Calgary
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Calgary 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
42%
15057
13%
46446
9%
15027
47%
15027
22%
31383

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%
898
11%
2685
7%
895
36%
895
15%
1963
January16th to endNight
36%
819
17%
2739
11%
819
45%
819
20%
1806
February1st to 15thNight
40%
700
12%
2417
10%
697
46%
697
19%
1595
February16th to endNight
39%
632
12%
1975
10%
632
44%
632
19%
1387
March1st to 15thNight
36%
720
13%
2118
8%
720
42%
720
21%
1490
March16th to endNight
33%
768
11%
2087
4%
768
38%
768
19%
1553
April1st to 15thNight
34%
629
10%
1709
5%
629
37%
629
18%
1295
April16th to endNight
36%
540
12%
1620
8%
540
40%
540
19%
1155
May1st to 15thNight
43%
418
10%
1415
9%
418
47%
418
22%
918
May16th to endNight
45%
374
4%
1309
3%
374
46%
374
15%
935
June1st to 15thNight
41%
360
0%
1260
0%
360
41%
360
14%
911
June16th to endNight
55%
360
0%
1260
0%
360
55%
360
22%
815
July1st to 15thNight
63%
340
2%
1190
0%
340
64%
340
26%
708
July16th to endNight
62%
376
10%
1281
11%
354
64%
354
29%
717
August1st to 15thNight
64%
388
10%
1436
13%
386
67%
386
24%
856
August16th to endNight
64%
525
18%
1575
15%
525
66%
525
40%
869
September1st to 15thNight
57%
609
18%
1659
13%
609
59%
609
34%
1038
September16th to endNight
54%
656
19%
1815
13%
656
59%
656
38%
1091
October1st to 15thNight
43%
660
17%
1944
10%
660
49%
660
23%
1328
October16th to endNight
45%
704
19%
2288
13%
704
54%
704
25%
1460
November1st to 15thNight
35%
821
18%
2396
10%
821
43%
821
24%
1600
November16th to endNight
33%
900
14%
2688
7%
900
40%
900
22%
1832
December1st to 15thNight
37%
900
12%
2700
8%
900
40%
900
17%
2000
December16th to endNight
37%
960
15%
2880
9%
960
42%
960
18%
2061

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
10%8%46%6%35%5%6%8%33%
47569
Night
8%8%47%6%35%5%6%8%35%
46596
Cloud CoverDay
10%8%36%6%35%5%6%8%33%
47570
Night
8%9%47%6%35%5%6%8%35%
46599
TransparencyDay
46%8%16%20%7%1
47223
Night
44%7%16%21%8%1
46446
SeeingDay
15%7%26%29%16%4
5873
Night
11%5%29%35%15%2
15065

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
6%11%5%7%426%5%6%8%34%
1253
16th to endDay
5%10%47%7%36%5%7%9%32%
1497
February1st to 15thDay
5%9%5%7%8%36%5%7%8%32%
1446
16th to endDay
5%10%6%10%7%47%5%6%8%27%
1497
March1st to 15thDay
49%5%9%8%47%5%5%8%30%
1842
16th to endDay
8%14%6%8%7%45%5%6%7%24%
2135
April1st to 15thDay
11%15%6%8%6%25%5%5%8%23%
2239
16th to endDay
13%12%36%6%36%5%6%7%27%
2340
May1st to 15thDay
11%9%36%6%35%5%6%7%32%
2534
16th to endDay
21%8%36%6%35%5%6%7%24%
2802
June1st to 15thDay
20%7%37%6%36%5%5%8%25%
2700
16th to endDay
13%6%26%6%45%5%7%8%33%
2700
July1st to 15thDay
10%425%5%36%6%6%9%39%
2700
16th to endDay
6%2145%35%6%7%9%45%
2799
August1st to 15thDay
12%5%24435%5%7%8%39%
2431
16th to endDay
9%4145%245%6%8%46%
2275
September1st to 15thDay
13%5%24422446%47%
1969
16th to endDay
9%7%35%5%2445%8%43%
1815
October1st to 15thDay
13%9%47%6%35%45%8%32%
1686
16th to endDay
7%9%46%5%35%5%6%7%37%
1584
November1st to 15thDay
7%10%47%6%35%6%5%8%34%
1449
16th to endDay
6%12%47%5%2345%8%37%
1272
December1st to 15thDay
410%6%11%9%47%6%6%5%28%
1260
16th to endDay
311%49%6%36%6%7%10%30%
1344
January1st to 15thNight
5%10%5%9%8%46%6%6%8%27%
2685
16th to endNight
411%48%435%5%7%9%34%
2739
February1st to 15thNight
6%8%5%7%6%46%5%7%7%34%
2406
16th to endNight
410%5%10%8%37%5%5%7%31%
1975
March1st to 15thNight
39%5%8%7%5%6%6%7%9%30%
2118
16th to endNight
6%13%6%8%6%35%6%6%8%28%
2084
April1st to 15thNight
12%13%37%7%35%5%5%7%27%
1709
16th to endNight
12%11%37%5%25%5%6%7%30%
1620
May1st to 15thNight
11%8%47%6%345%7%7%36%
1414
16th to endNight
19%6%246%35%5%5%8%30%
1309
June1st to 15thNight
17%9%37%5%35%5%6%7%29%
1260
16th to endNight
12%425%5%36%47%9%36%
1260
July1st to 15thNight
6%3246%35%5%7%8%46%
1260
16th to endNight
6%41433446%8%51%
1368
August1st to 15thNight
11%3144246%6%9%43%
1444
16th to endNight
7%4132235%5%8%54%
1575
September1st to 15thNight
12%6%1332345%8%48%
1659
16th to endNight
11%41432445%8%49%
1815
October1st to 15thNight
12%8%26%5%345%5%8%36%
1944
16th to endNight
7%8%46%4245%6%8%39%
2288
November1st to 15thNight
6%10%35%435%5%6%8%40%
2396
16th to endNight
5%11%5%7%6%45%45%8%35%
2688
December1st to 15thNight
410%6%9%8%5%6%6%5%7%29%
2700
16th to endNight
39%411%9%46%6%6%7%30%
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
7%11%47%6%25%5%7%8%34%
1253
16th to endDay
6%10%47%6%46%6%7%8%31%
1497
February1st to 15thDay
6%9%5%8%7%46%6%6%7%31%
1446
16th to endDay
5%10%6%10%7%46%6%6%7%27%
1497
March1st to 15thDay
411%410%8%46%5%6%8%30%
1842
16th to endDay
9%13%5%9%7%35%5%5%8%25%
2136
April1st to 15thDay
12%14%6%7%6%45%46%8%23%
2239
16th to endDay
13%12%36%6%45%5%5%7%28%
2340
May1st to 15thDay
11%9%36%7%35%5%6%8%33%
2534
16th to endDay
21%7%26%6%45%5%6%7%24%
2802
June1st to 15thDay
20%7%46%6%46%6%5%7%25%
2700
16th to endDay
13%6%26%6%45%6%7%9%32%
2700
July1st to 15thDay
10%4246%35%6%6%9%39%
2700
16th to endDay
5%3245%35%6%8%9%46%
2799
August1st to 15thDay
11%5%245%35%5%6%8%41%
2431
16th to endDay
9%415%5%245%5%9%45%
2275
September1st to 15thDay
13%6%15%5%23345%47%
1969
16th to endDay
9%6%26%6%3435%8%43%
1815
October1st to 15thDay
13%8%47%5%35%46%7%31%
1686
16th to endDay
6%9%45%5%346%6%8%38%
1584
November1st to 15thDay
7%10%47%6%35%5%5%8%33%
1449
16th to endDay
6%12%5%7%5%2345%9%36%
1272
December1st to 15thDay
411%5%10%8%5%7%6%5%6%27%
1260
16th to endDay
311%5%8%7%36%6%6%10%29%
1344
January1st to 15thNight
5%10%5%10%8%45%6%6%8%26%
2685
16th to endNight
5%11%48%425%7%6%9%33%
2739
February1st to 15thNight
5%9%5%7%6%45%5%6%7%34%
2406
16th to endNight
411%5%10%7%46%46%8%29%
1975
March1st to 15thNight
39%6%8%8%46%6%7%9%29%
2118
16th to endNight
7%13%6%8%5%36%6%6%8%27%
2087
April1st to 15thNight
12%12%48%6%36%46%7%27%
1709
16th to endNight
13%10%5%7%6%2446%8%30%
1620
May1st to 15thNight
11%8%37%5%3346%7%36%
1414
16th to endNight
19%5%35%5%36%5%5%8%29%
1309
June1st to 15thNight
17%8%47%426%6%5%6%28%
1260
16th to endNight
12%5%25%6%445%6%9%36%
1260
July1st to 15thNight
7%315%5%35%5%6%8%45%
1260
16th to endNight
6%31442446%8%52%
1368
August1st to 15thNight
10%4235%35%5%7%9%43%
1444
16th to endNight
8%31332245%9%54%
1575
September1st to 15thNight
12%6%132235%6%8%47%
1659
16th to endNight
10%41342446%8%50%
1815
October1st to 15thNight
12%8%36%5%35%46%7%35%
1944
16th to endNight
7%9%35%435%5%6%8%39%
2288
November1st to 15thNight
6%9%45%5%25%6%6%7%39%
2396
16th to endNight
5%11%5%7%6%345%6%8%35%
2688
December1st to 15thNight
410%5%9%8%5%7%6%5%7%28%
2700
16th to endNight
39%5%10%9%5%6%6%6%6%29%
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
45%7%15%23%6%2
1253
16th to endDay
46%8%14%15%10%3
1497
February1st to 15thDay
46%8%16%19%7%1
1446
16th to endDay
51%8%14%16%7%
1497
March1st to 15thDay
48%8%18%16%6%
1842
16th to endDay
55%8%14%16%4
2136
April1st to 15thDay
56%7%14%14%6%
2239
16th to endDay
52%7%14%16%7%1
2340
May1st to 15thDay
47%7%16%20%9%
2534
16th to endDay
55%7%15%15%4
2807
June1st to 15thDay
55%7%14%15%5%1
2700
16th to endDay
44%9%17%22%5%
2700
July1st to 15thDay
38%9%20%23%6%1
2541
16th to endDay
30%11%20%26%10%
2623
August1st to 15thDay
38%9%23%22%5%
2414
16th to endDay
33%7%20%27%10%1
2275
September1st to 15thDay
38%6%14%23%14%3
1969
16th to endDay
38%6%13%29%10%2
1815
October1st to 15thDay
49%6%15%19%7%
1686
16th to endDay
41%7%16%25%8%1
1584
November1st to 15thDay
47%7%14%21%7%1
1449
16th to endDay
44%5%18%21%9%1
1272
December1st to 15thDay
54%8%13%15%7%
1260
16th to endDay
46%7%16%18%9%1
1344
January1st to 15thNight
51%8%15%16%5%2
2685
16th to endNight
43%8%14%19%10%3
2739
February1st to 15thNight
45%6%15%20%9%1
2417
16th to endNight
50%6%13%18%11%
1975
March1st to 15thNight
46%8%18%19%5%
2118
16th to endNight
52%6%15%17%7%
2087
April1st to 15thNight
54%6%13%15%8%
1709
16th to endNight
49%6%13%21%6%1
1620
May1st to 15thNight
43%6%16%22%10%
1415
16th to endNight
50%8%15%17%5%1
1309
June1st to 15thNight
51%10%13%16%7%1
1260
16th to endNight
40%9%21%22%5%
1260
July1st to 15thNight
33%9%23%25%8%
1190
16th to endNight
29%9%17%31%10%1
1281
August1st to 15thNight
34%10%20%27%7%
1436
16th to endNight
25%7%20%30%13%2
1575
September1st to 15thNight
33%7%16%21%16%4
1659
16th to endNight
30%6%18%26%13%4
1815
October1st to 15thNight
45%7%14%22%8%1
1944
16th to endNight
39%8%17%25%9%
2288
November1st to 15thNight
40%8%15%22%12%1
2396
16th to endNight
45%6%18%17%9%2
2688
December1st to 15thNight
52%8%14%18%5%
2700
16th to endNight
50%7%13%20%7%
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
21%5%10%26%13%23%
60
16th to endDay
3425%32%18%15%
64
February1st to 15thDay
10%7%27%34%17%2
69
16th to endDay
12%425%41%14%
156
March1st to 15thDay
8%14%45%26%5%
270
16th to endDay
12%17%37%20%10%2
288
April1st to 15thDay
20%13%31%26%7%1
269
16th to endDay
25%11%22%27%10%2
270
May1st to 15thDay
15%7%28%26%17%4
371
16th to endDay
23%419%27%20%4
517
June1st to 15thDay
21%7%24%29%13%3
495
16th to endDay
14%5%28%29%17%4
495
July1st to 15thDay
12%422%30%25%5%
475
16th to endDay
7%429%35%18%4
468
August1st to 15thDay
15%321%34%19%7%
300
16th to endDay
11%8%25%34%14%6%
268
September1st to 15thDay
15%9%25%28%14%7%
255
16th to endDay
10%13%26%32%12%3
255
October1st to 15thDay
21%8%19%33%14%2
156
16th to endDay
15%120%35%20%6%
96
November1st to 15thDay
18%431%33%8%3
90
16th to endDay
9%6%25%19%24%14%
62
December1st to 15thDay
6%36%30%25%1
60
16th to endDay
12%420%28%25%9%
64
January1st to 15thNight
10%9%33%34%9%1
900
16th to endNight
9%9%34%34%10%1
819
February1st to 15thNight
9%7%28%34%15%4
704
16th to endNight
8%432%35%16%3
632
March1st to 15thNight
8%438%33%12%2
720
16th to endNight
13%5%31%35%12%1
768
April1st to 15thNight
16%6%29%31%14%1
629
16th to endNight
18%5%28%35%12%
540
May1st to 15thNight
14%6%28%31%18%
419
16th to endNight
21%419%33%19%
375
June1st to 15thNight
20%424%31%16%1
360
16th to endNight
15%319%42%18%1
360
July1st to 15thNight
7%120%40%28%2
340
16th to endNight
7%220%47%20%2
376
August1st to 15thNight
13%112%36%32%3
388
16th to endNight
8%219%41%26%
525
September1st to 15thNight
15%219%31%25%3
609
16th to endNight
12%324%37%18%3
656
October1st to 15thNight
16%327%33%16%2
660
16th to endNight
12%328%39%13%2
704
November1st to 15thNight
10%8%38%32%8%1
821
16th to endNight
9%7%39%31%10%1
900
December1st to 15thNight
9%7%34%34%13%2
900
16th to endNight
7%5%33%38%12%2
960
Page generated at 2017-08-13 12:16:57. Version ac04

Copyright 2017 A. Danko


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