Stellamar Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stellamar Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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%
15619
12%
46837
7%
15576
33%
15576
16%
34294

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
12%
900
5%
2506
2%
895
15%
895
6%
2172
January16th to endNight
15%
960
9%
2688
3%
960
20%
960
9%
2239
February1st to 15thNight
11%
720
7%
2289
1%
719
17%
719
8%
1874
February16th to endNight
20%
631
10%
1893
3%
631
27%
631
10%
1511
March1st to 15thNight
22%
720
15%
2109
7%
720
29%
720
17%
1500
March16th to endNight
29%
765
18%
2109
11%
765
36%
765
22%
1465
April1st to 15thNight
24%
539
15%
1761
8%
539
33%
539
17%
1250
April16th to endNight
31%
540
17%
1620
8%
540
40%
540
22%
1092
May1st to 15thNight
29%
540
12%
1620
7%
540
35%
540
19%
1135
May16th to endNight
39%
514
16%
1489
8%
513
48%
513
28%
938
June1st to 15thNight
35%
360
12%
1260
11%
360
41%
360
22%
790
June16th to endNight
44%
360
13%
1260
11%
360
49%
360
26%
755
July1st to 15thNight
51%
464
15%
1314
10%
464
55%
464
36%
782
July16th to endNight
55%
564
15%
1417
10%
531
57%
531
34%
885
August1st to 15thNight
51%
539
19%
1588
13%
536
58%
536
37%
909
August16th to endNight
50%
573
18%
1738
12%
573
56%
573
31%
1042
September1st to 15thNight
47%
630
17%
1890
11%
630
53%
630
29%
1178
September16th to endNight
44%
665
17%
1837
12%
665
47%
665
28%
1211
October1st to 15thNight
31%
660
17%
1889
10%
660
39%
660
22%
1321
October16th to endNight
20%
704
10%
2265
6%
704
26%
704
12%
1733
November1st to 15thNight
23%
700
14%
2276
9%
700
30%
700
13%
1687
November16th to endNight
15%
720
10%
2469
4%
720
23%
720
9%
1956
December1st to 15thNight
12%
891
3%
2691
1%
891
14%
891
6%
2360
December16th to endNight
10%
960
6%
2859
2%
960
14%
960
5%
2509

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%47%6%3445%6%30%
47941
Night
14%10%48%6%35%45%6%30%
47005
Cloud CoverDay
15%10%47%6%3445%6%30%
47950
Night
14%10%48%6%34446%30%
47010
TransparencyDay
53%5%10%19%9%1
47627
Night
53%5%11%18%8%
46837
SeeingDay
19%14%31%20%9%4
5967
Night
20%14%31%24%9%1
15622

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
16%16%7%15%10%45%435%12%
1432
16th to endDay
11%16%9%15%11%5%6%43311%
1536
February1st to 15thDay
12%15%9%11%12%5%5%43414%
1573
16th to endDay
12%17%7%11%8%5%5%45%417%
1580
March1st to 15thDay
12%10%5%9%7%35%446%29%
1841
16th to endDay
15%11%47%6%34446%33%
2124
April1st to 15thDay
19%14%36%42445%6%30%
2187
16th to endDay
16%11%35%5%2445%6%34%
2340
May1st to 15thDay
19%8%25%5%34447%33%
2331
16th to endDay
13%5%35%5%345%5%6%40%
2620
June1st to 15thDay
14%6%25%6%35%5%6%7%36%
2700
16th to endDay
15%6%25%5%345%6%8%36%
2700
July1st to 15thDay
12%5%34435%5%6%8%39%
2563
16th to endDay
10%5%26%5%26%46%8%39%
2655
August1st to 15thDay
10%5%26%6%45%5%6%9%37%
2361
16th to endDay
15%6%36%43445%6%39%
2462
September1st to 15thDay
14%7%25%5%34448%38%
2058
16th to endDay
14%6%25%5%345%5%8%38%
1829
October1st to 15thDay
22%9%37%5%33345%31%
1741
16th to endDay
22%17%5%8%6%35%445%16%
1606
November1st to 15thDay
17%13%48%6%335%47%24%
1582
16th to endDay
18%18%7%11%7%34446%13%
1488
December1st to 15thDay
16%18%9%15%9%4433312%
1269
16th to endDay
18%21%11%14%7%2424310%
1363
January1st to 15thNight
17%13%7%13%9%5%6%44413%
2506
16th to endNight
11%13%6%12%11%5%6%45%6%15%
2688
February1st to 15thNight
10%15%8%12%10%46%44418%
2287
16th to endNight
13%14%7%11%7%35%5%4421%
1893
March1st to 15thNight
12%10%47%5%45%45%5%34%
2096
16th to endNight
13%10%46%425%45%6%37%
2109
April1st to 15thNight
20%10%35%42445%6%31%
1761
16th to endNight
15%8%25%5%35%5%5%6%38%
1620
May1st to 15thNight
14%7%26%7%35%5%5%7%33%
1620
16th to endNight
11%6%3442446%7%44%
1487
June1st to 15thNight
12%5%35%5%3445%7%40%
1260
16th to endNight
10%5%235%35%5%5%10%43%
1260
July1st to 15thNight
7%5%145%245%5%7%49%
1394
16th to endNight
8%4244345%5%7%49%
1513
August1st to 15thNight
8%4234335%5%7%51%
1597
16th to endNight
11%4145%33447%49%
1738
September1st to 15thNight
13%5%25%424446%46%
1890
16th to endNight
16%4245%34448%41%
1837
October1st to 15thNight
20%7%26%423446%36%
1889
16th to endNight
22%11%47%6%3445%5%24%
2265
November1st to 15thNight
15%13%47%7%34447%25%
2276
16th to endNight
17%16%7%8%5%35%45%6%19%
2469
December1st to 15thNight
15%16%9%11%8%46%6%35%11%
2691
16th to endNight
17%17%9%12%8%4445%411%
2859

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
17%15%7%14%10%35%44412%
1432
16th to endDay
11%16%10%15%10%6%5%33311%
1536
February1st to 15thDay
12%15%9%12%12%45%445%14%
1573
16th to endDay
12%17%7%11%8%45%45%417%
1580
March1st to 15thDay
12%10%5%8%8%45%346%29%
1851
16th to endDay
15%11%47%6%23445%33%
2123
April1st to 15thDay
20%13%36%32445%6%29%
2187
16th to endDay
16%11%25%424446%35%
2340
May1st to 15thDay
19%7%26%6%34446%33%
2331
16th to endDay
13%5%35%5%35%45%6%40%
2620
June1st to 15thDay
13%6%36%6%35%46%8%36%
2700
16th to endDay
15%5%35%6%35%5%5%9%35%
2700
July1st to 15thDay
12%5%25%5%346%6%8%39%
2563
16th to endDay
10%6%35%5%35%46%9%39%
2655
August1st to 15thDay
10%5%26%6%45%5%6%9%37%
2361
16th to endDay
14%6%35%5%3445%6%39%
2462
September1st to 15thDay
14%6%36%5%3445%8%38%
2058
16th to endDay
15%5%345%4445%8%38%
1829
October1st to 15thDay
22%8%47%5%2434431%
1741
16th to endDay
22%16%5%8%6%34446%15%
1606
November1st to 15thDay
17%13%5%7%6%34447%25%
1582
16th to endDay
17%19%7%10%7%35%435%14%
1488
December1st to 15thDay
15%18%9%15%9%3333412%
1269
16th to endDay
17%21%10%14%8%2323410%
1363
January1st to 15thNight
17%13%6%13%10%45%5%4413%
2506
16th to endNight
11%13%7%12%11%46%5%46%16%
2688
February1st to 15thNight
11%15%8%11%9%46%445%18%
2280
16th to endNight
13%14%7%11%7%45%5%4421%
1893
March1st to 15thNight
13%10%47%5%35%445%34%
2109
16th to endNight
13%10%45%424446%37%
2109
April1st to 15thNight
19%11%25%4245%5%6%31%
1761
16th to endNight
15%8%345%25%446%38%
1620
May1st to 15thNight
13%8%36%7%445%5%7%33%
1619
16th to endNight
11%6%2443445%7%43%
1487
June1st to 15thNight
12%6%26%5%3445%8%40%
1260
16th to endNight
9%5%34335%5%5%9%42%
1260
July1st to 15thNight
7%3245%25%5%6%6%50%
1394
16th to endNight
8%414425%5%5%7%49%
1513
August1st to 15thNight
8%4244335%5%8%50%
1597
16th to endNight
11%4235%33447%48%
1738
September1st to 15thNight
13%5%25%424446%46%
1890
16th to endNight
16%4145%4445%8%41%
1837
October1st to 15thNight
20%7%26%5%23346%36%
1889
16th to endNight
22%10%47%6%3445%5%25%
2265
November1st to 15thNight
15%13%38%6%345%5%7%26%
2276
16th to endNight
18%15%6%8%6%35%445%19%
2469
December1st to 15thNight
15%15%8%12%9%45%5%45%12%
2691
16th to endNight
17%17%9%12%8%45%43411%
2859

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
74%6%7%9%1
1433
16th to endDay
77%36%8%2
1536
February1st to 15thDay
72%48%9%3
1575
16th to endDay
67%5%9%11%5%
1580
March1st to 15thDay
56%412%19%6%1
1851
16th to endDay
51%412%19%9%1
2124
April1st to 15thDay
54%39%20%11%
2187
16th to endDay
48%5%11%17%15%2
2340
May1st to 15thDay
50%5%7%21%12%2
2331
16th to endDay
42%5%11%23%14%1
2624
June1st to 15thDay
45%5%10%25%12%1
2700
16th to endDay
44%5%13%22%12%1
2700
July1st to 15thDay
38%6%10%25%16%1
2414
16th to endDay
41%6%12%22%15%1
2488
August1st to 15thDay
41%6%13%24%13%
2346
16th to endDay
44%5%12%23%12%1
2462
September1st to 15thDay
44%5%10%26%12%
2058
16th to endDay
43%5%14%25%10%
1829
October1st to 15thDay
55%47%22%8%
1741
16th to endDay
68%6%11%10%3
1606
November1st to 15thDay
57%5%12%17%6%
1582
16th to endDay
72%5%10%8%3
1488
December1st to 15thDay
77%5%7%7%1
1269
16th to endDay
79%48%5%2
1363
January1st to 15thNight
73%6%8%9%3
2506
16th to endNight
68%5%10%10%3
2688
February1st to 15thNight
67%5%10%12%3
2289
16th to endNight
64%5%12%12%5%
1893
March1st to 15thNight
51%411%21%9%
2109
16th to endNight
47%412%20%13%1
2109
April1st to 15thNight
51%5%7%23%10%1
1761
16th to endNight
45%411%19%16%2
1620
May1st to 15thNight
49%6%10%19%11%2
1620
16th to endNight
38%5%13%25%15%2
1489
June1st to 15thNight
41%5%12%23%14%1
1260
16th to endNight
36%6%15%26%13%1
1260
July1st to 15thNight
31%5%13%29%19%
1314
16th to endNight
32%7%16%26%15%1
1417
August1st to 15thNight
30%5%17%32%13%1
1588
16th to endNight
35%5%16%28%13%1
1738
September1st to 15thNight
37%5%13%28%13%1
1890
16th to endNight
41%5%16%27%9%
1837
October1st to 15thNight
48%410%24%11%
1889
16th to endNight
59%6%12%16%4
2265
November1st to 15thNight
57%5%13%16%6%
2276
16th to endNight
64%5%12%12%3
2469
December1st to 15thNight
72%8%9%7%1
2691
16th to endNight
75%5%7%7%3
2859

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%23%43%11%1
90
16th to endDay
30%14%40%7%6%1
96
February1st to 15thDay
26%23%38%10%1
90
16th to endDay
24%30%32%6%6%
81
March1st to 15thDay
26%23%29%16%4
141
16th to endDay
27%11%28%20%9%2
288
April1st to 15thDay
29%16%22%21%10%
270
16th to endDay
25%12%34%13%9%4
270
May1st to 15thDay
25%15%30%16%6%4
288
16th to endDay
16%19%32%21%7%2
475
June1st to 15thDay
17%18%36%20%5%2
495
16th to endDay
15%13%40%20%7%2
495
July1st to 15thDay
16%12%33%24%10%3
475
16th to endDay
12%11%33%26%10%4
515
August1st to 15thDay
13%5%28%27%13%11%
334
16th to endDay
21%6%24%23%15%8%
332
September1st to 15thDay
14%7%24%24%18%10%
315
16th to endDay
15%10%24%28%12%7%
259
October1st to 15thDay
26%9%34%18%9%1
255
16th to endDay
27%24%33%10%4
118
November1st to 15thDay
18%15%35%22%43
90
16th to endDay
20%25%32%20%1
68
December1st to 15thDay
26%33%31%35%
60
16th to endDay
31%43%19%41
67
January1st to 15thNight
26%19%30%16%5%
900
16th to endNight
19%18%33%21%5%
960
February1st to 15thNight
19%22%36%16%4
722
16th to endNight
22%17%33%22%4
631
March1st to 15thNight
20%21%30%21%5%
720
16th to endNight
20%13%30%26%7%
765
April1st to 15thNight
25%12%33%22%4
539
16th to endNight
21%12%31%25%7%
540
May1st to 15thNight
16%13%35%25%8%
540
16th to endNight
14%11%30%33%9%
515
June1st to 15thNight
13%10%31%33%10%
360
16th to endNight
11%7%31%36%12%
360
July1st to 15thNight
9%428%36%20%1
464
16th to endNight
10%426%38%18%1
564
August1st to 15thNight
11%327%34%21%2
539
16th to endNight
13%424%34%20%2
573
September1st to 15thNight
16%6%24%26%20%5%
630
16th to endNight
19%6%24%29%15%3
665
October1st to 15thNight
22%10%30%25%10%
660
16th to endNight
29%14%29%19%5%
704
November1st to 15thNight
24%16%31%18%7%
700
16th to endNight
27%16%35%17%3
720
December1st to 15thNight
23%22%35%15%3
891
16th to endNight
26%19%33%15%3
960
Page generated at 2017-09-18 07:38:26. Version ac04

Copyright 2017 A. Danko


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