Averted Vision Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Averted Vision 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
31%
14791
14%
46769
8%
14760
38%
14760
17%
32957

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
19%
720
11%
2506
5%
716
27%
716
11%
1863
January16th to endNight
19%
768
11%
2664
5%
768
28%
768
12%
1964
February1st to 15thNight
14%
704
8%
2250
2%
701
22%
701
9%
1765
February16th to endNight
20%
631
14%
1893
7%
631
30%
631
13%
1402
March1st to 15thNight
21%
720
14%
2160
9%
720
30%
720
15%
1599
March16th to endNight
24%
768
19%
1995
7%
768
33%
768
19%
1438
April1st to 15thNight
23%
718
14%
1796
4%
718
29%
718
19%
1330
April16th to endNight
28%
654
17%
1734
5%
654
35%
654
21%
1222
May1st to 15thNight
29%
456
16%
1536
10%
456
37%
456
17%
1066
May16th to endNight
40%
374
12%
1497
11%
374
46%
374
16%
996
June1st to 15thNight
38%
360
11%
1440
10%
360
47%
360
16%
968
June16th to endNight
51%
360
11%
1440
13%
360
57%
360
22%
864
July1st to 15thNight
53%
340
11%
1360
15%
340
57%
340
21%
834
July16th to endNight
57%
376
14%
1418
17%
354
62%
354
23%
847
August1st to 15thNight
54%
449
15%
1520
13%
447
58%
447
26%
923
August16th to endNight
56%
764
17%
1910
10%
764
59%
764
33%
1270
September1st to 15thNight
47%
700
17%
1750
9%
700
49%
700
30%
1189
September16th to endNight
49%
657
22%
1812
15%
657
53%
657
33%
1132
October1st to 15thNight
37%
660
18%
1928
13%
660
44%
660
20%
1365
October16th to endNight
28%
704
11%
2236
6%
704
35%
704
15%
1643
November1st to 15thNight
29%
700
15%
2277
10%
700
37%
700
17%
1577
November16th to endNight
27%
720
15%
2439
9%
720
36%
720
16%
1707
December1st to 15thNight
20%
720
8%
2520
4%
720
26%
720
10%
1904
December16th to endNight
19%
768
9%
2688
4%
768
25%
768
10%
2089

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
16%7%36%5%35%5%5%7%34%
47865
Night
17%7%36%5%3445%6%36%
46939
Cloud CoverDay
16%7%36%5%35%45%7%34%
47874
Night
17%8%36%5%34446%35%
46945
TransparencyDay
48%7%12%18%10%1
47553
Night
49%7%12%19%10%1
46769
SeeingDay
20%12%27%22%11%3
5664
Night
22%12%28%27%8%
14792

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%11%47%6%36%6%5%5%27%
1432
16th to endDay
12%9%47%6%46%5%6%7%29%
1557
February1st to 15thDay
12%13%5%9%6%45%5%5%5%26%
1609
16th to endDay
16%11%47%7%35%34430%
1580
March1st to 15thDay
18%9%46%5%44446%31%
1790
16th to endDay
16%8%36%5%2433439%
2228
April1st to 15thDay
19%6%36%435%345%36%
2152
16th to endDay
16%6%26%5%345%5%5%37%
2225
May1st to 15thDay
21%6%35%5%24446%33%
2426
16th to endDay
16%5%35%5%35%5%5%7%35%
2618
June1st to 15thDay
19%6%35%6%25%5%5%8%31%
2520
16th to endDay
15%5%25%5%36%6%7%9%31%
2520
July1st to 15thDay
11%5%25%6%45%7%6%9%35%
2520
16th to endDay
12%5%25%5%35%6%7%8%35%
2654
August1st to 15thDay
12%5%16%6%35%6%6%8%36%
2415
16th to endDay
11%425%5%35%45%8%43%
2292
September1st to 15thDay
15%423435%447%41%
2098
16th to endDay
14%5%13423446%49%
1818
October1st to 15thDay
19%7%37%7%24345%35%
1700
16th to endDay
20%7%27%6%25%45%6%30%
1636
November1st to 15thDay
16%6%25%5%4435%6%38%
1581
16th to endDay
17%7%35%5%35%447%35%
1518
December1st to 15thDay
19%10%5%7%5%34445%27%
1440
16th to endDay
21%14%48%6%24345%23%
1536
January1st to 15thNight
16%12%47%5%24446%30%
2506
16th to endNight
12%11%5%8%5%3445%6%31%
2664
February1st to 15thNight
12%10%5%8%8%46%45%6%26%
2249
16th to endNight
15%9%28%6%25%45%6%32%
1893
March1st to 15thNight
19%7%36%5%3444434%
2147
16th to endNight
16%8%35%424345%40%
1995
April1st to 15thNight
19%6%35%5%35%35%5%36%
1796
16th to endNight
19%6%25%423345%41%
1734
May1st to 15thNight
21%7%36%423345%36%
1536
16th to endNight
18%435%435%45%6%37%
1495
June1st to 15thNight
23%324445%46%6%33%
1440
16th to endNight
14%3144246%6%9%42%
1440
July1st to 15thNight
11%4245%36%36%10%40%
1440
16th to endNight
12%4244246%6%8%43%
1514
August1st to 15thNight
11%5%144345%6%8%45%
1530
16th to endNight
14%4133245%6%7%45%
1910
September1st to 15thNight
15%5%2442445%6%45%
1750
16th to endNight
12%4135%25%347%50%
1812
October1st to 15thNight
21%5%26%6%23445%37%
1928
16th to endNight
21%6%25%5%345%5%6%32%
2236
November1st to 15thNight
15%8%36%5%34345%38%
2277
16th to endNight
19%7%35%5%35%435%36%
2439
December1st to 15thNight
22%9%45%5%3445%5%29%
2520
16th to endNight
22%12%46%5%34446%26%
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%11%37%6%35%5%6%5%26%
1432
16th to endDay
12%10%48%7%45%5%5%8%27%
1557
February1st to 15thDay
13%13%5%9%6%45%5%46%24%
1609
16th to endDay
17%11%47%7%44335%29%
1580
March1st to 15thDay
18%10%47%5%35%445%30%
1800
16th to endDay
18%7%45%5%23335%39%
2227
April1st to 15thDay
19%7%36%435%436%35%
2152
16th to endDay
16%6%35%5%25%45%5%38%
2225
May1st to 15thDay
20%7%36%5%245%46%32%
2426
16th to endDay
16%6%25%5%35%45%8%36%
2618
June1st to 15thDay
20%6%26%5%35%45%8%31%
2520
16th to endDay
15%5%25%5%36%6%6%10%31%
2520
July1st to 15thDay
11%5%245%36%6%7%9%36%
2520
16th to endDay
12%425%6%35%6%7%9%35%
2654
August1st to 15thDay
12%5%25%5%46%6%6%8%36%
2415
16th to endDay
11%425%5%35%5%6%7%43%
2292
September1st to 15thDay
15%5%345%3445%7%42%
2098
16th to endDay
15%413323347%50%
1818
October1st to 15thDay
19%8%26%6%34345%36%
1700
16th to endDay
21%8%36%5%3445%5%30%
1636
November1st to 15thDay
16%6%36%5%34346%38%
1581
16th to endDay
18%8%35%435%45%6%35%
1518
December1st to 15thDay
20%10%6%7%5%3445%6%26%
1440
16th to endDay
23%14%5%7%6%34335%22%
1536
January1st to 15thNight
17%13%5%6%5%34446%29%
2506
16th to endNight
13%12%5%7%6%34447%29%
2664
February1st to 15thNight
12%11%5%10%6%45%45%7%25%
2242
16th to endNight
15%10%47%5%35%35%6%31%
1893
March1st to 15thNight
20%9%36%5%2443433%
2160
16th to endNight
17%7%46%433336%39%
1995
April1st to 15thNight
20%6%36%5%2435%6%34%
1796
16th to endNight
19%6%24424345%40%
1734
May1st to 15thNight
22%6%36%433336%35%
1536
16th to endNight
17%6%35%5%35%5%5%6%36%
1495
June1st to 15thNight
22%424435%5%5%8%32%
1440
16th to endNight
15%313435%5%410%43%
1440
July1st to 15thNight
11%425%5%35%5%6%10%39%
1440
16th to endNight
12%4145%245%6%9%42%
1514
August1st to 15thNight
11%5%2443446%9%44%
1530
16th to endNight
13%423335%45%7%44%
1910
September1st to 15thNight
17%5%24423446%44%
1750
16th to endNight
12%413434447%49%
1812
October1st to 15thNight
21%5%26%5%3434438%
1928
16th to endNight
21%7%35%5%3445%6%31%
2236
November1st to 15thNight
16%8%46%5%3444437%
2277
16th to endNight
19%7%36%5%25%335%36%
2439
December1st to 15thNight
23%10%45%5%3445%5%28%
2520
16th to endNight
23%12%46%42434426%
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
56%9%10%16%6%
1433
16th to endDay
55%8%13%14%6%
1557
February1st to 15thDay
61%7%10%14%5%
1612
16th to endDay
59%5%10%13%10%
1580
March1st to 15thDay
55%6%12%15%9%1
1800
16th to endDay
48%5%9%15%15%3
2228
April1st to 15thDay
51%6%9%19%12%2
2152
16th to endDay
46%7%9%20%13%3
2225
May1st to 15thDay
52%6%8%17%12%1
2426
16th to endDay
45%8%14%18%11%1
2622
June1st to 15thDay
51%8%14%16%8%
2520
16th to endDay
48%9%13%17%11%
2520
July1st to 15thDay
40%10%15%22%10%
2371
16th to endDay
41%9%16%22%9%
2487
August1st to 15thDay
41%10%16%21%8%
2401
16th to endDay
37%8%15%25%13%
2292
September1st to 15thDay
41%7%13%24%13%
2098
16th to endDay
35%6%11%29%16%
1818
October1st to 15thDay
52%6%9%20%9%1
1700
16th to endDay
54%7%13%15%6%
1636
November1st to 15thDay
45%8%14%20%10%1
1581
16th to endDay
50%6%14%17%10%
1518
December1st to 15thDay
58%8%13%13%5%
1440
16th to endDay
64%6%11%11%5%
1536
January1st to 15thNight
56%7%13%13%8%
2506
16th to endNight
55%7%10%16%8%1
2664
February1st to 15thNight
59%9%11%13%5%
2250
16th to endNight
54%6%11%18%7%1
1893
March1st to 15thNight
53%7%9%19%8%1
2160
16th to endNight
47%6%9%16%14%4
1995
April1st to 15thNight
50%5%11%18%12%1
1796
16th to endNight
45%6%8%19%15%3
1734
May1st to 15thNight
51%49%17%15%2
1536
16th to endNight
47%7%13%17%11%1
1497
June1st to 15thNight
49%6%14%19%9%
1440
16th to endNight
36%9%17%23%12%
1440
July1st to 15thNight
38%8%14%24%12%
1360
16th to endNight
36%9%15%25%11%1
1418
August1st to 15thNight
35%8%18%24%12%
1520
16th to endNight
36%7%15%26%13%
1910
September1st to 15thNight
40%5%12%26%13%
1750
16th to endNight
34%6%10%26%20%1
1812
October1st to 15thNight
49%6%9%19%13%1
1928
16th to endNight
53%7%14%16%7%
2236
November1st to 15thNight
49%6%12%16%12%2
2277
16th to endNight
51%6%13%20%7%
2439
December1st to 15thNight
57%7%14%15%4
2520
16th to endNight
62%6%12%12%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
23%31%21%13%8%1
60
16th to endDay
34%23%29%5%5%
67
February1st to 15thDay
24%26%33%11%3
126
16th to endDay
22%21%29%21%4
239
March1st to 15thDay
26%16%30%22%4
270
16th to endDay
26%19%25%16%10%2
288
April1st to 15thDay
27%15%28%18%8%1
270
16th to endDay
20%17%30%18%9%4
270
May1st to 15thDay
30%13%22%18%11%2
288
16th to endDay
18%12%32%22%10%3
331
June1st to 15thDay
21%11%30%24%11%1
315
16th to endDay
17%12%33%23%10%2
315
July1st to 15thDay
13%8%30%29%14%3
305
16th to endDay
14%433%31%13%3
326
August1st to 15thDay
15%6%28%23%20%6%
313
16th to endDay
13%5%20%29%19%11%
332
September1st to 15thDay
14%11%21%24%18%9%
294
16th to endDay
18%5%28%16%16%14%
254
October1st to 15thDay
25%9%18%24%16%5%
255
16th to endDay
22%16%26%28%5%
249
November1st to 15thDay
22%10%26%28%11%
235
16th to endDay
24%15%23%25%8%1
138
December1st to 15thDay
18%31%28%13%6%1
60
16th to endDay
28%29%32%7%1
64
January1st to 15thNight
24%17%32%22%3
720
16th to endNight
21%17%35%22%2
768
February1st to 15thNight
20%17%39%21%1
704
16th to endNight
22%19%31%21%4
631
March1st to 15thNight
26%17%30%22%2
720
16th to endNight
21%17%30%22%7%
768
April1st to 15thNight
23%18%30%22%4
718
16th to endNight
23%17%27%22%7%
654
May1st to 15thNight
23%11%28%27%8%
456
16th to endNight
17%8%30%29%13%
375
June1st to 15thNight
23%6%26%32%10%
360
16th to endNight
15%227%41%13%
360
July1st to 15thNight
14%321%43%15%1
340
16th to endNight
14%219%44%18%
376
August1st to 15thNight
14%223%42%15%1
449
16th to endNight
15%318%34%25%2
764
September1st to 15thNight
19%5%22%34%17%1
700
16th to endNight
14%428%28%19%5%
657
October1st to 15thNight
24%8%21%29%14%
660
16th to endNight
28%11%26%28%4
704
November1st to 15thNight
20%12%31%27%6%1
700
16th to endNight
23%14%29%22%8%1
720
December1st to 15thNight
29%15%29%20%4
720
16th to endNight
30%14%32%20%2
768
Page generated at 2017-09-11 19:35:31. Version ac04

Copyright 2017 A. Danko


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