Dorion
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dorion clear sky chart from 2005-11-06 to 2024-02-05.

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
31%
24576
8%
80619
4%
24482
35%
24482
9%
64257

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
24%
945
7%
4395
4%
926
29%
926
7%
3223
January11th to 20thNight
23%
942
5%
4410
1%
930
28%
930
4%
3616
January21st to endNight
23%
1031
5%
4877
2%
1023
28%
1023
6%
3902
February1st to 10thNight
29%
923
10%
2538
3%
923
35%
923
11%
2032
February11th to 20thNight
28%
843
12%
2238
5%
839
33%
839
12%
1802
February21st to endNight
24%
592
11%
1776
4%
592
30%
592
10%
1452
March1st to 10thNight
30%
720
10%
2160
5%
720
34%
720
11%
1728
March11th to 20thNight
29%
680
10%
2115
5%
680
34%
680
10%
1664
March21st to endNight
35%
594
13%
1980
9%
594
41%
594
10%
1569
April1st to 10thNight
30%
540
9%
1800
6%
540
35%
540
9%
1432
April11th to 20thNight
34%
533
11%
1745
8%
533
39%
533
10%
1377
April21st to endNight
38%
540
10%
1570
5%
540
41%
540
12%
1254
May1st to 10thNight
36%
540
9%
1440
5%
540
39%
540
12%
1181
May11th to 20thNight
39%
531
11%
1416
7%
531
42%
531
16%
1119
May21st to endNight
39%
583
7%
1552
4%
582
41%
582
12%
1263
June1st to 10thNight
37%
369
5%
1269
4%
369
38%
369
11%
990
June11th to 20thNight
40%
360
6%
1260
5%
360
43%
360
11%
951
June21st to endNight
40%
360
5%
1260
5%
360
42%
360
10%
977
July1st to 10thNight
50%
507
5%
1382
3%
507
52%
507
17%
1055
July11th to 20thNight
50%
522
7%
1392
4%
522
51%
522
17%
1069
July21st to endNight
56%
591
7%
1487
3%
558
56%
558
16%
1154
August1st to 10thNight
48%
537
9%
1423
4%
534
51%
534
18%
1078
August11th to 20thNight
51%
534
15%
1447
8%
534
57%
534
20%
1050
August21st to endNight
43%
594
10%
1965
7%
594
47%
594
15%
1411
September1st to 10thNight
49%
540
12%
1800
11%
540
53%
540
16%
1302
September11th to 20thNight
37%
590
12%
1850
8%
590
42%
590
15%
1368
September21st to endNight
34%
720
7%
1980
4%
720
36%
720
12%
1605
October1st to 10thNight
29%
720
8%
2120
4%
720
32%
720
10%
1695
October11th to 20thNight
28%
720
7%
2250
4%
720
31%
720
8%
1849
October21st to endNight
22%
792
6%
2574
3%
792
26%
792
8%
2116
November1st to 10thNight
25%
744
7%
2410
3%
744
30%
744
7%
1996
November11th to 20thNight
20%
950
6%
2660
2%
950
24%
950
7%
2312
November21st to endNight
19%
950
5%
2762
2%
950
22%
950
7%
2339
December1st to 10thNight
23%
950
8%
2850
1%
950
29%
950
8%
2345
December11th to 20thNight
23%
950
7%
3419
2%
949
27%
949
6%
2718
December21st to endNight
20%
1039
2%
5047
1%
1026
23%
1026
3%
4263

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%9%47%6%45%5%6%7%33%
77864
Night
13%10%48%7%45%5%6%7%32%
81025
TransparencyDay
33%36%11%14%6%1
77569
Night
36%35%10%14%5%
80854
SeeingDay
19%15%35%21%8%2
14779
Night
18%11%31%29%10%1
24610

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
11%10%5%9%8%46%6%6%8%28%
2527
11th to 20thDay
6%9%5%12%10%47%7%8%7%24%
2530
21st to endDay
12%16%11%12%6%45%45%6%18%
2783
February1st to 10thDay
7%10%49%7%46%6%5%8%34%
1514
11th to 20thDay
8%11%5%7%7%46%6%6%7%34%
1609
21st to endDay
7%11%6%8%8%5%6%5%5%8%32%
1480
March1st to 10thDay
10%10%6%9%7%45%445%37%
1798
11th to 20thDay
12%11%5%7%6%3446%7%35%
1857
21st to endDay
14%9%37%8%45%5%5%6%35%
2376
April1st to 10thDay
14%12%5%7%6%35%5%5%7%32%
2160
11th to 20thDay
17%10%48%6%4445%7%31%
2164
21st to endDay
16%12%36%6%35%5%5%5%34%
2388
May1st to 10thDay
17%9%46%6%45%5%6%7%30%
2520
11th to 20thDay
15%8%36%5%345%5%7%38%
2479
21st to endDay
17%7%35%5%35%5%6%7%37%
2725
June1st to 10thDay
18%6%25%5%35%46%7%37%
2690
11th to 20thDay
14%6%25%5%36%5%6%8%39%
2700
21st to endDay
17%6%25%6%45%5%6%8%37%
2700
July1st to 10thDay
11%426%5%35%5%7%10%42%
2533
11th to 20thDay
10%6%37%6%35%5%6%8%40%
2520
21st to endDay
11%5%26%6%46%5%7%8%40%
2743
August1st to 10thDay
9%5%25%7%46%7%8%9%38%
2507
11th to 20thDay
13%4245%45%5%7%7%44%
2453
21st to endDay
14%6%36%5%35%6%5%7%41%
2390
September1st to 10thDay
14%6%26%5%45%5%6%7%41%
2160
11th to 20thDay
17%7%37%5%3446%8%36%
2091
21st to endDay
18%8%37%6%445%5%8%31%
1980
October1st to 10thDay
20%11%46%7%3445%6%30%
1836
11th to 20thDay
18%11%5%8%7%45%5%6%7%23%
1710
21st to endDay
20%13%48%8%46%5%45%24%
1782
November1st to 10thDay
15%11%49%8%5%6%6%5%7%25%
1664
11th to 20thDay
18%15%5%10%7%35%5%5%5%23%
1520
21st to endDay
16%11%6%10%8%47%5%6%6%21%
1415
December1st to 10thDay
12%10%5%10%7%36%6%6%7%29%
1330
11th to 20thDay
12%13%6%8%8%46%6%6%7%26%
1671
21st to endDay
22%21%48%7%34345%21%
2559
January1st to 10thNight
10%14%6%8%5%45%6%7%8%27%
4428
11th to 20thNight
6%9%414%14%7%8%6%6%7%20%
4440
21st to endNight
9%13%8%12%8%45%5%6%7%21%
4884
February1st to 10thNight
7%9%5%9%7%47%7%7%7%32%
2538
11th to 20thNight
10%9%47%6%5%7%6%7%8%32%
2237
21st to endNight
8%11%6%10%7%5%5%6%5%6%31%
1776
March1st to 10thNight
9%8%49%6%46%5%6%7%35%
2149
11th to 20thNight
12%10%38%6%25%45%7%37%
2115
21st to endNight
12%9%46%7%4446%6%38%
1980
April1st to 10thNight
14%10%37%6%5%5%5%5%7%31%
1800
11th to 20thNight
17%10%37%5%345%5%8%32%
1745
21st to endNight
15%10%37%6%3445%8%36%
1570
May1st to 10thNight
18%9%45%5%45%5%46%36%
1440
11th to 20thNight
15%6%35%5%35%5%5%8%39%
1416
21st to endNight
19%7%35%5%35%5%5%6%38%
1551
June1st to 10thNight
16%7%36%7%35%5%5%7%37%
1269
11th to 20thNight
13%7%25%6%35%46%8%40%
1260
21st to endNight
17%5%35%5%36%5%6%9%36%
1260
July1st to 10thNight
9%436%5%35%5%6%8%47%
1422
11th to 20thNight
10%425%5%35%6%5%9%47%
1440
21st to endNight
8%425%436%5%8%9%47%
1575
August1st to 10thNight
10%4246%35%46%10%46%
1432
11th to 20thNight
12%6%2443345%7%50%
1447
21st to endNight
14%5%345%3445%7%47%
1965
September1st to 10thNight
13%425%435%45%7%48%
1800
11th to 20thNight
15%6%2442446%8%42%
1850
21st to endNight
19%7%47%5%3436%7%36%
1980
October1st to 10thNight
19%7%37%5%45%5%5%6%34%
2120
11th to 20thNight
16%10%47%6%445%6%7%31%
2250
21st to endNight
19%11%48%6%45%46%6%27%
2574
November1st to 10thNight
15%11%48%8%36%5%6%6%28%
2410
11th to 20thNight
17%12%5%10%7%46%5%5%6%23%
2660
21st to endNight
16%12%5%10%8%35%6%5%6%24%
2762
December1st to 10thNight
10%13%6%10%8%35%5%6%7%28%
2850
11th to 20thNight
11%12%6%10%6%35%5%5%7%29%
3526
21st to endNight
23%19%6%9%6%23345%20%
5104

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
40%26%15%15%4
2528
11th to 20thDay
44%25%12%18%1
2530
21st to endDay
53%23%11%8%4
2783
February1st to 10thDay
31%35%8%15%8%2
1514
11th to 20thDay
31%37%10%14%7%1
1618
21st to endDay
33%36%12%12%8%1
1480
March1st to 10thDay
34%36%7%14%7%1
1800
11th to 20thDay
34%36%9%13%8%1
1857
21st to endDay
33%38%11%10%7%1
2376
April1st to 10thDay
35%36%8%15%41
2160
11th to 20thDay
36%36%9%14%5%
2164
21st to endDay
34%36%8%10%10%2
2388
May1st to 10thDay
35%37%8%15%41
2520
11th to 20thDay
28%37%11%16%7%1
2483
21st to endDay
31%38%9%11%10%1
2725
June1st to 10thDay
29%38%10%15%8%
2690
11th to 20thDay
27%38%11%16%7%1
2700
21st to endDay
29%38%12%16%5%
2700
July1st to 10thDay
22%39%10%19%9%
2464
11th to 20thDay
24%39%11%19%6%1
2445
21st to endDay
28%39%10%16%5%
2591
August1st to 10thDay
24%39%15%16%6%1
2492
11th to 20thDay
23%35%11%22%9%
2453
21st to endDay
26%37%11%19%7%1
2390
September1st to 10thDay
26%38%11%18%7%
2160
11th to 20thDay
29%37%14%17%3
2091
21st to endDay
33%37%13%13%3
1980
October1st to 10thDay
34%36%11%16%2
1836
11th to 20thDay
40%36%10%11%2
1710
21st to endDay
37%39%8%13%3
1782
November1st to 10thDay
36%41%9%11%31
1664
11th to 20thDay
39%40%10%8%3
1520
21st to endDay
36%41%13%8%3
1415
December1st to 10thDay
34%42%12%10%2
1330
11th to 20thDay
39%32%10%14%41
1671
21st to endDay
54%24%8%13%2
2559
January1st to 10thNight
41%26%17%13%3
4428
11th to 20thNight
52%25%9%12%1
4440
21st to endNight
50%25%12%10%4
4884
February1st to 10thNight
33%36%9%14%8%1
2538
11th to 20thNight
31%38%8%13%9%1
2238
21st to endNight
36%36%8%14%5%1
1776
March1st to 10thNight
33%37%8%15%6%1
2160
11th to 20thNight
33%36%9%14%8%
2116
21st to endNight
33%37%9%11%7%2
1980
April1st to 10thNight
34%37%5%17%7%
1800
11th to 20thNight
34%35%8%14%7%1
1745
21st to endNight
34%36%6%13%9%3
1570
May1st to 10thNight
34%37%8%15%6%
1440
11th to 20thNight
28%38%9%15%8%1
1417
21st to endNight
31%39%6%13%10%1
1552
June1st to 10thNight
32%37%8%14%8%1
1269
11th to 20thNight
28%38%9%14%10%1
1260
21st to endNight
29%40%11%14%5%1
1260
July1st to 10thNight
23%39%9%18%10%1
1382
11th to 20thNight
23%40%10%20%7%
1392
21st to endNight
23%42%13%16%6%1
1487
August1st to 10thNight
23%38%15%18%5%1
1423
11th to 20thNight
21%36%9%24%10%
1447
21st to endNight
23%37%11%22%7%
1965
September1st to 10thNight
23%37%11%21%8%
1800
11th to 20thNight
25%37%13%22%3
1850
21st to endNight
32%38%12%16%2
1980
October1st to 10thNight
33%37%14%13%3
2120
11th to 20thNight
36%38%11%13%2
2250
21st to endNight
36%39%10%13%3
2574
November1st to 10thNight
33%42%10%11%31
2410
11th to 20thNight
40%40%9%9%2
2660
21st to endNight
36%41%11%9%4
2762
December1st to 10thNight
32%41%11%12%3
2850
11th to 20thNight
38%34%11%14%4
3525
21st to endNight
55%25%9%10%1
5104

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
17%12%43%21%7%
270
11th to 20thDay
15%13%39%25%7%1
270
21st to endDay
17%13%44%18%6%1
297
February1st to 10thDay
16%15%47%15%5%2
252
11th to 20thDay
14%21%42%19%4
240
21st to endDay
14%29%40%14%3
198
March1st to 10thDay
15%20%38%23%42
240
11th to 20thDay
16%24%39%12%7%2
243
21st to endDay
17%15%39%21%6%3
462
April1st to 10thDay
21%20%30%22%6%
420
11th to 20thDay
26%18%24%19%10%2
412
21st to endDay
23%18%29%19%8%3
468
May1st to 10thDay
20%19%35%17%7%1
603
11th to 20thDay
19%17%37%19%7%2
625
21st to endDay
21%16%34%22%5%1
679
June1st to 10thDay
20%13%40%19%7%2
630
11th to 20thDay
17%16%39%19%7%2
630
21st to endDay
18%14%35%23%8%2
630
July1st to 10thDay
10%12%39%26%11%3
621
11th to 20thDay
12%13%39%24%10%3
618
21st to endDay
10%11%36%26%12%5%
684
August1st to 10thDay
12%12%37%27%10%2
626
11th to 20thDay
16%9%31%28%12%4
589
21st to endDay
19%12%32%23%12%2
495
September1st to 10thDay
16%11%30%26%13%3
450
11th to 20thDay
21%13%32%21%11%2
450
21st to endDay
24%12%32%19%11%2
450
October1st to 10thDay
28%17%27%19%7%2
306
11th to 20thDay
22%20%34%21%3
270
21st to endDay
33%23%32%10%3
297
November1st to 10thDay
23%20%34%19%4
270
11th to 20thDay
29%22%34%10%4
270
21st to endDay
26%19%33%16%6%
220
December1st to 10thDay
23%13%33%21%7%3
180
11th to 20thDay
23%19%32%20%41
180
21st to endDay
24%17%31%21%6%1
234
January1st to 10thNight
17%12%39%26%6%1
950
11th to 20thNight
16%12%35%27%8%1
950
21st to endNight
17%8%38%27%9%1
1045
February1st to 10thNight
13%11%37%30%8%1
923
11th to 20thNight
16%12%36%26%9%1
843
21st to endNight
13%12%39%28%7%1
592
March1st to 10thNight
13%11%36%29%9%1
720
11th to 20thNight
18%16%30%28%6%1
680
21st to endNight
16%9%32%28%12%3
594
April1st to 10thNight
19%13%27%32%7%1
540
11th to 20thNight
22%10%27%29%12%1
533
21st to endNight
20%5%29%31%13%1
540
May1st to 10thNight
21%10%28%31%10%1
540
11th to 20thNight
17%9%29%34%9%2
531
21st to endNight
22%9%22%34%12%
584
June1st to 10thNight
18%7%30%34%12%
369
11th to 20thNight
16%6%29%40%8%1
360
21st to endNight
21%5%28%36%10%
360
July1st to 10thNight
12%430%39%14%1
507
11th to 20thNight
11%430%40%14%1
522
21st to endNight
9%426%41%19%1
591
August1st to 10thNight
12%429%38%16%1
537
11th to 20thNight
15%6%22%33%23%3
534
21st to endNight
18%7%28%28%17%2
594
September1st to 10thNight
16%6%24%34%18%2
540
11th to 20thNight
18%9%30%29%12%1
590
21st to endNight
23%9%27%28%12%1
720
October1st to 10thNight
24%12%30%23%10%1
720
11th to 20thNight
22%14%30%23%10%1
720
21st to endNight
27%10%33%23%7%
792
November1st to 10thNight
21%13%34%24%7%1
744
11th to 20thNight
25%16%30%21%7%1
950
21st to endNight
25%16%30%22%7%
950
December1st to 10thNight
18%15%34%25%8%1
950
11th to 20thNight
20%13%30%28%8%1
950
21st to endNight
23%13%30%27%6%1
1045
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