Golden Mean Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Golden Mean Observatory 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
42%
15241
21%
46815
13%
15202
51%
15202
26%
29044

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
27%
718
22%
2452
9%
716
44%
716
20%
1510
January16th to endNight
23%
768
23%
2496
9%
768
41%
768
22%
1544
February1st to 15thNight
25%
702
21%
2269
9%
701
42%
701
23%
1381
February16th to endNight
23%
631
26%
1893
8%
631
44%
631
24%
1172
March1st to 15thNight
29%
720
21%
2048
10%
720
42%
720
26%
1303
March16th to endNight
32%
768
22%
2058
10%
768
42%
768
27%
1348
April1st to 15thNight
30%
718
20%
1796
6%
718
37%
718
32%
1162
April16th to endNight
43%
720
20%
1800
8%
720
46%
720
33%
1166
May1st to 15thNight
41%
586
18%
1666
9%
586
46%
586
25%
1106
May16th to endNight
57%
374
18%
1497
18%
374
61%
374
23%
870
June1st to 15thNight
60%
360
19%
1440
21%
360
66%
360
25%
838
June16th to endNight
60%
360
15%
1440
18%
360
63%
360
24%
836
July1st to 15thNight
61%
340
14%
1360
17%
340
62%
340
22%
814
July16th to endNight
68%
505
17%
1536
15%
472
72%
472
32%
887
August1st to 15thNight
67%
578
18%
1648
13%
575
67%
575
33%
1013
August16th to endNight
66%
764
19%
1910
12%
764
66%
764
35%
1252
September1st to 15thNight
62%
700
24%
1750
15%
700
65%
700
36%
1125
September16th to endNight
56%
657
22%
1787
18%
657
58%
657
30%
1169
October1st to 15thNight
50%
660
24%
1980
22%
660
56%
660
27%
1261
October16th to endNight
39%
704
28%
2112
17%
704
54%
704
29%
1260
November1st to 15thNight
38%
700
23%
2258
14%
700
50%
700
28%
1345
November16th to endNight
36%
720
23%
2411
16%
720
48%
720
23%
1452
December1st to 15thNight
28%
720
19%
2520
8%
720
42%
720
19%
1580
December16th to endNight
26%
768
23%
2688
10%
768
42%
768
20%
1650

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%42442445%8%45%
47809
Night
14%5%2442445%7%43%
46998
Cloud CoverDay
13%42442445%8%44%
47819
Night
14%5%25%42445%7%43%
47002
TransparencyDay
37%412%25%17%2
47510
Night
39%311%24%17%3
46815
SeeingDay
16%6%23%26%18%8%
5741
Night
16%8%25%32%15%1
15246

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
15%6%44424446%41%
1483
16th to endDay
18%5%34424347%41%
1728
February1st to 15thDay
14%6%25%42445%7%41%
1592
16th to endDay
13%6%24435%45%6%43%
1580
March1st to 15thDay
16%415%423446%46%
1900
16th to endDay
17%5%34423346%43%
2166
April1st to 15thDay
13%414414447%47%
2152
16th to endDay
14%424424447%47%
2160
May1st to 15thDay
15%5%1432345%8%44%
2295
16th to endDay
13%3244235%6%9%46%
2618
June1st to 15thDay
10%313335%5%5%9%46%
2520
16th to endDay
7%313425%5%6%10%47%
2520
July1st to 15thDay
9%424435%46%9%44%
2520
16th to endDay
5%2235%35%7%7%11%43%
2522
August1st to 15thDay
9%5%25%5%3446%8%43%
2289
16th to endDay
9%315%5%345%6%8%45%
2292
September1st to 15thDay
12%42432445%7%48%
2098
16th to endDay
17%6%25%42445%6%39%
1840
October1st to 15thDay
19%413323345%47%
1650
16th to endDay
15%414422345%51%
1760
November1st to 15thDay
16%423324447%47%
1600
16th to endDay
15%5%2432345%7%46%
1548
December1st to 15thDay
15%5%25%42336%7%42%
1440
16th to endDay
18%6%26%334436%40%
1536
January1st to 15thNight
16%5%25%42445%7%41%
2452
16th to endNight
17%6%24423445%43%
2496
February1st to 15thNight
14%6%24423446%44%
2268
16th to endNight
15%6%34324246%46%
1893
March1st to 15thNight
15%5%25%424446%44%
2036
16th to endNight
17%6%35%324345%43%
2058
April1st to 15thNight
13%426%423347%45%
1796
16th to endNight
15%5%24323447%46%
1800
May1st to 15thNight
15%6%245%3446%8%38%
1666
16th to endNight
11%5%24435%45%9%43%
1495
June1st to 15thNight
11%3244445%6%10%41%
1440
16th to endNight
8%425%6%45%5%5%10%41%
1440
July1st to 15thNight
8%416%6%45%5%7%9%40%
1440
16th to endNight
6%325%5%35%6%6%11%41%
1643
August1st to 15thNight
8%435%5%35%5%6%7%44%
1659
16th to endNight
9%426%5%345%7%8%42%
1910
September1st to 15thNight
13%415%42445%6%47%
1750
16th to endNight
16%6%1433445%7%41%
1787
October1st to 15thNight
17%5%2442434446%
1980
16th to endNight
16%413313446%48%
2112
November1st to 15thNight
15%5%24313335%49%
2258
16th to endNight
15%6%2432445%7%43%
2411
December1st to 15thNight
16%6%344245%5%6%39%
2520
16th to endNight
18%6%25%324346%42%
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
15%5%45%32445%6%41%
1483
16th to endDay
17%5%25%424347%41%
1728
February1st to 15thDay
14%7%25%42445%7%41%
1592
16th to endDay
14%6%24435%45%6%43%
1580
March1st to 15thDay
15%424423446%45%
1911
16th to endDay
17%5%24424346%43%
2165
April1st to 15thDay
13%5%14423447%47%
2152
16th to endDay
14%42442435%7%47%
2160
May1st to 15thDay
14%6%2342345%8%44%
2295
16th to endDay
12%3234235%5%9%45%
2618
June1st to 15thDay
10%323335%6%5%10%45%
2520
16th to endDay
7%313425%5%6%10%47%
2520
July1st to 15thDay
9%424435%46%10%44%
2520
16th to endDay
5%2236%36%7%8%11%43%
2522
August1st to 15thDay
9%5%25%5%3447%9%42%
2289
16th to endDay
9%4145%246%6%8%45%
2292
September1st to 15thDay
12%4244245%47%47%
2098
16th to endDay
16%6%35%5%2445%7%39%
1840
October1st to 15thDay
18%413323446%46%
1650
16th to endDay
15%423422346%50%
1760
November1st to 15thDay
16%413414446%47%
1600
16th to endDay
15%424323447%46%
1548
December1st to 15thDay
15%5%35%42436%7%42%
1440
16th to endDay
18%5%26%433435%40%
1536
January1st to 15thNight
16%5%2442445%7%41%
2452
16th to endNight
17%6%24423445%43%
2496
February1st to 15thNight
14%6%25%423447%44%
2261
16th to endNight
15%6%23314246%46%
1893
March1st to 15thNight
15%5%24424446%44%
2048
16th to endNight
16%7%35%324346%43%
2058
April1st to 15thNight
13%5%26%423347%45%
1796
16th to endNight
15%5%24324346%46%
1800
May1st to 15thNight
14%6%245%245%5%8%38%
1665
16th to endNight
11%5%24445%5%5%8%43%
1495
June1st to 15thNight
10%325%435%5%5%10%41%
1440
16th to endNight
8%426%6%35%45%10%41%
1440
July1st to 15thNight
8%427%6%35%5%7%9%40%
1440
16th to endNight
6%325%5%36%6%7%11%41%
1643
August1st to 15thNight
7%5%26%5%35%5%6%7%44%
1659
16th to endNight
8%435%5%345%7%8%42%
1910
September1st to 15thNight
12%415%4245%47%47%
1750
16th to endNight
16%6%1332445%7%41%
1787
October1st to 15thNight
16%5%245%1433446%
1980
16th to endNight
16%423314346%48%
2112
November1st to 15thNight
15%5%25%313345%49%
2258
16th to endNight
15%6%3432445%7%44%
2411
December1st to 15thNight
16%7%344245%5%6%39%
2520
16th to endNight
17%7%25%324246%42%
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
42%313%22%13%4
1484
16th to endDay
43%29%26%16%3
1728
February1st to 15thDay
42%310%26%15%2
1595
16th to endDay
41%211%26%16%2
1580
March1st to 15thDay
38%312%25%16%3
1911
16th to endDay
41%310%23%17%3
2166
April1st to 15thDay
36%210%26%19%4
2152
16th to endDay
36%310%20%21%7%
2160
May1st to 15thDay
37%415%23%16%2
2295
16th to endDay
34%5%16%28%13%1
2622
June1st to 15thDay
33%5%16%28%14%1
2520
16th to endDay
30%6%16%25%18%2
2520
July1st to 15thDay
36%5%14%24%16%2
2371
16th to endDay
30%7%16%26%16%2
2366
August1st to 15thDay
36%413%26%16%1
2276
16th to endDay
34%5%14%22%18%4
2292
September1st to 15thDay
35%5%12%22%20%3
2098
16th to endDay
44%37%19%22%1
1840
October1st to 15thDay
39%39%27%16%3
1650
16th to endDay
35%27%29%21%3
1760
November1st to 15thDay
37%310%25%19%3
1600
16th to endDay
38%210%27%17%3
1548
December1st to 15thDay
41%313%25%13%3
1440
16th to endDay
46%310%24%13%1
1536
January1st to 15thNight
43%210%22%17%3
2452
16th to endNight
42%29%26%16%2
2496
February1st to 15thNight
41%19%27%17%2
2269
16th to endNight
39%28%25%20%2
1893
March1st to 15thNight
40%310%28%14%3
2048
16th to endNight
42%210%22%18%3
2058
April1st to 15thNight
38%211%21%20%4
1796
16th to endNight
38%310%22%19%6%
1800
May1st to 15thNight
42%5%11%22%15%2
1666
16th to endNight
37%6%16%23%15%1
1497
June1st to 15thNight
37%5%12%27%16%1
1440
16th to endNight
38%5%15%20%17%1
1440
July1st to 15thNight
39%6%16%21%12%3
1360
16th to endNight
31%7%16%29%13%
1536
August1st to 15thNight
36%416%23%18%
1648
16th to endNight
37%414%22%18%2
1910
September1st to 15thNight
35%5%13%22%18%4
1750
16th to endNight
40%48%21%21%3
1787
October1st to 15thNight
42%37%25%17%3
1980
16th to endNight
37%27%28%21%3
2112
November1st to 15thNight
38%28%23%20%6%
2258
16th to endNight
40%29%25%17%4
2411
December1st to 15thNight
43%411%23%13%3
2520
16th to endNight
43%212%24%14%2
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
17%17%39%21%21
69
16th to endDay
22%19%36%16%4
96
February1st to 15thDay
20%17%39%20%2
109
16th to endDay
15%15%38%27%3
239
March1st to 15thDay
17%12%31%31%5%1
270
16th to endDay
19%10%35%21%9%4
288
April1st to 15thDay
17%10%29%24%16%1
270
16th to endDay
18%6%24%26%20%3
270
May1st to 15thDay
25%10%25%20%13%4
288
16th to endDay
19%219%28%18%12%
331
June1st to 15thDay
13%423%26%19%12%
315
16th to endDay
9%221%34%24%7%
315
July1st to 15thDay
10%116%31%28%11%
305
16th to endDay
5%19%30%34%18%
326
August1st to 15thDay
12%115%26%29%14%
313
16th to endDay
9%7%30%31%20%
332
September1st to 15thDay
13%218%23%20%20%
294
16th to endDay
25%215%22%18%15%
254
October1st to 15thDay
18%322%26%20%9%
255
16th to endDay
13%8%28%26%20%1
272
November1st to 15thDay
19%424%26%19%5%
238
16th to endDay
17%15%29%19%14%3
168
December1st to 15thDay
16%20%23%25%10%5%
60
16th to endDay
32%6%35%18%6%
64
January1st to 15thNight
18%14%34%26%6%
720
16th to endNight
21%12%36%27%2
768
February1st to 15thNight
18%15%34%29%1
704
16th to endNight
17%16%37%25%3
631
March1st to 15thNight
18%14%33%27%6%
720
16th to endNight
19%8%33%29%8%1
768
April1st to 15thNight
15%8%40%27%6%
718
16th to endNight
17%6%26%36%11%
720
May1st to 15thNight
17%5%29%33%12%
586
16th to endNight
11%318%41%22%2
375
June1st to 15thNight
9%316%45%23%1
360
16th to endNight
10%114%46%25%1
360
July1st to 15thNight
10%110%45%31%2
340
16th to endNight
6%110%37%38%5%
505
August1st to 15thNight
10%18%42%34%3
578
16th to endNight
11%17%39%35%5%
764
September1st to 15thNight
14%12%34%32%4
700
16th to endNight
19%312%33%27%4
657
October1st to 15thNight
18%5%16%34%21%3
660
16th to endNight
20%10%26%25%15%1
704
November1st to 15thNight
17%7%29%27%15%2
700
16th to endNight
17%14%25%29%10%1
720
December1st to 15thNight
20%12%31%23%11%1
720
16th to endNight
21%11%34%28%3
768
Page generated at 2017-09-11 19:35:27. Version ac04

Copyright 2017 A. Danko


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