Okanagan Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Okanagan Observatory 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
41%
14675
10%
46191
8%
14644
43%
14644
17%
33141

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
25%
720
7%
2506
6%
716
27%
716
8%
2062
January16th to endNight
31%
768
8%
2688
7%
768
34%
768
11%
2067
February1st to 15thNight
34%
702
7%
2396
6%
699
37%
699
11%
1853
February16th to endNight
37%
632
11%
1952
10%
632
40%
632
16%
1432
March1st to 15thNight
27%
720
6%
2160
4%
720
29%
720
11%
1732
March16th to endNight
33%
768
9%
2007
4%
768
35%
768
16%
1571
April1st to 15thNight
42%
719
8%
1799
4%
719
44%
719
19%
1356
April16th to endNight
41%
509
11%
1589
10%
509
44%
509
17%
1148
May1st to 15thNight
53%
359
11%
1440
17%
359
56%
359
19%
891
May16th to endNight
54%
374
7%
1460
11%
374
55%
374
17%
977
June1st to 15thNight
46%
360
3%
1228
1%
360
46%
360
18%
841
June16th to endNight
54%
360
6%
1080
0%
360
54%
360
24%
716
July1st to 15thNight
67%
340
8%
1207
4%
340
69%
340
35%
611
July16th to endNight
71%
376
15%
1416
22%
354
76%
354
42%
616
August1st to 15thNight
75%
352
22%
1400
32%
350
78%
350
37%
650
August16th to endNight
65%
575
21%
1625
16%
575
68%
575
41%
900
September1st to 15thNight
62%
660
23%
1650
13%
660
65%
660
42%
990
September16th to endNight
54%
656
20%
1782
14%
656
57%
656
30%
1160
October1st to 15thNight
49%
660
13%
1974
12%
660
51%
660
22%
1320
October16th to endNight
36%
704
10%
2277
8%
704
41%
704
16%
1658
November1st to 15thNight
28%
700
9%
2374
8%
700
31%
700
10%
1880
November16th to endNight
25%
804
5%
2604
2%
804
28%
804
9%
2116
December1st to 15thNight
30%
900
7%
2700
5%
900
32%
900
10%
2181
December16th to endNight
21%
957
6%
2877
2%
957
24%
957
8%
2413

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
13%12%48%6%35%45%6%29%
47804
Night
12%13%47%6%3445%6%31%
46354
Cloud CoverDay
15%12%47%6%35%445%29%
47804
Night
14%13%47%5%34445%31%
46358
TransparencyDay
55%5%12%17%7%1
47472
Night
53%5%14%18%7%1
46191
SeeingDay
21%14%24%23%11%2
5907
Night
19%9%18%30%18%3
14679

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
17%15%6%9%7%36%5%46%15%
1432
16th to endDay
11%17%6%9%5%35%5%5%5%24%
1536
February1st to 15thDay
12%18%7%10%7%3445%420%
1468
16th to endDay
9%18%8%12%7%4444420%
1521
March1st to 15thDay
15%19%7%10%6%45%34416%
1800
16th to endDay
13%21%6%10%7%3445%416%
2216
April1st to 15thDay
13%18%6%10%8%46%45%5%15%
2149
16th to endDay
12%16%5%8%8%35%45%5%22%
2370
May1st to 15thDay
12%14%47%7%4435%6%29%
2511
16th to endDay
19%10%48%8%45%5%5%6%21%
2651
June1st to 15thDay
24%9%38%7%45%335%23%
2728
16th to endDay
18%8%38%6%36%5%5%5%28%
2880
July1st to 15thDay
8%425%5%35%45%7%47%
2671
16th to endDay
6%314434446%55%
2657
August1st to 15thDay
6%425%435%448%50%
2467
16th to endDay
9%5%25%5%35%5%5%7%44%
2223
September1st to 15thDay
9%5%25%323446%51%
1980
16th to endDay
16%8%15%424447%40%
1848
October1st to 15thDay
14%10%37%5%35%446%34%
1656
16th to endDay
22%14%37%5%33446%23%
1595
November1st to 15thDay
21%17%5%8%5%445%35%17%
1485
16th to endDay
13%19%7%8%5%35%5%45%20%
1344
December1st to 15thDay
10%14%6%10%6%46%6%7%7%19%
1260
16th to endDay
14%17%7%11%7%45%345%17%
1356
January1st to 15thNight
19%17%6%8%7%4444416%
2506
16th to endNight
11%16%7%9%8%35%45%6%21%
2688
February1st to 15thNight
13%18%6%9%5%34345%24%
2384
16th to endNight
9%16%6%9%6%3435%6%27%
1952
March1st to 15thNight
11%18%6%10%7%34446%21%
2160
16th to endNight
12%15%5%9%7%35%446%24%
2003
April1st to 15thNight
9%12%37%8%35%5%5%7%28%
1799
16th to endNight
9%13%38%7%35%45%6%30%
1589
May1st to 15thNight
9%10%35%5%45%6%45%39%
1439
16th to endNight
14%8%37%5%35%5%6%8%30%
1460
June1st to 15thNight
17%8%37%5%3445%8%32%
1228
16th to endNight
13%6%26%5%35%5%6%6%38%
1080
July1st to 15thNight
4425%41435%8%55%
1283
16th to endNight
413324347%63%
1512
August1st to 15thNight
4314323346%61%
1408
16th to endNight
5%323425%46%7%53%
1625
September1st to 15thNight
6%4245%24435%56%
1650
16th to endNight
11%8%25%423448%43%
1782
October1st to 15thNight
13%8%25%6%35%445%40%
1974
16th to endNight
18%11%37%5%3446%6%27%
2277
November1st to 15thNight
20%16%5%6%5%3345%5%21%
2374
16th to endNight
14%20%7%9%8%3433420%
2604
December1st to 15thNight
12%17%6%9%8%36%445%20%
2700
16th to endNight
14%19%7%10%8%45%445%16%
2877

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
18%17%6%9%6%47%34416%
1432
16th to endDay
13%18%6%8%6%34446%24%
1536
February1st to 15thDay
15%20%9%8%6%2445%420%
1468
16th to endDay
10%22%7%10%8%34345%19%
1521
March1st to 15thDay
19%20%7%9%6%35%34416%
1800
16th to endDay
17%22%6%9%6%34445%15%
2216
April1st to 15thDay
15%20%6%9%8%46%45%414%
2149
16th to endDay
14%17%5%8%7%35%445%22%
2370
May1st to 15thDay
14%15%47%6%3445%6%28%
2511
16th to endDay
21%10%39%7%46%45%5%21%
2651
June1st to 15thDay
27%8%47%7%35%345%22%
2728
16th to endDay
20%7%47%6%36%5%5%5%27%
2880
July1st to 15thDay
9%5%25%5%25%46%6%45%
2671
16th to endDay
7%3245%3445%6%53%
2657
August1st to 15thDay
7%4145%345%48%49%
2467
16th to endDay
10%5%25%6%35%5%6%5%43%
2223
September1st to 15thDay
10%5%24433345%51%
1980
16th to endDay
18%7%24423447%40%
1848
October1st to 15thDay
16%11%35%434446%33%
1656
16th to endDay
25%14%47%433336%23%
1595
November1st to 15thDay
26%16%5%7%6%3445%416%
1485
16th to endDay
16%19%7%7%5%35%5%4421%
1344
December1st to 15thDay
11%16%6%10%6%35%5%5%5%21%
1260
16th to endDay
17%18%8%9%7%35%34417%
1356
January1st to 15thNight
21%19%5%9%6%3343417%
2506
16th to endNight
13%18%7%9%6%35%346%21%
2688
February1st to 15thNight
16%19%47%5%34435%24%
2384
16th to endNight
10%18%6%8%6%34445%26%
1952
March1st to 15thNight
15%20%6%9%6%34335%21%
2160
16th to endNight
14%15%5%7%6%36%45%5%24%
2007
April1st to 15thNight
10%13%48%7%35%5%5%5%29%
1799
16th to endNight
10%15%36%6%36%5%46%31%
1589
May1st to 15thNight
11%10%36%6%25%446%38%
1439
16th to endNight
16%8%37%6%35%5%6%8%29%
1460
June1st to 15thNight
20%7%345%345%5%8%31%
1228
16th to endNight
14%5%16%5%35%46%6%39%
1080
July1st to 15thNight
5%41441445%7%55%
1283
16th to endNight
5%23323447%63%
1512
August1st to 15thNight
5%214423347%60%
1408
16th to endNight
6%413425%36%7%54%
1625
September1st to 15thNight
7%3245%24335%56%
1650
16th to endNight
14%7%25%423447%43%
1782
October1st to 15thNight
14%8%245%35%435%40%
1974
16th to endNight
21%10%36%5%2346%6%27%
2277
November1st to 15thNight
24%15%5%6%42445%5%21%
2374
16th to endNight
17%19%7%9%6%2433420%
2604
December1st to 15thNight
14%18%7%10%5%34445%20%
2700
16th to endNight
16%21%7%9%8%3343417%
2877

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
70%5%11%9%3
1432
16th to endDay
61%6%13%14%21
1536
February1st to 15thDay
65%7%13%10%2
1468
16th to endDay
66%312%11%5%
1521
March1st to 15thDay
70%5%11%10%1
1800
16th to endDay
71%5%12%8%2
2216
April1st to 15thDay
69%6%10%11%1
2149
16th to endDay
62%6%13%14%2
2370
May1st to 15thDay
55%412%18%8%
2511
16th to endDay
62%5%14%15%2
2655
June1st to 15thDay
64%410%13%5%1
2728
16th to endDay
55%5%11%19%8%
2880
July1st to 15thDay
36%6%10%22%18%5%
2519
16th to endDay
31%5%10%25%22%4
2490
August1st to 15thDay
31%6%13%29%15%3
2450
16th to endDay
37%5%13%28%13%1
2223
September1st to 15thDay
33%5%13%27%17%1
1980
16th to endDay
43%5%15%22%10%2
1848
October1st to 15thDay
49%5%16%22%6%
1656
16th to endDay
61%5%13%17%2
1595
November1st to 15thDay
67%7%9%11%2
1485
16th to endDay
63%7%12%11%4
1344
December1st to 15thDay
61%7%13%13%3
1260
16th to endDay
69%6%11%9%2
1356
January1st to 15thNight
70%410%10%3
2506
16th to endNight
61%5%14%11%42
2688
February1st to 15thNight
61%5%13%13%41
2396
16th to endNight
56%415%16%6%
1952
March1st to 15thNight
64%6%14%12%2
2160
16th to endNight
59%5%17%14%3
2007
April1st to 15thNight
53%6%17%17%4
1799
16th to endNight
51%7%16%19%4
1589
May1st to 15thNight
44%417%20%12%
1440
16th to endNight
49%5%19%22%3
1460
June1st to 15thNight
48%5%13%22%8%1
1228
16th to endNight
42%6%17%24%8%
1080
July1st to 15thNight
27%314%27%20%5%
1207
16th to endNight
21%315%28%27%4
1416
August1st to 15thNight
24%413%34%19%4
1400
16th to endNight
27%417%31%17%2
1625
September1st to 15thNight
29%412%31%18%4
1650
16th to endNight
39%5%14%25%12%2
1782
October1st to 15thNight
44%6%16%22%9%
1974
16th to endNight
54%5%15%20%3
2277
November1st to 15thNight
63%7%10%13%4
2374
16th to endNight
68%412%8%5%
2604
December1st to 15thNight
64%6%11%14%1
2700
16th to endNight
70%5%11%9%2
2877

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
10%321%26%23%15%
60
16th to endDay
20%17%28%23%9%1
64
February1st to 15thDay
28%17%23%20%6%3
128
16th to endDay
25%17%27%21%7%
229
March1st to 15thDay
32%26%28%10%1
270
16th to endDay
31%22%27%14%3
288
April1st to 15thDay
27%17%27%19%7%
269
16th to endDay
27%22%24%17%43
270
May1st to 15thDay
23%20%25%22%5%2
288
16th to endDay
25%10%16%22%18%5%
366
June1st to 15thDay
24%10%18%26%18%3
523
16th to endDay
19%11%23%25%16%2
675
July1st to 15thDay
10%11%26%31%16%2
453
16th to endDay
5%14%31%32%13%2
327
August1st to 15thDay
10%8%25%32%17%6%
300
16th to endDay
12%16%30%29%5%4
268
September1st to 15thDay
17%16%26%22%13%3
255
16th to endDay
23%10%30%21%10%2
255
October1st to 15thDay
26%16%26%20%9%1
255
16th to endDay
36%5%16%26%12%2
107
November1st to 15thDay
34%21%21%19%2
73
16th to endDay
20%13%25%18%11%11%
60
December1st to 15thDay
26%15%11%26%16%3
60
16th to endDay
21%15%26%23%7%4
64
January1st to 15thNight
30%9%19%26%10%2
720
16th to endNight
20%9%24%30%12%2
768
February1st to 15thNight
27%9%16%30%13%3
704
16th to endNight
15%12%22%28%19%2
632
March1st to 15thNight
23%13%23%26%11%1
720
16th to endNight
20%14%21%27%12%3
768
April1st to 15thNight
15%9%17%33%19%3
719
16th to endNight
13%9%21%37%15%1
509
May1st to 15thNight
15%6%14%37%23%2
360
16th to endNight
17%5%12%28%29%6%
375
June1st to 15thNight
20%8%13%30%23%3
360
16th to endNight
17%5%11%41%19%4
360
July1st to 15thNight
7%5%11%32%37%4
340
16th to endNight
4217%34%37%4
376
August1st to 15thNight
7%16%29%43%11%
352
16th to endNight
7%5%14%36%32%4
575
September1st to 15thNight
8%6%13%26%29%14%
660
16th to endNight
17%5%14%30%25%7%
656
October1st to 15thNight
17%7%17%31%22%3
660
16th to endNight
25%7%21%26%15%4
704
November1st to 15thNight
31%13%19%27%7%1
700
16th to endNight
27%12%20%24%11%3
804
December1st to 15thNight
22%11%20%33%9%1
900
16th to endNight
25%13%27%26%7%
957
Page generated at 2017-08-13 11:16:58. Version ac04

Copyright 2017 A. Danko


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