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 2017-03-22.

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%
14366
16%
45258
7%
14335
37%
14335
16%
30849

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%
732
22%
1913
7%
732
33%
732
17%
1329
April1st to 15thNight
16%
658
15%
1646
3%
658
24%
658
16%
1231
April16th to endNight
24%
591
16%
1581
4%
591
33%
591
21%
1085
May1st to 15thNight
26%
459
17%
1449
9%
459
36%
459
17%
974
May16th to endNight
35%
342
12%
1369
9%
342
44%
342
15%
909
June1st to 15thNight
32%
330
12%
1320
10%
330
43%
330
14%
888
June16th to endNight
46%
330
11%
1320
11%
330
54%
330
22%
781
July1st to 15thNight
47%
310
14%
1240
16%
310
53%
310
23%
730
July16th to endNight
52%
348
13%
1306
14%
326
58%
326
24%
750
August1st to 15thNight
48%
434
17%
1415
10%
432
55%
432
28%
853
August16th to endNight
50%
700
17%
1750
8%
700
54%
700
32%
1164
September1st to 15thNight
42%
660
20%
1664
9%
660
47%
660
30%
1099
September16th to endNight
47%
657
24%
1815
16%
657
53%
657
32%
1127
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%
45630
Night
15%8%36%5%35%5%5%6%35%
45428
Cloud CoverDay
16%7%36%6%35%5%5%7%33%
45640
Night
15%7%35%5%3445%6%37%
45433
TransparencyDay
48%7%11%19%11%1
45318
Night
45%7%12%20%12%1
45258
SeeingDay
20%18%26%19%11%4
5060
Night
20%20%27%22%8%
14367

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
14%7%46%5%34446%36%
2107
April1st to 15thDay
17%9%47%6%3443432%
1972
16th to endDay
14%8%35%6%3445%5%37%
2048
May1st to 15thDay
23%7%36%444445%30%
2180
16th to endDay
17%6%25%5%345%6%8%34%
2394
June1st to 15thDay
23%6%35%5%45%45%8%26%
2310
16th to endDay
17%7%25%6%46%5%6%8%29%
2310
July1st to 15thDay
13%6%26%6%46%6%6%8%32%
2310
16th to endDay
13%5%25%5%46%6%6%9%33%
2458
August1st to 15thDay
14%6%26%6%35%6%6%9%32%
2191
16th to endDay
12%6%36%6%35%5%6%7%36%
2100
September1st to 15thDay
13%7%26%6%44446%38%
1966
16th to endDay
14%5%24424447%46%
1815
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%42445%5%38%
1913
April1st to 15thNight
16%10%37%6%245%5%5%32%
1646
16th to endNight
18%7%36%424445%39%
1581
May1st to 15thNight
17%8%46%42346%5%36%
1449
16th to endNight
15%8%35%5%2446%7%34%
1367
June1st to 15thNight
21%6%36%5%23447%33%
1320
16th to endNight
15%4243245%5%8%43%
1320
July1st to 15thNight
11%5%25%5%245%6%8%41%
1320
16th to endNight
10%6%25%5%246%5%8%43%
1402
August1st to 15thNight
11%4245%25%45%7%45%
1425
16th to endNight
13%5%15%5%2445%7%44%
1750
September1st to 15thNight
13%6%25%42445%6%44%
1664
16th to endNight
13%5%24313446%49%
1815
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
15%7%46%5%33446%38%
2107
April1st to 15thDay
17%8%47%6%3444434%
1972
16th to endDay
14%7%36%5%3445%6%38%
2048
May1st to 15thDay
24%6%35%5%4445%5%30%
2180
16th to endDay
18%5%25%6%25%5%6%8%34%
2394
June1st to 15thDay
23%7%245%45%45%9%27%
2310
16th to endDay
16%6%26%6%36%5%6%9%29%
2310
July1st to 15thDay
12%6%26%6%46%5%7%8%32%
2310
16th to endDay
13%5%25%6%35%6%7%9%34%
2458
August1st to 15thDay
14%5%26%6%46%5%6%9%33%
2191
16th to endDay
13%5%25%5%45%5%6%7%36%
2100
September1st to 15thDay
14%5%37%6%35%346%39%
1966
16th to endDay
14%5%1442345%6%46%
1815
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
13%7%26%5%3445%5%40%
1912
April1st to 15thNight
16%9%36%6%345%5%5%33%
1646
16th to endNight
17%8%344235%45%40%
1581
May1st to 15thNight
18%8%36%42345%6%36%
1449
16th to endNight
16%6%45%4245%6%6%35%
1367
June1st to 15thNight
21%6%36%5%13446%35%
1320
16th to endNight
15%43332445%7%44%
1320
July1st to 15thNight
11%426%5%245%5%8%43%
1320
16th to endNight
10%5%245%245%6%8%43%
1402
August1st to 15thNight
10%5%244345%47%47%
1425
16th to endNight
13%5%23425%45%7%45%
1750
September1st to 15thNight
13%5%15%5%2435%6%45%
1664
16th to endNight
14%423324345%50%
1815
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
46%5%10%18%15%3
2107
April1st to 15thDay
53%47%19%12%1
1972
16th to endDay
44%6%7%23%14%3
2048
May1st to 15thDay
53%5%7%20%11%1
2180
16th to endDay
45%8%14%18%11%1
2398
June1st to 15thDay
53%7%13%18%6%
2310
16th to endDay
47%8%14%17%11%
2310
July1st to 15thDay
46%6%11%23%10%1
2161
16th to endDay
42%7%17%19%12%
2291
August1st to 15thDay
45%8%12%22%10%
2177
16th to endDay
42%7%10%25%12%
2100
September1st to 15thDay
45%5%10%22%15%
1966
16th to endDay
37%5%8%24%21%1
1815
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%
1913
April1st to 15thNight
51%5%10%18%13%1
1646
16th to endNight
44%5%10%19%16%3
1581
May1st to 15thNight
47%410%18%16%2
1449
16th to endNight
45%9%15%17%10%1
1369
June1st to 15thNight
49%6%14%20%8%
1320
16th to endNight
37%7%17%24%12%
1320
July1st to 15thNight
36%7%13%30%10%
1240
16th to endNight
35%7%18%25%11%1
1306
August1st to 15thNight
34%7%17%26%12%1
1415
16th to endNight
37%6%12%29%12%
1750
September1st to 15thNight
39%5%14%24%16%
1664
16th to endNight
34%5%8%26%23%1
1815
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
22%28%24%12%9%2
250
April1st to 15thDay
26%23%25%13%9%
210
16th to endDay
17%19%29%19%9%6%
210
May1st to 15thDay
32%17%19%17%6%6%
228
16th to endDay
17%14%32%21%12%1
267
June1st to 15thDay
23%15%25%21%13%
255
16th to endDay
16%10%30%25%14%2
255
July1st to 15thDay
16%9%33%24%13%2
245
16th to endDay
11%10%31%29%14%3
270
August1st to 15thDay
15%9%24%27%14%8%
253
16th to endDay
15%6%18%25%20%13%
268
September1st to 15thDay
12%12%21%23%18%10%
255
16th to endDay
16%10%22%17%19%13%
254
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%6%
732
April1st to 15thNight
22%23%32%17%3
658
16th to endNight
23%19%29%18%8%
591
May1st to 15thNight
22%17%29%22%8%
459
16th to endNight
18%9%30%26%13%
343
June1st to 15thNight
23%11%24%28%10%
330
16th to endNight
16%6%25%38%12%
330
July1st to 15thNight
12%6%28%37%16%
310
16th to endNight
10%6%23%39%19%
348
August1st to 15thNight
13%5%27%36%16%1
434
16th to endNight
15%5%21%32%21%3
700
September1st to 15thNight
15%9%26%29%16%1
660
16th to endNight
16%9%22%26%19%5%
657
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 2017-03-23 07:36:18. Version ac04

Copyright 2017 A. Danko


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