Brodie Road Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brodie Road Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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
25%
14646
14%
46847
7%
14615
33%
14615
15%
33152

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
3%
716
20%
716
7%
2012
January16th to endNight
16%
768
10%
2685
4%
768
25%
768
9%
2003
February1st to 15thNight
15%
703
10%
2287
4%
701
22%
701
9%
1743
February16th to endNight
18%
631
14%
1913
5%
631
29%
631
11%
1412
March1st to 15thNight
16%
720
14%
2145
6%
720
25%
720
12%
1614
March16th to endNight
25%
768
20%
2001
8%
768
33%
768
19%
1393
April1st to 15thNight
21%
718
17%
1796
5%
718
28%
718
18%
1323
April16th to endNight
22%
648
17%
1728
3%
648
31%
648
17%
1217
May1st to 15thNight
26%
366
17%
1446
11%
366
39%
366
13%
970
May16th to endNight
24%
375
14%
1497
8%
374
40%
374
14%
954
June1st to 15thNight
27%
360
9%
1440
6%
360
38%
360
12%
981
June16th to endNight
36%
360
10%
1440
9%
360
45%
360
17%
888
July1st to 15thNight
43%
340
15%
1360
19%
340
50%
340
22%
762
July16th to endNight
42%
376
13%
1418
15%
354
52%
354
23%
817
August1st to 15thNight
50%
389
15%
1460
14%
387
56%
387
22%
876
August16th to endNight
45%
747
19%
1893
8%
747
51%
747
32%
1212
September1st to 15thNight
42%
720
16%
1800
7%
720
45%
720
28%
1233
September16th to endNight
43%
665
22%
1807
14%
665
49%
665
30%
1145
October1st to 15thNight
27%
660
19%
1972
11%
660
37%
660
19%
1351
October16th to endNight
21%
704
11%
2236
6%
704
28%
704
13%
1677
November1st to 15thNight
24%
700
17%
2289
9%
700
35%
700
14%
1610
November16th to endNight
17%
720
12%
2520
5%
720
26%
720
9%
1856
December1st to 15thNight
13%
720
8%
2520
3%
720
20%
720
7%
1976
December16th to endNight
8%
768
10%
2688
2%
768
17%
768
6%
2127

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
18%8%36%5%3445%6%32%
47944
Night
18%9%36%5%34446%32%
47016
Cloud CoverDay
18%8%36%5%35%45%6%32%
47953
Night
18%9%36%5%34446%32%
47022
TransparencyDay
51%411%20%10%1
47631
Night
53%311%20%10%1
46847
SeeingDay
21%20%26%19%9%2
5540
Night
20%24%23%21%8%
14647

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
23%14%5%9%6%3434320%
1432
16th to endDay
15%17%5%7%6%4445%5%24%
1539
February1st to 15thDay
15%13%411%6%445%46%22%
1575
16th to endDay
20%12%5%7%7%44326%25%
1560
March1st to 15thDay
17%12%5%9%8%3433427%
1802
16th to endDay
18%8%35%424346%37%
2223
April1st to 15thDay
23%9%36%5%13345%33%
2152
16th to endDay
20%8%26%424345%35%
2237
May1st to 15thDay
20%7%36%5%34346%32%
2511
16th to endDay
21%426%5%25%45%6%34%
2618
June1st to 15thDay
24%7%25%5%35%447%30%
2520
16th to endDay
19%5%345%35%5%7%8%30%
2520
July1st to 15thDay
12%6%35%5%45%5%6%8%37%
2520
16th to endDay
12%435%6%35%6%7%9%34%
2654
August1st to 15thDay
12%6%25%6%35%5%6%9%35%
2488
16th to endDay
11%314435%5%6%8%44%
2297
September1st to 15thDay
16%6%2432445%7%41%
2160
16th to endDay
15%6%24323246%46%
1859
October1st to 15thDay
20%8%35%434446%35%
1658
16th to endDay
25%10%36%7%2444425%
1636
November1st to 15thDay
16%7%46%6%45%5%46%32%
1567
16th to endDay
22%11%37%5%33345%26%
1440
December1st to 15thDay
25%13%48%5%35%45%6%18%
1440
16th to endDay
25%16%5%8%6%2433420%
1536
January1st to 15thNight
20%15%6%9%7%3444419%
2506
16th to endNight
14%14%5%9%7%44445%25%
2685
February1st to 15thNight
14%12%5%10%8%46%5%5%5%22%
2285
16th to endNight
16%11%5%9%5%345%45%27%
1913
March1st to 15thNight
19%12%47%6%34345%28%
2132
16th to endNight
17%9%35%5%2333440%
2001
April1st to 15thNight
25%8%35%5%23345%33%
1796
16th to endNight
21%8%345%33345%37%
1728
May1st to 15thNight
22%7%45%424445%35%
1446
16th to endNight
17%6%245%3445%7%37%
1495
June1st to 15thNight
24%6%25%4345%5%6%30%
1440
16th to endNight
16%5%25%5%26%5%6%9%35%
1440
July1st to 15thNight
10%415%425%5%6%10%42%
1440
16th to endNight
10%425%5%245%6%9%42%
1514
August1st to 15thNight
10%6%25%42447%10%39%
1470
16th to endNight
11%424434448%47%
1893
September1st to 15thNight
14%6%25%6%34447%40%
1800
16th to endNight
17%423423346%47%
1807
October1st to 15thNight
19%7%36%434446%36%
1972
16th to endNight
25%9%47%5%34345%27%
2236
November1st to 15thNight
20%8%35%434446%32%
2289
16th to endNight
22%10%48%6%25%445%26%
2520
December1st to 15thNight
22%15%5%7%6%34345%21%
2520
16th to endNight
25%16%5%7%6%2433420%
2688

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
22%13%5%8%6%35%34421%
1432
16th to endDay
15%16%5%6%6%35%5%46%25%
1539
February1st to 15thDay
15%12%411%6%45%45%5%22%
1575
16th to endDay
18%12%5%8%6%35%445%26%
1560
March1st to 15thDay
17%11%5%9%8%35%33427%
1812
16th to endDay
18%7%35%5%23445%38%
2222
April1st to 15thDay
23%8%37%5%32345%33%
2152
16th to endDay
20%6%25%5%34346%35%
2237
May1st to 15thDay
20%7%26%5%35%446%33%
2511
16th to endDay
19%6%25%43445%7%35%
2618
June1st to 15thDay
23%6%35%5%34447%31%
2520
16th to endDay
18%5%25%5%36%5%6%8%31%
2520
July1st to 15thDay
12%5%35%5%35%5%6%8%38%
2520
16th to endDay
12%5%25%436%5%7%9%36%
2654
August1st to 15thDay
12%425%6%45%5%5%9%35%
2488
16th to endDay
10%414435%6%5%8%45%
2297
September1st to 15thDay
16%5%244235%5%7%42%
2160
16th to endDay
15%5%25%324346%46%
1859
October1st to 15thDay
20%6%36%5%245%5%5%35%
1658
16th to endDay
23%10%37%7%25%5%45%25%
1636
November1st to 15thDay
15%8%35%5%36%46%6%33%
1567
16th to endDay
21%10%46%6%33445%27%
1440
December1st to 15thDay
25%12%47%5%35%46%6%18%
1440
16th to endDay
26%15%5%7%6%2442321%
1536
January1st to 15thNight
19%14%5%9%7%345%45%19%
2506
16th to endNight
13%14%6%8%7%44435%25%
2685
February1st to 15thNight
14%12%5%10%9%36%5%45%21%
2278
16th to endNight
16%11%5%7%5%35%5%5%5%27%
1913
March1st to 15thNight
20%10%5%6%6%34345%28%
2145
16th to endNight
16%10%35%43333440%
2001
April1st to 15thNight
25%7%35%423335%33%
1796
16th to endNight
21%7%24434445%37%
1728
May1st to 15thNight
22%6%35%6%24345%36%
1446
16th to endNight
18%5%346%2445%6%37%
1495
June1st to 15thNight
24%7%245%25%45%6%30%
1440
16th to endNight
15%6%25%425%5%6%9%36%
1440
July1st to 15thNight
10%324435%5%7%9%42%
1440
16th to endNight
11%5%244345%6%7%44%
1514
August1st to 15thNight
9%5%26%5%245%7%9%40%
1470
16th to endNight
11%4235%34448%47%
1893
September1st to 15thNight
15%5%35%5%3445%6%40%
1800
16th to endNight
16%5%23423345%47%
1807
October1st to 15thNight
19%6%26%42445%6%36%
1972
16th to endNight
24%8%47%5%3444428%
2236
November1st to 15thNight
20%8%36%5%345%45%32%
2289
16th to endNight
21%9%48%5%34446%27%
2520
December1st to 15thNight
22%15%47%6%3444422%
2520
16th to endNight
25%16%47%5%2433421%
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
68%28%14%5%
1433
16th to endDay
60%411%15%8%
1539
February1st to 15thDay
62%210%19%4
1577
16th to endDay
61%310%14%9%1
1560
March1st to 15thDay
61%211%14%8%1
1812
16th to endDay
48%29%18%15%4
2223
April1st to 15thDay
54%26%21%12%2
2152
16th to endDay
50%38%18%14%4
2237
May1st to 15thDay
52%37%19%14%1
2511
16th to endDay
49%411%20%12%1
2622
June1st to 15thDay
53%310%20%10%
2520
16th to endDay
48%5%13%21%9%
2520
July1st to 15thDay
41%5%13%27%12%
2371
16th to endDay
43%6%16%24%9%
2487
August1st to 15thDay
44%6%16%23%9%
2474
16th to endDay
36%5%16%28%12%
2297
September1st to 15thDay
40%413%28%12%
2160
16th to endDay
39%311%34%10%
1859
October1st to 15thDay
50%310%24%10%
1658
16th to endDay
62%311%15%7%
1636
November1st to 15thDay
50%5%14%18%10%
1567
16th to endDay
60%311%17%6%
1440
December1st to 15thDay
67%413%11%3
1440
16th to endDay
68%310%11%5%
1536
January1st to 15thNight
67%410%12%4
2506
16th to endNight
61%310%16%7%
2685
February1st to 15thNight
63%211%17%4
2287
16th to endNight
57%29%18%10%
1913
March1st to 15thNight
59%38%19%8%1
2145
16th to endNight
48%28%20%15%4
2001
April1st to 15thNight
54%26%20%14%1
1796
16th to endNight
49%37%18%16%3
1728
May1st to 15thNight
51%46%18%15%4
1446
16th to endNight
45%5%10%22%13%2
1497
June1st to 15thNight
52%411%20%10%
1440
16th to endNight
44%414%21%15%
1440
July1st to 15thNight
34%6%12%29%15%
1360
16th to endNight
36%5%16%25%14%
1418
August1st to 15thNight
38%6%18%24%11%
1460
16th to endNight
35%415%32%11%
1893
September1st to 15thNight
44%310%27%13%
1800
16th to endNight
38%310%34%13%
1807
October1st to 15thNight
48%410%25%11%
1972
16th to endNight
60%212%17%6%
2236
November1st to 15thNight
52%413%18%9%1
2289
16th to endNight
60%212%18%5%
2520
December1st to 15thNight
65%411%16%3
2520
16th to endNight
67%210%12%6%
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
30%25%16%20%8%
60
16th to endDay
30%20%29%15%4
65
February1st to 15thDay
35%26%30%5%2
90
16th to endDay
28%26%26%16%2
219
March1st to 15thDay
22%30%28%15%2
270
16th to endDay
23%25%27%14%5%3
288
April1st to 15thDay
25%28%25%11%6%1
270
16th to endDay
20%28%25%15%9%
270
May1st to 15thDay
25%23%23%17%6%2
288
16th to endDay
21%25%28%16%7%1
331
June1st to 15thDay
26%20%28%18%5%
315
16th to endDay
19%19%30%22%7%1
315
July1st to 15thDay
15%14%31%21%13%2
305
16th to endDay
14%14%26%28%14%2
326
August1st to 15thDay
13%12%24%31%13%4
313
16th to endDay
12%9%28%24%16%8%
332
September1st to 15thDay
16%11%22%20%19%8%
315
16th to endDay
18%16%24%15%14%10%
259
October1st to 15thDay
21%17%22%23%13%1
255
16th to endDay
26%26%20%19%6%
249
November1st to 15thDay
18%24%26%20%9%1
221
16th to endDay
33%15%28%20%3
60
December1st to 15thDay
33%16%31%16%1
60
16th to endDay
42%17%37%3
64
January1st to 15thNight
21%30%26%17%3
720
16th to endNight
19%31%26%17%5%
768
February1st to 15thNight
18%29%28%19%3
704
16th to endNight
20%30%24%19%4
631
March1st to 15thNight
23%28%25%18%3
720
16th to endNight
19%27%22%23%6%
768
April1st to 15thNight
24%27%23%21%3
718
16th to endNight
21%28%24%18%6%
648
May1st to 15thNight
21%24%22%21%8%2
366
16th to endNight
14%25%30%21%7%
375
June1st to 15thNight
22%23%19%28%6%
360
16th to endNight
14%21%23%26%12%1
360
July1st to 15thNight
11%18%22%29%16%
340
16th to endNight
11%18%22%31%14%1
376
August1st to 15thNight
13%11%17%35%19%2
389
16th to endNight
10%13%24%27%21%2
747
September1st to 15thNight
16%13%21%32%14%1
720
16th to endNight
18%15%19%23%20%2
665
October1st to 15thNight
21%19%27%21%9%
660
16th to endNight
27%19%24%21%6%
704
November1st to 15thNight
18%25%25%21%8%
700
16th to endNight
21%32%22%14%8%
720
December1st to 15thNight
28%30%21%16%3
720
16th to endNight
29%30%23%11%4
768
Page generated at 2017-09-18 08:38:19. Version ac04

Copyright 2017 A. Danko


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