Sirius Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sirius Astronomical Observatory clear sky chart from 2005-11-05 to 2017-09-19.

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
27%
14955
19%
46852
8%
14923
39%
14923
21%
30430

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
16%
720
21%
2506
7%
716
34%
716
17%
1584
January16th to endNight
17%
768
21%
2673
6%
768
36%
768
15%
1684
February1st to 15thNight
13%
704
17%
2183
4%
701
29%
701
16%
1465
February16th to endNight
16%
631
24%
1893
7%
631
38%
631
19%
1235
March1st to 15thNight
15%
720
17%
2160
5%
720
30%
720
16%
1469
March16th to endNight
19%
768
24%
2010
7%
768
33%
768
22%
1334
April1st to 15thNight
19%
718
17%
1796
4%
718
26%
718
20%
1299
April16th to endNight
22%
639
18%
1719
4%
639
32%
639
21%
1171
May1st to 15thNight
22%
540
16%
1620
7%
540
31%
540
18%
1130
May16th to endNight
31%
380
12%
1502
8%
379
38%
379
17%
942
June1st to 15thNight
33%
360
13%
1440
9%
360
46%
360
16%
946
June16th to endNight
43%
360
14%
1440
14%
360
52%
360
25%
831
July1st to 15thNight
44%
340
12%
1360
15%
340
48%
340
23%
825
July16th to endNight
47%
376
15%
1418
16%
354
54%
354
22%
854
August1st to 15thNight
44%
502
17%
1573
11%
500
49%
500
29%
956
August16th to endNight
52%
764
21%
1910
11%
764
55%
764
35%
1223
September1st to 15thNight
40%
720
21%
1830
9%
720
46%
720
31%
1199
September16th to endNight
46%
673
26%
1858
18%
673
51%
673
32%
1162
October1st to 15thNight
35%
660
23%
1875
12%
660
46%
660
25%
1232
October16th to endNight
24%
704
16%
2252
5%
704
37%
704
21%
1469
November1st to 15thNight
28%
700
21%
2277
9%
700
45%
700
22%
1439
November16th to endNight
24%
720
20%
2349
8%
720
39%
720
19%
1533
December1st to 15thNight
22%
720
17%
2520
6%
720
36%
720
16%
1646
December16th to endNight
16%
768
19%
2688
5%
768
34%
768
14%
1802

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
17%6%25%42445%7%39%
47970
Night
17%6%25%42445%6%40%
47022
Cloud CoverDay
17%6%25%42445%7%39%
47980
Night
17%6%25%424446%40%
47027
TransparencyDay
44%411%22%15%2
47658
Night
43%411%22%15%2
46852
SeeingDay
22%13%30%21%9%3
5852
Night
22%13%31%24%7%
14955

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%5%334245%5%7%40%
1432
16th to endDay
16%6%144235%6%7%40%
1549
February1st to 15thDay
16%7%345%36%5%5%7%34%
1678
16th to endDay
17%7%25%435%446%39%
1580
March1st to 15thDay
20%6%26%434347%37%
1790
16th to endDay
18%6%245%23346%42%
2212
April1st to 15thDay
19%7%35%414346%38%
2152
16th to endDay
18%424424346%44%
2240
May1st to 15thDay
24%5%35%43435%6%33%
2335
16th to endDay
17%5%24424348%40%
2618
June1st to 15thDay
22%6%34434447%35%
2520
16th to endDay
12%6%36%5%345%6%9%36%
2520
July1st to 15thDay
12%6%25%6%36%6%5%8%37%
2520
16th to endDay
13%425%5%36%5%6%9%37%
2654
August1st to 15thDay
12%6%26%6%35%6%6%8%36%
2364
16th to endDay
11%425%5%25%5%6%6%43%
2292
September1st to 15thDay
13%5%245%24445%45%
2130
16th to endDay
14%424323446%49%
1848
October1st to 15thDay
18%6%24323246%42%
1753
16th to endDay
16%5%25%5%23446%42%
1618
November1st to 15thDay
19%6%25%414335%43%
1581
16th to endDay
18%425%424345%43%
1608
December1st to 15thDay
19%7%24413446%39%
1440
16th to endDay
23%8%25%31435%6%34%
1536
January1st to 15thNight
18%7%25%423346%40%
2506
16th to endNight
17%8%35%423345%41%
2673
February1st to 15thNight
15%8%35%5%35%346%37%
2182
16th to endNight
17%7%25%424445%41%
1893
March1st to 15thNight
19%7%25%42435%6%37%
2147
16th to endNight
18%6%34323346%44%
2010
April1st to 15thNight
18%7%35%5%3444437%
1796
16th to endNight
21%5%26%424345%40%
1719
May1st to 15thNight
21%6%26%5%2345%6%35%
1620
16th to endNight
19%425%33446%8%37%
1500
June1st to 15thNight
22%6%144235%47%37%
1440
16th to endNight
12%425%42446%7%44%
1440
July1st to 15thNight
12%426%435%5%6%10%38%
1440
16th to endNight
10%435%5%35%7%6%9%37%
1514
August1st to 15thNight
11%4245%2447%7%44%
1583
16th to endNight
12%324435%45%8%45%
1910
September1st to 15thNight
14%5%34425%45%6%44%
1830
16th to endNight
14%5%2432334449%
1858
October1st to 15thNight
17%6%25%33335%6%44%
1875
16th to endNight
19%6%25%423445%40%
2252
November1st to 15thNight
18%6%24322345%44%
2277
16th to endNight
20%6%25%424445%39%
2349
December1st to 15thNight
21%6%35%424336%38%
2520
16th to endNight
22%8%24433445%36%
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
16%6%244246%6%6%40%
1432
16th to endDay
16%6%25%3335%5%7%41%
1549
February1st to 15thDay
16%7%25%6%26%45%7%34%
1678
16th to endDay
17%7%245%34445%39%
1580
March1st to 15thDay
20%6%26%434347%36%
1800
16th to endDay
18%6%34423345%43%
2212
April1st to 15thDay
20%7%35%423346%39%
2152
16th to endDay
18%424435%336%44%
2240
May1st to 15thDay
25%6%25%42435%6%33%
2335
16th to endDay
17%5%2442445%8%39%
2618
June1st to 15thDay
22%6%3443435%7%34%
2520
16th to endDay
13%5%35%5%35%46%9%36%
2520
July1st to 15thDay
12%6%25%5%45%5%6%7%37%
2520
16th to endDay
13%425%5%45%5%6%9%36%
2654
August1st to 15thDay
12%6%26%5%35%5%6%7%36%
2364
16th to endDay
11%5%25%5%345%5%7%43%
2292
September1st to 15thDay
14%5%245%3445%6%44%
2130
16th to endDay
15%424324346%48%
1848
October1st to 15thDay
18%6%25%313445%42%
1753
16th to endDay
17%5%15%5%235%46%42%
1618
November1st to 15thDay
19%6%24423335%43%
1581
16th to endDay
17%5%245%24345%43%
1608
December1st to 15thDay
19%7%24424337%40%
1440
16th to endDay
23%8%25%324347%34%
1536
January1st to 15thNight
18%7%25%333446%40%
2506
16th to endNight
17%8%35%323446%40%
2673
February1st to 15thNight
15%8%35%5%2445%5%38%
2175
16th to endNight
17%7%24424345%41%
1893
March1st to 15thNight
19%7%35%5%2435%6%37%
2160
16th to endNight
18%6%33423345%43%
2009
April1st to 15thNight
18%6%35%5%3444437%
1796
16th to endNight
21%5%25%423345%40%
1719
May1st to 15thNight
21%6%26%5%33446%35%
1620
16th to endNight
18%5%244235%5%9%37%
1500
June1st to 15thNight
22%5%25%424446%36%
1440
16th to endNight
12%335%5%2446%7%44%
1440
July1st to 15thNight
12%5%25%4345%6%10%38%
1440
16th to endNight
11%5%26%5%35%6%6%9%37%
1514
August1st to 15thNight
10%5%2444446%8%43%
1583
16th to endNight
12%424425%45%7%46%
1910
September1st to 15thNight
14%5%2443346%7%43%
1830
16th to endNight
14%425%313435%49%
1858
October1st to 15thNight
17%6%15%33335%5%44%
1875
16th to endNight
18%6%25%423445%40%
2252
November1st to 15thNight
18%6%24313446%44%
2277
16th to endNight
20%6%24434445%39%
2349
December1st to 15thNight
21%6%25%424346%38%
2520
16th to endNight
22%7%245%23445%36%
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
42%5%13%24%10%2
1433
16th to endDay
41%411%26%14%1
1549
February1st to 15thDay
48%412%21%12%1
1681
16th to endDay
46%39%24%13%2
1580
March1st to 15thDay
48%212%23%9%2
1800
16th to endDay
44%38%21%17%4
2212
April1st to 15thDay
46%39%20%16%2
2152
16th to endDay
42%38%22%18%3
2240
May1st to 15thDay
51%48%20%13%2
2335
16th to endDay
43%5%13%21%13%2
2622
June1st to 15thDay
49%412%21%10%1
2520
16th to endDay
43%6%12%22%13%
2520
July1st to 15thDay
44%6%10%21%15%1
2371
16th to endDay
41%5%14%22%13%2
2487
August1st to 15thDay
43%5%12%21%15%
2350
16th to endDay
38%5%9%27%18%1
2292
September1st to 15thDay
39%411%21%20%2
2130
16th to endDay
36%37%24%25%2
1848
October1st to 15thDay
42%410%24%15%2
1753
16th to endDay
41%311%25%14%2
1618
November1st to 15thDay
44%313%18%17%2
1581
16th to endDay
43%210%26%14%2
1608
December1st to 15thDay
45%316%19%13%1
1440
16th to endDay
49%5%14%18%11%
1536
January1st to 15thNight
44%312%23%12%2
2506
16th to endNight
44%310%22%16%2
2673
February1st to 15thNight
47%412%21%12%2
2183
16th to endNight
44%39%23%16%2
1893
March1st to 15thNight
47%411%20%13%2
2160
16th to endNight
42%38%22%18%5%
2010
April1st to 15thNight
49%49%20%15%2
1796
16th to endNight
45%38%21%16%4
1719
May1st to 15thNight
49%49%18%14%3
1620
16th to endNight
43%7%18%17%11%1
1502
June1st to 15thNight
47%5%13%19%12%1
1440
16th to endNight
37%5%14%27%14%
1440
July1st to 15thNight
40%6%14%23%14%
1360
16th to endNight
39%6%16%23%11%2
1418
August1st to 15thNight
36%5%14%25%15%2
1573
16th to endNight
36%411%29%16%
1910
September1st to 15thNight
38%411%25%18%1
1830
16th to endNight
37%46%23%26%1
1858
October1st to 15thNight
42%410%22%17%3
1875
16th to endNight
45%313%22%13%
2252
November1st to 15thNight
41%411%20%18%2
2277
16th to endNight
46%311%23%12%2
2349
December1st to 15thNight
47%314%20%12%
2520
16th to endNight
50%312%21%12%1
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
20%33%30%15%1
60
16th to endDay
28%19%43%8%
67
February1st to 15thDay
24%24%32%17%1
194
16th to endDay
20%24%34%15%4
239
March1st to 15thDay
30%18%30%17%3
270
16th to endDay
23%23%30%14%5%1
288
April1st to 15thDay
27%17%31%17%6%
270
16th to endDay
23%14%32%18%7%2
270
May1st to 15thDay
38%11%26%13%9%1
288
16th to endDay
22%12%32%22%9%1
331
June1st to 15thDay
24%13%25%22%10%2
315
16th to endDay
16%14%33%24%8%1
315
July1st to 15thDay
20%7%29%29%12%1
305
16th to endDay
15%5%29%31%14%4
326
August1st to 15thDay
14%6%30%30%10%7%
313
16th to endDay
13%5%27%27%18%8%
332
September1st to 15thDay
15%11%28%23%14%6%
315
16th to endDay
17%6%27%20%11%16%
266
October1st to 15thDay
23%6%25%25%12%5%
255
16th to endDay
20%16%31%21%8%1
246
November1st to 15thDay
25%12%27%22%10%2
235
16th to endDay
23%15%30%19%9%2
228
December1st to 15thDay
18%25%41%10%5%
60
16th to endDay
39%25%21%12%1
64
January1st to 15thNight
23%19%36%16%3
720
16th to endNight
24%19%32%20%2
768
February1st to 15thNight
20%19%39%19%1
704
16th to endNight
24%19%35%18%2
631
March1st to 15thNight
25%20%34%16%2
720
16th to endNight
23%18%35%19%3
768
April1st to 15thNight
22%18%35%20%2
718
16th to endNight
24%16%33%20%4
639
May1st to 15thNight
26%15%31%20%4
540
16th to endNight
21%7%34%28%7%
380
June1st to 15thNight
25%6%28%30%8%
360
16th to endNight
15%432%38%8%
360
July1st to 15thNight
14%330%37%14%
340
16th to endNight
11%427%40%14%1
376
August1st to 15thNight
13%429%38%14%
502
16th to endNight
15%321%39%18%2
764
September1st to 15thNight
17%6%29%32%13%
720
16th to endNight
17%6%24%28%20%3
673
October1st to 15thNight
22%9%29%26%11%1
660
16th to endNight
24%13%32%22%5%
704
November1st to 15thNight
23%12%30%23%8%1
700
16th to endNight
25%14%30%20%8%
720
December1st to 15thNight
26%14%32%21%4
720
16th to endNight
28%17%34%17%1
768
Page generated at 2017-09-20 04:49:58. Version ac04

Copyright 2017 A. Danko


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