Og's Bog
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Og's Bog clear sky chart from 2005-11-06 to 2024-01-12.

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%
22800
15%
74466
8%
22751
37%
22751
17%
52149

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
13%
759
10%
2649
3%
757
21%
757
8%
2078
January11th to 20thNight
14%
727
8%
2397
3%
727
20%
727
7%
1958
January21st to endNight
18%
792
12%
2574
5%
792
27%
792
10%
1973
February1st to 10thNight
10%
720
11%
2340
1%
720
20%
720
9%
1803
February11th to 20thNight
12%
700
13%
2275
3%
700
25%
700
10%
1742
February21st to endNight
16%
592
14%
1872
4%
592
27%
592
12%
1371
March1st to 10thNight
18%
720
16%
1980
5%
720
28%
720
15%
1436
March11th to 20thNight
21%
720
18%
1980
8%
720
31%
720
17%
1415
March21st to endNight
26%
792
19%
2178
8%
792
36%
792
21%
1502
April1st to 10thNight
19%
720
14%
1845
4%
720
25%
720
18%
1371
April11th to 20thNight
26%
637
19%
1701
7%
637
34%
637
23%
1170
April21st to endNight
29%
540
17%
1620
7%
540
37%
540
20%
1115
May1st to 10thNight
36%
540
16%
1620
9%
540
43%
540
25%
1073
May11th to 20thNight
37%
377
23%
1439
16%
377
52%
377
24%
823
May21st to endNight
43%
388
18%
1551
14%
388
56%
388
29%
815
June1st to 10thNight
36%
360
15%
1440
12%
360
50%
360
22%
844
June11th to 20thNight
43%
360
17%
1374
18%
360
52%
360
25%
784
June21st to endNight
44%
360
17%
1260
16%
360
53%
360
27%
716
July1st to 10thNight
58%
350
18%
1275
19%
350
66%
350
35%
651
July11th to 20thNight
50%
348
20%
1392
25%
348
60%
348
30%
737
July21st to endNight
52%
571
18%
1654
14%
540
57%
540
36%
944
August1st to 10thNight
56%
537
19%
1600
13%
534
61%
534
37%
916
August11th to 20thNight
60%
534
23%
1598
15%
534
66%
534
37%
904
August21st to endNight
48%
656
22%
1844
11%
656
54%
656
33%
1126
September1st to 10thNight
48%
720
18%
1800
8%
720
52%
720
35%
1140
September11th to 20thNight
50%
720
28%
1919
15%
720
57%
720
38%
1129
September21st to endNight
42%
720
20%
2006
14%
720
47%
720
27%
1331
October1st to 10thNight
36%
720
17%
2160
12%
720
43%
720
21%
1470
October11th to 20thNight
24%
720
14%
2160
7%
720
34%
720
17%
1537
October21st to endNight
18%
792
15%
2376
7%
792
29%
792
13%
1808
November1st to 10thNight
26%
740
19%
2478
12%
740
37%
740
18%
1652
November11th to 20thNight
20%
760
14%
2660
7%
760
31%
760
12%
1913
November21st to endNight
19%
760
9%
2660
5%
760
26%
760
10%
2027
December1st to 10thNight
13%
760
8%
2660
3%
760
19%
760
9%
2099
December11th to 20thNight
13%
760
6%
3258
2%
758
20%
758
6%
2556
December21st to endNight
10%
828
3%
4871
0%
817
17%
817
3%
4220

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%10%48%6%45%5%5%7%31%
75002
Night
15%11%47%6%35%5%5%7%32%
74687
TransparencyDay
52%5%11%20%10%1
74717
Night
51%5%11%21%10%1
74509
SeeingDay
20%16%31%20%9%4
13632
Night
20%14%31%24%10%1
22813

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 10thDay
14%14%6%12%11%47%6%5%6%17%
1517
11th to 20thDay
15%18%6%10%9%5%5%5%5%5%17%
1588
21st to endDay
12%17%9%12%9%5%5%5%5%5%17%
1782
February1st to 10thDay
15%16%5%12%9%5%7%5%5%5%16%
1620
11th to 20thDay
12%15%7%11%9%45%5%5%6%21%
1573
21st to endDay
17%18%5%11%6%35%445%24%
1380
March1st to 10thDay
13%12%6%9%9%4445%5%28%
1977
11th to 20thDay
12%14%6%9%7%45%44431%
1980
21st to endDay
18%13%37%6%34445%32%
2178
April1st to 10thDay
15%15%5%7%6%35%45%6%28%
2114
11th to 20thDay
19%11%35%4245%47%35%
2223
21st to endDay
20%9%47%5%33446%33%
2340
May1st to 10thDay
16%8%47%5%35%46%7%34%
2340
11th to 20thDay
16%8%25%6%35%45%7%39%
2451
21st to endDay
12%5%35%6%35%6%6%8%42%
2725
June1st to 10thDay
16%6%25%5%35%5%7%8%37%
2520
11th to 20thDay
13%6%25%5%35%5%6%10%40%
2578
21st to endDay
14%5%25%5%45%5%6%8%40%
2700
July1st to 10thDay
9%425%5%36%6%6%9%44%
2642
11th to 20thDay
10%5%37%6%46%6%7%9%38%
2520
21st to endDay
10%6%37%7%46%6%7%10%33%
2564
August1st to 10thDay
10%5%25%6%46%6%8%9%38%
2327
11th to 20thDay
8%7%37%7%46%6%7%10%36%
2303
21st to endDay
13%6%35%6%46%5%6%8%38%
2494
September1st to 10thDay
13%6%36%7%45%5%6%7%38%
2160
11th to 20thDay
12%6%36%5%45%5%5%8%41%
2038
21st to endDay
14%7%37%7%45%5%6%7%35%
1954
October1st to 10thDay
20%9%37%6%35%446%32%
1800
11th to 20thDay
21%10%49%7%345%5%6%26%
1800
21st to endDay
26%17%37%5%3445%5%20%
1980
November1st to 10thDay
13%14%47%7%45%5%5%8%29%
1596
11th to 20thDay
13%14%5%8%8%46%5%6%7%23%
1520
21st to endDay
17%17%7%11%7%36%5%5%5%18%
1520
December1st to 10thDay
16%17%9%13%9%45%5%5%414%
1520
11th to 20thDay
18%15%6%13%7%36%5%5%6%18%
1906
21st to endDay
26%18%8%15%6%3433310%
2772
January1st to 10thNight
15%16%7%10%8%45%6%5%5%19%
2649
11th to 20thNight
17%15%7%10%9%47%5%5%5%16%
2397
21st to endNight
11%13%7%10%9%47%6%5%7%21%
2574
February1st to 10thNight
14%15%6%10%8%45%45%7%22%
2340
11th to 20thNight
13%14%7%10%7%5%6%5%5%6%24%
2273
21st to endNight
13%13%5%10%7%45%5%5%6%27%
1872
March1st to 10thNight
12%10%5%9%7%45%5%46%33%
1970
11th to 20thNight
14%12%5%9%5%35%345%35%
1979
21st to endNight
15%10%36%6%3445%5%39%
2178
April1st to 10thNight
18%10%5%7%6%345%5%6%31%
1845
11th to 20thNight
16%9%345%35%5%5%7%38%
1701
21st to endNight
14%11%46%5%35%5%5%6%36%
1620
May1st to 10thNight
16%7%25%5%345%6%7%39%
1620
11th to 20thNight
13%6%35%43445%7%47%
1438
21st to endNight
10%425%325%45%9%52%
1550
June1st to 10thNight
12%5%35%6%45%5%5%9%41%
1440
11th to 20thNight
10%336%5%35%7%6%9%43%
1374
21st to endNight
11%5%25%6%245%5%8%47%
1260
July1st to 10thNight
5%4344335%37%57%
1312
11th to 20thNight
9%5%25%5%35%5%5%8%50%
1440
21st to endNight
7%5%14435%6%6%8%51%
1751
August1st to 10thNight
7%6%244445%5%8%52%
1611
11th to 20thNight
6%5%34435%5%6%10%50%
1598
21st to endNight
10%6%2444446%8%47%
1844
September1st to 10thNight
9%5%35%5%346%7%8%47%
1800
11th to 20thNight
11%5%2442345%7%53%
1919
21st to endNight
15%7%36%6%34347%42%
2006
October1st to 10thNight
18%7%36%6%445%5%7%37%
2160
11th to 20thNight
18%10%38%5%346%5%6%32%
2160
21st to endNight
22%11%47%6%45%5%5%7%24%
2376
November1st to 10thNight
16%10%36%6%3445%6%36%
2478
11th to 20thNight
16%13%47%6%45%6%6%7%27%
2660
21st to endNight
17%15%6%9%6%45%5%5%7%22%
2660
December1st to 10thNight
19%15%6%10%7%35%5%6%6%18%
2660
11th to 20thNight
15%18%7%10%7%45%5%5%7%18%
3288
21st to endNight
27%18%7%13%6%35%44410%
4884

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
67%6%11%12%5%
1518
11th to 20thDay
68%5%10%11%6%1
1588
21st to endDay
68%5%7%12%8%1
1782
February1st to 10thDay
69%5%7%15%41
1620
11th to 20thDay
64%6%7%15%7%1
1582
21st to endDay
64%48%16%8%1
1380
March1st to 10thDay
58%411%16%10%1
1980
11th to 20thDay
57%48%18%11%2
1980
21st to endDay
55%48%17%13%2
2178
April1st to 10thDay
57%5%9%19%10%1
2114
11th to 20thDay
49%48%24%15%1
2223
21st to endDay
52%410%20%12%2
2340
May1st to 10thDay
49%49%22%15%1
2340
11th to 20thDay
45%5%9%25%14%1
2455
21st to endDay
40%5%16%24%14%2
2725
June1st to 10thDay
43%5%12%23%16%1
2520
11th to 20thDay
39%5%13%25%16%1
2578
21st to endDay
40%5%14%26%14%1
2700
July1st to 10thDay
36%5%13%25%19%2
2571
11th to 20thDay
40%5%13%30%11%1
2445
21st to endDay
44%6%13%23%13%1
2421
August1st to 10thDay
39%6%17%25%12%2
2314
11th to 20thDay
40%6%17%25%11%
2303
21st to endDay
42%6%13%26%11%1
2494
September1st to 10thDay
43%6%12%27%10%2
2160
11th to 20thDay
40%5%12%30%13%
2038
21st to endDay
48%412%27%8%1
1954
October1st to 10thDay
53%412%19%11%1
1800
11th to 20thDay
58%411%20%7%1
1800
21st to endDay
66%411%13%6%
1980
November1st to 10thDay
53%6%12%20%9%1
1596
11th to 20thDay
60%413%14%8%1
1520
21st to endDay
68%5%12%13%3
1520
December1st to 10thDay
72%5%10%11%2
1520
11th to 20thDay
65%9%11%11%4
1906
21st to endDay
80%46%9%2
2772
January1st to 10thNight
65%5%10%14%6%
2649
11th to 20thNight
68%6%9%10%5%1
2397
21st to endNight
61%5%10%16%7%1
2574
February1st to 10thNight
61%6%9%18%5%
2340
11th to 20thNight
61%5%9%17%8%1
2275
21st to endNight
58%311%19%8%1
1872
March1st to 10thNight
51%6%12%20%10%1
1980
11th to 20thNight
52%310%21%12%2
1980
21st to endNight
48%49%22%15%3
2178
April1st to 10thNight
54%49%19%13%1
1845
11th to 20thNight
46%410%22%16%2
1701
21st to endNight
48%5%10%20%15%2
1620
May1st to 10thNight
44%410%23%16%3
1620
11th to 20thNight
39%410%27%18%3
1439
21st to endNight
31%5%16%26%17%4
1551
June1st to 10thNight
39%6%10%26%17%2
1440
11th to 20thNight
36%5%12%25%20%2
1374
21st to endNight
36%414%29%16%1
1260
July1st to 10thNight
28%5%12%28%24%3
1275
11th to 20thNight
32%412%34%17%2
1392
21st to endNight
30%6%15%32%15%3
1654
August1st to 10thNight
32%418%32%14%1
1600
11th to 20thNight
29%5%15%35%14%2
1598
21st to endNight
35%5%13%31%15%1
1844
September1st to 10thNight
34%6%16%29%13%1
1800
11th to 20thNight
31%411%35%18%1
1919
21st to endNight
43%413%29%11%
2006
October1st to 10thNight
48%411%22%15%1
2160
11th to 20thNight
52%5%12%23%7%
2160
21st to endNight
59%5%10%16%10%
2376
November1st to 10thNight
48%5%12%24%10%1
2478
11th to 20thNight
55%5%12%18%9%1
2660
21st to endNight
61%5%15%15%31
2660
December1st to 10thNight
65%6%12%14%4
2660
11th to 20thNight
65%5%12%14%3
3288
21st to endNight
78%5%9%7%2
4884

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
21%22%35%17%41
180
11th to 20thDay
26%25%29%14%42
224
21st to endDay
25%25%34%13%3
264
February1st to 10thDay
32%30%27%9%2
240
11th to 20thDay
26%29%40%5%1
240
21st to endDay
38%31%26%6%
200
March1st to 10thDay
23%22%35%16%4
420
11th to 20thDay
22%20%38%15%5%
420
21st to endDay
30%20%30%14%5%1
462
April1st to 10thDay
23%24%32%14%6%
420
11th to 20thDay
31%19%26%13%8%3
412
21st to endDay
25%20%33%15%5%2
420
May1st to 10thDay
23%15%31%18%10%3
423
11th to 20thDay
22%15%29%21%9%4
447
21st to endDay
14%15%29%25%12%5%
485
June1st to 10thDay
17%14%33%26%8%2
450
11th to 20thDay
17%13%31%24%13%2
508
21st to endDay
17%11%36%23%9%3
630
July1st to 10thDay
10%7%33%29%16%4
566
11th to 20thDay
11%7%32%28%14%7%
444
21st to endDay
11%7%36%28%11%6%
488
August1st to 10thDay
9%8%26%30%15%11%
446
11th to 20thDay
9%7%29%27%19%9%
439
21st to endDay
16%8%29%23%15%7%
495
September1st to 10thDay
14%11%27%26%13%8%
450
11th to 20thDay
12%9%28%23%18%12%
450
21st to endDay
15%14%30%21%15%5%
450
October1st to 10thDay
25%14%24%20%12%5%
450
11th to 20thDay
24%19%34%17%6%1
450
21st to endDay
34%18%28%15%4
495
November1st to 10thDay
25%22%30%18%41
246
11th to 20thDay
27%21%34%13%41
180
21st to endDay
29%23%37%10%1
180
December1st to 10thDay
28%27%31%13%2
180
11th to 20thDay
28%29%28%12%21
180
21st to endDay
26%28%35%8%3
198
January1st to 10thNight
24%22%34%14%5%1
760
11th to 20thNight
27%20%31%18%4
727
21st to endNight
19%16%36%22%7%
792
February1st to 10thNight
21%23%38%16%2
720
11th to 20thNight
21%21%38%15%4
703
21st to endNight
20%23%35%18%3
592
March1st to 10thNight
21%22%33%20%3
720
11th to 20thNight
23%20%32%20%5%1
720
21st to endNight
22%16%32%22%8%
792
April1st to 10thNight
24%16%35%21%3
720
11th to 20thNight
20%17%35%19%8%1
637
21st to endNight
21%13%31%26%8%
540
May1st to 10thNight
19%7%30%31%12%2
540
11th to 20thNight
15%8%32%34%10%1
377
21st to endNight
10%8%35%32%15%1
389
June1st to 10thNight
14%7%35%33%12%
360
11th to 20thNight
12%9%29%35%15%
360
21st to endNight
12%5%31%36%16%1
360
July1st to 10thNight
7%325%42%20%2
350
11th to 20thNight
13%428%34%19%2
348
21st to endNight
8%430%38%19%2
571
August1st to 10thNight
11%123%37%26%2
537
11th to 20thNight
7%6%19%42%24%3
534
21st to endNight
13%427%32%22%2
656
September1st to 10thNight
11%7%28%30%19%5%
720
11th to 20thNight
14%6%25%29%21%5%
720
21st to endNight
18%10%23%28%18%4
720
October1st to 10thNight
21%9%29%24%15%2
720
11th to 20thNight
24%14%33%20%8%1
720
21st to endNight
29%16%29%21%4
792
November1st to 10thNight
23%15%31%23%8%1
740
11th to 20thNight
23%21%29%20%6%1
760
21st to endNight
26%17%32%22%4
760
December1st to 10thNight
29%18%35%14%31
760
11th to 20thNight
23%22%34%17%4
760
21st to endNight
32%17%31%18%2
836
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