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 2017-04-07.

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%
15433
20%
45586
12%
15386
44%
15386
32%
27237

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%
900
21%
2327
9%
895
38%
895
33%
1473
January16th to endNight
25%
960
20%
2496
8%
960
33%
960
33%
1567
February1st to 15thNight
24%
880
15%
2288
5%
876
30%
876
23%
1613
February16th to endNight
24%
669
20%
1931
5%
669
35%
669
30%
1193
March1st to 15thNight
31%
540
20%
1980
12%
540
41%
540
25%
1141
March16th to endNight
25%
576
14%
2112
9%
576
34%
576
19%
1352
April1st to 15thNight
26%
515
19%
1801
12%
515
40%
515
26%
1047
April16th to endNight
23%
495
15%
1513
8%
495
33%
495
24%
979
May1st to 15thNight
31%
494
17%
1485
13%
494
37%
494
24%
971
May16th to endNight
35%
515
12%
1540
9%
513
39%
513
31%
948
June1st to 15thNight
47%
495
18%
1372
10%
495
51%
495
39%
797
June16th to endNight
50%
495
18%
1411
10%
495
54%
495
52%
710
July1st to 15thNight
58%
465
17%
1395
12%
465
61%
465
41%
763
July16th to endNight
56%
522
19%
1468
17%
489
63%
489
46%
767
August1st to 15thNight
68%
494
22%
1475
25%
491
71%
491
42%
805
August16th to endNight
63%
525
22%
1624
23%
525
66%
525
39%
890
September1st to 15thNight
52%
495
24%
1743
24%
495
58%
495
31%
978
September16th to endNight
54%
492
25%
1815
20%
492
63%
492
36%
901
October1st to 15thNight
41%
627
27%
1947
20%
627
47%
627
31%
1137
October16th to endNight
38%
704
26%
2112
13%
704
48%
704
38%
1149
November1st to 15thNight
38%
815
28%
2215
13%
815
48%
815
41%
1240
November16th to endNight
29%
900
22%
2441
8%
900
39%
900
35%
1448
December1st to 15thNight
26%
900
17%
2520
7%
900
34%
900
26%
1643
December16th to endNight
26%
960
20%
2575
8%
960
35%
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
24%5%24423345%38%
45629
Night
23%5%13323335%43%
45782
Cloud CoverDay
11%6%25%42445%7%44%
45627
Night
10%5%24424347%50%
45782
TransparencyDay
37%6%13%24%15%2
45327
Night
33%5%13%26%17%3
45587
SeeingDay
13%7%27%31%16%3
5164
Night
13%8%32%33%12%
15434

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
30%6%1442333435%
1960
16th to endDay
32%7%25%5%3334426%
2115
May1st to 15thDay
30%5%25%5%24345%31%
2136
16th to endDay
31%5%14324346%31%
2222
June1st to 15thDay
26%415%323446%36%
2252
16th to endDay
21%21232345%7%44%
2212
July1st to 15thDay
25%31342346%7%35%
2145
16th to endDay
23%21333445%7%40%
2284
August1st to 15thDay
16%31342345%8%44%
2145
16th to endDay
16%414434347%46%
2225
September1st to 15thDay
18%4245%33347%42%
1884
16th to endDay
15%31332345%6%50%
1815
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
26%5%2431324440%
1801
16th to endNight
31%5%25%423435%32%
1513
May1st to 15thNight
28%5%25%323345%36%
1484
16th to endNight
29%31332325%7%36%
1539
June1st to 15thNight
24%22324336%46%
1372
16th to endNight
19%11113349%52%
1411
July1st to 15thNight
24%22212448%45%
1485
16th to endNight
22%11332235%9%44%
1576
August1st to 15thNight
13%11331346%9%50%
1485
16th to endNight
14%41332334455%
1624
September1st to 15thNight
18%413324337%45%
1743
16th to endNight
15%312323445%54%
1815
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
15%7%25%424435%43%
1960
16th to endDay
17%8%35%5%35%45%5%35%
2115
May1st to 15thDay
16%6%36%5%25%45%6%35%
2136
16th to endDay
14%5%26%4345%5%8%38%
2222
June1st to 15thDay
9%5%26%5%25%5%48%43%
2252
16th to endDay
5%214425%6%6%9%50%
2212
July1st to 15thDay
9%4245%25%5%7%9%42%
2145
16th to endDay
6%3244345%6%10%48%
2284
August1st to 15thDay
7%3244245%6%9%47%
2145
16th to endDay
9%5%145%3445%7%48%
2225
September1st to 15thDay
11%425%5%3435%7%46%
1884
16th to endDay
7%31342446%7%53%
1815
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%
1801
16th to endNight
16%6%2442335%5%43%
1513
May1st to 15thNight
12%6%4443445%7%41%
1484
16th to endNight
10%425%32445%10%46%
1539
June1st to 15thNight
7%313325%45%9%54%
1372
16th to endNight
31122335%11%61%
1411
July1st to 15thNight
7%2133235%5%10%53%
1485
16th to endNight
5%1134245%7%10%54%
1576
August1st to 15thNight
332432446%10%54%
1485
16th to endNight
6%314424445%58%
1624
September1st to 15thNight
11%413424447%50%
1743
16th to endNight
7%31222445%6%58%
1815
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%11%21%17%
1960
16th to endDay
48%6%11%21%10%
2115
May1st to 15thDay
48%7%11%21%11%
2136
16th to endDay
42%8%15%20%10%1
2226
June1st to 15thDay
37%8%14%24%14%1
2252
16th to endDay
26%8%18%28%16%2
2212
July1st to 15thDay
34%8%14%27%12%3
2006
16th to endDay
28%7%14%30%15%2
2129
August1st to 15thDay
30%8%14%26%18%1
2131
16th to endDay
33%7%11%24%17%6%
2225
September1st to 15thDay
37%5%13%19%18%5%
1884
16th to endDay
28%7%11%27%23%
1815
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
36%410%25%20%2
1801
16th to endNight
41%5%12%23%16%
1513
May1st to 15thNight
41%6%13%21%15%1
1485
16th to endNight
34%7%19%22%14%1
1541
June1st to 15thNight
26%7%18%29%14%3
1372
16th to endNight
16%6%14%35%23%3
1411
July1st to 15thNight
25%6%15%30%16%4
1395
16th to endNight
23%415%32%22%1
1468
August1st to 15thNight
23%7%17%29%19%3
1475
16th to endNight
28%5%10%26%21%7%
1624
September1st to 15thNight
33%412%22%19%7%
1743
16th to endNight
25%5%11%27%26%3
1815
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
23%10%30%24%10%
149
16th to endDay
25%12%35%17%7%1
345
May1st to 15thDay
17%12%31%24%10%1
393
16th to endDay
20%7%30%27%10%2
437
June1st to 15thDay
10%431%33%17%3
420
16th to endDay
5%230%35%20%4
420
July1st to 15thDay
12%219%40%22%3
400
16th to endDay
7%112%43%31%3
445
August1st to 15thDay
7%115%41%30%3
418
16th to endDay
10%216%35%28%6%
393
September1st to 15thDay
9%227%34%20%5%
159
16th to endDay
8%125%45%12%6%
90
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%37%30%5%
515
16th to endNight
18%11%36%25%7%
495
May1st to 15thNight
13%10%32%31%9%
495
16th to endNight
11%6%33%34%12%
515
June1st to 15thNight
9%326%44%17%
495
16th to endNight
5%228%46%17%
495
July1st to 15thNight
7%117%47%24%1
465
16th to endNight
415%50%27%
522
August1st to 15thNight
412%51%29%2
494
16th to endNight
6%216%38%31%4
525
September1st to 15thNight
13%320%37%21%3
495
16th to endNight
7%325%37%23%2
492
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 2017-04-08 04:35:17. Version ac04

Copyright 2017 A. Danko


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