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 2017-04-09.

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
38%
15336
22%
45568
12%
15299
49%
15299
24%
28801

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
28%
694
21%
1802
8%
694
39%
694
26%
1159
April16th to endNight
34%
629
22%
1619
7%
629
43%
629
26%
1080
May1st to 15thNight
36%
495
16%
1485
7%
495
44%
495
20%
986
May16th to endNight
51%
513
16%
1540
8%
513
57%
513
24%
962
June1st to 15thNight
55%
495
18%
1485
14%
495
59%
495
27%
922
June16th to endNight
59%
495
16%
1485
10%
495
65%
495
28%
923
July1st to 15thNight
57%
465
13%
1395
10%
465
59%
465
23%
920
July16th to endNight
59%
522
15%
1469
11%
489
66%
489
25%
961
August1st to 15thNight
59%
494
18%
1474
15%
491
62%
491
23%
991
August16th to endNight
63%
640
16%
1690
11%
640
65%
640
26%
1152
September1st to 15thNight
62%
660
24%
1705
19%
660
63%
660
31%
1139
September16th to endNight
42%
657
17%
1818
12%
657
48%
657
19%
1310
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%
45686
Night
14%42442445%7%45%
45761
Cloud CoverDay
14%4244345%5%7%42%
45696
Night
13%42442445%7%45%
45765
TransparencyDay
39%7%12%21%16%3
45397
Night
37%6%11%21%18%4
45568
SeeingDay
16%14%18%21%19%10%
5026
Night
14%20%21%25%16%1
15344

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%
2010
16th to endDay
14%5%245%34346%43%
2020
May1st to 15thDay
17%425%5%35%6%5%7%35%
2136
16th to endDay
10%5%25%5%35%6%7%8%39%
2223
June1st to 15thDay
10%3145%26%6%7%10%41%
2145
16th to endDay
8%3245%36%6%7%9%42%
2145
July1st to 15thDay
10%5%25%6%46%8%7%10%32%
2145
16th to endDay
7%436%6%47%7%7%11%34%
2283
August1st to 15thDay
11%5%25%6%37%6%8%9%32%
2145
16th to endDay
11%5%36%6%36%6%6%9%34%
2147
September1st to 15thDay
10%425%425%5%6%8%44%
1922
16th to endDay
23%5%25%424445%36%
1812
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%5%25%324347%46%
1802
16th to endNight
14%434334445%46%
1619
May1st to 15thNight
13%5%25%5%345%47%41%
1485
16th to endNight
10%324435%5%5%11%42%
1538
June1st to 15thNight
10%323425%5%7%11%43%
1485
16th to endNight
6%324425%5%7%12%45%
1485
July1st to 15thNight
8%425%446%6%7%9%39%
1485
16th to endNight
5%2246%36%7%8%12%38%
1577
August1st to 15thNight
11%425%5%35%5%7%10%37%
1485
16th to endNight
8%425%6%46%7%6%10%37%
1690
September1st to 15thNight
10%425%5%345%7%6%44%
1705
16th to endNight
20%8%26%5%23345%35%
1818
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%50%
2010
16th to endDay
14%4246%35%446%44%
2020
May1st to 15thDay
17%5%25%5%35%6%6%7%35%
2136
16th to endDay
10%5%245%36%6%6%9%39%
2223
June1st to 15thDay
9%3236%35%6%7%9%41%
2145
16th to endDay
7%3245%36%6%7%9%42%
2145
July1st to 15thDay
10%5%35%5%46%7%8%10%32%
2145
16th to endDay
7%336%5%47%7%7%11%34%
2283
August1st to 15thDay
12%426%6%46%6%8%9%32%
2145
16th to endDay
11%5%25%6%36%6%7%9%34%
2147
September1st to 15thDay
10%425%5%25%5%6%8%44%
1922
16th to endDay
23%5%345%23446%36%
1812
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%324347%46%
1802
16th to endNight
14%5%24425%445%46%
1619
May1st to 15thNight
13%435%5%345%5%7%40%
1484
16th to endNight
10%313435%5%6%10%43%
1538
June1st to 15thNight
10%323435%5%7%11%43%
1485
16th to endNight
5%3144346%7%11%46%
1485
July1st to 15thNight
7%5%24436%6%8%9%39%
1485
16th to endNight
5%325%6%5%5%7%8%11%37%
1577
August1st to 15thNight
10%425%5%35%47%10%37%
1485
16th to endNight
8%425%6%46%6%7%11%37%
1690
September1st to 15thNight
9%5%26%435%46%6%44%
1705
16th to endNight
20%8%36%5%22445%35%
1818
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
31%5%11%25%17%8%
2010
16th to endDay
41%48%19%18%6%
2020
May1st to 15thDay
45%9%15%17%10%2
2136
16th to endDay
37%9%14%25%10%1
2227
June1st to 15thDay
35%10%18%23%11%1
2145
16th to endDay
34%11%16%20%15%2
2145
July1st to 15thDay
41%10%15%15%12%2
2006
16th to endDay
38%11%18%20%9%
2128
August1st to 15thDay
42%11%14%19%9%
2132
16th to endDay
42%11%15%18%10%1
2147
September1st to 15thDay
35%9%14%17%20%3
1922
16th to endDay
48%6%7%16%18%1
1812
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
37%410%20%20%6%
1802
16th to endNight
38%6%8%19%18%8%
1619
May1st to 15thNight
40%8%15%19%13%1
1485
16th to endNight
34%8%18%25%11%2
1540
June1st to 15thNight
33%9%18%25%12%2
1485
16th to endNight
28%12%17%20%17%3
1485
July1st to 15thNight
37%10%14%19%13%4
1395
16th to endNight
34%12%17%22%11%1
1469
August1st to 15thNight
39%10%15%18%14%1
1474
16th to endNight
38%10%15%22%10%2
1690
September1st to 15thNight
37%7%12%19%17%5%
1705
16th to endNight
50%6%8%15%18%1
1818
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
15%22%26%20%11%2
245
16th to endDay
18%18%17%19%17%9%
210
May1st to 15thDay
17%17%25%21%10%7%
228
16th to endDay
15%13%10%19%28%12%
267
June1st to 15thDay
10%12%12%23%22%17%
255
16th to endDay
10%12%12%21%29%13%
255
July1st to 15thDay
13%8%11%24%28%13%
245
16th to endDay
6%11%6%18%31%24%
270
August1st to 15thDay
13%7%8%16%35%18%
253
16th to endDay
11%7%6%17%30%27%
268
September1st to 15thDay
10%7%7%18%32%24%
255
16th to endDay
33%10%9%16%20%9%
254
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%27%27%23%6%
694
16th to endNight
15%22%23%26%12%
629
May1st to 15thNight
13%22%23%25%14%
495
16th to endNight
12%19%10%26%29%1
515
June1st to 15thNight
8%18%9%30%27%4
495
16th to endNight
6%18%10%28%33%3
495
July1st to 15thNight
10%14%9%27%32%6%
465
16th to endNight
5%18%6%27%35%6%
522
August1st to 15thNight
11%10%7%33%34%2
494
16th to endNight
9%10%6%26%40%6%
640
September1st to 15thNight
10%9%9%27%37%5%
660
16th to endNight
25%11%11%24%25%1
657
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 2017-04-10 09:00:36. Version ac04

Copyright 2017 A. Danko


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