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 2017-04-01.

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
40%
14375
10%
45175
8%
14344
43%
14344
17%
32558

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
43%
663
8%
1659
4%
663
45%
663
19%
1247
April16th to endNight
41%
467
11%
1457
9%
467
44%
467
17%
1051
May1st to 15thNight
53%
329
12%
1320
18%
329
56%
329
20%
805
May16th to endNight
53%
342
6%
1335
9%
342
54%
342
17%
902
June1st to 15thNight
44%
330
4%
1126
1%
330
44%
330
18%
779
June16th to endNight
54%
330
5%
990
0%
330
54%
330
23%
668
July1st to 15thNight
65%
310
9%
1100
4%
310
67%
310
34%
566
July16th to endNight
70%
348
13%
1304
18%
326
74%
326
41%
577
August1st to 15thNight
74%
330
22%
1312
32%
328
77%
328
35%
628
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
14%12%48%6%35%45%6%29%
45951
Night
12%13%47%6%3445%6%30%
45338
Cloud CoverDay
16%12%47%6%35%445%28%
45951
Night
14%13%47%5%34445%30%
45342
TransparencyDay
55%5%12%17%7%1
45619
Night
53%5%14%18%7%1
45175
SeeingDay
21%15%25%23%11%2
5321
Night
19%9%18%29%17%3
14379

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
12%17%6%10%8%46%45%5%16%
1974
16th to endDay
12%15%5%8%7%45%45%5%23%
2172
May1st to 15thDay
12%14%37%7%3435%6%30%
2301
16th to endDay
20%10%49%8%45%5%5%6%20%
2424
June1st to 15thDay
26%9%37%6%44335%23%
2500
16th to endDay
19%8%48%7%36%5%5%5%26%
2640
July1st to 15thDay
9%5%25%5%35%45%7%45%
2449
16th to endDay
7%3245%34446%52%
2461
August1st to 15thDay
6%425%436%5%5%8%47%
2310
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%6%5%7%29%
1659
16th to endNight
9%13%38%7%35%45%7%31%
1457
May1st to 15thNight
9%11%35%5%45%5%35%40%
1319
16th to endNight
14%7%38%5%35%5%6%8%29%
1335
June1st to 15thNight
18%8%37%5%3435%7%31%
1126
16th to endNight
13%6%26%5%36%5%6%6%36%
990
July1st to 15thNight
4425%5%1435%7%54%
1176
16th to endNight
5%113324347%62%
1400
August1st to 15thNight
5%315%433347%58%
1320
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
14%19%6%9%8%5%6%45%5%15%
1974
16th to endDay
13%16%6%8%7%35%45%5%23%
2172
May1st to 15thDay
13%14%36%6%3445%6%29%
2301
16th to endDay
22%10%49%7%46%45%5%19%
2424
June1st to 15thDay
28%8%47%6%35%345%22%
2500
16th to endDay
21%7%47%6%36%5%5%5%25%
2640
July1st to 15thDay
9%5%25%5%25%5%6%7%43%
2449
16th to endDay
7%4245%3445%6%51%
2461
August1st to 15thDay
8%4145%35%5%5%9%46%
2310
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%12%38%7%36%5%5%6%29%
1659
16th to endNight
9%15%36%6%36%5%46%31%
1457
May1st to 15thNight
10%10%35%5%25%446%39%
1319
16th to endNight
16%7%37%6%45%5%6%8%28%
1335
June1st to 15thNight
21%7%345%345%5%7%31%
1126
16th to endNight
14%6%26%6%35%46%6%37%
990
July1st to 15thNight
5%5%1442435%7%53%
1176
16th to endNight
5%21332345%7%62%
1400
August1st to 15thNight
6%2145%23347%58%
1320
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%7%10%10%1
1974
16th to endDay
60%6%14%14%3
2172
May1st to 15thDay
54%412%19%8%
2301
16th to endDay
63%5%14%13%2
2428
June1st to 15thDay
64%410%13%6%1
2500
16th to endDay
56%5%11%17%7%
2640
July1st to 15thDay
38%6%11%22%17%4
2297
16th to endDay
33%5%11%26%18%4
2294
August1st to 15thDay
33%6%14%30%11%2
2293
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
52%7%19%17%4
1659
16th to endNight
50%7%17%19%4
1457
May1st to 15thNight
43%417%21%12%
1320
16th to endNight
50%5%20%20%2
1335
June1st to 15thNight
49%5%13%21%8%1
1126
16th to endNight
44%6%18%23%7%
990
July1st to 15thNight
29%315%28%19%4
1100
16th to endNight
22%316%29%24%3
1304
August1st to 15thNight
25%414%35%16%2
1312
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
22%18%28%21%8%
211
16th to endDay
24%23%25%16%5%3
210
May1st to 15thDay
21%20%25%24%6%2
228
16th to endDay
26%12%18%22%16%5%
299
June1st to 15thDay
25%10%18%25%16%3
445
16th to endDay
20%10%22%26%16%2
585
July1st to 15thDay
12%12%26%30%16%2
381
16th to endDay
6%15%32%31%11%2
271
August1st to 15thDay
12%9%26%33%14%3
255
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
14%9%17%33%20%4
663
16th to endNight
13%9%22%36%15%1
467
May1st to 15thNight
14%6%15%35%24%3
330
16th to endNight
17%5%12%28%29%6%
343
June1st to 15thNight
20%8%15%28%23%3
330
16th to endNight
17%5%11%41%19%3
330
July1st to 15thNight
8%6%12%32%35%4
310
16th to endNight
4218%33%37%4
348
August1st to 15thNight
7%27%30%42%10%
330
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 2017-04-02 04:39:03. Version ac04

Copyright 2017 A. Danko


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