Star Kyst Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Star Kyst Observatory clear sky chart from 2005-11-05 to 2017-09-21.

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
47%
15905
30%
46926
15%
15861
61%
15861
47%
23184

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
35%
861
33%
2470
14%
859
54%
859
55%
1095
January16th to endNight
35%
768
35%
2496
17%
768
58%
768
51%
1053
February1st to 15thNight
30%
702
29%
2275
11%
698
53%
698
46%
1033
February16th to endNight
30%
632
36%
1894
9%
632
58%
632
50%
868
March1st to 15thNight
36%
720
32%
2059
12%
720
54%
720
50%
998
March16th to endNight
35%
714
31%
2058
11%
714
52%
714
48%
1010
April1st to 15thNight
36%
539
28%
1798
12%
539
56%
539
43%
817
April16th to endNight
37%
540
27%
1800
15%
540
55%
540
37%
904
May1st to 15thNight
41%
539
22%
1647
13%
539
53%
539
34%
916
May16th to endNight
50%
563
21%
1497
10%
561
60%
561
44%
824
June1st to 15thNight
61%
540
26%
1440
16%
540
69%
540
56%
714
June16th to endNight
73%
540
29%
1440
23%
540
78%
540
59%
699
July1st to 15thNight
73%
510
16%
1360
15%
510
74%
510
35%
839
July16th to endNight
74%
564
16%
1527
15%
531
76%
531
34%
912
August1st to 15thNight
72%
539
17%
1644
16%
536
73%
536
35%
922
August16th to endNight
72%
573
24%
1910
24%
573
75%
573
34%
1058
September1st to 15thNight
68%
540
27%
1800
25%
540
75%
540
37%
962
September16th to endNight
69%
547
37%
1840
31%
547
78%
547
50%
859
October1st to 15thNight
51%
660
33%
1980
18%
660
64%
660
50%
961
October16th to endNight
53%
704
39%
2112
18%
704
69%
704
57%
960
November1st to 15thNight
46%
850
36%
2250
16%
850
59%
850
60%
1056
November16th to endNight
41%
900
39%
2421
16%
900
58%
900
60%
1106
December1st to 15thNight
30%
900
27%
2520
7%
900
47%
900
49%
1214
December16th to endNight
33%
960
29%
2688
9%
960
50%
960
43%
1404

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
4424435%5%5%7%53%
47946
Night
2312213347%64%
47109
TransparencyDay
27%413%26%21%6%
47630
Night
19%415%31%23%5%
46927
SeeingDay
9%15%27%26%16%4
5796
Night
49%33%32%17%2
15911

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
21222346%10%62%
1477
16th to endDay
22242345%6%64%
1728
February1st to 15thDay
31442445%7%60%
1588
16th to endDay
2144345%6%7%60%
1580
March1st to 15thDay
424434449%57%
1899
16th to endDay
15%2433445%8%54%
2166
April1st to 15thDay
27%133235%6%10%54%
2150
16th to endDay
49%24425%5%6%9%46%
2160
May1st to 15thDay
6%7%35%5%36%6%6%8%41%
2300
16th to endDay
5%6%15%5%36%5%5%8%45%
2616
June1st to 15thDay
4313435%46%8%54%
2520
16th to endDay
32135%35%5%5%7%55%
2520
July1st to 15thDay
9%426%6%46%6%6%7%39%
2520
16th to endDay
7%5%36%7%5%8%6%8%7%34%
2533
August1st to 15thDay
9%6%36%6%46%5%6%7%36%
2307
16th to endDay
7%426%6%36%6%6%7%41%
2292
September1st to 15thDay
7%425%5%35%5%5%6%47%
2160
16th to endDay
441342344461%
1911
October1st to 15thDay
431342445%6%59%
1650
16th to endDay
331322335%6%65%
1760
November1st to 15thDay
21213347%72%
1597
16th to endDay
113222226%74%
1536
December1st to 15thDay
313413337%66%
1440
16th to endDay
3232135%5%9%61%
1536
January1st to 15thNight
111112238%74%
2470
16th to endNight
212212236%73%
2496
February1st to 15thNight
123213336%68%
2264
16th to endNight
212213347%70%
1894
March1st to 15thNight
1313213346%68%
2059
16th to endNight
1422213247%65%
2058
April1st to 15thNight
131221345%9%63%
1798
16th to endNight
47%2231335%5%61%
1800
May1st to 15thNight
5%7%3432335%9%52%
1646
16th to endNight
5%5%1232335%9%57%
1497
June1st to 15thNight
2212112449%67%
1440
16th to endNight
2122446%9%65%
1440
July1st to 15thNight
6%224435%6%7%10%46%
1440
16th to endNight
4413435%5%7%10%47%
1633
August1st to 15thNight
5%4134235%6%8%51%
1653
16th to endNight
5%3245%245%7%9%50%
1910
September1st to 15thNight
6%3134345%6%7%54%
1800
16th to endNight
3312212246%68%
1840
October1st to 15thNight
332213337%68%
1980
16th to endNight
2212112347%70%
2112
November1st to 15thNight
111112337%73%
2250
16th to endNight
212112346%74%
2421
December1st to 15thNight
312313336%70%
2520
16th to endNight
223323247%65%
2688

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%222%36%18%2
1478
16th to endDay
18%216%35%21%5%
1728
February1st to 15thDay
19%417%36%17%4
1588
16th to endDay
18%312%37%24%3
1580
March1st to 15thDay
23%313%32%23%3
1899
16th to endDay
25%412%32%20%4
2166
April1st to 15thDay
24%314%32%18%6%
2150
16th to endDay
33%311%27%20%2
2160
May1st to 15thDay
37%412%25%18%1
2300
16th to endDay
34%5%13%23%19%4
2620
June1st to 15thDay
25%411%20%24%13%
2520
16th to endDay
25%5%7%19%28%14%
2520
July1st to 15thDay
38%6%13%17%15%9%
2371
16th to endDay
41%9%17%17%9%4
2376
August1st to 15thDay
41%7%14%14%14%6%
2292
16th to endDay
36%7%13%22%17%3
2292
September1st to 15thDay
34%411%17%22%8%
2160
16th to endDay
23%39%26%30%7%
1911
October1st to 15thDay
23%37%26%30%7%
1650
16th to endDay
18%28%29%31%8%
1760
November1st to 15thDay
11%313%29%29%13%
1597
16th to endDay
14%110%35%30%8%
1536
December1st to 15thDay
19%318%37%17%3
1440
16th to endDay
18%7%21%31%16%4
1536
January1st to 15thNight
12%121%38%22%3
2470
16th to endNight
13%215%34%28%5%
2496
February1st to 15thNight
17%315%40%19%3
2275
16th to endNight
15%212%37%27%4
1894
March1st to 15thNight
17%213%36%24%3
2059
16th to endNight
18%313%38%22%2
2058
April1st to 15thNight
18%314%33%24%4
1798
16th to endNight
26%213%34%19%3
1800
May1st to 15thNight
31%315%30%17%2
1647
16th to endNight
23%5%18%28%20%4
1498
June1st to 15thNight
16%315%24%24%15%
1440
16th to endNight
14%411%25%28%16%
1440
July1st to 15thNight
30%9%18%18%15%8%
1360
16th to endNight
29%9%26%21%9%3
1527
August1st to 15thNight
27%8%21%19%15%7%
1644
16th to endNight
28%8%18%23%17%4
1910
September1st to 15thNight
27%5%17%22%18%9%
1800
16th to endNight
19%310%32%28%6%
1840
October1st to 15thNight
18%310%29%28%8%
1980
16th to endNight
15%29%32%35%5%
2112
November1st to 15thNight
11%313%30%30%10%
2250
16th to endNight
12%110%39%29%7%
2421
December1st to 15thNight
16%222%33%22%2
2520
16th to endNight
20%5%18%32%19%3
2688

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
6%15%24%26%24%2
90
16th to endDay
6%8%33%38%13%
96
February1st to 15thDay
5%32%28%26%5%1
90
16th to endDay
33%29%19%14%2
81
March1st to 15thDay
5%34%31%21%6%
189
16th to endDay
9%37%36%11%3
288
April1st to 15thDay
9%34%31%16%5%2
269
16th to endDay
15%34%29%14%4
270
May1st to 15thDay
11%22%31%23%9%1
352
16th to endDay
13%12%26%27%15%4
517
June1st to 15thDay
5%13%28%27%18%6%
495
16th to endDay
47%25%32%22%7%
495
July1st to 15thDay
9%5%19%24%30%10%
475
16th to endDay
9%417%33%25%9%
392
August1st to 15thDay
14%5%26%30%18%4
315
16th to endDay
11%5%25%35%17%4
332
September1st to 15thDay
12%9%30%28%14%4
315
16th to endDay
8%8%32%28%15%4
183
October1st to 15thDay
37%30%20%32%6%
90
16th to endDay
13%10%14%36%21%3
96
November1st to 15thDay
211%22%26%30%7%
90
16th to endDay
328%34%28%4
90
December1st to 15thDay
5%30%36%25%2
90
16th to endDay
16%30%44%7%1
96
January1st to 15thNight
315%41%26%10%1
864
16th to endNight
114%43%29%8%1
768
February1st to 15thNight
110%50%30%6%
704
16th to endNight
114%50%28%4
632
March1st to 15thNight
310%44%32%8%
720
16th to endNight
311%46%30%7%
714
April1st to 15thNight
413%43%32%6%
539
16th to endNight
9%10%37%31%9%
540
May1st to 15thNight
11%9%30%34%12%1
540
16th to endNight
7%6%27%35%19%3
563
June1st to 15thNight
3425%42%21%2
540
16th to endNight
2316%41%32%3
540
July1st to 15thNight
7%26%32%44%6%
510
16th to endNight
7%1431%48%7%
564
August1st to 15thNight
7%26%33%43%5%
539
16th to endNight
6%9%32%42%7%
573
September1st to 15thNight
7%113%39%31%6%
540
16th to endNight
5%318%39%27%6%
547
October1st to 15thNight
36%33%34%17%4
660
16th to endNight
27%33%37%14%3
704
November1st to 15thNight
111%37%35%13%1
850
16th to endNight
214%40%32%10%1
900
December1st to 15thNight
414%47%27%5%
900
16th to endNight
214%44%29%9%
960
Page generated at 2017-09-22 05:35:38. Version ac04

Copyright 2017 A. Danko


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