ORAS new observatory site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ORAS new observatory site clear sky chart from 2005-11-05 to 2018-01-20.

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%
15564
14%
48540
9%
15523
37%
15523
17%
35011

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
10%
778
8%
2583
3%
776
16%
776
6%
2169
January16th to endNight
12%
788
8%
2560
3%
788
18%
788
7%
2117
February1st to 15thNight
13%
704
8%
2287
4%
701
19%
701
8%
1894
February16th to endNight
15%
631
9%
1968
3%
631
23%
631
10%
1548
March1st to 15thNight
19%
720
14%
1980
6%
720
26%
720
13%
1565
March16th to endNight
23%
768
18%
2112
8%
768
31%
768
19%
1513
April1st to 15thNight
23%
718
12%
1835
4%
718
29%
718
19%
1370
April16th to endNight
30%
597
18%
1677
7%
597
37%
597
25%
1117
May1st to 15thNight
35%
540
14%
1620
9%
540
41%
540
18%
1149
May16th to endNight
47%
405
17%
1528
15%
405
54%
405
22%
951
June1st to 15thNight
48%
360
15%
1440
14%
360
58%
360
23%
844
June16th to endNight
48%
360
15%
1440
16%
360
55%
360
22%
874
July1st to 15thNight
55%
369
14%
1389
16%
369
59%
369
24%
831
July16th to endNight
66%
564
16%
1595
13%
531
67%
531
33%
960
August1st to 15thNight
64%
539
19%
1609
16%
536
67%
536
33%
967
August16th to endNight
63%
646
21%
1792
15%
646
65%
646
36%
1090
September1st to 15thNight
51%
720
21%
1827
14%
720
54%
720
31%
1210
September16th to endNight
49%
717
24%
1995
19%
717
53%
717
29%
1298
October1st to 15thNight
41%
720
17%
2160
15%
720
45%
720
24%
1423
October16th to endNight
25%
768
14%
2304
8%
768
34%
768
16%
1697
November1st to 15thNight
35%
760
18%
2467
14%
760
43%
760
19%
1672
November16th to endNight
21%
780
12%
2730
8%
780
28%
780
10%
2068
December1st to 15thNight
14%
780
6%
2730
4%
780
17%
780
6%
2234
December16th to endNight
11%
832
6%
2912
2%
832
16%
832
6%
2450

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
18%10%47%6%3445%6%28%
48978
Night
16%10%47%5%34446%31%
48725
Cloud CoverDay
17%10%47%6%3445%6%28%
48988
Night
16%10%47%5%34446%31%
48729
TransparencyDay
55%5%11%17%9%
48681
Night
53%5%11%18%10%1
48540
SeeingDay
24%11%25%20%12%5%
5799
Night
23%12%27%24%11%1
15567

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
19%14%9%10%9%3423417%
1682
16th to endDay
16%17%9%11%10%4433413%
1768
February1st to 15thDay
18%20%7%10%8%4433315%
1575
16th to endDay
17%15%6%10%8%25%345%20%
1503
March1st to 15thDay
20%13%6%9%6%23446%22%
1969
16th to endDay
18%10%5%7%6%34446%28%
2112
April1st to 15thDay
21%14%36%5%22446%29%
2113
16th to endDay
22%9%34423345%35%
2293
May1st to 15thDay
20%9%36%6%25%45%7%28%
2331
16th to endDay
16%6%25%5%36%5%6%7%34%
2587
June1st to 15thDay
17%6%35%5%345%5%7%34%
2520
16th to endDay
16%6%25%6%36%5%6%10%30%
2520
July1st to 15thDay
12%6%25%6%46%5%6%7%34%
2486
16th to endDay
12%6%36%6%37%6%7%9%31%
2465
August1st to 15thDay
12%6%26%6%46%7%6%9%30%
2340
16th to endDay
14%5%25%6%45%6%6%8%35%
2397
September1st to 15thDay
17%9%25%5%34446%35%
2130
16th to endDay
16%6%36%5%34446%38%
1963
October1st to 15thDay
22%8%246%33346%34%
1800
16th to endDay
24%11%36%5%24446%26%
1920
November1st to 15thDay
14%10%37%5%2445%6%34%
1720
16th to endDay
22%16%46%5%34445%23%
1560
December1st to 15thDay
20%20%8%8%5%3443415%
1560
16th to endDay
22%18%7%14%8%3333311%
1664
January1st to 15thNight
21%16%7%12%7%3432316%
2583
16th to endNight
15%17%9%10%6%5%4445%16%
2560
February1st to 15thNight
16%15%6%11%8%5%5%33318%
2285
16th to endNight
17%12%6%11%8%25%445%22%
1968
March1st to 15thNight
20%10%5%8%6%34445%25%
1968
16th to endNight
16%10%46%423446%34%
2112
April1st to 15thNight
20%11%36%424436%31%
1835
16th to endNight
13%8%26%5%24447%39%
1677
May1st to 15thNight
18%7%35%6%335%5%7%33%
1620
16th to endNight
12%6%345%35%45%8%41%
1526
June1st to 15thNight
11%425%42445%9%43%
1440
16th to endNight
10%427%5%35%46%9%39%
1440
July1st to 15thNight
7%6%35%5%36%35%8%44%
1471
16th to endNight
10%3144345%6%8%46%
1703
August1st to 15thNight
8%415%5%235%5%8%47%
1620
16th to endNight
11%313315%45%8%49%
1792
September1st to 15thNight
13%5%2442345%6%45%
1827
16th to endNight
14%6%25%5%33447%43%
1995
October1st to 15thNight
16%6%26%5%24436%41%
2160
16th to endNight
25%8%25%5%24445%29%
2304
November1st to 15thNight
17%9%25%424447%35%
2467
16th to endNight
21%14%47%5%34446%23%
2730
December1st to 15thNight
21%16%7%10%7%2434416%
2730
16th to endNight
21%17%7%10%6%35%345%13%
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
19%14%9%10%8%4433417%
1682
16th to endDay
16%18%8%12%9%45%33313%
1768
February1st to 15thDay
18%19%7%10%7%5%443315%
1575
16th to endDay
17%14%5%10%7%25%34421%
1503
March1st to 15thDay
20%13%6%8%6%24446%21%
1980
16th to endDay
18%10%5%7%6%34446%28%
2111
April1st to 15thDay
21%13%45%5%23346%29%
2113
16th to endDay
22%9%34423345%35%
2293
May1st to 15thDay
19%9%36%5%35%46%6%28%
2331
16th to endDay
16%6%25%5%35%5%6%7%34%
2587
June1st to 15thDay
17%6%35%5%35%45%7%34%
2520
16th to endDay
16%6%246%45%5%7%10%30%
2520
July1st to 15thDay
11%7%36%6%46%5%6%7%34%
2486
16th to endDay
12%6%26%6%37%6%7%8%31%
2465
August1st to 15thDay
12%6%26%6%46%7%6%9%30%
2340
16th to endDay
14%5%26%5%45%5%6%8%35%
2397
September1st to 15thDay
17%9%26%43445%5%35%
2130
16th to endDay
16%6%36%5%34446%38%
1963
October1st to 15thDay
22%8%25%5%33346%34%
1800
16th to endDay
24%10%37%5%2435%5%26%
1920
November1st to 15thDay
14%9%36%5%2445%7%34%
1720
16th to endDay
22%15%47%5%34345%23%
1560
December1st to 15thDay
21%19%9%8%5%34335%15%
1560
16th to endDay
22%18%7%13%8%3333212%
1664
January1st to 15thNight
21%16%7%12%7%3432316%
2583
16th to endNight
15%17%8%10%6%45%43417%
2560
February1st to 15thNight
16%14%6%11%8%5%5%44219%
2278
16th to endNight
17%12%6%11%7%3444422%
1968
March1st to 15thNight
20%11%5%8%6%35%435%25%
1980
16th to endNight
16%10%5%6%423446%34%
2112
April1st to 15thNight
20%11%35%424436%32%
1835
16th to endNight
13%8%26%5%24448%39%
1677
May1st to 15thNight
17%7%35%6%4445%6%33%
1619
16th to endNight
12%5%34435%45%8%41%
1526
June1st to 15thNight
11%5%25%5%2346%9%43%
1440
16th to endNight
10%437%5%35%45%10%39%
1440
July1st to 15thNight
7%6%25%5%35%35%8%44%
1471
16th to endNight
10%4134246%6%8%46%
1703
August1st to 15thNight
8%425%4335%5%9%46%
1620
16th to endNight
11%323325%5%5%9%49%
1792
September1st to 15thNight
13%5%25%42345%6%45%
1827
16th to endNight
14%5%25%5%33347%43%
1995
October1st to 15thNight
16%7%25%5%24446%41%
2160
16th to endNight
24%8%26%5%34446%29%
2304
November1st to 15thNight
17%8%25%434447%35%
2467
16th to endNight
21%14%5%6%5%34346%23%
2730
December1st to 15thNight
21%16%7%9%7%3435%416%
2730
16th to endNight
21%17%7%10%6%35%345%14%
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
72%39%10%4
1683
16th to endDay
75%411%6%1
1768
February1st to 15thDay
73%5%7%9%4
1577
16th to endDay
66%49%13%5%
1503
March1st to 15thDay
63%411%14%5%
1980
16th to endDay
56%49%19%9%
2112
April1st to 15thDay
56%312%16%10%
2113
16th to endDay
50%5%8%17%14%3
2293
May1st to 15thDay
54%5%10%18%9%1
2331
16th to endDay
46%7%15%17%11%1
2591
June1st to 15thDay
47%7%10%23%10%
2520
16th to endDay
46%7%13%20%10%
2520
July1st to 15thDay
47%7%9%20%13%2
2339
16th to endDay
45%8%13%19%12%
2310
August1st to 15thDay
46%8%13%22%8%
2327
16th to endDay
42%7%13%20%13%2
2397
September1st to 15thDay
48%6%9%19%14%1
2130
16th to endDay
46%5%10%23%14%
1963
October1st to 15thDay
51%411%18%13%
1800
16th to endDay
57%5%13%16%6%
1920
November1st to 15thDay
48%5%11%18%12%2
1720
16th to endDay
63%411%14%5%
1560
December1st to 15thDay
72%5%10%9%3
1560
16th to endDay
78%47%7%1
1664
January1st to 15thNight
73%37%10%4
2583
16th to endNight
69%410%10%3
2560
February1st to 15thNight
70%38%12%4
2287
16th to endNight
64%49%16%5%
1968
March1st to 15thNight
60%5%7%17%7%
1980
16th to endNight
50%410%21%11%1
2112
April1st to 15thNight
53%49%18%13%
1835
16th to endNight
42%5%11%21%14%4
1677
May1st to 15thNight
49%7%9%18%12%2
1620
16th to endNight
39%7%14%21%14%1
1528
June1st to 15thNight
36%7%14%26%14%
1440
16th to endNight
39%7%14%20%16%1
1440
July1st to 15thNight
38%6%12%20%20%1
1389
16th to endNight
32%7%15%23%18%3
1595
August1st to 15thNight
32%7%14%28%16%
1609
16th to endNight
30%7%13%28%15%3
1792
September1st to 15thNight
38%6%11%23%18%2
1827
16th to endNight
40%49%26%17%1
1995
October1st to 15thNight
44%5%13%19%16%1
2160
16th to endNight
55%413%17%8%
2304
November1st to 15thNight
47%5%11%19%11%4
2467
16th to endNight
61%49%17%6%
2730
December1st to 15thNight
69%5%10%10%3
2730
16th to endNight
73%411%9%1
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
29%34%23%9%3
120
16th to endDay
38%29%26%4
109
February1st to 15thDay
33%33%31%2
90
16th to endDay
25%19%43%11%
108
March1st to 15thDay
32%18%29%14%4
270
16th to endDay
28%15%32%15%6%2
288
April1st to 15thDay
32%16%23%18%7%1
270
16th to endDay
24%10%30%18%11%4
270
May1st to 15thDay
32%12%23%19%9%2
288
16th to endDay
21%8%30%18%13%7%
331
June1st to 15thDay
21%10%26%27%12%2
315
16th to endDay
22%11%25%24%12%3
315
July1st to 15thDay
16%5%26%28%14%8%
305
16th to endDay
13%322%27%25%8%
326
August1st to 15thDay
17%222%23%22%10%
313
16th to endDay
18%318%28%15%15%
332
September1st to 15thDay
20%5%20%20%20%12%
315
16th to endDay
17%7%17%20%23%13%
314
October1st to 15thDay
26%6%22%25%16%3
315
16th to endDay
31%13%28%16%8%
336
November1st to 15thDay
24%11%26%21%13%2
193
16th to endDay
23%27%33%12%3
90
December1st to 15thDay
40%21%20%12%24
90
16th to endDay
36%23%33%6%
96
January1st to 15thNight
32%20%32%11%3
780
16th to endNight
26%21%34%16%1
788
February1st to 15thNight
29%20%31%17%
704
16th to endNight
26%20%32%18%2
631
March1st to 15thNight
28%16%31%19%4
720
16th to endNight
24%14%34%19%6%
768
April1st to 15thNight
29%13%30%19%6%
718
16th to endNight
19%8%36%25%8%1
597
May1st to 15thNight
23%9%22%33%10%
540
16th to endNight
13%5%28%32%18%2
406
June1st to 15thNight
12%429%37%15%
360
16th to endNight
13%227%35%20%
360
July1st to 15thNight
11%120%44%18%1
369
16th to endNight
11%213%43%26%2
564
August1st to 15thNight
11%116%44%24%2
539
16th to endNight
11%216%32%31%4
646
September1st to 15thNight
17%419%29%25%3
720
16th to endNight
17%5%19%23%25%6%
717
October1st to 15thNight
21%6%25%28%16%2
720
16th to endNight
30%13%26%22%6%
768
November1st to 15thNight
23%10%26%28%10%
760
16th to endNight
31%17%25%18%6%
780
December1st to 15thNight
33%19%26%15%4
780
16th to endNight
30%21%31%14%1
832
Page generated at 2018-01-21 12:19:23. Version ac04

Copyright 2018 A. Danko


ORAS new observatory site Clear Sky Chart |Charts Home