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 2017-09-24.

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%
15887
22%
47129
12%
15850
50%
15850
24%
29809

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%
717
24%
2327
9%
716
40%
716
19%
1427
January16th to endNight
24%
768
24%
2496
10%
768
42%
768
22%
1520
February1st to 15thNight
23%
701
22%
2287
8%
701
41%
701
20%
1383
February16th to endNight
19%
631
27%
1865
8%
631
39%
631
24%
1140
March1st to 15thNight
26%
720
25%
1980
11%
720
38%
720
25%
1252
March16th to endNight
28%
768
20%
2112
9%
768
38%
768
22%
1412
April1st to 15thNight
30%
718
21%
1862
7%
718
40%
718
27%
1190
April16th to endNight
34%
686
21%
1766
7%
686
43%
686
25%
1187
May1st to 15thNight
35%
540
16%
1620
6%
540
43%
540
20%
1071
May16th to endNight
50%
561
16%
1684
8%
561
56%
561
23%
1065
June1st to 15thNight
56%
540
17%
1620
13%
540
60%
540
27%
1007
June16th to endNight
59%
540
17%
1620
11%
540
65%
540
27%
1012
July1st to 15thNight
60%
510
12%
1530
9%
510
62%
510
24%
999
July16th to endNight
60%
564
16%
1595
12%
531
67%
531
26%
1031
August1st to 15thNight
59%
539
17%
1609
13%
536
61%
536
23%
1091
August16th to endNight
64%
699
18%
1845
13%
699
66%
699
27%
1248
September1st to 15thNight
60%
720
22%
1860
17%
720
62%
720
30%
1250
September16th to endNight
45%
693
19%
1917
13%
693
50%
693
20%
1362
October1st to 15thNight
45%
660
27%
1980
23%
660
54%
660
27%
1237
October16th to endNight
44%
704
33%
2112
19%
704
62%
704
33%
1188
November1st to 15thNight
39%
700
28%
2101
18%
700
52%
700
30%
1206
November16th to endNight
35%
720
26%
2358
14%
720
51%
720
25%
1355
December1st to 15thNight
27%
720
21%
2487
11%
720
42%
720
18%
1546
December16th to endNight
22%
768
23%
2496
8%
768
39%
768
16%
1630

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%4244345%5%7%42%
47772
Night
14%42442445%7%45%
47322
Cloud CoverDay
14%4244345%5%7%42%
47782
Night
13%42442445%7%45%
47326
TransparencyDay
39%7%12%21%16%3
47483
Night
37%6%11%21%18%4
47129
SeeingDay
16%13%19%22%19%9%
5688
Night
14%19%21%26%16%1
15895

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
18%5%2332445%5%44%
1611
16th to endDay
16%6%14323346%48%
1728
February1st to 15thDay
14%5%25%5%13447%45%
1575
16th to endDay
16%414335%35%6%44%
1606
March1st to 15thDay
14%5%24334447%46%
1969
16th to endDay
18%5%25%433445%42%
2112
April1st to 15thDay
11%31432345%8%51%
2086
16th to endDay
15%5%145%34446%42%
2204
May1st to 15thDay
17%425%5%35%6%5%6%36%
2331
16th to endDay
11%425%6%25%6%7%9%38%
2431
June1st to 15thDay
9%3146%35%6%7%10%41%
2340
16th to endDay
8%325%5%46%6%7%9%41%
2340
July1st to 15thDay
10%5%26%6%46%8%6%10%32%
2340
16th to endDay
7%436%6%46%6%7%11%35%
2465
August1st to 15thDay
12%5%25%6%37%6%8%9%31%
2340
16th to endDay
11%5%26%6%36%6%6%9%34%
2343
September1st to 15thDay
11%425%425%5%6%7%44%
2097
16th to endDay
22%5%25%424446%36%
1902
October1st to 15thDay
18%41431224452%
1650
16th to endDay
14%41432324454%
1760
November1st to 15thDay
13%413424345%52%
1757
16th to endDay
16%323324446%48%
1593
December1st to 15thDay
15%5%14434445%45%
1464
16th to endDay
22%5%2332335%6%41%
1728
January1st to 15thNight
16%5%24423335%47%
2327
16th to endNight
16%5%24324445%46%
2496
February1st to 15thNight
16%5%13334345%47%
2285
16th to endNight
12%5%1342445%6%47%
1865
March1st to 15thNight
14%5%24324445%48%
1968
16th to endNight
17%5%24424346%43%
2112
April1st to 15thNight
13%425%334447%46%
1862
16th to endNight
15%424434445%45%
1766
May1st to 15thNight
14%5%25%4345%47%41%
1620
16th to endNight
11%424435%5%5%11%41%
1682
June1st to 15thNight
9%324425%47%11%43%
1620
16th to endNight
7%324425%5%7%12%45%
1620
July1st to 15thNight
8%425%446%6%8%10%40%
1620
16th to endNight
5%2246%46%7%8%12%38%
1703
August1st to 15thNight
11%5%26%5%35%6%7%10%36%
1620
16th to endNight
8%325%6%46%7%6%10%38%
1845
September1st to 15thNight
10%5%25%5%345%6%5%44%
1860
16th to endNight
19%7%26%5%24445%36%
1917
October1st to 15thNight
17%424323345%48%
1980
16th to endNight
12%313423335%57%
2112
November1st to 15thNight
13%423312345%54%
2101
16th to endNight
15%314323345%51%
2358
December1st to 15thNight
16%6%35%423435%44%
2487
16th to endNight
21%425%423346%40%
2496

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
18%5%2332445%6%44%
1611
16th to endDay
16%5%24323336%47%
1728
February1st to 15thDay
14%6%25%5%13346%46%
1575
16th to endDay
16%414325%45%6%45%
1606
March1st to 15thDay
13%5%24324446%46%
1980
16th to endDay
18%5%25%323446%42%
2111
April1st to 15thDay
11%414323448%51%
2086
16th to endDay
15%4246%35%446%43%
2204
May1st to 15thDay
17%5%25%5%35%6%6%7%35%
2331
16th to endDay
11%5%245%36%6%6%9%38%
2431
June1st to 15thDay
9%3246%45%5%7%9%41%
2340
16th to endDay
8%4245%36%6%7%9%41%
2340
July1st to 15thDay
10%5%25%5%47%7%7%10%32%
2340
16th to endDay
7%336%5%47%7%7%11%35%
2465
August1st to 15thDay
12%426%6%46%6%8%9%32%
2340
16th to endDay
10%5%25%6%36%6%7%9%35%
2343
September1st to 15thDay
11%425%5%25%5%6%7%45%
2097
16th to endDay
22%5%345%23446%36%
1902
October1st to 15thDay
18%41421224452%
1650
16th to endDay
14%323322245%54%
1760
November1st to 15thDay
14%314324345%52%
1757
16th to endDay
15%31433445%6%48%
1593
December1st to 15thDay
15%5%24434445%45%
1464
16th to endDay
22%5%1332335%6%41%
1728
January1st to 15thNight
16%5%24423335%48%
2327
16th to endNight
16%5%2432445%5%46%
2496
February1st to 15thNight
15%5%23333346%47%
2278
16th to endNight
12%6%2342445%6%47%
1865
March1st to 15thNight
13%5%34323346%48%
1980
16th to endNight
18%42442445%6%43%
2112
April1st to 15thNight
13%425%334347%46%
1862
16th to endNight
15%5%24425%446%45%
1766
May1st to 15thNight
14%425%43445%7%41%
1619
16th to endNight
12%413435%5%6%10%41%
1682
June1st to 15thNight
9%324435%5%7%11%43%
1620
16th to endNight
6%3144346%7%11%45%
1620
July1st to 15thNight
7%4245%36%6%8%10%40%
1620
16th to endNight
5%3246%5%5%7%8%11%38%
1703
August1st to 15thNight
10%5%25%6%45%5%7%9%36%
1620
16th to endNight
8%425%6%46%6%7%11%38%
1845
September1st to 15thNight
10%5%26%435%46%6%44%
1860
16th to endNight
19%7%26%5%23445%37%
1917
October1st to 15thNight
17%414323345%47%
1980
16th to endNight
12%313323335%57%
2112
November1st to 15thNight
13%413322345%54%
2101
16th to endNight
15%314323345%51%
2358
December1st to 15thNight
16%6%24433445%43%
2487
16th to endNight
21%5%25%423446%40%
2496

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%19%3
1612
16th to endDay
38%47%25%17%5%
1728
February1st to 15thDay
38%5%9%22%19%4
1577
16th to endDay
38%5%13%22%17%3
1606
March1st to 15thDay
37%5%10%22%18%5%
1980
16th to endDay
43%6%8%21%15%4
2112
April1st to 15thDay
30%5%12%26%17%8%
2086
16th to endDay
41%5%9%19%17%6%
2204
May1st to 15thDay
45%8%14%16%11%3
2331
16th to endDay
38%9%14%25%10%1
2435
June1st to 15thDay
34%9%17%23%12%1
2340
16th to endDay
35%11%15%19%15%2
2340
July1st to 15thDay
41%11%15%15%12%2
2201
16th to endDay
37%11%17%21%10%
2310
August1st to 15thDay
43%11%14%19%9%
2327
16th to endDay
41%10%16%19%10%1
2343
September1st to 15thDay
35%8%13%19%19%3
2097
16th to endDay
47%5%7%18%19%1
1902
October1st to 15thDay
35%39%26%18%5%
1650
16th to endDay
33%37%26%21%6%
1760
November1st to 15thDay
34%49%18%25%8%
1757
16th to endDay
35%48%23%23%4
1593
December1st to 15thDay
39%49%22%18%4
1464
16th to endDay
44%411%19%17%3
1728
January1st to 15thNight
39%49%16%22%7%
2327
16th to endNight
39%48%23%19%5%
2496
February1st to 15thNight
37%47%23%21%5%
2287
16th to endNight
36%411%24%19%4
1865
March1st to 15thNight
37%49%23%19%4
1980
16th to endNight
41%5%10%21%16%3
2112
April1st to 15thNight
36%410%21%20%6%
1862
16th to endNight
39%6%9%18%17%8%
1766
May1st to 15thNight
40%8%14%19%14%2
1620
16th to endNight
35%8%18%24%11%2
1684
June1st to 15thNight
33%9%17%24%12%1
1620
16th to endNight
29%12%17%19%17%3
1620
July1st to 15thNight
35%10%16%19%13%3
1530
16th to endNight
33%12%17%22%12%1
1595
August1st to 15thNight
40%10%15%18%13%1
1609
16th to endNight
38%9%16%22%10%2
1845
September1st to 15thNight
38%7%11%20%17%4
1860
16th to endNight
48%6%8%16%18%1
1917
October1st to 15thNight
38%5%7%25%19%4
1980
16th to endNight
30%36%25%25%8%
2112
November1st to 15thNight
32%38%18%26%10%
2101
16th to endNight
35%38%22%23%6%
2358
December1st to 15thNight
42%49%20%18%4
2487
16th to endNight
45%410%18%17%3
2496

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
22%16%40%16%31
90
16th to endDay
22%27%32%15%2
96
February1st to 15thDay
18%22%43%13%2
90
16th to endDay
16%20%38%18%5%
150
March1st to 15thDay
16%21%31%22%8%
270
16th to endDay
18%20%28%24%7%
288
April1st to 15thDay
14%20%25%24%12%2
270
16th to endDay
20%15%20%21%14%7%
270
May1st to 15thDay
17%20%26%21%9%6%
288
16th to endDay
16%11%15%18%25%11%
331
June1st to 15thDay
9%10%15%24%23%16%
315
16th to endDay
12%11%15%22%26%12%
315
July1st to 15thDay
12%7%10%26%32%11%
305
16th to endDay
5%10%7%22%33%20%
326
August1st to 15thDay
14%6%12%19%30%17%
313
16th to endDay
9%6%8%22%26%25%
332
September1st to 15thDay
13%6%13%17%27%20%
315
16th to endDay
29%9%9%16%23%12%
287
October1st to 15thDay
23%10%18%22%17%7%
255
16th to endDay
13%11%19%31%21%2
272
November1st to 15thDay
18%14%24%23%16%2
265
16th to endDay
12%11%17%27%24%5%
85
December1st to 15thDay
17%12%35%25%6%3
64
16th to endDay
34%19%19%22%3
96
January1st to 15thNight
15%28%28%22%4
720
16th to endNight
16%24%32%24%2
768
February1st to 15thNight
18%26%28%24%1
704
16th to endNight
14%26%36%20%3
631
March1st to 15thNight
16%24%29%23%5%
720
16th to endNight
17%22%26%26%5%
768
April1st to 15thNight
13%26%27%24%7%
718
16th to endNight
17%20%23%26%12%
686
May1st to 15thNight
14%21%23%25%13%
540
16th to endNight
13%18%11%26%28%1
563
June1st to 15thNight
8%17%10%30%28%4
540
16th to endNight
7%17%11%28%32%2
540
July1st to 15thNight
9%12%9%28%33%6%
510
16th to endNight
5%16%7%28%35%5%
564
August1st to 15thNight
12%10%7%33%33%2
539
16th to endNight
9%9%7%27%40%5%
699
September1st to 15thNight
11%9%10%28%35%5%
720
16th to endNight
23%10%10%23%27%3
693
October1st to 15thNight
18%12%19%25%20%3
660
16th to endNight
12%14%25%29%16%1
704
November1st to 15thNight
13%18%23%29%12%2
700
16th to endNight
12%24%24%24%13%
720
December1st to 15thNight
16%23%26%25%7%
720
16th to endNight
21%23%28%23%3
768
Page generated at 2017-09-25 09:02:27. Version ac04

Copyright 2017 A. Danko


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