ARGUS Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ARGUS Dark Sky Site clear sky chart from 2005-11-05 to 2017-09-10.

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%
15827
17%
46730
11%
15785
44%
15785
22%
31910

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
16%
900
12%
2506
4%
895
23%
895
13%
1961
January16th to endNight
18%
924
11%
2652
5%
924
24%
924
14%
2034
February1st to 15thNight
21%
701
10%
2139
4%
701
27%
701
15%
1582
February16th to endNight
22%
631
15%
1893
5%
631
30%
631
16%
1381
March1st to 15thNight
28%
720
13%
2139
8%
720
32%
720
16%
1570
March16th to endNight
28%
725
16%
2069
8%
725
35%
725
20%
1457
April1st to 15thNight
31%
539
15%
1797
9%
539
40%
539
19%
1222
April16th to endNight
35%
540
21%
1677
11%
540
45%
540
25%
1089
May1st to 15thNight
35%
540
14%
1620
9%
540
40%
540
20%
1155
May16th to endNight
51%
562
16%
1625
11%
561
54%
561
27%
1060
June1st to 15thNight
60%
540
17%
1440
11%
540
65%
540
37%
884
June16th to endNight
58%
540
18%
1440
12%
540
62%
540
33%
926
July1st to 15thNight
63%
510
16%
1360
14%
510
64%
510
35%
856
July16th to endNight
72%
564
21%
1450
17%
531
74%
531
41%
846
August1st to 15thNight
71%
539
21%
1609
18%
536
73%
536
37%
930
August16th to endNight
67%
573
20%
1881
19%
573
71%
573
33%
1068
September1st to 15thNight
64%
592
27%
1817
24%
592
67%
592
36%
1043
September16th to endNight
62%
657
26%
1815
19%
657
65%
657
36%
1107
October1st to 15thNight
51%
660
27%
1820
20%
660
57%
660
33%
1113
October16th to endNight
30%
704
17%
2271
12%
704
39%
704
20%
1508
November1st to 15thNight
36%
700
24%
2276
17%
700
47%
700
26%
1373
November16th to endNight
27%
720
16%
2340
11%
720
35%
720
16%
1668
December1st to 15thNight
21%
786
10%
2406
4%
786
26%
786
12%
1862
December16th to endNight
16%
960
9%
2688
2%
960
23%
960
10%
2215

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%8%36%5%35%45%7%35%
47900
Night
14%8%36%5%24446%37%
46903
Cloud CoverDay
14%8%36%5%3445%7%35%
47909
Night
15%8%36%5%24446%37%
46908
TransparencyDay
47%6%11%20%12%1
47591
Night
46%5%11%20%13%2
46730
SeeingDay
16%6%25%24%19%8%
5839
Night
18%8%27%29%14%1
15831

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
21%14%6%8%5%4435%421%
1432
16th to endDay
13%19%7%8%5%44436%22%
1570
February1st to 15thDay
16%14%5%10%6%35%445%23%
1721
16th to endDay
15%13%5%10%6%34445%25%
1580
March1st to 15thDay
20%11%6%8%6%23347%24%
1811
16th to endDay
17%9%5%7%6%2345%7%30%
2166
April1st to 15thDay
19%9%36%424446%33%
2151
16th to endDay
17%8%26%5%24447%35%
2283
May1st to 15thDay
20%7%37%6%35%447%29%
2331
16th to endDay
13%5%25%6%36%5%6%7%38%
2488
June1st to 15thDay
10%425%5%35%5%6%7%41%
2520
16th to endDay
9%425%5%46%6%7%9%38%
2520
July1st to 15thDay
9%5%25%5%345%6%8%42%
2520
16th to endDay
6%4245%36%8%7%10%40%
2616
August1st to 15thDay
7%315%6%35%6%7%8%44%
2340
16th to endDay
8%425%6%35%5%7%7%43%
2318
September1st to 15thDay
11%5%24435%45%6%45%
2019
16th to endDay
11%5%245%34448%44%
1815
October1st to 15thDay
14%6%26%4335%46%42%
1810
16th to endDay
19%8%35%42445%6%34%
1600
November1st to 15thDay
13%7%24424346%46%
1582
16th to endDay
20%11%47%6%24346%29%
1620
December1st to 15thDay
20%14%6%9%7%34335%21%
1551
16th to endDay
22%18%6%8%6%25%34418%
1536
January1st to 15thNight
20%14%5%8%6%34235%25%
2506
16th to endNight
15%14%7%8%5%34335%26%
2652
February1st to 15thNight
16%13%6%7%5%24345%30%
2137
16th to endNight
15%12%5%8%6%34335%31%
1893
March1st to 15thNight
16%10%46%6%35%445%31%
2126
16th to endNight
15%8%46%5%25%45%6%33%
2069
April1st to 15thNight
16%6%35%5%35%5%5%7%35%
1797
16th to endNight
18%6%2442345%7%40%
1677
May1st to 15thNight
21%5%35%6%24447%33%
1620
16th to endNight
11%5%25%5%2446%7%42%
1623
June1st to 15thNight
7%3244245%48%49%
1440
16th to endNight
8%425%5%3446%10%44%
1440
July1st to 15thNight
7%3246%245%6%9%47%
1440
16th to endNight
5%3244245%6%10%50%
1549
August1st to 15thNight
5%4233245%6%9%49%
1620
16th to endNight
7%32443445%8%50%
1881
September1st to 15thNight
10%32342345%7%52%
1817
16th to endNight
11%41442445%7%49%
1815
October1st to 15thNight
11%5%24423347%49%
1820
16th to endNight
19%7%245%23445%39%
2271
November1st to 15thNight
13%7%35%32335%7%45%
2276
16th to endNight
19%9%37%6%33446%31%
2340
December1st to 15thNight
21%12%6%8%5%24435%25%
2406
16th to endNight
24%15%5%8%5%33435%19%
2688

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
20%15%5%8%6%4435%5%21%
1432
16th to endDay
14%18%7%8%5%35%435%22%
1570
February1st to 15thDay
16%15%5%9%7%35%345%23%
1721
16th to endDay
15%13%5%10%6%35%35%5%26%
1580
March1st to 15thDay
21%11%6%8%5%24347%24%
1821
16th to endDay
17%10%47%6%3345%7%30%
2165
April1st to 15thDay
19%9%35%424446%33%
2151
16th to endDay
17%7%36%5%34347%34%
2283
May1st to 15thDay
19%8%27%6%35%447%29%
2331
16th to endDay
13%5%25%6%35%6%5%7%38%
2488
June1st to 15thDay
10%435%5%35%5%6%7%42%
2520
16th to endDay
9%425%5%36%6%7%9%38%
2520
July1st to 15thDay
10%425%5%345%6%9%42%
2520
16th to endDay
7%4145%36%7%7%9%40%
2616
August1st to 15thDay
7%3245%35%6%7%8%44%
2340
16th to endDay
9%325%6%45%6%6%6%43%
2318
September1st to 15thDay
11%5%245%25%45%7%45%
2019
16th to endDay
12%5%245%2445%8%44%
1815
October1st to 15thDay
14%6%25%42445%6%42%
1810
16th to endDay
20%7%26%42445%6%35%
1600
November1st to 15thDay
13%7%24333346%46%
1582
16th to endDay
20%10%46%6%24345%29%
1620
December1st to 15thDay
20%15%5%9%7%34335%21%
1551
16th to endDay
22%18%6%8%6%25%34418%
1536
January1st to 15thNight
20%14%5%8%6%3423425%
2506
16th to endNight
16%14%7%8%5%34435%26%
2652
February1st to 15thNight
16%13%6%7%433345%30%
2130
16th to endNight
15%12%5%7%6%34345%31%
1893
March1st to 15thNight
17%11%47%5%35%445%31%
2139
16th to endNight
15%9%46%5%25%45%6%34%
2069
April1st to 15thNight
16%6%25%5%35%45%7%35%
1797
16th to endNight
17%7%2442345%7%39%
1677
May1st to 15thNight
21%5%36%6%2345%7%33%
1619
16th to endNight
11%5%25%6%2445%7%42%
1623
June1st to 15thNight
7%335%4245%5%8%49%
1440
16th to endNight
8%5%15%5%3445%10%45%
1440
July1st to 15thNight
7%4245%236%6%8%47%
1440
16th to endNight
442442446%9%51%
1549
August1st to 15thNight
5%4233245%6%10%49%
1620
16th to endNight
7%3244345%5%8%50%
1881
September1st to 15thNight
10%32342345%7%52%
1817
16th to endNight
11%3244235%5%7%50%
1815
October1st to 15thNight
11%425%424347%50%
1820
16th to endNight
19%6%25%5%23445%39%
2271
November1st to 15thNight
13%7%25%31335%6%45%
2276
16th to endNight
19%9%36%6%34337%31%
2340
December1st to 15thNight
21%12%6%9%5%24335%25%
2406
16th to endNight
24%15%6%9%5%23335%19%
2688

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
65%310%14%6%
1433
16th to endDay
63%5%11%13%5%
1570
February1st to 15thDay
63%410%13%7%
1723
16th to endDay
58%5%12%18%4
1580
March1st to 15thDay
60%411%15%6%
1821
16th to endDay
53%5%14%20%5%1
2166
April1st to 15thDay
50%5%10%21%11%
2151
16th to endDay
48%5%10%19%10%5%
2283
May1st to 15thDay
55%6%11%17%9%
2331
16th to endDay
43%8%11%21%13%2
2492
June1st to 15thDay
38%7%10%23%17%1
2520
16th to endDay
38%8%13%19%16%2
2520
July1st to 15thDay
38%7%10%22%17%3
2371
16th to endDay
35%8%17%22%13%2
2452
August1st to 15thDay
33%8%15%24%16%1
2327
16th to endDay
36%8%10%21%16%5%
2318
September1st to 15thDay
37%7%11%21%18%3
2019
16th to endDay
36%7%8%24%21%1
1815
October1st to 15thDay
40%6%10%23%17%1
1810
16th to endDay
48%5%12%22%11%
1600
November1st to 15thDay
39%411%23%18%2
1582
16th to endDay
56%411%19%6%
1620
December1st to 15thDay
65%5%9%15%3
1551
16th to endDay
69%48%12%3
1536
January1st to 15thNight
62%38%15%9%
2506
16th to endNight
60%413%15%6%
2652
February1st to 15thNight
56%413%16%7%
2139
16th to endNight
55%411%19%8%
1893
March1st to 15thNight
54%5%10%18%8%2
2139
16th to endNight
49%5%12%22%7%1
2069
April1st to 15thNight
46%7%10%21%13%1
1797
16th to endNight
42%5%9%22%14%5%
1677
May1st to 15thNight
49%7%10%21%9%1
1620
16th to endNight
39%8%11%21%15%4
1625
June1st to 15thNight
31%7%11%26%21%2
1440
16th to endNight
34%7%14%22%15%4
1440
July1st to 15thNight
32%7%12%22%19%4
1360
16th to endNight
27%7%15%26%18%4
1450
August1st to 15thNight
28%7%14%22%24%2
1609
16th to endNight
30%7%12%22%21%5%
1881
September1st to 15thNight
30%5%10%25%21%5%
1817
16th to endNight
32%5%9%23%24%3
1815
October1st to 15thNight
34%410%25%22%1
1820
16th to endNight
46%5%9%25%11%1
2271
November1st to 15thNight
38%49%22%20%3
2276
16th to endNight
53%410%21%8%
2340
December1st to 15thNight
61%410%15%7%
2406
16th to endNight
68%48%13%4
2688

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
28%14%38%10%5%2
90
16th to endDay
29%12%37%16%4
96
February1st to 15thDay
21%17%46%12%2
90
16th to endDay
20%16%35%16%9%1
81
March1st to 15thDay
30%16%31%18%2
111
16th to endDay
25%8%30%23%10%1
288
April1st to 15thDay
22%9%34%21%10%1
270
16th to endDay
19%9%29%22%14%5%
270
May1st to 15thDay
26%8%27%23%9%4
288
16th to endDay
16%6%28%23%16%9%
388
June1st to 15thDay
12%5%25%29%21%6%
495
16th to endDay
11%6%31%24%18%7%
495
July1st to 15thDay
12%125%27%21%11%
475
16th to endDay
8%114%29%30%15%
476
August1st to 15thDay
9%110%26%32%19%
313
16th to endDay
11%214%20%35%15%
332
September1st to 15thDay
13%214%26%29%12%
294
16th to endDay
15%313%21%34%10%
254
October1st to 15thDay
12%6%22%27%22%8%
255
16th to endDay
25%8%38%26%1
112
November1st to 15thDay
8%10%24%24%25%6%
90
16th to endDay
28%11%37%15%6%
90
December1st to 15thDay
28%13%34%16%6%
90
16th to endDay
28%19%41%8%2
96
January1st to 15thNight
26%13%36%18%4
900
16th to endNight
20%15%34%24%4
924
February1st to 15thNight
24%10%35%25%3
704
16th to endNight
22%12%35%24%4
631
March1st to 15thNight
22%12%30%27%6%
720
16th to endNight
19%9%36%26%7%1
725
April1st to 15thNight
19%10%35%27%7%
539
16th to endNight
21%6%33%25%11%1
540
May1st to 15thNight
23%427%33%10%
540
16th to endNight
14%222%39%19%1
563
June1st to 15thNight
8%224%43%20%
540
16th to endNight
10%221%40%25%
540
July1st to 15thNight
9%218%40%27%2
510
16th to endNight
6%12%39%36%4
564
August1st to 15thNight
7%13%42%30%5%
539
16th to endNight
7%16%32%36%6%
573
September1st to 15thNight
12%314%36%28%4
592
16th to endNight
12%315%33%31%3
657
October1st to 15thNight
14%6%21%32%20%4
660
16th to endNight
22%10%32%23%9%
704
November1st to 15thNight
17%10%32%26%11%1
700
16th to endNight
25%13%29%22%9%
720
December1st to 15thNight
28%12%30%21%6%
786
16th to endNight
31%12%32%19%4
960
Page generated at 2017-09-11 19:35:23. Version ac04

Copyright 2017 A. Danko


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