Prince George Centre Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prince George Centre Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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
38%
23235
8%
74968
6%
23179
41%
23179
13%
56544

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
23%
936
6%
2923
3%
933
27%
933
7%
2466
January11th to 20thNight
24%
807
7%
2721
4%
807
27%
807
7%
2250
January21st to endNight
25%
880
9%
2970
6%
880
30%
880
9%
2425
February1st to 10thNight
29%
732
8%
2493
6%
732
33%
732
9%
1979
February11th to 20thNight
31%
701
10%
2274
7%
700
35%
700
12%
1760
February21st to endNight
37%
592
13%
1924
9%
592
43%
592
15%
1380
March1st to 10thNight
36%
720
11%
2174
8%
720
39%
720
15%
1637
March11th to 20thNight
34%
720
13%
1979
7%
720
38%
720
16%
1484
March21st to endNight
43%
792
10%
2098
5%
792
44%
792
16%
1642
April1st to 10thNight
44%
720
8%
1800
4%
720
45%
720
18%
1391
April11th to 20thNight
40%
542
10%
1610
7%
542
43%
542
16%
1214
April21st to endNight
40%
378
10%
1458
10%
378
46%
378
14%
1022
May1st to 10thNight
41%
360
5%
1440
7%
360
44%
360
12%
1031
May11th to 20thNight
50%
354
4%
1311
3%
354
50%
354
15%
913
May21st to endNight
48%
388
0%
1240
0%
388
48%
388
18%
883
June1st to 10thNight
44%
360
0%
1080
0%
360
44%
360
15%
806
June11th to 20thNight
45%
360
0%
1080
0%
360
45%
360
16%
826
June21st to endNight
53%
360
0%
1080
0%
360
53%
360
18%
785
July1st to 10thNight
58%
350
0%
1050
0%
350
58%
350
21%
726
July11th to 20thNight
60%
348
0%
1214
0%
348
60%
348
20%
795
July21st to endNight
62%
394
4%
1302
3%
372
65%
372
25%
805
August1st to 10thNight
68%
358
8%
1363
12%
356
69%
356
27%
764
August11th to 20thNight
66%
399
16%
1467
20%
399
70%
399
27%
848
August21st to endNight
49%
594
11%
1782
10%
594
50%
594
17%
1315
September1st to 10thNight
52%
716
11%
1796
6%
716
54%
716
25%
1274
September11th to 20thNight
57%
720
18%
1800
11%
720
60%
720
29%
1221
September21st to endNight
40%
720
13%
2060
7%
720
43%
720
18%
1513
October1st to 10thNight
42%
720
9%
2160
7%
720
45%
720
18%
1550
October11th to 20thNight
37%
720
10%
2163
8%
720
41%
720
15%
1634
October21st to endNight
30%
792
10%
2713
6%
792
37%
792
12%
2034
November1st to 10thNight
28%
740
9%
2590
6%
740
32%
740
9%
2027
November11th to 20thNight
26%
760
9%
2660
6%
760
32%
760
9%
2093
November21st to endNight
25%
981
7%
2943
3%
981
29%
981
9%
2418
December1st to 10thNight
34%
1040
9%
3040
5%
1040
37%
1040
12%
2399
December11th to 20thNight
27%
1040
6%
3747
3%
1039
31%
1039
8%
3167
December21st to endNight
24%
1141
5%
5463
4%
1114
29%
1114
6%
4067

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
10%10%48%7%46%6%6%8%29%
74484
Night
11%13%5%9%7%46%6%6%7%27%
75227
TransparencyDay
51%10%16%17%5%
74157
Night
54%10%14%16%6%
75072
SeeingDay
14%12%26%26%17%4
15195
Night
17%11%24%29%17%2
23243

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
11%15%8%12%9%49%6%7%6%14%
1257
11th to 20thDay
9%18%7%12%11%5%5%5%5%7%16%
1267
21st to endDay
11%15%7%12%9%5%6%5%5%7%18%
1386
February1st to 10thDay
15%15%5%9%7%46%45%7%24%
1464
11th to 20thDay
10%16%5%9%8%46%6%5%6%25%
1575
21st to endDay
6%14%6%9%9%45%5%5%7%31%
1332
March1st to 10thDay
7%15%6%8%7%46%47%8%29%
1782
11th to 20thDay
6%13%5%9%8%47%7%6%8%27%
1980
21st to endDay
7%14%6%10%8%46%5%6%7%27%
2258
April1st to 10thDay
5%12%7%11%9%5%7%8%6%7%24%
2160
11th to 20thDay
10%13%6%9%9%5%7%6%6%6%24%
2298
21st to endDay
12%11%48%7%5%7%5%5%7%28%
2502
May1st to 10thDay
12%11%5%10%7%45%6%5%7%28%
2520
11th to 20thDay
10%7%5%8%7%47%7%6%8%32%
2583
21st to endDay
11%8%48%8%5%7%6%6%8%30%
3032
June1st to 10thDay
10%8%48%9%5%7%7%6%9%28%
2880
11th to 20thDay
14%8%48%7%5%6%7%7%8%26%
2880
21st to endDay
9%8%47%7%47%6%7%9%33%
2880
July1st to 10thDay
11%7%27%7%36%6%6%9%35%
2880
11th to 20thDay
10%7%37%6%46%6%7%9%35%
2702
21st to endDay
8%5%35%6%36%7%7%9%42%
2938
August1st to 10thDay
6%5%25%6%35%6%6%10%45%
2567
11th to 20thDay
7%5%26%5%35%6%6%10%44%
2431
21st to endDay
10%8%47%9%48%6%6%9%30%
2574
September1st to 10thDay
10%6%36%7%5%5%5%6%8%38%
2164
11th to 20thDay
10%6%45%5%45%6%7%9%38%
2160
21st to endDay
15%8%39%7%36%6%6%7%30%
1899
October1st to 10thDay
15%10%37%6%46%6%6%8%30%
1800
11th to 20thDay
14%11%46%7%45%7%7%7%28%
1797
21st to endDay
15%12%47%7%45%5%46%31%
1642
November1st to 10thDay
17%13%49%7%45%5%5%6%25%
1488
11th to 20thDay
9%14%6%13%8%47%5%7%8%19%
1520
21st to endDay
12%19%8%8%8%47%5%5%6%18%
1214
December1st to 10thDay
12%13%5%11%9%5%6%5%7%7%20%
1140
11th to 20thDay
13%20%5%11%9%45%5%5%6%18%
1442
21st to endDay
6%15%5%11%9%47%6%6%7%24%
2090
January1st to 10thNight
11%18%7%12%9%48%5%5%6%15%
2923
11th to 20thNight
13%17%6%11%8%5%6%6%5%5%18%
2721
21st to endNight
12%15%6%10%9%46%7%5%6%20%
2970
February1st to 10thNight
13%19%6%9%7%45%5%45%22%
2493
11th to 20thNight
11%17%6%10%7%36%45%6%25%
2272
21st to endNight
8%13%5%10%8%46%5%5%6%31%
1924
March1st to 10thNight
8%13%6%10%8%47%5%6%6%28%
2174
11th to 20thNight
6%13%6%8%8%5%6%6%7%7%29%
1979
21st to endNight
7%12%5%10%8%5%7%7%6%7%25%
2098
April1st to 10thNight
8%12%5%9%8%47%7%7%8%26%
1800
11th to 20thNight
8%13%48%8%47%7%7%8%25%
1610
21st to endNight
10%12%48%8%37%6%6%6%31%
1458
May1st to 10thNight
11%10%6%9%7%46%6%6%7%28%
1440
11th to 20thNight
11%8%47%7%5%8%7%7%8%29%
1311
21st to endNight
12%9%47%7%46%6%5%8%31%
1240
June1st to 10thNight
14%7%47%8%5%7%6%8%8%26%
1080
11th to 20thNight
14%9%48%8%46%6%6%8%27%
1080
21st to endNight
10%6%5%6%8%5%9%6%7%9%28%
1080
July1st to 10thNight
7%8%37%8%5%8%6%8%9%33%
1080
11th to 20thNight
10%6%37%6%45%6%6%7%39%
1255
21st to endNight
11%5%25%5%45%6%5%8%42%
1379
August1st to 10thNight
6%5%25%6%445%5%9%49%
1370
11th to 20thNight
6%425%6%36%6%5%9%47%
1467
21st to endNight
12%9%48%8%46%6%5%8%31%
1782
September1st to 10thNight
11%8%37%6%35%6%6%9%37%
1796
11th to 20thNight
10%7%35%5%36%5%6%7%44%
1800
21st to endNight
15%10%38%6%36%5%6%7%32%
2060
October1st to 10thNight
13%10%47%7%36%5%6%8%32%
2160
11th to 20thNight
15%12%48%7%45%5%6%7%27%
2163
21st to endNight
14%12%5%7%7%45%5%6%7%28%
2713
November1st to 10thNight
16%13%5%8%7%46%5%6%6%24%
2590
11th to 20thNight
10%14%5%11%8%5%5%6%5%7%24%
2660
21st to endNight
10%18%5%10%8%46%6%6%7%20%
2943
December1st to 10thNight
10%14%5%10%6%5%7%6%5%6%25%
3040
11th to 20thNight
13%19%6%10%8%5%5%46%6%18%
3750
21st to endNight
6%15%5%10%9%5%8%6%7%7%23%
5566

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
67%11%12%8%3
1257
11th to 20thDay
67%10%10%7%41
1267
21st to endDay
65%9%12%10%5%1
1386
February1st to 10thDay
60%8%12%10%9%1
1464
11th to 20thDay
59%9%17%11%41
1584
21st to endDay
52%9%14%15%8%2
1332
March1st to 10thDay
51%10%13%17%9%1
1782
11th to 20thDay
50%12%16%16%6%
1980
21st to endDay
55%9%16%15%5%
2258
April1st to 10thDay
56%11%13%15%5%1
2160
11th to 20thDay
57%8%12%18%5%
2298
21st to endDay
54%8%14%17%7%
2502
May1st to 10thDay
54%9%15%17%5%
2520
11th to 20thDay
48%10%14%18%9%1
2586
21st to endDay
50%10%15%18%6%1
3033
June1st to 10thDay
50%12%13%17%8%1
2880
11th to 20thDay
52%11%15%19%4
2880
21st to endDay
45%12%17%20%6%
2880
July1st to 10thDay
43%11%16%22%7%1
2801
11th to 20thDay
42%11%22%21%4
2620
21st to endDay
34%12%24%24%6%
2775
August1st to 10thDay
33%11%25%25%6%
2549
11th to 20thDay
34%11%24%24%7%
2431
21st to endDay
49%11%18%18%4
2574
September1st to 10thDay
42%11%23%19%5%
2164
11th to 20thDay
40%11%18%24%6%
2160
21st to endDay
50%13%16%16%41
1899
October1st to 10thDay
48%11%22%16%3
1800
11th to 20thDay
52%11%16%19%2
1797
21st to endDay
53%11%16%15%5%
1642
November1st to 10thDay
60%8%14%13%5%1
1488
11th to 20thDay
61%11%13%11%4
1520
21st to endDay
66%11%10%10%3
1214
December1st to 10thDay
59%12%15%11%3
1140
11th to 20thDay
68%9%10%8%5%
1444
21st to endDay
55%11%15%13%5%
2090
January1st to 10thNight
67%10%12%9%3
2923
11th to 20thNight
66%9%11%7%6%1
2721
21st to endNight
63%10%11%11%41
2970
February1st to 10thNight
63%8%11%10%8%1
2493
11th to 20thNight
59%8%14%13%5%
2274
21st to endNight
52%7%15%16%8%2
1924
March1st to 10thNight
53%10%14%14%9%1
2174
11th to 20thNight
52%9%13%19%7%1
1980
21st to endNight
55%10%14%16%5%
2098
April1st to 10thNight
51%11%13%19%7%
1800
11th to 20thNight
54%9%12%19%6%
1610
21st to endNight
51%8%10%20%10%1
1458
May1st to 10thNight
53%9%15%16%6%
1440
11th to 20thNight
47%12%13%19%9%1
1311
21st to endNight
48%10%14%22%6%
1240
June1st to 10thNight
52%11%11%17%8%1
1080
11th to 20thNight
53%11%12%18%5%
1080
21st to endNight
46%12%17%19%5%
1080
July1st to 10thNight
44%10%16%19%10%1
1050
11th to 20thNight
42%10%18%24%5%1
1214
21st to endNight
35%11%23%23%8%
1302
August1st to 10thNight
31%10%22%28%9%
1363
11th to 20thNight
33%9%19%30%8%1
1467
21st to endNight
50%11%17%18%41
1782
September1st to 10thNight
41%11%19%22%6%1
1796
11th to 20thNight
37%10%16%28%9%
1800
21st to endNight
49%10%15%18%8%
2060
October1st to 10thNight
49%9%20%18%4
2160
11th to 20thNight
53%10%17%16%4
2163
21st to endNight
53%11%14%17%5%
2713
November1st to 10thNight
59%11%12%13%5%
2590
11th to 20thNight
59%11%12%12%5%
2660
21st to endNight
62%11%12%11%4
2943
December1st to 10thNight
57%11%13%14%5%
3040
11th to 20thNight
66%11%10%9%4
3747
21st to endNight
55%12%14%13%5%
5566

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
13%16%29%26%13%3
180
11th to 20thDay
13%22%28%24%10%2
162
21st to endDay
20%20%27%18%13%2
176
February1st to 10thDay
26%23%26%17%6%2
212
11th to 20thDay
16%16%34%24%8%1
335
21st to endDay
14%21%31%23%8%4
280
March1st to 10thDay
15%16%30%24%13%2
406
11th to 20thDay
15%18%31%23%12%1
420
21st to endDay
16%22%25%19%13%4
462
April1st to 10thDay
13%18%32%25%11%2
420
11th to 20thDay
16%18%30%18%14%4
412
21st to endDay
14%17%30%23%13%3
420
May1st to 10thDay
16%13%29%27%11%4
423
11th to 20thDay
12%8%26%31%19%5%
552
21st to endDay
12%8%26%27%23%4
795
June1st to 10thDay
14%11%27%29%18%2
810
11th to 20thDay
17%9%26%27%18%4
810
21st to endDay
11%6%25%29%24%4
810
July1st to 10thDay
14%6%19%31%26%4
796
11th to 20thDay
12%9%21%27%25%5%
619
21st to endDay
8%5%21%33%27%5%
684
August1st to 10thDay
7%7%21%31%28%7%
507
11th to 20thDay
8%9%24%30%22%7%
437
21st to endDay
11%11%27%29%17%5%
495
September1st to 10thDay
15%11%25%28%17%4
450
11th to 20thDay
12%12%25%26%19%6%
450
21st to endDay
18%16%33%19%12%3
450
October1st to 10thDay
22%11%24%24%15%3
450
11th to 20thDay
20%14%30%22%13%1
447
21st to endDay
21%16%26%24%10%3
227
November1st to 10thDay
31%16%24%19%7%3
180
11th to 20thDay
17%19%29%22%8%5%
180
21st to endDay
22%15%32%18%10%3
180
December1st to 10thDay
17%8%28%27%16%3
180
11th to 20thDay
14%12%28%29%16%2
180
21st to endDay
21%12%25%26%15%2
198
January1st to 10thNight
22%15%28%25%8%2
937
11th to 20thNight
22%13%29%24%12%
807
21st to endNight
19%15%30%23%12%1
880
February1st to 10thNight
25%16%21%25%12%2
732
11th to 20thNight
19%12%25%30%13%1
704
21st to endNight
15%12%24%32%14%3
592
March1st to 10thNight
15%13%27%29%14%3
720
11th to 20thNight
14%13%29%28%14%1
720
21st to endNight
12%11%21%29%22%4
792
April1st to 10thNight
14%10%19%33%20%3
720
11th to 20thNight
14%7%26%31%18%4
542
21st to endNight
12%10%27%31%18%1
378
May1st to 10thNight
14%9%22%35%16%4
360
11th to 20thNight
13%421%35%24%3
354
21st to endNight
14%7%18%33%26%2
389
June1st to 10thNight
16%6%23%34%19%3
360
11th to 20thNight
18%420%32%22%4
360
21st to endNight
13%419%35%28%1
360
July1st to 10thNight
11%317%39%29%1
350
11th to 20thNight
13%316%36%29%3
348
21st to endNight
12%313%36%29%6%
394
August1st to 10thNight
9%314%29%39%7%
358
11th to 20thNight
8%314%37%35%4
399
21st to endNight
16%418%34%24%4
594
September1st to 10thNight
14%5%18%34%26%2
716
11th to 20thNight
13%6%16%30%29%6%
720
21st to endNight
19%10%24%27%17%2
720
October1st to 10thNight
21%8%21%31%17%3
720
11th to 20thNight
21%8%25%28%16%1
720
21st to endNight
21%14%28%25%12%1
792
November1st to 10thNight
24%16%23%27%8%2
740
11th to 20thNight
19%17%29%25%9%1
760
21st to endNight
20%16%29%25%8%2
981
December1st to 10thNight
17%13%25%31%13%2
1040
11th to 20thNight
22%12%27%27%11%1
1040
21st to endNight
17%13%30%28%11%1
1144
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Copyright 2024 Attilla Danko


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