay
21%8%31%27%9%1
270
16th to endDay
20%434%24%11%4
270
May1st to 15thDay
23%224%28%14%6%
288
16th to endDay
12%326%32%20%4
331
June1st to 15thDay
20%323%30%21%1
315
16th to endDay
18%121%33%20%5%
315
July1st to 15thDay
12%14%34%29%8%
305
16th to endDay
10%122%32%23%8%
326
August1st to 15thDay
9%116%33%27%11%
313
16th to endDay
14%115%26%26%15%
332
September1st to 15thDay
13%317%25%26%13%
315
16th to endDay
16%317%28%19%14%
275
October1st to 15thDay
17%5%27%28%16%5%
255
16th to endDay
26%11%27%27%5%
272
November1st to 15thDay
19%5%30%33%10%1
115
16th to endDay
23%15%25%26%10%
60
December1st to 15thDay
15%20%41%13%8%1
60
16th to endDay
28%17%46%7%
64
January1st to 15thNight
25%16%36%16%4
720
16th to endNight
21%11%36%24%6%
768
February1st to 15thNight
20%14%41%20%3
704
16th to endNight
20%12%36%26%4
631
March1st to 15thNight
23%11%34%26%4
720
16th to endNight
18%7%32%27%11%1
768
April1st to 15thNight
21%9%31%31%6%
718
16th to endNight
15%6%30%31%13%1
594
May1st to 15thNight
18%223%36%16%2
450
16th to endNight
13%223%36%22%1
375
June1st to 15thNight
15%125%39%18%1
360
16th to endNight
11%122%42%21%
360
July1st to 15thNight
6%16%51%23%2
340
16th to endNight
9%116%41%27%3
441
August1st to 15thNight
10%112%41%30%4
539
16th to endNight
10%17%36%30%4
647
September1st to 15thNight
16%318%31%25%5%
720
16th to endNight
16%5%17%27%26%7%
681
October1st to 15thNight
22%6%25%26%16%2
660
16th to endNight
24%8%32%27%6%
704
November1st to 15thNight
21%7%28%28%12%1
700
16th to endNight
25%11%29%23%8%1
720
December1st to 15thNight
29%12%36%17%4
720
16th to endNight
27%11%38%19%2
768
Page generated at 2017-09-22 07:35:31. Version ac04

Copyright 2017 A. Danko


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