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 2024-09-29.

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%
25216
11%
95292
6%
24996
37%
24996
14%
66311

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
10%
4402
5%
926
31%
926
10%
3153
January11th to 20thNight
23%
942
8%
4409
4%
930
30%
930
8%
3405
January21st to endNight
23%
1031
6%
4877
3%
1023
29%
1023
8%
3813
February1st to 10thNight
29%
950
13%
2613
4%
950
35%
950
19%
1904
February11th to 20thNight
28%
891
16%
2366
6%
887
35%
887
20%
1703
February21st to endNight
24%
628
16%
1884
5%
628
32%
628
18%
1361
March1st to 10thNight
29%
758
19%
3714
9%
743
36%
743
13%
2371
March11th to 20thNight
28%
710
14%
3680
8%
697
36%
697
11%
2434
March21st to endNight
34%
620
12%
3397
15%
605
45%
605
11%
2317
April1st to 10thNight
30%
570
14%
1900
10%
570
37%
570
17%
1327
April11th to 20thNight
33%
563
15%
1843
10%
563
40%
563
18%
1260
April21st to endNight
37%
570
14%
1657
8%
570
42%
570
23%
1132
May1st to 10thNight
36%
566
18%
2480
6%
559
42%
559
15%
1470
May11th to 20thNight
38%
554
10%
2464
9%
541
43%
541
17%
1552
May21st to endNight
39%
605
8%
2712
5%
593
42%
593
14%
1674
June1st to 10thNight
35%
389
7%
1339
6%
389
38%
389
19%
900
June11th to 20thNight
40%
380
7%
1330
6%
380
42%
380
20%
854
June21st to endNight
40%
380
6%
1330
7%
380
42%
380
17%
894
July1st to 10thNight
49%
526
5%
2389
5%
517
52%
517
19%
1437
July11th to 20thNight
50%
539
8%
2197
6%
533
52%
533
23%
1256
July21st to endNight
54%
614
10%
2311
7%
569
56%
569
22%
1408
August1st to 10thNight
47%
558
15%
2331
8%
545
52%
545
20%
1455
August11th to 20thNight
51%
547
12%
2372
11%
543
57%
543
23%
1332
August21st to endNight
43%
616
11%
3252
11%
605
49%
605
15%
1997
September1st to 10thNight
49%
570
19%
1900
15%
570
55%
570
27%
1155
September11th to 20thNight
38%
623
13%
1953
9%
623
43%
623
23%
1288
September21st to endNight
36%
756
13%
2079
9%
756
39%
756
22%
1476
October1st to 10thNight
29%
720
12%
2120
7%
720
33%
720
17%
1508
October11th to 20thNight
27%
720
11%
2250
6%
720
33%
720
15%
1635
October21st to endNight
22%
792
9%
2574
4%
792
28%
792
12%
1965
November1st to 10thNight
25%
744
12%
2410
7%
744
31%
744
12%
1815
November11th to 20thNight
20%
950
8%
2660
3%
950
24%
950
11%
2125
November21st to endNight
19%
950
7%
2762
3%
950
23%
950
10%
2220
December1st to 10thNight
23%
950
10%
2850
3%
950
29%
950
13%
2152
December11th to 20thNight
23%
950
11%
3436
5%
949
28%
949
11%
2465
December21st to endNight
20%
1039
5%
5049
4%
1026
24%
1026
5%
4098

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
13%9%38%5%5%5%46%7%34%
101205
Night
13%10%49%5%5%5%46%7%33%
97171
TransparencyDay
46%8%14%21%9%1
100963
Night
49%8%14%20%8%1
97031
SeeingDay
18%16%35%21%8%2
15797
Night
18%11%31%29%10%1
25359

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%11%411%6%6%5%5%6%8%27%
2527
11th to 20thDay
6%10%5%14%8%6%7%5%8%7%24%
2530
21st to endDay
12%16%11%13%5%6%445%6%18%
2783
February1st to 10thDay
7%12%311%5%5%6%5%5%7%33%
1564
11th to 20thDay
7%11%5%9%7%6%5%5%5%7%33%
1701
21st to endDay
6%12%5%10%7%7%5%46%7%32%
1570
March1st to 10thDay
10%9%37%5%5%445%6%40%
3118
11th to 20thDay
7%10%6%12%6%6%6%45%6%32%
3287
21st to endDay
16%13%410%6%5%4345%31%
4165
April1st to 10thDay
13%13%5%8%5%45%45%7%32%
2280
11th to 20thDay
17%11%49%6%5%436%7%30%
2286
21st to endDay
16%12%37%6%4445%5%34%
2521
May1st to 10thDay
17%10%37%44435%7%37%
4428
11th to 20thDay
13%8%37%5%4446%7%38%
4399
21st to endDay
15%8%26%5%4446%6%39%
4837
June1st to 10thDay
18%7%26%5%4446%7%37%
2840
11th to 20thDay
13%7%26%5%5%6%36%8%38%
2850
21st to endDay
17%6%26%5%5%5%46%8%36%
2850
July1st to 10thDay
10%426%5%5%6%5%8%11%39%
4453
11th to 20thDay
8%5%26%45%5%5%8%9%44%
4440
21st to endDay
12%6%26%44447%10%42%
4814
August1st to 10thDay
10%5%38%6%6%6%5%8%9%34%
4423
11th to 20thDay
12%41444447%8%47%
4302
21st to endDay
11%6%37%45%5%5%6%9%40%
4194
September1st to 10thDay
13%6%27%45%5%36%7%41%
2280
11th to 20thDay
16%6%37%44436%9%36%
2207
21st to endDay
17%8%38%5%4445%8%33%
2069
October1st to 10thDay
20%12%37%6%4435%6%30%
1836
11th to 20thDay
18%12%49%6%5%5%46%7%22%
1710
21st to endDay
20%13%49%6%6%5%445%24%
1782
November1st to 10thDay
14%12%410%8%6%5%46%7%25%
1664
11th to 20thDay
17%16%5%11%5%5%5%35%5%22%
1520
21st to endDay
15%12%5%12%7%6%6%46%6%21%
1415
December1st to 10thDay
11%11%5%11%6%45%5%6%6%29%
1330
11th to 20thDay
12%14%5%9%7%5%5%47%6%26%
1671
21st to endDay
21%22%48%6%43245%21%
2559
January1st to 10thNight
10%15%5%9%45%5%5%7%7%27%
4428
11th to 20thNight
5%9%416%12%9%7%46%7%20%
4440
21st to endNight
9%14%8%14%7%5%5%46%7%21%
4884
February1st to 10thNight
8%9%5%10%6%5%7%6%7%7%31%
2613
11th to 20thNight
10%9%38%6%7%6%5%7%8%30%
2365
21st to endNight
7%12%5%11%6%7%5%45%7%30%
1884
March1st to 10thNight
11%10%49%5%5%5%46%7%34%
3722
11th to 20thNight
9%15%49%6%5%5%35%7%33%
3699
21st to endNight
16%12%47%5%6%435%5%33%
3466
April1st to 10thNight
14%12%38%5%6%5%45%7%31%
1900
11th to 20thNight
17%10%38%5%4446%8%32%
1843
21st to endNight
16%11%37%6%4335%7%36%
1657
May1st to 10thNight
17%9%2434345%6%42%
2523
11th to 20thNight
14%7%27%5%5%5%46%6%38%
2506
21st to endNight
21%7%25%34435%5%42%
2750
June1st to 10thNight
16%9%27%5%5%445%7%36%
1339
11th to 20thNight
13%8%27%5%45%36%7%40%
1330
21st to endNight
17%5%25%5%46%37%9%36%
1330
July1st to 10thNight
8%6%27%5%5%446%9%43%
2512
11th to 20thNight
7%426%445%5%5%9%49%
2530
21st to endNight
10%5%25%345%46%10%46%
2750
August1st to 10thNight
12%6%25%5%45%46%10%41%
2517
11th to 20thNight
12%42444446%9%48%
2534
21st to endNight
15%6%36%43435%6%45%
3461
September1st to 10thNight
13%5%26%345%46%7%47%
1900
11th to 20thNight
15%6%25%44447%8%42%
1953
21st to endNight
18%7%37%44336%7%38%
2079
October1st to 10thNight
19%8%38%45%5%45%6%34%
2120
11th to 20thNight
16%11%38%5%5%5%46%7%31%
2250
21st to endNight
19%12%39%6%5%5%45%6%27%
2574
November1st to 10thNight
14%12%39%6%5%5%5%6%6%28%
2410
11th to 20thNight
17%13%5%12%6%5%5%45%5%23%
2660
21st to endNight
15%13%412%6%45%5%5%7%23%
2762
December1st to 10thNight
10%13%5%11%6%45%36%7%28%
2850
11th to 20thNight
10%13%6%11%5%5%5%45%7%29%
3526
21st to endNight
22%19%6%10%5%33245%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
51%11%16%16%6%
2528
11th to 20thDay
55%7%14%21%3
2530
21st to endDay
65%7%12%10%5%
2783
February1st to 10thDay
46%8%14%20%11%1
1564
11th to 20thDay
47%6%15%21%10%1
1710
21st to endDay
49%5%13%18%14%1
1570
March1st to 10thDay
44%6%13%21%15%1
3120
11th to 20thDay
50%7%13%20%9%1
3287
21st to endDay
54%6%10%13%15%2
4165
April1st to 10thDay
51%6%11%19%11%2
2280
11th to 20thDay
52%7%12%21%8%1
2286
21st to endDay
49%6%10%17%15%2
2521
May1st to 10thDay
45%7%11%20%16%1
4440
11th to 20thDay
41%8%13%24%12%2
4403
21st to endDay
42%9%15%16%16%2
4837
June1st to 10thDay
45%8%14%19%13%1
2840
11th to 20thDay
41%8%13%25%11%1
2850
21st to endDay
45%8%15%23%9%1
2850
July1st to 10thDay
35%11%20%23%11%1
4384
11th to 20thDay
32%8%19%32%7%
4365
21st to endDay
37%8%15%32%8%1
4662
August1st to 10thDay
40%10%16%26%7%1
4408
11th to 20thDay
33%8%19%29%11%
4344
21st to endDay
39%8%14%28%10%
4193
September1st to 10thDay
40%8%16%26%10%
2280
11th to 20thDay
44%9%20%22%4
2207
21st to endDay
48%8%18%19%6%
2069
October1st to 10thDay
55%7%14%20%4
1836
11th to 20thDay
58%8%14%17%3
1710
21st to endDay
62%8%12%16%3
1782
November1st to 10thDay
58%8%14%15%5%1
1664
11th to 20thDay
63%6%14%13%4
1520
21st to endDay
63%9%14%8%5%
1415
December1st to 10thDay
55%11%16%13%5%
1330
11th to 20thDay
55%7%17%15%5%1
1671
21st to endDay
67%6%9%14%5%
2559
January1st to 10thNight
52%11%16%16%5%
4428
11th to 20thNight
62%7%11%16%4
4440
21st to endNight
61%10%12%12%5%
4884
February1st to 10thNight
49%8%13%19%10%1
2613
11th to 20thNight
49%6%14%20%10%1
2366
21st to endNight
52%6%12%20%10%1
1884
March1st to 10thNight
48%7%13%18%13%2
3733
11th to 20thNight
50%7%13%20%9%1
3700
21st to endNight
52%6%9%17%14%2
3466
April1st to 10thNight
51%6%10%21%12%
1900
11th to 20thNight
49%6%11%21%12%2
1843
21st to endNight
46%5%12%21%13%3
1657
May1st to 10thNight
41%7%14%24%13%1
2530
11th to 20thNight
43%8%12%25%9%3
2507
21st to endNight
44%7%10%21%17%1
2751
June1st to 10thNight
46%7%12%20%13%2
1339
11th to 20thNight
42%8%11%22%15%1
1330
21st to endNight
43%11%15%21%9%1
1330
July1st to 10thNight
38%9%18%22%13%1
2472
11th to 20thNight
28%11%20%32%8%1
2482
21st to endNight
32%8%14%33%11%
2662
August1st to 10thNight
38%8%17%30%7%1
2508
11th to 20thNight
32%7%20%32%9%
2558
21st to endNight
41%8%16%25%11%
3461
September1st to 10thNight
36%8%16%28%12%
1900
11th to 20thNight
40%10%20%26%4
1953
21st to endNight
47%7%17%23%6%
2079
October1st to 10thNight
48%9%18%19%6%
2120
11th to 20thNight
50%10%16%20%41
2250
21st to endNight
56%10%14%15%5%
2574
November1st to 10thNight
57%8%13%17%41
2410
11th to 20thNight
62%7%14%13%4
2660
21st to endNight
62%8%14%11%4
2762
December1st to 10thNight
55%8%15%17%5%
2850
11th to 20thNight
53%8%14%19%6%
3525
21st to endNight
68%7%9%13%3
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%16%46%15%6%1
270
11th to 20thDay
13%20%43%20%4
270
21st to endDay
14%30%40%14%3
225
March1st to 10thDay
16%21%39%20%31
270
11th to 20thDay
15%26%40%12%6%1
274
21st to endDay
18%15%39%21%6%2
506
April1st to 10thDay
20%21%30%22%6%
460
11th to 20thDay
26%20%25%19%9%2
452
21st to endDay
23%19%29%18%8%3
511
May1st to 10thDay
21%20%35%17%7%2
653
11th to 20thDay
18%18%37%18%6%2
675
21st to endDay
22%16%35%21%6%1
734
June1st to 10thDay
20%14%40%19%7%2
680
11th to 20thDay
18%16%39%19%7%2
680
21st to endDay
19%14%34%23%8%1
680
July1st to 10thDay
10%12%38%27%11%3
671
11th to 20thDay
12%12%39%24%10%3
668
21st to endDay
10%11%35%26%13%5%
739
August1st to 10thDay
12%13%37%26%10%2
676
11th to 20thDay
16%8%31%29%12%4
637
21st to endDay
18%13%33%22%11%3
539
September1st to 10thDay
16%12%31%27%13%3
490
11th to 20thDay
20%12%32%22%12%2
490
21st to endDay
22%13%31%20%11%2
483
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%12%37%30%8%1
950
11th to 20thNight
15%12%37%26%9%1
891
21st to endNight
13%12%39%28%7%1
628
March1st to 10thNight
14%12%36%28%9%1
760
11th to 20thNight
18%17%30%28%6%1
717
21st to endNight
16%9%33%28%11%2
627
April1st to 10thNight
19%13%27%32%7%1
570
11th to 20thNight
22%11%27%28%11%1
563
21st to endNight
21%6%28%31%13%1
570
May1st to 10thNight
21%10%28%31%10%1
570
11th to 20thNight
17%9%29%34%9%1
561
21st to endNight
23%9%22%34%12%
617
June1st to 10thNight
17%7%31%33%11%
389
11th to 20thNight
16%7%30%39%8%1
380
21st to endNight
21%5%29%36%10%
380
July1st to 10thNight
12%430%39%14%1
537
11th to 20thNight
11%5%28%42%13%1
552
21st to endNight
9%426%41%20%1
624
August1st to 10thNight
12%5%28%39%16%1
567
11th to 20thNight
14%6%21%34%23%2
564
21st to endNight
18%7%28%28%17%2
627
September1st to 10thNight
16%6%24%35%18%2
570
11th to 20thNight
18%9%30%30%12%1
623
21st to endNight
22%9%26%30%12%1
756
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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