The Sky's The Limit Observatory and Nature Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Sky's The Limit Observatory and Nature Center clear sky chart from 2005-11-05 to

2017-09-12
.

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
75%
16062
39%
46905
31%
16020
82%
16020
65%
20363

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
69%
720
34%
2327
30%
716
78%
716
50%
1052
January16th to endNight
63%
768
39%
2375
29%
768
76%
768
49%
1126
February1st to 15thNight
68%
700
39%
2109
32%
699
79%
699
57%
943
February16th to endNight
61%
632
38%
1895
36%
632
70%
632
50%
919
March1st to 15thNight
65%
720
37%
2128
31%
720
76%
720
60%
931
March16th to endNight
68%
768
39%
2094
28%
768
78%
768
61%
967
April1st to 15thNight
60%
719
39%
1799
18%
719
71%
719
64%
871
April16th to endNight
65%
697
44%
1777
21%
697
76%
697
76%
772
May1st to 15thNight
72%
539
43%
1619
29%
539
79%
539
78%
609
May16th to endNight
73%
562
40%
1685
29%
561
79%
561
76%
649
June1st to 15thNight
81%
540
35%
1620
30%
540
83%
540
81%
606
June16th to endNight
85%
540
37%
1620
32%
540
86%
540
81%
616
July1st to 15thNight
90%
510
32%
1530
28%
510
90%
510
68%
638
July16th to endNight
87%
564
36%
1593
30%
531
88%
531
59%
724
August1st to 15thNight
92%
685
37%
1759
25%
682
92%
682
75%
806
August16th to endNight
93%
764
44%
1910
30%
764
93%
764
75%
889
September1st to 15thNight
92%
706
39%
1864
32%
706
93%
706
76%
825
September16th to endNight
89%
656
47%
1815
42%
656
93%
656
85%
724
October1st to 15thNight
77%
660
45%
1815
37%
660
85%
660
74%
781
October16th to endNight
82%
704
46%
2120
43%
704
89%
704
74%
837
November1st to 15thNight
76%
700
40%
2275
36%
700
87%
700
66%
902
November16th to endNight
75%
720
43%
2340
42%
720
83%
720
62%
949
December1st to 15thNight
69%
720
37%
2340
32%
720
80%
720
50%
1060
December16th to endNight
62%
768
37%
2496
31%
768
73%
768
45%
1167

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
111212335%75%
47751
Night
111212235%76%
47103
TransparencyDay
11%25%13%26%41%
47446
Night
11%25%13%27%39%
46909
SeeingDay
39%20%35%23%7%
5775
Night
2415%32%36%9%
16068

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
121232235%6%67%
1611
16th to endDay
2213223346%65%
1848
February1st to 15thDay
1112114347%68%
1751
16th to endDay
2123245%47%65%
1579
March1st to 15thDay
111112347%73%
1830
16th to endDay
11222336%75%
2127
April1st to 15thDay
111121235%6%73%
2149
16th to endDay
1112484%
2181
May1st to 15thDay
11111125%82%
2331
16th to endDay
111122484%
2429
June1st to 15thDay
222385%
2340
16th to endDay
111111287%
2340
July1st to 15thDay
211212247%71%
2340
16th to endDay
221232335%6%65%
2467
August1st to 15thDay
111113335%76%
2190
16th to endDay
111212345%74%
2292
September1st to 15thDay
11212346%74%
2015
16th to endDay
111122285%
1815
October1st to 15thDay
121232478%
1815
16th to endDay
112225%81%
1749
November1st to 15thDay
111112326%76%
1584
16th to endDay
111212246%74%
1620
December1st to 15thDay
2113223448%65%
1620
16th to endDay
3213313447%63%
1728
January1st to 15thNight
212323447%67%
2327
16th to endNight
2212313445%67%
2375
February1st to 15thNight
1212113246%71%
2101
16th to endNight
22232345%8%64%
1895
March1st to 15thNight
111213347%71%
2128
16th to endNight
12213236%74%
2094
April1st to 15thNight
12212335%76%
1799
16th to endNight
111225%84%
1777
May1st to 15thNight
1135%84%
1619
16th to endNight
11112485%
1684
June1st to 15thNight
111387%
1620
16th to endNight
111189%
1620
July1st to 15thNight
11212235%77%
1620
16th to endNight
2112223345%70%
1701
August1st to 15thNight
2111223480%
1768
16th to endNight
11111245%79%
1910
September1st to 15thNight
11112245%79%
1864
16th to endNight
111289%
1815
October1st to 15thNight
1111235%80%
1815
16th to endNight
1111125%82%
2120
November1st to 15thNight
1113235%79%
2275
16th to endNight
21211213477%
2340
December1st to 15thNight
2211313346%68%
2340
16th to endNight
3212323346%66%
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
17%36%18%31%22%
1612
16th to endDay
20%35%18%28%23%
1848
February1st to 15thDay
15%36%17%29%27%
1751
16th to endDay
16%5%7%17%31%21%
1579
March1st to 15thDay
11%2418%30%32%
1830
16th to endDay
11%25%20%33%26%
2127
April1st to 15thDay
13%2413%34%31%
2149
16th to endDay
6%1414%33%40%
2181
May1st to 15thDay
7%1310%29%47%
2331
16th to endDay
7%39%28%49%
2432
June1st to 15thDay
6%126%17%65%
2340
16th to endDay
7%139%77%
2340
July1st to 15thDay
12%349%17%51%
2201
16th to endDay
17%46%15%22%34%
2312
August1st to 15thDay
11%249%22%50%
2175
16th to endDay
12%35%9%22%46%
2292
September1st to 15thDay
11%27%10%18%50%
2015
16th to endDay
7%125%22%61%
1815
October1st to 15thDay
10%149%29%44%
1815
16th to endDay
8%1411%24%48%
1749
November1st to 15thDay
11%2413%32%34%
1584
16th to endDay
12%15%16%30%33%
1620
December1st to 15thDay
17%38%22%25%22%
1620
16th to endDay
20%49%22%25%17%
1728
January1st to 15thNight
16%46%16%29%26%
2327
16th to endNight
18%36%19%23%28%
2375
February1st to 15thNight
14%26%16%28%29%
2112
16th to endNight
18%4419%30%22%
1895
March1st to 15thNight
12%26%16%32%28%
2128
16th to endNight
12%27%17%33%27%
2094
April1st to 15thNight
12%15%15%35%28%
1799
16th to endNight
5%1413%33%40%
1777
May1st to 15thNight
5%1312%34%43%
1620
16th to endNight
5%1312%34%42%
1685
June1st to 15thNight
5%29%18%63%
1620
16th to endNight
6%15%8%77%
1620
July1st to 15thNight
10%238%17%57%
1530
16th to endNight
15%36%14%26%33%
1593
August1st to 15thNight
8%2410%22%51%
1759
16th to endNight
9%2310%23%51%
1910
September1st to 15thNight
8%26%10%21%51%
1864
16th to endNight
4125%23%62%
1815
October1st to 15thNight
9%149%33%41%
1815
16th to endNight
7%15%11%23%51%
2120
November1st to 15thNight
9%2411%34%37%
2275
16th to endNight
11%2315%31%35%
2340
December1st to 15thNight
16%5%8%17%27%26%
2340
16th to endNight
18%410%19%27%19%
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
11%7%27%37%15%
90
16th to endDay
6%17%25%32%13%3
216
February1st to 15thDay
412%30%31%18%3
266
16th to endDay
8%20%27%24%18%
238
March1st to 15thDay
318%20%31%21%3
270
16th to endDay
318%22%34%16%3
288
April1st to 15thDay
10%19%25%24%14%5%
269
16th to endDay
422%28%27%14%2
270
May1st to 15thDay
313%25%36%16%4
288
16th to endDay
10%26%36%19%6%
330
June1st to 15thDay
15%26%34%25%6%
315
16th to endDay
2221%33%26%13%
315
July1st to 15thDay
212%41%29%14%
305
16th to endDay
28%42%29%16%
327
August1st to 15thDay
113%46%26%11%
315
16th to endDay
29%36%34%16%
332
September1st to 15thDay
2216%42%31%6%
300
16th to endDay
28%15%36%29%7%
255
October1st to 15thDay
112%22%40%21%2
255
16th to endDay
16%20%30%36%4
165
November1st to 15thDay
110%16%24%34%13%
90
16th to endDay
28%35%22%23%7%
90
December1st to 15thDay
314%11%36%33%1
90
16th to endDay
7%10%23%39%18%
96
January1st to 15thNight
25%18%39%23%9%
720
16th to endNight
45%22%33%27%7%
768
February1st to 15thNight
25%18%38%28%6%
704
16th to endNight
26%25%37%21%6%
632
March1st to 15thNight
27%21%34%27%7%
720
16th to endNight
18%17%36%27%8%
768
April1st to 15thNight
18%25%33%24%5%
719
16th to endNight
7%24%33%27%6%
697
May1st to 15thNight
1419%35%34%4
540
16th to endNight
5%18%37%32%5%
563
June1st to 15thNight
215%43%35%3
540
16th to endNight
111%36%45%4
540
July1st to 15thNight
2329%55%8%
510
16th to endNight
2326%59%8%
564
August1st to 15thNight
1321%60%12%
685
16th to endNight
1216%59%20%
764
September1st to 15thNight
1225%55%14%
706
16th to endNight
17%30%46%14%
656
October1st to 15thNight
116%35%35%9%
660
16th to endNight
1210%31%39%15%
704
November1st to 15thNight
118%31%37%10%
700
16th to endNight
2413%32%32%14%
720
December1st to 15thNight
4317%39%28%6%
720
16th to endNight
5%8%19%35%24%6%
768
Page generated at 2017-09-13 04:39:13. Version ac04

Copyright 2017 A. Danko


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