Acadia University
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Acadia University clear sky chart from 2005-11-06 to 2024-01-10.

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
22%
23571
11%
74200
5%
23511
29%
23511
12%
56110

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
8%
849
6%
2646
2%
846
14%
846
5%
2264
January11th to 20thNight
12%
770
5%
2452
1%
770
17%
770
5%
2101
January21st to endNight
13%
792
9%
2574
3%
792
21%
792
8%
2052
February1st to 10thNight
10%
720
7%
2340
3%
720
16%
720
5%
1954
February11th to 20thNight
10%
703
7%
2276
2%
700
17%
700
6%
1865
February21st to endNight
15%
592
12%
1907
3%
592
27%
592
11%
1439
March1st to 10thNight
14%
720
13%
1980
4%
720
23%
720
12%
1554
March11th to 20thNight
20%
720
12%
1980
4%
720
26%
720
13%
1525
March21st to endNight
18%
792
14%
2178
3%
792
28%
792
15%
1642
April1st to 10thNight
14%
562
11%
1822
4%
562
22%
562
11%
1380
April11th to 20thNight
17%
534
16%
1684
6%
534
27%
534
14%
1213
April21st to endNight
20%
540
12%
1620
4%
540
27%
540
14%
1206
May1st to 10thNight
23%
540
12%
1580
6%
540
29%
540
15%
1187
May11th to 20thNight
27%
532
14%
1417
6%
532
33%
532
19%
1052
May21st to endNight
24%
583
11%
1551
3%
582
31%
582
20%
1135
June1st to 10thNight
27%
540
9%
1440
4%
540
30%
540
17%
1092
June11th to 20thNight
33%
374
13%
1274
8%
374
39%
374
16%
881
June21st to endNight
34%
360
8%
1260
5%
360
37%
360
14%
945
July1st to 10thNight
39%
350
10%
1225
6%
350
45%
350
19%
792
July11th to 20thNight
42%
488
9%
1358
6%
488
46%
488
22%
957
July21st to endNight
43%
590
10%
1571
9%
558
44%
558
21%
1137
August1st to 10thNight
46%
538
13%
1600
10%
534
48%
534
24%
1070
August11th to 20thNight
41%
532
12%
1596
7%
532
45%
532
19%
1137
August21st to endNight
45%
594
17%
1861
10%
594
51%
594
25%
1185
September1st to 10thNight
42%
540
18%
1800
13%
540
50%
540
24%
1126
September11th to 20thNight
39%
627
20%
1887
13%
627
47%
627
25%
1208
September21st to endNight
32%
720
19%
2023
9%
720
40%
720
23%
1363
October1st to 10thNight
32%
720
18%
2160
9%
720
40%
720
23%
1424
October11th to 20thNight
25%
720
17%
2160
7%
720
34%
720
19%
1494
October21st to endNight
19%
792
15%
2376
6%
792
28%
792
12%
1768
November1st to 10thNight
21%
814
13%
2545
6%
814
29%
814
13%
1877
November11th to 20thNight
17%
850
12%
2660
6%
850
24%
850
10%
2113
November21st to endNight
16%
850
7%
2660
2%
850
22%
850
9%
2111
December1st to 10thNight
11%
850
6%
2660
1%
850
16%
850
6%
2231
December11th to 20thNight
8%
850
5%
3242
1%
849
12%
849
4%
2805
December21st to endNight
9%
923
4%
4835
1%
907
16%
907
3%
3825

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%11%48%7%45%45%6%29%
75173
Night
18%12%5%8%7%45%45%6%27%
74470
TransparencyDay
56%6%11%18%9%1
74876
Night
57%6%11%17%8%1
74302
SeeingDay
26%17%30%19%7%1
16122
Night
27%16%29%22%6%
23583

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
16%17%8%12%10%5%6%44413%
1473
11th to 20thDay
19%16%6%11%10%5%7%435%14%
1508
21st to endDay
13%10%7%12%13%7%8%5%45%16%
1782
February1st to 10thDay
17%12%7%13%10%6%5%445%16%
1620
11th to 20thDay
17%15%5%12%10%6%5%5%4418%
1573
21st to endDay
10%12%7%10%9%5%4347%28%
1344
March1st to 10thDay
15%17%6%10%10%4433424%
1976
11th to 20thDay
12%12%7%11%9%45%446%28%
1980
21st to endDay
16%16%6%8%6%3343431%
2178
April1st to 10thDay
21%14%5%9%6%4435%5%25%
2137
11th to 20thDay
18%13%35%434448%33%
2224
21st to endDay
22%11%37%6%3445%7%27%
2340
May1st to 10thDay
23%11%36%6%35%5%5%6%26%
2380
11th to 20thDay
21%9%36%5%34446%35%
2478
21st to endDay
18%10%36%6%4445%8%32%
2724
June1st to 10thDay
25%8%46%6%35%45%7%26%
2520
11th to 20thDay
22%8%36%5%3446%7%31%
2700
21st to endDay
23%9%47%5%35%5%5%7%28%
2700
July1st to 10thDay
15%8%36%5%3446%10%36%
2700
11th to 20thDay
14%7%36%5%35%6%7%9%35%
2534
21st to endDay
17%9%47%6%46%5%6%8%29%
2651
August1st to 10thDay
14%6%26%6%36%6%6%8%37%
2327
11th to 20thDay
15%8%36%6%45%5%7%7%34%
2304
21st to endDay
14%6%25%43346%8%45%
2494
September1st to 10thDay
16%7%245%3445%7%43%
2160
11th to 20thDay
18%7%25%423446%44%
2070
21st to endDay
17%6%35%5%24447%43%
1936
October1st to 10thDay
18%7%35%5%3445%8%38%
1800
11th to 20thDay
19%9%36%5%345%5%7%33%
1800
21st to endDay
19%13%47%7%34446%29%
1980
November1st to 10thDay
21%13%48%5%45%336%28%
1531
11th to 20thDay
17%17%6%8%7%45%446%23%
1520
21st to endDay
18%15%6%9%8%46%45%5%20%
1520
December1st to 10thDay
23%18%7%12%7%4443416%
1520
11th to 20thDay
24%17%7%12%10%4433312%
1906
21st to endDay
21%15%11%12%9%3434414%
2783
January1st to 10thNight
17%16%8%13%10%5%445%414%
2646
11th to 20thNight
17%14%6%12%10%5%8%5%45%14%
2452
21st to endNight
13%12%5%11%11%6%6%5%5%6%18%
2574
February1st to 10thNight
17%14%5%12%12%46%5%5%416%
2340
11th to 20thNight
17%13%6%11%11%5%6%445%17%
2273
21st to endNight
12%14%6%11%7%5%5%45%5%26%
1907
March1st to 10thNight
15%15%6%9%9%445%35%25%
1971
11th to 20thNight
16%12%6%9%7%5%5%5%5%6%25%
1979
21st to endNight
17%13%6%8%6%33435%31%
2178
April1st to 10thNight
22%13%6%6%7%4444426%
1822
11th to 20thNight
21%12%5%6%5%34446%32%
1684
21st to endNight
22%12%36%5%35%445%29%
1620
May1st to 10thNight
22%13%36%6%35%45%6%29%
1580
11th to 20thNight
22%9%36%5%34447%32%
1416
21st to endNight
15%10%47%5%35%46%8%33%
1550
June1st to 10thNight
25%8%25%6%345%5%9%28%
1440
11th to 20thNight
21%7%36%5%45%45%6%35%
1274
21st to endNight
22%8%45%6%45%5%6%7%29%
1260
July1st to 10thNight
16%6%36%425%5%7%11%35%
1260
11th to 20thNight
13%7%345%46%7%8%10%33%
1404
21st to endNight
14%8%36%7%37%6%6%8%31%
1663
August1st to 10thNight
15%6%25%5%445%6%8%41%
1612
11th to 20thNight
15%7%36%6%445%8%9%32%
1596
21st to endNight
15%5%35%5%35%45%7%44%
1861
September1st to 10thNight
12%6%35%5%35%5%5%8%43%
1800
11th to 20thNight
16%7%36%42345%7%43%
1887
21st to endNight
17%6%35%5%345%5%7%39%
2023
October1st to 10thNight
17%7%25%4445%6%7%41%
2160
11th to 20thNight
18%7%36%6%345%6%8%35%
2160
21st to endNight
24%11%47%5%34446%29%
2376
November1st to 10thNight
20%11%46%6%35%45%5%30%
2545
11th to 20thNight
17%16%49%8%45%45%5%22%
2660
21st to endNight
20%15%6%9%7%34445%23%
2660
December1st to 10thNight
22%17%5%13%8%35%445%15%
2660
11th to 20thNight
20%20%7%12%8%4433415%
3293
21st to endNight
24%15%7%11%7%3333420%
4884

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
75%5%10%7%3
1474
11th to 20thDay
74%5%8%10%2
1508
21st to endDay
68%8%8%11%6%
1782
February1st to 10thDay
70%5%9%10%6%1
1620
11th to 20thDay
69%6%9%11%5%
1581
21st to endDay
56%5%10%18%9%1
1344
March1st to 10thDay
65%48%14%8%1
1980
11th to 20thDay
58%5%10%16%10%1
1980
21st to endDay
59%37%18%11%2
2178
April1st to 10thDay
61%5%7%13%11%3
2137
11th to 20thDay
51%49%21%13%1
2224
21st to endDay
57%411%18%9%2
2340
May1st to 10thDay
58%5%9%17%9%2
2380
11th to 20thDay
50%6%9%22%13%1
2482
21st to endDay
52%7%12%20%9%1
2724
June1st to 10thDay
58%6%11%18%7%
2520
11th to 20thDay
51%7%12%19%10%1
2700
21st to endDay
56%7%11%15%10%1
2700
July1st to 10thDay
42%9%16%21%11%1
2625
11th to 20thDay
44%9%15%23%9%1
2457
21st to endDay
52%7%13%21%6%1
2503
August1st to 10thDay
44%8%15%23%10%
2314
11th to 20thDay
46%8%15%22%8%
2304
21st to endDay
38%5%16%27%13%1
2494
September1st to 10thDay
41%5%14%24%14%2
2160
11th to 20thDay
43%412%23%16%1
2070
21st to endDay
41%5%10%28%15%1
1936
October1st to 10thDay
45%5%12%26%11%1
1800
11th to 20thDay
49%7%13%23%7%
1800
21st to endDay
57%5%10%18%9%
1980
November1st to 10thDay
59%6%9%17%8%1
1531
11th to 20thDay
61%7%13%13%5%1
1520
21st to endDay
66%7%12%12%4
1520
December1st to 10thDay
73%6%7%10%4
1520
11th to 20thDay
75%6%7%8%31
1905
21st to endDay
73%6%12%7%3
2783
January1st to 10thNight
72%7%9%10%2
2646
11th to 20thNight
72%8%9%8%3
2452
21st to endNight
65%6%12%13%41
2574
February1st to 10thNight
70%6%9%9%6%
2340
11th to 20thNight
68%6%10%10%5%1
2276
21st to endNight
59%5%10%17%8%1
1907
March1st to 10thNight
61%5%9%15%9%1
1980
11th to 20thNight
58%6%10%14%10%2
1980
21st to endNight
57%49%18%10%2
2178
April1st to 10thNight
60%5%9%13%10%3
1822
11th to 20thNight
55%5%6%19%14%1
1684
21st to endNight
56%5%11%14%11%2
1620
May1st to 10thNight
57%5%11%17%9%1
1580
11th to 20thNight
53%6%8%22%11%1
1417
21st to endNight
49%7%15%21%7%1
1551
June1st to 10thNight
53%8%11%21%6%
1440
11th to 20thNight
51%6%11%21%10%1
1274
21st to endNight
54%10%10%16%8%2
1260
July1st to 10thNight
42%10%19%20%9%
1225
11th to 20thNight
44%10%17%20%9%1
1358
21st to endNight
47%10%16%19%8%
1571
August1st to 10thNight
41%9%13%27%9%
1600
11th to 20thNight
46%11%16%19%8%
1596
21st to endNight
39%7%15%27%11%
1861
September1st to 10thNight
38%8%11%29%12%1
1800
11th to 20thNight
41%5%12%28%14%1
1887
21st to endNight
43%7%10%26%14%1
2023
October1st to 10thNight
43%6%12%24%14%1
2160
11th to 20thNight
47%7%14%26%7%
2160
21st to endNight
56%6%10%17%11%1
2376
November1st to 10thNight
55%6%12%18%9%1
2545
11th to 20thNight
62%7%10%14%6%
2660
21st to endNight
63%7%13%13%4
2660
December1st to 10thNight
71%5%10%11%3
2660
11th to 20thNight
75%5%7%10%4
3295
21st to endNight
69%5%10%13%3
4884

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
30%25%31%12%2
332
11th to 20thDay
31%24%31%11%4
340
21st to endDay
21%27%35%15%3
374
February1st to 10thDay
30%23%34%11%2
340
11th to 20thDay
33%30%22%14%1
336
21st to endDay
21%21%39%15%3
284
March1st to 10thDay
27%25%33%11%4
420
11th to 20thDay
25%24%35%12%4
420
21st to endDay
31%24%27%12%5%
462
April1st to 10thDay
39%22%26%11%1
420
11th to 20thDay
24%25%32%14%31
412
21st to endDay
28%18%31%15%9%
420
May1st to 10thDay
32%19%29%14%5%2
463
11th to 20thDay
25%18%26%24%6%1
624
21st to endDay
27%14%32%20%7%1
680
June1st to 10thDay
31%11%27%21%8%1
630
11th to 20thDay
26%12%30%24%8%
630
21st to endDay
27%9%28%24%9%2
630
July1st to 10thDay
21%7%33%28%10%1
620
11th to 20thDay
20%6%32%27%14%2
618
21st to endDay
24%6%29%28%12%1
591
August1st to 10thDay
13%7%32%34%11%3
446
11th to 20thDay
21%8%29%25%13%4
439
21st to endDay
16%13%28%24%16%3
495
September1st to 10thDay
18%10%34%27%10%2
450
11th to 20thDay
24%15%26%24%10%2
450
21st to endDay
20%15%31%20%12%2
428
October1st to 10thDay
23%13%30%22%9%4
360
11th to 20thDay
24%19%28%19%9%2
360
21st to endDay
27%22%28%18%5%1
396
November1st to 10thDay
30%17%30%17%41
365
11th to 20thDay
36%21%24%13%6%1
370
21st to endDay
32%22%31%13%21
370
December1st to 10thDay
35%22%29%12%21
370
11th to 20thDay
39%25%26%9%1
370
21st to endDay
34%24%28%11%31
407
January1st to 10thNight
31%22%31%15%2
849
11th to 20thNight
31%21%30%16%3
770
21st to endNight
26%23%32%15%4
792
February1st to 10thNight
31%23%30%14%2
720
11th to 20thNight
32%24%28%13%2
703
21st to endNight
24%21%33%18%4
592
March1st to 10thNight
28%20%32%18%2
720
11th to 20thNight
24%19%31%21%5%
720
21st to endNight
28%18%30%18%6%
792
April1st to 10thNight
33%17%30%17%4
562
11th to 20thNight
27%18%33%16%6%
534
21st to endNight
30%17%29%17%6%1
540
May1st to 10thNight
31%12%29%21%6%
540
11th to 20thNight
27%10%30%26%7%
532
21st to endNight
21%10%38%26%5%
583
June1st to 10thNight
28%10%30%25%6%
540
11th to 20thNight
25%9%26%34%6%1
374
21st to endNight
24%7%28%31%10%1
360
July1st to 10thNight
19%5%29%38%9%
350
11th to 20thNight
16%6%28%36%13%
488
21st to endNight
19%5%25%41%9%1
590
August1st to 10thNight
16%5%25%41%13%1
538
11th to 20thNight
18%7%27%32%15%1
532
21st to endNight
17%7%24%34%18%1
594
September1st to 10thNight
15%9%29%35%12%1
540
11th to 20thNight
19%10%26%32%12%1
627
21st to endNight
22%11%31%25%10%2
720
October1st to 10thNight
22%11%32%24%10%1
720
11th to 20thNight
23%14%33%20%8%1
720
21st to endNight
33%19%25%19%5%
792
November1st to 10thNight
28%19%27%20%5%
814
11th to 20thNight
30%21%26%18%4
850
21st to endNight
33%19%28%18%2
850
December1st to 10thNight
34%21%28%14%3
850
11th to 20thNight
34%25%27%11%2
850
21st to endNight
32%22%27%16%31
935
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