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 2018-02-22.

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
44%
16569
24%
49034
16%
16522
52%
16522
33%
29053

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%
975
23%
2522
8%
970
41%
970
34%
1568
January16th to endNight
33%
1040
28%
2704
10%
1040
44%
1040
35%
1653
February1st to 15thNight
26%
955
18%
2483
7%
951
33%
951
27%
1667
February16th to endNight
28%
686
25%
2004
10%
686
40%
686
28%
1251
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%
539
22%
1851
15%
539
47%
539
28%
1059
April16th to endNight
34%
540
21%
1734
16%
540
45%
540
24%
1094
May1st to 15thNight
41%
539
19%
1620
15%
539
48%
539
28%
1034
May16th to endNight
48%
563
21%
1685
17%
561
54%
561
31%
1010
June1st to 15thNight
65%
540
21%
1443
14%
540
69%
540
45%
828
June16th to endNight
66%
540
25%
1494
17%
540
70%
540
50%
800
July1st to 15thNight
70%
510
18%
1530
18%
510
71%
510
41%
834
July16th to endNight
76%
564
25%
1594
26%
531
79%
531
46%
823
August1st to 15thNight
75%
539
26%
1610
31%
536
76%
536
43%
857
August16th to endNight
73%
573
28%
1829
33%
573
76%
573
43%
940
September1st to 15thNight
65%
540
26%
1845
29%
540
68%
540
33%
1014
September16th to endNight
64%
537
31%
1980
29%
537
70%
537
35%
1003
October1st to 15thNight
49%
717
28%
2157
21%
717
53%
717
35%
1241
October16th to endNight
41%
768
32%
2304
18%
768
52%
768
39%
1241
November1st to 15thNight
40%
798
30%
2318
15%
798
52%
798
36%
1320
November16th to endNight
33%
975
26%
2687
11%
975
44%
975
33%
1630
December1st to 15thNight
31%
975
21%
2730
9%
975
41%
975
30%
1721
December16th to endNight
30%
1040
22%
2818
9%
1040
40%
1040
24%
1944

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
12%6%25%42445%7%44%
49199
Night
11%5%24423346%50%
49229
TransparencyDay
39%312%26%15%2
48899
Night
35%311%27%18%3
49034
SeeingDay
13%5%23%29%21%5%
6349
Night
14%6%28%33%14%1
16570

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%6%26%5%2344448%
1746
16th to endDay
12%7%35%422347%46%
1872
February1st to 15thDay
11%10%36%434236%41%
1710
16th to endDay
14%9%36%424346%41%
1623
March1st to 15thDay
15%7%37%5%35%446%36%
1980
16th to endDay
23%9%25%42343434%
2110
April1st to 15thDay
15%8%34424446%42%
2097
16th to endDay
20%7%36%5%2435%6%34%
2223
May1st to 15thDay
19%7%35%5%34346%36%
2331
16th to endDay
15%6%26%5%35%447%37%
2430
June1st to 15thDay
8%415%6%25%6%6%8%44%
2511
16th to endDay
6%2124245%6%10%52%
2461
July1st to 15thDay
8%4244346%6%8%44%
2340
16th to endDay
6%424436%6%6%10%45%
2466
August1st to 15thDay
6%415%5%35%46%10%45%
2340
16th to endDay
8%3134245%6%9%48%
2372
September1st to 15thDay
12%5%2442345%6%48%
2112
16th to endDay
9%31343445%7%52%
1970
October1st to 15thDay
14%5%23423445%51%
1800
16th to endDay
11%5%2441343454%
1920
November1st to 15thDay
11%6%24323447%50%
1869
16th to endDay
16%5%23212337%50%
1601
December1st to 15thDay
15%6%35%423336%44%
1560
16th to endDay
15%7%46%5%24336%40%
1755
January1st to 15thNight
11%6%14423436%50%
2522
16th to endNight
8%6%24424446%51%
2704
February1st to 15thNight
12%9%35%424346%42%
2473
16th to endNight
12%8%25%423346%46%
2004
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%
1851
16th to endNight
16%6%25%5%23336%43%
1734
May1st to 15thNight
14%5%35%424446%44%
1619
16th to endNight
13%42432436%10%43%
1683
June1st to 15thNight
5%3234236%6%9%53%
1443
16th to endNight
421322447%8%58%
1494
July1st to 15thNight
6%2144335%6%9%52%
1620
16th to endNight
42133245%6%9%54%
1702
August1st to 15thNight
5%21432445%8%56%
1620
16th to endNight
5%31442445%6%57%
1829
September1st to 15thNight
10%41432445%7%51%
1845
16th to endNight
7%31343445%7%54%
1980
October1st to 15thNight
14%414223335%54%
2157
16th to endNight
9%32331233460%
2304
November1st to 15thNight
12%413323336%55%
2318
16th to endNight
15%5%23313235%52%
2687
December1st to 15thNight
16%7%24312346%46%
2730
16th to endNight
15%9%45%5%23345%40%
2818

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
39%211%27%17%1
1747
16th to endDay
39%214%26%15%1
1872
February1st to 15thDay
46%414%24%8%1
1711
16th to endDay
45%211%25%12%2
1623
March1st to 15thDay
48%311%21%12%2
1980
16th to endDay
53%213%19%9%1
2112
April1st to 15thDay
43%312%25%14%
2097
16th to endDay
50%311%22%11%
2223
May1st to 15thDay
48%411%23%11%
2331
16th to endDay
45%415%22%10%
2434
June1st to 15thDay
35%5%14%25%16%1
2511
16th to endDay
25%5%16%33%16%2
2461
July1st to 15thDay
33%5%15%29%13%2
2201
16th to endDay
30%5%15%33%13%2
2311
August1st to 15thDay
32%417%26%17%1
2326
16th to endDay
31%5%12%27%17%5%
2372
September1st to 15thDay
36%310%26%17%5%
2112
16th to endDay
31%310%31%19%3
1970
October1st to 15thDay
35%39%23%21%5%
1800
16th to endDay
34%19%28%19%5%
1920
November1st to 15thDay
33%310%27%20%5%
1869
16th to endDay
36%29%28%21%
1601
December1st to 15thDay
42%311%30%12%
1560
16th to endDay
46%213%23%10%3
1755
January1st to 15thNight
35%212%28%18%1
2522
16th to endNight
33%312%30%16%2
2704
February1st to 15thNight
42%312%25%14%1
2483
16th to endNight
40%210%26%17%2
2004
March1st to 15thNight
40%310%24%16%4
1980
16th to endNight
45%311%23%13%1
2112
April1st to 15thNight
36%39%25%21%3
1851
16th to endNight
43%39%24%17%1
1734
May1st to 15thNight
40%412%24%16%1
1620
16th to endNight
35%416%28%12%1
1685
June1st to 15thNight
26%417%30%18%2
1443
16th to endNight
21%414%32%22%3
1494
July1st to 15thNight
28%313%33%16%3
1530
16th to endNight
23%316%30%23%2
1594
August1st to 15thNight
24%414%34%18%3
1610
16th to endNight
25%311%27%25%6%
1829
September1st to 15thNight
32%410%25%19%7%
1845
16th to endNight
29%39%31%23%3
1980
October1st to 15thNight
33%38%23%23%7%
2157
16th to endNight
28%28%30%24%6%
2304
November1st to 15thNight
31%310%26%22%6%
2318
16th to endNight
35%27%28%22%2
2687
December1st to 15thNight
39%313%28%15%
2730
16th to endNight
47%311%22%12%3
2818

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
27%12%27%26%5%
135
16th to endDay
15%10%40%23%8%
144
February1st to 15thDay
12%20%42%20%4
135
16th to endDay
19%23%38%14%5%1
100
March1st to 15thDay
26%17%36%15%3
90
16th to endDay
27%12%34%17%6%2
96
April1st to 15thDay
15%12%33%25%11%
216
16th to endDay
24%7%32%24%11%
333
May1st to 15thDay
18%8%29%28%12%2
468
16th to endDay
19%427%29%14%4
517
June1st to 15thDay
7%421%35%25%6%
495
16th to endDay
7%226%34%25%4
495
July1st to 15thDay
11%214%34%29%8%
475
16th to endDay
6%16%32%42%10%
515
August1st to 15thDay
8%17%35%38%8%
493
16th to endDay
9%111%32%35%9%
412
September1st to 15thDay
10%111%29%35%11%
267
16th to endDay
12%116%40%19%10%
135
October1st to 15thDay
14%228%34%8%10%
135
16th to endDay
11%6%43%29%9%1
144
November1st to 15thDay
19%5%19%29%18%7%
135
16th to endDay
25%13%28%21%8%1
135
December1st to 15thDay
11%14%40%22%7%3
135
16th to endDay
20%13%41%20%3
144
January1st to 15thNight
15%10%38%27%6%1
975
16th to endNight
12%10%38%32%5%
1040
February1st to 15thNight
16%11%39%29%3
955
16th to endNight
18%11%37%29%3
686
March1st to 15thNight
16%8%35%32%6%
540
16th to endNight
20%8%35%30%4
576
April1st to 15thNight
14%10%34%32%8%
539
16th to endNight
18%6%34%30%10%
540
May1st to 15thNight
15%6%29%34%12%1
540
16th to endNight
15%325%34%18%2
563
June1st to 15thNight
7%219%45%25%1
540
16th to endNight
4222%48%21%1
540
July1st to 15thNight
9%12%45%30%1
510
16th to endNight
5%7%37%45%3
564
August1st to 15thNight
6%15%43%38%4
539
16th to endNight
7%9%39%39%3
573
September1st to 15thNight
13%113%38%28%5%
540
16th to endNight
8%217%38%26%6%
537
October1st to 15thNight
15%424%33%20%2
717
16th to endNight
12%7%34%32%11%
768
November1st to 15thNight
15%7%31%30%14%
798
16th to endNight
18%9%35%27%8%
975
December1st to 15thNight
19%9%33%30%5%
975
16th to endNight
20%9%33%31%5%
1040
Page generated at 2018-02-23 10:21:28. Version ac04

Copyright 2018 A. Danko


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