3 Angels Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the 3 Angels Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
58%
15104
23%
47104
19%
15060
63%
15060
31%
28080

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
40%
720
26%
2148
14%
716
51%
716
29%
1309
January16th to endNight
35%
768
26%
2304
14%
768
44%
768
25%
1485
February1st to 15thNight
39%
704
28%
2109
13%
700
51%
700
33%
1251
February16th to endNight
34%
631
23%
1893
12%
631
42%
631
25%
1224
March1st to 15thNight
41%
720
23%
2160
14%
720
48%
720
27%
1360
March16th to endNight
53%
588
26%
1989
22%
588
59%
588
32%
1096
April1st to 15thNight
50%
539
25%
1797
21%
539
58%
539
30%
1046
April16th to endNight
58%
540
28%
1800
26%
540
66%
540
39%
936
May1st to 15thNight
66%
539
21%
1799
20%
539
71%
539
33%
1022
May16th to endNight
73%
561
22%
1722
22%
561
75%
561
35%
979
June1st to 15thNight
78%
540
12%
1620
13%
540
78%
540
32%
980
June16th to endNight
76%
540
16%
1620
17%
540
77%
540
30%
1012
July1st to 15thNight
81%
510
12%
1642
13%
510
81%
510
29%
1006
July16th to endNight
80%
564
10%
1772
13%
531
80%
531
26%
1130
August1st to 15thNight
84%
539
12%
1788
14%
536
84%
536
32%
1057
August16th to endNight
72%
573
14%
1910
17%
573
72%
573
23%
1248
September1st to 15thNight
72%
567
19%
1827
20%
567
73%
567
28%
1123
September16th to endNight
70%
689
26%
1903
22%
689
71%
689
34%
1182
October1st to 15thNight
70%
660
33%
1815
26%
660
74%
660
48%
966
October16th to endNight
60%
704
34%
2101
28%
704
66%
704
43%
1118
November1st to 15thNight
59%
700
32%
2223
28%
700
66%
700
36%
1225
November16th to endNight
52%
720
31%
2340
25%
720
62%
720
35%
1277
December1st to 15thNight
45%
720
25%
2340
20%
720
52%
720
27%
1408
December16th to endNight
36%
768
20%
2482
13%
768
43%
768
21%
1640

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
10%5%25%5%35%5%6%8%39%
47762
Night
9%42442445%8%47%
47330
TransparencyDay
38%8%12%18%16%6%
47487
Night
33%7%13%18%18%8%
47110
SeeingDay
11%314%23%26%18%
5066
Night
11%418%28%27%8%
15107

By Month

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
11%5%345%24447%44%
1790
16th to endDay
18%5%2443333445%
1920
February1st to 15thDay
13%5%24424347%48%
1750
16th to endDay
15%6%25%433446%42%
1580
March1st to 15thDay
15%5%245%25%45%7%42%
1800
16th to endDay
11%5%25%42445%7%45%
2242
April1st to 15thDay
11%4245%345%5%8%43%
2151
16th to endDay
10%42442447%9%46%
2160
May1st to 15thDay
10%4235%36%5%7%9%41%
2151
16th to endDay
8%425%6%36%5%7%9%40%
2388
June1st to 15thDay
8%5%25%6%47%7%9%12%30%
2340
16th to endDay
7%5%36%7%5%7%7%10%11%28%
2340
July1st to 15thDay
6%7%47%8%39%7%9%12%23%
2214
16th to endDay
8%6%37%8%48%8%8%10%23%
2276
August1st to 15thDay
7%5%37%8%5%8%9%10%11%22%
2160
16th to endDay
10%6%28%7%47%7%7%9%27%
2292
September1st to 15thDay
9%5%36%7%37%6%8%9%32%
2121
16th to endDay
7%5%25%7%45%6%6%6%42%
1894
October1st to 15thDay
6%414424447%53%
1815
16th to endDay
7%41342445%7%54%
1768
November1st to 15thDay
9%414314346%56%
1632
16th to endDay
8%4145%24445%55%
1620
December1st to 15thDay
12%6%35%5%23346%45%
1620
16th to endDay
19%6%36%5%3435%6%35%
1738
January1st to 15thNight
12%5%24424347%47%
2148
16th to endNight
19%5%24423335%44%
2304
February1st to 15thNight
13%41332335%6%50%
2103
16th to endNight
16%6%245%24436%43%
1893
March1st to 15thNight
13%6%245%25%35%7%43%
2160
16th to endNight
11%413314347%52%
1989
April1st to 15thNight
11%414425%45%6%49%
1797
16th to endNight
7%21342345%7%56%
1800
May1st to 15thNight
7%42343445%10%49%
1799
16th to endNight
5%414425%46%11%48%
1722
June1st to 15thNight
5%414435%6%8%13%41%
1620
16th to endNight
6%3245%35%5%8%13%41%
1620
July1st to 15thNight
43245%35%7%10%12%41%
1742
16th to endNight
33246%37%7%9%14%37%
1892
August1st to 15thNight
23234348%10%16%39%
1800
16th to endNight
6%425%7%36%7%7%10%39%
1910
September1st to 15thNight
5%5%15%6%35%7%8%12%39%
1827
16th to endNight
7%5%25%43445%8%48%
1903
October1st to 15thNight
5%313322348%61%
1815
16th to endNight
9%313312335%61%
2101
November1st to 15thNight
8%324423446%55%
2223
16th to endNight
8%324424445%55%
2340
December1st to 15thNight
12%5%25%42445%6%46%
2340
16th to endNight
17%7%35%5%33445%38%
2482

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
37%47%16%22%10%
1791
16th to endDay
42%3417%22%9%
1920
February1st to 15thDay
36%410%15%22%11%
1752
16th to endDay
40%5%6%18%21%8%
1580
March1st to 15thDay
40%48%20%18%7%
1800
16th to endDay
36%6%10%19%19%7%
2244
April1st to 15thDay
35%6%9%20%19%8%
2151
16th to endDay
31%7%11%23%19%6%
2160
May1st to 15thDay
35%9%10%20%16%7%
2151
16th to endDay
34%9%14%23%16%2
2392
June1st to 15thDay
39%11%16%21%9%
2340
16th to endDay
41%11%18%18%8%
2340
July1st to 15thDay
45%16%18%14%4
2085
16th to endDay
46%15%18%16%2
2133
August1st to 15thDay
45%16%20%11%6%
2148
16th to endDay
47%13%15%15%6%1
2292
September1st to 15thDay
40%11%16%15%11%4
2121
16th to endDay
38%8%12%18%15%6%
1894
October1st to 15thDay
28%5%10%15%25%14%
1815
16th to endDay
27%47%14%28%18%
1768
November1st to 15thDay
28%47%18%29%11%
1632
16th to endDay
29%5%6%16%25%15%
1620
December1st to 15thDay
39%47%21%20%6%
1620
16th to endDay
50%47%17%16%4
1738
January1st to 15thNight
36%47%15%24%10%
2148
16th to endNight
42%35%13%23%10%
2304
February1st to 15thNight
34%46%18%21%13%
2112
16th to endNight
42%5%6%13%20%11%
1893
March1st to 15thNight
40%49%16%22%6%
2160
16th to endNight
31%411%21%22%8%
1989
April1st to 15thNight
33%6%10%19%20%10%
1797
16th to endNight
24%6%12%26%22%7%
1800
May1st to 15thNight
30%6%12%22%21%6%
1800
16th to endNight
28%7%17%24%19%2
1724
June1st to 15thNight
30%10%24%23%10%
1620
16th to endNight
30%12%21%24%9%
1620
July1st to 15thNight
28%14%30%20%5%
1642
16th to endNight
31%14%30%20%2
1772
August1st to 15thNight
25%14%35%19%4
1788
16th to endNight
37%12%25%15%6%3
1910
September1st to 15thNight
33%10%21%16%12%5%
1827
16th to endNight
32%8%16%19%16%7%
1903
October1st to 15thNight
22%411%20%23%17%
1815
16th to endNight
26%27%14%25%22%
2101
November1st to 15thNight
29%46%17%29%12%
2223
16th to endNight
29%46%18%21%18%
2340
December1st to 15thNight
36%5%9%20%21%6%
2340
16th to endNight
46%47%19%15%6%
2482

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
13%15%30%28%10%2
90
16th to endDay
19%22%32%19%5%
96
February1st to 15thDay
12%15%35%24%10%2
90
16th to endDay
8%12%44%25%8%
81
March1st to 15thDay
21%6%50%20%11
90
16th to endDay
13%9%25%30%19%1
231
April1st to 15thDay
17%8%25%27%20%2
270
16th to endDay
11%222%32%25%4
270
May1st to 15thDay
8%422%27%27%9%
288
16th to endDay
13%210%29%26%16%
331
June1st to 15thDay
15%6%23%26%26%
315
16th to endDay
13%5%19%31%29%
315
July1st to 15thDay
9%213%33%40%
305
16th to endDay
8%216%37%34%
326
August1st to 15thDay
8%15%13%35%35%
313
16th to endDay
10%6%14%36%31%
332
September1st to 15thDay
7%11%21%31%26%
315
16th to endDay
10%1426%34%21%
283
October1st to 15thDay
5%116%29%38%10%
255
16th to endDay
11%314%38%19%12%
104
November1st to 15thDay
18%421%34%17%3
90
16th to endDay
6%14%30%31%13%4
90
December1st to 15thDay
15%8%33%33%7%1
90
16th to endDay
26%11%25%22%12%2
96
January1st to 15thNight
15%9%30%35%8%
720
16th to endNight
19%10%28%32%8%
768
February1st to 15thNight
16%7%33%31%10%
704
16th to endNight
18%9%32%31%7%
631
March1st to 15thNight
15%10%28%33%11%
720
16th to endNight
13%5%24%33%22%1
588
April1st to 15thNight
12%6%26%34%19%1
539
16th to endNight
8%324%35%25%2
540
May1st to 15thNight
9%214%40%29%3
540
16th to endNight
7%19%32%41%7%
563
June1st to 15thNight
8%5%24%48%12%
540
16th to endNight
7%317%48%22%
540
July1st to 15thNight
5%210%50%30%
510
16th to endNight
5%1112%44%34%
564
August1st to 15thNight
427%50%35%
539
16th to endNight
9%313%47%24%
573
September1st to 15thNight
7%17%17%42%22%
567
16th to endNight
10%7%29%44%7%
689
October1st to 15thNight
6%115%35%35%5%
660
16th to endNight
11%320%31%27%5%
704
November1st to 15thNight
8%5%20%38%22%4
700
16th to endNight
10%5%27%36%18%1
720
December1st to 15thNight
14%8%25%31%17%1
720
16th to endNight
20%7%29%28%13%
768
Page generated at 2017-09-24 08:15:57. Version ac04

Copyright 2017 A. Danko


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