Dark Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dark Star Observatory clear sky chart from 2005-11-05 to 2019-07-16.

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
39%
18313
22%
54393
12%
18276
50%
18276
24%
34473

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
22%
837
24%
2717
9%
836
40%
836
19%
1676
January16th to endNight
25%
896
25%
2912
12%
896
42%
896
22%
1759
February1st to 15thNight
24%
821
21%
2677
9%
821
40%
821
20%
1652
February16th to endNight
20%
735
25%
2173
8%
735
38%
735
23%
1366
March1st to 15thNight
25%
840
25%
2310
11%
840
38%
840
24%
1480
March16th to endNight
28%
896
20%
2464
9%
896
38%
896
23%
1632
April1st to 15thNight
28%
838
21%
2174
7%
838
39%
838
26%
1413
April16th to endNight
34%
791
21%
2037
7%
791
43%
791
26%
1351
May1st to 15thNight
38%
630
17%
1890
8%
630
45%
630
22%
1235
May16th to endNight
50%
657
15%
1972
9%
657
55%
657
23%
1258
June1st to 15thNight
56%
630
17%
1890
14%
630
60%
630
27%
1185
June16th to endNight
60%
630
17%
1890
12%
630
65%
630
28%
1169
July1st to 15thNight
64%
600
14%
1800
12%
600
66%
600
26%
1157
July16th to endNight
60%
615
15%
1748
11%
582
66%
582
26%
1137
August1st to 15thNight
59%
575
18%
1715
14%
572
62%
572
23%
1168
August16th to endNight
64%
757
17%
1999
12%
757
66%
757
29%
1332
September1st to 15thNight
59%
780
22%
2015
17%
780
61%
780
30%
1368
September16th to endNight
46%
777
19%
2148
14%
777
51%
777
21%
1523
October1st to 15thNight
48%
780
26%
2340
23%
780
57%
780
27%
1455
October16th to endNight
43%
832
32%
2496
19%
832
60%
832
34%
1398
November1st to 15thNight
38%
820
27%
2461
17%
820
50%
820
27%
1482
November16th to endNight
37%
840
26%
2752
15%
840
52%
840
27%
1552
December1st to 15thNight
27%
840
21%
2901
10%
840
42%
840
17%
1836
December16th to endNight
23%
896
22%
2912
8%
896
40%
896
17%
1889

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
14%42443445%7%42%
54890
Night
14%42442445%7%44%
54586
Cloud CoverDay
14%42443445%7%42%
54900
Night
14%5%2442445%7%44%
54590
TransparencyDay
39%7%12%21%15%3
54601
Night
38%6%11%21%17%4
54393
SeeingDay
17%12%21%22%17%8%
8072
Night
15%18%21%26%16%2
18321

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
17%6%2332345%5%44%
1881
16th to endDay
16%5%14323336%48%
2016
February1st to 15thDay
15%5%25%5%14447%44%
1845
16th to endDay
18%424335%45%6%42%
1870
March1st to 15thDay
16%5%24323447%45%
2299
16th to endDay
17%5%25%333446%42%
2464
April1st to 15thDay
12%414423448%49%
2434
16th to endDay
15%425%5%3445%7%43%
2539
May1st to 15thDay
16%425%5%35%6%5%7%37%
2721
16th to endDay
11%5%25%5%25%6%7%9%38%
2847
June1st to 15thDay
10%3145%25%6%7%9%41%
2730
16th to endDay
8%3245%45%5%7%10%41%
2730
July1st to 15thDay
9%425%6%46%7%6%11%34%
2730
16th to endDay
8%436%6%46%6%7%11%34%
2676
August1st to 15thDay
11%5%25%6%37%5%8%10%32%
2487
16th to endDay
10%5%25%6%36%6%6%9%35%
2539
September1st to 15thDay
13%4244245%6%7%43%
2272
16th to endDay
22%5%25%42445%6%36%
2141
October1st to 15thDay
18%41431224450%
1950
16th to endDay
13%31332324455%
2080
November1st to 15thDay
17%413424345%48%
2057
16th to endDay
14%313324446%50%
1858
December1st to 15thDay
17%6%15%424445%43%
1708
16th to endDay
22%6%2332345%6%40%
2016
January1st to 15thNight
16%5%24423335%47%
2717
16th to endNight
16%5%24323445%48%
2912
February1st to 15thNight
16%5%13334446%45%
2675
16th to endNight
15%5%1342445%6%45%
2173
March1st to 15thNight
15%5%24423345%47%
2298
16th to endNight
17%424424346%44%
2464
April1st to 15thNight
13%5%24434448%44%
2174
16th to endNight
15%424324345%46%
2037
May1st to 15thNight
13%425%5%3445%7%42%
1890
16th to endNight
12%424425%5%5%10%41%
1970
June1st to 15thNight
11%324425%47%11%42%
1890
16th to endNight
7%314425%5%7%12%45%
1890
July1st to 15thNight
7%425%346%6%7%9%42%
1890
16th to endNight
6%2246%46%7%8%12%37%
1856
August1st to 15thNight
11%5%26%5%35%6%6%10%36%
1726
16th to endNight
8%315%5%45%7%6%10%40%
1999
September1st to 15thNight
11%5%25%5%345%6%6%43%
2015
16th to endNight
20%7%25%5%24445%37%
2148
October1st to 15thNight
16%423333346%47%
2340
16th to endNight
12%312433335%57%
2496
November1st to 15thNight
16%424312345%51%
2461
16th to endNight
14%314323346%52%
2752
December1st to 15thNight
17%6%35%433435%42%
2901
16th to endNight
20%425%42435%6%39%
2912

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
17%5%24324446%44%
1881
16th to endDay
16%5%24323336%48%
2016
February1st to 15thDay
15%6%25%424347%44%
1845
16th to endDay
18%42432445%6%42%
1870
March1st to 15thDay
15%5%2432445%7%45%
2310
16th to endDay
17%5%24423446%43%
2463
April1st to 15thDay
12%414423448%49%
2434
16th to endDay
14%4245%35%446%43%
2539
May1st to 15thDay
15%5%25%5%35%5%6%7%37%
2721
16th to endDay
11%5%245%36%6%6%9%38%
2847
June1st to 15thDay
9%4245%35%6%7%9%41%
2730
16th to endDay
8%3245%36%5%7%10%41%
2730
July1st to 15thDay
9%425%5%47%7%7%10%35%
2730
16th to endDay
8%437%5%47%7%7%11%34%
2676
August1st to 15thDay
12%426%6%46%6%8%9%33%
2487
16th to endDay
10%5%25%6%36%6%7%9%36%
2539
September1st to 15thDay
13%425%5%245%6%7%43%
2272
16th to endDay
22%5%345%2445%7%35%
2141
October1st to 15thDay
17%41431234450%
1950
16th to endDay
13%32331224455%
2080
November1st to 15thDay
17%414324345%49%
2057
16th to endDay
14%313323446%50%
1858
December1st to 15thDay
16%6%2443444443%
1708
16th to endDay
22%6%1332335%6%40%
2016
January1st to 15thNight
16%5%24423335%47%
2717
16th to endNight
16%6%24323345%47%
2912
February1st to 15thNight
16%5%23434446%45%
2668
16th to endNight
15%6%2332445%6%45%
2173
March1st to 15thNight
14%5%34423345%47%
2310
16th to endNight
17%424424446%44%
2464
April1st to 15thNight
13%5%25%424448%44%
2174
16th to endNight
15%5%24424446%46%
2037
May1st to 15thNight
13%425%43445%7%42%
1889
16th to endNight
12%4135%35%46%10%41%
1970
June1st to 15thNight
11%424425%47%11%42%
1890
16th to endNight
7%3144345%7%12%45%
1890
July1st to 15thNight
6%424446%6%7%10%42%
1890
16th to endNight
5%3246%5%6%7%8%11%37%
1856
August1st to 15thNight
10%5%25%6%45%5%7%10%36%
1726
16th to endNight
8%325%5%36%6%7%10%40%
1999
September1st to 15thNight
11%5%26%5%35%46%6%43%
2015
16th to endNight
19%7%25%5%23445%37%
2148
October1st to 15thNight
16%414423346%47%
2340
16th to endNight
12%213333335%57%
2496
November1st to 15thNight
16%5%2332234451%
2461
16th to endNight
13%314323345%52%
2752
December1st to 15thNight
17%6%25%433445%42%
2901
16th to endNight
20%5%25%42345%6%39%
2912

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
40%6%10%20%18%4
1882
16th to endDay
38%48%25%17%6%
2016
February1st to 15thDay
39%5%10%21%18%3
1847
16th to endDay
41%5%12%20%16%3
1870
March1st to 15thDay
38%5%10%21%19%5%
2310
16th to endDay
42%5%8%21%17%4
2464
April1st to 15thDay
33%5%12%25%16%7%
2434
16th to endDay
40%5%10%20%16%6%
2539
May1st to 15thDay
43%8%14%19%10%2
2721
16th to endDay
38%10%14%26%8%1
2851
June1st to 15thDay
35%9%17%23%12%1
2730
16th to endDay
35%11%16%20%15%2
2730
July1st to 15thDay
38%11%15%17%13%2
2591
16th to endDay
38%11%17%21%10%
2521
August1st to 15thDay
42%11%15%19%9%
2474
16th to endDay
40%10%16%19%10%2
2539
September1st to 15thDay
36%8%14%18%18%2
2272
16th to endDay
47%6%8%18%18%1
2141
October1st to 15thDay
36%49%26%18%4
1950
16th to endDay
32%36%27%22%6%
2080
November1st to 15thDay
37%49%17%23%7%
2057
16th to endDay
33%49%23%24%4
1858
December1st to 15thDay
42%49%22%17%4
1708
16th to endDay
43%412%20%16%2
2016
January1st to 15thNight
40%49%16%22%7%
2717
16th to endNight
38%48%23%19%5%
2912
February1st to 15thNight
39%48%23%19%4
2677
16th to endNight
38%411%23%17%4
2173
March1st to 15thNight
39%48%21%21%5%
2310
16th to endNight
40%5%9%21%17%4
2464
April1st to 15thNight
38%5%10%22%18%5%
2174
16th to endNight
38%6%10%19%17%7%
2037
May1st to 15thNight
39%8%14%20%14%2
1890
16th to endNight
36%8%17%25%10%1
1972
June1st to 15thNight
33%9%18%24%12%1
1890
16th to endNight
29%11%17%20%16%3
1890
July1st to 15thNight
34%11%15%21%13%3
1800
16th to endNight
33%12%18%22%11%1
1748
August1st to 15thNight
40%10%15%18%13%1
1715
16th to endNight
36%9%17%23%10%2
1999
September1st to 15thNight
39%7%13%19%15%4
2015
16th to endNight
48%6%8%17%18%1
2148
October1st to 15thNight
37%5%8%25%18%4
2340
16th to endNight
30%36%25%26%7%
2496
November1st to 15thNight
36%38%18%23%9%
2461
16th to endNight
33%39%22%24%6%
2752
December1st to 15thNight
43%49%21%16%4
2901
16th to endNight
44%410%19%16%3
2912

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%19%36%16%3
180
16th to endDay
24%21%35%14%3
192
February1st to 15thDay
24%20%36%14%4
180
16th to endDay
25%18%34%15%4
239
March1st to 15thDay
21%20%34%18%5%
390
16th to endDay
18%18%32%23%6%
416
April1st to 15thDay
19%17%31%20%9%1
390
16th to endDay
19%15%24%22%12%5%
379
May1st to 15thDay
15%15%27%24%10%7%
408
16th to endDay
18%9%15%23%24%8%
459
June1st to 15thDay
10%10%17%25%22%12%
435
16th to endDay
10%9%16%25%25%12%
435
July1st to 15thDay
10%5%8%24%36%15%
425
16th to endDay
8%9%9%23%31%18%
391
August1st to 15thDay
14%5%12%19%30%17%
358
16th to endDay
10%5%8%23%26%26%
396
September1st to 15thDay
16%5%13%16%25%23%
375
16th to endDay
27%8%10%21%21%10%
374
October1st to 15thDay
21%7%18%23%19%9%
375
16th to endDay
13%12%25%27%18%3
400
November1st to 15thDay
24%13%23%21%14%1
385
16th to endDay
10%17%22%26%18%4
170
December1st to 15thDay
22%10%39%20%41
128
16th to endDay
30%16%30%21%2
192
January1st to 15thNight
16%27%28%22%4
840
16th to endNight
17%22%31%24%3
896
February1st to 15thNight
19%25%27%24%2
824
16th to endNight
17%23%35%20%3
735
March1st to 15thNight
17%23%30%22%4
840
16th to endNight
17%21%28%26%5%
896
April1st to 15thNight
14%23%29%25%6%
838
16th to endNight
17%20%24%26%11%
791
May1st to 15thNight
14%18%23%27%16%
630
16th to endNight
13%15%11%28%28%1
659
June1st to 15thNight
10%15%10%30%27%4
630
16th to endNight
8%15%11%28%33%3
630
July1st to 15thNight
9%11%8%28%36%7%
600
16th to endNight
6%15%7%29%35%5%
615
August1st to 15thNight
12%9%8%33%34%3
575
16th to endNight
9%8%7%27%40%7%
757
September1st to 15thNight
11%9%10%26%34%7%
780
16th to endNight
23%9%10%24%28%2
777
October1st to 15thNight
18%10%17%26%22%5%
780
16th to endNight
12%14%26%28%16%1
832
November1st to 15thNight
17%16%22%29%11%2
820
16th to endNight
12%22%25%26%13%
840
December1st to 15thNight
18%21%26%26%7%
840
16th to endNight
21%21%28%24%3
896
Page generated at 2019-07-17 08:53:08. Version ac04

Copyright 2019 A. Danko


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