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 2017-04-28.

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%
14293
11%
45627
7%
14262
32%
14262
14%
34191

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%
564
16%
1632
5%
564
34%
564
19%
1150
May1st to 15thNight
29%
432
16%
1422
11%
432
38%
432
17%
967
May16th to endNight
31%
343
11%
1369
11%
342
38%
342
14%
940
June1st to 15thNight
32%
330
9%
1320
9%
330
39%
330
12%
934
June16th to endNight
44%
330
8%
1320
11%
330
47%
330
18%
858
July1st to 15thNight
49%
310
11%
1240
16%
310
52%
310
20%
769
July16th to endNight
50%
348
9%
1306
11%
326
52%
326
20%
803
August1st to 15thNight
50%
389
13%
1370
13%
387
52%
387
20%
907
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%5%34445%26%
46075
Night
19%12%48%6%34445%27%
45797
TransparencyDay
59%311%18%7%
45763
Night
60%310%17%7%
45627
SeeingDay
29%12%25%19%9%2
5133
Night
28%11%25%24%9%
14294

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%433435%32%
2274
May1st to 15thDay
22%8%35%5%34446%31%
2207
16th to endDay
22%7%36%6%35%5%5%7%26%
2394
June1st to 15thDay
31%6%35%5%3445%6%24%
2310
16th to endDay
21%7%46%5%3445%8%29%
2310
July1st to 15thDay
17%5%36%5%36%6%5%8%31%
2310
16th to endDay
18%6%26%6%36%6%6%8%26%
2458
August1st to 15thDay
20%6%26%7%35%5%6%8%25%
2239
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%
1632
May1st to 15thNight
20%9%37%424447%32%
1422
16th to endNight
21%6%36%5%345%5%6%30%
1367
June1st to 15thNight
30%5%35%5%1445%7%26%
1320
16th to endNight
19%6%35%325%7%5%8%33%
1320
July1st to 15thNight
15%6%25%5%37%5%5%8%34%
1320
16th to endNight
13%5%35%5%25%6%7%7%37%
1402
August1st to 15thNight
16%6%26%6%35%6%6%9%32%
1380
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
2274
May1st to 15thDay
54%28%21%12%
2207
16th to endDay
56%411%18%8%
2398
June1st to 15thDay
60%411%15%6%
2310
16th to endDay
52%412%21%8%
2310
July1st to 15thDay
47%5%15%24%7%
2161
16th to endDay
53%416%20%4
2291
August1st to 15thDay
54%5%16%19%3
2225
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
1632
May1st to 15thNight
51%27%20%15%1
1422
16th to endNight
54%411%19%8%1
1369
June1st to 15thNight
57%410%20%7%
1320
16th to endNight
46%5%13%24%9%
1320
July1st to 15thNight
43%5%16%24%9%
1240
16th to endNight
42%5%18%22%9%
1306
August1st to 15thNight
47%416%23%6%
1370
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%29%12%10%2
259
May1st to 15thDay
32%10%30%13%10%2
228
16th to endDay
25%12%29%23%7%1
267
June1st to 15thDay
36%12%22%18%9%
255
16th to endDay
25%10%32%21%9%
255
July1st to 15thDay
22%6%31%25%10%3
245
16th to endDay
23%6%29%30%8%1
270
August1st to 15thDay
27%5%26%20%17%2
253
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%
564
May1st to 15thNight
26%7%30%23%10%
432
16th to endNight
24%7%28%30%8%
343
June1st to 15thNight
35%5%17%30%10%
330
16th to endNight
20%6%22%36%12%
330
July1st to 15thNight
15%323%36%19%1
310
16th to endNight
15%122%43%17%
348
August1st to 15thNight
20%316%39%19%
389
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 2017-04-29 09:45:10. Version ac04

Copyright 2017 A. Danko


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