SWAOG Light Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SWAOG Light Site clear sky chart from 2005-11-05 to 2017-09-19.

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
36%
15977
17%
46858
10%
15936
43%
15936
23%
31395

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
20%
900
13%
2506
4%
895
28%
895
18%
1832
January16th to endNight
19%
960
13%
2655
4%
960
26%
960
15%
2001
February1st to 15thNight
20%
797
13%
2208
3%
797
28%
797
19%
1573
February16th to endNight
26%
631
18%
1893
7%
631
36%
631
18%
1317
March1st to 15thNight
26%
720
13%
2160
7%
720
31%
720
17%
1531
March16th to endNight
28%
624
15%
2013
10%
624
34%
624
18%
1397
April1st to 15thNight
28%
539
15%
1797
10%
539
38%
539
19%
1224
April16th to endNight
32%
540
19%
1734
10%
540
43%
540
22%
1160
May1st to 15thNight
35%
540
16%
1596
8%
540
43%
540
21%
1118
May16th to endNight
48%
561
17%
1498
9%
561
54%
561
31%
970
June1st to 15thNight
50%
540
16%
1440
10%
540
54%
540
35%
899
June16th to endNight
47%
540
16%
1440
9%
540
52%
540
30%
957
July1st to 15thNight
58%
510
17%
1360
11%
510
61%
510
39%
826
July16th to endNight
67%
564
22%
1417
15%
531
70%
531
42%
832
August1st to 15thNight
74%
539
21%
1572
20%
536
76%
536
41%
879
August16th to endNight
65%
573
21%
1910
20%
573
70%
573
35%
1056
September1st to 15thNight
61%
543
29%
1803
28%
543
67%
543
37%
962
September16th to endNight
56%
673
25%
1858
18%
673
61%
673
33%
1134
October1st to 15thNight
46%
660
26%
1897
19%
660
53%
660
31%
1157
October16th to endNight
27%
704
18%
2238
10%
704
38%
704
21%
1467
November1st to 15thNight
31%
700
23%
2276
15%
700
42%
700
24%
1407
November16th to endNight
25%
759
17%
2379
8%
759
35%
759
18%
1622
December1st to 15thNight
20%
900
13%
2520
4%
900
27%
900
17%
1879
December16th to endNight
15%
960
11%
2688
2%
960
22%
960
11%
2195

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%3445%7%36%
47960
Night
15%8%35%424446%40%
47026
Cloud CoverDay
14%8%36%5%3445%7%36%
47969
Night
15%7%35%424446%40%
47031
TransparencyDay
46%6%12%20%11%1
47646
Night
44%5%11%22%13%1
46858
SeeingDay
15%10%29%25%13%5%
5982
Night
18%9%30%28%12%1
15982

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
16%13%47%6%35%36%7%25%
1432
16th to endDay
13%15%7%10%5%34436%25%
1566
February1st to 15thDay
15%14%6%7%5%45%435%28%
1654
16th to endDay
16%10%48%6%24347%31%
1580
March1st to 15thDay
16%12%5%8%42445%6%29%
1790
16th to endDay
19%9%47%5%34346%30%
2221
April1st to 15thDay
19%10%46%5%34345%31%
2151
16th to endDay
21%7%24434447%34%
2224
May1st to 15thDay
19%10%35%5%35%46%7%29%
2352
16th to endDay
14%5%35%435%6%5%7%37%
2617
June1st to 15thDay
13%5%25%435%45%7%43%
2520
16th to endDay
10%5%35%5%36%5%8%8%36%
2520
July1st to 15thDay
8%324435%6%6%8%44%
2520
16th to endDay
7%425%6%35%6%7%9%40%
2655
August1st to 15thDay
8%5%25%5%35%5%7%9%40%
2374
16th to endDay
10%4245%35%6%7%9%40%
2292
September1st to 15thDay
13%324424446%48%
2144
16th to endDay
10%5%25%4345%6%8%43%
1848
October1st to 15thDay
14%6%25%5%24337%43%
1730
16th to endDay
19%8%25%5%33347%36%
1633
November1st to 15thDay
14%9%4442335%6%41%
1582
16th to endDay
18%8%5%6%423435%35%
1579
December1st to 15thDay
17%13%5%7%5%35%345%27%
1440
16th to endDay
22%15%5%7%6%24345%22%
1536
January1st to 15thNight
17%11%46%5%24345%34%
2506
16th to endNight
14%12%6%9%5%24445%29%
2655
February1st to 15thNight
15%12%46%5%23345%35%
2206
16th to endNight
15%11%46%5%2335%6%34%
1893
March1st to 15thNight
16%10%46%5%2434436%
2147
16th to endNight
17%8%35%5%35%35%7%34%
2013
April1st to 15thNight
17%7%37%5%24445%36%
1797
16th to endNight
18%8%26%313446%39%
1734
May1st to 15thNight
18%6%25%5%35%5%5%7%35%
1596
16th to endNight
12%32442446%9%44%
1496
June1st to 15thNight
11%42343445%6%49%
1440
16th to endNight
9%5%24437%5%7%9%41%
1440
July1st to 15thNight
6%325%4245%6%8%52%
1440
16th to endNight
5%3233335%8%9%51%
1513
August1st to 15thNight
42144345%6%9%53%
1581
16th to endNight
9%31342345%9%52%
1910
September1st to 15thNight
10%313323337%56%
1803
16th to endNight
9%42443435%7%49%
1858
October1st to 15thNight
13%5%14424246%50%
1897
16th to endNight
20%7%25%422346%40%
2238
November1st to 15thNight
14%7%24423345%46%
2276
16th to endNight
18%9%46%423345%37%
2379
December1st to 15thNight
21%9%47%5%23335%31%
2520
16th to endNight
24%15%5%8%6%2433421%
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
16%13%48%6%35%35%7%25%
1432
16th to endDay
13%15%7%10%6%24436%24%
1566
February1st to 15thDay
15%14%7%7%5%35%435%27%
1654
16th to endDay
16%10%48%6%24347%31%
1580
March1st to 15thDay
16%12%5%7%434446%29%
1800
16th to endDay
18%9%47%5%34446%30%
2220
April1st to 15thDay
19%10%46%5%34445%31%
2151
16th to endDay
21%8%2443445%6%34%
2224
May1st to 15thDay
19%10%35%5%35%46%7%29%
2352
16th to endDay
14%5%35%435%6%6%7%37%
2617
June1st to 15thDay
13%5%25%43445%7%43%
2520
16th to endDay
10%5%35%5%46%5%8%8%36%
2520
July1st to 15thDay
8%3245%35%6%6%9%44%
2520
16th to endDay
7%425%6%35%6%7%9%40%
2655
August1st to 15thDay
8%5%25%6%36%5%6%9%40%
2374
16th to endDay
10%4245%35%6%6%9%41%
2292
September1st to 15thDay
13%324425%447%48%
2144
16th to endDay
10%5%244345%6%8%43%
1848
October1st to 15thDay
14%6%25%5%23447%43%
1730
16th to endDay
19%8%25%6%23347%36%
1633
November1st to 15thDay
14%9%4442435%5%41%
1582
16th to endDay
18%8%5%6%423445%35%
1579
December1st to 15thDay
18%13%5%7%5%25%345%28%
1440
16th to endDay
22%14%5%7%6%24335%22%
1536
January1st to 15thNight
17%11%46%5%24435%34%
2506
16th to endNight
14%12%7%8%6%24445%29%
2655
February1st to 15thNight
15%12%46%5%23445%35%
2199
16th to endNight
15%10%46%5%1345%6%34%
1893
March1st to 15thNight
17%10%46%5%2434436%
2160
16th to endNight
17%8%35%5%35%45%7%34%
2013
April1st to 15thNight
17%6%36%5%24445%36%
1797
16th to endNight
18%8%25%323446%39%
1734
May1st to 15thNight
18%6%25%5%36%5%5%7%35%
1595
16th to endNight
12%32442446%9%44%
1496
June1st to 15thNight
11%42343445%6%49%
1440
16th to endNight
9%5%24437%5%7%8%41%
1440
July1st to 15thNight
6%315%32446%8%52%
1440
16th to endNight
5%3243345%7%10%51%
1513
August1st to 15thNight
42244345%6%9%53%
1581
16th to endNight
9%31332345%8%52%
1910
September1st to 15thNight
10%313323337%56%
1803
16th to endNight
9%42443435%7%50%
1858
October1st to 15thNight
13%5%24424346%50%
1897
16th to endNight
20%7%25%422346%40%
2238
November1st to 15thNight
14%7%245%23345%46%
2276
16th to endNight
18%9%46%423345%37%
2379
December1st to 15thNight
21%10%47%5%23345%31%
2520
16th to endNight
24%14%5%8%6%2433421%
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
57%5%13%14%8%
1433
16th to endDay
61%411%14%7%
1566
February1st to 15thDay
59%410%15%8%1
1656
16th to endDay
53%6%12%19%6%1
1580
March1st to 15thDay
55%6%11%18%6%
1800
16th to endDay
54%5%13%19%5%
2221
April1st to 15thDay
54%49%19%10%
2151
16th to endDay
48%6%13%16%11%3
2224
May1st to 15thDay
53%7%11%20%6%
2352
16th to endDay
43%7%12%19%14%2
2621
June1st to 15thDay
39%6%11%23%17%1
2520
16th to endDay
41%8%13%20%13%2
2520
July1st to 15thDay
34%8%14%26%13%2
2371
16th to endDay
35%9%16%21%13%3
2488
August1st to 15thDay
38%7%13%25%13%1
2359
16th to endDay
36%8%12%23%16%2
2292
September1st to 15thDay
34%6%10%25%19%3
2144
16th to endDay
37%6%10%28%16%1
1848
October1st to 15thDay
41%5%11%25%14%1
1730
16th to endDay
48%413%22%9%2
1633
November1st to 15thDay
43%411%23%14%2
1582
16th to endDay
50%5%12%23%7%
1579
December1st to 15thDay
59%413%16%6%
1440
16th to endDay
64%5%10%11%7%
1536
January1st to 15thNight
52%5%12%18%10%
2506
16th to endNight
56%5%12%16%9%
2655
February1st to 15thNight
51%413%20%9%
2208
16th to endNight
49%5%12%21%8%1
1893
March1st to 15thNight
52%412%17%10%2
2160
16th to endNight
49%6%14%19%8%1
2013
April1st to 15thNight
48%410%20%13%1
1797
16th to endNight
44%5%10%22%11%4
1734
May1st to 15thNight
47%6%10%23%10%
1596
16th to endNight
35%8%14%20%18%2
1498
June1st to 15thNight
33%6%12%25%18%3
1440
16th to endNight
36%9%12%21%18%1
1440
July1st to 15thNight
29%7%13%28%18%3
1360
16th to endNight
25%8%17%25%19%4
1417
August1st to 15thNight
25%6%16%30%18%1
1572
16th to endNight
29%6%14%27%17%4
1910
September1st to 15thNight
28%410%27%26%2
1803
16th to endNight
33%6%9%31%17%2
1858
October1st to 15thNight
35%49%27%20%1
1897
16th to endNight
45%410%25%12%1
2238
November1st to 15thNight
40%48%24%17%4
2276
16th to endNight
49%412%22%11%
2379
December1st to 15thNight
55%410%19%8%
2520
16th to endNight
67%38%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
25%14%40%18%1
90
16th to endDay
22%17%31%19%7%1
96
February1st to 15thDay
22%31%37%8%
90
16th to endDay
22%18%35%14%6%2
81
March1st to 15thDay
36%25%23%12%2
90
16th to endDay
29%10%29%21%8%1
243
April1st to 15thDay
24%13%28%23%9%
270
16th to endDay
23%13%27%21%9%4
270
May1st to 15thDay
22%14%30%19%9%3
309
16th to endDay
17%12%33%21%11%4
517
June1st to 15thDay
12%8%34%27%12%4
495
16th to endDay
12%11%36%25%9%5%
495
July1st to 15thDay
8%5%34%28%14%9%
475
16th to endDay
6%5%28%34%17%8%
515
August1st to 15thDay
8%219%36%20%12%
401
16th to endDay
11%416%30%25%11%
332
September1st to 15thDay
11%420%33%23%7%
315
16th to endDay
11%6%21%28%24%8%
266
October1st to 15thDay
12%10%25%31%16%3
170
16th to endDay
27%19%36%14%2
96
November1st to 15thDay
11%12%30%30%12%4
90
16th to endDay
40%13%31%8%6%
90
December1st to 15thDay
20%27%32%16%3
90
16th to endDay
31%31%33%22
96
January1st to 15thNight
21%14%38%20%4
900
16th to endNight
19%14%36%26%2
960
February1st to 15thNight
22%11%37%22%5%
800
16th to endNight
19%13%34%25%5%
631
March1st to 15thNight
21%12%34%23%7%
720
16th to endNight
20%8%37%24%9%
624
April1st to 15thNight
20%13%32%26%6%
539
16th to endNight
22%8%34%25%8%
540
May1st to 15thNight
21%6%32%28%10%
540
16th to endNight
12%5%28%35%16%
563
June1st to 15thNight
13%329%39%14%
540
16th to endNight
10%431%37%16%
540
July1st to 15thNight
8%123%40%23%1
510
16th to endNight
5%18%46%25%2
564
August1st to 15thNight
5%12%48%29%4
539
16th to endNight
10%116%36%30%3
573
September1st to 15thNight
12%218%33%28%3
543
16th to endNight
11%5%20%33%25%3
673
October1st to 15thNight
15%7%25%32%17%1
660
16th to endNight
21%12%33%22%9%
704
November1st to 15thNight
17%12%35%23%9%1
700
16th to endNight
21%15%32%22%7%
759
December1st to 15thNight
27%12%34%21%4
900
16th to endNight
31%12%33%19%3
960
Page generated at 2017-09-20 03:49:57. Version ac04

Copyright 2017 A. Danko


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