Cima
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cima clear sky chart from 2005-11-05 to 2017-08-12.

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
65%
15821
36%
46570
27%
15781
75%
15781
55%
21578

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
54%
719
32%
2327
23%
716
68%
716
44%
1109
January16th to endNight
51%
768
34%
2430
23%
768
66%
768
40%
1221
February1st to 15thNight
56%
698
36%
2112
26%
698
69%
698
49%
1023
February16th to endNight
52%
632
33%
1895
29%
632
63%
632
42%
974
March1st to 15thNight
55%
720
33%
2112
26%
720
68%
720
46%
1056
March16th to endNight
56%
768
34%
2112
23%
768
66%
768
49%
1061
April1st to 15thNight
47%
719
35%
1805
14%
719
59%
719
50%
930
April16th to endNight
55%
654
40%
1734
18%
654
68%
654
60%
787
May1st to 15thNight
61%
540
38%
1619
22%
539
70%
539
64%
664
May16th to endNight
59%
561
36%
1685
22%
561
69%
561
62%
688
June1st to 15thNight
70%
540
32%
1620
26%
540
75%
540
67%
663
June16th to endNight
78%
540
37%
1620
29%
540
83%
540
80%
613
July1st to 15thNight
87%
510
30%
1530
26%
510
89%
510
64%
662
July16th to endNight
81%
564
31%
1593
27%
531
82%
531
51%
798
August1st to 15thNight
87%
600
38%
1649
27%
597
89%
597
67%
745
August16th to endNight
87%
700
40%
1750
27%
700
88%
700
70%
856
September1st to 15thNight
84%
660
38%
1754
29%
660
87%
660
65%
839
September16th to endNight
79%
656
46%
1815
36%
656
87%
656
78%
748
October1st to 15thNight
72%
660
43%
1815
34%
660
80%
660
62%
837
October16th to endNight
73%
704
43%
2142
35%
704
83%
704
63%
906
November1st to 15thNight
67%
700
38%
2275
33%
700
79%
700
57%
964
November16th to endNight
67%
720
40%
2340
35%
720
77%
720
53%
1017
December1st to 15thNight
59%
720
34%
2340
27%
720
71%
720
42%
1147
December16th to endNight
52%
768
34%
2496
26%
768
65%
768
37%
1270

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
2212223335%69%
47399
Night
2212213345%69%
46765
TransparencyDay
16%25%14%26%34%
47094
Night
16%25%15%27%32%
46571
SeeingDay
412%27%36%15%3
5563
Night
37%18%31%30%8%
15830

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
2413212337%66%
1611
16th to endDay
3413433337%61%
1792
February1st to 15thDay
331222345%5%64%
1751
16th to endDay
35%245%23346%58%
1579
March1st to 15thDay
2312212347%66%
1847
16th to endDay
2312223347%65%
2112
April1st to 15thDay
321231434466%
2140
16th to endDay
211121123475%
2223
May1st to 15thDay
12112236%76%
2331
16th to endDay
1311212235%74%
2429
June1st to 15thDay
1121225%80%
2340
16th to endDay
111111285%
2340
July1st to 15thDay
3212323446%64%
2340
16th to endDay
4214435%5%47%56%
2467
August1st to 15thDay
1212323445%69%
2213
16th to endDay
3211223336%68%
2100
September1st to 15thDay
21132333472%
1876
16th to endDay
121122380%
1815
October1st to 15thDay
2212211235%73%
1815
16th to endDay
11121223477%
1726
November1st to 15thDay
131221224472%
1584
16th to endDay
2212212347%68%
1620
December1st to 15thDay
34243225%5%8%57%
1620
16th to endDay
45%24323447%57%
1728
January1st to 15thNight
221442445%5%63%
2327
16th to endNight
3424323346%61%
2430
February1st to 15thNight
2423312337%64%
2101
16th to endNight
4423423345%60%
1895
March1st to 15thNight
13133245%6%6%61%
2112
16th to endNight
2213223448%64%
2112
April1st to 15thNight
2213322245%69%
1805
16th to endNight
111112235%76%
1734
May1st to 15thNight
11212246%75%
1619
16th to endNight
11112225%78%
1684
June1st to 15thNight
1112122480%
1620
16th to endNight
112288%
1620
July1st to 15thNight
111131335%5%71%
1620
16th to endNight
6%21231446%7%59%
1701
August1st to 15thNight
111213345%74%
1658
16th to endNight
112212336%73%
1750
September1st to 15thNight
11221324473%
1754
16th to endNight
111111286%
1815
October1st to 15thNight
21121224475%
1815
16th to endNight
111121223476%
2142
November1st to 15thNight
1222212235%73%
2275
16th to endNight
2312213335%70%
2340
December1st to 15thNight
3313424447%59%
2340
16th to endNight
4325%423337%58%
2496

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
19%16%21%33%17%
1612
16th to endDay
25%26%18%28%18%
1792
February1st to 15thDay
19%27%17%28%23%
1751
16th to endDay
27%26%15%32%15%
1579
March1st to 15thDay
16%25%19%32%23%
1847
16th to endDay
18%27%20%32%18%
2112
April1st to 15thDay
20%2417%32%23%
2140
16th to endDay
13%1417%31%31%
2223
May1st to 15thDay
10%1416%31%35%
2331
16th to endDay
14%1411%30%37%
2432
June1st to 15thDay
9%138%18%59%
2340
16th to endDay
8%11312%72%
2340
July1st to 15thDay
18%25%10%16%47%
2201
16th to endDay
21%38%15%20%30%
2312
August1st to 15thDay
15%3410%23%42%
2198
16th to endDay
16%3410%25%39%
2100
September1st to 15thDay
13%36%11%20%44%
1876
16th to endDay
8%137%27%51%
1815
October1st to 15thDay
15%1311%30%37%
1815
16th to endDay
11%2412%28%39%
1726
November1st to 15thDay
15%1417%32%28%
1584
16th to endDay
16%25%16%30%27%
1620
December1st to 15thDay
24%39%19%24%17%
1620
16th to endDay
28%28%22%24%13%
1728
January1st to 15thNight
21%36%18%29%20%
2327
16th to endNight
24%26%19%22%24%
2430
February1st to 15thNight
20%27%18%26%24%
2112
16th to endNight
24%26%17%31%16%
1895
March1st to 15thNight
20%35%18%30%22%
2112
16th to endNight
18%27%20%31%18%
2112
April1st to 15thNight
17%25%19%34%21%
1805
16th to endNight
10%1418%30%33%
1734
May1st to 15thNight
10%15%16%33%32%
1620
16th to endNight
9%25%14%35%32%
1685
June1st to 15thNight
10%129%18%57%
1620
16th to endNight
6%16%12%71%
1620
July1st to 15thNight
12%25%10%18%50%
1530
16th to endNight
20%47%13%23%31%
1593
August1st to 15thNight
11%2414%22%44%
1649
16th to endNight
12%1412%25%43%
1750
September1st to 15thNight
14%26%11%23%42%
1754
16th to endNight
7%18%26%54%
1815
October1st to 15thNight
12%2311%32%37%
1815
16th to endNight
11%1410%25%45%
2142
November1st to 15thNight
15%1314%35%29%
2275
16th to endNight
16%15%16%26%33%
2340
December1st to 15thNight
23%27%16%29%19%
2340
16th to endNight
26%28%20%26%15%
2496

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
20%16%37%21%4
90
16th to endDay
9%18%28%28%11%3
160
February1st to 15thDay
6%15%42%23%10%2
266
16th to endDay
7%24%33%22%10%
238
March1st to 15thDay
5%20%30%29%14%1
270
16th to endDay
5%23%31%27%9%1
288
April1st to 15thDay
8%26%33%19%8%4
269
16th to endDay
5%32%28%22%10%1
270
May1st to 15thDay
214%34%34%12%2
288
16th to endDay
212%39%31%11%2
330
June1st to 15thDay
18%37%35%13%2
315
16th to endDay
15%22%46%20%4
315
July1st to 15thDay
219%51%20%4
305
16th to endDay
6%10%53%22%6%
327
August1st to 15thDay
3417%52%17%5%
300
16th to endDay
417%47%23%6%
268
September1st to 15thDay
1228%48%16%1
255
16th to endDay
110%21%42%21%2
255
October1st to 15thDay
413%32%36%12%1
255
16th to endDay
411%25%33%24%
133
November1st to 15thDay
221%12%27%26%10%
90
16th to endDay
8%21%28%24%16%
90
December1st to 15thDay
7%16%21%34%20%
90
16th to endDay
10%16%27%28%16%1
96
January1st to 15thNight
47%27%30%21%7%
720
16th to endNight
7%9%23%31%21%6%
768
February1st to 15thNight
46%25%34%23%5%
704
16th to endNight
7%9%25%33%17%6%
632
March1st to 15thNight
411%23%32%22%5%
720
16th to endNight
312%22%31%23%5%
768
April1st to 15thNight
416%26%27%18%5%
719
16th to endNight
115%24%31%20%5%
654
May1st to 15thNight
28%26%32%25%4
540
16th to endNight
12%23%30%29%3
563
June1st to 15thNight
16%18%40%30%2
540
16th to endNight
118%37%39%2
540
July1st to 15thNight
25%35%51%5%
510
16th to endNight
6%5%28%53%5%
564
August1st to 15thNight
26%30%52%8%
600
16th to endNight
2425%49%18%
700
September1st to 15thNight
26%28%45%15%
660
16th to endNight
2212%27%34%19%
656
October1st to 15thNight
35%14%38%30%7%
660
16th to endNight
15%15%30%31%14%
704
November1st to 15thNight
2421%32%31%8%
700
16th to endNight
5%7%16%31%27%11%
720
December1st to 15thNight
6%7%20%33%25%6%
720
16th to endNight
8%12%22%30%20%5%
768
Page generated at 2017-08-13 11:16:40. Version ac04

Copyright 2017 A. Danko


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