Bon Accord Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bon Accord Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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%
15154
10%
46448
7%
15128
46%
15128
18%
33335

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
35%
895
6%
2685
4%
895
37%
895
13%
2094
January16th to endNight
33%
914
13%
2834
8%
914
39%
914
17%
2060
February1st to 15thNight
42%
698
7%
2443
6%
697
45%
697
14%
1779
February16th to endNight
46%
632
10%
2025
11%
632
48%
632
18%
1449
March1st to 15thNight
41%
720
13%
2112
10%
720
44%
720
19%
1543
March16th to endNight
40%
768
10%
2089
6%
767
41%
767
17%
1608
April1st to 15thNight
43%
594
11%
1674
7%
594
46%
594
19%
1235
April16th to endNight
42%
540
12%
1620
11%
540
45%
540
20%
1144
May1st to 15thNight
47%
371
7%
1287
6%
371
49%
371
20%
860
May16th to endNight
43%
374
0%
1309
0%
374
43%
374
14%
919
June1st to 15thNight
44%
360
0%
1239
0%
360
44%
360
13%
923
June16th to endNight
53%
360
0%
1080
0%
360
53%
360
20%
763
July1st to 15thNight
60%
340
0%
1122
0%
340
60%
340
24%
711
July16th to endNight
60%
376
2%
1239
1%
354
61%
354
23%
771
August1st to 15thNight
65%
366
5%
1379
7%
364
66%
364
23%
848
August16th to endNight
58%
573
13%
1719
12%
573
60%
573
27%
1115
September1st to 15thNight
57%
607
15%
1729
12%
607
59%
607
32%
1075
September16th to endNight
53%
656
19%
1815
12%
656
58%
656
34%
1110
October1st to 15thNight
44%
660
14%
1977
10%
660
48%
660
21%
1376
October16th to endNight
40%
715
14%
2299
10%
715
47%
715
18%
1615
November1st to 15thNight
33%
875
13%
2492
8%
875
37%
875
16%
1886
November16th to endNight
30%
900
9%
2700
4%
900
35%
900
13%
2106
December1st to 15thNight
31%
900
8%
2700
5%
900
34%
900
11%
2162
December16th to endNight
39%
960
11%
2880
5%
960
43%
960
15%
2183

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
10%8%47%6%45%5%6%8%31%
48248
Night
9%9%48%7%35%5%6%7%31%
46597
TransparencyDay
48%9%18%18%5%
47897
Night
49%8%16%18%6%
46452
SeeingDay
14%5%21%30%20%6%
6358
Night
14%424%35%17%2
15167

By Month

Percentage Cloud Cover NW (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
6%11%7%10%8%6%7%5%6%6%24%
1253
16th to endDay
7%13%5%9%8%445%5%7%27%
1401
February1st to 15thDay
8%11%5%9%6%45%5%7%8%25%
1418
16th to endDay
5%13%7%10%7%46%6%6%7%23%
1449
March1st to 15thDay
7%11%6%12%7%36%5%6%9%21%
1848
16th to endDay
12%11%6%9%5%36%6%7%7%23%
2129
April1st to 15thDay
11%11%36%6%3445%8%32%
2274
16th to endDay
12%10%47%6%45%5%5%7%31%
2340
May1st to 15thDay
10%8%46%6%35%6%5%8%35%
2661
16th to endDay
17%6%36%6%35%46%7%31%
2802
June1st to 15thDay
16%7%48%7%46%5%5%7%25%
2718
16th to endDay
14%6%26%6%35%7%7%8%30%
2880
July1st to 15thDay
11%5%245%36%5%7%10%37%
2766
16th to endDay
9%425%5%35%6%7%9%39%
2846
August1st to 15thDay
9%5%15%5%45%6%8%10%37%
2571
16th to endDay
7%5%26%5%35%6%6%8%42%
2483
September1st to 15thDay
11%6%26%6%345%5%8%40%
2149
16th to endDay
10%5%145%3436%9%43%
1815
October1st to 15thDay
13%8%47%5%45%446%35%
1653
16th to endDay
11%9%47%6%35%5%6%7%32%
1562
November1st to 15thDay
11%10%5%7%7%46%45%8%28%
1366
16th to endDay
5%12%6%11%7%45%46%7%29%
1260
December1st to 15thDay
7%13%7%11%8%6%7%5%6%6%19%
1260
16th to endDay
6%9%6%10%9%6%7%6%7%7%21%
1344
January1st to 15thNight
7%12%5%11%8%5%7%5%5%7%24%
2685
16th to endNight
6%11%5%10%7%45%45%7%31%
2834
February1st to 15thNight
7%8%5%11%8%5%7%5%5%7%28%
2434
16th to endNight
7%10%6%6%7%36%6%6%7%30%
2025
March1st to 15thNight
7%8%5%9%8%45%6%6%8%29%
2112
16th to endNight
10%12%5%10%8%45%5%6%8%22%
2088
April1st to 15thNight
10%10%37%7%46%5%5%5%31%
1674
16th to endNight
13%10%36%7%245%5%8%32%
1620
May1st to 15thNight
10%7%47%7%45%5%6%7%34%
1286
16th to endNight
19%8%26%6%35%45%7%28%
1309
June1st to 15thNight
15%10%47%7%47%6%6%7%24%
1239
16th to endNight
12%5%26%6%36%8%8%8%30%
1080
July1st to 15thNight
10%415%5%345%8%11%38%
1191
16th to endNight
9%415%5%36%5%8%8%40%
1323
August1st to 15thNight
7%425%436%6%8%9%42%
1386
16th to endNight
9%5%25%5%446%6%8%40%
1719
September1st to 15thNight
10%5%35%32335%7%47%
1729
16th to endNight
10%32442346%7%50%
1815
October1st to 15thNight
12%8%47%6%3445%7%34%
1977
16th to endNight
9%9%38%6%25%6%7%7%32%
2299
November1st to 15thNight
13%11%5%7%6%45%45%6%27%
2492
16th to endNight
7%13%6%11%8%45%5%5%6%26%
2700
December1st to 15thNight
9%14%6%12%8%36%5%5%6%22%
2700
16th to endNight
5%11%5%11%7%5%6%7%6%9%24%
2880

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
57%10%13%12%4
1253
16th to endDay
55%7%13%15%7%1
1401
February1st to 15thDay
53%7%19%12%5%
1418
16th to endDay
55%9%12%16%4
1449
March1st to 15thDay
57%8%15%15%3
1848
16th to endDay
56%9%15%14%4
2130
April1st to 15thDay
48%8%17%17%6%
2274
16th to endDay
51%8%15%16%6%1
2340
May1st to 15thDay
46%7%14%22%9%
2661
16th to endDay
49%8%13%19%9%
2807
June1st to 15thDay
55%9%16%15%3
2718
16th to endDay
47%10%20%16%4
2880
July1st to 15thDay
39%10%23%22%3
2606
16th to endDay
37%12%28%19%1
2667
August1st to 15thDay
37%13%30%16%2
2553
16th to endDay
36%10%27%21%4
2483
September1st to 15thDay
40%9%20%22%6%1
2149
16th to endDay
36%8%19%28%6%1
1815
October1st to 15thDay
48%6%17%22%4
1653
16th to endDay
47%9%14%24%3
1562
November1st to 15thDay
54%6%16%17%4
1366
16th to endDay
54%8%15%16%4
1260
December1st to 15thDay
64%8%12%12%2
1260
16th to endDay
58%9%13%12%6%
1344
January1st to 15thNight
58%8%16%12%3
2685
16th to endNight
51%7%15%17%6%1
2834
February1st to 15thNight
53%8%17%13%6%
2445
16th to endNight
49%8%15%17%7%1
2025
March1st to 15thNight
50%7%15%19%6%
2112
16th to endNight
56%6%13%16%5%
2091
April1st to 15thNight
51%6%14%17%8%1
1674
16th to endNight
48%7%13%16%12%1
1620
May1st to 15thNight
45%7%13%19%13%1
1287
16th to endNight
52%6%12%17%8%1
1309
June1st to 15thNight
55%8%13%16%5%
1239
16th to endNight
44%11%21%18%3
1080
July1st to 15thNight
35%12%24%22%5%
1122
16th to endNight
36%11%24%24%3
1239
August1st to 15thNight
33%13%27%22%1
1379
16th to endNight
37%9%20%25%6%
1719
September1st to 15thNight
34%6%18%29%8%1
1729
16th to endNight
31%7%17%29%10%2
1815
October1st to 15thNight
46%7%15%22%7%
1977
16th to endNight
46%9%16%23%4
2299
November1st to 15thNight
55%6%12%19%4
2492
16th to endNight
57%9%14%13%41
2700
December1st to 15thNight
61%8%12%11%4
2700
16th to endNight
54%9%15%16%4
2880

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%6%16%35%25%5%
60
16th to endDay
7%120%42%18%9%
64
February1st to 15thDay
17%422%31%17%6%
63
16th to endDay
15%218%36%21%5%
108
March1st to 15thDay
12%430%36%13%3
270
16th to endDay
16%321%32%22%3
288
April1st to 15thDay
14%7%24%33%18%1
269
16th to endDay
20%5%21%30%16%5%
270
May1st to 15thDay
12%7%22%30%18%7%
453
16th to endDay
17%418%31%18%9%
517
June1st to 15thDay
18%6%22%28%18%5%
513
16th to endDay
14%418%30%22%8%
675
July1st to 15thDay
11%216%33%28%7%
540
16th to endDay
11%421%28%27%5%
515
August1st to 15thDay
11%216%26%26%16%
372
16th to endDay
9%6%24%31%24%3
332
September1st to 15thDay
14%7%24%31%16%6%
300
16th to endDay
13%13%26%27%14%5%
255
October1st to 15thDay
25%6%22%26%11%7%
131
16th to endDay
18%327%26%20%4
96
November1st to 15thDay
26%122%38%10%
83
16th to endDay
10%133%25%10%20%
60
December1st to 15thDay
18%25%31%18%6%
60
16th to endDay
6%318%32%26%12%
64
January1st to 15thNight
12%5%28%36%14%2
900
16th to endNight
12%8%31%31%13%2
914
February1st to 15thNight
11%5%22%38%18%3
704
16th to endNight
11%322%38%19%3
632
March1st to 15thNight
11%329%37%14%3
720
16th to endNight
15%424%34%19%2
768
April1st to 15thNight
16%325%36%17%1
594
16th to endNight
17%5%24%34%16%
540
May1st to 15thNight
13%5%22%36%20%1
372
16th to endNight
22%417%33%19%2
375
June1st to 15thNight
21%418%36%15%3
360
16th to endNight
14%220%32%27%2
360
July1st to 15thNight
12%17%42%25%
340
16th to endNight
11%217%38%26%3
376
August1st to 15thNight
8%214%34%34%5%
366
16th to endNight
10%319%38%26%1
573
September1st to 15thNight
14%218%37%24%1
607
16th to endNight
12%5%24%40%14%2
656
October1st to 15thNight
17%324%37%15%1
660
16th to endNight
15%6%27%35%14%
715
November1st to 15thNight
18%6%30%31%10%2
875
16th to endNight
11%6%31%34%12%3
900
December1st to 15thNight
17%7%26%31%14%3
900
16th to endNight
9%5%25%34%20%4
960
Page generated at 2017-09-13 05:39:06. Version ac04

Copyright 2017 A. Danko


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