Sirius Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sirius Observatory clear sky chart from 2005-11-05 to 2017-04-24.

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
36%
15099
15%
45582
10%
15060
42%
15060
21%
31399

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
17%
898
10%
2506
3%
895
23%
895
12%
1977
January16th to endNight
20%
835
10%
2563
3%
835
28%
835
12%
1990
February1st to 15thNight
16%
701
11%
2283
2%
701
26%
701
11%
1730
February16th to endNight
23%
631
15%
1893
6%
631
31%
631
14%
1404
March1st to 15thNight
24%
720
15%
2063
8%
720
30%
720
17%
1490
March16th to endNight
34%
768
18%
2112
10%
768
40%
768
22%
1471
April1st to 15thNight
28%
608
15%
1812
8%
608
35%
608
21%
1252
April16th to endNight
39%
522
21%
1566
9%
522
48%
522
26%
1006
May1st to 15thNight
42%
495
15%
1485
9%
495
48%
495
23%
1015
May16th to endNight
52%
505
16%
1532
12%
505
57%
505
30%
932
June1st to 15thNight
52%
330
18%
1166
18%
330
60%
330
27%
695
June16th to endNight
57%
335
17%
1160
17%
335
62%
335
30%
668
July1st to 15thNight
66%
465
18%
1240
15%
465
68%
465
41%
736
July16th to endNight
67%
522
15%
1396
11%
489
69%
489
37%
822
August1st to 15thNight
66%
494
20%
1474
16%
491
69%
491
36%
863
August16th to endNight
62%
525
23%
1575
16%
525
67%
525
36%
921
September1st to 15thNight
57%
624
24%
1768
18%
624
61%
624
32%
1086
September16th to endNight
59%
657
22%
1815
17%
657
63%
657
34%
1123
October1st to 15thNight
46%
660
20%
1914
15%
660
52%
660
29%
1227
October16th to endNight
25%
704
14%
2189
8%
704
33%
704
16%
1578
November1st to 15thNight
36%
700
21%
2276
16%
700
44%
700
22%
1481
November16th to endNight
26%
720
13%
2454
9%
720
32%
720
14%
1736
December1st to 15thNight
15%
720
9%
2520
2%
720
22%
720
10%
1902
December16th to endNight
15%
960
8%
2820
2%
960
20%
960
10%
2294

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
13%8%37%6%35%5%5%7%32%
46004
Night
15%8%36%5%3445%6%35%
45762
Cloud CoverDay
14%8%37%6%35%45%7%32%
46014
Night
15%8%36%5%3445%6%35%
45766
TransparencyDay
49%5%12%20%10%1
45702
Night
48%5%11%21%11%1
45582
SeeingDay
16%7%25%24%16%8%
5179
Night
19%8%28%30%12%1
15106

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%13%6%11%8%35%446%19%
1432
16th to endDay
15%16%8%10%9%4445%5%15%
1659
February1st to 15thDay
14%14%6%10%9%45%5%5%5%19%
1578
16th to endDay
12%13%6%10%7%45%45%6%23%
1580
March1st to 15thDay
16%11%6%8%7%24446%28%
1885
16th to endDay
16%10%5%8%6%44345%28%
2112
April1st to 15thDay
18%10%46%5%2445%7%30%
2145
16th to endDay
16%8%36%5%3345%6%37%
2253
May1st to 15thDay
17%8%27%5%35%5%47%33%
2136
16th to endDay
14%5%25%435%45%7%40%
2228
June1st to 15thDay
10%5%36%5%25%5%5%9%38%
2461
16th to endDay
9%426%6%46%6%7%10%36%
2466
July1st to 15thDay
7%425%5%45%6%6%9%42%
2310
16th to endDay
8%425%7%46%6%7%10%37%
2357
August1st to 15thDay
9%426%6%45%6%7%9%37%
2145
16th to endDay
11%5%25%5%35%5%6%8%39%
2275
September1st to 15thDay
12%6%25%5%35%7%5%9%37%
1848
16th to endDay
12%6%25%5%3447%9%37%
1815
October1st to 15thDay
13%7%36%5%35%45%6%38%
1716
16th to endDay
21%9%37%5%33436%31%
1680
November1st to 15thDay
14%7%36%6%35%5%46%35%
1582
16th to endDay
16%11%48%6%35%446%26%
1503
December1st to 15thDay
15%13%6%11%7%345%45%22%
1437
16th to endDay
20%16%6%9%7%24345%18%
1401
January1st to 15thNight
22%11%5%7%6%34446%24%
2506
16th to endNight
13%13%7%9%7%35%5%46%24%
2563
February1st to 15thNight
13%14%5%9%5%35%445%27%
2281
16th to endNight
15%10%49%7%4435%5%28%
1893
March1st to 15thNight
17%10%47%5%34346%32%
2051
16th to endNight
16%7%35%5%25%45%5%36%
2112
April1st to 15thNight
19%7%36%42445%6%34%
1812
16th to endNight
15%6%25%42445%8%41%
1566
May1st to 15thNight
15%6%25%5%45%5%5%7%36%
1485
16th to endNight
11%424424447%47%
1530
June1st to 15thNight
8%5%26%435%5%5%9%43%
1166
16th to endNight
9%5%245%245%7%7%45%
1160
July1st to 15thNight
7%42333445%8%53%
1320
16th to endNight
5%223425%5%6%9%50%
1501
August1st to 15thNight
6%325%4345%7%8%49%
1485
16th to endNight
10%424423446%53%
1575
September1st to 15thNight
12%42443345%6%49%
1768
16th to endNight
10%5%244246%5%7%47%
1815
October1st to 15thNight
14%5%25%4245%6%6%42%
1914
16th to endNight
21%8%36%6%245%6%6%30%
2189
November1st to 15thNight
14%7%25%425%5%6%6%39%
2276
16th to endNight
18%11%36%5%35%45%7%27%
2454
December1st to 15thNight
19%12%5%8%6%34446%24%
2520
16th to endNight
21%14%6%9%6%34345%20%
2820

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
16%14%6%11%8%35%35%5%19%
1432
16th to endDay
15%15%8%9%9%4445%5%16%
1659
February1st to 15thDay
14%14%5%11%7%45%46%6%18%
1578
16th to endDay
13%13%6%10%7%36%45%6%23%
1580
March1st to 15thDay
17%12%5%8%6%34446%28%
1896
16th to endDay
16%10%5%8%7%34446%28%
2111
April1st to 15thDay
19%9%46%42445%7%30%
2145
16th to endDay
16%8%35%5%2335%7%37%
2253
May1st to 15thDay
18%7%27%5%35%447%33%
2136
16th to endDay
14%5%26%43445%8%40%
2228
June1st to 15thDay
11%5%25%5%35%5%6%9%38%
2461
16th to endDay
9%425%6%35%6%7%10%37%
2466
July1st to 15thDay
7%4245%35%5%7%9%42%
2310
16th to endDay
8%425%6%36%6%7%10%38%
2357
August1st to 15thDay
9%425%6%45%6%7%7%38%
2145
16th to endDay
11%5%25%5%35%5%6%8%40%
2275
September1st to 15thDay
12%6%25%6%35%5%6%9%37%
1848
16th to endDay
13%6%25%5%3447%8%38%
1815
October1st to 15thDay
13%7%26%5%35%45%7%38%
1716
16th to endDay
22%9%26%5%33435%31%
1680
November1st to 15thDay
14%7%27%6%345%5%7%35%
1582
16th to endDay
16%11%48%6%35%45%6%26%
1503
December1st to 15thDay
16%12%7%10%6%345%35%22%
1437
16th to endDay
21%16%6%9%6%24346%18%
1401
January1st to 15thNight
22%12%5%7%6%34345%24%
2506
16th to endNight
14%13%7%8%7%35%445%24%
2563
February1st to 15thNight
13%14%5%9%6%35%445%26%
2274
16th to endNight
15%11%5%8%6%44345%28%
1893
March1st to 15thNight
18%9%46%5%33346%32%
2063
16th to endNight
16%7%35%5%25%45%6%36%
2112
April1st to 15thNight
19%7%36%42445%7%34%
1812
16th to endNight
15%5%3442445%8%40%
1566
May1st to 15thNight
16%5%25%5%35%5%5%7%36%
1484
16th to endNight
12%5%24424447%47%
1530
June1st to 15thNight
8%5%35%4345%6%9%43%
1166
16th to endNight
9%5%1443447%9%45%
1160
July1st to 15thNight
7%413324448%53%
1320
16th to endNight
5%2244345%6%9%50%
1501
August1st to 15thNight
7%3144346%6%9%48%
1485
16th to endNight
10%423423446%53%
1575
September1st to 15thNight
12%424424447%49%
1768
16th to endNight
10%425%4245%47%47%
1815
October1st to 15thNight
15%5%2442445%7%42%
1914
16th to endNight
22%8%35%5%25%45%6%30%
2189
November1st to 15thNight
14%8%24425%5%6%6%39%
2276
16th to endNight
19%11%35%5%3435%7%28%
2454
December1st to 15thNight
20%13%5%8%5%34445%24%
2520
16th to endNight
22%14%6%9%6%34345%20%
2820

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
66%5%10%12%5%
1433
16th to endDay
70%5%8%11%4
1659
February1st to 15thDay
65%5%8%15%5%
1580
16th to endDay
60%5%9%16%7%1
1580
March1st to 15thDay
57%6%11%16%7%
1896
16th to endDay
56%410%19%8%1
2112
April1st to 15thDay
53%410%20%10%
2145
16th to endDay
47%413%17%14%2
2253
May1st to 15thDay
51%411%21%10%1
2136
16th to endDay
42%5%12%23%14%2
2232
June1st to 15thDay
41%6%13%23%14%1
2461
16th to endDay
39%6%14%21%14%1
2466
July1st to 15thDay
34%6%11%27%17%1
2161
16th to endDay
38%8%15%21%13%2
2199
August1st to 15thDay
39%8%13%23%13%2
2132
16th to endDay
39%6%11%26%13%1
2275
September1st to 15thDay
41%6%14%24%11%
1848
16th to endDay
40%5%13%28%11%
1815
October1st to 15thDay
44%412%22%14%1
1716
16th to endDay
55%315%18%6%
1680
November1st to 15thDay
47%6%10%23%10%1
1582
16th to endDay
57%5%12%17%6%1
1503
December1st to 15thDay
64%411%14%4
1437
16th to endDay
68%311%11%3
1401
January1st to 15thNight
62%5%9%15%7%
2506
16th to endNight
61%412%15%4
2563
February1st to 15thNight
59%5%9%16%7%
2283
16th to endNight
58%39%20%7%
1893
March1st to 15thNight
53%410%20%9%1
2063
16th to endNight
47%5%11%23%10%1
2112
April1st to 15thNight
49%411%20%13%
1812
16th to endNight
40%5%10%20%18%3
1566
May1st to 15thNight
46%5%11%21%12%2
1485
16th to endNight
37%412%24%16%4
1532
June1st to 15thNight
36%6%11%27%16%1
1166
16th to endNight
33%5%15%23%19%2
1160
July1st to 15thNight
29%5%9%31%21%2
1240
16th to endNight
28%8%17%24%18%3
1396
August1st to 15thNight
30%6%14%31%13%2
1474
16th to endNight
32%411%31%17%2
1575
September1st to 15thNight
36%411%28%16%1
1768
16th to endNight
35%5%12%31%14%
1815
October1st to 15thNight
39%5%12%23%18%
1914
16th to endNight
53%412%21%6%
2189
November1st to 15thNight
43%6%11%25%11%1
2276
16th to endNight
54%415%18%6%
2454
December1st to 15thNight
61%413%14%5%
2520
16th to endNight
66%411%12%5%
2820

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
23%16%35%21%21
90
16th to endDay
31%14%36%13%4
96
February1st to 15thDay
18%18%47%13%1
90
16th to endDay
18%18%43%13%6%
81
March1st to 15thDay
27%13%28%23%5%
186
16th to endDay
25%5%30%25%10%2
288
April1st to 15thDay
21%12%30%22%10%3
270
16th to endDay
22%6%28%17%15%9%
243
May1st to 15thDay
21%327%25%16%5%
228
16th to endDay
16%423%24%20%10%
267
June1st to 15thDay
14%6%30%28%15%4
406
16th to endDay
10%428%29%18%8%
420
July1st to 15thDay
9%321%33%20%11%
400
16th to endDay
7%421%32%21%11%
343
August1st to 15thDay
9%113%30%24%20%
253
16th to endDay
12%412%23%26%20%
268
September1st to 15thDay
14%316%19%25%20%
255
16th to endDay
17%314%23%29%11%
254
October1st to 15thDay
14%5%25%28%19%6%
255
16th to endDay
28%9%34%20%5%1
192
November1st to 15thDay
7%16%33%25%15%1
90
16th to endDay
26%18%35%14%5%
71
December1st to 15thDay
23%28%31%13%11
60
16th to endDay
28%17%43%9%
73
January1st to 15thNight
26%13%34%19%41
900
16th to endNight
21%10%35%27%4
835
February1st to 15thNight
20%14%39%21%3
704
16th to endNight
21%12%30%29%5%
631
March1st to 15thNight
22%10%34%26%5%
720
16th to endNight
20%8%30%30%9%1
768
April1st to 15thNight
23%10%31%28%5%
608
16th to endNight
18%5%30%32%10%1
522
May1st to 15thNight
17%5%27%36%12%1
495
16th to endNight
13%321%39%19%2
507
June1st to 15thNight
10%327%44%13%
330
16th to endNight
10%221%47%17%
335
July1st to 15thNight
9%16%41%27%4
465
16th to endNight
5%217%47%24%3
522
August1st to 15thNight
6%214%41%31%3
494
16th to endNight
10%216%35%30%5%
525
September1st to 15thNight
13%318%32%26%4
624
16th to endNight
12%317%36%24%5%
657
October1st to 15thNight
17%425%32%17%3
660
16th to endNight
25%12%31%25%5%
704
November1st to 15thNight
18%9%30%24%15%1
700
16th to endNight
23%12%30%24%8%
720
December1st to 15thNight
26%12%37%18%5%
720
16th to endNight
28%10%35%22%3
960
Page generated at 2017-04-25 07:48:25. Version ac04

Copyright 2017 A. Danko


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