RISS Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the RISS Observatory clear sky chart from 2005-11-05 to 2018-02-13.

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
74%
16106
35%
48727
30%
16068
80%
16068
53%
23195

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
75%
776
33%
2522
34%
776
79%
776
54%
1132
January16th to endNight
66%
832
37%
2704
33%
832
76%
832
46%
1306
February1st to 15thNight
71%
745
37%
2370
35%
744
81%
744
57%
1046
February16th to endNight
62%
632
41%
1796
32%
632
72%
632
55%
883
March1st to 15thNight
66%
720
42%
1980
32%
720
75%
720
61%
946
March16th to endNight
70%
768
39%
2112
27%
768
79%
768
61%
1000
April1st to 15thNight
67%
665
37%
1924
26%
665
76%
665
59%
887
April16th to endNight
66%
540
44%
1800
35%
540
80%
540
67%
682
May1st to 15thNight
71%
539
38%
1671
30%
539
80%
539
69%
667
May16th to endNight
78%
562
43%
1684
36%
561
84%
561
74%
662
June1st to 15thNight
84%
540
35%
1620
30%
540
85%
540
67%
678
June16th to endNight
85%
540
29%
1620
27%
540
86%
540
53%
774
July1st to 15thNight
80%
510
14%
1530
12%
510
80%
510
33%
893
July16th to endNight
76%
564
12%
1593
10%
531
76%
531
24%
1055
August1st to 15thNight
81%
539
19%
1611
18%
536
81%
536
33%
960
August16th to endNight
81%
573
26%
1892
26%
573
81%
573
34%
1056
September1st to 15thNight
76%
705
24%
1965
21%
705
77%
705
36%
1199
September16th to endNight
86%
716
41%
1980
34%
716
89%
716
63%
937
October1st to 15thNight
80%
720
38%
2112
31%
720
85%
720
67%
920
October16th to endNight
84%
768
44%
2304
39%
768
88%
768
69%
973
November1st to 15thNight
81%
760
42%
2280
36%
760
85%
760
69%
952
November16th to endNight
70%
780
42%
2418
37%
780
76%
780
54%
1127
December1st to 15thNight
70%
780
37%
2535
36%
780
75%
780
49%
1169
December16th to endNight
65%
832
37%
2704
36%
832
71%
832
47%
1291

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
221342445%6%61%
49304
Night
221232345%6%66%
48930
TransparencyDay
21%46%12%27%27%
48999
Night
18%37%15%29%25%
48736
SeeingDay
5%7%18%29%27%12%
5837
Night
3213%38%35%6%
16119

By Month

Percentage Cloud Cover SW (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
122333445%6%62%
1746
16th to endDay
231432245%5%62%
1872
February1st to 15thDay
2213322235%69%
1749
16th to endDay
2314413345%66%
1677
March1st to 15thDay
121232345%6%67%
1980
16th to endDay
1212213235%71%
2112
April1st to 15thDay
1112213345%71%
2024
16th to endDay
11111122381%
2160
May1st to 15thDay
12212225%78%
2276
16th to endDay
1111222480%
2429
June1st to 15thDay
111212235%76%
2340
16th to endDay
2213435%45%6%60%
2340
July1st to 15thDay
5%335%7%5%8%8%9%9%33%
2340
16th to endDay
7%6%47%9%6%8%8%8%10%22%
2467
August1st to 15thDay
6%5%36%8%5%7%8%7%9%31%
2340
16th to endDay
3315%7%5%7%8%8%10%38%
2309
September1st to 15thDay
7%425%7%45%6%6%7%40%
1992
16th to endDay
3113423345%64%
1980
October1st to 15thDay
1112324336%71%
1846
16th to endDay
11222224476%
1920
November1st to 15thDay
111212347%73%
1909
16th to endDay
2212212335%71%
1869
December1st to 15thDay
3212323446%63%
1755
16th to endDay
231422335%7%63%
1872
January1st to 15thNight
221332335%6%67%
2522
16th to endNight
3313423446%62%
2704
February1st to 15thNight
211231235%6%69%
2366
16th to endNight
1112324445%67%
1796
March1st to 15thNight
1112312446%69%
1980
16th to endNight
1212213335%72%
2112
April1st to 15thNight
111232334472%
1924
16th to endNight
1112122480%
1800
May1st to 15thNight
1112235%78%
1671
16th to endNight
111122384%
1684
June1st to 15thNight
3121223378%
1620
16th to endNight
121141345%5%66%
1620
July1st to 15thNight
2325%5%36%6%8%15%40%
1620
16th to endNight
44246%47%8%12%16%28%
1701
August1st to 15thNight
2234436%7%9%10%45%
1620
16th to endNight
4324435%6%8%11%45%
1892
September1st to 15thNight
5%3245%35%5%6%9%48%
1965
16th to endNight
211212345%72%
1980
October1st to 15thNight
1212335%76%
2112
16th to endNight
1121133478%
2304
November1st to 15thNight
111212336%75%
2280
16th to endNight
3213312335%69%
2418
December1st to 15thNight
3212322446%65%
2535
16th to endNight
221341335%5%64%
2704

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
20%27%13%32%23%
1747
16th to endDay
22%2417%29%23%
1872
February1st to 15thDay
18%2312%32%30%
1749
16th to endDay
21%2314%31%27%
1677
March1st to 15thDay
17%239%37%31%
1980
16th to endDay
16%128%36%33%
2112
April1st to 15thDay
13%129%39%33%
2024
16th to endDay
10%116%30%49%
2160
May1st to 15thDay
10%127%28%49%
2276
16th to endDay
8%226%30%49%
2432
June1st to 15thDay
11%125%23%54%
2340
16th to endDay
21%35%9%22%36%
2340
July1st to 15thDay
37%12%16%13%11%8%
2201
16th to endDay
50%12%20%11%4
2312
August1st to 15thDay
42%10%14%16%13%2
2325
16th to endDay
34%9%16%17%13%8%
2309
September1st to 15thDay
37%7%9%17%19%8%
1992
16th to endDay
19%25%16%33%21%
1980
October1st to 15thDay
15%25%15%28%31%
1846
16th to endDay
12%2313%30%38%
1920
November1st to 15thDay
11%1415%36%29%
1909
16th to endDay
17%1314%31%31%
1869
December1st to 15thDay
21%25%17%35%17%
1755
16th to endDay
20%27%19%32%17%
1872
January1st to 15thNight
18%27%15%32%24%
2522
16th to endNight
22%25%16%32%20%
2704
February1st to 15thNight
15%2415%29%31%
2377
16th to endNight
18%2415%34%24%
1796
March1st to 15thNight
15%2313%32%33%
1980
16th to endNight
15%1410%36%31%
2112
April1st to 15thNight
15%1212%39%27%
1924
16th to endNight
10%128%30%46%
1800
May1st to 15thNight
8%238%33%43%
1672
16th to endNight
7%2210%35%42%
1685
June1st to 15thNight
11%12428%50%
1620
16th to endNight
17%4310%25%38%
1620
July1st to 15thNight
28%10%24%17%11%8%
1530
16th to endNight
35%14%30%14%41
1593
August1st to 15thNight
28%11%18%20%18%3
1611
16th to endNight
27%8%20%18%16%8%
1892
September1st to 15thNight
29%8%12%20%20%8%
1965
16th to endNight
13%36%16%39%19%
1980
October1st to 15thNight
12%27%18%30%28%
2112
16th to endNight
10%2415%28%38%
2304
November1st to 15thNight
11%15%20%34%27%
2280
16th to endNight
19%1313%30%31%
2418
December1st to 15thNight
20%25%18%34%18%
2535
16th to endNight
22%17%19%30%17%
2704

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
4422%37%27%3
135
16th to endDay
36%17%34%29%8%
144
February1st to 15thDay
49%16%30%29%9%
192
16th to endDay
6%23%29%22%16%1
238
March1st to 15thDay
416%31%22%18%6%
270
16th to endDay
418%27%24%16%8%
288
April1st to 15thDay
317%30%28%15%5%
269
16th to endDay
219%32%27%11%5%
270
May1st to 15thDay
216%34%24%14%6%
288
16th to endDay
27%28%38%18%5%
330
June1st to 15thDay
4222%40%20%9%
315
16th to endDay
410%39%32%12%
315
July1st to 15thDay
8%6%32%36%16%
305
16th to endDay
10%1425%33%23%
327
August1st to 15thDay
10%1221%36%27%
315
16th to endDay
5%321%43%25%
332
September1st to 15thDay
10%9%30%37%11%
315
16th to endDay
5%317%30%32%10%
315
October1st to 15thDay
218%27%33%17%
181
16th to endDay
1211%25%32%26%
144
November1st to 15thDay
25%18%28%34%11%
135
16th to endDay
8%21%27%31%11%
135
December1st to 15thDay
7%5%17%31%28%10%
135
16th to endDay
7%11%18%24%28%9%
144
January1st to 15thNight
3214%47%28%4
780
16th to endNight
4219%44%25%3
832
February1st to 15thNight
2317%42%28%5%
752
16th to endNight
1427%44%19%2
632
March1st to 15thNight
1423%42%24%4
720
16th to endNight
2318%44%26%4
768
April1st to 15thNight
2422%48%21%1
665
16th to endNight
1326%47%19%2
540
May1st to 15thNight
1222%45%27%2
540
16th to endNight
1115%46%31%2
563
June1st to 15thNight
37%50%35%1
540
16th to endNight
2437%51%3
540
July1st to 15thNight
4223%58%10%
510
16th to endNight
7%114%59%16%
564
August1st to 15thNight
4113%60%18%
539
16th to endNight
6%16%58%17%
573
September1st to 15thNight
8%219%55%12%
705
16th to endNight
45%35%46%7%
716
October1st to 15thNight
13%40%36%7%
720
16th to endNight
18%35%43%9%
768
November1st to 15thNight
212%40%37%6%
760
16th to endNight
5%117%37%32%6%
780
December1st to 15thNight
5%315%43%27%5%
780
16th to endNight
5%220%42%23%5%
832
Page generated at 2018-02-13 18:45:57. Version ac04

Copyright 2018 A. Danko


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