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 2018-01-12.

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
31%
15284
14%
48351
8%
15253
38%
15253
17%
34000

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%
765
11%
2662
5%
761
27%
761
11%
1965
January16th to endNight
19%
768
11%
2664
5%
768
28%
768
12%
1964
February1st to 15thNight
14%
704
8%
2250
2%
701
21%
701
9%
1765
February16th to endNight
21%
631
14%
1893
7%
631
31%
631
13%
1402
March1st to 15thNight
21%
720
14%
2160
9%
720
30%
720
15%
1599
March16th to endNight
25%
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
30%
456
16%
1536
10%
456
38%
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
48%
360
16%
968
June16th to endNight
50%
360
11%
1440
13%
360
56%
360
22%
864
July1st to 15thNight
53%
340
11%
1360
15%
340
57%
340
21%
834
July16th to endNight
56%
376
14%
1418
17%
354
61%
354
23%
847
August1st to 15thNight
53%
449
15%
1520
13%
447
57%
447
26%
923
August16th to endNight
56%
764
17%
1910
10%
764
59%
764
33%
1270
September1st to 15thNight
48%
720
17%
1800
9%
720
51%
720
31%
1219
September16th to endNight
51%
717
24%
1977
17%
717
56%
717
35%
1219
October1st to 15thNight
37%
720
17%
2103
13%
720
44%
720
21%
1476
October16th to endNight
28%
768
12%
2439
7%
768
36%
768
15%
1782
November1st to 15thNight
28%
760
15%
2472
9%
760
36%
760
17%
1717
November16th to endNight
28%
780
16%
2643
9%
780
37%
780
16%
1822
December1st to 15thNight
20%
780
9%
2730
4%
780
27%
780
10%
2066
December16th to endNight
19%
832
10%
2912
4%
832
25%
832
10%
2246

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%45%7%35%
48992
Night
17%7%36%5%3445%6%36%
48521
Cloud CoverDay
16%7%36%5%35%45%7%34%
49001
Night
17%7%36%5%34446%35%
48527
TransparencyDay
48%7%12%19%10%1
48680
Night
49%7%12%19%10%1
48351
SeeingDay
20%13%27%22%11%4
6023
Night
21%12%28%27%9%
15285

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%11%47%6%35%6%5%5%28%
1520
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%42%
2160
16th to endDay
13%5%13423446%51%
1983
October1st to 15thDay
19%7%26%6%24335%37%
1854
16th to endDay
20%6%27%5%25%45%6%31%
1785
November1st to 15thDay
16%7%25%5%4335%6%38%
1716
16th to endDay
17%7%35%5%35%347%35%
1644
December1st to 15thDay
19%10%5%7%5%34446%28%
1560
16th to endDay
21%14%49%6%24345%24%
1664
January1st to 15thNight
15%12%47%5%24446%31%
2662
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%42442445%6%45%
1800
16th to endNight
11%3125%25%347%51%
1977
October1st to 15thNight
20%5%26%6%23445%39%
2103
16th to endNight
20%6%25%5%245%5%6%33%
2439
November1st to 15thNight
15%8%36%5%34345%38%
2472
16th to endNight
18%6%35%5%35%435%38%
2643
December1st to 15thNight
21%9%46%5%3445%5%29%
2730
16th to endNight
22%11%36%5%34446%27%
2912

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%11%37%6%35%5%6%5%27%
1520
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%43%
2160
16th to endDay
14%413323346%51%
1983
October1st to 15thDay
19%8%25%6%34345%37%
1854
16th to endDay
21%7%36%5%3445%5%31%
1785
November1st to 15thDay
16%6%36%5%34346%38%
1716
16th to endDay
17%8%35%435%35%6%35%
1644
December1st to 15thDay
20%10%6%7%5%3445%6%27%
1560
16th to endDay
22%13%5%8%6%34335%23%
1664
January1st to 15thNight
16%12%5%6%5%34446%29%
2662
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
16%5%24423446%45%
1800
16th to endNight
11%413434447%51%
1977
October1st to 15thNight
20%5%26%5%2334439%
2103
16th to endNight
21%7%35%5%3445%6%32%
2439
November1st to 15thNight
16%8%46%5%345%4437%
2472
16th to endNight
18%7%36%5%35%335%37%
2643
December1st to 15thNight
22%11%45%5%3445%6%28%
2730
16th to endNight
23%12%47%42434426%
2912

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
55%9%10%16%6%
1521
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
40%7%13%23%14%
2160
16th to endDay
34%5%10%30%17%
1983
October1st to 15thDay
50%6%9%21%10%1
1854
16th to endDay
53%7%13%17%6%
1785
November1st to 15thDay
46%7%14%19%10%1
1716
16th to endDay
49%6%15%17%10%
1644
December1st to 15thDay
58%8%13%13%5%
1560
16th to endDay
64%6%10%11%6%
1664
January1st to 15thNight
55%7%13%13%8%
2662
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%14%
1800
16th to endNight
32%6%11%27%20%1
1977
October1st to 15thNight
48%5%10%20%13%1
2103
16th to endNight
52%7%14%17%7%
2439
November1st to 15thNight
49%6%12%17%11%2
2472
16th to endNight
49%6%14%21%8%
2643
December1st to 15thNight
57%7%14%14%4
2730
16th to endNight
61%6%12%12%6%
2912

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
18%30%25%15%8%1
82
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%10%21%25%18%9%
315
16th to endDay
16%5%26%16%17%16%
314
October1st to 15thDay
23%8%21%23%17%5%
315
16th to endDay
23%15%26%27%6%
302
November1st to 15thDay
23%11%25%27%11%
280
16th to endDay
25%17%24%22%8%1
174
December1st to 15thDay
21%26%30%13%7%1
90
16th to endDay
28%29%31%10%1
96
January1st to 15thNight
23%17%33%22%2
765
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%21%34%17%1
720
16th to endNight
13%426%28%20%6%
717
October1st to 15thNight
24%8%21%30%15%
720
16th to endNight
27%12%26%28%5%
768
November1st to 15thNight
20%12%31%26%7%
760
16th to endNight
22%14%30%22%8%1
780
December1st to 15thNight
29%15%29%21%4
780
16th to endNight
29%14%32%20%2
832
Page generated at 2018-01-12 22:01:36. Version ac04

Copyright 2018 A. Danko


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