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 2017-09-22.

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
43%
15931
23%
47115
13%
15884
51%
15884
32%
28034

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
34%
900
22%
2327
9%
895
43%
895
33%
1473
January16th to endNight
29%
960
26%
2496
10%
960
40%
960
33%
1567
February1st to 15thNight
28%
880
15%
2288
5%
876
34%
876
23%
1613
February16th to endNight
29%
669
24%
1931
7%
669
42%
669
30%
1193
March1st to 15thNight
35%
540
22%
1980
13%
540
47%
540
25%
1141
March16th to endNight
28%
576
15%
2112
9%
576
37%
576
19%
1352
April1st to 15thNight
32%
539
19%
1881
12%
539
46%
539
26%
1084
April16th to endNight
30%
540
21%
1650
13%
540
43%
540
24%
1079
May1st to 15thNight
40%
539
18%
1620
15%
539
47%
539
25%
1045
May16th to endNight
44%
563
17%
1684
11%
561
51%
561
32%
1029
June1st to 15thNight
58%
540
19%
1497
11%
540
62%
540
40%
860
June16th to endNight
61%
540
24%
1539
15%
540
65%
540
51%
788
July1st to 15thNight
68%
510
17%
1530
13%
510
70%
510
41%
832
July16th to endNight
70%
564
25%
1594
23%
531
73%
531
45%
839
August1st to 15thNight
74%
539
23%
1610
25%
536
77%
536
43%
868
August16th to endNight
69%
573
26%
1773
28%
573
73%
573
40%
955
September1st to 15thNight
60%
540
24%
1902
25%
540
65%
540
33%
1037
September16th to endNight
58%
513
29%
1891
23%
513
68%
513
36%
937
October1st to 15thNight
45%
627
28%
1947
20%
627
51%
627
31%
1137
October16th to endNight
40%
704
28%
2112
14%
704
51%
704
38%
1149
November1st to 15thNight
43%
815
30%
2215
14%
815
54%
815
41%
1240
November16th to endNight
35%
900
25%
2441
10%
900
46%
900
35%
1448
December1st to 15thNight
30%
900
19%
2520
8%
900
39%
900
26%
1643
December16th to endNight
32%
960
23%
2575
10%
960
42%
960
27%
1725

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
23%5%14423346%39%
47747
Night
23%413323345%44%
47311
Cloud CoverDay
11%6%25%42445%7%45%
47745
Night
10%5%24423347%50%
47311
TransparencyDay
37%6%13%24%15%2
47445
Night
33%5%13%26%17%3
47116
SeeingDay
13%7%27%31%17%3
5940
Night
12%8%31%34%12%
15932

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
25%415%333446%37%
1611
16th to endDay
25%7%25%41334336%
1728
February1st to 15thDay
25%7%35%423346%34%
1575
16th to endDay
24%6%37%323235%38%
1554
March1st to 15thDay
26%8%145%2335%5%32%
1980
16th to endDay
30%8%24422335%31%
2112
April1st to 15thDay
29%6%1442333435%
2065
16th to endDay
31%7%25%5%33445%27%
2307
May1st to 15thDay
28%5%14424345%34%
2331
16th to endDay
30%414324346%33%
2430
June1st to 15thDay
24%415%323446%39%
2457
16th to endDay
19%21332345%7%45%
2413
July1st to 15thDay
23%31342346%7%37%
2340
16th to endDay
22%21333445%7%41%
2466
August1st to 15thDay
15%31342445%8%44%
2340
16th to endDay
15%414433347%47%
2428
September1st to 15thDay
17%4145%33347%44%
2055
16th to endDay
15%313323446%49%
1881
October1st to 15thDay
20%42332243448%
1672
16th to endDay
17%413312335%51%
1760
November1st to 15thDay
20%41232223451%
1641
16th to endDay
28%5%1321133443%
1517
December1st to 15thDay
28%7%25%424335%32%
1440
16th to endDay
26%8%37%31234433%
1644
January1st to 15thNight
22%5%23433335%41%
2327
16th to endNight
24%6%25%322335%41%
2496
February1st to 15thNight
23%7%35%5%2333434%
2278
16th to endNight
23%6%24323336%40%
1931
March1st to 15thNight
25%5%2442333441%
1980
16th to endNight
30%6%23323345%34%
2112
April1st to 15thNight
25%5%24313245%41%
1881
16th to endNight
31%5%25%423335%32%
1650
May1st to 15thNight
27%5%24323345%38%
1619
16th to endNight
27%31432325%7%38%
1683
June1st to 15thNight
22%22324336%47%
1497
16th to endNight
18%11213349%52%
1539
July1st to 15thNight
22%22212448%46%
1620
16th to endNight
21%11332335%9%45%
1702
August1st to 15thNight
12%11331345%9%52%
1620
16th to endNight
13%31331334457%
1773
September1st to 15thNight
17%413323347%47%
1902
16th to endNight
15%312323346%54%
1891
October1st to 15thNight
21%42321323449%
1947
16th to endNight
18%41221222456%
2112
November1st to 15thNight
20%313222235%53%
2215
16th to endNight
26%31221233447%
2441
December1st to 15thNight
27%7%1442333436%
2520
16th to endNight
28%8%25%31223438%
2575

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
9%5%26%44445%7%46%
1611
16th to endDay
10%8%36%42445%5%44%
1728
February1st to 15thDay
11%8%47%5%2435%7%39%
1575
16th to endDay
9%7%37%424346%44%
1554
March1st to 15thDay
12%8%25%5%35%46%6%38%
1980
16th to endDay
18%10%45%5%23346%35%
2110
April1st to 15thDay
14%7%25%424445%43%
2065
16th to endDay
18%8%35%5%3445%5%35%
2307
May1st to 15thDay
15%6%36%5%25%45%6%37%
2331
16th to endDay
14%5%26%4345%48%40%
2430
June1st to 15thDay
8%425%5%25%5%48%45%
2457
16th to endDay
5%214425%6%6%9%50%
2413
July1st to 15thDay
8%3245%25%5%7%9%44%
2340
16th to endDay
6%3234345%6%10%49%
2466
August1st to 15thDay
7%3244245%6%9%47%
2340
16th to endDay
9%4145%2445%7%49%
2428
September1st to 15thDay
10%425%5%3435%7%48%
2055
16th to endDay
7%31442446%7%53%
1881
October1st to 15thDay
11%5%23323436%52%
1672
16th to endDay
11%414423436%54%
1760
November1st to 15thDay
7%413323336%58%
1641
16th to endDay
13%6%34313346%49%
1517
December1st to 15thDay
12%8%35%5%35%5%5%6%40%
1440
16th to endDay
13%9%48%423347%38%
1644
January1st to 15thNight
7%6%24444446%49%
2327
16th to endNight
8%6%26%423346%50%
2496
February1st to 15thNight
10%9%47%6%35%446%38%
2278
16th to endNight
9%7%24324447%48%
1931
March1st to 15thNight
9%6%25%5%25%346%49%
1980
16th to endNight
18%8%34323347%39%
2112
April1st to 15thNight
11%5%245%23346%49%
1881
16th to endNight
17%6%24423346%43%
1650
May1st to 15thNight
12%6%4443445%6%43%
1619
16th to endNight
10%42432435%10%47%
1683
June1st to 15thNight
6%412325%45%8%55%
1497
16th to endNight
311132435%11%61%
1539
July1st to 15thNight
6%2134235%5%10%54%
1620
16th to endNight
5%1134245%6%10%54%
1702
August1st to 15thNight
332432345%10%55%
1620
16th to endNight
6%314423445%59%
1773
September1st to 15thNight
10%413423447%52%
1902
16th to endNight
7%31322445%6%58%
1891
October1st to 15thNight
13%424313245%52%
1947
16th to endNight
11%5%13213225%59%
2112
November1st to 15thNight
7%413222346%59%
2215
16th to endNight
12%5%23323345%54%
2441
December1st to 15thNight
11%8%25%5%24445%45%
2520
16th to endNight
14%9%35%323247%43%
2575

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
37%5%15%26%14%1
1612
16th to endDay
40%5%15%24%12%1
1728
February1st to 15thDay
44%6%16%22%8%2
1576
16th to endDay
40%5%13%24%14%2
1554
March1st to 15thDay
44%5%11%23%13%1
1980
16th to endDay
50%5%13%20%8%1
2112
April1st to 15thDay
42%6%12%21%16%
2065
16th to endDay
48%7%11%21%10%
2307
May1st to 15thDay
46%7%10%21%12%
2331
16th to endDay
41%8%15%21%11%1
2434
June1st to 15thDay
35%7%13%25%15%1
2457
16th to endDay
26%7%18%28%16%2
2413
July1st to 15thDay
32%8%14%28%13%2
2201
16th to endDay
27%7%15%29%16%2
2311
August1st to 15thDay
29%8%15%26%17%1
2326
16th to endDay
32%6%11%24%18%5%
2428
September1st to 15thDay
35%5%13%21%18%5%
2055
16th to endDay
28%7%11%28%22%
1881
October1st to 15thDay
32%6%10%24%23%3
1672
16th to endDay
31%412%26%20%4
1760
November1st to 15thDay
27%412%27%22%5%
1641
16th to endDay
36%5%9%29%18%1
1517
December1st to 15thDay
43%5%16%23%9%
1440
16th to endDay
46%5%14%21%11%1
1644
January1st to 15thNight
35%415%26%17%
2327
16th to endNight
34%5%14%26%15%3
2496
February1st to 15thNight
46%6%11%22%11%2
2288
16th to endNight
35%5%12%23%18%3
1931
March1st to 15thNight
35%6%12%24%17%3
1980
16th to endNight
45%5%14%21%10%2
2112
April1st to 15thNight
35%410%26%19%2
1881
16th to endNight
42%5%12%22%15%
1650
May1st to 15thNight
40%6%13%22%16%1
1620
16th to endNight
33%7%19%23%15%1
1685
June1st to 15thNight
26%7%16%31%14%3
1497
16th to endNight
18%6%14%34%23%3
1539
July1st to 15thNight
24%6%15%31%17%4
1530
16th to endNight
24%414%32%22%1
1594
August1st to 15thNight
22%7%17%30%18%2
1610
16th to endNight
26%5%10%27%22%7%
1773
September1st to 15thNight
31%412%25%19%7%
1902
16th to endNight
25%5%11%28%25%3
1891
October1st to 15thNight
34%48%23%23%5%
1947
16th to endNight
29%210%29%23%4
2112
November1st to 15thNight
25%412%25%23%8%
2215
16th to endNight
32%310%31%19%2
2441
December1st to 15thNight
40%5%13%27%12%
2520
16th to endNight
41%5%13%24%12%2
2575

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
22%13%43%15%41
90
16th to endDay
17%14%39%23%4
96
February1st to 15thDay
13%21%44%15%5%
90
16th to endDay
12%19%45%9%12%
81
March1st to 15thDay
13%23%42%20%1
90
16th to endDay
25%16%38%15%4
96
April1st to 15thDay
20%10%32%27%8%
184
16th to endDay
25%13%35%17%7%1
417
May1st to 15thDay
17%11%31%25%11%1
468
16th to endDay
19%7%33%27%9%2
517
June1st to 15thDay
8%429%34%19%4
495
16th to endDay
5%433%35%17%4
495
July1st to 15thDay
10%218%39%24%4
475
16th to endDay
7%111%42%32%4
515
August1st to 15thDay
7%115%40%30%3
493
16th to endDay
10%216%36%27%6%
468
September1st to 15thDay
7%225%33%23%7%
210
16th to endDay
8%29%42%12%5%
108
October1st to 15thDay
10%11%25%37%5%10%
90
16th to endDay
7%9%40%29%12%1
96
November1st to 15thDay
10%322%40%18%5%
90
16th to endDay
33%10%42%10%4
90
December1st to 15thDay
13%20%45%14%33
90
16th to endDay
26%20%31%19%2
96
January1st to 15thNight
11%12%37%30%7%
900
16th to endNight
13%10%41%29%5%
960
February1st to 15thNight
15%11%38%30%3
880
16th to endNight
13%11%41%27%5%
669
March1st to 15thNight
12%10%37%32%7%
540
16th to endNight
23%9%37%23%5%
576
April1st to 15thNight
14%11%38%30%5%
539
16th to endNight
19%11%35%25%7%
540
May1st to 15thNight
13%10%31%34%10%
540
16th to endNight
11%6%34%34%12%
563
June1st to 15thNight
8%225%43%18%
540
16th to endNight
4229%46%16%
540
July1st to 15thNight
7%117%47%25%1
510
16th to endNight
415%51%27%
564
August1st to 15thNight
412%51%30%1
539
16th to endNight
6%215%40%31%4
573
September1st to 15thNight
12%319%37%23%3
540
16th to endNight
7%326%36%23%2
513
October1st to 15thNight
16%5%29%30%16%1
627
16th to endNight
14%7%33%32%10%
704
November1st to 15thNight
9%11%32%35%10%
815
16th to endNight
15%11%36%29%7%
900
December1st to 15thNight
17%12%36%28%5%
900
16th to endNight
19%8%34%30%6%
960
Page generated at 2017-09-23 05:43:44. Version ac04

Copyright 2017 A. Danko


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