Penticton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Penticton clear sky chart from 2005-11-06 to 2024-03-23.

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%
22982
11%
80686
9%
22888
46%
22888
16%
57555

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
24%
758
5%
4389
5%
736
27%
736
4%
3729
January11th to 20thNight
29%
753
17%
4309
7%
740
32%
740
7%
2891
January21st to endNight
30%
831
4%
4862
6%
814
34%
814
6%
4168
February1st to 10thNight
28%
760
8%
2608
6%
760
31%
760
11%
2014
February11th to 20thNight
34%
741
11%
2404
7%
740
39%
740
15%
1753
February21st to endNight
36%
628
11%
1898
9%
628
39%
628
13%
1469
March1st to 10thNight
37%
760
10%
2280
8%
760
41%
760
14%
1735
March11th to 20thNight
40%
760
13%
2191
9%
760
44%
760
18%
1591
March21st to endNight
39%
800
9%
2029
4%
800
42%
800
15%
1588
April1st to 10thNight
44%
720
9%
1800
3%
720
46%
720
19%
1355
April11th to 20thNight
40%
701
13%
1769
6%
701
45%
701
21%
1300
April21st to endNight
40%
424
14%
1504
12%
424
46%
424
18%
1015
May1st to 10thNight
48%
360
13%
1440
15%
360
57%
360
21%
864
May11th to 20thNight
61%
354
12%
1416
19%
354
62%
354
20%
880
May21st to endNight
53%
388
7%
1552
10%
388
55%
388
17%
1022
June1st to 10thNight
47%
360
6%
1288
3%
360
48%
360
19%
851
June11th to 20thNight
48%
360
6%
1102
1%
360
49%
360
22%
728
June21st to endNight
57%
360
9%
1081
1%
360
58%
360
30%
664
July1st to 10thNight
65%
350
9%
1233
6%
350
67%
350
34%
640
July11th to 20thNight
63%
348
15%
1392
15%
348
71%
348
35%
652
July21st to endNight
73%
394
23%
1488
33%
372
82%
372
56%
542
August1st to 10thNight
73%
358
22%
1424
30%
356
77%
356
37%
661
August11th to 20thNight
74%
372
30%
1440
33%
372
80%
372
46%
613
August21st to endNight
64%
769
24%
1957
16%
769
67%
769
43%
1148
September1st to 10thNight
61%
720
23%
1800
12%
720
65%
720
43%
1066
September11th to 20thNight
64%
720
26%
1818
16%
720
67%
720
38%
1126
September21st to endNight
56%
720
20%
1993
14%
720
59%
720
31%
1263
October1st to 10thNight
53%
720
14%
2160
13%
720
56%
720
25%
1411
October11th to 20thNight
47%
720
16%
2207
13%
720
52%
720
20%
1526
October21st to endNight
38%
792
13%
2574
9%
792
44%
792
17%
1817
November1st to 10thNight
31%
740
9%
2481
8%
740
33%
740
12%
1919
November11th to 20thNight
29%
760
8%
2660
5%
760
34%
760
11%
2035
November21st to endNight
30%
819
6%
2719
3%
819
33%
819
10%
2178
December1st to 10thNight
31%
950
9%
2850
6%
950
34%
950
13%
2218
December11th to 20thNight
25%
950
3%
3507
2%
949
27%
949
7%
2984
December21st to endNight
21%
962
5%
5061
4%
946
26%
946
5%
4139

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%9%47%7%46%6%6%7%35%
78849
Night
8%12%5%8%7%46%6%6%7%32%
80977
TransparencyDay
48%10%13%18%10%2
78570
Night
50%9%13%18%9%1
80836
SeeingDay
13%18%30%25%12%3
14280
Night
12%11%27%31%17%2
23003

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
9%17%8%13%10%5%6%6%6%7%12%
2539
11th to 20thDay
12%13%48%8%45%6%10%11%19%
2516
21st to endDay
13%23%7%10%7%36%6%5%415%
2794
February1st to 10thDay
6%13%5%12%9%5%6%7%5%6%26%
1570
11th to 20thDay
6%11%7%10%9%46%6%7%7%27%
1665
21st to endDay
5%12%5%12%10%5%6%7%6%8%23%
1555
March1st to 10thDay
5%11%6%9%8%5%6%7%7%9%26%
1900
11th to 20thDay
6%11%48%7%5%6%6%6%8%31%
1985
21st to endDay
7%13%6%10%8%5%7%6%7%9%24%
2372
April1st to 10thDay
9%11%5%8%8%5%7%6%6%8%27%
2160
11th to 20thDay
8%11%46%7%5%6%7%7%8%31%
2141
21st to endDay
7%11%48%7%46%6%6%9%32%
2455
May1st to 10thDay
9%7%36%7%45%6%6%9%38%
2520
11th to 20thDay
9%7%36%7%46%8%6%9%36%
2477
21st to endDay
12%9%38%7%36%6%6%8%34%
2723
June1st to 10thDay
14%7%47%7%46%5%6%7%33%
2668
11th to 20thDay
14%7%38%7%47%6%6%7%31%
2853
21st to endDay
9%426%6%46%6%7%8%42%
2874
July1st to 10thDay
6%425%5%46%5%6%7%50%
2687
11th to 20thDay
43236%35%45%7%58%
2520
21st to endDay
321232345%6%68%
2741
August1st to 10thDay
42135%35%5%5%8%60%
2507
11th to 20thDay
4213335%45%8%61%
2457
21st to endDay
5%4245%46%6%6%8%50%
2399
September1st to 10thDay
6%5%245%2445%7%58%
2160
11th to 20thDay
8%5%25%6%45%6%6%6%48%
2141
21st to endDay
9%7%35%4346%5%8%46%
1965
October1st to 10thDay
9%7%26%7%46%5%6%5%45%
1800
11th to 20thDay
8%7%46%7%46%6%5%7%38%
1752
21st to endDay
10%11%48%7%46%6%6%7%31%
1782
November1st to 10thDay
12%12%5%8%8%47%6%7%8%25%
1597
11th to 20thDay
9%11%6%10%10%5%7%7%5%6%25%
1520
21st to endDay
8%12%7%10%8%5%8%7%7%6%22%
1440
December1st to 10thDay
7%13%5%11%9%5%8%7%7%7%21%
1330
11th to 20thDay
8%17%6%13%8%47%7%7%8%14%
1682
21st to endDay
10%15%6%12%9%6%7%7%6%7%15%
2602
January1st to 10thNight
10%19%11%14%9%46%5%5%5%11%
4406
11th to 20thNight
8%14%6%9%8%447%8%14%16%
4382
21st to endNight
14%24%7%11%8%46%44413%
4862
February1st to 10thNight
8%14%6%11%10%5%6%5%5%7%24%
2608
11th to 20thNight
7%14%5%8%8%45%6%5%7%31%
2402
21st to endNight
7%15%5%10%7%46%6%6%6%28%
1898
March1st to 10thNight
5%10%5%9%8%6%7%6%7%8%29%
2280
11th to 20thNight
6%9%48%7%45%6%6%9%35%
2191
21st to endNight
7%10%5%8%8%5%7%6%7%8%30%
2029
April1st to 10thNight
7%9%36%6%46%6%6%10%36%
1800
11th to 20thNight
7%7%37%6%47%6%7%9%37%
1769
21st to endNight
8%8%37%7%5%6%5%6%8%37%
1504
May1st to 10thNight
8%6%26%6%36%5%7%7%44%
1440
11th to 20thNight
8%6%26%446%7%8%11%38%
1416
21st to endNight
11%7%46%5%5%5%5%5%9%39%
1552
June1st to 10thNight
10%8%36%6%25%6%6%10%38%
1288
11th to 20thNight
11%6%26%5%346%6%8%42%
1102
21st to endNight
6%3146%35%5%6%7%52%
1081
July1st to 10thNight
5%314425%6%7%6%58%
1268
11th to 20thNight
3113435%5%7%7%62%
1440
21st to endNight
2112223347%74%
1576
August1st to 10thNight
421333445%7%63%
1432
11th to 20thNight
321322345%9%67%
1440
21st to endNight
33144346%6%8%58%
1957
September1st to 10thNight
5%3244245%5%7%60%
1800
11th to 20thNight
6%5%2443445%8%55%
1818
21st to endNight
7%6%36%5%25%5%6%8%48%
1993
October1st to 10thNight
9%6%36%6%35%6%5%6%46%
2160
11th to 20thNight
9%8%37%6%45%5%6%7%41%
2207
21st to endNight
10%12%47%5%45%6%6%7%34%
2574
November1st to 10thNight
12%13%5%7%7%46%6%7%7%26%
2481
11th to 20thNight
8%12%6%9%8%47%6%6%7%26%
2660
21st to endNight
8%14%6%11%9%5%7%7%6%7%20%
2719
December1st to 10thNight
7%14%8%12%8%46%6%5%8%21%
2850
11th to 20thNight
10%17%7%12%10%5%7%7%7%6%13%
3510
21st to endNight
11%20%7%10%9%5%6%5%6%6%14%
5082

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
69%10%9%9%2
2539
11th to 20thDay
54%9%15%14%36%
2540
21st to endDay
71%8%9%8%3
2794
February1st to 10thDay
59%10%12%12%6%1
1570
11th to 20thDay
58%10%13%12%6%1
1674
21st to endDay
61%10%12%12%5%
1555
March1st to 10thDay
56%13%13%12%6%1
1900
11th to 20thDay
54%10%14%17%5%
1985
21st to endDay
60%12%13%10%4
2372
April1st to 10thDay
58%12%13%13%41
2160
11th to 20thDay
55%11%9%16%8%1
2141
21st to endDay
51%11%12%18%8%1
2455
May1st to 10thDay
45%9%15%22%8%1
2520
11th to 20thDay
50%10%14%19%6%
2480
21st to endDay
53%10%12%19%6%
2724
June1st to 10thDay
52%9%11%15%9%4
2668
11th to 20thDay
53%12%12%17%6%
2853
21st to endDay
40%11%15%19%14%1
2874
July1st to 10thDay
34%8%12%24%17%6%
2613
11th to 20thDay
27%5%13%25%23%7%
2445
21st to endDay
18%6%11%26%30%8%
2589
August1st to 10thDay
23%8%14%26%21%8%
2490
11th to 20thDay
22%7%14%30%22%5%
2457
21st to endDay
31%9%14%30%15%2
2399
September1st to 10thDay
28%8%16%29%17%3
2160
11th to 20thDay
37%10%10%23%18%3
2141
21st to endDay
39%8%18%21%12%2
1965
October1st to 10thDay
43%8%13%27%9%
1800
11th to 20thDay
46%9%16%20%9%
1752
21st to endDay
52%10%14%18%6%
1782
November1st to 10thDay
59%11%12%12%6%
1597
11th to 20thDay
59%12%11%13%5%1
1520
21st to endDay
59%10%14%12%5%1
1440
December1st to 10thDay
55%10%15%16%4
1330
11th to 20thDay
62%13%12%8%5%
1684
21st to endDay
66%11%10%9%4
2602
January1st to 10thNight
74%7%9%8%2
4406
11th to 20thNight
53%8%12%15%7%5%
4420
21st to endNight
73%7%8%8%3
4862
February1st to 10thNight
59%8%13%12%6%1
2608
11th to 20thNight
54%7%14%17%7%1
2404
21st to endNight
57%9%14%13%7%
1898
March1st to 10thNight
54%10%14%14%8%
2280
11th to 20thNight
50%8%15%20%7%
2192
21st to endNight
53%11%15%15%5%
2029
April1st to 10thNight
45%14%18%18%6%
1800
11th to 20thNight
46%10%14%19%11%
1769
21st to endNight
45%9%13%23%10%
1504
May1st to 10thNight
38%9%16%24%12%1
1440
11th to 20thNight
38%11%20%23%8%
1416
21st to endNight
45%9%16%24%6%
1552
June1st to 10thNight
44%9%13%22%11%3
1288
11th to 20thNight
40%9%16%24%10%
1102
21st to endNight
29%12%16%26%13%2
1081
July1st to 10thNight
25%8%12%29%19%6%
1233
11th to 20thNight
21%8%14%27%26%4
1392
21st to endNight
12%313%31%34%7%
1488
August1st to 10thNight
23%6%11%27%25%8%
1424
11th to 20thNight
17%5%14%33%26%3
1440
21st to endNight
23%9%14%34%17%3
1957
September1st to 10thNight
24%8%14%31%20%4
1800
11th to 20thNight
28%9%12%26%21%4
1818
21st to endNight
34%9%17%26%12%2
1993
October1st to 10thNight
40%8%16%25%10%1
2160
11th to 20thNight
46%8%12%23%10%1
2207
21st to endNight
50%7%14%21%8%
2574
November1st to 10thNight
58%10%13%13%5%1
2481
11th to 20thNight
58%9%14%12%5%2
2660
21st to endNight
61%10%12%11%5%1
2719
December1st to 10thNight
58%9%12%17%4
2850
11th to 20thNight
68%10%11%7%3
3507
21st to endNight
64%13%10%9%4
5082

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
16%22%29%20%11%3
180
11th to 20thDay
15%17%30%23%12%3
180
21st to endDay
17%19%36%21%7%1
198
February1st to 10thDay
14%22%42%18%4
230
11th to 20thDay
12%22%38%21%5%1
365
21st to endDay
13%20%38%19%9%1
375
March1st to 10thDay
15%27%30%19%7%1
460
11th to 20thDay
11%25%27%23%11%2
460
21st to endDay
17%25%30%18%9%1
471
April1st to 10thDay
23%23%28%16%7%2
420
11th to 20thDay
16%28%26%17%9%4
412
21st to endDay
15%22%32%18%10%2
420
May1st to 10thDay
13%21%32%22%9%2
423
11th to 20thDay
15%14%28%25%14%4
448
21st to endDay
15%15%27%25%15%3
485
June1st to 10thDay
15%17%27%28%12%2
598
11th to 20thDay
16%18%31%22%11%2
783
21st to endDay
9%12%30%27%19%3
804
July1st to 10thDay
7%13%32%33%14%1
608
11th to 20thDay
7%15%29%30%16%3
444
21st to endDay
410%28%37%14%6%
487
August1st to 10thDay
6%8%26%36%18%6%
447
11th to 20thDay
5%9%30%31%19%6%
437
21st to endDay
7%17%27%28%14%6%
495
September1st to 10thDay
9%16%32%26%12%5%
450
11th to 20thDay
11%15%28%26%16%4
450
21st to endDay
16%20%31%20%11%4
450
October1st to 10thDay
14%21%26%22%13%3
450
11th to 20thDay
16%20%26%24%10%3
402
21st to endDay
16%18%34%22%8%1
297
November1st to 10thDay
19%20%29%26%6%
233
11th to 20thDay
17%25%29%19%8%2
180
21st to endDay
15%21%28%21%13%3
180
December1st to 10thDay
16%16%24%22%18%4
180
11th to 20thDay
13%20%34%22%8%2
180
21st to endDay
13%15%34%29%7%2
198
January1st to 10thNight
17%16%33%24%9%1
760
11th to 20thNight
14%12%33%29%10%2
760
21st to endNight
12%13%33%30%11%2
836
February1st to 10thNight
15%13%33%28%9%2
760
11th to 20thNight
12%9%32%34%11%1
744
21st to endNight
11%14%28%29%17%1
628
March1st to 10thNight
11%12%31%26%18%2
760
11th to 20thNight
9%13%31%30%15%1
760
21st to endNight
11%13%29%32%14%1
800
April1st to 10thNight
10%12%25%35%15%3
720
11th to 20thNight
10%11%32%28%18%1
701
21st to endNight
11%11%33%30%14%1
424
May1st to 10thNight
10%9%26%37%17%1
360
11th to 20thNight
11%319%38%27%2
354
21st to endNight
13%6%20%31%27%2
389
June1st to 10thNight
13%7%25%39%14%1
360
11th to 20thNight
13%8%25%35%19%1
360
21st to endNight
6%6%24%38%24%2
360
July1st to 10thNight
6%5%19%39%30%1
350
11th to 20thNight
46%24%40%24%2
348
21st to endNight
4417%42%30%2
394
August1st to 10thNight
4314%36%39%3
358
11th to 20thNight
5%116%37%38%3
372
21st to endNight
5%5%20%37%30%3
769
September1st to 10thNight
6%7%22%36%26%3
720
11th to 20thNight
8%7%15%32%29%9%
720
21st to endNight
11%7%22%34%23%3
720
October1st to 10thNight
13%7%18%33%25%3
720
11th to 20thNight
12%12%25%33%17%2
720
21st to endNight
16%11%29%29%12%3
792
November1st to 10thNight
18%12%34%28%7%1
740
11th to 20thNight
17%17%28%24%12%1
760
21st to endNight
15%15%31%27%10%3
819
December1st to 10thNight
13%14%29%31%11%2
950
11th to 20thNight
16%14%34%27%8%1
950
21st to endNight
18%14%34%26%8%
965
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