Burk Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burk Astronomical Observatory clear sky chart from 2005-11-05 to 2018-08-29.

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
35%
17274
26%
50612
11%
17228
50%
17228
31%
27557

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
18%
975
27%
2716
6%
970
37%
970
26%
1393
January16th to endNight
15%
894
31%
2766
7%
894
41%
894
23%
1356
February1st to 15thNight
14%
761
23%
2469
3%
758
37%
758
19%
1284
February16th to endNight
13%
684
28%
2050
3%
684
39%
684
23%
1134
March1st to 15thNight
24%
780
27%
2282
8%
780
41%
780
31%
1210
March16th to endNight
28%
744
23%
2200
9%
744
42%
744
27%
1262
April1st to 15thNight
26%
584
22%
1948
8%
584
46%
584
24%
1097
April16th to endNight
30%
579
20%
1929
10%
579
44%
579
22%
1148
May1st to 15thNight
39%
585
19%
1680
12%
585
46%
585
27%
1075
May16th to endNight
50%
611
17%
1626
11%
609
55%
609
32%
1023
June1st to 15thNight
54%
585
21%
1560
13%
585
60%
585
42%
881
June16th to endNight
65%
585
27%
1560
19%
585
69%
585
56%
788
July1st to 15thNight
73%
555
19%
1480
15%
555
75%
555
44%
842
July16th to endNight
75%
612
24%
1555
21%
579
76%
579
45%
868
August1st to 15thNight
70%
575
22%
1748
22%
572
73%
572
41%
928
August16th to endNight
67%
615
29%
2050
28%
615
73%
615
40%
1057
September1st to 15thNight
64%
540
26%
1800
23%
540
73%
540
38%
947
September16th to endNight
60%
546
35%
1932
29%
546
71%
546
42%
923
October1st to 15thNight
39%
720
26%
2160
11%
720
51%
720
30%
1232
October16th to endNight
30%
804
34%
2340
10%
804
48%
804
34%
1233
November1st to 15thNight
31%
950
28%
2470
9%
950
44%
950
38%
1346
November16th to endNight
20%
975
33%
2649
6%
975
43%
975
33%
1377
December1st to 15thNight
15%
975
21%
2730
2%
975
32%
975
22%
1515
December16th to endNight
16%
1040
25%
2912
4%
1040
35%
1040
25%
1638

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
5%4244345%6%8%50%
51658
Night
442332345%7%59%
50784
TransparencyDay
29%8%14%23%17%5%
51333
Night
24%6%15%27%20%5%
50612
SeeingDay
11%18%33%23%11%3
7175
Night
8%21%30%25%12%1
17277

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
142442235%8%61%
1552
16th to endDay
32332345%8%61%
1820
February1st to 15thDay
426%4245%5%8%56%
1724
16th to endDay
6%2432425%9%56%
1710
March1st to 15thDay
2425%42335%8%57%
2005
16th to endDay
47%24425%46%9%47%
2376
April1st to 15thDay
5%6%2442445%8%49%
2330
16th to endDay
10%7%25%5%35%5%6%8%39%
2306
May1st to 15thDay
13%8%25%425%5%6%6%37%
2597
16th to endDay
10%6%25%6%36%6%7%8%36%
2840
June1st to 15thDay
5%314335%7%8%9%46%
2730
16th to endDay
3213325%5%7%9%54%
2730
July1st to 15thDay
6%325%5%35%5%7%8%46%
2730
16th to endDay
43146%46%7%7%9%43%
2867
August1st to 15thDay
6%325%6%46%6%6%9%41%
2456
16th to endDay
44245%45%5%6%9%48%
2449
September1st to 15thDay
8%413424447%53%
2160
16th to endDay
5%413423346%59%
2026
October1st to 15thDay
6%424323446%55%
1800
16th to endDay
45%1231345%6%61%
1870
November1st to 15thDay
231241446%8%59%
1718
16th to endDay
131332345%9%61%
1638
December1st to 15thDay
242432446%8%56%
1560
16th to endDay
25%4442336%6%57%
1664
January1st to 15thNight
313323347%66%
2716
16th to endNight
1313413346%66%
2766
February1st to 15thNight
15%24423447%61%
2458
16th to endNight
16%34443335%59%
2050
March1st to 15thNight
1324323348%61%
2282
16th to endNight
46%2432345%7%54%
2200
April1st to 15thNight
47%2442345%7%52%
1948
16th to endNight
11%8%23322447%48%
1929
May1st to 15thNight
13%6%2422445%7%47%
1679
16th to endNight
8%5%2443445%8%49%
1625
June1st to 15thNight
5%21331445%10%57%
1560
16th to endNight
32211235%7%67%
1560
July1st to 15thNight
5%31332446%11%53%
1560
16th to endNight
23143245%6%8%56%
1651
August1st to 15thNight
42134246%6%9%54%
1757
16th to endNight
44133245%6%8%55%
2050
September1st to 15thNight
9%413313347%57%
1800
16th to endNight
5%31231235%5%64%
1932
October1st to 15thNight
7%6%13323345%57%
2160
16th to endNight
45%22313336%63%
2340
November1st to 15thNight
2312223348%63%
2470
16th to endNight
132221335%8%64%
2649
December1st to 15thNight
2424322447%60%
2730
16th to endNight
243442345%7%58%
2912

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
21%8%21%30%14%3
1553
16th to endDay
20%5%18%31%18%4
1820
February1st to 15thDay
25%9%22%29%10%3
1724
16th to endDay
25%6%15%31%18%3
1710
March1st to 15thDay
25%6%16%27%20%3
2005
16th to endDay
31%9%15%25%14%3
2376
April1st to 15thDay
32%7%14%24%13%6%
2330
16th to endDay
40%8%14%21%12%2
2306
May1st to 15thDay
43%8%11%20%13%
2597
16th to endDay
40%11%13%19%11%2
2844
June1st to 15thDay
28%11%15%18%17%8%
2730
16th to endDay
22%8%12%23%21%12%
2730
July1st to 15thDay
33%8%13%15%17%11%
2581
16th to endDay
31%10%13%21%14%8%
2701
August1st to 15thDay
34%11%12%16%13%9%
2441
16th to endDay
30%8%12%20%21%6%
2449
September1st to 15thDay
28%6%11%19%22%11%
2160
16th to endDay
25%6%9%23%30%4
2026
October1st to 15thDay
29%6%12%22%23%5%
1800
16th to endDay
22%5%12%28%25%6%
1870
November1st to 15thDay
21%7%16%26%21%7%
1718
16th to endDay
19%7%13%32%22%4
1638
December1st to 15thDay
24%6%20%31%14%2
1560
16th to endDay
27%5%18%27%18%3
1664
January1st to 15thNight
19%5%20%30%19%4
2716
16th to endNight
19%5%16%31%21%5%
2766
February1st to 15thNight
24%6%21%32%12%2
2469
16th to endNight
26%413%28%21%4
2050
March1st to 15thNight
21%6%14%28%24%3
2282
16th to endNight
27%7%13%31%17%2
2200
April1st to 15thNight
30%7%14%29%14%4
1948
16th to endNight
35%6%12%26%16%2
1929
May1st to 15thNight
36%8%15%24%14%
1680
16th to endNight
31%9%18%23%14%2
1626
June1st to 15thNight
22%8%18%22%18%9%
1560
16th to endNight
15%5%9%30%23%14%
1560
July1st to 15thNight
24%6%16%24%17%10%
1480
16th to endNight
22%7%16%28%14%9%
1555
August1st to 15thNight
23%8%17%22%17%10%
1748
16th to endNight
23%6%12%24%23%8%
2050
September1st to 15thNight
26%5%13%19%20%14%
1800
16th to endNight
20%5%9%29%29%4
1932
October1st to 15thNight
27%7%11%21%24%6%
2160
16th to endNight
23%410%27%27%6%
2340
November1st to 15thNight
19%6%15%25%25%7%
2470
16th to endNight
18%6%13%31%25%5%
2649
December1st to 15thNight
23%6%20%28%16%3
2730
16th to endNight
25%6%19%28%17%2
2912

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%26%37%16%43
135
16th to endDay
7%40%30%19%
144
February1st to 15thDay
13%43%34%7%
135
16th to endDay
5%40%33%18%2
120
March1st to 15thDay
14%29%36%16%3
190
16th to endDay
13%35%39%9%2
352
April1st to 15thDay
16%37%33%10%1
329
16th to endDay
24%27%33%11%11
318
May1st to 15thDay
20%19%30%18%9%2
504
16th to endDay
14%14%29%22%14%3
597
June1st to 15thDay
7%10%33%28%16%3
570
16th to endDay
5%7%40%25%16%4
570
July1st to 15thDay
8%324%32%24%6%
550
16th to endDay
6%423%36%22%7%
582
August1st to 15thDay
9%5%38%33%10%1
359
16th to endDay
8%9%36%30%11%3
385
September1st to 15thDay
11%11%39%27%8%1
315
16th to endDay
10%12%35%24%11%4
192
October1st to 15thDay
9%14%39%23%8%3
135
16th to endDay
10%29%31%19%6%2
144
November1st to 15thDay
5%19%37%18%13%5%
135
16th to endDay
15%40%33%11%
135
December1st to 15thDay
13%47%26%12%
135
16th to endDay
350%31%13%2
144
January1st to 15thNight
8%38%32%13%5%2
975
16th to endNight
8%41%31%13%4
894
February1st to 15thNight
6%38%35%15%3
764
16th to endNight
8%34%39%15%2
684
March1st to 15thNight
427%41%19%6%
780
16th to endNight
7%25%35%25%4
744
April1st to 15thNight
12%18%39%23%5%
584
16th to endNight
19%18%28%24%8%
579
May1st to 15thNight
18%10%27%27%13%1
585
16th to endNight
11%8%25%31%21%1
611
June1st to 15thNight
5%7%29%38%17%2
585
16th to endNight
4323%44%21%1
585
July1st to 15thNight
7%112%41%33%4
555
16th to endNight
4110%43%36%3
612
August1st to 15thNight
418%43%30%2
575
16th to endNight
5%217%38%31%4
615
September1st to 15thNight
12%317%37%24%5%
540
16th to endNight
7%6%22%38%21%4
546
October1st to 15thNight
12%18%27%27%12%2
720
16th to endNight
10%22%34%20%9%2
804
November1st to 15thNight
7%22%36%23%7%1
950
16th to endNight
6%31%39%18%3
975
December1st to 15thNight
7%38%35%14%3
975
16th to endNight
6%33%39%15%4
1040
Page generated at 2018-08-30 03:34:23. Version ac04

Copyright 2018 A. Danko


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