Bishop's University Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bishop's University Astronomical Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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
27%
14513
11%
46467
7%
14482
32%
14482
14%
34711

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
14%
720
7%
2506
4%
716
18%
716
6%
2066
January16th to endNight
17%
768
8%
2688
5%
768
21%
768
7%
2204
February1st to 15thNight
16%
703
6%
2309
3%
701
20%
701
7%
1920
February16th to endNight
18%
631
9%
1893
5%
631
24%
631
10%
1513
March1st to 15thNight
20%
720
13%
2160
8%
720
27%
720
12%
1676
March16th to endNight
26%
768
17%
2017
7%
768
33%
768
18%
1501
April1st to 15thNight
23%
718
15%
1796
4%
718
29%
718
17%
1402
April16th to endNight
26%
570
16%
1650
5%
570
34%
570
19%
1158
May1st to 15thNight
29%
471
15%
1551
10%
471
37%
471
17%
1069
May16th to endNight
31%
375
11%
1497
10%
374
39%
374
14%
1017
June1st to 15thNight
33%
360
9%
1440
9%
360
39%
360
13%
1000
June16th to endNight
43%
360
8%
1440
10%
360
47%
360
18%
935
July1st to 15thNight
48%
340
11%
1360
15%
340
51%
340
19%
849
July16th to endNight
51%
376
11%
1418
14%
354
53%
354
21%
865
August1st to 15thNight
50%
414
13%
1463
13%
412
52%
412
20%
955
August16th to endNight
50%
630
18%
1680
10%
630
52%
630
32%
1075
September1st to 15thNight
42%
660
12%
1685
6%
660
44%
660
26%
1177
September16th to endNight
43%
657
19%
1815
13%
657
46%
657
30%
1161
October1st to 15thNight
30%
660
16%
1892
9%
660
37%
660
19%
1368
October16th to endNight
23%
704
9%
2288
5%
704
28%
704
12%
1763
November1st to 15thNight
22%
700
14%
2277
10%
700
29%
700
12%
1720
November16th to endNight
22%
720
12%
2434
10%
720
27%
720
10%
1877
December1st to 15thNight
13%
720
5%
2520
1%
720
17%
720
6%
2133
December16th to endNight
11%
768
7%
2688
4%
768
15%
768
4%
2307

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
20%11%47%6%34446%26%
47512
Night
19%12%47%6%34445%27%
46637
TransparencyDay
59%311%18%7%
47200
Night
59%310%17%7%
46467
SeeingDay
29%12%26%19%9%2
5548
Night
28%11%25%24%9%
14514

By Month

Percentage Cloud Cover NE (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
19%17%6%12%8%46%43412%
1432
16th to endDay
13%16%7%11%9%45%5%4417%
1536
February1st to 15thDay
13%18%8%14%10%46%43213%
1552
16th to endDay
13%17%8%11%8%45%33419%
1580
March1st to 15thDay
17%15%5%9%6%4433423%
1790
16th to endDay
19%12%5%9%6%3232430%
2202
April1st to 15thDay
23%13%37%42433428%
2152
16th to endDay
22%10%35%433436%32%
2308
May1st to 15thDay
24%8%36%5%44445%29%
2409
16th to endDay
22%7%36%6%35%5%5%7%26%
2618
June1st to 15thDay
30%6%35%43445%6%24%
2520
16th to endDay
21%6%46%6%3445%8%28%
2520
July1st to 15thDay
17%6%36%5%36%6%5%8%30%
2520
16th to endDay
18%6%26%5%35%6%6%8%28%
2654
August1st to 15thDay
20%6%26%7%35%5%6%8%25%
2390
16th to endDay
17%6%25%5%2445%7%38%
2168
September1st to 15thDay
21%7%25%324345%38%
1944
16th to endDay
20%6%25%324347%39%
1815
October1st to 15thDay
24%10%35%424346%29%
1737
16th to endDay
26%16%36%5%3434421%
1584
November1st to 15thDay
22%15%46%42435%426%
1581
16th to endDay
19%16%6%7%5%24435%24%
1524
December1st to 15thDay
23%19%7%8%6%25%33314%
1440
16th to endDay
24%20%8%11%6%25%32213%
1536
January1st to 15thNight
17%18%7%12%7%45%34416%
2506
16th to endNight
12%17%7%12%8%46%5%3416%
2688
February1st to 15thNight
12%15%8%14%9%5%6%33416%
2308
16th to endNight
15%16%8%10%6%35%33322%
1893
March1st to 15thNight
19%14%6%7%6%3433426%
2147
16th to endNight
18%12%5%7%43433333%
2017
April1st to 15thNight
23%12%36%6%3434427%
1796
16th to endNight
22%9%35%423246%35%
1650
May1st to 15thNight
21%9%36%423447%31%
1551
16th to endNight
21%6%36%5%345%5%6%30%
1495
June1st to 15thNight
29%5%3441445%7%27%
1440
16th to endNight
19%5%35%3247%5%8%33%
1440
July1st to 15thNight
15%6%25%5%37%5%5%8%34%
1440
16th to endNight
13%5%35%5%25%5%7%7%38%
1514
August1st to 15thNight
15%6%26%5%346%6%9%33%
1473
16th to endNight
14%425%43335%7%44%
1680
September1st to 15thNight
19%6%25%5%33445%39%
1685
16th to endNight
20%5%13322336%45%
1815
October1st to 15thNight
22%9%36%5%24335%33%
1892
16th to endNight
28%11%36%43434423%
2288
November1st to 15thNight
19%14%37%5%44346%25%
2277
16th to endNight
22%15%5%9%5%2333326%
2434
December1st to 15thNight
24%18%7%9%8%2422314%
2520
16th to endNight
21%23%6%11%7%3433312%
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
77%27%9%2
1433
16th to endDay
69%29%14%3
1536
February1st to 15thDay
78%16%10%2
1555
16th to endDay
70%18%11%6%1
1580
March1st to 15thDay
65%38%13%6%1
1800
16th to endDay
59%28%18%9%1
2202
April1st to 15thDay
60%26%18%9%2
2152
16th to endDay
54%28%18%12%3
2308
May1st to 15thDay
57%28%19%11%
2409
16th to endDay
55%412%17%8%
2622
June1st to 15thDay
59%411%16%6%
2520
16th to endDay
53%412%21%7%
2520
July1st to 15thDay
47%5%15%24%6%
2371
16th to endDay
51%416%21%5%
2487
August1st to 15thDay
54%6%16%19%3
2376
16th to endDay
44%316%25%10%
2168
September1st to 15thDay
47%412%26%9%
1944
16th to endDay
45%312%26%12%
1815
October1st to 15thDay
56%212%20%7%
1737
16th to endDay
65%311%15%4
1584
November1st to 15thDay
60%411%15%7%1
1581
16th to endDay
63%311%15%6%
1524
December1st to 15thDay
75%29%10%2
1440
16th to endDay
79%26%6%4
1536
January1st to 15thNight
72%29%11%3
2506
16th to endNight
72%27%13%3
2688
February1st to 15thNight
73%27%12%3
2309
16th to endNight
67%28%12%8%
1893
March1st to 15thNight
63%27%17%7%1
2160
16th to endNight
56%18%17%12%2
2017
April1st to 15thNight
60%25%17%12%1
1796
16th to endNight
51%38%20%13%2
1650
May1st to 15thNight
53%37%19%15%1
1551
16th to endNight
52%413%19%8%1
1497
June1st to 15thNight
55%311%21%7%
1440
16th to endNight
46%6%14%23%9%
1440
July1st to 15thNight
43%5%16%23%10%
1360
16th to endNight
42%5%18%23%9%
1418
August1st to 15thNight
46%417%24%6%
1463
16th to endNight
39%317%27%11%
1680
September1st to 15thNight
47%314%25%8%
1685
16th to endNight
39%313%29%12%
1815
October1st to 15thNight
54%210%22%9%
1892
16th to endNight
63%310%17%5%
2288
November1st to 15thNight
61%311%15%6%1
2277
16th to endNight
64%29%16%6%
2434
December1st to 15thNight
76%28%11%2
2520
16th to endNight
78%26%8%3
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
23%16%36%20%3
60
16th to endDay
39%14%32%10%11
64
February1st to 15thDay
30%21%25%17%5%
138
16th to endDay
28%19%27%20%31
239
March1st to 15thDay
35%18%19%24%2
270
16th to endDay
29%16%23%15%11%3
288
April1st to 15thDay
37%14%23%17%6%1
270
16th to endDay
31%13%30%11%10%2
270
May1st to 15thDay
38%9%28%11%10%2
288
16th to endDay
25%16%26%22%7%
331
June1st to 15thDay
33%13%26%18%8%
315
16th to endDay
26%12%34%18%7%
315
July1st to 15thDay
23%8%32%23%9%2
305
16th to endDay
22%6%29%31%8%1
326
August1st to 15thDay
25%5%26%22%17%2
297
16th to endDay
23%5%20%22%19%8%
268
September1st to 15thDay
22%5%24%20%16%10%
255
16th to endDay
21%11%22%21%13%9%
254
October1st to 15thDay
28%15%22%14%15%4
252
16th to endDay
39%13%20%17%9%
240
November1st to 15thDay
31%12%24%22%7%1
235
16th to endDay
35%15%18%18%7%4
144
December1st to 15thDay
43%16%25%11%11
60
16th to endDay
48%15%29%41
64
January1st to 15thNight
29%17%29%19%3
720
16th to endNight
24%17%30%22%5%
768
February1st to 15thNight
23%17%32%23%4
704
16th to endNight
28%15%29%21%5%
631
March1st to 15thNight
32%13%27%21%4
720
16th to endNight
26%15%27%20%9%1
768
April1st to 15thNight
33%11%25%22%5%
718
16th to endNight
28%13%27%21%8%
570
May1st to 15thNight
28%7%29%23%10%
471
16th to endNight
24%7%28%30%8%
375
June1st to 15thNight
35%5%18%30%9%
360
16th to endNight
19%6%25%36%11%
360
July1st to 15thNight
16%324%37%17%1
340
16th to endNight
15%121%42%18%
376
August1st to 15thNight
19%316%39%19%
414
16th to endNight
17%221%34%20%2
630
September1st to 15thNight
23%5%21%31%15%1
660
16th to endNight
23%5%24%26%17%2
657
October1st to 15thNight
30%8%23%22%13%1
660
16th to endNight
37%10%23%21%5%
704
November1st to 15thNight
28%14%28%18%9%
700
16th to endNight
32%14%23%17%9%1
720
December1st to 15thNight
36%16%25%16%4
720
16th to endNight
37%15%23%17%31
768
Page generated at 2017-08-13 14:16:50. Version ac04

Copyright 2017 A. Danko


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