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 2005-11-05 to 2017-08-12.

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%
15043
14%
46443
9%
15011
47%
15011
23%
30366

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
32%
900
13%
2685
7%
895
37%
895
18%
1880
January16th to endNight
33%
805
19%
2725
12%
805
44%
805
21%
1737
February1st to 15thNight
38%
700
14%
2419
11%
697
46%
697
21%
1534
February16th to endNight
38%
632
15%
1968
10%
632
46%
632
22%
1328
March1st to 15thNight
33%
720
15%
2122
7%
720
42%
720
23%
1439
March16th to endNight
32%
768
12%
2082
4%
768
38%
768
19%
1507
April1st to 15thNight
34%
635
11%
1715
4%
635
38%
635
19%
1250
April16th to endNight
36%
540
12%
1620
10%
540
39%
540
20%
1127
May1st to 15thNight
43%
416
11%
1425
10%
416
48%
416
21%
921
May16th to endNight
46%
374
5%
1309
4%
374
47%
374
15%
929
June1st to 15thNight
42%
360
1%
1260
0%
360
42%
360
17%
884
June16th to endNight
54%
360
1%
1260
0%
360
54%
360
27%
763
July1st to 15thNight
63%
340
3%
1190
0%
340
64%
340
28%
687
July16th to endNight
64%
376
10%
1293
12%
354
67%
354
31%
703
August1st to 15thNight
67%
385
13%
1433
17%
383
69%
383
28%
802
August16th to endNight
63%
525
18%
1575
15%
525
66%
525
40%
857
September1st to 15thNight
56%
616
19%
1664
12%
616
59%
616
38%
1001
September16th to endNight
54%
656
21%
1815
14%
656
60%
656
39%
1068
October1st to 15thNight
42%
660
17%
1941
10%
660
49%
660
23%
1320
October16th to endNight
45%
704
20%
2288
13%
704
55%
704
26%
1418
November1st to 15thNight
34%
811
18%
2386
10%
811
43%
811
26%
1515
November16th to endNight
30%
900
14%
2688
5%
900
39%
900
22%
1782
December1st to 15thNight
36%
900
14%
2700
9%
900
41%
900
18%
1921
December16th to endNight
35%
960
16%
2880
8%
960
42%
960
19%
1993

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
9%8%36%5%35%5%6%8%35%
47565
Night
7%8%36%6%35%5%6%8%39%
46595
Cloud CoverDay
10%8%36%5%35%5%6%8%35%
47566
Night
7%9%46%5%35%5%6%8%38%
46598
TransparencyDay
44%8%16%20%8%1
47221
Night
41%7%16%22%10%1
46443
SeeingDay
15%9%28%28%14%3
5862
Night
11%6%30%34%14%2
15049

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 15thDay
48%48%435%5%6%9%38%
1253
16th to endDay
39%410%6%26%5%5%9%36%
1509
February1st to 15thDay
38%48%6%36%6%7%9%35%
1443
16th to endDay
210%7%9%7%46%5%7%8%30%
1506
March1st to 15thDay
27%47%8%5%6%5%6%8%35%
1837
16th to endDay
7%12%6%9%7%46%5%6%7%26%
2141
April1st to 15thDay
11%13%5%8%6%35%46%7%27%
2233
16th to endDay
12%12%36%6%345%6%7%29%
2340
May1st to 15thDay
11%10%36%6%26%6%6%7%33%
2523
16th to endDay
22%7%46%6%45%5%6%8%23%
2802
June1st to 15thDay
20%7%37%6%45%5%6%7%24%
2700
16th to endDay
14%5%25%6%45%5%7%9%32%
2700
July1st to 15thDay
10%425%435%5%7%8%40%
2700
16th to endDay
5%414436%5%8%9%45%
2786
August1st to 15thDay
11%5%25%425%6%7%8%40%
2433
16th to endDay
10%4144345%6%7%48%
2275
September1st to 15thDay
13%5%14423346%49%
1963
16th to endDay
10%5%24425%45%8%46%
1815
October1st to 15thDay
11%10%37%6%4445%7%33%
1685
16th to endDay
6%9%36%4346%7%8%37%
1584
November1st to 15thDay
6%9%45%5%45%46%8%39%
1461
16th to endDay
411%5%6%5%235%5%8%41%
1272
December1st to 15thDay
37%5%11%8%47%6%6%7%30%
1260
16th to endDay
210%48%5%446%8%11%33%
1344
January1st to 15thNight
310%5%8%8%45%6%5%8%32%
2685
16th to endNight
38%5%7%6%345%6%8%39%
2725
February1st to 15thNight
38%47%6%35%5%7%9%38%
2408
16th to endNight
38%6%11%6%345%6%6%37%
1968
March1st to 15thNight
28%47%8%36%5%8%9%34%
2122
16th to endNight
412%5%8%7%35%5%7%9%29%
2079
April1st to 15thNight
10%13%6%6%6%245%5%7%31%
1715
16th to endNight
10%12%48%43435%7%34%
1620
May1st to 15thNight
10%9%35%6%2445%9%38%
1424
16th to endNight
20%7%26%5%245%5%7%31%
1309
June1st to 15thNight
17%8%36%5%3445%7%32%
1260
16th to endNight
12%4135%345%7%11%41%
1260
July1st to 15thNight
6%315%5%345%7%7%48%
1260
16th to endNight
6%4143245%5%6%54%
1382
August1st to 15thNight
12%31343336%9%48%
1441
16th to endNight
9%31221346%9%55%
1575
September1st to 15thNight
12%6%13322346%52%
1664
16th to endNight
10%5%1332345%9%50%
1815
October1st to 15thNight
11%9%35%6%3445%6%38%
1941
16th to endNight
7%8%345%25%5%5%8%42%
2288
November1st to 15thNight
49%345%35%5%6%7%43%
2386
16th to endNight
49%5%9%6%25%46%8%37%
2688
December1st to 15thNight
39%48%9%47%6%6%9%31%
2700
16th to endNight
29%410%7%46%6%6%7%33%
2880

Percentage Cloud Cover SW (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
5%10%5%7%445%46%8%37%
1253
16th to endDay
5%10%5%8%5%3446%9%36%
1509
February1st to 15thDay
410%5%8%5%37%46%9%34%
1443
16th to endDay
311%7%8%6%47%6%6%7%30%
1506
March1st to 15thDay
310%48%7%35%6%6%9%33%
1837
16th to endDay
8%13%6%9%7%46%5%6%7%25%
2142
April1st to 15thDay
12%13%6%7%6%35%5%48%26%
2233
16th to endDay
13%12%47%5%35%5%6%7%29%
2340
May1st to 15thDay
11%9%35%5%36%5%6%7%34%
2523
16th to endDay
22%7%27%5%345%7%8%24%
2802
June1st to 15thDay
21%7%36%6%36%5%6%7%25%
2700
16th to endDay
15%5%35%5%45%6%6%9%33%
2700
July1st to 15thDay
10%425%5%246%6%9%41%
2700
16th to endDay
6%324425%6%7%9%46%
2786
August1st to 15thDay
12%5%24426%5%7%8%40%
2433
16th to endDay
10%41443446%8%47%
2275
September1st to 15thDay
13%5%24423345%49%
1963
16th to endDay
9%6%2443445%8%45%
1815
October1st to 15thDay
12%10%47%5%35%5%5%8%32%
1685
16th to endDay
7%9%35%5%25%5%7%9%37%
1584
November1st to 15thDay
7%10%36%6%35%5%5%7%38%
1461
16th to endDay
6%10%5%6%5%24349%39%
1272
December1st to 15thDay
38%413%8%5%8%5%5%8%28%
1260
16th to endDay
310%5%7%6%36%5%8%10%31%
1344
January1st to 15thNight
410%5%8%8%46%5%6%8%30%
2685
16th to endNight
49%48%5%35%47%8%37%
2725
February1st to 15thNight
49%47%445%6%5%9%36%
2408
16th to endNight
410%7%9%6%35%5%46%35%
1968
March1st to 15thNight
29%48%6%45%7%7%9%32%
2122
16th to endNight
5%12%7%8%6%445%7%8%29%
2082
April1st to 15thNight
12%14%47%5%35%447%30%
1715
16th to endNight
13%11%38%5%3435%6%34%
1620
May1st to 15thNight
11%9%46%43445%9%37%
1424
16th to endNight
19%7%35%5%3446%7%31%
1309
June1st to 15thNight
17%8%26%6%345%5%7%31%
1260
16th to endNight
11%5%245%35%5%7%10%40%
1260
July1st to 15thNight
7%3245%4435%9%48%
1260
16th to endNight
7%3144235%6%8%52%
1382
August1st to 15thNight
11%41332447%10%46%
1441
16th to endNight
9%31321345%9%55%
1575
September1st to 15thNight
13%7%13312346%52%
1664
16th to endNight
10%41332345%7%51%
1815
October1st to 15thNight
12%9%27%5%3445%7%38%
1941
16th to endNight
8%9%244245%7%8%42%
2288
November1st to 15thNight
5%10%35%435%46%7%42%
2386
16th to endNight
5%10%5%8%6%3445%9%36%
2688
December1st to 15thNight
310%5%10%7%47%5%5%7%30%
2700
16th to endNight
210%5%9%8%46%6%6%7%31%
2880

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
40%7%16%26%6%2
1253
16th to endDay
43%6%15%19%10%4
1509
February1st to 15thDay
42%7%17%22%7%2
1443
16th to endDay
48%8%15%18%9%
1506
March1st to 15thDay
42%10%19%20%6%
1837
16th to endDay
55%8%14%15%5%
2142
April1st to 15thDay
54%7%14%16%6%
2233
16th to endDay
51%8%14%17%7%1
2340
May1st to 15thDay
45%8%15%20%9%
2523
16th to endDay
56%8%14%14%5%
2807
June1st to 15thDay
55%8%14%14%6%1
2700
16th to endDay
44%10%17%19%7%1
2700
July1st to 15thDay
38%10%19%22%8%1
2541
16th to endDay
31%10%17%26%12%1
2612
August1st to 15thDay
37%10%21%22%6%1
2416
16th to endDay
31%8%19%28%10%1
2275
September1st to 15thDay
36%5%14%23%17%2
1963
16th to endDay
35%6%14%30%11%2
1815
October1st to 15thDay
47%7%14%19%9%1
1685
16th to endDay
39%9%16%24%8%1
1584
November1st to 15thDay
42%8%17%22%8%1
1461
16th to endDay
40%6%17%23%8%2
1272
December1st to 15thDay
50%6%16%17%8%
1260
16th to endDay
41%6%17%22%10%2
1344
January1st to 15thNight
46%7%17%19%6%2
2685
16th to endNight
40%7%14%21%12%3
2725
February1st to 15thNight
40%7%16%22%10%1
2419
16th to endNight
46%413%21%12%
1968
March1st to 15thNight
41%8%19%23%5%
2122
16th to endNight
49%7%15%18%8%
2082
April1st to 15thNight
51%5%14%17%9%
1715
16th to endNight
48%5%15%22%6%1
1620
May1st to 15thNight
43%7%14%24%9%
1425
16th to endNight
51%8%16%17%5%1
1309
June1st to 15thNight
50%7%14%17%8%
1260
16th to endNight
35%8%19%26%9%
1260
July1st to 15thNight
32%7%20%27%11%
1190
16th to endNight
29%8%16%31%12%2
1293
August1st to 15thNight
31%8%21%28%9%
1433
16th to endNight
24%7%18%31%15%2
1575
September1st to 15thNight
33%318%23%19%2
1664
16th to endNight
30%5%18%28%13%5%
1815
October1st to 15thNight
44%7%13%21%11%1
1941
16th to endNight
36%7%18%25%10%
2288
November1st to 15thNight
36%7%16%23%14%1
2386
16th to endNight
43%6%18%17%9%3
2688
December1st to 15thNight
47%8%15%20%7%
2700
16th to endNight
47%6%13%22%9%
2880

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
11%5%21%25%15%21%
60
16th to endDay
14%6%17%37%15%9%
64
February1st to 15thDay
7%10%35%35%8%2
68
16th to endDay
7%9%24%42%15%
165
March1st to 15thDay
6%15%51%21%4
270
16th to endDay
10%20%38%22%7%2
288
April1st to 15thDay
21%19%30%22%6%
269
16th to endDay
20%14%27%27%7%2
270
May1st to 15thDay
17%10%28%22%16%3
360
16th to endDay
23%7%18%25%19%4
517
June1st to 15thDay
21%9%24%27%13%3
495
16th to endDay
17%5%29%28%15%4
495
July1st to 15thDay
14%422%28%25%4
475
16th to endDay
8%6%30%33%17%3
455
August1st to 15thDay
17%427%28%16%6%
300
16th to endDay
11%10%32%31%8%4
268
September1st to 15thDay
20%9%25%27%13%3
255
16th to endDay
14%14%28%30%10%1
255
October1st to 15thDay
16%11%29%29%11%1
161
16th to endDay
12%25%33%21%7%
96
November1st to 15thDay
14%12%26%37%5%3
90
16th to endDay
9%6%25%24%17%16%
62
December1st to 15thDay
16%23%43%18%6%
60
16th to endDay
7%9%18%35%18%9%
64
January1st to 15thNight
8%12%35%33%8%1
900
16th to endNight
8%11%35%33%9%1
805
February1st to 15thNight
7%9%30%32%14%5%
704
16th to endNight
7%433%34%16%3
632
March1st to 15thNight
6%6%42%32%8%3
720
16th to endNight
9%7%33%37%10%1
768
April1st to 15thNight
16%7%30%30%13%1
635
16th to endNight
19%6%26%34%12%
540
May1st to 15thNight
15%5%27%33%17%
417
16th to endNight
21%420%33%18%1
375
June1st to 15thNight
20%5%23%33%16%1
360
16th to endNight
13%120%38%23%1
360
July1st to 15thNight
10%214%43%27%2
340
16th to endNight
6%217%46%23%2
376
August1st to 15thNight
13%111%36%31%5%
385
16th to endNight
9%318%41%24%2
525
September1st to 15thNight
17%318%29%25%6%
616
16th to endNight
12%323%38%15%5%
656
October1st to 15thNight
16%426%33%14%3
660
16th to endNight
12%5%27%37%13%3
704
November1st to 15thNight
10%10%37%32%6%1
811
16th to endNight
8%8%42%29%8%2
900
December1st to 15thNight
7%8%34%33%12%2
900
16th to endNight
5%8%36%34%11%2
960
Page generated at 2017-08-13 12:16:12. Version ac04

Copyright 2017 A. Danko


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