ASKC Dark Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ASKC Dark Site clear sky chart from 2005-11-05 to 2017-04-07.

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
44%
15366
24%
45541
15%
15319
52%
15319
32%
27066

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
31%
900
24%
2327
9%
895
41%
895
34%
1445
January16th to endNight
33%
960
28%
2496
10%
960
44%
960
35%
1540
February1st to 15thNight
27%
880
19%
2288
7%
876
33%
876
27%
1541
February16th to endNight
29%
652
26%
1914
10%
652
41%
652
29%
1171
March1st to 15thNight
34%
540
23%
1980
14%
540
46%
540
24%
1178
March16th to endNight
31%
576
17%
2112
11%
576
41%
576
20%
1343
April1st to 15thNight
35%
515
23%
1771
16%
515
48%
515
27%
1021
April16th to endNight
35%
495
21%
1590
15%
495
46%
495
25%
993
May1st to 15thNight
40%
494
20%
1485
16%
494
48%
494
27%
958
May16th to endNight
48%
515
19%
1541
16%
513
53%
513
30%
934
June1st to 15thNight
64%
495
22%
1323
15%
495
68%
495
44%
763
June16th to endNight
67%
495
23%
1369
16%
495
71%
495
50%
732
July1st to 15thNight
69%
465
19%
1395
18%
465
69%
465
40%
771
July16th to endNight
76%
522
23%
1468
24%
489
78%
489
45%
762
August1st to 15thNight
76%
494
27%
1475
33%
491
77%
491
44%
780
August16th to endNight
74%
525
26%
1676
31%
525
76%
525
42%
862
September1st to 15thNight
64%
495
27%
1691
30%
495
67%
495
32%
955
September16th to endNight
64%
492
30%
1815
27%
492
70%
492
36%
919
October1st to 15thNight
50%
657
29%
1977
23%
657
55%
657
37%
1120
October16th to endNight
40%
704
30%
2112
16%
704
51%
704
38%
1161
November1st to 15thNight
42%
735
32%
2135
16%
735
55%
735
38%
1197
November16th to endNight
32%
900
25%
2480
11%
900
43%
900
32%
1517
December1st to 15thNight
30%
900
20%
2520
8%
900
40%
900
28%
1626
December16th to endNight
31%
960
23%
2601
10%
960
41%
960
25%
1777

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
13%6%25%42445%7%43%
45675
Night
11%5%24423346%49%
45736
TransparencyDay
39%413%26%14%2
45375
Night
35%311%27%18%3
45541
SeeingDay
13%5%22%29%22%5%
5119
Night
14%6%28%33%14%1
15367

By Month

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%5%26%5%2343449%
1611
16th to endDay
13%7%36%422347%44%
1728
February1st to 15thDay
12%10%45%434236%42%
1575
16th to endDay
14%8%36%414346%42%
1566
March1st to 15thDay
15%7%37%5%35%446%36%
1980
16th to endDay
23%9%25%42343434%
2110
April1st to 15thDay
16%8%34423445%42%
1992
16th to endDay
20%7%36%5%2435%6%34%
2038
May1st to 15thDay
20%7%35%5%34446%34%
2136
16th to endDay
16%7%26%5%35%447%35%
2222
June1st to 15thDay
9%415%6%25%6%6%8%42%
2302
16th to endDay
6%2124245%5%10%52%
2256
July1st to 15thDay
8%5%244346%6%9%43%
2145
16th to endDay
6%4245%36%6%6%10%44%
2284
August1st to 15thDay
6%415%435%46%9%46%
2145
16th to endDay
9%3134245%6%9%47%
2173
September1st to 15thDay
13%5%2442345%6%45%
1936
16th to endDay
9%31343445%7%52%
1806
October1st to 15thDay
14%5%2342244451%
1650
16th to endDay
12%5%2441343453%
1760
November1st to 15thDay
10%5%23313447%52%
1722
16th to endDay
17%5%23312337%48%
1478
December1st to 15thDay
16%7%35%423336%42%
1440
16th to endDay
16%7%46%414236%41%
1620
January1st to 15thNight
11%6%14423335%51%
2327
16th to endNight
9%6%24424446%50%
2496
February1st to 15thNight
11%9%35%424346%42%
2278
16th to endNight
11%7%35%423346%47%
1914
March1st to 15thNight
12%6%26%5%23246%45%
1980
16th to endNight
18%7%2442445%5%39%
2112
April1st to 15thNight
11%6%2442335%6%48%
1771
16th to endNight
15%6%35%423336%44%
1590
May1st to 15thNight
13%5%35%43445%6%43%
1484
16th to endNight
13%5%25%32446%10%42%
1539
June1st to 15thNight
5%3244235%5%9%53%
1323
16th to endNight
421322347%8%58%
1369
July1st to 15thNight
6%3144335%6%8%51%
1485
16th to endNight
5%2133345%6%9%54%
1576
August1st to 15thNight
5%21432445%8%57%
1485
16th to endNight
431442445%7%57%
1676
September1st to 15thNight
11%41432445%7%48%
1691
16th to endNight
7%31343445%7%54%
1815
October1st to 15thNight
14%413223235%55%
1977
16th to endNight
10%42342233458%
2112
November1st to 15thNight
10%413313335%57%
2135
16th to endNight
15%6%23213235%52%
2480
December1st to 15thNight
17%8%34312347%43%
2520
16th to endNight
15%8%35%423345%41%
2601

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
38%211%27%17%1
1612
16th to endDay
40%214%26%13%1
1728
February1st to 15thDay
45%414%25%9%1
1576
16th to endDay
44%211%25%13%2
1566
March1st to 15thDay
48%311%21%12%2
1980
16th to endDay
53%213%19%9%1
2112
April1st to 15thDay
44%310%25%14%
1992
16th to endDay
49%312%22%11%
2038
May1st to 15thDay
49%411%21%11%
2136
16th to endDay
46%416%21%9%
2226
June1st to 15thDay
36%5%15%25%14%1
2302
16th to endDay
26%5%16%33%16%2
2256
July1st to 15thDay
34%5%16%28%12%2
2006
16th to endDay
31%5%15%32%13%1
2129
August1st to 15thDay
32%5%17%25%18%1
2131
16th to endDay
31%6%12%27%15%5%
2173
September1st to 15thDay
38%410%23%16%6%
1936
16th to endDay
31%410%30%19%3
1806
October1st to 15thDay
35%210%24%21%4
1650
16th to endDay
35%19%29%18%5%
1760
November1st to 15thDay
31%310%27%21%5%
1722
16th to endDay
38%210%28%20%
1478
December1st to 15thDay
43%312%29%11%
1440
16th to endDay
46%213%24%10%3
1620
January1st to 15thNight
35%212%27%19%1
2327
16th to endNight
34%313%30%16%2
2496
February1st to 15thNight
43%311%25%14%1
2288
16th to endNight
38%211%27%17%2
1914
March1st to 15thNight
40%310%24%16%4
1980
16th to endNight
45%311%23%13%1
2112
April1st to 15thNight
37%38%24%22%3
1771
16th to endNight
42%310%24%18%1
1590
May1st to 15thNight
41%413%25%14%1
1485
16th to endNight
36%417%27%11%1
1541
June1st to 15thNight
26%5%18%30%17%2
1323
16th to endNight
21%415%32%22%3
1369
July1st to 15thNight
29%313%33%16%4
1395
16th to endNight
24%316%30%22%1
1468
August1st to 15thNight
23%5%13%34%19%3
1475
16th to endNight
25%411%27%24%7%
1676
September1st to 15thNight
33%410%23%19%8%
1691
16th to endNight
28%39%30%24%3
1815
October1st to 15thNight
32%38%24%24%6%
1977
16th to endNight
29%28%31%22%5%
2112
November1st to 15thNight
29%29%26%23%7%
2135
16th to endNight
36%27%28%21%3
2480
December1st to 15thNight
41%313%27%13%
2520
16th to endNight
46%311%22%12%4
2601

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
25%16%31%22%4
90
16th to endDay
18%13%37%21%7%1
96
February1st to 15thDay
7%23%42%20%6%
90
16th to endDay
14%20%41%14%6%1
81
March1st to 15thDay
26%17%36%15%3
90
16th to endDay
27%12%34%17%6%2
96
April1st to 15thDay
18%14%32%24%9%
181
16th to endDay
21%6%33%25%12%
268
May1st to 15thDay
19%8%29%27%12%1
393
16th to endDay
21%424%29%15%4
437
June1st to 15thDay
7%422%34%24%6%
420
16th to endDay
7%121%35%28%5%
420
July1st to 15thDay
11%216%35%26%7%
400
16th to endDay
6%27%32%40%10%
445
August1st to 15thDay
8%16%34%39%9%
418
16th to endDay
10%110%30%36%10%
341
September1st to 15thDay
12%111%31%33%9%
211
16th to endDay
10%120%36%17%14%
90
October1st to 15thDay
11%127%34%12%13%
90
16th to endDay
11%239%34%10%2
96
November1st to 15thDay
11%6%17%28%24%11%
90
16th to endDay
34%15%26%15%6%1
90
December1st to 15thDay
15%13%36%23%6%4
90
16th to endDay
22%11%37%23%4
96
January1st to 15thNight
15%11%38%27%6%1
900
16th to endNight
13%10%38%32%5%
960
February1st to 15thNight
16%11%37%30%3
880
16th to endNight
16%11%38%30%3
652
March1st to 15thNight
16%8%35%32%6%
540
16th to endNight
20%8%35%30%4
576
April1st to 15thNight
15%10%34%32%8%
515
16th to endNight
17%6%34%30%10%
495
May1st to 15thNight
15%6%29%34%12%1
495
16th to endNight
15%325%33%19%2
515
June1st to 15thNight
7%219%45%24%1
495
16th to endNight
3221%48%23%1
495
July1st to 15thNight
9%13%44%30%2
465
16th to endNight
6%7%38%43%2
522
August1st to 15thNight
5%15%43%38%4
494
16th to endNight
7%9%38%40%4
525
September1st to 15thNight
14%113%39%26%4
495
16th to endNight
8%217%37%26%6%
492
October1st to 15thNight
14%323%33%21%2
657
16th to endNight
13%7%34%31%11%
704
November1st to 15thNight
13%7%31%31%15%
735
16th to endNight
18%10%34%26%8%
900
December1st to 15thNight
20%9%33%30%4
900
16th to endNight
19%8%33%32%5%
960
Page generated at 2017-04-08 04:35:17. Version ac04

Copyright 2017 A. Danko


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