Bay Ridges Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bay Ridges Observatory clear sky chart from 2005-11-05 to 2018-04-23.

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
39%
15667
14%
49582
10%
15632
44%
15632
20%
34314

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
17%
778
8%
2700
3%
776
24%
776
9%
2145
January16th to endNight
21%
832
11%
2704
5%
832
28%
832
11%
2137
February1st to 15thNight
18%
762
10%
2482
4%
761
26%
761
11%
1931
February16th to endNight
24%
683
13%
2184
6%
683
34%
683
15%
1597
March1st to 15thNight
27%
780
14%
2145
7%
780
33%
780
18%
1595
March16th to endNight
37%
832
21%
2288
11%
832
46%
832
27%
1528
April1st to 15thNight
36%
778
16%
1959
7%
778
41%
778
24%
1414
April16th to endNight
48%
596
20%
1710
11%
596
53%
596
29%
1103
May1st to 15thNight
53%
474
16%
1554
15%
474
57%
474
24%
993
May16th to endNight
61%
374
17%
1497
20%
374
66%
374
26%
823
June1st to 15thNight
56%
360
12%
1440
15%
360
63%
360
22%
850
June16th to endNight
61%
360
13%
1440
20%
360
63%
360
25%
831
July1st to 15thNight
73%
340
16%
1360
26%
340
75%
340
34%
691
July16th to endNight
69%
468
17%
1503
19%
439
70%
439
31%
846
August1st to 15thNight
70%
539
18%
1609
15%
536
72%
536
35%
940
August16th to endNight
67%
634
24%
1780
15%
634
70%
634
37%
1068
September1st to 15thNight
59%
720
20%
1800
10%
720
63%
720
36%
1170
September16th to endNight
58%
717
23%
2007
17%
717
61%
717
33%
1234
October1st to 15thNight
43%
720
17%
2160
17%
720
47%
720
23%
1485
October16th to endNight
29%
768
13%
2304
8%
768
37%
768
17%
1683
November1st to 15thNight
38%
760
17%
2584
15%
760
45%
760
19%
1746
November16th to endNight
28%
780
10%
2730
7%
780
34%
780
13%
2005
December1st to 15thNight
17%
780
7%
2730
3%
780
21%
780
9%
2133
December16th to endNight
14%
832
7%
2912
2%
832
20%
832
8%
2366

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
14%7%36%6%35%5%5%8%34%
49935
Night
15%7%36%5%3445%7%35%
49760
Cloud CoverDay
14%7%36%5%35%5%5%7%35%
49945
Night
16%7%36%5%3445%6%35%
49765
TransparencyDay
46%6%14%20%10%1
49632
Night
48%5%12%20%11%1
49582
SeeingDay
17%421%29%20%6%
6038
Night
19%6%26%30%15%2
15672

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
17%11%5%7%7%35%446%24%
1565
16th to endDay
13%13%6%10%8%45%5%47%19%
1872
February1st to 15thDay
14%13%5%10%8%35%436%22%
1710
16th to endDay
17%11%38%6%35%447%27%
1572
March1st to 15thDay
15%9%48%7%46%446%28%
2134
16th to endDay
15%7%35%5%35%445%38%
2288
April1st to 15thDay
20%8%47%5%3446%6%29%
2319
16th to endDay
17%6%25%5%24346%40%
2374
May1st to 15thDay
13%6%35%6%35%45%8%35%
2397
16th to endDay
11%425%5%25%46%7%42%
2618
June1st to 15thDay
13%6%25%5%35%5%6%9%36%
2520
16th to endDay
11%424445%5%7%11%38%
2520
July1st to 15thDay
7%4145%36%6%7%9%44%
2520
16th to endDay
9%424446%5%8%10%39%
2559
August1st to 15thDay
7%425%6%35%6%6%9%42%
2340
16th to endDay
8%4245%35%5%6%8%44%
2409
September1st to 15thDay
13%414435%5%5%7%42%
2160
16th to endDay
12%4245%34448%44%
1950
October1st to 15thDay
18%6%27%5%35%5%46%35%
1800
16th to endDay
21%8%46%6%245%47%27%
1920
November1st to 15thDay
14%8%37%7%35%46%7%31%
1604
16th to endDay
18%9%38%7%45%45%8%24%
1560
December1st to 15thDay
17%13%5%8%7%35%5%48%19%
1560
16th to endDay
20%11%5%8%7%35%46%7%18%
1664
January1st to 15thNight
21%12%47%6%24446%23%
2700
16th to endNight
14%11%6%7%7%46%45%7%23%
2704
February1st to 15thNight
14%14%5%8%6%35%5%5%6%24%
2480
16th to endNight
15%9%47%6%5%4446%29%
2184
March1st to 15thNight
17%8%5%7%7%35%345%32%
2133
16th to endNight
14%6%36%435%335%43%
2288
April1st to 15thNight
19%6%36%5%2445%6%35%
1959
16th to endNight
12%5%35%43345%6%43%
1710
May1st to 15thNight
15%425%5%35%5%5%7%39%
1554
16th to endNight
12%32442445%7%49%
1495
June1st to 15thNight
12%4245%36%46%8%41%
1440
16th to endNight
11%5%246%3446%9%43%
1440
July1st to 15thNight
5%32341445%8%55%
1440
16th to endNight
8%3135%245%6%9%48%
1606
August1st to 15thNight
6%4144235%6%8%50%
1620
16th to endNight
8%42433445%6%52%
1780
September1st to 15thNight
12%3243345%5%7%47%
1800
16th to endNight
12%42442345%6%48%
2007
October1st to 15thNight
18%6%27%43345%6%37%
2160
16th to endNight
21%8%36%43445%6%30%
2304
November1st to 15thNight
17%6%26%6%25%45%6%35%
2584
16th to endNight
20%8%36%5%25%5%6%7%26%
2730
December1st to 15thNight
19%13%47%6%35%45%6%22%
2730
16th to endNight
21%12%48%7%45%5%5%7%17%
2912

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
18%11%5%8%7%45%447%22%
1565
16th to endDay
13%13%5%11%9%45%5%47%18%
1872
February1st to 15thDay
15%14%49%8%45%446%21%
1710
16th to endDay
17%11%47%7%4435%6%28%
1572
March1st to 15thDay
16%9%47%7%35%6%46%27%
2145
16th to endDay
15%7%35%5%34446%39%
2287
April1st to 15thDay
21%7%36%5%3436%6%30%
2319
16th to endDay
17%6%245%2435%6%41%
2374
May1st to 15thDay
14%6%25%5%35%5%6%8%37%
2397
16th to endDay
11%326%5%25%46%7%44%
2618
June1st to 15thDay
14%5%245%346%6%9%37%
2520
16th to endDay
11%314435%5%7%10%41%
2520
July1st to 15thDay
7%314426%5%8%9%45%
2520
16th to endDay
9%413436%6%6%10%42%
2559
August1st to 15thDay
7%4246%35%6%6%9%43%
2340
16th to endDay
8%424335%5%5%8%47%
2409
September1st to 15thDay
14%413435%5%48%43%
2160
16th to endDay
12%5%245%24448%45%
1950
October1st to 15thDay
19%6%26%5%35%446%36%
1800
16th to endDay
21%8%45%6%3445%6%27%
1920
November1st to 15thDay
15%7%27%6%35%45%7%32%
1604
16th to endDay
18%10%37%7%46%45%8%24%
1560
December1st to 15thDay
18%12%5%8%6%5%5%45%7%19%
1560
16th to endDay
21%13%6%8%6%35%46%7%17%
1664
January1st to 15thNight
21%13%47%6%35%45%6%20%
2700
16th to endNight
15%12%6%8%7%36%46%7%21%
2704
February1st to 15thNight
14%14%5%8%7%3445%7%23%
2473
16th to endNight
16%9%47%7%45%45%5%29%
2184
March1st to 15thNight
18%9%5%7%6%34345%31%
2145
16th to endNight
15%6%35%42443444%
2288
April1st to 15thNight
19%7%35%5%2436%6%35%
1959
16th to endNight
13%6%15%43445%6%43%
1710
May1st to 15thNight
16%3245%45%45%7%39%
1554
16th to endNight
11%4143245%47%48%
1495
June1st to 15thNight
12%5%25%445%5%5%8%41%
1440
16th to endNight
11%4145%3436%8%43%
1440
July1st to 15thNight
5%22342436%7%56%
1440
16th to endNight
8%3143345%5%9%48%
1606
August1st to 15thNight
7%3234345%6%8%49%
1620
16th to endNight
8%314435%45%5%53%
1780
September1st to 15thNight
12%423325%5%5%7%47%
1800
16th to endNight
12%5%144235%46%49%
2007
October1st to 15thNight
19%5%26%5%2345%6%38%
2160
16th to endNight
22%8%36%5%25%446%30%
2304
November1st to 15thNight
17%6%25%5%2446%6%35%
2584
16th to endNight
21%8%36%5%35%5%5%6%27%
2730
December1st to 15thNight
19%13%5%7%5%36%45%5%22%
2730
16th to endNight
21%12%5%8%8%35%5%5%6%17%
2912

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
61%6%13%12%5%
1566
16th to endDay
65%8%10%10%4
1872
February1st to 15thDay
64%5%11%14%3
1712
16th to endDay
56%6%13%16%6%
1572
March1st to 15thDay
56%6%12%16%8%
2145
16th to endDay
46%410%21%14%2
2288
April1st to 15thDay
52%5%11%18%11%
2319
16th to endDay
43%5%10%21%15%3
2374
May1st to 15thDay
43%6%13%22%13%
2397
16th to endDay
38%5%16%24%13%2
2622
June1st to 15thDay
41%7%14%23%12%
2520
16th to endDay
35%7%19%23%12%
2520
July1st to 15thDay
30%7%15%26%17%1
2371
16th to endDay
35%8%16%25%11%1
2400
August1st to 15thDay
34%7%17%24%13%1
2327
16th to endDay
32%5%17%31%11%1
2409
September1st to 15thDay
37%7%17%25%11%1
2160
16th to endDay
36%6%15%29%11%
1950
October1st to 15thDay
48%5%13%21%9%1
1800
16th to endDay
55%5%18%14%4
1920
November1st to 15thDay
50%7%15%18%7%1
1604
16th to endDay
57%6%15%15%4
1560
December1st to 15thDay
64%7%15%10%2
1560
16th to endDay
65%8%10%11%3
1664
January1st to 15thNight
63%6%11%11%5%
2700
16th to endNight
61%7%10%14%4
2704
February1st to 15thNight
60%7%10%16%4
2482
16th to endNight
57%312%18%7%
2184
March1st to 15thNight
56%312%19%7%1
2145
16th to endNight
44%39%24%16%2
2288
April1st to 15thNight
49%410%19%15%
1959
16th to endNight
39%5%11%21%18%3
1710
May1st to 15thNight
43%412%22%14%2
1554
16th to endNight
34%5%13%26%16%3
1497
June1st to 15thNight
39%5%12%25%15%1
1440
16th to endNight
37%5%13%24%17%1
1440
July1st to 15thNight
26%6%12%26%24%2
1360
16th to endNight
31%7%13%26%17%3
1503
August1st to 15thNight
30%7%18%28%14%1
1609
16th to endNight
31%5%10%33%16%1
1780
September1st to 15thNight
35%5%14%27%15%1
1800
16th to endNight
34%5%11%32%14%
2007
October1st to 15thNight
47%5%10%23%13%
2160
16th to endNight
54%5%14%17%7%
2304
November1st to 15thNight
47%6%13%19%11%1
2584
16th to endNight
55%6%16%15%5%
2730
December1st to 15thNight
62%6%13%13%4
2730
16th to endNight
66%6%11%9%4
2912

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
19%18%34%21%5%1
93
16th to endDay
27%8%35%23%5%
144
February1st to 15thDay
25%7%49%15%2
135
16th to endDay
24%10%37%21%6%
143
March1st to 15thDay
23%7%31%27%9%
330
16th to endDay
22%330%31%10%2
352
April1st to 15thDay
22%6%29%32%8%
330
16th to endDay
20%423%30%16%4
289
May1st to 15thDay
18%215%36%20%7%
288
16th to endDay
12%15%38%27%5%
331
June1st to 15thDay
17%214%37%24%2
315
16th to endDay
14%13%38%27%5%
315
July1st to 15thDay
10%11%28%39%10%
305
16th to endDay
10%111%36%31%8%
326
August1st to 15thDay
8%10%30%36%13%
313
16th to endDay
12%112%23%34%16%
332
September1st to 15thDay
10%212%27%32%14%
315
16th to endDay
13%313%27%23%18%
314
October1st to 15thDay
21%225%26%17%6%
315
16th to endDay
25%9%30%22%11%
336
November1st to 15thDay
19%5%24%34%13%1
141
16th to endDay
22%11%32%24%8%1
90
December1st to 15thDay
15%16%33%26%6%1
90
16th to endDay
27%16%39%16%
96
January1st to 15thNight
28%11%35%18%5%
780
16th to endNight
20%9%36%27%5%
832
February1st to 15thNight
21%12%37%22%4
764
16th to endNight
21%8%36%26%6%
683
March1st to 15thNight
23%6%33%30%6%
780
16th to endNight
18%5%31%29%12%2
832
April1st to 15thNight
22%6%27%34%9%
778
16th to endNight
16%326%37%14%2
596
May1st to 15thNight
17%119%36%23%1
474
16th to endNight
13%214%41%26%2
375
June1st to 15thNight
13%317%38%23%2
360
16th to endNight
11%113%41%29%2
360
July1st to 15thNight
7%29%43%32%5%
340
16th to endNight
9%110%41%32%4
468
August1st to 15thNight
9%10%38%34%7%
539
16th to endNight
9%212%35%32%7%
634
September1st to 15thNight
14%316%28%28%8%
720
16th to endNight
14%414%29%27%10%
717
October1st to 15thNight
22%422%28%19%3
720
16th to endNight
25%8%27%28%9%
768
November1st to 15thNight
21%6%26%30%12%2
760
16th to endNight
24%10%27%26%9%1
780
December1st to 15thNight
29%9%37%19%4
780
16th to endNight
26%10%37%22%2
832
Page generated at 2018-04-24 10:03:06. Version ac04

Copyright 2018 A. Danko


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