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 2005-11-05 to 2017-09-16.

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%
14795
7%
46712
5%
14766
41%
14766
13%
35866

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
24%
803
5%
2740
3%
800
26%
800
6%
2357
January16th to endNight
28%
800
8%
2880
7%
800
31%
800
8%
2337
February1st to 15thNight
31%
703
6%
2390
5%
702
33%
702
9%
1913
February16th to endNight
42%
632
9%
2053
7%
632
45%
632
14%
1515
March1st to 15thNight
29%
720
10%
2109
6%
720
32%
720
12%
1666
March16th to endNight
42%
768
8%
2054
4%
767
44%
767
14%
1615
April1st to 15thNight
41%
664
8%
1744
5%
664
42%
664
15%
1377
April16th to endNight
38%
432
7%
1512
7%
432
41%
432
10%
1174
May1st to 15thNight
43%
359
4%
1428
4%
359
44%
359
12%
1032
May16th to endNight
46%
374
0%
1228
0%
374
46%
374
15%
908
June1st to 15thNight
45%
360
0%
1080
0%
360
45%
360
15%
818
June16th to endNight
50%
360
0%
1080
0%
360
50%
360
17%
807
July1st to 15thNight
56%
340
0%
1073
0%
340
56%
340
18%
757
July16th to endNight
62%
376
3%
1239
2%
354
64%
354
26%
747
August1st to 15thNight
68%
360
10%
1393
13%
358
71%
358
26%
784
August16th to endNight
54%
544
10%
1690
11%
544
55%
544
19%
1196
September1st to 15thNight
61%
717
14%
1797
9%
717
62%
717
32%
1196
September16th to endNight
44%
660
13%
1820
7%
660
46%
660
19%
1345
October1st to 15thNight
42%
660
9%
1980
6%
660
45%
660
17%
1445
October16th to endNight
31%
704
7%
2321
4%
704
35%
704
10%
1863
November1st to 15thNight
28%
700
6%
2450
4%
700
31%
700
8%
1968
November16th to endNight
28%
837
7%
2699
4%
837
32%
837
10%
2148
December1st to 15thNight
30%
930
7%
2880
5%
930
32%
930
10%
2332
December16th to endNight
26%
992
6%
3072
3%
992
29%
992
8%
2566

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
11%9%48%7%46%6%6%7%27%
48091
Night
12%12%5%8%7%46%5%5%6%26%
46854
TransparencyDay
53%9%16%15%4
47733
Night
56%9%14%14%4
46716
SeeingDay
14%9%27%26%18%3
6821
Night
18%9%22%29%18%2
14803

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
13%17%7%10%7%47%6%7%412%
1209
16th to endDay
12%13%8%10%7%46%46%6%19%
1344
February1st to 15thDay
17%12%5%9%6%46%5%5%6%21%
1471
16th to endDay
8%13%6%8%7%45%45%7%29%
1421
March1st to 15thDay
9%16%6%8%6%45%5%6%6%23%
1848
16th to endDay
7%10%6%10%8%37%6%6%8%24%
2166
April1st to 15thDay
8%14%6%10%8%47%6%6%6%20%
2202
16th to endDay
14%13%6%10%8%47%5%45%20%
2448
May1st to 15thDay
12%10%49%7%47%5%46%26%
2523
16th to endDay
11%8%38%7%5%7%6%6%7%26%
2882
June1st to 15thDay
13%7%37%7%5%6%6%5%8%28%
2880
16th to endDay
12%7%48%7%47%6%6%7%27%
2880
July1st to 15thDay
12%6%36%6%46%6%6%8%33%
2821
16th to endDay
8%5%35%5%36%6%7%8%39%
2846
August1st to 15thDay
5%425%6%45%6%7%9%42%
2559
16th to endDay
11%6%38%7%46%5%5%8%31%
2512
September1st to 15thDay
10%5%25%5%345%6%7%43%
2162
16th to endDay
13%6%36%8%36%5%5%8%30%
1829
October1st to 15thDay
15%9%37%6%36%6%7%6%26%
1650
16th to endDay
16%13%37%7%45%7%5%6%23%
1551
November1st to 15thDay
15%12%5%7%6%5%5%5%5%6%23%
1408
16th to endDay
11%16%7%9%9%45%5%5%5%19%
1247
December1st to 15thDay
12%13%5%9%7%46%5%7%6%20%
1080
16th to endDay
8%17%7%9%10%45%5%6%6%17%
1152
January1st to 15thNight
13%17%7%12%9%46%5%4414%
2740
16th to endNight
14%16%5%9%6%46%6%46%20%
2880
February1st to 15thNight
15%16%6%9%7%345%45%21%
2378
16th to endNight
8%10%5%10%8%46%5%5%6%29%
2053
March1st to 15thNight
10%14%5%10%7%46%45%5%24%
2109
16th to endNight
7%11%6%8%8%47%7%6%7%22%
2054
April1st to 15thNight
10%14%48%8%46%5%5%7%25%
1744
16th to endNight
12%12%48%8%47%6%5%6%23%
1512
May1st to 15thNight
13%8%5%7%8%37%5%5%7%26%
1427
16th to endNight
11%10%47%6%5%7%6%6%7%26%
1228
June1st to 15thNight
14%8%46%5%48%7%5%7%27%
1080
16th to endNight
11%6%46%8%46%6%7%9%26%
1080
July1st to 15thNight
10%6%46%6%5%6%7%5%7%33%
1137
16th to endNight
9%5%245%35%46%7%44%
1323
August1st to 15thNight
6%4146%35%5%6%8%47%
1400
16th to endNight
11%6%37%6%46%6%6%8%33%
1690
September1st to 15thNight
9%5%25%6%2445%7%45%
1797
16th to endNight
13%8%38%6%36%5%6%7%31%
1820
October1st to 15thNight
14%8%46%6%35%35%7%32%
1980
16th to endNight
17%12%5%7%6%35%5%5%7%21%
2321
November1st to 15thNight
14%12%47%8%46%7%6%5%22%
2450
16th to endNight
12%16%6%8%7%35%5%6%7%21%
2699
December1st to 15thNight
14%16%5%8%7%35%445%23%
2880
16th to endNight
8%16%6%11%9%47%5%5%6%17%
3072

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%10%12%5%
1209
16th to endDay
64%8%11%9%5%
1344
February1st to 15thDay
61%8%14%10%4
1471
16th to endDay
54%6%16%15%5%
1421
March1st to 15thDay
60%7%11%13%5%
1848
16th to endDay
56%9%18%13%3
2166
April1st to 15thDay
61%8%12%13%3
2202
16th to endDay
64%6%11%13%3
2448
May1st to 15thDay
55%8%14%15%5%
2523
16th to endDay
54%11%14%16%3
2886
June1st to 15thDay
52%10%13%17%6%
2880
16th to endDay
51%11%16%17%3
2880
July1st to 15thDay
46%10%16%19%7%
2656
16th to endDay
36%11%25%22%3
2667
August1st to 15thDay
34%11%25%23%4
2541
16th to endDay
48%10%19%18%3
2512
September1st to 15thDay
38%9%23%21%6%
2162
16th to endDay
49%11%16%18%3
1829
October1st to 15thDay
53%11%19%14%2
1650
16th to endDay
59%12%16%10%1
1551
November1st to 15thDay
60%8%15%10%5%
1408
16th to endDay
65%9%10%12%1
1247
December1st to 15thDay
61%10%15%11%2
1080
16th to endDay
65%9%14%8%2
1152
January1st to 15thNight
71%7%11%7%2
2740
16th to endNight
64%8%11%8%5%1
2880
February1st to 15thNight
64%7%12%9%6%
2390
16th to endNight
54%7%16%14%6%
2053
March1st to 15thNight
60%7%10%14%5%
2109
16th to endNight
56%9%17%12%3
2058
April1st to 15thNight
56%9%10%16%6%
1744
16th to endNight
60%8%12%12%5%
1512
May1st to 15thNight
55%6%12%15%9%
1428
16th to endNight
52%10%14%19%3
1228
June1st to 15thNight
53%10%10%19%5%
1080
16th to endNight
49%11%17%17%3
1080
July1st to 15thNight
47%9%13%16%11%1
1073
16th to endNight
35%8%25%25%3
1239
August1st to 15thNight
33%8%19%30%7%
1393
16th to endNight
46%10%19%19%3
1690
September1st to 15thNight
36%8%18%27%8%
1797
16th to endNight
49%9%15%19%6%
1820
October1st to 15thNight
50%8%19%16%3
1980
16th to endNight
59%11%14%12%1
2321
November1st to 15thNight
60%11%13%9%4
2450
16th to endNight
61%8%13%12%3
2699
December1st to 15thNight
63%8%12%13%2
2880
16th to endNight
66%9%11%10%2
3072

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
8%320%33%30%5%
60
16th to endDay
18%14%23%20%20%3
64
February1st to 15thDay
23%12%31%20%9%3
150
16th to endDay
14%11%29%27%10%5%
211
March1st to 15thDay
17%19%41%15%5%
267
16th to endDay
13%17%31%27%8%
288
April1st to 15thDay
17%17%33%18%10%1
269
16th to endDay
20%15%32%22%8%
270
May1st to 15thDay
16%11%29%28%11%3
300
16th to endDay
12%8%26%27%21%4
596
June1st to 15thDay
17%8%24%25%21%3
675
16th to endDay
13%5%25%27%22%4
675
July1st to 15thDay
14%8%20%28%24%3
590
16th to endDay
8%6%22%33%26%2
515
August1st to 15thDay
4322%32%30%6%
354
16th to endDay
14%8%29%30%15%1
332
September1st to 15thDay
15%8%25%27%18%4
315
16th to endDay
15%15%32%21%13%1
258
October1st to 15thDay
20%9%26%24%16%1
255
16th to endDay
24%6%26%27%13%1
133
November1st to 15thDay
26%15%33%15%6%3
60
16th to endDay
16%5%35%18%16%8%
60
December1st to 15thDay
13%6%25%21%26%6%
60
16th to endDay
18%7%15%29%23%4
64
January1st to 15thNight
23%13%24%26%10%1
805
16th to endNight
21%13%27%24%12%1
800
February1st to 15thNight
25%11%19%26%14%1
707
16th to endNight
12%8%21%33%19%3
632
March1st to 15thNight
17%14%31%24%10%1
720
16th to endNight
13%9%21%31%22%2
768
April1st to 15thNight
15%8%20%31%20%4
664
16th to endNight
16%9%26%30%16%1
432
May1st to 15thNight
15%7%20%35%17%4
360
16th to endNight
14%420%30%25%3
375
June1st to 15thNight
16%323%27%25%3
360
16th to endNight
12%218%35%26%3
360
July1st to 15thNight
13%317%32%29%3
340
16th to endNight
10%216%35%29%5%
376
August1st to 15thNight
8%110%28%41%9%
360
16th to endNight
15%315%33%28%3
544
September1st to 15thNight
11%414%32%33%3
717
16th to endNight
18%7%22%27%18%5%
660
October1st to 15thNight
20%6%21%32%16%2
660
16th to endNight
24%11%24%24%14%
704
November1st to 15thNight
22%15%26%27%7%2
700
16th to endNight
21%12%27%25%10%2
837
December1st to 15thNight
23%10%23%27%13%1
930
16th to endNight
18%12%27%27%12%1
992
Page generated at 2017-09-17 09:05:43. Version ac04

Copyright 2017 A. Danko


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