SkyScapes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SkyScapes Observatory clear sky chart from 2005-11-05 to 2017-12-01.

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
67%
16463
41%
47875
29%
16421
78%
16421
65%
20455

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
72%
717
36%
2327
32%
716
80%
716
52%
1036
January16th to endNight
63%
768
41%
2337
31%
768
76%
768
50%
1086
February1st to 15thNight
65%
700
40%
2108
31%
699
80%
699
57%
941
February16th to endNight
53%
632
38%
1895
28%
632
70%
632
49%
900
March1st to 15thNight
56%
720
38%
2136
29%
720
72%
720
59%
917
March16th to endNight
55%
768
40%
2079
23%
768
70%
768
63%
922
April1st to 15thNight
44%
719
40%
1799
14%
719
61%
719
60%
861
April16th to endNight
48%
720
44%
1800
14%
720
65%
720
71%
792
May1st to 15thNight
49%
548
43%
1627
20%
547
64%
547
72%
616
May16th to endNight
45%
562
42%
1685
19%
561
62%
561
71%
626
June1st to 15thNight
52%
540
38%
1620
22%
540
63%
540
79%
592
June16th to endNight
64%
540
39%
1620
26%
540
73%
540
84%
600
July1st to 15thNight
82%
510
32%
1530
26%
510
85%
510
70%
634
July16th to endNight
82%
582
37%
1610
27%
548
84%
548
64%
706
August1st to 15thNight
86%
717
38%
1790
24%
713
88%
713
78%
822
August16th to endNight
89%
764
45%
1910
31%
764
91%
764
77%
887
September1st to 15thNight
86%
720
40%
1896
29%
720
91%
720
76%
838
September16th to endNight
79%
716
51%
1980
40%
716
89%
716
84%
777
October1st to 15thNight
68%
720
45%
1980
31%
720
82%
720
74%
818
October16th to endNight
78%
768
50%
2292
43%
768
88%
768
75%
897
November1st to 15thNight
75%
760
40%
2470
37%
760
86%
760
66%
974
November16th to endNight
74%
780
44%
2535
42%
780
84%
780
63%
1023
December1st to 15thNight
69%
724
38%
2353
35%
724
79%
724
52%
1043
December16th to endNight
60%
768
38%
2496
31%
768
71%
768
49%
1147

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
111112235%77%
48542
Night
11112235%79%
48076
TransparencyDay
11%2412%26%42%
48239
Night
9%2413%27%42%
47880
SeeingDay
212%26%33%19%4
6114
Night
17%21%33%27%8%
16471

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
1112323245%71%
1611
16th to endDay
212223348%67%
1886
February1st to 15thDay
211113338%70%
1751
16th to endDay
21122346%9%65%
1579
March1st to 15thDay
111112338%74%
1821
16th to endDay
1113346%76%
2142
April1st to 15thDay
1211337%76%
2149
16th to endDay
1126%85%
2160
May1st to 15thDay
11212484%
2322
16th to endDay
112388%
2429
June1st to 15thDay
112388%
2340
16th to endDay
11190%
2340
July1st to 15thDay
112213345%72%
2340
16th to endDay
112323448%66%
2447
August1st to 15thDay
11212335%76%
2160
16th to endDay
111112335%74%
2292
September1st to 15thDay
11112243476%
2064
16th to endDay
1111111287%
1980
October1st to 15thDay
11235%82%
1980
16th to endDay
1124482%
1927
November1st to 15thDay
1211345%77%
1719
16th to endDay
111212346%75%
1755
December1st to 15thDay
22222225%8%67%
1620
16th to endDay
2112223346%69%
1728
January1st to 15thNight
122213446%71%
2327
16th to endNight
312312345%70%
2337
February1st to 15thNight
121234475%
2101
16th to endNight
11122445%8%66%
1895
March1st to 15thNight
111112336%76%
2136
16th to endNight
1112248%75%
2079
April1st to 15thNight
11111223380%
1799
16th to endNight
1112486%
1800
May1st to 15thNight
112487%
1627
16th to endNight
112290%
1684
June1st to 15thNight
112291%
1620
16th to endNight
11191%
1620
July1st to 15thNight
1112235%80%
1620
16th to endNight
212112235%75%
1719
August1st to 15thNight
11222483%
1800
16th to endNight
1111112483%
1910
September1st to 15thNight
11123482%
1896
16th to endNight
1291%
1980
October1st to 15thNight
123484%
1980
16th to endNight
11113484%
2292
November1st to 15thNight
11111235%80%
2470
16th to endNight
111112235%77%
2535
December1st to 15thNight
1112223348%70%
2353
16th to endNight
311323346%68%
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
16%46%15%28%28%
1612
16th to endDay
17%37%17%25%28%
1886
February1st to 15thDay
14%35%14%31%30%
1751
16th to endDay
16%47%22%26%22%
1579
March1st to 15thDay
11%2415%31%33%
1821
16th to endDay
11%2418%33%29%
2142
April1st to 15thDay
11%3412%40%28%
2149
16th to endDay
41216%34%40%
2160
May1st to 15thDay
7%1210%31%45%
2322
16th to endDay
5%1211%32%47%
2432
June1st to 15thDay
5%118%19%63%
2340
16th to endDay
5%1310%78%
2340
July1st to 15thDay
14%327%20%51%
2201
16th to endDay
15%46%16%23%32%
2293
August1st to 15thDay
10%3210%23%49%
2146
16th to endDay
12%248%21%49%
2292
September1st to 15thDay
12%338%19%52%
2064
16th to endDay
7%11323%62%
1980
October1st to 15thDay
7%2211%26%49%
1980
16th to endDay
7%339%22%54%
1927
November1st to 15thDay
10%2414%30%38%
1719
16th to endDay
11%35%12%28%37%
1755
December1st to 15thDay
17%45%20%22%28%
1620
16th to endDay
16%48%23%27%19%
1728
January1st to 15thNight
14%45%16%27%30%
2327
16th to endNight
16%36%17%23%32%
2337
February1st to 15thNight
13%3416%27%34%
2112
16th to endNight
16%47%18%28%24%
1895
March1st to 15thNight
11%26%16%30%32%
2136
16th to endNight
9%26%19%32%29%
2079
April1st to 15thNight
9%35%15%40%25%
1799
16th to endNight
5%1314%36%39%
1800
May1st to 15thNight
41312%31%45%
1628
16th to endNight
4211%36%43%
1685
June1st to 15thNight
419%23%61%
1620
16th to endNight
438%81%
1620
July1st to 15thNight
8%326%20%59%
1530
16th to endNight
12%26%14%27%37%
1610
August1st to 15thNight
7%2110%24%53%
1790
16th to endNight
8%128%22%56%
1910
September1st to 15thNight
7%328%22%56%
1896
16th to endNight
4326%64%
1980
October1st to 15thNight
5%2212%29%48%
1980
16th to endNight
6%2310%22%55%
2292
November1st to 15thNight
9%2311%33%39%
2470
16th to endNight
10%2413%31%37%
2535
December1st to 15thNight
15%37%20%25%27%
2353
16th to endNight
16%48%22%24%22%
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
7%22%14%40%15%
90
16th to endDay
318%31%31%12%2
254
February1st to 15thDay
217%28%37%13%
266
16th to endDay
6%26%30%26%9%
238
March1st to 15thDay
419%31%27%13%2
270
16th to endDay
322%31%28%12%1
288
April1st to 15thDay
5%25%33%21%12%1
269
16th to endDay
225%36%22%11%1
270
May1st to 15thDay
317%36%29%10%3
288
16th to endDay
17%37%26%13%3
330
June1st to 15thDay
113%30%29%20%4
315
16th to endDay
1330%29%26%8%
315
July1st to 15thDay
218%43%25%9%
305
16th to endDay
314%37%32%12%
327
August1st to 15thDay
1217%40%27%10%
315
16th to endDay
1115%39%31%11%
332
September1st to 15thDay
2325%45%16%6%
315
16th to endDay
28%26%40%17%4
315
October1st to 15thDay
13%28%40%16%
315
16th to endDay
9%23%31%28%6%
241
November1st to 15thDay
112%18%31%29%5%
135
16th to endDay
114%22%29%24%7%
135
December1st to 15thDay
18%16%42%26%4
90
16th to endDay
5%16%25%33%19%
96
January1st to 15thNight
26%15%34%30%11%
720
16th to endNight
46%19%33%27%7%
768
February1st to 15thNight
16%22%30%27%10%
704
16th to endNight
212%30%28%20%6%
632
March1st to 15thNight
210%28%30%22%5%
720
16th to endNight
213%28%29%20%5%
768
April1st to 15thNight
118%34%24%16%4
719
16th to endNight
17%33%25%17%6%
720
May1st to 15thNight
13%35%31%16%2
548
16th to endNight
16%36%28%15%2
563
June1st to 15thNight
9%37%36%15%1
540
16th to endNight
1231%45%17%2
540
July1st to 15thNight
113%50%28%4
510
16th to endNight
219%48%34%4
582
August1st to 15thNight
9%44%37%6%
717
16th to endNight
25%36%45%9%
764
September1st to 15thNight
10%33%45%8%
720
16th to endNight
316%34%34%10%
716
October1st to 15thNight
7%22%30%30%8%
720
16th to endNight
414%30%32%17%
768
November1st to 15thNight
318%35%30%11%
760
16th to endNight
2415%29%30%17%
780
December1st to 15thNight
26%18%32%30%9%
724
16th to endNight
48%23%30%25%7%
768
Page generated at 2017-12-02 06:14:24. Version ac04

Copyright 2017 A. Danko


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