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 2017-09-17.

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
36%
15991
25%
46870
11%
15945
50%
15945
31%
25596

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
19%
900
28%
2506
6%
895
39%
895
26%
1289
January16th to endNight
14%
825
31%
2553
6%
825
40%
825
22%
1261
February1st to 15thNight
15%
701
23%
2275
3%
698
37%
698
19%
1188
February16th to endNight
12%
632
27%
1894
3%
632
38%
632
22%
1049
March1st to 15thNight
22%
720
26%
2106
7%
720
39%
720
29%
1140
March16th to endNight
28%
687
23%
2031
9%
687
42%
687
27%
1164
April1st to 15thNight
29%
539
21%
1798
8%
539
47%
539
24%
1014
April16th to endNight
29%
540
20%
1800
10%
540
43%
540
22%
1075
May1st to 15thNight
38%
540
18%
1551
11%
540
45%
540
27%
986
May16th to endNight
48%
563
17%
1498
10%
561
54%
561
31%
947
June1st to 15thNight
52%
540
19%
1440
11%
540
58%
540
41%
826
June16th to endNight
67%
540
28%
1440
19%
540
72%
540
59%
713
July1st to 15thNight
71%
510
17%
1360
14%
510
73%
510
42%
785
July16th to endNight
76%
564
25%
1426
22%
531
77%
531
45%
796
August1st to 15thNight
70%
539
21%
1638
21%
536
72%
536
40%
876
August16th to endNight
69%
573
30%
1910
29%
573
74%
573
40%
978
September1st to 15thNight
64%
540
26%
1800
23%
540
73%
540
38%
947
September16th to endNight
62%
506
35%
1791
30%
506
72%
506
45%
833
October1st to 15thNight
39%
660
26%
1980
12%
660
51%
660
29%
1139
October16th to endNight
31%
737
31%
2145
10%
737
48%
737
34%
1134
November1st to 15thNight
30%
875
29%
2275
9%
875
44%
875
38%
1238
November16th to endNight
21%
900
32%
2445
7%
900
42%
900
33%
1277
December1st to 15thNight
15%
900
20%
2520
3%
900
32%
900
21%
1425
December16th to endNight
17%
960
25%
2688
4%
960
36%
960
25%
1516

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%
47923
Night
442332345%7%58%
47042
TransparencyDay
29%8%14%23%17%5%
47598
Night
24%6%15%27%19%5%
46870
SeeingDay
11%16%32%23%11%3
5903
Night
8%21%30%25%12%1
15994

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
1424422348%61%
1432
16th to endDay
32432345%8%61%
1680
February1st to 15thDay
426%4245%5%8%55%
1588
16th to endDay
16%25%31426%9%55%
1580
March1st to 15thDay
2435%42335%8%55%
1851
16th to endDay
46%24425%46%8%48%
2193
April1st to 15thDay
6%6%24425%5%5%8%48%
2150
16th to endDay
10%7%25%5%35%5%7%8%38%
2160
May1st to 15thDay
12%8%25%425%5%6%6%38%
2397
16th to endDay
10%6%25%6%46%6%7%8%36%
2616
June1st to 15thDay
6%314335%7%8%9%45%
2520
16th to endDay
2213325%5%7%9%56%
2520
July1st to 15thDay
6%4245%35%5%7%8%45%
2520
16th to endDay
43146%46%7%7%9%43%
2644
August1st to 15thDay
6%325%6%46%6%6%9%41%
2313
16th to endDay
44245%35%46%8%48%
2292
September1st to 15thDay
8%413424447%53%
2160
16th to endDay
4413423346%61%
1872
October1st to 15thDay
6%424324446%54%
1650
16th to endDay
46%1231345%6%60%
1714
November1st to 15thDay
231241446%8%59%
1583
16th to endDay
131332345%9%60%
1512
December1st to 15thDay
25%3432446%8%54%
1440
16th to endDay
25%4442335%7%57%
1536
January1st to 15thNight
313323347%66%
2506
16th to endNight
1413413346%66%
2553
February1st to 15thNight
15%24423447%60%
2264
16th to endNight
17%34343335%59%
1894
March1st to 15thNight
1325%323348%60%
2106
16th to endNight
46%2431345%8%54%
2031
April1st to 15thNight
46%2443446%7%52%
1798
16th to endNight
11%8%23323447%48%
1800
May1st to 15thNight
12%6%2421445%7%47%
1550
16th to endNight
8%5%2443445%8%49%
1497
June1st to 15thNight
5%31341445%10%56%
1440
16th to endNight
22211235%7%69%
1440
July1st to 15thNight
5%31432446%11%52%
1440
16th to endNight
2214335%5%6%8%57%
1522
August1st to 15thNight
42134246%6%10%53%
1647
16th to endNight
441232446%8%56%
1910
September1st to 15thNight
9%413313347%57%
1800
16th to endNight
421231235%6%65%
1791
October1st to 15thNight
7%6%13323345%56%
1980
16th to endNight
45%22313336%62%
2145
November1st to 15thNight
2312223348%64%
2275
16th to endNight
132221335%8%64%
2445
December1st to 15thNight
2425%32345%7%58%
2520
16th to endNight
2434423447%58%
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
21%7%21%31%14%3
1433
16th to endDay
21%5%18%32%17%4
1680
February1st to 15thDay
25%9%21%29%9%3
1588
16th to endDay
25%7%16%31%16%3
1580
March1st to 15thDay
26%6%17%27%18%3
1851
16th to endDay
30%9%15%25%15%3
2193
April1st to 15thDay
32%8%14%24%13%6%
2150
16th to endDay
40%8%14%22%11%2
2160
May1st to 15thDay
43%8%11%20%14%
2397
16th to endDay
41%12%13%19%11%2
2620
June1st to 15thDay
29%11%16%18%17%6%
2520
16th to endDay
20%8%12%24%22%12%
2520
July1st to 15thDay
34%8%13%16%15%12%
2371
16th to endDay
31%10%14%21%13%8%
2478
August1st to 15thDay
35%11%12%16%13%9%
2298
16th to endDay
30%7%11%20%22%6%
2292
September1st to 15thDay
28%6%11%19%22%11%
2160
16th to endDay
23%6%10%24%31%4
1872
October1st to 15thDay
29%7%12%22%22%5%
1650
16th to endDay
22%5%13%28%25%5%
1714
November1st to 15thDay
21%7%16%25%21%7%
1583
16th to endDay
19%7%13%32%21%5%
1512
December1st to 15thDay
26%6%20%31%13%1
1440
16th to endDay
27%6%18%26%17%3
1536
January1st to 15thNight
19%5%20%30%19%4
2506
16th to endNight
20%5%16%31%21%5%
2553
February1st to 15thNight
24%6%20%33%12%2
2275
16th to endNight
26%5%14%28%20%4
1894
March1st to 15thNight
22%7%14%29%22%3
2106
16th to endNight
27%7%13%31%17%2
2031
April1st to 15thNight
30%7%14%27%14%5%
1798
16th to endNight
36%6%12%27%15%1
1800
May1st to 15thNight
35%8%15%24%14%
1551
16th to endNight
31%9%18%23%13%2
1498
June1st to 15thNight
23%8%19%23%16%7%
1440
16th to endNight
13%6%9%30%24%15%
1440
July1st to 15thNight
25%7%16%23%15%10%
1360
16th to endNight
22%7%16%28%14%10%
1426
August1st to 15thNight
23%8%17%21%18%10%
1638
16th to endNight
23%6%11%24%25%8%
1910
September1st to 15thNight
26%5%13%19%20%14%
1800
16th to endNight
18%5%9%30%30%4
1791
October1st to 15thNight
27%7%12%21%24%5%
1980
16th to endNight
23%411%28%26%5%
2145
November1st to 15thNight
18%6%16%24%25%8%
2275
16th to endNight
18%6%12%31%25%5%
2445
December1st to 15thNight
25%7%21%28%15%2
2520
16th to endNight
25%7%19%28%16%1
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
15%22%33%16%6%5%
90
16th to endDay
8%42%27%19%11
96
February1st to 15thDay
12%43%34%8%1
90
16th to endDay
7%37%30%20%3
81
March1st to 15thDay
14%30%36%14%3
141
16th to endDay
13%34%41%9%2
288
April1st to 15thDay
16%33%33%13%2
269
16th to endDay
25%30%32%8%11
270
May1st to 15thDay
19%21%30%17%9%2
432
16th to endDay
14%15%30%22%13%3
517
June1st to 15thDay
8%9%32%28%16%3
495
16th to endDay
46%41%24%17%5%
495
July1st to 15thDay
9%325%32%22%6%
475
16th to endDay
6%321%37%23%7%
503
August1st to 15thDay
9%5%37%34%11%1
315
16th to endDay
8%6%37%32%11%3
332
September1st to 15thDay
11%11%39%27%8%1
315
16th to endDay
5%12%37%24%14%5%
147
October1st to 15thDay
8%8%41%25%12%3
90
16th to endDay
12%21%31%25%6%3
96
November1st to 15thDay
416%31%21%17%8%
90
16th to endDay
20%37%31%11%
90
December1st to 15thDay
12%48%25%13%
90
16th to endDay
346%30%16%3
96
January1st to 15thNight
8%38%30%13%6%2
900
16th to endNight
8%42%30%12%4
825
February1st to 15thNight
6%38%34%15%3
704
16th to endNight
8%35%39%13%2
632
March1st to 15thNight
428%42%17%6%
720
16th to endNight
8%25%35%25%4
687
April1st to 15thNight
11%18%37%25%5%
539
16th to endNight
18%19%28%24%7%
540
May1st to 15thNight
18%11%28%27%13%1
540
16th to endNight
11%9%25%31%20%1
563
June1st to 15thNight
6%6%30%38%15%2
540
16th to endNight
3322%45%23%1
540
July1st to 15thNight
7%112%41%33%4
510
16th to endNight
3110%42%37%3
564
August1st to 15thNight
418%44%30%2
539
16th to endNight
5%215%38%31%5%
573
September1st to 15thNight
12%317%37%24%5%
540
16th to endNight
5%5%23%38%22%4
506
October1st to 15thNight
12%19%26%26%13%2
660
16th to endNight
10%21%34%21%9%2
737
November1st to 15thNight
7%23%37%22%8%1
875
16th to endNight
6%30%39%19%3
900
December1st to 15thNight
8%37%35%14%4
900
16th to endNight
6%33%38%16%4
960
Page generated at 2017-09-18 06:38:24. Version ac04

Copyright 2017 A. Danko


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