Blackstar II Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blackstar II Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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%
14904
16%
46902
7%
14873
37%
14873
17%
31939

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
14%
720
15%
2506
5%
716
27%
716
10%
1760
January16th to endNight
13%
768
15%
2670
4%
768
29%
768
10%
1879
February1st to 15thNight
9%
704
13%
2216
2%
701
22%
701
9%
1630
February16th to endNight
15%
631
19%
1893
5%
631
31%
631
11%
1333
March1st to 15thNight
17%
720
14%
2160
5%
720
28%
720
12%
1553
March16th to endNight
21%
768
22%
2003
7%
768
33%
768
17%
1400
April1st to 15thNight
18%
718
14%
1796
3%
718
25%
718
17%
1340
April16th to endNight
23%
645
17%
1725
4%
645
32%
645
20%
1195
May1st to 15thNight
25%
501
16%
1581
8%
501
34%
501
16%
1082
May16th to endNight
34%
374
12%
1497
9%
374
42%
374
15%
1000
June1st to 15thNight
33%
360
12%
1440
10%
360
43%
360
15%
948
June16th to endNight
45%
360
11%
1440
10%
360
53%
360
21%
866
July1st to 15thNight
47%
340
13%
1360
16%
340
53%
340
23%
800
July16th to endNight
53%
376
15%
1418
16%
354
59%
354
24%
814
August1st to 15thNight
49%
474
16%
1545
10%
472
55%
472
29%
922
August16th to endNight
52%
764
19%
1910
10%
764
55%
764
33%
1258
September1st to 15thNight
41%
720
20%
1815
9%
720
47%
720
30%
1195
September16th to endNight
48%
689
24%
1902
17%
689
53%
689
32%
1190
October1st to 15thNight
32%
660
21%
1900
11%
660
42%
660
20%
1288
October16th to endNight
22%
704
13%
2246
4%
704
32%
704
15%
1563
November1st to 15thNight
26%
700
20%
2277
10%
700
40%
700
18%
1487
November16th to endNight
23%
720
17%
2394
8%
720
35%
720
14%
1649
December1st to 15thNight
17%
720
12%
2520
4%
720
28%
720
9%
1794
December16th to endNight
13%
768
14%
2688
4%
768
25%
768
8%
1993

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
16%8%36%6%35%5%5%7%32%
48008
Night
15%7%36%5%35%5%5%6%35%
47072
Cloud CoverDay
16%7%36%6%35%5%5%7%33%
48018
Night
15%7%35%5%3445%6%37%
47077
TransparencyDay
48%7%11%19%11%1
47696
Night
45%7%12%20%12%1
46902
SeeingDay
21%18%26%19%10%3
5791
Night
21%20%27%22%8%
14905

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
12%9%36%7%5%7%6%5%7%27%
1432
16th to endDay
13%9%48%8%46%6%5%6%27%
1551
February1st to 15thDay
13%9%5%9%8%46%5%6%6%24%
1644
16th to endDay
15%9%49%8%25%445%30%
1580
March1st to 15thDay
16%9%48%6%35%46%6%29%
1790
16th to endDay
16%8%46%5%34446%35%
2220
April1st to 15thDay
17%9%47%6%34435%32%
2152
16th to endDay
14%7%36%6%345%5%5%36%
2234
May1st to 15thDay
24%7%36%444445%29%
2379
16th to endDay
18%6%25%5%345%6%7%33%
2618
June1st to 15thDay
22%6%35%5%35%45%8%28%
2520
16th to endDay
17%7%26%6%36%5%6%8%29%
2520
July1st to 15thDay
13%6%26%5%46%6%6%8%32%
2520
16th to endDay
13%5%25%5%45%6%6%8%34%
2654
August1st to 15thDay
14%6%26%6%35%6%6%8%32%
2390
16th to endDay
12%5%26%5%35%5%6%8%37%
2292
September1st to 15thDay
13%7%26%6%44446%39%
2145
16th to endDay
14%5%24424447%45%
1895
October1st to 15thDay
19%10%36%42434434%
1727
16th to endDay
18%11%45%6%2445%5%30%
1625
November1st to 15thDay
14%9%36%42345%6%38%
1581
16th to endDay
17%7%35%6%25%45%6%34%
1563
December1st to 15thDay
17%11%38%6%45%347%28%
1440
16th to endDay
17%11%6%9%7%3445%5%23%
1536
January1st to 15thNight
15%8%46%7%45%6%6%7%28%
2506
16th to endNight
11%10%47%7%36%5%6%7%28%
2670
February1st to 15thNight
13%7%47%7%47%6%6%7%25%
2215
16th to endNight
14%9%37%5%25%5%6%6%32%
1893
March1st to 15thNight
16%9%36%5%37%5%5%5%30%
2147
16th to endNight
14%7%37%5%2445%5%38%
2003
April1st to 15thNight
16%10%37%6%345%5%5%32%
1796
16th to endNight
19%7%36%424445%39%
1725
May1st to 15thNight
19%8%46%42346%5%34%
1581
16th to endNight
15%8%35%5%3446%7%33%
1495
June1st to 15thNight
21%6%26%5%13447%35%
1440
16th to endNight
15%4243245%5%8%42%
1440
July1st to 15thNight
12%5%25%5%2446%8%42%
1440
16th to endNight
10%6%25%5%245%5%8%44%
1514
August1st to 15thNight
11%4245%2445%7%46%
1555
16th to endNight
12%5%15%5%24447%45%
1910
September1st to 15thNight
13%6%25%424446%44%
1815
16th to endNight
13%5%24314446%49%
1902
October1st to 15thNight
18%7%35%42434440%
1900
16th to endNight
18%8%36%6%3345%6%33%
2246
November1st to 15thNight
14%8%35%5%2445%6%40%
2277
16th to endNight
15%8%46%6%35%5%5%6%33%
2394
December1st to 15thNight
19%9%36%6%35%5%5%7%27%
2520
16th to endNight
18%10%37%6%36%7%6%6%24%
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
12%8%46%6%47%7%5%6%30%
1432
16th to endDay
13%7%37%7%46%5%5%7%30%
1551
February1st to 15thDay
13%8%48%8%46%5%6%6%26%
1644
16th to endDay
15%9%38%7%44445%32%
1580
March1st to 15thDay
17%10%46%5%345%5%6%30%
1800
16th to endDay
16%7%46%5%33445%37%
2220
April1st to 15thDay
17%8%47%5%34445%33%
2152
16th to endDay
14%7%36%5%345%5%6%37%
2234
May1st to 15thDay
25%7%35%5%4445%5%29%
2379
16th to endDay
19%5%25%6%25%5%5%8%33%
2618
June1st to 15thDay
22%7%245%45%45%9%28%
2520
16th to endDay
17%6%26%6%36%5%6%9%29%
2520
July1st to 15thDay
13%6%26%6%45%5%6%8%33%
2520
16th to endDay
13%5%25%6%446%6%8%34%
2654
August1st to 15thDay
14%5%26%6%46%5%6%9%32%
2390
16th to endDay
12%5%25%5%45%5%6%8%38%
2292
September1st to 15thDay
14%5%26%6%35%446%39%
2145
16th to endDay
14%5%15%5%2345%6%45%
1895
October1st to 15thDay
19%9%26%5%24345%35%
1727
16th to endDay
18%9%36%5%2445%5%32%
1625
November1st to 15thDay
14%7%25%5%235%5%6%39%
1581
16th to endDay
18%6%36%414446%37%
1563
December1st to 15thDay
16%9%37%6%36%346%31%
1440
16th to endDay
16%11%5%7%7%345%5%6%26%
1536
January1st to 15thNight
15%8%35%6%25%6%6%7%31%
2506
16th to endNight
12%8%36%5%46%5%5%7%32%
2670
February1st to 15thNight
12%8%37%6%46%6%6%7%29%
2208
16th to endNight
14%9%35%5%45%45%6%34%
1893
March1st to 15thNight
17%8%26%5%35%5%5%7%32%
2160
16th to endNight
14%7%26%5%34445%40%
2002
April1st to 15thNight
16%9%36%6%345%45%34%
1796
16th to endNight
18%8%34423445%40%
1725
May1st to 15thNight
20%8%36%42346%6%34%
1581
16th to endNight
16%6%45%4245%6%6%34%
1495
June1st to 15thNight
21%6%36%413346%37%
1440
16th to endNight
15%42333445%7%43%
1440
July1st to 15thNight
12%425%5%245%5%8%43%
1440
16th to endNight
11%5%245%245%6%8%43%
1514
August1st to 15thNight
10%5%244335%5%7%47%
1555
16th to endNight
12%5%2342445%6%46%
1910
September1st to 15thNight
13%5%15%42435%7%45%
1815
16th to endNight
13%423323445%50%
1902
October1st to 15thNight
19%7%25%433245%41%
1900
16th to endNight
18%7%26%5%3445%7%34%
2246
November1st to 15thNight
14%8%35%424345%42%
2277
16th to endNight
15%7%36%5%46%45%6%35%
2394
December1st to 15thNight
19%8%35%5%35%5%6%7%30%
2520
16th to endNight
17%9%35%6%25%6%6%7%27%
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
50%8%10%21%7%1
1433
16th to endDay
50%9%12%17%8%1
1551
February1st to 15thDay
55%8%11%14%9%
1647
16th to endDay
53%6%8%17%12%1
1580
March1st to 15thDay
52%6%11%18%10%1
1800
16th to endDay
48%5%10%17%14%3
2220
April1st to 15thDay
53%47%20%11%1
2152
16th to endDay
44%7%7%22%14%3
2234
May1st to 15thDay
55%5%6%19%10%1
2379
16th to endDay
46%8%13%18%11%1
2622
June1st to 15thDay
51%7%13%19%8%
2520
16th to endDay
48%8%14%17%11%
2520
July1st to 15thDay
46%7%11%22%11%
2371
16th to endDay
43%7%16%19%12%
2487
August1st to 15thDay
45%7%13%22%10%
2376
16th to endDay
40%7%10%26%13%
2292
September1st to 15thDay
44%6%10%22%15%1
2145
16th to endDay
38%5%9%25%20%1
1895
October1st to 15thDay
51%5%7%21%11%2
1727
16th to endDay
51%7%12%16%10%1
1625
November1st to 15thDay
43%7%14%20%11%1
1581
16th to endDay
46%6%11%20%12%1
1563
December1st to 15thDay
52%6%14%16%9%
1440
16th to endDay
57%8%11%14%8%
1536
January1st to 15thNight
49%8%11%17%11%2
2506
16th to endNight
49%8%10%18%11%1
2670
February1st to 15thNight
51%9%12%16%9%1
2216
16th to endNight
48%6%10%21%11%2
1893
March1st to 15thNight
49%7%12%18%9%1
2160
16th to endNight
44%6%8%19%15%5%
2003
April1st to 15thNight
51%5%10%18%13%1
1796
16th to endNight
45%5%9%19%16%2
1725
May1st to 15thNight
49%410%18%15%1
1581
16th to endNight
45%9%15%17%10%1
1497
June1st to 15thNight
47%6%14%21%9%
1440
16th to endNight
38%7%17%23%12%
1440
July1st to 15thNight
36%7%13%30%11%
1360
16th to endNight
35%7%17%25%12%1
1418
August1st to 15thNight
34%7%19%26%12%1
1545
16th to endNight
36%6%12%30%13%
1910
September1st to 15thNight
38%5%13%24%17%1
1815
16th to endNight
35%5%8%26%22%1
1902
October1st to 15thNight
46%410%20%14%3
1900
16th to endNight
49%6%14%20%9%
2246
November1st to 15thNight
43%5%11%19%15%2
2277
16th to endNight
48%7%12%18%11%1
2394
December1st to 15thNight
50%9%14%17%8%
2520
16th to endNight
52%11%10%16%8%
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
23%38%25%6%5%1
60
16th to endDay
26%32%28%11%
67
February1st to 15thDay
21%36%30%8%2
160
16th to endDay
20%30%28%17%2
239
March1st to 15thDay
30%25%27%13%3
270
16th to endDay
26%28%22%11%8%2
288
April1st to 15thDay
26%24%27%12%9%
270
16th to endDay
19%18%30%18%7%4
270
May1st to 15thDay
34%19%20%14%5%5%
288
16th to endDay
20%16%31%19%10%1
331
June1st to 15thDay
22%15%28%21%11%
315
16th to endDay
19%15%31%20%11%1
315
July1st to 15thDay
17%8%36%23%11%1
305
16th to endDay
13%8%31%29%13%3
326
August1st to 15thDay
16%11%23%25%15%7%
313
16th to endDay
14%7%21%26%17%11%
332
September1st to 15thDay
14%13%24%21%15%9%
315
16th to endDay
15%9%23%17%19%13%
283
October1st to 15thDay
24%12%22%20%14%4
255
16th to endDay
23%21%25%20%7%
247
November1st to 15thDay
21%20%26%21%8%1
235
16th to endDay
24%27%20%16%8%2
183
December1st to 15thDay
25%38%25%6%5%
60
16th to endDay
26%40%25%7%
64
January1st to 15thNight
22%26%31%15%3
720
16th to endNight
21%29%29%17%1
768
February1st to 15thNight
20%30%34%14%1
704
16th to endNight
23%31%26%15%2
631
March1st to 15thNight
25%26%27%18%2
720
16th to endNight
20%28%25%18%5%
768
April1st to 15thNight
23%22%31%18%3
718
16th to endNight
24%19%29%18%7%
645
May1st to 15thNight
24%17%28%21%7%
501
16th to endNight
20%9%30%26%12%
375
June1st to 15thNight
24%10%24%29%11%
360
16th to endNight
16%6%26%38%11%
360
July1st to 15thNight
13%5%26%38%15%
340
16th to endNight
10%5%22%39%20%
376
August1st to 15thNight
13%5%27%35%17%1
474
16th to endNight
15%5%20%33%21%3
764
September1st to 15thNight
15%9%26%29%16%1
720
16th to endNight
16%8%22%26%19%5%
689
October1st to 15thNight
25%13%23%25%10%1
660
16th to endNight
24%22%26%21%4
704
November1st to 15thNight
20%21%25%22%8%1
700
16th to endNight
21%23%27%18%7%1
720
December1st to 15thNight
24%27%27%15%4
720
16th to endNight
25%33%25%13%2
768
Page generated at 2017-09-24 09:15:44. Version ac04

Copyright 2017 A. Danko


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