SWAOG Dark Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SWAOG Dark Site clear sky chart from 2005-11-05 to

2017-09-12
.

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%
15947
18%
46793
11%
15905
45%
15905
24%
31134

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
21%
900
14%
2506
3%
895
31%
895
19%
1820
January16th to endNight
22%
960
12%
2634
4%
960
29%
960
17%
1996
February1st to 15thNight
22%
809
14%
2220
3%
809
30%
809
19%
1590
February16th to endNight
28%
631
18%
1893
7%
631
37%
631
18%
1310
March1st to 15thNight
29%
720
14%
2160
8%
720
33%
720
18%
1510
March16th to endNight
30%
606
15%
2007
10%
606
37%
606
19%
1393
April1st to 15thNight
29%
539
15%
1797
10%
539
39%
539
21%
1205
April16th to endNight
34%
540
19%
1752
11%
540
43%
540
22%
1162
May1st to 15thNight
36%
540
16%
1584
7%
540
43%
540
23%
1080
May16th to endNight
52%
562
18%
1497
10%
561
57%
561
32%
965
June1st to 15thNight
53%
540
17%
1440
11%
540
57%
540
36%
903
June16th to endNight
52%
540
17%
1440
10%
540
56%
540
31%
943
July1st to 15thNight
64%
510
17%
1360
11%
510
66%
510
38%
833
July16th to endNight
71%
564
22%
1417
17%
531
74%
531
43%
821
August1st to 15thNight
78%
539
20%
1588
19%
536
79%
536
40%
892
August16th to endNight
68%
573
21%
1910
22%
573
71%
573
35%
1048
September1st to 15thNight
66%
530
28%
1767
29%
530
70%
530
38%
927
September16th to endNight
58%
651
25%
1809
19%
651
62%
651
35%
1096
October1st to 15thNight
50%
660
27%
1914
20%
660
56%
660
34%
1137
October16th to endNight
30%
704
19%
2225
11%
704
39%
704
22%
1441
November1st to 15thNight
33%
700
23%
2276
17%
700
44%
700
25%
1392
November16th to endNight
29%
769
17%
2389
9%
769
37%
769
20%
1608
December1st to 15thNight
24%
900
13%
2520
5%
900
30%
900
17%
1881
December16th to endNight
19%
960
11%
2688
3%
960
25%
960
11%
2181

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%7%36%5%3445%7%36%
47876
Night
14%7%35%424446%40%
46962
Cloud CoverDay
14%7%36%5%3445%7%37%
47885
Night
14%7%35%424446%40%
46967
TransparencyDay
45%6%12%21%11%1
47562
Night
43%5%12%22%14%2
46794
SeeingDay
15%6%25%26%18%6%
5950
Night
18%7%28%31%13%1
15951

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
14%13%6%8%6%35%45%6%26%
1432
16th to endDay
14%14%5%9%6%345%36%25%
1587
February1st to 15thDay
15%12%5%7%5%35%45%428%
1642
16th to endDay
15%9%48%5%34346%33%
1580
March1st to 15thDay
16%11%36%6%245%47%30%
1790
16th to endDay
17%8%47%6%35%448%29%
2228
April1st to 15thDay
18%10%5%6%42445%6%31%
2151
16th to endDay
19%7%26%5%3345%7%35%
2206
May1st to 15thDay
18%9%36%6%35%46%7%29%
2365
16th to endDay
14%6%25%5%345%6%8%37%
2617
June1st to 15thDay
10%6%245%35%45%7%44%
2520
16th to endDay
9%5%35%6%36%5%7%8%37%
2520
July1st to 15thDay
7%4145%35%6%6%9%46%
2520
16th to endDay
6%4246%36%6%7%9%42%
2655
August1st to 15thDay
6%425%6%346%7%8%43%
2361
16th to endDay
10%424435%5%7%9%42%
2292
September1st to 15thDay
12%4135%34446%49%
2107
16th to endDay
8%5%26%5%235%5%9%45%
1815
October1st to 15thDay
14%6%25%42345%7%43%
1714
16th to endDay
17%7%36%5%23437%38%
1647
November1st to 15thDay
13%8%35%414446%42%
1582
16th to endDay
18%9%46%5%33336%34%
1569
December1st to 15thDay
18%11%47%6%34445%28%
1440
16th to endDay
22%13%6%7%5%34446%22%
1536
January1st to 15thNight
16%11%47%424446%34%
2506
16th to endNight
13%11%7%8%6%34446%28%
2634
February1st to 15thNight
14%12%5%6%424336%35%
2218
16th to endNight
15%9%46%5%33445%35%
1893
March1st to 15thNight
17%10%36%434335%37%
2147
16th to endNight
17%9%37%5%2446%6%33%
2007
April1st to 15thNight
17%8%36%5%2435%5%37%
1797
16th to endNight
19%7%25%423347%38%
1752
May1st to 15thNight
18%5%25%5%345%49%35%
1584
16th to endNight
10%4245%35%46%9%44%
1496
June1st to 15thNight
11%425%42445%5%50%
1440
16th to endNight
7%4346%35%5%6%10%41%
1440
July1st to 15thNight
6%315%5%245%6%8%51%
1440
16th to endNight
43134245%7%10%51%
1513
August1st to 15thNight
3314425%5%6%9%53%
1597
16th to endNight
9%41332436%9%51%
1910
September1st to 15thNight
10%313313347%57%
1767
16th to endNight
8%3244345%48%50%
1809
October1st to 15thNight
11%5%1432435%6%51%
1914
16th to endNight
19%7%25%322336%42%
2225
November1st to 15thNight
13%7%345%13335%47%
2276
16th to endNight
19%7%36%423346%38%
2389
December1st to 15thNight
21%9%46%5%34435%31%
2520
16th to endNight
24%12%48%6%34325%22%
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
14%13%5%8%6%35%446%26%
1432
16th to endDay
14%14%6%9%7%345%36%24%
1587
February1st to 15thDay
15%12%5%7%5%445%45%28%
1642
16th to endDay
15%10%38%5%33446%33%
1580
March1st to 15thDay
17%10%46%6%25%5%37%30%
1800
16th to endDay
17%9%46%6%35%447%30%
2227
April1st to 15thDay
18%9%5%6%433446%32%
2151
16th to endDay
20%7%25%43345%6%35%
2206
May1st to 15thDay
18%9%36%5%3445%8%28%
2365
16th to endDay
14%5%25%5%3446%8%37%
2617
June1st to 15thDay
10%5%245%35%45%7%44%
2520
16th to endDay
9%5%35%6%36%5%8%7%37%
2520
July1st to 15thDay
7%4145%35%5%6%9%46%
2520
16th to endDay
6%4246%36%6%7%9%43%
2655
August1st to 15thDay
7%425%5%35%6%7%8%43%
2361
16th to endDay
10%4245%35%5%7%8%42%
2292
September1st to 15thDay
12%413434437%49%
2107
16th to endDay
8%5%35%5%2445%8%45%
1815
October1st to 15thDay
14%7%25%42335%7%43%
1714
16th to endDay
17%7%26%423447%38%
1647
November1st to 15thDay
13%8%25%424446%42%
1582
16th to endDay
18%8%5%7%424346%34%
1569
December1st to 15thDay
18%11%5%6%6%34345%28%
1440
16th to endDay
23%13%6%7%5%24436%22%
1536
January1st to 15thNight
16%11%46%5%24336%34%
2506
16th to endNight
13%11%7%8%6%3435%6%29%
2634
February1st to 15thNight
14%12%5%6%5%23336%35%
2211
16th to endNight
15%9%47%5%34445%35%
1893
March1st to 15thNight
17%10%46%43433438%
2160
16th to endNight
17%9%37%5%3445%6%33%
2007
April1st to 15thNight
17%8%35%5%2435%5%37%
1797
16th to endNight
20%6%25%423446%38%
1752
May1st to 15thNight
18%5%25%5%3445%8%35%
1583
16th to endNight
10%4145%35%46%9%44%
1496
June1st to 15thNight
11%425%42345%6%50%
1440
16th to endNight
8%5%245%35%5%6%9%42%
1440
July1st to 15thNight
6%3245%245%5%8%51%
1440
16th to endNight
4313425%5%7%10%51%
1513
August1st to 15thNight
3313425%5%5%9%54%
1597
16th to endNight
9%31332436%8%51%
1910
September1st to 15thNight
10%313313247%57%
1767
16th to endNight
8%3145%345%5%7%50%
1809
October1st to 15thNight
11%5%1341435%6%51%
1914
16th to endNight
19%7%34322335%42%
2225
November1st to 15thNight
13%6%35%423335%47%
2276
16th to endNight
19%7%36%42335%5%38%
2389
December1st to 15thNight
22%8%47%5%34435%31%
2520
16th to endNight
24%12%49%6%3433423%
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
58%5%12%14%9%
1433
16th to endDay
60%5%11%13%7%
1587
February1st to 15thDay
57%6%11%16%7%1
1644
16th to endDay
52%6%12%20%6%1
1580
March1st to 15thDay
53%6%13%19%6%
1800
16th to endDay
53%6%14%19%5%
2228
April1st to 15thDay
52%5%9%21%9%
2151
16th to endDay
48%6%13%17%11%3
2206
May1st to 15thDay
52%7%10%21%6%
2365
16th to endDay
43%7%12%20%15%1
2621
June1st to 15thDay
38%6%11%25%16%1
2520
16th to endDay
40%8%12%21%14%1
2520
July1st to 15thDay
33%7%14%26%15%2
2371
16th to endDay
33%9%18%22%14%2
2488
August1st to 15thDay
34%7%14%26%14%1
2346
16th to endDay
35%8%13%23%16%2
2292
September1st to 15thDay
33%6%11%23%19%4
2107
16th to endDay
35%5%10%28%18%1
1815
October1st to 15thDay
39%5%11%26%14%1
1714
16th to endDay
47%413%22%10%2
1647
November1st to 15thDay
42%5%10%24%14%2
1582
16th to endDay
51%413%22%7%
1569
December1st to 15thDay
58%412%17%6%
1440
16th to endDay
63%5%11%11%7%
1536
January1st to 15thNight
52%5%12%18%11%
2506
16th to endNight
56%415%14%8%
2634
February1st to 15thNight
52%311%21%9%
2220
16th to endNight
50%5%12%21%9%1
1893
March1st to 15thNight
50%412%19%10%2
2160
16th to endNight
50%5%14%19%9%1
2007
April1st to 15thNight
47%410%21%13%2
1797
16th to endNight
45%410%22%11%4
1752
May1st to 15thNight
45%5%13%23%11%
1584
16th to endNight
34%8%14%20%19%2
1498
June1st to 15thNight
33%5%12%25%19%3
1440
16th to endNight
36%7%13%20%18%3
1440
July1st to 15thNight
30%6%12%27%19%2
1360
16th to endNight
24%7%16%27%19%4
1417
August1st to 15thNight
25%8%17%28%18%2
1588
16th to endNight
29%6%13%27%18%4
1910
September1st to 15thNight
27%411%26%26%3
1767
16th to endNight
31%6%10%28%19%3
1809
October1st to 15thNight
33%411%27%21%2
1914
16th to endNight
44%311%24%14%1
2225
November1st to 15thNight
40%49%23%17%4
2276
16th to endNight
47%413%22%11%
2389
December1st to 15thNight
55%411%19%7%
2520
16th to endNight
66%49%13%5%
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
22%8%35%25%7%
90
16th to endDay
20%11%36%17%12%1
96
February1st to 15thDay
18%18%43%15%3
90
16th to endDay
25%8%30%22%12%
81
March1st to 15thDay
37%12%26%17%5%
90
16th to endDay
23%11%32%19%10%2
231
April1st to 15thDay
23%11%30%22%11%
270
16th to endDay
24%9%23%28%9%4
270
May1st to 15thDay
24%10%26%25%10%3
322
16th to endDay
17%7%29%23%16%4
517
June1st to 15thDay
13%326%31%19%5%
495
16th to endDay
10%5%33%29%14%6%
495
July1st to 15thDay
9%5%22%28%22%11%
475
16th to endDay
7%123%30%25%11%
515
August1st to 15thDay
8%115%33%24%16%
412
16th to endDay
9%313%28%31%12%
332
September1st to 15thDay
11%314%31%30%8%
299
16th to endDay
10%320%29%27%8%
254
October1st to 15thDay
11%7%24%27%24%4
154
16th to endDay
21%11%35%25%6%
96
November1st to 15thDay
10%11%24%33%13%7%
90
16th to endDay
38%11%30%10%10%
90
December1st to 15thDay
18%16%31%24%7%1
90
16th to endDay
29%16%45%5%3
96
January1st to 15thNight
22%10%38%21%5%
900
16th to endNight
19%11%35%30%3
960
February1st to 15thNight
22%9%36%25%5%
812
16th to endNight
20%10%34%27%6%
631
March1st to 15thNight
21%11%31%28%6%
720
16th to endNight
20%8%35%25%8%1
606
April1st to 15thNight
20%11%35%26%6%
539
16th to endNight
22%7%33%26%10%
540
May1st to 15thNight
21%5%31%30%10%
540
16th to endNight
11%5%25%38%18%
563
June1st to 15thNight
13%225%43%14%
540
16th to endNight
11%225%41%17%
540
July1st to 15thNight
8%18%41%28%1
510
16th to endNight
415%45%30%3
564
August1st to 15thNight
47%49%32%4
539
16th to endNight
10%114%35%34%2
573
September1st to 15thNight
11%215%37%28%4
530
16th to endNight
9%419%37%26%3
651
October1st to 15thNight
16%424%33%18%1
660
16th to endNight
23%9%30%25%9%
704
November1st to 15thNight
17%9%34%27%11%1
700
16th to endNight
22%11%31%25%8%
769
December1st to 15thNight
27%10%31%24%5%
900
16th to endNight
30%9%32%23%3
960
Page generated at 2017-09-13 06:39:23. Version ac04

Copyright 2017 A. Danko


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