Banner Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Banner Creek Observatory clear sky chart from 2005-11-05 to 2019-06-19.

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
37%
18327
20%
54169
12%
18280
45%
18280
32%
32398

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
30%
1050
21%
2717
9%
1045
39%
1045
32%
1744
January16th to endNight
26%
1120
21%
2912
8%
1120
34%
1120
33%
1834
February1st to 15thNight
24%
1030
15%
2678
5%
1026
30%
1026
23%
1883
February16th to endNight
24%
779
18%
2249
5%
779
33%
779
27%
1432
March1st to 15thNight
30%
630
21%
2310
12%
630
42%
630
24%
1332
March16th to endNight
25%
672
14%
2464
9%
672
33%
672
18%
1594
April1st to 15thNight
27%
629
19%
2195
12%
629
40%
629
26%
1276
April16th to endNight
25%
624
15%
1906
9%
624
35%
624
25%
1232
May1st to 15thNight
35%
629
16%
1890
13%
629
41%
629
26%
1215
May16th to endNight
39%
659
14%
1972
10%
657
44%
657
33%
1190
June1st to 15thNight
52%
630
21%
1747
13%
630
56%
630
43%
977
June16th to endNight
50%
597
18%
1699
10%
597
54%
597
49%
881
July1st to 15thNight
62%
555
18%
1665
14%
555
64%
555
43%
893
July16th to endNight
59%
612
21%
1738
19%
579
65%
579
44%
917
August1st to 15thNight
67%
575
22%
1717
24%
572
71%
572
43%
931
August16th to endNight
63%
621
24%
1921
25%
621
66%
621
40%
1039
September1st to 15thNight
54%
585
25%
2060
26%
585
59%
585
32%
1132
September16th to endNight
55%
582
26%
2145
21%
582
64%
582
37%
1054
October1st to 15thNight
39%
741
25%
2301
18%
741
45%
741
29%
1392
October16th to endNight
39%
832
27%
2496
13%
832
50%
832
38%
1352
November1st to 15thNight
37%
955
27%
2595
13%
955
47%
955
39%
1495
November16th to endNight
31%
1050
22%
2848
8%
1050
41%
1050
36%
1677
December1st to 15thNight
28%
1050
18%
2940
8%
1050
36%
1050
28%
1883
December16th to endNight
25%
1120
20%
3004
8%
1120
35%
1120
25%
2043

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
22%5%24423346%40%
54526
Night
21%5%14323345%44%
54365
Cloud CoverDay
11%6%25%42445%7%44%
54524
Night
10%5%24423347%50%
54365
TransparencyDay
37%6%13%24%15%2
54224
Night
33%5%13%26%18%3
54170
SeeingDay
14%7%29%29%15%3
8230
Night
13%8%32%33%12%
18328

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
23%5%25%333346%38%
1881
16th to endDay
24%8%25%42334436%
2016
February1st to 15thDay
23%8%26%5%23345%33%
1845
16th to endDay
23%7%37%423245%36%
1809
March1st to 15thDay
24%8%1442335%5%35%
2310
16th to endDay
28%9%34422335%30%
2464
April1st to 15thDay
26%6%2442343437%
2411
16th to endDay
29%7%25%5%33445%29%
2656
May1st to 15thDay
26%5%25%424346%34%
2721
16th to endDay
27%414324446%34%
2846
June1st to 15thDay
21%314423446%42%
2866
16th to endDay
18%21332445%7%44%
2660
July1st to 15thDay
21%31342346%7%40%
2535
16th to endDay
21%21333445%7%42%
2674
August1st to 15thDay
15%31342446%8%44%
2486
16th to endDay
15%41443435%7%46%
2631
September1st to 15thDay
18%4145%33347%43%
2226
16th to endDay
14%313323346%50%
2145
October1st to 15thDay
21%5%23322345%45%
1976
16th to endDay
16%413312335%53%
2080
November1st to 15thDay
21%5%1331233449%
1921
16th to endDay
25%5%14211335%45%
1769
December1st to 15thDay
25%7%24424345%35%
1680
16th to endDay
24%8%27%41234434%
1918
January1st to 15thNight
21%6%24432345%41%
2717
16th to endNight
22%6%25%323335%41%
2912
February1st to 15thNight
22%8%36%5%2334435%
2668
16th to endNight
23%6%24423335%39%
2249
March1st to 15thNight
22%6%2442333442%
2310
16th to endNight
29%7%24413345%34%
2464
April1st to 15thNight
22%6%24323245%41%
2195
16th to endNight
29%5%24323345%35%
1906
May1st to 15thNight
25%5%14323346%39%
1889
16th to endNight
24%31432335%7%40%
1971
June1st to 15thNight
20%22224337%50%
1747
16th to endNight
17%11223449%52%
1699
July1st to 15thNight
20%23212447%49%
1755
16th to endNight
19%11332335%9%45%
1846
August1st to 15thNight
12%21331345%8%52%
1727
16th to endNight
12%31331334456%
1921
September1st to 15thNight
17%413323347%47%
2060
16th to endNight
14%312223346%55%
2145
October1st to 15thNight
22%5%2321323447%
2301
16th to endNight
16%412213225%57%
2496
November1st to 15thNight
19%413222245%51%
2595
16th to endNight
23%31321233448%
2848
December1st to 15thNight
24%7%1442333440%
2940
16th to endNight
25%8%25%32223437%
3004

Percentage Cloud Cover SE (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
10%6%26%44445%7%45%
1881
16th to endDay
10%9%36%43445%5%43%
2016
February1st to 15thDay
11%9%47%5%3335%6%38%
1845
16th to endDay
10%7%37%5%24346%42%
1809
March1st to 15thDay
12%9%25%5%3445%6%40%
2310
16th to endDay
18%10%45%5%23346%34%
2462
April1st to 15thDay
14%7%25%434445%43%
2411
16th to endDay
17%7%35%5%3445%6%36%
2656
May1st to 15thDay
15%6%36%5%35%45%6%37%
2721
16th to endDay
14%426%435%6%5%7%40%
2846
June1st to 15thDay
8%425%425%5%5%8%47%
2866
16th to endDay
5%324425%6%6%9%50%
2660
July1st to 15thDay
8%324425%5%7%9%46%
2535
16th to endDay
6%323435%5%6%10%49%
2674
August1st to 15thDay
7%3145%245%7%9%47%
2486
16th to endDay
9%4145%3445%8%48%
2631
September1st to 15thDay
11%4245%34347%47%
2226
16th to endDay
7%41442445%7%53%
2145
October1st to 15thDay
14%6%23423446%48%
1976
16th to endDay
11%413423335%56%
2080
November1st to 15thDay
9%5%13423336%55%
1921
16th to endDay
12%6%34313246%50%
1769
December1st to 15thDay
11%8%35%43445%6%42%
1680
16th to endDay
13%9%48%423446%37%
1918
January1st to 15thNight
8%7%34433446%48%
2717
16th to endNight
8%6%25%423446%50%
2912
February1st to 15thNight
10%9%47%6%35%446%39%
2668
16th to endNight
10%7%25%434446%46%
2249
March1st to 15thNight
9%6%245%25%346%49%
2310
16th to endNight
18%8%3442335%6%38%
2464
April1st to 15thNight
10%6%245%2435%7%48%
2195
16th to endNight
17%6%24423346%44%
1906
May1st to 15thNight
12%6%3443446%6%43%
1889
16th to endNight
10%42432335%10%47%
1971
June1st to 15thNight
6%31222435%9%57%
1747
16th to endNight
411232345%11%59%
1699
July1st to 15thNight
6%21332345%10%56%
1755
16th to endNight
42144245%7%10%53%
1846
August1st to 15thNight
33143235%5%10%55%
1727
16th to endNight
6%314324445%58%
1921
September1st to 15thNight
11%413323446%52%
2060
16th to endNight
8%312223446%59%
2145
October1st to 15thNight
15%5%24313335%50%
2301
16th to endNight
10%5%13213225%60%
2496
November1st to 15thNight
8%5%13222346%57%
2595
16th to endNight
10%423323445%55%
2848
December1st to 15thNight
11%7%25%424445%46%
2940
16th to endNight
13%10%36%323246%42%
3004

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
38%5%14%25%14%1
1882
16th to endDay
41%6%15%23%12%1
2016
February1st to 15thDay
45%6%16%21%7%2
1846
16th to endDay
42%5%13%22%14%1
1809
March1st to 15thDay
43%5%11%22%14%2
2310
16th to endDay
51%5%13%20%8%1
2464
April1st to 15thDay
42%6%13%22%15%
2411
16th to endDay
46%7%11%23%10%
2656
May1st to 15thDay
46%7%11%21%12%
2721
16th to endDay
41%8%15%22%10%1
2850
June1st to 15thDay
33%7%13%26%16%1
2866
16th to endDay
27%8%18%27%16%2
2660
July1st to 15thDay
31%8%13%28%13%4
2396
16th to endDay
28%7%15%29%16%2
2519
August1st to 15thDay
30%8%15%27%16%1
2472
16th to endDay
33%7%11%25%17%5%
2631
September1st to 15thDay
36%5%12%21%17%5%
2226
16th to endDay
29%6%11%28%22%1
2145
October1st to 15thDay
36%6%10%22%21%3
1976
16th to endDay
30%411%27%21%5%
2080
November1st to 15thDay
30%413%26%20%4
1921
16th to endDay
34%49%29%19%1
1769
December1st to 15thDay
41%5%16%24%10%1
1680
16th to endDay
46%5%13%20%11%1
1918
January1st to 15thNight
37%415%25%17%
2717
16th to endNight
35%5%14%26%15%2
2912
February1st to 15thNight
45%6%13%21%10%2
2678
16th to endNight
38%5%11%21%18%4
2249
March1st to 15thNight
36%5%11%24%18%3
2310
16th to endNight
46%5%14%21%10%2
2464
April1st to 15thNight
35%5%11%26%18%2
2195
16th to endNight
41%5%12%23%15%1
1906
May1st to 15thNight
39%6%14%22%14%1
1890
16th to endNight
32%6%19%24%14%1
1973
June1st to 15thNight
24%6%16%32%16%3
1747
16th to endNight
18%7%14%33%22%3
1699
July1st to 15thNight
23%6%14%31%18%5%
1665
16th to endNight
24%414%33%21%1
1738
August1st to 15thNight
23%7%16%30%19%2
1717
16th to endNight
26%5%11%28%21%6%
1921
September1st to 15thNight
31%411%24%20%6%
2060
16th to endNight
25%412%28%25%3
2145
October1st to 15thNight
37%48%22%21%5%
2301
16th to endNight
28%39%27%26%4
2496
November1st to 15thNight
28%412%25%22%6%
2595
16th to endNight
31%311%31%19%2
2848
December1st to 15thNight
38%5%13%27%13%1
2940
16th to endNight
43%5%12%22%13%2
3004

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
18%12%41%20%6%
180
16th to endDay
19%14%43%19%3
192
February1st to 15thDay
20%20%45%11%3
180
16th to endDay
18%20%44%9%7%
159
March1st to 15thDay
21%17%40%18%1
180
16th to endDay
27%14%37%14%5%1
192
April1st to 15thDay
20%12%36%24%5%
290
16th to endDay
22%13%35%17%8%1
548
May1st to 15thDay
17%10%31%27%11%1
618
16th to endDay
19%7%32%27%11%2
677
June1st to 15thDay
7%429%34%18%4
645
16th to endDay
6%332%37%16%3
587
July1st to 15thDay
9%116%36%27%7%
550
16th to endDay
7%113%42%30%4
595
August1st to 15thDay
8%116%39%30%3
549
16th to endDay
11%218%34%25%6%
543
September1st to 15thDay
12%222%29%26%7%
261
16th to endDay
11%228%37%15%4
180
October1st to 15thDay
23%8%32%26%36%
180
16th to endDay
11%10%39%27%9%1
192
November1st to 15thDay
18%7%27%30%12%2
180
16th to endDay
23%11%35%20%10%
180
December1st to 15thDay
13%17%41%19%5%2
180
16th to endDay
22%18%34%21%3
192
January1st to 15thNight
12%12%37%30%7%
1050
16th to endNight
13%10%40%30%5%
1120
February1st to 15thNight
15%12%38%29%3
1030
16th to endNight
15%12%40%26%5%
779
March1st to 15thNight
13%10%37%30%6%
630
16th to endNight
23%9%37%23%5%
672
April1st to 15thNight
13%11%39%29%5%
629
16th to endNight
19%11%35%24%8%
624
May1st to 15thNight
14%9%30%34%10%
630
16th to endNight
11%6%32%35%13%1
659
June1st to 15thNight
8%325%44%19%
630
16th to endNight
5%229%45%16%
597
July1st to 15thNight
6%117%45%27%1
555
16th to endNight
414%50%27%1
612
August1st to 15thNight
413%48%30%2
575
16th to endNight
6%218%38%30%3
621
September1st to 15thNight
14%319%36%23%3
585
16th to endNight
8%325%37%22%2
582
October1st to 15thNight
19%6%29%28%14%
741
16th to endNight
13%7%34%32%10%
832
November1st to 15thNight
11%10%33%34%9%
955
16th to endNight
14%10%36%30%8%
1050
December1st to 15thNight
16%12%34%29%6%
1050
16th to endNight
18%9%35%29%6%
1120
Page generated at 2019-06-20 07:02:28. Version ac04

Copyright 2019 A. Danko


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