Black Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Star Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
26%
14952
16%
47045
7%
14921
36%
14921
17%
31959

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%
720
14%
2506
6%
716
24%
716
9%
1772
January16th to endNight
12%
768
15%
2664
4%
768
27%
768
9%
1875
February1st to 15thNight
9%
704
12%
2224
2%
701
21%
701
8%
1647
February16th to endNight
14%
631
17%
1893
5%
631
30%
631
11%
1339
March1st to 15thNight
15%
720
14%
2160
5%
720
26%
720
12%
1573
March16th to endNight
21%
768
22%
1999
7%
768
32%
768
17%
1400
April1st to 15thNight
19%
718
14%
1796
3%
718
25%
718
17%
1333
April16th to endNight
23%
651
17%
1731
4%
651
32%
651
20%
1190
May1st to 15thNight
23%
492
17%
1572
7%
492
34%
492
17%
1064
May16th to endNight
33%
374
12%
1497
9%
374
42%
374
15%
981
June1st to 15thNight
34%
360
12%
1440
9%
360
45%
360
15%
948
June16th to endNight
45%
360
12%
1440
12%
360
53%
360
23%
857
July1st to 15thNight
46%
340
13%
1360
16%
340
53%
340
23%
789
July16th to endNight
54%
376
15%
1418
16%
354
60%
354
24%
808
August1st to 15thNight
49%
473
17%
1544
11%
471
55%
471
29%
916
August16th to endNight
51%
764
20%
1910
10%
764
54%
764
34%
1241
September1st to 15thNight
38%
720
21%
1809
8%
720
44%
720
31%
1184
September16th to endNight
47%
717
26%
1980
18%
717
53%
717
34%
1201
October1st to 15thNight
33%
684
20%
1973
12%
684
42%
684
22%
1315
October16th to endNight
20%
704
13%
2241
4%
704
31%
704
14%
1552
November1st to 15thNight
25%
700
20%
2277
9%
700
38%
700
17%
1494
November16th to endNight
22%
720
17%
2403
8%
720
34%
720
13%
1646
December1st to 15thNight
16%
720
12%
2520
3%
720
26%
720
9%
1817
December16th to endNight
13%
768
12%
2688
4%
768
24%
768
7%
2017

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%8%36%6%3445%6%32%
48156
Night
16%8%36%5%3445%6%34%
47215
Cloud CoverDay
16%8%36%6%35%45%6%32%
48166
Night
16%8%36%5%35%45%6%35%
47220
TransparencyDay
50%411%20%11%1
47844
Night
48%412%21%11%1
47045
SeeingDay
23%16%27%19%10%3
5830
Night
23%17%26%22%8%1
14953

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
14%10%5%7%7%46%6%5%5%25%
1432
16th to endDay
13%11%5%10%7%45%45%6%25%
1557
February1st to 15thDay
13%13%5%9%9%46%445%22%
1636
16th to endDay
16%10%6%10%6%34345%28%
1580
March1st to 15thDay
18%9%5%8%6%3445%6%27%
1790
16th to endDay
17%9%46%5%23435%35%
2221
April1st to 15thDay
18%11%37%5%2434432%
2152
16th to endDay
15%7%36%5%3445%6%36%
2229
May1st to 15thDay
24%8%35%5%3445%5%30%
2388
16th to endDay
19%6%26%4245%5%7%34%
2618
June1st to 15thDay
24%6%25%5%35%5%5%9%28%
2520
16th to endDay
18%6%36%5%35%5%6%8%28%
2520
July1st to 15thDay
13%6%35%6%46%5%6%9%32%
2520
16th to endDay
14%5%25%5%45%6%6%8%35%
2654
August1st to 15thDay
14%7%26%5%35%5%7%8%31%
2390
16th to endDay
13%5%25%6%35%46%8%37%
2292
September1st to 15thDay
16%6%26%5%3445%6%38%
2151
16th to endDay
15%42432345%6%47%
1980
October1st to 15thDay
20%8%37%5%2234436%
1784
16th to endDay
21%11%46%5%24445%28%
1631
November1st to 15thDay
15%9%36%6%13346%37%
1581
16th to endDay
18%7%5%6%5%2445%5%33%
1554
December1st to 15thDay
19%11%5%7%6%35%34427%
1440
16th to endDay
18%15%6%8%6%3444422%
1536
January1st to 15thNight
16%11%48%7%36%445%26%
2506
16th to endNight
13%11%5%9%6%46%5%5%426%
2664
February1st to 15thNight
13%9%6%8%8%47%6%5%6%22%
2223
16th to endNight
14%11%5%7%5%35%5%5%5%30%
1893
March1st to 15thNight
18%10%37%6%35%44429%
2147
16th to endNight
15%9%47%424445%36%
1999
April1st to 15thNight
18%10%46%6%24345%32%
1796
16th to endNight
18%8%25%4235%45%39%
1731
May1st to 15thNight
20%7%45%5%2345%6%34%
1572
16th to endNight
18%7%26%5%25%36%8%34%
1495
June1st to 15thNight
23%6%25%424248%34%
1440
16th to endNight
14%5%23425%6%5%8%42%
1440
July1st to 15thNight
13%425%5%3446%8%41%
1440
16th to endNight
12%4234247%5%8%43%
1514
August1st to 15thNight
12%425%4345%5%7%45%
1554
16th to endNight
12%425%5%2445%7%44%
1910
September1st to 15thNight
16%5%24433346%46%
1809
16th to endNight
14%423323446%50%
1980
October1st to 15thNight
19%6%25%5%2434440%
1973
16th to endNight
19%10%36%5%23446%31%
2241
November1st to 15thNight
15%9%26%424446%39%
2277
16th to endNight
15%9%37%6%35%35%5%32%
2403
December1st to 15thNight
20%11%48%7%24446%25%
2520
16th to endNight
20%13%48%7%35%5%4422%
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
13%10%47%6%47%6%5%7%26%
1432
16th to endDay
13%9%49%9%46%5%46%26%
1557
February1st to 15thDay
14%11%6%8%8%37%5%5%6%23%
1636
16th to endDay
15%11%6%8%6%44345%29%
1580
March1st to 15thDay
17%10%48%6%3435%6%28%
1800
16th to endDay
16%9%46%6%23445%36%
2221
April1st to 15thDay
17%10%47%6%34345%31%
2152
16th to endDay
15%7%25%5%35%45%6%36%
2229
May1st to 15thDay
24%7%26%5%34445%30%
2388
16th to endDay
18%5%36%5%345%5%7%34%
2618
June1st to 15thDay
22%5%35%5%35%45%8%28%
2520
16th to endDay
17%6%35%6%35%5%6%9%29%
2520
July1st to 15thDay
14%5%25%6%36%6%6%8%33%
2520
16th to endDay
13%5%35%6%36%5%6%8%35%
2654
August1st to 15thDay
15%6%25%5%25%6%6%8%33%
2390
16th to endDay
13%5%36%5%35%5%6%7%38%
2292
September1st to 15thDay
15%5%36%5%34446%39%
2151
16th to endDay
14%5%24423347%46%
1980
October1st to 15thDay
20%9%26%5%2334436%
1784
16th to endDay
20%11%36%5%3345%5%30%
1631
November1st to 15thDay
14%9%36%42345%6%37%
1581
16th to endDay
17%8%36%5%35%436%33%
1554
December1st to 15thDay
18%10%47%6%35%45%5%27%
1440
16th to endDay
17%14%6%8%8%3335%5%22%
1536
January1st to 15thNight
15%9%5%8%7%35%6%46%27%
2506
16th to endNight
13%10%48%6%46%6%5%5%27%
2664
February1st to 15thNight
13%8%48%8%47%6%5%6%24%
2216
16th to endNight
13%12%46%6%25%5%5%5%31%
1893
March1st to 15thNight
17%10%37%6%36%45%5%29%
2160
16th to endNight
15%9%46%5%24436%37%
1998
April1st to 15thNight
17%11%36%5%35%445%32%
1796
16th to endNight
18%8%35%423445%39%
1731
May1st to 15thNight
19%8%35%5%2345%5%35%
1572
16th to endNight
16%7%36%5%2445%7%34%
1495
June1st to 15thNight
21%6%25%5%24347%35%
1440
16th to endNight
14%424425%5%5%8%42%
1440
July1st to 15thNight
12%4345%26%448%42%
1440
16th to endNight
12%5%243245%6%8%43%
1514
August1st to 15thNight
12%415%43445%7%46%
1554
16th to endNight
12%425%42445%8%45%
1910
September1st to 15thNight
15%5%24423447%45%
1809
16th to endNight
13%5%23323346%51%
1980
October1st to 15thNight
19%6%25%42434440%
1973
16th to endNight
19%10%27%6%24445%33%
2241
November1st to 15thNight
15%9%25%5%24445%40%
2277
16th to endNight
15%8%46%7%45%35%6%32%
2403
December1st to 15thNight
20%10%47%6%245%5%5%26%
2520
16th to endNight
19%11%48%7%35%5%5%5%23%
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
54%410%19%8%1
1433
16th to endDay
55%413%17%8%
1557
February1st to 15thDay
59%410%14%8%
1639
16th to endDay
57%38%18%12%1
1580
March1st to 15thDay
55%211%18%9%1
1800
16th to endDay
50%29%17%15%3
2221
April1st to 15thDay
54%38%20%11%1
2152
16th to endDay
47%38%21%15%2
2229
May1st to 15thDay
55%36%21%10%1
2388
16th to endDay
47%5%13%20%11%1
2622
June1st to 15thDay
52%5%13%19%8%
2520
16th to endDay
50%5%13%18%11%
2520
July1st to 15thDay
46%5%11%23%11%
2371
16th to endDay
44%416%21%12%
2487
August1st to 15thDay
45%6%13%23%10%
2376
16th to endDay
41%5%10%27%14%
2292
September1st to 15thDay
46%410%22%15%1
2151
16th to endDay
37%47%27%21%1
1980
October1st to 15thDay
51%37%23%11%2
1784
16th to endDay
54%313%16%9%1
1631
November1st to 15thDay
45%415%20%13%1
1581
16th to endDay
50%311%20%12%1
1554
December1st to 15thDay
56%313%17%8%
1440
16th to endDay
62%311%14%7%
1536
January1st to 15thNight
55%311%16%10%2
2506
16th to endNight
54%310%19%10%1
2664
February1st to 15thNight
57%412%15%8%
2224
16th to endNight
52%311%20%10%1
1893
March1st to 15thNight
55%311%18%9%1
2160
16th to endNight
47%38%20%14%4
1999
April1st to 15thNight
53%310%19%11%1
1796
16th to endNight
45%49%21%16%2
1731
May1st to 15thNight
50%210%19%15%1
1572
16th to endNight
48%6%15%18%9%1
1497
June1st to 15thNight
49%413%21%9%
1440
16th to endNight
38%6%17%25%11%
1440
July1st to 15thNight
38%413%31%11%
1360
16th to endNight
36%6%17%26%12%1
1418
August1st to 15thNight
36%418%28%10%1
1544
16th to endNight
37%412%31%13%
1910
September1st to 15thNight
38%412%26%17%
1809
16th to endNight
34%49%28%22%1
1980
October1st to 15thNight
45%311%21%15%2
1973
16th to endNight
52%314%21%8%
2241
November1st to 15thNight
46%410%20%15%2
2277
16th to endNight
52%213%19%10%1
2403
December1st to 15thNight
56%413%17%7%
2520
16th to endNight
60%410%16%7%
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
28%33%25%6%5%1
60
16th to endDay
26%25%37%10%
67
February1st to 15thDay
28%30%30%7%1
152
16th to endDay
24%29%29%12%3
239
March1st to 15thDay
30%23%27%15%2
270
16th to endDay
27%26%23%12%7%2
288
April1st to 15thDay
30%19%26%14%8%1
270
16th to endDay
20%17%32%14%8%5%
270
May1st to 15thDay
36%16%22%12%7%4
288
16th to endDay
21%14%30%24%8%1
331
June1st to 15thDay
25%11%29%20%13%
315
16th to endDay
21%12%32%19%13%1
315
July1st to 15thDay
18%7%37%23%12%
305
16th to endDay
15%7%29%29%13%4
326
August1st to 15thDay
15%12%23%25%15%7%
313
16th to endDay
13%7%22%27%17%11%
332
September1st to 15thDay
17%12%22%21%16%8%
315
16th to endDay
17%8%21%18%18%15%
314
October1st to 15thDay
23%11%24%21%14%6%
278
16th to endDay
29%19%26%16%8%
249
November1st to 15thDay
23%18%25%23%8%
235
16th to endDay
24%25%20%18%8%2
174
December1st to 15thDay
26%38%21%11%1
60
16th to endDay
39%31%21%7%
64
January1st to 15thNight
25%26%29%15%2
720
16th to endNight
25%26%28%17%1
768
February1st to 15thNight
23%29%31%13%1
704
16th to endNight
27%28%25%15%2
631
March1st to 15thNight
29%24%26%16%2
720
16th to endNight
26%22%24%20%5%
768
April1st to 15thNight
28%18%29%19%4
718
16th to endNight
27%17%28%17%7%1
651
May1st to 15thNight
26%13%29%22%6%
492
16th to endNight
20%8%29%27%13%
375
June1st to 15thNight
24%9%24%28%13%
360
16th to endNight
16%5%26%39%11%
360
July1st to 15thNight
15%5%27%37%14%
340
16th to endNight
12%322%41%20%
376
August1st to 15thNight
14%324%38%16%1
473
16th to endNight
14%419%35%21%3
764
September1st to 15thNight
18%8%27%26%17%1
720
16th to endNight
16%9%21%26%19%6%
717
October1st to 15thNight
23%12%24%25%11%2
684
16th to endNight
27%20%26%20%4
704
November1st to 15thNight
23%21%25%21%7%1
700
16th to endNight
25%21%26%18%7%1
720
December1st to 15thNight
29%25%24%15%4
720
16th to endNight
31%27%25%13%2
768
Page generated at 2017-10-07 14:07:46. Version ac04

Copyright 2017 A. Danko


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