Astronight Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astronight 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
28%
14852
18%
46742
8%
14820
39%
14820
20%
30699

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
17%
720
19%
2506
6%
716
33%
716
16%
1615
January16th to endNight
15%
768
18%
2688
4%
768
33%
768
14%
1740
February1st to 15thNight
17%
704
16%
2198
4%
701
31%
701
17%
1489
February16th to endNight
19%
631
22%
1893
7%
631
38%
631
18%
1249
March1st to 15thNight
18%
720
17%
2154
6%
720
32%
720
16%
1498
March16th to endNight
21%
768
22%
2032
7%
768
34%
768
21%
1390
April1st to 15thNight
21%
718
17%
1796
4%
718
29%
718
21%
1269
April16th to endNight
22%
588
17%
1668
4%
588
31%
588
20%
1143
May1st to 15thNight
25%
540
15%
1620
7%
540
32%
540
17%
1131
May16th to endNight
27%
411
11%
1533
7%
410
35%
410
15%
1029
June1st to 15thNight
30%
360
11%
1440
8%
360
42%
360
14%
977
June16th to endNight
36%
360
11%
1440
11%
360
45%
360
21%
898
July1st to 15thNight
45%
340
12%
1360
14%
340
51%
340
21%
825
July16th to endNight
49%
376
15%
1418
15%
354
55%
354
21%
868
August1st to 15thNight
46%
503
16%
1574
12%
501
50%
501
26%
994
August16th to endNight
52%
716
20%
1862
10%
716
55%
716
32%
1216
September1st to 15thNight
38%
700
19%
1808
8%
700
44%
700
33%
1171
September16th to endNight
46%
657
25%
1815
17%
657
54%
657
35%
1096
October1st to 15thNight
33%
660
22%
1842
10%
660
44%
660
25%
1212
October16th to endNight
25%
704
16%
2288
6%
704
39%
704
20%
1494
November1st to 15thNight
32%
700
21%
2277
11%
700
45%
700
22%
1444
November16th to endNight
24%
720
19%
2340
8%
720
38%
720
18%
1514
December1st to 15thNight
21%
720
17%
2502
5%
720
36%
720
16%
1633
December16th to endNight
16%
768
18%
2688
4%
768
32%
768
14%
1804

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
17%5%25%42445%7%39%
47892
Night
17%6%25%424446%41%
46912
Cloud CoverDay
17%6%2443445%6%39%
47902
Night
17%6%25%424446%40%
46917
TransparencyDay
43%6%11%21%14%2
47580
Night
43%5%12%21%15%2
46742
SeeingDay
22%13%31%20%9%2
5861
Night
21%12%33%24%7%
14852

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
17%6%35%435%446%40%
1432
16th to endDay
16%5%24424446%43%
1536
February1st to 15thDay
16%7%25%425%6%5%6%35%
1661
16th to endDay
14%9%35%5%24445%39%
1580
March1st to 15thDay
20%8%35%425%45%6%35%
1795
16th to endDay
18%6%35%5%24346%40%
2190
April1st to 15thDay
18%7%26%424447%38%
2152
16th to endDay
19%425%42435%6%39%
2292
May1st to 15thDay
24%7%25%434445%32%
2332
16th to endDay
17%5%25%43445%7%40%
2590
June1st to 15thDay
25%5%245%25%45%7%32%
2520
16th to endDay
16%425%5%35%5%6%7%35%
2520
July1st to 15thDay
13%5%25%5%35%5%7%9%37%
2520
16th to endDay
12%5%25%5%25%5%6%8%39%
2654
August1st to 15thDay
11%5%25%5%45%5%7%9%37%
2362
16th to endDay
11%414425%5%5%7%45%
2338
September1st to 15thDay
14%4235%2445%6%46%
2040
16th to endDay
14%424333246%50%
1815
October1st to 15thDay
20%42442335%6%40%
1787
16th to endDay
17%5%25%42445%5%42%
1584
November1st to 15thDay
20%6%34322345%43%
1581
16th to endDay
17%5%25%423335%44%
1620
December1st to 15thDay
19%6%25%5%23335%39%
1455
16th to endDay
23%8%24324446%34%
1536
January1st to 15thNight
16%8%35%433345%40%
2506
16th to endNight
15%9%35%423445%40%
2688
February1st to 15thNight
14%9%35%5%2445%6%37%
2197
16th to endNight
16%8%34423437%40%
1893
March1st to 15thNight
18%7%35%335%346%37%
2141
16th to endNight
17%7%3442433344%
2032
April1st to 15thNight
18%7%35%5%24445%38%
1796
16th to endNight
22%5%245%2434440%
1668
May1st to 15thNight
20%6%244345%46%35%
1620
16th to endNight
20%5%25%33445%7%35%
1531
June1st to 15thNight
24%6%24434447%34%
1440
16th to endNight
15%4335%2445%7%40%
1440
July1st to 15thNight
13%5%25%43445%8%41%
1440
16th to endNight
12%6%25%5%25%6%48%40%
1514
August1st to 15thNight
9%425%5%36%5%6%7%43%
1584
16th to endNight
13%31443445%7%45%
1862
September1st to 15thNight
14%5%145%12446%47%
1808
16th to endNight
14%423323336%52%
1815
October1st to 15thNight
19%5%13423345%44%
1842
16th to endNight
19%6%1442345%6%39%
2288
November1st to 15thNight
17%5%25%423445%44%
2277
16th to endNight
18%6%25%424346%41%
2340
December1st to 15thNight
19%6%34423445%39%
2502
16th to endNight
19%7%35%424446%36%
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
17%5%25%4245%45%41%
1432
16th to endDay
16%5%25%42445%6%43%
1536
February1st to 15thDay
17%7%25%435%5%6%6%35%
1661
16th to endDay
14%8%35%5%3345%5%39%
1580
March1st to 15thDay
20%8%25%424445%35%
1805
16th to endDay
19%6%245%24346%39%
2190
April1st to 15thDay
18%7%35%5%24446%37%
2152
16th to endDay
19%4245%34447%39%
2292
May1st to 15thDay
23%8%26%424445%32%
2332
16th to endDay
17%5%34434447%39%
2590
June1st to 15thDay
24%5%2342445%7%32%
2520
16th to endDay
16%426%435%5%6%8%34%
2520
July1st to 15thDay
12%5%26%5%35%5%6%9%37%
2520
16th to endDay
11%5%25%5%36%6%6%8%38%
2654
August1st to 15thDay
11%5%245%45%6%6%9%38%
2362
16th to endDay
11%424435%5%6%7%44%
2338
September1st to 15thDay
14%5%24423446%46%
2040
16th to endDay
14%5%14323345%50%
1815
October1st to 15thDay
20%4235%2435%6%41%
1787
16th to endDay
16%6%25%32435%6%42%
1584
November1st to 15thDay
20%7%23423335%43%
1581
16th to endDay
17%6%24423345%43%
1620
December1st to 15thDay
18%6%25%5%34345%40%
1455
16th to endDay
22%9%34325%345%34%
1536
January1st to 15thNight
16%8%25%5%34345%40%
2506
16th to endNight
15%9%25%423445%40%
2688
February1st to 15thNight
14%9%35%6%2445%6%37%
2190
16th to endNight
17%8%34323345%41%
1893
March1st to 15thNight
19%6%35%435%346%36%
2154
16th to endNight
16%8%3432333444%
2031
April1st to 15thNight
18%7%25%5%33445%38%
1796
16th to endNight
22%425%5%23335%40%
1668
May1st to 15thNight
21%6%25%425%5%5%6%35%
1620
16th to endNight
20%5%25%3245%5%8%35%
1531
June1st to 15thNight
23%7%25%32445%6%34%
1440
16th to endNight
15%425%425%45%8%40%
1440
July1st to 15thNight
12%5%25%5%245%5%8%41%
1440
16th to endNight
12%5%25%446%45%7%39%
1514
August1st to 15thNight
9%4245%35%5%6%6%43%
1584
16th to endNight
12%4145%3445%8%45%
1862
September1st to 15thNight
13%5%24423347%47%
1808
16th to endNight
13%414313346%51%
1815
October1st to 15thNight
19%5%2342334444%
1842
16th to endNight
19%6%2442435%7%39%
2288
November1st to 15thNight
17%5%25%323346%44%
2277
16th to endNight
18%6%35%424346%40%
2340
December1st to 15thNight
19%6%25%424346%38%
2502
16th to endNight
19%8%35%433445%37%
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
44%6%10%23%11%3
1433
16th to endDay
40%5%12%26%13%1
1536
February1st to 15thDay
46%7%13%19%12%1
1664
16th to endDay
45%5%11%20%14%3
1580
March1st to 15thDay
49%5%11%18%11%3
1805
16th to endDay
44%410%20%14%6%
2190
April1st to 15thDay
46%410%18%15%3
2152
16th to endDay
43%5%8%20%18%3
2292
May1st to 15thDay
52%48%17%13%2
2332
16th to endDay
43%7%12%21%12%2
2594
June1st to 15thDay
50%7%12%18%10%1
2520
16th to endDay
44%8%13%18%14%
2520
July1st to 15thDay
40%8%12%22%14%1
2371
16th to endDay
40%8%14%21%12%2
2487
August1st to 15thDay
41%8%14%22%11%1
2348
16th to endDay
34%8%12%26%16%1
2338
September1st to 15thDay
37%6%11%22%20%1
2040
16th to endDay
35%5%7%23%24%2
1815
October1st to 15thDay
44%5%10%22%14%3
1787
16th to endDay
41%6%12%24%13%1
1584
November1st to 15thDay
43%412%23%14%1
1581
16th to endDay
42%5%13%20%16%1
1620
December1st to 15thDay
46%415%16%15%
1455
16th to endDay
50%5%13%18%10%
1536
January1st to 15thNight
45%412%20%13%2
2506
16th to endNight
45%411%20%15%2
2688
February1st to 15thNight
46%6%13%20%11%2
2198
16th to endNight
44%410%22%15%2
1893
March1st to 15thNight
48%5%9%19%13%3
2154
16th to endNight
43%48%17%19%5%
2032
April1st to 15thNight
46%410%17%17%2
1796
16th to endNight
46%410%17%16%4
1668
May1st to 15thNight
48%5%10%17%14%3
1620
16th to endNight
46%8%13%18%11%1
1533
June1st to 15thNight
50%6%12%19%10%
1440
16th to endNight
41%7%13%20%15%1
1440
July1st to 15thNight
39%8%13%24%14%
1360
16th to endNight
40%7%14%25%10%1
1418
August1st to 15thNight
37%8%13%23%15%1
1574
16th to endNight
36%7%11%25%18%
1862
September1st to 15thNight
36%6%13%24%18%
1808
16th to endNight
33%48%24%27%1
1815
October1st to 15thNight
41%5%12%21%15%3
1842
16th to endNight
43%5%13%23%12%
2288
November1st to 15thNight
41%5%11%21%17%2
2277
16th to endNight
44%412%21%14%2
2340
December1st to 15thNight
46%5%14%20%12%
2502
16th to endNight
48%5%12%21%12%
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
21%26%26%21%3
60
16th to endDay
29%21%35%12%
64
February1st to 15thDay
26%18%33%18%3
219
16th to endDay
19%22%35%18%4
239
March1st to 15thDay
27%20%33%14%3
270
16th to endDay
25%20%32%11%7%1
288
April1st to 15thDay
24%18%33%14%9%
270
16th to endDay
24%15%33%17%6%2
270
May1st to 15thDay
34%15%26%13%6%2
288
16th to endDay
21%12%36%24%5%
331
June1st to 15thDay
25%11%35%18%8%
315
16th to endDay
18%14%38%21%42
315
July1st to 15thDay
18%8%30%28%11%1
305
16th to endDay
13%7%31%30%14%2
326
August1st to 15thDay
15%8%30%27%15%3
313
16th to endDay
12%6%30%27%17%6%
332
September1st to 15thDay
20%8%27%22%14%5%
294
16th to endDay
18%8%27%18%13%13%
254
October1st to 15thDay
25%9%21%22%14%5%
254
16th to endDay
20%17%28%25%7%
240
November1st to 15thDay
27%10%31%18%10%2
235
16th to endDay
24%17%28%15%12%1
240
December1st to 15thDay
26%26%30%10%5%
75
16th to endDay
26%25%37%10%
64
January1st to 15thNight
21%18%37%19%2
720
16th to endNight
24%17%36%18%2
768
February1st to 15thNight
20%18%38%21%1
704
16th to endNight
22%19%35%18%4
631
March1st to 15thNight
24%18%35%19%2
720
16th to endNight
21%18%34%19%6%
768
April1st to 15thNight
22%17%36%19%4
718
16th to endNight
23%15%34%19%6%
588
May1st to 15thNight
24%13%32%22%5%
540
16th to endNight
21%9%37%25%5%
411
June1st to 15thNight
23%6%33%27%7%1
360
16th to endNight
17%436%31%8%
360
July1st to 15thNight
12%430%39%11%1
340
16th to endNight
13%228%40%14%
376
August1st to 15thNight
11%430%40%12%
503
16th to endNight
14%324%38%17%1
716
September1st to 15thNight
17%433%28%14%
700
16th to endNight
16%5%25%28%20%3
657
October1st to 15thNight
23%10%27%25%11%1
660
16th to endNight
24%12%32%23%6%
704
November1st to 15thNight
19%12%30%25%10%1
700
16th to endNight
22%16%30%22%6%1
720
December1st to 15thNight
25%15%33%20%3
720
16th to endNight
24%18%36%17%2
768
Page generated at 2017-09-11 19:35:25. Version ac04

Copyright 2017 A. Danko


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