Chestermere
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chestermere clear sky chart from 2005-11-06 to 2024-02-25.

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
43%
23596
14%
80702
9%
23531
48%
23531
21%
52565

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
37%
936
14%
4679
8%
926
42%
926
11%
3217
January11th to 20thNight
37%
938
19%
4617
10%
925
44%
925
13%
3006
January21st to endNight
35%
823
12%
4788
11%
814
46%
814
13%
2805
February1st to 10thNight
38%
760
13%
2660
12%
760
43%
760
16%
1826
February11th to 20thNight
38%
742
13%
2405
10%
740
45%
740
18%
1665
February21st to endNight
41%
610
16%
1876
11%
610
49%
610
21%
1280
March1st to 10thNight
40%
720
14%
2160
12%
720
45%
720
20%
1535
March11th to 20thNight
39%
720
18%
1999
11%
720
45%
720
24%
1382
March21st to endNight
38%
792
11%
2152
5%
792
42%
792
20%
1583
April1st to 10thNight
35%
666
14%
1746
5%
666
40%
666
21%
1286
April11th to 20thNight
35%
533
13%
1601
8%
533
40%
533
19%
1159
April21st to endNight
35%
540
11%
1620
8%
540
40%
540
20%
1132
May1st to 10thNight
40%
463
9%
1499
8%
463
44%
463
19%
1036
May11th to 20thNight
51%
354
14%
1239
15%
354
53%
354
25%
766
May21st to endNight
44%
388
5%
1358
3%
388
45%
388
17%
939
June1st to 10thNight
43%
360
2%
1260
1%
360
44%
360
17%
875
June11th to 20thNight
46%
360
1%
1260
0%
360
46%
360
18%
878
June21st to endNight
57%
360
1%
1260
0%
360
57%
360
27%
767
July1st to 10thNight
66%
350
2%
1225
0%
350
66%
350
28%
711
July11th to 20thNight
60%
348
6%
1218
4%
348
62%
348
25%
725
July21st to endNight
67%
394
14%
1354
16%
372
71%
372
37%
679
August1st to 10thNight
62%
358
13%
1424
17%
356
65%
356
25%
798
August11th to 20thNight
64%
512
16%
1580
14%
512
68%
512
37%
894
August21st to endNight
62%
594
22%
1782
17%
594
65%
594
37%
1007
September1st to 10thNight
53%
624
18%
1722
13%
624
55%
624
33%
1083
September11th to 20thNight
55%
720
19%
1980
13%
720
59%
720
33%
1245
September21st to endNight
48%
720
21%
1980
13%
720
54%
720
34%
1223
October1st to 10thNight
48%
720
20%
2060
13%
720
53%
720
27%
1357
October11th to 20thNight
43%
720
18%
2286
10%
720
52%
720
26%
1448
October21st to endNight
38%
792
18%
2574
12%
792
47%
792
22%
1703
November1st to 10thNight
32%
847
16%
2512
9%
847
40%
847
21%
1764
November11th to 20thNight
32%
950
18%
2721
9%
950
41%
950
24%
1835
November21st to endNight
38%
950
15%
2850
7%
950
45%
950
25%
1853
December1st to 10thNight
38%
950
16%
2850
10%
950
43%
950
20%
1994
December11th to 20thNight
37%
949
14%
3465
8%
949
41%
949
18%
2354
December21st to endNight
38%
1033
10%
4940
7%
1026
44%
1026
14%
2755

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%45%6%6%8%37%
77875
Night
7%9%48%6%45%5%6%8%37%
81384
TransparencyDay
42%8%15%23%10%2
77581
Night
43%8%15%22%11%2
81258
SeeingDay
12%7%26%31%18%6%
14315
Night
11%5%29%37%15%2
23647

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
39%6%11%8%346%6%9%35%
2219
11th to 20thDay
49%311%8%46%8%8%8%32%
2234
21st to endDay
5%7%37%8%5%6%5%7%9%39%
2794
February1st to 10thDay
411%7%10%8%47%7%6%7%28%
1520
11th to 20thDay
6%10%5%9%8%47%7%7%7%29%
1662
21st to endDay
411%6%11%8%45%6%6%8%31%
1473
March1st to 10thDay
411%6%10%9%46%5%6%8%31%
1800
11th to 20thDay
6%10%47%6%5%5%5%7%8%37%
1960
21st to endDay
8%14%6%9%7%46%5%6%7%27%
2200
April1st to 10thDay
8%14%5%9%7%47%6%6%9%27%
2214
11th to 20thDay
11%13%48%7%446%6%8%29%
2310
21st to endDay
11%12%48%6%46%6%6%7%31%
2340
May1st to 10thDay
13%11%48%7%446%6%8%29%
2460
11th to 20thDay
12%7%37%7%35%6%7%8%35%
2654
21st to endDay
21%7%35%6%446%6%7%30%
2917
June1st to 10thDay
17%6%37%6%47%6%7%8%28%
2700
11th to 20thDay
20%8%47%6%45%6%7%8%26%
2700
21st to endDay
8%5%25%6%35%6%8%10%42%
2700
July1st to 10thDay
9%5%246%46%6%7%9%43%
2700
11th to 20thDay
9%4245%35%6%7%8%45%
2700
21st to endDay
5%324435%5%7%10%53%
2880
August1st to 10thDay
10%5%25%4346%6%8%46%
2507
11th to 20thDay
8%5%2443447%10%49%
2321
21st to endDay
10%5%245%346%6%9%48%
2574
September1st to 10thDay
9%7%25%5%3345%7%50%
2236
11th to 20thDay
14%8%3443345%9%43%
1980
21st to endDay
9%8%36%7%345%5%8%44%
1980
October1st to 10thDay
12%10%37%5%345%5%7%39%
1900
11th to 20thDay
10%8%36%6%36%5%6%8%39%
1671
21st to endDay
7%10%37%7%45%5%6%8%36%
1782
November1st to 10thDay
9%14%6%8%6%445%6%7%31%
1547
11th to 20thDay
7%11%47%6%445%6%7%39%
1456
21st to endDay
5%11%6%8%6%445%8%10%36%
1330
December1st to 10thDay
5%12%6%9%9%45%5%5%7%34%
1330
11th to 20thDay
410%6%11%9%46%7%5%8%30%
1682
21st to endDay
38%37%5%45%5%6%9%44%
2442
January1st to 10thNight
412%5%10%9%5%6%7%7%8%27%
4726
11th to 20thNight
38%5%13%6%46%7%7%8%33%
4695
21st to endNight
410%49%7%45%5%6%8%38%
4862
February1st to 10thNight
5%10%5%11%8%5%6%5%6%8%31%
2660
11th to 20thNight
6%12%5%9%7%5%6%6%7%8%30%
2404
21st to endNight
310%6%11%9%46%6%6%8%32%
1876
March1st to 10thNight
5%10%6%9%9%5%5%6%7%8%30%
2160
11th to 20thNight
5%10%5%7%7%46%6%7%8%34%
1999
21st to endNight
6%14%5%9%6%46%5%7%9%29%
2152
April1st to 10thNight
9%13%48%6%46%5%6%8%29%
1746
11th to 20thNight
11%12%5%9%6%35%6%6%6%30%
1601
21st to endNight
11%10%5%8%5%45%5%6%9%32%
1620
May1st to 10thNight
11%11%48%5%35%5%6%9%33%
1499
11th to 20thNight
10%7%36%6%35%47%8%42%
1239
21st to endNight
18%7%36%6%36%5%7%9%31%
1358
June1st to 10thNight
15%8%47%6%35%6%7%8%32%
1260
11th to 20thNight
18%5%45%6%46%5%7%10%30%
1260
21st to endNight
8%426%6%46%6%8%9%42%
1260
July1st to 10thNight
7%5%245%45%5%6%8%48%
1260
11th to 20thNight
8%5%24437%6%7%10%43%
1260
21st to endNight
44134345%5%9%58%
1434
August1st to 10thNight
9%436%5%345%6%9%46%
1432
11th to 20thNight
8%3234345%8%10%49%
1580
21st to endNight
8%415%4245%6%10%52%
1782
September1st to 10thNight
9%7%26%4345%7%7%46%
1722
11th to 20thNight
13%6%24423448%49%
1980
21st to endNight
10%6%25%5%25%5%6%9%46%
1980
October1st to 10thNight
11%9%36%5%35%37%8%41%
2060
11th to 20thNight
8%8%36%5%45%5%7%8%41%
2286
21st to endNight
7%10%47%6%35%6%7%8%37%
2574
November1st to 10thNight
9%13%5%7%5%36%5%5%7%35%
2512
11th to 20thNight
410%48%7%35%6%7%8%38%
2721
21st to endNight
411%5%7%6%345%8%8%39%
2850
December1st to 10thNight
5%11%5%9%8%5%6%6%6%7%34%
2850
11th to 20thNight
29%5%10%9%5%6%7%7%9%32%
3510
21st to endNight
48%47%7%45%5%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
44%7%15%23%9%2
2219
11th to 20thDay
46%6%11%16%17%4
2255
21st to endDay
38%9%15%29%8%1
2794
February1st to 10thDay
53%7%16%14%9%2
1520
11th to 20thDay
49%7%14%19%9%2
1671
21st to endDay
50%7%13%18%11%1
1473
March1st to 10thDay
50%7%18%15%9%1
1800
11th to 20thDay
43%7%14%23%11%2
1961
21st to endDay
53%8%16%17%6%1
2200
April1st to 10thDay
51%8%15%17%8%1
2214
11th to 20thDay
50%7%13%19%9%1
2310
21st to endDay
51%6%13%19%9%1
2340
May1st to 10thDay
51%8%13%19%7%
2460
11th to 20thDay
43%9%15%23%10%1
2658
21st to endDay
51%7%13%22%7%
2918
June1st to 10thDay
49%9%14%19%7%1
2700
11th to 20thDay
51%10%14%16%7%2
2700
21st to endDay
33%9%20%27%9%2
2700
July1st to 10thDay
34%10%19%24%11%2
2626
11th to 20thDay
34%8%20%26%11%1
2619
21st to endDay
23%9%19%33%14%2
2720
August1st to 10thDay
33%9%18%29%9%2
2490
11th to 20thDay
30%7%21%30%10%2
2321
21st to endDay
31%8%18%28%14%1
2574
September1st to 10thDay
34%6%15%27%14%5%
2236
11th to 20thDay
39%6%13%26%13%2
1980
21st to endDay
38%7%14%27%12%3
1980
October1st to 10thDay
43%7%14%24%10%2
1900
11th to 20thDay
41%8%14%25%10%3
1671
21st to endDay
44%7%13%24%11%1
1782
November1st to 10thDay
51%7%12%19%10%1
1547
11th to 20thDay
43%7%16%23%9%1
1456
21st to endDay
42%8%17%23%9%2
1330
December1st to 10thDay
50%7%12%16%12%3
1330
11th to 20thDay
49%8%15%20%7%1
1684
21st to endDay
34%8%11%24%18%5%
2442
January1st to 10thNight
50%10%12%20%6%2
4726
11th to 20thNight
48%7%11%16%14%4
4736
21st to endNight
41%8%15%24%11%1
4862
February1st to 10thNight
50%6%13%18%11%2
2660
11th to 20thNight
49%7%13%19%11%1
2405
21st to endNight
47%6%12%21%12%2
1876
March1st to 10thNight
48%8%13%23%6%1
2160
11th to 20thNight
45%6%15%20%13%1
1999
21st to endNight
52%7%15%18%8%1
2152
April1st to 10thNight
50%7%13%19%11%1
1746
11th to 20thNight
52%6%12%19%9%1
1601
21st to endNight
47%8%15%20%8%2
1620
May1st to 10thNight
46%9%14%20%10%1
1499
11th to 20thNight
39%7%14%27%11%1
1239
21st to endNight
48%8%15%21%6%1
1358
June1st to 10thNight
48%9%14%19%10%
1260
11th to 20thNight
47%9%16%18%7%2
1260
21st to endNight
34%10%21%25%9%1
1260
July1st to 10thNight
33%8%21%26%11%1
1225
11th to 20thNight
32%12%18%25%10%2
1218
21st to endNight
23%8%18%33%16%2
1354
August1st to 10thNight
33%8%18%28%11%2
1424
11th to 20thNight
26%9%21%29%13%1
1580
21st to endNight
28%7%17%30%15%4
1782
September1st to 10thNight
34%8%14%25%14%5%
1722
11th to 20thNight
34%7%15%26%13%5%
1980
21st to endNight
33%7%18%25%14%4
1980
October1st to 10thNight
41%7%13%25%13%2
2060
11th to 20thNight
38%9%16%23%12%3
2286
21st to endNight
43%8%14%24%11%1
2574
November1st to 10thNight
47%7%13%19%11%2
2512
11th to 20thNight
42%8%17%19%13%1
2721
21st to endNight
41%7%19%21%10%3
2850
December1st to 10thNight
48%7%12%20%9%3
2850
11th to 20thNight
45%10%18%21%6%1
3507
21st to endNight
38%7%12%25%14%4
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
6%6%25%37%14%12%
180
11th to 20thDay
7%8%29%32%17%6%
180
21st to endDay
6%7%23%42%19%4
198
February1st to 10thDay
15%7%26%37%11%5%
180
11th to 20thDay
8%7%32%37%14%3
269
21st to endDay
7%431%36%19%3
315
March1st to 10thDay
8%11%35%29%13%5%
420
11th to 20thDay
8%11%31%31%15%4
420
21st to endDay
12%12%32%26%12%6%
462
April1st to 10thDay
12%12%33%27%14%2
420
11th to 20thDay
14%9%26%31%14%4
412
21st to endDay
19%13%26%28%12%3
420
May1st to 10thDay
18%9%24%24%18%6%
467
11th to 20thDay
15%425%29%21%5%
625
21st to endDay
18%5%21%26%22%7%
679
June1st to 10thDay
17%5%23%34%17%4
630
11th to 20thDay
20%8%27%28%15%2
630
21st to endDay
10%5%22%33%23%7%
630
July1st to 10thDay
10%419%34%25%8%
621
11th to 20thDay
12%322%35%24%5%
618
21st to endDay
6%422%36%24%8%
626
August1st to 10thDay
10%6%22%31%23%8%
447
11th to 20thDay
8%321%34%27%7%
437
21st to endDay
10%5%21%31%22%11%
495
September1st to 10thDay
12%6%28%30%19%5%
450
11th to 20thDay
19%6%21%28%18%7%
450
21st to endDay
14%11%27%31%13%5%
450
October1st to 10thDay
16%8%24%28%19%6%
370
11th to 20thDay
11%8%31%29%16%5%
270
21st to endDay
15%12%33%25%12%3
297
November1st to 10thDay
17%9%29%30%11%3
270
11th to 20thDay
15%7%35%33%8%2
239
21st to endDay
6%6%37%24%19%8%
180
December1st to 10thDay
5%6%36%34%14%5%
180
11th to 20thDay
6%8%34%36%13%3
180
21st to endDay
9%5%23%35%23%5%
198
January1st to 10thNight
9%8%32%38%11%2
950
11th to 20thNight
10%6%35%36%12%1
946
21st to endNight
11%8%32%36%11%2
836
February1st to 10thNight
8%8%30%34%17%4
760
11th to 20thNight
12%5%30%39%13%1
744
21st to endNight
7%428%36%21%4
610
March1st to 10thNight
8%5%30%38%15%4
720
11th to 20thNight
9%7%33%38%12%2
720
21st to endNight
11%5%31%37%13%3
792
April1st to 10thNight
12%7%31%34%15%1
666
11th to 20thNight
17%7%30%33%13%
533
21st to endNight
16%7%30%36%11%
540
May1st to 10thNight
14%8%28%32%18%
463
11th to 20thNight
13%6%25%38%18%
354
21st to endNight
21%322%33%20%1
389
June1st to 10thNight
18%6%23%36%16%1
360
11th to 20thNight
17%426%38%14%1
360
21st to endNight
11%419%41%24%1
360
July1st to 10thNight
9%315%45%27%1
350
11th to 20thNight
9%222%45%19%3
348
21st to endNight
5%320%47%24%2
394
August1st to 10thNight
12%213%43%28%2
358
11th to 20thNight
9%317%47%23%1
512
21st to endNight
10%320%42%25%1
594
September1st to 10thNight
13%424%38%20%3
624
11th to 20thNight
16%418%38%21%2
720
21st to endNight
12%5%29%36%16%2
720
October1st to 10thNight
16%424%37%17%2
720
11th to 20thNight
12%431%34%16%3
720
21st to endNight
11%7%34%36%12%1
792
November1st to 10thNight
15%7%36%31%10%1
847
11th to 20thNight
10%8%40%31%9%1
950
21st to endNight
9%5%37%36%10%2
950
December1st to 10thNight
10%5%33%35%14%2
950
11th to 20thNight
7%438%40%10%1
950
21st to endNight
11%432%38%12%3
1045
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