Rothney Astrophysical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rothney Astrophysical Observatory clear sky chart from 2005-11-06 to 2024-03-28.

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
41%
23684
15%
81079
10%
23611
48%
23611
22%
51018

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
34%
942
15%
4672
8%
926
41%
926
12%
3028
January11th to 20thNight
35%
903
21%
4551
11%
892
44%
892
15%
2867
January21st to endNight
33%
828
14%
4804
11%
814
48%
814
13%
2760
February1st to 10thNight
35%
760
14%
2660
11%
760
43%
760
18%
1724
February11th to 20thNight
34%
743
15%
2420
10%
740
43%
740
20%
1616
February21st to endNight
38%
628
18%
1907
12%
628
48%
628
23%
1281
March1st to 10thNight
36%
760
17%
2280
10%
760
44%
760
22%
1552
March11th to 20thNight
39%
760
21%
2125
10%
760
48%
760
28%
1375
March21st to endNight
37%
820
12%
2211
5%
820
41%
820
21%
1595
April1st to 10thNight
35%
684
14%
1764
4%
684
40%
684
22%
1269
April11th to 20thNight
33%
533
14%
1601
9%
533
36%
533
19%
1120
April21st to endNight
36%
540
12%
1620
9%
540
40%
540
22%
1098
May1st to 10thNight
41%
447
9%
1509
8%
447
46%
447
18%
1026
May11th to 20thNight
49%
354
14%
1239
16%
354
52%
354
25%
760
May21st to endNight
45%
388
6%
1358
4%
388
47%
388
18%
933
June1st to 10thNight
44%
360
3%
1260
1%
360
45%
360
20%
829
June11th to 20thNight
40%
360
2%
1260
0%
360
40%
360
19%
853
June21st to endNight
61%
360
2%
1260
0%
360
61%
360
30%
731
July1st to 10thNight
65%
350
3%
1225
0%
350
65%
350
30%
696
July11th to 20thNight
61%
348
7%
1218
5%
348
63%
348
29%
694
July21st to endNight
66%
394
15%
1387
19%
372
71%
372
37%
685
August1st to 10thNight
65%
358
15%
1424
19%
356
69%
356
27%
770
August11th to 20thNight
66%
500
18%
1568
17%
500
69%
500
39%
845
August21st to endNight
60%
594
23%
1782
18%
594
64%
594
40%
979
September1st to 10thNight
54%
648
19%
1732
11%
648
58%
648
37%
1060
September11th to 20thNight
56%
720
21%
1980
13%
720
60%
720
34%
1220
September21st to endNight
47%
720
23%
1980
13%
720
55%
720
36%
1206
October1st to 10thNight
48%
720
20%
2043
13%
720
54%
720
28%
1338
October11th to 20thNight
42%
720
19%
2304
11%
720
52%
720
28%
1382
October21st to endNight
37%
792
19%
2574
11%
792
48%
792
24%
1644
November1st to 10thNight
33%
820
17%
2485
9%
820
43%
820
22%
1676
November11th to 20thNight
31%
950
21%
2736
9%
950
42%
950
26%
1727
November21st to endNight
32%
950
16%
2850
6%
950
42%
950
26%
1790
December1st to 10thNight
37%
950
17%
2850
10%
950
43%
950
22%
1895
December11th to 20thNight
37%
949
15%
3473
9%
949
44%
949
18%
2301
December21st to endNight
34%
1031
12%
4967
8%
1026
42%
1026
15%
2693

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
8%8%47%6%45%5%7%8%38%
78216
Night
6%8%47%7%45%5%6%8%40%
81725
TransparencyDay
41%8%16%22%11%2
77924
Night
40%7%15%23%12%3
81598
SeeingDay
12%10%28%30%15%4
14408
Night
10%7%31%36%14%2
23727

By Month

Percentage Cloud Cover NW (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
26%6%12%7%46%6%7%10%35%
2219
11th to 20thDay
28%410%7%46%6%7%8%38%
2277
21st to endDay
27%48%7%46%5%6%9%42%
2794
February1st to 10thDay
38%410%9%46%7%7%8%33%
1520
11th to 20thDay
29%5%8%9%47%7%7%9%32%
1646
21st to endDay
19%7%11%9%5%5%5%7%8%33%
1546
March1st to 10thDay
38%5%8%9%6%7%6%6%8%35%
1900
11th to 20thDay
38%47%7%36%5%8%9%39%
2054
21st to endDay
6%13%6%10%8%47%6%6%7%27%
2299
April1st to 10thDay
9%12%5%10%7%46%5%7%8%29%
2196
11th to 20thDay
10%13%5%8%7%35%5%5%8%31%
2310
21st to endDay
11%11%36%7%35%6%6%8%32%
2340
May1st to 10thDay
12%12%47%6%36%6%7%8%28%
2446
11th to 20thDay
13%8%36%6%36%6%7%8%35%
2654
21st to endDay
21%7%46%6%45%5%7%8%27%
2917
June1st to 10thDay
18%7%37%7%5%6%6%7%8%27%
2700
11th to 20thDay
21%9%37%6%45%5%7%7%25%
2700
21st to endDay
10%425%6%46%6%7%10%41%
2700
July1st to 10thDay
9%5%25%5%46%6%8%8%42%
2700
11th to 20thDay
9%5%25%435%5%7%9%45%
2700
21st to endDay
4414435%5%7%9%53%
2847
August1st to 10thDay
10%5%25%436%6%7%8%45%
2507
11th to 20thDay
9%5%25%435%5%6%9%49%
2333
21st to endDay
10%5%25%4345%6%7%49%
2574
September1st to 10thDay
10%5%25%43445%7%49%
2224
11th to 20thDay
12%7%25%5%345%6%6%46%
1980
21st to endDay
9%8%35%435%45%8%46%
1980
October1st to 10thDay
11%10%46%6%4445%6%40%
1916
11th to 20thDay
7%9%48%6%446%6%9%39%
1653
21st to endDay
5%11%47%5%45%6%8%8%38%
1782
November1st to 10thDay
6%14%6%7%7%445%6%8%35%
1575
11th to 20thDay
5%10%37%5%245%7%8%44%
1443
21st to endDay
39%6%8%5%35%6%5%10%40%
1330
December1st to 10thDay
37%5%11%8%37%5%6%8%37%
1330
11th to 20thDay
28%6%11%7%5%6%7%7%9%32%
1682
21st to endDay
38%37%6%345%6%10%45%
2442
January1st to 10thNight
210%5%10%9%5%6%8%7%9%30%
4726
11th to 20thNight
25%5%10%9%5%6%8%6%8%35%
4636
21st to endNight
39%48%8%5%5%5%5%8%39%
4862
February1st to 10thNight
39%49%8%46%6%7%9%35%
2660
11th to 20thNight
311%7%9%7%45%6%7%9%34%
2419
21st to endNight
27%6%12%9%45%5%5%7%37%
1907
March1st to 10thNight
29%410%10%46%6%7%8%34%
2280
11th to 20thNight
48%47%7%36%5%7%10%39%
2125
21st to endNight
5%14%6%9%6%35%5%7%8%32%
2211
April1st to 10thNight
6%14%5%8%7%35%5%5%8%33%
1764
11th to 20thNight
10%12%7%8%6%3445%7%34%
1601
21st to endNight
9%11%48%445%5%6%8%36%
1620
May1st to 10thNight
11%12%46%6%35%5%6%9%33%
1509
11th to 20thNight
12%6%36%5%345%5%9%42%
1239
21st to endNight
20%6%36%5%35%5%6%8%33%
1358
June1st to 10thNight
15%8%36%5%4446%8%36%
1260
11th to 20thNight
19%8%35%6%445%7%9%32%
1260
21st to endNight
8%5%225%35%6%7%11%47%
1260
July1st to 10thNight
7%415%5%436%7%8%50%
1260
11th to 20thNight
7%425%436%5%7%7%48%
1260
21st to endNight
6%41442345%7%59%
1468
August1st to 10thNight
11%42343446%9%50%
1432
11th to 20thNight
9%41342347%11%53%
1568
21st to endNight
9%31342346%8%55%
1782
September1st to 10thNight
9%7%245%3445%8%49%
1732
11th to 20thNight
13%7%2432435%7%50%
1980
21st to endNight
10%8%25%42346%8%48%
1980
October1st to 10thNight
10%9%35%5%345%5%7%44%
2043
11th to 20thNight
7%9%35%5%345%7%9%44%
2304
21st to endNight
6%8%47%6%36%6%5%8%40%
2574
November1st to 10thNight
5%13%5%6%5%36%6%6%7%38%
2485
11th to 20thNight
38%47%6%45%5%6%9%44%
2736
21st to endNight
38%49%6%35%5%6%8%41%
2850
December1st to 10thNight
39%47%8%47%6%6%9%36%
2850
11th to 20thNight
17%49%9%47%7%7%10%34%
3510
21st to endNight
28%48%6%45%6%6%7%44%
5214

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
39%8%15%25%11%3
2219
11th to 20thDay
42%6%11%19%20%4
2298
21st to endDay
34%9%17%30%9%1
2794
February1st to 10thDay
46%8%16%19%8%3
1520
11th to 20thDay
45%7%16%21%9%2
1655
21st to endDay
48%7%14%18%13%1
1546
March1st to 10thDay
44%9%18%19%9%1
1900
11th to 20thDay
37%8%16%24%12%2
2055
21st to endDay
52%10%15%16%6%1
2299
April1st to 10thDay
50%9%15%19%7%1
2196
11th to 20thDay
50%8%13%19%9%1
2310
21st to endDay
48%8%15%20%8%1
2340
May1st to 10thDay
50%10%15%18%6%1
2446
11th to 20thDay
44%9%14%22%10%1
2658
21st to endDay
52%8%16%18%5%1
2918
June1st to 10thDay
51%9%15%15%8%1
2700
11th to 20thDay
54%9%15%14%7%1
2700
21st to endDay
34%11%19%23%10%2
2700
July1st to 10thDay
35%10%18%22%12%2
2626
11th to 20thDay
33%9%17%25%14%2
2619
21st to endDay
25%9%16%31%16%2
2689
August1st to 10thDay
33%10%17%28%10%2
2490
11th to 20thDay
29%9%23%27%9%3
2333
21st to endDay
31%8%17%28%14%2
2574
September1st to 10thDay
33%7%17%24%16%3
2224
11th to 20thDay
37%7%15%25%14%2
1980
21st to endDay
35%7%17%26%13%3
1980
October1st to 10thDay
43%6%14%25%10%2
1916
11th to 20thDay
40%8%16%23%10%3
1653
21st to endDay
41%9%14%22%12%2
1782
November1st to 10thDay
47%7%13%20%11%1
1575
11th to 20thDay
37%7%17%25%11%2
1443
21st to endDay
39%8%17%24%9%4
1330
December1st to 10thDay
44%7%15%18%12%4
1330
11th to 20thDay
45%8%18%19%9%1
1684
21st to endDay
34%6%11%25%19%5%
2442
January1st to 10thNight
45%10%15%21%8%2
4726
11th to 20thNight
44%8%12%17%14%6%
4677
21st to endNight
40%8%15%24%12%1
4862
February1st to 10thNight
44%7%14%20%12%3
2660
11th to 20thNight
44%7%15%19%12%2
2420
21st to endNight
45%5%12%23%13%3
1907
March1st to 10thNight
44%8%15%23%9%1
2280
11th to 20thNight
38%7%17%24%13%2
2125
21st to endNight
48%8%16%18%9%1
2211
April1st to 10thNight
48%7%14%20%11%1
1764
11th to 20thNight
50%6%14%20%9%1
1601
21st to endNight
45%7%16%21%9%2
1620
May1st to 10thNight
47%7%14%21%10%1
1509
11th to 20thNight
38%8%15%29%9%1
1239
21st to endNight
48%8%15%21%7%1
1358
June1st to 10thNight
45%7%17%21%10%
1260
11th to 20thNight
47%8%16%19%9%2
1260
21st to endNight
30%10%20%27%12%1
1260
July1st to 10thNight
31%8%20%25%15%1
1225
11th to 20thNight
31%8%20%25%12%3
1218
21st to endNight
24%7%14%32%20%3
1387
August1st to 10thNight
31%8%18%29%12%2
1424
11th to 20thNight
25%7%23%31%13%1
1568
21st to endNight
25%7%15%31%18%3
1782
September1st to 10thNight
32%5%18%25%16%3
1732
11th to 20thNight
34%6%14%28%14%4
1980
21st to endNight
33%5%18%26%13%5%
1980
October1st to 10thNight
39%8%13%24%15%2
2043
11th to 20thNight
35%7%17%25%13%3
2304
21st to endNight
40%7%16%24%12%1
2574
November1st to 10thNight
44%7%14%20%13%2
2485
11th to 20thNight
37%7%17%22%16%2
2736
21st to endNight
38%7%18%22%12%4
2850
December1st to 10thNight
43%8%14%21%11%4
2850
11th to 20thNight
41%11%18%21%8%1
3507
21st to endNight
36%6%12%25%14%6%
5214

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
46%24%38%16%12%
180
11th to 20thDay
8%6%29%37%16%3
180
21st to endDay
7%8%22%44%15%4
198
February1st to 10thDay
7%13%36%30%9%5%
180
11th to 20thDay
7%10%30%38%14%2
261
21st to endDay
414%30%34%15%2
358
March1st to 10thDay
6%13%41%27%11%2
460
11th to 20thDay
8%13%34%29%13%3
460
21st to endDay
11%15%35%24%11%3
491
April1st to 10thDay
12%16%35%28%9%1
420
11th to 20thDay
16%16%26%26%14%2
412
21st to endDay
14%19%30%24%11%3
420
May1st to 10thDay
18%12%27%26%12%5%
439
11th to 20thDay
18%9%22%27%21%4
625
21st to endDay
19%7%22%28%19%4
679
June1st to 10thDay
17%10%26%33%11%3
630
11th to 20thDay
23%10%28%26%11%3
630
21st to endDay
11%6%27%30%21%5%
630
July1st to 10thDay
12%5%24%32%22%5%
621
11th to 20thDay
13%5%26%32%20%3
618
21st to endDay
5%7%29%36%18%6%
593
August1st to 10thDay
12%427%32%19%6%
447
11th to 20thDay
10%5%27%34%17%7%
437
21st to endDay
9%10%27%31%14%8%
495
September1st to 10thDay
13%10%30%28%15%4
450
11th to 20thDay
16%8%25%32%15%3
450
21st to endDay
13%16%27%29%12%3
450
October1st to 10thDay
12%10%29%28%18%4
386
11th to 20thDay
14%10%28%30%13%5%
270
21st to endDay
12%14%36%24%10%3
297
November1st to 10thDay
16%12%31%29%10%3
270
11th to 20thDay
13%12%28%34%9%3
233
21st to endDay
7%10%32%31%11%10%
180
December1st to 10thDay
6%6%31%39%12%6%
180
11th to 20thDay
311%33%39%9%5%
180
21st to endDay
5%9%23%34%22%7%
198
January1st to 10thNight
7%11%36%34%10%1
950
11th to 20thNight
6%7%39%37%9%1
913
21st to endNight
7%12%36%35%9%1
836
February1st to 10thNight
6%12%33%31%13%5%
760
11th to 20thNight
8%8%32%37%13%1
744
21st to endNight
5%6%34%33%18%4
628
March1st to 10thNight
5%6%39%34%12%4
760
11th to 20thNight
7%7%36%36%11%2
760
21st to endNight
10%9%31%36%12%3
820
April1st to 10thNight
13%7%32%33%14%2
684
11th to 20thNight
16%9%31%33%10%
533
21st to endNight
16%8%31%34%10%1
540
May1st to 10thNight
15%8%26%35%15%1
447
11th to 20thNight
14%5%26%34%21%1
354
21st to endNight
20%421%36%17%1
389
June1st to 10thNight
18%6%23%37%15%1
360
11th to 20thNight
19%5%28%33%14%1
360
21st to endNight
10%220%39%27%2
360
July1st to 10thNight
9%415%45%25%1
350
11th to 20thNight
10%219%49%17%2
348
21st to endNight
6%318%44%26%3
394
August1st to 10thNight
13%213%41%28%3
358
11th to 20thNight
10%216%44%25%3
500
21st to endNight
9%421%43%22%2
594
September1st to 10thNight
13%424%34%20%4
648
11th to 20thNight
18%417%38%19%4
720
21st to endNight
13%5%28%37%12%5%
720
October1st to 10thNight
14%327%38%15%3
720
11th to 20thNight
11%6%32%33%14%3
720
21st to endNight
9%8%34%36%11%2
792
November1st to 10thNight
12%10%37%31%9%1
820
11th to 20thNight
8%12%41%32%6%1
950
21st to endNight
6%8%44%31%9%2
950
December1st to 10thNight
7%8%37%33%12%2
950
11th to 20thNight
48%39%38%9%1
950
21st to endNight
7%8%36%35%12%2
1045
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