Sudbury
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sudbury clear sky chart from 2005-11-05 to 2018-03-11.

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
30%
15919
13%
49083
8%
15881
36%
15881
18%
34943

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
20%
974
9%
2910
4%
970
24%
970
11%
2309
January16th to endNight
25%
946
12%
2818
6%
946
31%
946
12%
2198
February1st to 15thNight
23%
763
11%
2482
6%
761
30%
761
13%
1834
February16th to endNight
22%
683
12%
2168
4%
683
30%
683
13%
1638
March1st to 15thNight
23%
764
12%
2153
6%
764
29%
764
17%
1553
March16th to endNight
31%
768
19%
2112
10%
768
40%
768
25%
1415
April1st to 15thNight
28%
650
15%
1774
8%
650
33%
650
21%
1277
April16th to endNight
31%
540
17%
1620
10%
540
38%
540
22%
1117
May1st to 15thNight
33%
474
15%
1554
10%
474
42%
474
19%
1049
May16th to endNight
36%
375
13%
1448
10%
374
46%
374
21%
881
June1st to 15thNight
35%
360
10%
1260
9%
360
41%
360
20%
815
June16th to endNight
42%
360
10%
1260
8%
360
47%
360
24%
771
July1st to 15thNight
47%
340
15%
1190
14%
340
52%
340
32%
670
July16th to endNight
51%
456
15%
1380
13%
428
54%
428
30%
829
August1st to 15thNight
49%
539
14%
1609
11%
536
53%
536
28%
1047
August16th to endNight
50%
573
19%
1719
11%
573
56%
573
29%
1071
September1st to 15thNight
44%
708
17%
1842
9%
708
48%
708
32%
1181
September16th to endNight
45%
717
20%
1980
14%
717
49%
717
30%
1295
October1st to 15thNight
32%
720
16%
2154
12%
720
40%
720
21%
1496
October16th to endNight
24%
768
13%
2373
8%
768
32%
768
13%
1821
November1st to 15thNight
27%
760
13%
2616
9%
760
34%
760
15%
1868
November16th to endNight
24%
780
11%
2730
7%
780
30%
780
11%
2096
December1st to 15thNight
19%
861
9%
2811
3%
861
26%
861
10%
2200
December16th to endNight
19%
1040
10%
3120
4%
1040
24%
1040
10%
2512

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
17%10%36%6%3445%6%31%
49557
Night
17%10%46%6%34446%31%
49244
Cloud CoverDay
17%9%36%5%3445%6%31%
49567
Night
17%10%46%5%34446%31%
49249
TransparencyDay
53%311%20%9%
49236
Night
53%312%20%9%1
49083
SeeingDay
21%10%27%24%11%4
6382
Night
23%8%28%28%10%
15921

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
20%17%5%8%5%2334424%
1358
16th to endDay
17%16%6%9%7%3435%5%19%
1755
February1st to 15thDay
10%15%48%9%45%45%6%24%
1710
16th to endDay
15%17%49%6%3444424%
1588
March1st to 15thDay
15%11%36%6%34347%32%
2033
16th to endDay
12%9%37%5%33346%40%
2112
April1st to 15thDay
21%9%35%5%34446%31%
2182
16th to endDay
21%8%24423347%38%
2340
May1st to 15thDay
19%9%26%6%2445%6%32%
2397
16th to endDay
17%6%26%5%35%5%5%7%36%
2665
June1st to 15thDay
15%8%36%6%35%5%5%8%30%
2700
16th to endDay
16%7%36%6%35%5%6%7%31%
2700
July1st to 15thDay
12%5%36%5%35%5%5%8%38%
2700
16th to endDay
12%6%26%7%36%5%7%7%34%
2690
August1st to 15thDay
14%7%36%5%36%46%8%32%
2340
16th to endDay
14%7%25%6%35%45%8%35%
2483
September1st to 15thDay
14%7%26%6%34448%37%
2106
16th to endDay
20%5%25%5%24446%37%
1980
October1st to 15thDay
20%9%45%5%34446%31%
1806
16th to endDay
28%12%39%5%23435%21%
1850
November1st to 15thDay
21%11%49%5%3435%5%26%
1571
16th to endDay
24%17%5%8%7%3333319%
1560
December1st to 15thDay
18%18%5%9%6%35%335%19%
1475
16th to endDay
20%16%7%8%6%25%45%5%17%
1456
January1st to 15thNight
19%15%5%9%6%35%335%21%
2910
16th to endNight
15%14%6%9%7%35%45%6%20%
2818
February1st to 15thNight
11%13%5%9%9%35%5%5%5%24%
2480
16th to endNight
15%15%5%7%7%44445%25%
2168
March1st to 15thNight
16%10%47%6%34346%32%
2141
16th to endNight
14%8%35%5%24446%41%
2112
April1st to 15thNight
18%11%45%423346%33%
1774
16th to endNight
18%8%345%34346%36%
1620
May1st to 15thNight
16%7%36%5%35%45%5%35%
1554
16th to endNight
14%5%26%5%2445%8%40%
1446
June1st to 15thNight
13%7%35%5%35%6%5%8%35%
1260
16th to endNight
11%435%5%3446%10%39%
1260
July1st to 15thNight
10%324435%46%8%46%
1260
16th to endNight
8%425%4245%6%9%44%
1476
August1st to 15thNight
13%5%25%6%24446%43%
1620
16th to endNight
12%5%25%4245%5%7%43%
1719
September1st to 15thNight
13%5%2443445%6%45%
1842
16th to endNight
14%5%25%433447%43%
1980
October1st to 15thNight
22%8%35%42345%5%35%
2154
16th to endNight
27%9%37%5%34345%24%
2373
November1st to 15thNight
18%11%46%6%34446%28%
2616
16th to endNight
24%12%46%5%35%445%23%
2730
December1st to 15thNight
19%16%48%7%25%345%22%
2811
16th to endNight
21%14%6%8%6%35%445%18%
3120

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
20%16%6%8%5%2433424%
1358
16th to endDay
17%16%6%9%7%3435%5%20%
1755
February1st to 15thDay
10%15%5%7%9%35%45%6%24%
1710
16th to endDay
15%17%5%8%6%25%44425%
1588
March1st to 15thDay
17%11%36%6%34337%33%
2044
16th to endDay
12%9%37%5%23346%41%
2111
April1st to 15thDay
21%9%35%5%24446%31%
2182
16th to endDay
21%8%14423346%39%
2340
May1st to 15thDay
19%8%36%5%2435%6%33%
2397
16th to endDay
17%6%25%5%35%45%6%37%
2665
June1st to 15thDay
15%7%36%6%35%5%5%8%31%
2700
16th to endDay
16%7%26%5%35%6%5%7%32%
2700
July1st to 15thDay
13%436%5%35%45%8%38%
2700
16th to endDay
13%5%26%6%35%5%6%8%35%
2690
August1st to 15thDay
15%7%26%435%5%6%9%32%
2340
16th to endDay
14%6%26%6%35%45%7%36%
2483
September1st to 15thDay
15%6%26%6%24448%37%
2106
16th to endDay
20%5%25%5%24446%37%
1980
October1st to 15thDay
20%9%35%5%24446%32%
1806
16th to endDay
29%12%28%5%24435%21%
1850
November1st to 15thDay
22%11%48%6%2425%6%26%
1571
16th to endDay
24%16%5%7%7%3334319%
1560
December1st to 15thDay
19%18%6%8%6%34335%19%
1475
16th to endDay
20%17%6%8%6%25%445%17%
1456
January1st to 15thNight
20%15%5%8%6%34435%21%
2910
16th to endNight
15%14%7%8%7%35%45%6%21%
2818
February1st to 15thNight
11%13%5%8%9%45%5%5%5%25%
2473
16th to endNight
16%14%48%7%34445%24%
2168
March1st to 15thNight
17%10%47%5%34346%32%
2153
16th to endNight
14%7%36%5%24436%41%
2112
April1st to 15thNight
19%11%45%423436%33%
1774
16th to endNight
18%7%35%5%34345%36%
1620
May1st to 15thNight
17%7%35%6%35%45%5%35%
1554
16th to endNight
14%5%25%5%2445%8%40%
1446
June1st to 15thNight
14%6%35%5%36%5%5%8%35%
1260
16th to endNight
11%5%346%3446%9%40%
1260
July1st to 15thNight
9%324435%35%9%46%
1260
16th to endNight
9%43443447%9%44%
1476
August1st to 15thNight
13%5%25%6%33346%43%
1620
16th to endNight
12%4144345%5%7%44%
1719
September1st to 15thNight
13%5%1443445%6%46%
1842
16th to endNight
15%425%423437%44%
1980
October1st to 15thNight
22%8%25%5%23345%35%
2154
16th to endNight
27%10%27%5%34345%25%
2373
November1st to 15thNight
18%11%46%5%34446%29%
2616
16th to endNight
24%12%46%5%34445%23%
2730
December1st to 15thNight
19%16%48%6%34345%22%
2811
16th to endNight
22%15%5%8%6%35%445%18%
3120

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
64%211%15%6%
1359
16th to endDay
66%25%17%6%
1755
February1st to 15thDay
59%313%16%5%
1712
16th to endDay
62%27%16%9%
1588
March1st to 15thDay
52%213%18%11%
2044
16th to endDay
45%110%24%14%3
2112
April1st to 15thDay
53%310%19%10%1
2182
16th to endDay
47%37%25%13%2
2340
May1st to 15thDay
51%310%19%12%2
2397
16th to endDay
46%412%20%14%
2669
June1st to 15thDay
49%412%21%11%
2700
16th to endDay
49%6%11%21%9%1
2700
July1st to 15thDay
41%411%27%14%
2541
16th to endDay
45%5%11%25%10%
2523
August1st to 15thDay
46%5%17%20%8%1
2327
16th to endDay
46%415%28%5%
2483
September1st to 15thDay
45%317%24%8%
2106
16th to endDay
47%416%25%6%
1980
October1st to 15thDay
52%412%18%11%
1806
16th to endDay
66%311%12%6%
1850
November1st to 15thDay
59%412%16%8%
1571
16th to endDay
69%310%12%4
1560
December1st to 15thDay
68%39%14%4
1475
16th to endDay
69%29%12%5%
1456
January1st to 15thNight
66%29%14%6%
2910
16th to endNight
63%38%17%6%
2818
February1st to 15thNight
60%213%17%6%
2482
16th to endNight
61%210%16%8%
2168
March1st to 15thNight
54%212%19%10%1
2153
16th to endNight
44%310%20%16%4
2112
April1st to 15thNight
52%28%19%15%1
1774
16th to endNight
49%29%19%16%2
1620
May1st to 15thNight
50%39%22%12%2
1554
16th to endNight
42%412%22%15%2
1448
June1st to 15thNight
45%412%23%11%2
1260
16th to endNight
40%5%15%23%13%1
1260
July1st to 15thNight
33%414%30%15%1
1190
16th to endNight
36%5%17%27%13%
1380
August1st to 15thNight
42%418%22%11%1
1609
16th to endNight
38%5%16%28%10%
1719
September1st to 15thNight
38%417%29%9%1
1842
16th to endNight
40%5%13%33%7%
1980
October1st to 15thNight
50%313%21%11%
2154
16th to endNight
61%310%17%6%
2373
November1st to 15thNight
54%414%19%7%
2616
16th to endNight
63%411%15%5%
2730
December1st to 15thNight
65%311%15%4
2811
16th to endNight
67%38%13%6%
3120

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
31%14%31%18%4
90
16th to endDay
33%425%19%13%2
143
February1st to 15thDay
24%15%33%25%1
135
16th to endDay
32%15%30%18%2
120
March1st to 15thDay
22%14%29%26%7%
260
16th to endDay
21%9%29%26%10%3
288
April1st to 15thDay
23%10%25%26%12%2
270
16th to endDay
29%11%25%15%10%6%
270
May1st to 15thDay
25%9%24%21%14%5%
288
16th to endDay
20%14%29%22%10%2
378
June1st to 15thDay
20%14%28%25%8%2
495
16th to endDay
21%10%31%23%10%3
495
July1st to 15thDay
12%11%29%29%13%4
475
16th to endDay
12%6%32%28%12%7%
443
August1st to 15thDay
18%420%27%19%10%
313
16th to endDay
20%5%21%21%17%12%
332
September1st to 15thDay
16%5%23%26%18%9%
315
16th to endDay
21%7%23%28%11%7%
314
October1st to 15thDay
23%11%29%23%11%1
315
16th to endDay
28%15%30%19%41
266
November1st to 15thDay
30%9%31%22%3
101
16th to endDay
30%15%31%18%4
90
December1st to 15thDay
35%11%31%15%6%
90
16th to endDay
28%13%34%19%4
96
January1st to 15thNight
27%10%29%23%7%
975
16th to endNight
23%8%28%29%8%1
946
February1st to 15thNight
17%11%35%30%4
764
16th to endNight
22%13%30%26%6%
683
March1st to 15thNight
23%15%29%25%6%
764
16th to endNight
19%9%32%26%10%1
768
April1st to 15thNight
24%11%31%27%5%
650
16th to endNight
25%7%29%26%9%1
540
May1st to 15thNight
19%5%31%31%10%
474
16th to endNight
17%7%33%32%8%
375
June1st to 15thNight
20%6%30%32%10%
360
16th to endNight
13%430%36%13%
360
July1st to 15thNight
10%334%41%9%
340
16th to endNight
10%129%40%15%2
456
August1st to 15thNight
16%321%33%23%2
539
16th to endNight
14%223%36%21%1
573
September1st to 15thNight
17%327%27%20%1
708
16th to endNight
17%426%30%17%3
717
October1st to 15thNight
26%5%29%26%10%1
720
16th to endNight
33%10%25%23%5%
768
November1st to 15thNight
25%11%28%25%8%
760
16th to endNight
32%9%24%24%7%
780
December1st to 15thNight
30%11%29%22%4
861
16th to endNight
30%11%25%24%6%
1040
Page generated at 2018-03-12 13:28:08. Version ac04

Copyright 2018 A. Danko


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