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 2018-01-12.

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%
16548
40%
48403
32%
16506
82%
16506
65%
20975

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%
764
33%
2471
29%
760
78%
760
49%
1131
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%
720
39%
1902
33%
720
93%
720
76%
842
September16th to endNight
89%
716
50%
1980
44%
716
93%
716
86%
785
October1st to 15thNight
78%
720
44%
1980
36%
720
85%
720
76%
841
October16th to endNight
83%
768
48%
2313
45%
768
90%
768
75%
906
November1st to 15thNight
78%
760
38%
2470
35%
760
88%
760
65%
990
November16th to endNight
76%
780
44%
2535
44%
780
83%
780
62%
1032
December1st to 15thNight
69%
780
37%
2535
32%
780
79%
780
51%
1131
December16th to endNight
63%
832
38%
2704
32%
832
74%
832
46%
1251

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%
48931
Night
111212235%76%
48601
TransparencyDay
11%25%13%25%41%
48626
Night
11%25%13%27%39%
48407
SeeingDay
39%20%35%24%7%
6180
Night
2314%33%36%9%
16554

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
2313322346%66%
1710
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%75%
2058
16th to endDay
111122285%
1980
October1st to 15thDay
121232480%
1980
16th to endDay
11212481%
1908
November1st to 15thDay
111112327%74%
1719
16th to endDay
112212347%73%
1755
December1st to 15thDay
2112223347%66%
1755
16th to endDay
2213314447%64%
1872
January1st to 15thNight
131232345%7%66%
2471
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%
1902
16th to endNight
111290%
1980
October1st to 15thNight
111112481%
1980
16th to endNight
111112483%
2313
November1st to 15thNight
1113235%78%
2470
16th to endNight
212112135%76%
2535
December1st to 15thNight
2211313346%69%
2535
16th to endNight
3212323347%66%
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
18%36%18%31%20%
1711
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
10%26%10%19%49%
2058
16th to endDay
6%125%22%61%
1980
October1st to 15thDay
10%148%27%48%
1980
16th to endDay
8%1410%24%50%
1908
November1st to 15thDay
12%25%15%31%33%
1719
16th to endDay
12%15%15%30%33%
1755
December1st to 15thDay
17%37%21%24%25%
1755
16th to endDay
19%49%21%26%18%
1872
January1st to 15thNight
17%46%17%29%24%
2471
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%25%10%21%51%
1902
16th to endNight
4115%23%64%
1980
October1st to 15thNight
8%148%31%45%
1980
16th to endNight
7%1410%22%53%
2313
November1st to 15thNight
10%3411%34%35%
2470
16th to endNight
11%2314%32%35%
2535
December1st to 15thNight
15%47%16%26%28%
2535
16th to endNight
18%410%18%28%20%
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
9%7%23%38%20%
123
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
1116%42%30%6%
315
16th to endDay
18%16%36%29%7%
315
October1st to 15thDay
10%23%39%23%2
315
16th to endDay
15%18%29%33%11%
219
November1st to 15thDay
16%18%31%32%8%
135
16th to endDay
17%28%24%26%11%
135
December1st to 15thDay
214%12%34%33%2
135
16th to endDay
5%9%18%32%25%7%
144
January1st to 15thNight
25%17%40%23%9%
764
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%
720
16th to endNight
7%30%46%14%
716
October1st to 15thNight
116%35%37%8%
720
16th to endNight
129%30%40%15%
768
November1st to 15thNight
117%33%37%9%
760
16th to endNight
2413%32%33%13%
780
December1st to 15thNight
4318%38%29%6%
780
16th to endNight
5%8%18%34%25%6%
832
Page generated at 2018-01-12 19:01:37. Version ac04

Copyright 2018 A. Danko


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