Brooklin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brooklin Observatory clear sky chart from 2005-11-06 to 2024-03-08.

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%
23326
16%
80754
7%
23219
36%
23219
15%
54133

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 10thNight
13%
754
19%
4343
4%
737
29%
737
7%
2562
January11th to 20thNight
13%
760
17%
4349
2%
740
26%
740
6%
2657
January21st to endNight
14%
831
12%
4733
4%
814
33%
814
7%
3121
February1st to 10thNight
14%
760
16%
2470
4%
760
29%
760
12%
1743
February11th to 20thNight
13%
743
17%
2306
3%
740
31%
740
13%
1541
February21st to endNight
16%
628
20%
1884
4%
628
36%
628
16%
1279
March1st to 10thNight
14%
751
20%
2229
4%
751
32%
751
16%
1540
March11th to 20thNight
20%
720
16%
1980
6%
720
30%
720
17%
1411
March21st to endNight
22%
792
20%
2178
6%
792
33%
792
19%
1505
April1st to 10thNight
17%
720
16%
1834
3%
720
25%
720
16%
1371
April11th to 20thNight
24%
550
17%
1614
5%
550
33%
550
19%
1109
April21st to endNight
25%
540
14%
1620
6%
540
31%
540
17%
1164
May1st to 10thNight
26%
540
13%
1620
7%
540
32%
540
17%
1184
May11th to 20thNight
25%
532
13%
1594
8%
532
32%
532
17%
1147
May21st to endNight
33%
462
13%
1545
11%
461
39%
461
16%
1091
June1st to 10thNight
32%
360
11%
1260
10%
360
39%
360
14%
923
June11th to 20thNight
40%
360
13%
1260
13%
360
46%
360
19%
841
June21st to endNight
38%
360
10%
1260
10%
360
42%
360
15%
908
July1st to 10thNight
43%
350
11%
1327
12%
350
49%
350
16%
908
July11th to 20thNight
46%
348
11%
1392
13%
348
51%
348
16%
934
July21st to endNight
45%
438
13%
1528
14%
414
47%
414
17%
1032
August1st to 10thNight
44%
538
12%
1600
9%
534
46%
534
22%
1090
August11th to 20thNight
43%
532
13%
1596
8%
532
47%
532
19%
1131
August21st to endNight
47%
594
21%
1782
11%
594
53%
594
26%
1135
September1st to 10thNight
43%
715
19%
1894
9%
715
50%
715
32%
1214
September11th to 20thNight
39%
720
21%
1980
11%
720
46%
720
29%
1244
September21st to endNight
36%
720
23%
1980
11%
720
46%
720
28%
1278
October1st to 10thNight
36%
720
19%
2035
11%
720
44%
720
23%
1371
October11th to 20thNight
29%
720
21%
2160
7%
720
42%
720
21%
1402
October21st to endNight
20%
792
15%
2564
6%
792
31%
792
15%
1777
November1st to 10thNight
27%
740
19%
2407
9%
740
40%
740
18%
1566
November11th to 20thNight
22%
775
23%
2501
9%
775
40%
775
16%
1617
November21st to endNight
18%
850
18%
2660
3%
850
34%
850
14%
1773
December1st to 10thNight
14%
850
15%
2726
3%
850
27%
850
13%
1966
December11th to 20thNight
15%
850
16%
3432
3%
849
30%
849
10%
2255
December21st to endNight
11%
911
11%
5111
1%
891
28%
891
7%
3343

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
19%7%35%5%3445%7%39%
78215
Night
20%8%35%5%3445%6%38%
81335
TransparencyDay
46%6%12%21%13%2
77924
Night
48%6%11%21%13%2
81161
SeeingDay
25%16%32%20%7%1
14820
Night
26%15%29%22%7%1
23346

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 10thDay
18%7%26%5%34345%40%
2517
11th to 20thDay
18%7%34334446%44%
2520
21st to endDay
18%10%36%43345%7%37%
2870
February1st to 10thDay
18%11%36%5%25%6%5%8%33%
1710
11th to 20thDay
14%9%36%6%35%45%6%38%
1761
21st to endDay
14%9%48%5%3445%6%38%
1570
March1st to 10thDay
17%10%36%6%35%35%6%36%
1887
11th to 20thDay
18%6%35%5%35%445%42%
1980
21st to endDay
19%9%36%5%33445%39%
2178
April1st to 10thDay
22%9%35%5%34446%35%
2124
11th to 20thDay
19%8%36%5%2335%7%39%
2294
21st to endDay
23%9%25%5%34446%35%
2340
May1st to 10thDay
23%9%36%425%5%5%6%33%
2340
11th to 20thDay
21%7%35%4335%5%6%39%
2301
21st to endDay
21%7%35%435%5%5%8%35%
2742
June1st to 10thDay
24%7%36%6%35%45%7%32%
2700
11th to 20thDay
20%7%36%433447%39%
2700
21st to endDay
26%7%36%5%335%5%7%31%
2700
July1st to 10thDay
20%5%25%5%25%46%8%38%
2589
11th to 20thDay
17%6%26%4345%7%8%39%
2520
21st to endDay
16%6%25%5%35%5%6%9%38%
2679
August1st to 10thDay
15%5%244245%6%9%41%
2327
11th to 20thDay
15%6%25%5%35%5%7%8%38%
2304
21st to endDay
14%5%25%5%3445%8%47%
2574
September1st to 10thDay
13%5%245%24449%49%
2061
11th to 20thDay
14%5%24324346%53%
1980
21st to endDay
18%6%245%24448%43%
1980
October1st to 10thDay
17%6%25%5%345%5%6%42%
1924
11th to 20thDay
20%5%35%43445%7%41%
1800
21st to endDay
23%8%34433446%37%
1787
November1st to 10thDay
18%6%25%6%2345%6%42%
1671
11th to 20thDay
21%6%243345%48%41%
1677
21st to endDay
21%8%26%423345%41%
1520
December1st to 10thDay
24%8%25%5%34447%34%
1449
11th to 20thDay
24%9%35%5%23446%36%
1668
21st to endDay
25%10%35%433446%34%
2471
January1st to 10thNight
15%9%36%5%34446%40%
4429
11th to 20thNight
15%10%38%6%34446%38%
4440
21st to endNight
17%11%47%5%34447%33%
4784
February1st to 10thNight
18%9%36%6%35%5%5%6%34%
2470
11th to 20thNight
14%8%47%6%345%5%7%38%
2303
21st to endNight
16%8%37%5%34446%39%
1884
March1st to 10thNight
17%10%37%5%24446%38%
2220
11th to 20thNight
18%8%46%6%35%5%6%6%34%
1979
21st to endNight
19%9%36%5%23346%41%
2178
April1st to 10thNight
24%9%35%6%4443434%
1834
11th to 20thNight
21%7%46%43445%7%35%
1614
21st to endNight
25%9%25%5%34346%33%
1620
May1st to 10thNight
22%9%46%5%335%6%7%29%
1620
11th to 20thNight
24%7%246%445%6%7%31%
1593
21st to endNight
22%9%36%5%35%437%34%
1544
June1st to 10thNight
26%9%36%435%46%6%29%
1260
11th to 20thNight
20%7%35%4345%5%7%37%
1260
21st to endNight
27%10%25%5%25%446%31%
1260
July1st to 10thNight
20%9%35%5%3446%8%33%
1367
11th to 20thNight
20%8%34445%45%9%33%
1440
21st to endNight
20%6%35%6%345%5%6%35%
1618
August1st to 10thNight
17%7%25%335%6%5%9%37%
1612
11th to 20thNight
17%8%37%5%346%6%8%34%
1596
21st to endNight
16%5%245%25%5%47%45%
1782
September1st to 10thNight
15%5%1343446%7%48%
1894
11th to 20thNight
17%6%34323347%49%
1980
21st to endNight
19%5%2332445%7%46%
1980
October1st to 10thNight
20%6%25%4345%5%6%40%
2035
11th to 20thNight
18%6%35%43445%6%42%
2160
21st to endNight
25%8%345%34346%37%
2564
November1st to 10thNight
19%6%245%35%446%42%
2407
11th to 20thNight
19%6%25%4345%5%6%42%
2501
21st to endNight
19%7%3443445%6%41%
2660
December1st to 10thNight
24%8%35%5%3435%6%33%
2726
11th to 20thNight
24%8%34423347%39%
3531
21st to endNight
25%9%35%423445%37%
5190

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 10thDay
47%5%14%24%9%1
2518
11th to 20thDay
42%6%12%25%12%2
2520
21st to endDay
48%5%14%20%12%1
2870
February1st to 10thDay
50%6%12%17%13%2
1710
11th to 20thDay
48%5%12%19%14%1
1769
21st to endDay
48%5%12%20%10%5%
1570
March1st to 10thDay
50%5%12%17%15%3
1891
11th to 20thDay
44%5%10%20%17%4
1980
21st to endDay
47%410%17%16%5%
2178
April1st to 10thDay
51%5%9%16%15%4
2124
11th to 20thDay
46%5%11%22%15%3
2294
21st to endDay
51%49%17%15%4
2340
May1st to 10thDay
51%5%8%20%13%3
2340
11th to 20thDay
46%5%9%23%15%2
2305
21st to endDay
48%8%11%20%12%1
2742
June1st to 10thDay
52%8%12%19%9%1
2700
11th to 20thDay
47%6%10%20%15%2
2700
21st to endDay
52%8%12%16%10%2
2700
July1st to 10thDay
43%9%14%22%11%
2519
11th to 20thDay
41%10%13%23%12%1
2445
21st to endDay
41%9%15%24%10%1
2529
August1st to 10thDay
39%8%17%27%9%
2314
11th to 20thDay
42%9%13%22%13%
2304
21st to endDay
35%7%13%25%18%1
2574
September1st to 10thDay
33%7%14%26%18%1
2061
11th to 20thDay
34%6%12%26%20%3
1980
21st to endDay
41%5%10%26%17%1
1980
October1st to 10thDay
42%6%12%23%15%2
1924
11th to 20thDay
43%5%13%28%11%1
1800
21st to endDay
49%411%21%13%1
1787
November1st to 10thDay
44%5%14%22%14%1
1671
11th to 20thDay
42%6%10%22%18%3
1677
21st to endDay
47%416%22%10%1
1520
December1st to 10thDay
52%6%13%19%10%1
1449
11th to 20thDay
51%5%11%18%13%2
1668
21st to endDay
53%6%12%18%8%3
2471
January1st to 10thNight
45%5%14%25%10%2
4429
11th to 20thNight
49%5%14%20%11%2
4440
21st to endNight
51%6%11%21%10%1
4784
February1st to 10thNight
52%5%12%17%12%2
2470
11th to 20thNight
47%5%11%20%15%2
2306
21st to endNight
46%5%10%20%14%4
1884
March1st to 10thNight
49%48%20%15%3
2229
11th to 20thNight
49%5%12%15%16%3
1980
21st to endNight
47%48%19%18%3
2178
April1st to 10thNight
54%5%8%13%16%4
1834
11th to 20thNight
49%5%9%20%16%1
1614
21st to endNight
53%410%16%13%3
1620
May1st to 10thNight
53%6%8%18%13%1
1620
11th to 20thNight
52%7%10%19%11%2
1594
21st to endNight
52%6%8%20%13%1
1545
June1st to 10thNight
56%6%9%20%8%1
1260
11th to 20thNight
47%7%13%20%11%2
1260
21st to endNight
55%6%9%18%9%2
1260
July1st to 10thNight
49%8%12%20%11%
1327
11th to 20thNight
49%7%13%21%10%
1392
21st to endNight
48%8%13%21%9%2
1528
August1st to 10thNight
44%8%14%24%9%
1600
11th to 20thNight
48%8%14%19%11%
1596
21st to endNight
39%7%11%23%20%1
1782
September1st to 10thNight
36%7%12%28%16%1
1894
11th to 20thNight
38%411%25%19%2
1980
21st to endNight
40%5%9%28%17%1
1980
October1st to 10thNight
44%5%11%23%14%2
2035
11th to 20thNight
43%5%12%26%13%1
2160
21st to endNight
51%410%20%13%1
2564
November1st to 10thNight
44%6%12%23%15%1
2407
11th to 20thNight
44%6%11%22%17%2
2501
21st to endNight
45%6%13%19%15%2
2660
December1st to 10thNight
54%5%10%20%11%
2726
11th to 20thNight
48%5%11%20%15%1
3532
21st to endNight
51%6%13%18%11%2
5190

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 10thDay
29%24%29%14%3
180
11th to 20thDay
37%18%32%10%21
180
21st to endDay
25%22%35%16%2
257
February1st to 10thDay
29%24%29%14%4
370
11th to 20thDay
26%32%31%9%2
413
21st to endDay
27%22%31%17%2
382
March1st to 10thDay
28%21%35%15%1
448
11th to 20thDay
26%25%29%16%4
420
21st to endDay
30%21%27%16%6%1
462
April1st to 10thDay
34%20%31%10%41
420
11th to 20thDay
27%21%33%14%5%
412
21st to endDay
27%17%36%15%41
420
May1st to 10thDay
29%18%32%15%41
423
11th to 20thDay
19%22%34%20%31
447
21st to endDay
25%14%36%17%7%1
561
June1st to 10thDay
25%13%32%22%7%1
630
11th to 20thDay
24%12%31%22%10%1
630
21st to endDay
28%8%28%25%8%2
630
July1st to 10thDay
24%7%34%24%10%1
514
11th to 20thDay
20%6%34%29%10%2
444
21st to endDay
16%7%38%27%10%2
488
August1st to 10thDay
16%8%32%30%12%1
446
11th to 20thDay
18%8%31%27%13%3
439
21st to endDay
16%11%32%28%11%2
495
September1st to 10thDay
16%8%37%28%10%2
450
11th to 20thDay
19%13%31%20%10%6%
450
21st to endDay
21%10%34%22%9%4
450
October1st to 10thDay
19%16%27%25%10%2
421
11th to 20thDay
23%16%31%21%8%2
360
21st to endDay
32%16%30%17%5%1
396
November1st to 10thDay
25%18%30%21%5%1
365
11th to 20thDay
30%18%32%15%31
370
21st to endDay
32%21%28%14%4
370
December1st to 10thDay
28%19%34%13%41
299
11th to 20thDay
35%30%26%8%2
180
21st to endDay
40%20%24%15%2
198
January1st to 10thNight
26%24%32%16%3
760
11th to 20thNight
30%22%30%14%3
760
21st to endNight
21%27%30%18%4
836
February1st to 10thNight
28%21%34%15%3
760
11th to 20thNight
23%29%30%15%31
743
21st to endNight
26%19%33%18%4
628
March1st to 10thNight
26%19%35%17%2
751
11th to 20thNight
24%19%32%19%6%
720
21st to endNight
23%17%32%21%6%1
792
April1st to 10thNight
33%14%33%17%4
720
11th to 20thNight
25%13%33%24%5%
550
21st to endNight
29%13%26%24%7%1
540
May1st to 10thNight
27%9%31%24%8%1
540
11th to 20thNight
26%9%35%25%6%
532
21st to endNight
27%7%26%30%10%1
462
June1st to 10thNight
31%8%23%29%8%2
360
11th to 20thNight
24%6%24%32%13%1
360
21st to endNight
34%318%33%11%1
360
July1st to 10thNight
25%421%37%13%
350
11th to 20thNight
24%222%37%15%1
348
21st to endNight
21%322%39%13%2
438
August1st to 10thNight
21%5%24%36%14%1
538
11th to 20thNight
21%422%38%14%1
532
21st to endNight
19%5%21%36%18%1
594
September1st to 10thNight
17%429%34%14%2
715
11th to 20thNight
21%9%25%26%14%4
720
21st to endNight
21%9%28%26%13%3
720
October1st to 10thNight
24%10%25%25%15%1
720
11th to 20thNight
21%15%29%23%11%1
720
21st to endNight
31%16%30%18%5%
792
November1st to 10thNight
26%15%26%24%7%1
740
11th to 20thNight
28%20%26%19%7%1
775
21st to endNight
27%22%29%16%6%
850
December1st to 10thNight
31%19%33%13%4
850
11th to 20thNight
31%24%27%15%3
850
21st to endNight
31%21%30%14%4
920
Page generated at 2024-03-05 07:23:59. Version ac07

Copyright © 2024 Attilla Danko.


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