This page made possible by the sponsorship of: Samuel Linton.

Calgary
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Calgary clear sky chart from 2005-11-06 to 2024-01-15.

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
40%
23440
14%
74698
9%
23400
46%
23400
22%
48747

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
33%
949
13%
2836
7%
946
39%
946
17%
2021
January11th to 20thNight
35%
908
17%
2752
9%
908
43%
908
21%
1871
January21st to endNight
33%
792
20%
2772
11%
792
46%
792
19%
1790
February1st to 10thNight
35%
720
14%
2520
11%
720
42%
720
17%
1692
February11th to 20thNight
33%
703
13%
2287
9%
700
41%
700
17%
1594
February21st to endNight
37%
592
16%
1809
11%
592
46%
592
20%
1251
March1st to 10thNight
38%
720
14%
2160
10%
720
43%
720
21%
1511
March11th to 20thNight
37%
720
19%
2008
9%
720
45%
720
25%
1376
March21st to endNight
35%
792
11%
2141
5%
792
39%
792
20%
1565
April1st to 10thNight
33%
675
13%
1755
4%
675
39%
675
20%
1298
April11th to 20thNight
30%
533
13%
1601
7%
533
36%
533
18%
1158
April21st to endNight
33%
540
11%
1620
8%
540
38%
540
20%
1139
May1st to 10thNight
37%
449
8%
1494
7%
449
42%
449
18%
1027
May11th to 20thNight
50%
354
13%
1239
14%
354
53%
354
25%
752
May21st to endNight
43%
388
5%
1358
3%
388
45%
388
17%
941
June1st to 10thNight
40%
360
2%
1260
1%
360
41%
360
16%
869
June11th to 20thNight
42%
360
1%
1260
0%
360
42%
360
17%
880
June21st to endNight
57%
360
1%
1260
0%
360
57%
360
25%
770
July1st to 10thNight
62%
350
2%
1225
0%
350
63%
350
28%
712
July11th to 20thNight
53%
348
6%
1218
3%
348
55%
348
25%
735
July21st to endNight
66%
394
14%
1366
17%
372
70%
372
36%
684
August1st to 10thNight
61%
358
12%
1424
17%
356
65%
356
24%
812
August11th to 20thNight
65%
503
16%
1571
15%
503
68%
503
36%
899
August21st to endNight
60%
594
22%
1782
17%
594
63%
594
38%
996
September1st to 10thNight
51%
635
18%
1724
12%
635
54%
635
33%
1081
September11th to 20thNight
53%
720
19%
1980
12%
720
57%
720
33%
1236
September21st to endNight
46%
720
21%
1980
12%
720
53%
720
34%
1239
October1st to 10thNight
45%
720
20%
2052
12%
720
52%
720
27%
1348
October11th to 20thNight
41%
720
18%
2299
10%
720
50%
720
26%
1442
October21st to endNight
36%
792
18%
2574
11%
792
46%
792
22%
1681
November1st to 10thNight
30%
836
17%
2501
8%
836
40%
836
20%
1738
November11th to 20thNight
30%
950
18%
2736
9%
950
40%
950
24%
1811
November21st to endNight
33%
950
16%
2850
6%
950
42%
950
24%
1855
December1st to 10thNight
34%
950
16%
2850
10%
950
40%
950
21%
1971
December11th to 20thNight
34%
949
14%
3474
8%
949
40%
949
18%
2312
December21st to endNight
33%
1036
10%
4960
7%
1026
40%
1026
15%
2690

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%47%6%46%6%6%8%36%
74635
Night
7%9%47%6%45%6%6%8%37%
75152
TransparencyDay
43%8%16%22%10%2
74320
Night
42%8%15%22%11%2
74985
SeeingDay
13%9%29%30%16%4
14201
Night
11%7%32%35%14%2
23453

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
5%10%6%9%6%35%5%7%9%36%
1329
11th to 20thDay
410%5%7%6%36%6%8%9%34%
1320
21st to endDay
5%9%49%8%5%7%5%7%10%32%
1584
February1st to 10thDay
38%6%10%9%5%8%6%7%8%29%
1440
11th to 20thDay
5%9%5%9%10%5%7%6%7%8%28%
1561
21st to endDay
410%7%10%7%47%6%6%9%30%
1444
March1st to 10thDay
410%6%10%9%5%7%6%6%8%30%
1800
11th to 20thDay
5%9%5%7%7%46%6%8%9%35%
1950
21st to endDay
7%14%7%9%8%45%6%6%8%26%
2214
April1st to 10thDay
8%13%6%9%8%46%6%6%9%25%
2204
11th to 20thDay
11%14%5%8%6%45%5%6%7%29%
2310
21st to endDay
11%13%47%6%46%6%6%8%29%
2340
May1st to 10thDay
12%13%47%7%45%6%7%8%28%
2463
11th to 20thDay
13%7%37%6%5%6%6%7%8%33%
2654
21st to endDay
20%8%36%7%36%5%6%7%28%
2917
June1st to 10thDay
17%6%47%6%47%7%6%8%27%
2700
11th to 20thDay
20%8%37%8%46%6%7%8%25%
2700
21st to endDay
9%5%25%5%46%6%8%9%41%
2700
July1st to 10thDay
9%436%5%46%6%6%10%41%
2700
11th to 20thDay
10%425%5%35%6%7%9%44%
2700
21st to endDay
5%3145%35%6%7%10%51%
2868
August1st to 10thDay
11%5%24435%6%7%8%45%
2507
11th to 20thDay
9%5%24435%5%6%9%49%
2329
21st to endDay
10%5%145%35%5%7%8%47%
2574
September1st to 10thDay
11%6%35%5%33448%49%
2233
11th to 20thDay
14%8%35%5%3345%8%43%
1980
21st to endDay
8%8%36%6%35%46%8%43%
1980
October1st to 10thDay
12%10%46%5%35%5%5%7%38%
1908
11th to 20thDay
9%9%47%6%35%6%6%8%38%
1660
21st to endDay
7%10%5%6%6%46%5%6%7%37%
1782
November1st to 10thDay
9%12%6%8%7%345%5%8%32%
1556
11th to 20thDay
6%11%37%6%5%5%5%6%8%39%
1444
21st to endDay
5%10%5%8%6%346%6%10%37%
1330
December1st to 10thDay
410%5%10%8%46%5%6%7%34%
1330
11th to 20thDay
310%5%12%9%47%6%7%7%30%
1682
21st to endDay
39%48%6%35%5%5%9%44%
2442
January1st to 10thNight
410%5%9%9%6%6%6%7%9%29%
2836
11th to 20thNight
48%5%9%7%47%7%7%10%31%
2752
21st to endNight
411%48%6%46%5%8%9%35%
2772
February1st to 10thNight
48%5%9%9%5%6%6%7%7%33%
2520
11th to 20thNight
5%11%6%9%7%47%6%7%8%30%
2286
21st to endNight
39%6%12%8%5%6%5%6%7%33%
1809
March1st to 10thNight
310%5%10%8%5%6%6%7%8%32%
2160
11th to 20thNight
410%47%7%46%7%7%9%35%
2008
21st to endNight
6%13%6%9%5%45%6%7%9%29%
2141
April1st to 10thNight
8%13%49%8%46%5%5%8%29%
1755
11th to 20thNight
11%12%410%7%346%6%8%29%
1601
21st to endNight
11%11%49%6%36%6%6%8%32%
1620
May1st to 10thNight
12%9%48%7%45%5%6%7%33%
1494
11th to 20thNight
11%7%45%6%346%5%9%41%
1239
21st to endNight
19%7%36%5%35%5%7%8%31%
1358
June1st to 10thNight
15%9%37%6%35%5%6%8%33%
1260
11th to 20thNight
19%6%36%5%46%5%6%10%30%
1260
21st to endNight
7%425%6%46%5%9%10%41%
1260
July1st to 10thNight
8%425%5%35%5%7%8%48%
1260
11th to 20thNight
9%5%25%7%45%6%6%10%43%
1260
21st to endNight
442433446%8%58%
1446
August1st to 10thNight
9%425%6%346%6%9%46%
1432
11th to 20thNight
8%4243345%6%10%51%
1571
21st to endNight
8%5%243245%6%9%52%
1782
September1st to 10thNight
10%7%25%4336%6%8%47%
1724
11th to 20thNight
13%7%343245%48%48%
1980
21st to endNight
10%7%25%4445%6%9%46%
1980
October1st to 10thNight
11%9%36%5%35%5%6%8%40%
2052
11th to 20thNight
7%8%36%6%35%6%6%9%41%
2299
21st to endNight
7%10%5%7%6%35%6%6%8%37%
2574
November1st to 10thNight
8%13%5%7%5%35%5%6%7%36%
2501
11th to 20thNight
49%47%7%45%6%7%8%40%
2736
21st to endNight
5%9%48%6%45%5%6%9%38%
2850
December1st to 10thNight
410%5%9%8%46%6%6%7%34%
2850
11th to 20thNight
28%5%10%10%5%5%6%7%10%32%
3510
21st to endNight
38%38%6%45%6%6%7%43%
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
42%7%15%24%8%4
1329
11th to 20thDay
44%8%14%21%9%4
1320
21st to endDay
46%8%15%16%13%2
1584
February1st to 10thDay
49%8%16%16%9%2
1440
11th to 20thDay
49%9%14%19%8%1
1570
21st to endDay
49%7%14%17%11%1
1444
March1st to 10thDay
49%8%18%16%8%1
1800
11th to 20thDay
42%8%15%23%11%2
1951
21st to endDay
54%8%15%16%6%1
2214
April1st to 10thDay
52%9%16%16%7%
2204
11th to 20thDay
52%7%12%19%9%1
2310
21st to endDay
51%7%14%19%8%1
2340
May1st to 10thDay
51%8%15%18%6%
2463
11th to 20thDay
44%8%15%23%10%1
2658
21st to endDay
52%8%14%20%6%1
2918
June1st to 10thDay
51%10%15%16%7%1
2700
11th to 20thDay
54%9%14%15%6%2
2700
21st to endDay
35%11%19%25%9%2
2700
July1st to 10thDay
36%11%19%23%10%2
2626
11th to 20thDay
35%9%19%26%10%1
2619
21st to endDay
24%10%18%32%14%1
2708
August1st to 10thDay
33%9%19%28%9%2
2490
11th to 20thDay
29%8%25%27%9%2
2329
21st to endDay
32%8%18%28%12%2
2574
September1st to 10thDay
34%7%16%26%13%4
2233
11th to 20thDay
39%6%14%26%12%2
1980
21st to endDay
38%7%14%26%12%3
1980
October1st to 10thDay
44%7%14%24%9%2
1908
11th to 20thDay
41%7%16%24%9%3
1660
21st to endDay
43%7%15%23%11%1
1782
November1st to 10thDay
51%6%12%19%10%1
1556
11th to 20thDay
42%6%16%24%10%2
1444
21st to endDay
41%7%18%23%10%2
1330
December1st to 10thDay
48%7%13%17%12%3
1330
11th to 20thDay
49%8%16%18%8%1
1684
21st to endDay
36%7%12%22%18%5%
2442
January1st to 10thNight
48%9%13%18%10%3
2836
11th to 20thNight
44%8%15%22%7%3
2752
21st to endNight
43%7%14%19%14%2
2772
February1st to 10thNight
47%7%13%19%11%3
2520
11th to 20thNight
49%7%14%19%10%1
2287
21st to endNight
48%6%12%20%12%2
1809
March1st to 10thNight
46%9%15%23%7%1
2160
11th to 20thNight
44%6%16%20%13%1
2008
21st to endNight
50%7%16%18%8%1
2141
April1st to 10thNight
51%7%13%18%11%1
1755
11th to 20thNight
51%8%13%19%8%1
1601
21st to endNight
48%8%15%20%8%2
1620
May1st to 10thNight
47%8%15%19%10%1
1494
11th to 20thNight
37%8%16%28%10%1
1239
21st to endNight
48%9%15%21%6%1
1358
June1st to 10thNight
47%10%14%19%10%
1260
11th to 20thNight
48%9%17%17%7%2
1260
21st to endNight
34%11%22%25%8%1
1260
July1st to 10thNight
32%9%23%23%11%1
1225
11th to 20thNight
34%11%19%23%11%2
1218
21st to endNight
23%8%17%33%17%2
1366
August1st to 10thNight
33%10%17%28%10%1
1424
11th to 20thNight
27%10%23%29%11%1
1571
21st to endNight
27%7%17%31%15%3
1782
September1st to 10thNight
33%8%16%25%15%4
1724
11th to 20thNight
35%6%16%26%13%5%
1980
21st to endNight
34%7%18%24%14%4
1980
October1st to 10thNight
41%7%14%24%13%1
2052
11th to 20thNight
38%8%16%25%11%3
2299
21st to endNight
42%8%16%23%11%1
2574
November1st to 10thNight
47%8%12%20%12%2
2501
11th to 20thNight
40%8%17%19%14%1
2736
21st to endNight
40%8%17%21%10%3
2850
December1st to 10thNight
47%7%13%20%10%3
2850
11th to 20thNight
44%9%18%21%7%1
3507
21st to endNight
37%7%13%24%14%5%
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
7%9%28%34%11%11%
180
11th to 20thDay
7%11%32%27%21%3
168
21st to endDay
8%8%29%36%14%5%
176
February1st to 10thDay
9%12%39%26%10%4
160
11th to 20thDay
10%9%38%32%9%2
234
21st to endDay
7%6%32%37%15%2
310
March1st to 10thDay
9%11%38%27%11%4
420
11th to 20thDay
10%14%30%32%12%3
420
21st to endDay
12%16%34%21%11%5%
462
April1st to 10thDay
14%14%37%24%9%1
420
11th to 20thDay
17%10%28%30%12%3
412
21st to endDay
21%14%26%26%12%2
420
May1st to 10thDay
18%11%26%27%15%3
456
11th to 20thDay
17%6%25%27%20%4
625
21st to endDay
19%5%22%29%20%5%
679
June1st to 10thDay
17%8%27%30%14%3
630
11th to 20thDay
22%9%27%29%11%2
630
21st to endDay
11%5%25%32%21%6%
630
July1st to 10thDay
10%5%25%32%23%5%
621
11th to 20thDay
12%428%33%20%4
618
21st to endDay
5%5%27%36%20%7%
614
August1st to 10thDay
12%5%26%32%20%6%
447
11th to 20thDay
10%422%36%22%6%
437
21st to endDay
10%8%23%30%20%9%
495
September1st to 10thDay
11%9%30%30%16%4
450
11th to 20thDay
20%6%24%29%15%5%
450
21st to endDay
13%14%27%31%12%3
450
October1st to 10thDay
16%8%28%28%16%5%
378
11th to 20thDay
11%11%32%29%13%4
270
21st to endDay
16%13%35%23%11%2
297
November1st to 10thDay
17%11%31%29%8%3
270
11th to 20thDay
15%12%38%24%9%2
234
21st to endDay
8%8%37%25%15%7%
180
December1st to 10thDay
7%5%39%32%13%3
180
11th to 20thDay
7%9%41%27%13%3
180
21st to endDay
10%6%28%35%18%4
198
January1st to 10thNight
8%10%36%34%10%2
950
11th to 20thNight
7%8%39%35%9%1
908
21st to endNight
10%11%36%33%9%1
792
February1st to 10thNight
8%10%33%32%14%4
720
11th to 20thNight
10%8%35%37%10%1
704
21st to endNight
6%7%32%33%18%4
592
March1st to 10thNight
8%5%36%34%13%3
720
11th to 20thNight
8%7%36%35%11%2
720
21st to endNight
13%6%31%34%13%3
792
April1st to 10thNight
13%8%30%33%15%1
675
11th to 20thNight
17%5%35%32%11%
533
21st to endNight
15%9%31%34%11%
540
May1st to 10thNight
17%8%28%30%17%
449
11th to 20thNight
14%8%23%40%16%
354
21st to endNight
20%423%34%18%1
389
June1st to 10thNight
19%8%26%32%15%1
360
11th to 20thNight
21%327%34%15%1
360
21st to endNight
9%319%46%20%2
360
July1st to 10thNight
9%219%42%26%1
350
11th to 20thNight
11%224%43%17%2
348
21st to endNight
6%220%47%23%3
394
August1st to 10thNight
13%213%41%29%3
358
11th to 20thNight
10%219%44%23%2
503
21st to endNight
10%421%42%23%
594
September1st to 10thNight
14%326%35%20%2
635
11th to 20thNight
16%420%38%18%3
720
21st to endNight
13%5%31%34%15%2
720
October1st to 10thNight
16%428%34%16%2
720
11th to 20thNight
12%5%33%33%15%2
720
21st to endNight
12%7%34%36%10%1
792
November1st to 10thNight
15%8%39%29%9%1
836
11th to 20thNight
8%10%44%29%8%1
950
21st to endNight
8%8%42%32%9%2
950
December1st to 10thNight
10%7%37%30%13%2
950
11th to 20thNight
5%7%40%38%8%2
950
21st to endNight
8%6%38%35%11%2
1045
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