Banff
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Banff clear sky chart from 2005-11-05 to 2017-12-20.

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
25%
15504
8%
48056
4%
15471
29%
15471
15%
35113

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
11%
900
5%
2685
1%
895
13%
895
7%
2255
January16th to endNight
12%
777
9%
2697
4%
777
19%
777
9%
2031
February1st to 15thNight
17%
700
5%
2454
3%
697
20%
697
9%
1894
February16th to endNight
23%
632
9%
1938
5%
632
28%
632
14%
1443
March1st to 15thNight
14%
720
7%
2151
2%
720
20%
720
12%
1659
March16th to endNight
21%
768
8%
2041
2%
767
25%
767
15%
1573
April1st to 15thNight
25%
659
6%
1739
2%
659
28%
659
13%
1348
April16th to endNight
29%
540
7%
1620
5%
540
31%
540
13%
1212
May1st to 15thNight
39%
371
7%
1411
8%
371
41%
371
15%
962
May16th to endNight
41%
374
4%
1309
3%
374
42%
374
13%
974
June1st to 15thNight
32%
360
0%
1260
0%
360
32%
360
12%
935
June16th to endNight
37%
360
0%
1260
0%
360
37%
360
17%
842
July1st to 15thNight
50%
340
1%
1190
0%
340
50%
340
24%
736
July16th to endNight
55%
376
9%
1324
9%
354
59%
354
27%
747
August1st to 15thNight
63%
360
14%
1432
17%
358
69%
358
26%
800
August16th to endNight
52%
573
19%
1719
15%
573
54%
573
35%
988
September1st to 15thNight
46%
709
13%
1825
8%
709
48%
709
31%
1174
September16th to endNight
35%
716
16%
1980
9%
716
41%
716
26%
1282
October1st to 15thNight
26%
720
11%
2134
5%
720
32%
720
17%
1539
October16th to endNight
20%
768
11%
2496
4%
768
29%
768
14%
1796
November1st to 15thNight
12%
847
7%
2590
2%
847
17%
847
10%
2025
November16th to endNight
13%
975
6%
2925
2%
975
17%
975
12%
2270
December1st to 15thNight
17%
975
8%
2925
4%
975
21%
975
11%
2270
December16th to endNight
11%
984
7%
2951
1%
984
17%
984
10%
2358

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
8%10%5%9%8%46%6%6%8%26%
48815
Night
37%49%8%46%6%8%10%30%
48211
TransparencyDay
53%12%15%12%4
48474
Night
44%15%18%15%5%
48058
SeeingDay
17%21%33%19%7%1
6244
Night
8%18%41%22%8%
15510

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
14410%10%5%8%7%10%12%24%
1256
16th to endDay
1449%9%410%8%8%11%27%
1536
February1st to 15thDay
25%410%9%6%7%7%9%10%25%
1410
16th to endDay
16%5%14%10%6%8%8%7%8%21%
1536
March1st to 15thDay
8%6%12%9%5%9%6%6%10%23%
1809
16th to endDay
315%9%14%10%46%6%6%7%14%
2178
April1st to 15thDay
6%17%9%14%9%5%6%5%46%14%
2208
16th to endDay
8%20%8%13%7%35%45%5%19%
2340
May1st to 15thDay
9%17%5%8%7%35%5%5%6%24%
2537
16th to endDay
21%14%5%10%7%35%445%17%
2802
June1st to 15thDay
22%14%49%8%35%445%16%
2700
16th to endDay
17%10%5%9%8%46%5%5%6%21%
2700
July1st to 15thDay
11%7%38%9%46%6%6%7%27%
2700
16th to endDay
7%5%27%6%36%6%7%8%37%
2751
August1st to 15thDay
10%7%37%7%46%6%6%7%32%
2520
16th to endDay
10%6%36%6%35%5%5%7%39%
2483
September1st to 15thDay
10%9%36%7%34346%39%
2133
16th to endDay
8%7%36%7%46%5%6%7%36%
1980
October1st to 15thDay
7%10%48%8%46%6%7%9%25%
1824
16th to endDay
38%47%7%36%6%8%9%33%
1728
November1st to 15thDay
26%310%9%47%6%9%10%29%
1582
16th to endDay
17%37%6%5%6%7%10%12%31%
1365
December1st to 15thDay
15%49%9%46%7%8%10%31%
1365
16th to endDay
6%5%9%9%5%7%8%9%11%24%
1372
January1st to 15thNight
16%6%12%11%6%9%8%9%10%15%
2685
16th to endNight
6%5%11%10%6%8%7%8%10%24%
2697
February1st to 15thNight
27%412%10%5%8%7%8%10%21%
2442
16th to endNight
6%5%11%11%5%8%8%8%7%25%
1938
March1st to 15thNight
6%5%9%8%6%7%8%9%11%25%
2151
16th to endNight
18%6%10%9%36%7%7%10%28%
2040
April1st to 15thNight
411%6%9%8%45%5%7%10%26%
1739
16th to endNight
411%6%9%6%45%6%7%7%28%
1620
May1st to 15thNight
6%11%49%4345%6%8%36%
1410
16th to endNight
15%9%36%6%25%5%8%8%28%
1309
June1st to 15thNight
14%8%49%6%345%5%8%29%
1260
16th to endNight
12%7%145%345%7%9%37%
1260
July1st to 15thNight
45%26%43447%9%46%
1260
16th to endNight
5%4234346%7%8%50%
1415
August1st to 15thNight
8%315%5%3346%9%48%
1440
16th to endNight
5%4133245%6%9%53%
1719
September1st to 15thNight
7%8%2442345%8%48%
1825
16th to endNight
7%5%234335%6%9%47%
1980
October1st to 15thNight
49%39%7%36%5%5%9%35%
2134
16th to endNight
27%49%8%45%6%8%9%32%
2496
November1st to 15thNight
18%49%10%5%8%8%9%10%22%
2590
16th to endNight
7%6%10%10%6%8%7%8%11%22%
2925
December1st to 15thNight
15%411%10%5%8%7%10%14%20%
2925
16th to endNight
5%412%13%7%9%7%8%11%17%
2951

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
46%21%17%9%41
1256
16th to endDay
45%18%19%10%32
1536
February1st to 15thDay
48%16%20%8%41
1410
16th to endDay
56%12%15%9%5%
1536
March1st to 15thDay
54%16%16%10%2
1809
16th to endDay
66%11%13%6%1
2179
April1st to 15thDay
69%8%13%6%1
2208
16th to endDay
66%9%12%9%1
2340
May1st to 15thDay
56%9%16%12%3
2537
16th to endDay
69%8%11%7%2
2807
June1st to 15thDay
70%8%8%10%1
2700
16th to endDay
62%9%12%11%3
2700
July1st to 15thDay
53%10%13%13%7%1
2541
16th to endDay
43%9%14%20%10%
2580
August1st to 15thDay
47%10%16%19%5%
2503
16th to endDay
41%9%15%23%8%
2483
September1st to 15thDay
45%7%16%19%10%
2133
16th to endDay
45%10%15%20%6%
1980
October1st to 15thDay
52%13%14%13%6%
1824
16th to endDay
42%15%21%14%4
1728
November1st to 15thDay
44%20%21%10%3
1582
16th to endDay
38%18%24%10%6%
1365
December1st to 15thDay
42%21%18%13%4
1365
16th to endDay
44%18%20%9%5%
1372
January1st to 15thNight
54%21%12%7%21
2685
16th to endNight
48%16%17%9%5%2
2697
February1st to 15thNight
50%17%17%8%41
2454
16th to endNight
50%11%16%14%5%1
1938
March1st to 15thNight
44%19%19%10%4
2151
16th to endNight
48%13%20%13%3
2043
April1st to 15thNight
50%13%19%10%4
1739
16th to endNight
51%11%20%12%3
1620
May1st to 15thNight
46%10%19%18%5%
1411
16th to endNight
52%12%16%16%3
1309
June1st to 15thNight
53%10%15%16%4
1260
16th to endNight
41%11%20%20%5%
1260
July1st to 15thNight
34%11%21%21%10%1
1190
16th to endNight
29%10%16%29%13%
1324
August1st to 15thNight
31%9%20%31%7%
1432
16th to endNight
24%10%21%32%9%
1719
September1st to 15thNight
32%9%22%23%11%
1825
16th to endNight
31%13%21%24%9%
1980
October1st to 15thNight
43%13%18%16%7%
2134
16th to endNight
42%16%20%16%3
2496
November1st to 15thNight
48%19%18%9%4
2590
16th to endNight
45%20%18%9%42
2925
December1st to 15thNight
45%20%16%11%5%
2925
16th to endNight
51%18%15%10%3
2951

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
16%41%33%10%6%
60
16th to endDay
123%42%17%9%6%
64
February1st to 15thDay
8%30%45%9%6%
62
16th to endDay
8%22%44%19%41
195
March1st to 15thDay
12%41%35%9%
270
16th to endDay
12%31%39%14%1
288
April1st to 15thDay
18%29%34%15%1
269
16th to endDay
21%27%31%15%4
270
May1st to 15thDay
19%20%31%20%7%
327
16th to endDay
27%11%23%23%11%2
517
June1st to 15thDay
26%18%27%18%8%
495
16th to endDay
18%20%32%19%8%1
495
July1st to 15thDay
17%14%28%24%14%1
475
16th to endDay
14%17%37%20%7%1
420
August1st to 15thDay
15%15%31%27%7%1
315
16th to endDay
16%20%36%19%6%
332
September1st to 15thDay
21%24%29%16%6%1
315
16th to endDay
20%25%30%19%2
315
October1st to 15thDay
18%24%33%15%6%1
237
16th to endDay
7%22%43%18%6%
144
November1st to 15thDay
7%21%48%14%42
127
16th to endDay
7%20%47%10%6%7%
90
December1st to 15thDay
310%46%22%15%2
90
16th to endDay
227%43%23%2
72
January1st to 15thNight
6%27%51%12%2
900
16th to endNight
5%27%47%14%4
777
February1st to 15thNight
7%20%44%19%7%
704
16th to endNight
214%51%23%6%
632
March1st to 15thNight
5%21%52%16%3
720
16th to endNight
6%17%46%21%7%
768
April1st to 15thNight
8%18%35%30%7%
659
16th to endNight
9%15%37%27%9%
540
May1st to 15thNight
11%10%33%32%12%
372
16th to endNight
21%6%24%27%19%1
375
June1st to 15thNight
16%12%33%21%15%
360
16th to endNight
16%11%27%30%13%
360
July1st to 15thNight
10%8%28%34%17%
340
16th to endNight
7%6%23%44%16%
376
August1st to 15thNight
9%415%44%24%1
360
16th to endNight
9%9%26%35%17%
573
September1st to 15thNight
12%9%28%27%17%4
709
16th to endNight
11%15%33%25%12%
716
October1st to 15thNight
10%15%40%25%7%
720
16th to endNight
7%19%47%21%3
768
November1st to 15thNight
8%26%48%12%4
847
16th to endNight
5%25%51%13%21
975
December1st to 15thNight
5%21%48%17%6%
975
16th to endNight
322%53%15%4
984
Page generated at 2017-12-21 05:04:42. Version ac04

Copyright 2017 A. Danko


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