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 2018-02-22.

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%
15887
13%
48971
9%
15857
47%
15857
22%
33019

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
35%
973
11%
2910
7%
970
39%
970
16%
2110
January16th to endNight
36%
887
18%
2967
12%
887
46%
887
20%
1948
February1st to 15thNight
41%
760
13%
2623
11%
757
46%
757
18%
1752
February16th to endNight
39%
660
12%
2066
11%
660
43%
660
18%
1460
March1st to 15thNight
37%
720
13%
2118
8%
720
43%
720
21%
1490
March16th to endNight
33%
768
11%
2087
4%
768
39%
768
19%
1553
April1st to 15thNight
32%
629
10%
1709
5%
629
36%
629
18%
1295
April16th to endNight
36%
540
12%
1620
8%
540
40%
540
19%
1155
May1st to 15thNight
42%
418
10%
1415
9%
418
46%
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
53%
360
0%
1260
0%
360
53%
360
22%
815
July1st to 15thNight
62%
340
2%
1190
0%
340
62%
340
26%
708
July16th to endNight
62%
376
10%
1281
11%
354
64%
354
29%
717
August1st to 15thNight
65%
399
10%
1471
13%
397
67%
397
24%
873
August16th to endNight
65%
573
20%
1719
17%
573
67%
573
41%
936
September1st to 15thNight
57%
665
17%
1811
12%
665
58%
665
34%
1121
September16th to endNight
56%
716
21%
1980
14%
716
60%
716
37%
1200
October1st to 15thNight
44%
720
16%
2121
9%
720
49%
720
23%
1445
October16th to endNight
43%
768
19%
2496
13%
768
52%
768
25%
1587
November1st to 15thNight
36%
891
17%
2601
10%
891
44%
891
23%
1760
November16th to endNight
34%
975
15%
2912
7%
975
41%
975
22%
1973
December1st to 15thNight
39%
975
13%
2925
9%
975
42%
975
18%
2119
December16th to endNight
37%
1040
15%
3120
9%
1040
42%
1040
18%
2238

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%34%
49323
Night
7%8%47%6%35%5%6%8%36%
49121
Cloud CoverDay
10%8%36%6%35%5%6%8%34%
49324
Night
7%9%47%6%35%5%6%8%35%
49124
TransparencyDay
45%7%16%20%7%1
48977
Night
44%7%16%21%9%1
48971
SeeingDay
15%7%26%29%16%4
6424
Night
11%5%29%35%15%2
15895

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%5%25%5%6%9%34%
1358
16th to endDay
5%10%47%7%36%5%7%9%32%
1622
February1st to 15thDay
5%10%5%8%8%36%5%7%7%31%
1570
16th to endDay
5%10%6%10%7%47%5%6%8%27%
1552
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%40%
2481
16th to endDay
9%4144245%6%9%48%
2483
September1st to 15thDay
13%5%24422446%48%
2147
16th to endDay
8%7%35%5%3345%8%43%
1980
October1st to 15thDay
14%10%47%5%35%45%7%32%
1839
16th to endDay
7%8%46%5%35%6%6%8%37%
1728
November1st to 15thDay
7%10%5%8%7%345%5%8%33%
1573
16th to endDay
6%12%47%5%3346%8%38%
1378
December1st to 15thDay
39%5%10%8%47%6%6%5%30%
1365
16th to endDay
311%5%9%7%36%6%6%10%29%
1456
January1st to 15thNight
5%10%5%9%8%5%6%6%6%8%27%
2910
16th to endNight
410%47%445%5%7%9%34%
2967
February1st to 15thNight
6%8%5%7%7%45%5%6%7%34%
2612
16th to endNight
49%5%10%8%47%5%6%7%30%
2066
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
10%3144346%6%9%44%
1479
16th to endNight
7%4132235%5%8%55%
1719
September1st to 15thNight
12%5%1332245%7%49%
1811
16th to endNight
10%41432445%8%49%
1980
October1st to 15thNight
11%8%26%5%345%5%7%36%
2121
16th to endNight
7%8%46%4245%6%8%39%
2496
November1st to 15thNight
6%10%46%5%35%5%6%8%38%
2601
16th to endNight
5%10%5%7%6%45%5%6%8%35%
2912
December1st to 15thNight
410%5%9%8%46%6%5%7%31%
2925
16th to endNight
39%411%9%45%6%6%7%29%
3120

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%5%7%6%25%5%7%8%33%
1358
16th to endDay
5%10%47%6%46%6%7%8%31%
1622
February1st to 15thDay
6%9%6%8%7%46%6%6%7%30%
1570
16th to endDay
5%10%6%10%7%46%6%6%7%27%
1552
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
12%5%245%345%6%8%41%
2481
16th to endDay
8%4144245%5%9%47%
2483
September1st to 15thDay
12%6%14423345%48%
2147
16th to endDay
9%6%36%5%3335%8%43%
1980
October1st to 15thDay
13%9%47%5%35%46%7%31%
1839
16th to endDay
7%9%45%6%346%6%8%37%
1728
November1st to 15thDay
7%11%47%6%35%5%5%8%32%
1573
16th to endDay
6%12%47%5%2345%9%36%
1378
December1st to 15thDay
410%5%10%8%5%7%6%5%6%29%
1365
16th to endDay
312%5%9%7%46%6%6%9%28%
1456
January1st to 15thNight
5%10%5%9%8%46%6%6%8%26%
2910
16th to endNight
411%48%435%7%6%9%34%
2967
February1st to 15thNight
5%9%48%7%45%5%6%7%33%
2612
16th to endNight
310%5%11%7%46%46%8%28%
2066
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%6%9%43%
1479
16th to endNight
7%31332245%8%55%
1719
September1st to 15thNight
12%5%1332346%7%48%
1811
16th to endNight
10%41342446%7%49%
1980
October1st to 15thNight
11%8%36%5%35%46%8%36%
2121
16th to endNight
7%9%35%435%5%6%9%39%
2496
November1st to 15thNight
6%9%46%5%25%6%6%7%37%
2601
16th to endNight
5%11%5%7%6%345%6%8%35%
2912
December1st to 15thNight
49%5%9%8%47%6%5%7%31%
2925
16th to endNight
310%5%10%9%5%6%6%6%7%28%
3120

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%22%6%2
1358
16th to endDay
46%8%14%15%10%3
1622
February1st to 15thDay
48%8%15%18%7%1
1570
16th to endDay
52%8%14%17%7%
1552
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
37%9%23%22%5%
2464
16th to endDay
31%7%20%29%10%1
2483
September1st to 15thDay
37%6%14%23%15%3
2147
16th to endDay
38%6%13%28%11%2
1980
October1st to 15thDay
49%6%14%20%8%
1839
16th to endDay
41%7%16%24%8%
1728
November1st to 15thDay
48%7%14%20%7%1
1573
16th to endDay
43%5%17%22%8%1
1378
December1st to 15thDay
51%8%13%16%8%1
1365
16th to endDay
48%6%15%17%10%1
1456
January1st to 15thNight
50%8%15%17%5%2
2910
16th to endNight
42%8%14%19%11%3
2967
February1st to 15thNight
47%6%14%20%10%1
2623
16th to endNight
51%6%13%18%10%
2066
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
33%10%19%27%7%
1471
16th to endNight
24%6%20%31%14%2
1719
September1st to 15thNight
32%7%15%22%17%4
1811
16th to endNight
31%6%17%26%14%4
1980
October1st to 15thNight
44%7%14%22%9%1
2121
16th to endNight
38%8%17%24%10%
2496
November1st to 15thNight
41%8%14%21%12%1
2601
16th to endNight
44%7%18%18%8%2
2912
December1st to 15thNight
50%8%14%20%6%1
2925
16th to endNight
50%6%13%20%7%
3120

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
17%5%12%28%17%17%
90
16th to endDay
3328%35%19%10%
96
February1st to 15thDay
13%5%27%33%16%3
103
16th to endDay
11%426%40%14%2
175
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%220%34%19%7%
315
16th to endDay
9%6%22%34%17%8%
332
September1st to 15thDay
15%7%26%27%15%6%
315
16th to endDay
12%11%23%30%16%6%
315
October1st to 15thDay
22%7%22%28%15%4
207
16th to endDay
14%6%28%30%15%4
144
November1st to 15thDay
18%428%33%8%5%
135
16th to endDay
9%5%36%22%16%9%
93
December1st to 15thDay
5%36%28%23%5%
90
16th to endDay
14%325%32%18%6%
96
January1st to 15thNight
10%9%31%35%10%2
975
16th to endNight
9%8%35%35%9%1
887
February1st to 15thNight
9%7%27%35%14%4
764
16th to endNight
7%431%36%16%3
660
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
399
16th to endNight
8%218%42%27%
573
September1st to 15thNight
15%220%32%25%3
665
16th to endNight
11%323%37%20%3
716
October1st to 15thNight
16%327%33%16%2
720
16th to endNight
12%430%38%12%2
768
November1st to 15thNight
10%8%36%32%9%2
891
16th to endNight
9%7%39%31%9%1
975
December1st to 15thNight
8%6%33%35%13%2
975
16th to endNight
7%5%33%39%11%2
1040
Page generated at 2018-02-23 09:21:38. Version ac04

Copyright 2018 A. Danko


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