Fort Nelson
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Nelson clear sky chart from 2005-11-06 to 2024-02-15.

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
43%
23725
9%
81410
7%
23654
46%
23654
14%
60218

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
41%
1015
7%
5342
6%
1006
43%
1006
6%
4463
January11th to 20thNight
40%
1012
13%
4977
8%
1009
42%
1009
7%
3721
January21st to endNight
36%
957
9%
5252
11%
938
40%
938
7%
4122
February1st to 10thNight
40%
850
10%
2850
10%
850
42%
850
13%
2159
February11th to 20thNight
38%
722
13%
2428
10%
721
44%
721
14%
1765
February21st to endNight
47%
592
12%
1924
13%
592
49%
592
16%
1406
March1st to 10thNight
45%
720
14%
2237
12%
720
47%
720
19%
1602
March11th to 20thNight
35%
720
13%
2006
9%
720
38%
720
15%
1544
March21st to endNight
46%
792
12%
2072
8%
792
47%
792
21%
1539
April1st to 10thNight
40%
654
10%
1734
6%
654
43%
654
19%
1313
April11th to 20thNight
47%
448
12%
1516
14%
448
51%
448
19%
1011
April21st to endNight
43%
360
5%
1440
4%
360
45%
360
14%
989
May1st to 10thNight
40%
360
0%
1277
0%
360
40%
360
17%
869
May11th to 20thNight
45%
354
0%
1062
0%
354
45%
354
21%
723
May21st to endNight
54%
388
0%
1164
0%
388
54%
388
22%
794
June1st to 10thNight
48%
360
0%
917
0%
360
48%
360
22%
667
June11th to 20thNight
53%
360
0%
900
0%
360
53%
360
19%
693
June21st to endNight
52%
360
0%
900
0%
360
52%
360
23%
660
July1st to 10thNight
55%
350
0%
875
0%
350
55%
350
23%
646
July11th to 20thNight
53%
348
0%
946
0%
348
53%
348
21%
687
July21st to endNight
60%
394
0%
1150
0%
372
61%
372
22%
786
August1st to 10thNight
59%
358
0%
1246
0%
356
59%
356
21%
808
August11th to 20thNight
48%
356
5%
1377
3%
356
51%
356
18%
908
August21st to endNight
52%
499
8%
1687
10%
499
54%
499
16%
1203
September1st to 10thNight
50%
656
10%
1736
7%
656
52%
656
24%
1218
September11th to 20thNight
51%
720
15%
1800
8%
720
54%
720
27%
1273
September21st to endNight
41%
720
10%
2056
6%
720
43%
720
17%
1551
October1st to 10thNight
40%
720
10%
2160
7%
720
44%
720
19%
1544
October11th to 20thNight
40%
720
14%
2288
9%
720
47%
720
18%
1611
October21st to endNight
39%
792
11%
2772
7%
792
46%
792
14%
2000
November1st to 10thNight
37%
792
14%
2642
12%
792
42%
792
12%
2039
November11th to 20thNight
33%
1028
7%
3016
5%
1028
35%
1028
11%
2449
November21st to endNight
43%
1040
12%
3040
8%
1040
46%
1040
16%
2279
December1st to 10thNight
42%
1040
11%
3040
9%
1040
43%
1040
14%
2368
December11th to 20thNight
41%
1039
13%
3853
5%
1039
45%
1039
11%
2855
December21st to endNight
43%
1129
7%
5728
8%
1114
45%
1114
8%
3953

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%10%48%7%46%6%6%8%30%
77046
Night
9%12%5%10%8%46%6%6%7%26%
81967
TransparencyDay
50%8%15%21%6%
76712
Night
55%8%12%18%7%1
81881
SeeingDay
14%6%21%30%22%7%
15958
Night
14%5%20%35%22%4
23812

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
6%14%7%18%14%6%8%7%5%5%11%
1579
11th to 20thDay
6%11%411%13%8%8%10%6%9%13%
1832
21st to endDay
10%17%6%12%7%46%5%6%8%20%
2410
February1st to 10thDay
8%10%8%11%10%5%7%7%6%7%22%
1330
11th to 20thDay
5%13%6%12%10%45%5%6%9%24%
1513
21st to endDay
6%11%7%12%8%6%6%46%6%28%
1332
March1st to 10thDay
5%12%6%10%8%46%5%6%7%30%
1723
11th to 20thDay
7%18%9%11%8%45%45%6%24%
1952
21st to endDay
7%14%6%10%7%46%35%8%31%
2283
April1st to 10thDay
7%12%5%8%8%45%5%7%8%31%
2223
11th to 20thDay
7%10%5%7%7%35%6%8%9%33%
2392
21st to endDay
11%13%5%7%7%46%5%6%8%28%
2520
May1st to 10thDay
10%9%47%6%45%5%6%8%37%
2680
11th to 20thDay
12%8%36%5%45%47%8%40%
2833
21st to endDay
14%5%36%6%46%6%6%9%36%
3111
June1st to 10thDay
14%8%37%6%46%6%7%7%32%
3042
11th to 20thDay
18%8%46%6%36%6%7%8%28%
3060
21st to endDay
13%6%36%7%45%7%7%9%33%
3060
July1st to 10thDay
16%7%36%7%45%6%6%8%33%
3060
11th to 20thDay
12%7%36%7%5%6%6%7%10%30%
2984
21st to endDay
11%6%36%8%46%7%7%9%34%
3099
August1st to 10thDay
12%6%26%6%45%6%7%9%38%
2686
11th to 20thDay
11%5%26%6%45%5%6%10%40%
2522
21st to endDay
16%7%37%6%445%5%7%36%
2668
September1st to 10thDay
13%7%35%5%45%5%7%8%38%
2224
11th to 20thDay
12%7%36%6%36%5%6%8%37%
2160
21st to endDay
14%7%37%7%46%6%6%6%33%
1901
October1st to 10thDay
12%11%46%6%45%5%6%8%32%
1800
11th to 20thDay
11%14%47%7%345%7%8%30%
1669
21st to endDay
12%13%5%8%7%45%5%6%7%27%
1584
November1st to 10thDay
15%18%6%9%7%4445%5%22%
1417
11th to 20thDay
10%15%8%14%10%446%5%6%19%
1162
21st to endDay
6%12%6%13%10%5%7%5%6%6%24%
1140
December1st to 10thDay
11%15%5%8%10%5%7%5%5%9%21%
1140
11th to 20thDay
7%14%7%11%10%47%5%7%9%20%
1217
21st to endDay
411%7%10%8%5%6%47%7%30%
1738
January1st to 10thNight
5%15%7%16%11%6%7%7%5%5%13%
5366
11th to 20thNight
6%11%411%12%6%6%10%9%9%14%
5051
21st to endNight
10%19%8%11%9%45%45%6%19%
5276
February1st to 10thNight
7%13%7%13%9%5%6%5%6%6%24%
2850
11th to 20thNight
6%12%7%12%8%45%5%5%7%28%
2426
21st to endNight
5%13%6%10%8%6%5%6%6%6%28%
1924
March1st to 10thNight
5%12%5%10%9%5%6%6%5%6%31%
2237
11th to 20thNight
6%16%8%11%9%45%5%5%7%24%
2005
21st to endNight
7%13%5%9%9%35%5%7%7%31%
2072
April1st to 10thNight
7%14%6%10%7%46%5%5%7%30%
1734
11th to 20thNight
5%13%5%7%6%46%6%7%7%33%
1516
21st to endNight
13%10%45%7%5%6%7%7%6%30%
1440
May1st to 10thNight
11%11%5%5%6%46%5%6%8%34%
1277
11th to 20thNight
12%9%37%7%35%6%6%9%34%
1062
21st to endNight
14%7%37%5%36%5%7%9%34%
1164
June1st to 10thNight
14%6%36%8%46%6%8%9%30%
917
11th to 20thNight
14%8%37%8%47%7%8%8%25%
900
21st to endNight
11%6%37%8%46%6%7%9%33%
900
July1st to 10thNight
17%5%27%7%45%5%6%9%34%
900
11th to 20thNight
15%7%36%7%5%6%6%7%8%32%
976
21st to endNight
10%6%36%7%48%7%8%10%30%
1218
August1st to 10thNight
10%7%46%6%45%7%7%8%38%
1253
11th to 20thNight
13%6%36%6%46%7%7%10%33%
1377
21st to endNight
15%8%37%8%37%6%6%9%29%
1687
September1st to 10thNight
11%6%37%7%35%7%8%8%35%
1736
11th to 20thNight
10%8%37%6%35%5%7%11%35%
1800
21st to endNight
16%8%37%7%5%7%6%6%6%28%
2056
October1st to 10thNight
11%10%49%7%5%46%5%8%31%
2160
11th to 20thNight
10%12%5%8%6%45%5%6%7%32%
2288
21st to endNight
10%13%5%9%7%46%6%6%7%28%
2772
November1st to 10thNight
13%17%6%10%7%45%435%26%
2642
11th to 20thNight
8%19%8%12%9%35%45%5%21%
3016
21st to endNight
8%11%5%10%10%46%47%7%26%
3040
December1st to 10thNight
8%14%7%10%10%5%5%5%5%8%23%
3040
11th to 20thNight
6%13%7%14%8%46%5%6%8%25%
3971
21st to endNight
5%11%5%11%10%5%7%6%7%8%25%
5918

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
73%6%7%10%4
1579
11th to 20thDay
65%6%7%15%6%1
1850
21st to endDay
60%6%12%16%6%
2410
February1st to 10thDay
59%7%10%15%8%1
1330
11th to 20thDay
56%6%16%17%4
1521
21st to endDay
55%6%12%20%7%
1332
March1st to 10thDay
51%6%14%20%8%1
1723
11th to 20thDay
61%5%11%17%5%
1952
21st to endDay
52%6%17%20%5%
2283
April1st to 10thDay
48%8%15%21%7%1
2223
11th to 20thDay
44%8%14%24%10%
2392
21st to endDay
52%7%14%18%9%
2520
May1st to 10thDay
43%7%17%24%8%1
2680
11th to 20thDay
41%7%13%25%13%1
2837
21st to endDay
43%8%12%28%9%1
3112
June1st to 10thDay
48%9%14%22%7%1
3042
11th to 20thDay
50%10%13%20%7%
3060
21st to endDay
43%10%18%24%5%
3060
July1st to 10thDay
46%9%18%24%3
2976
11th to 20thDay
47%11%20%20%2
2891
21st to endDay
41%12%22%20%4
2927
August1st to 10thDay
41%11%20%23%5%
2668
11th to 20thDay
39%11%24%23%3
2522
21st to endDay
47%8%21%21%3
2668
September1st to 10thDay
41%10%21%21%6%
2224
11th to 20thDay
43%10%20%24%4
2160
21st to endDay
47%10%16%20%7%
1901
October1st to 10thDay
48%7%15%24%5%1
1800
11th to 20thDay
50%8%15%23%5%
1669
21st to endDay
55%7%14%20%4
1584
November1st to 10thDay
65%5%8%18%4
1417
11th to 20thDay
66%8%9%13%4
1162
21st to endDay
59%5%10%16%8%2
1140
December1st to 10thDay
60%7%13%13%6%
1140
11th to 20thDay
58%7%10%16%8%
1219
21st to endDay
51%6%10%19%12%2
1738
January1st to 10thNight
71%7%7%10%41
5366
11th to 20thNight
60%7%7%14%10%1
5095
21st to endNight
66%7%9%14%5%
5276
February1st to 10thNight
58%6%9%16%9%1
2850
11th to 20thNight
55%6%14%18%7%
2428
21st to endNight
54%7%12%19%7%1
1924
March1st to 10thNight
51%6%12%20%10%1
2237
11th to 20thNight
59%6%9%20%7%1
2006
21st to endNight
52%6%15%20%7%1
2072
April1st to 10thNight
53%8%11%19%9%
1734
11th to 20thNight
46%7%11%22%14%1
1516
21st to endNight
51%7%11%19%10%1
1440
May1st to 10thNight
47%8%14%19%12%
1277
11th to 20thNight
44%8%11%22%11%3
1062
21st to endNight
45%8%12%25%10%1
1164
June1st to 10thNight
47%9%14%23%7%
917
11th to 20thNight
51%11%13%17%8%
900
21st to endNight
46%10%15%20%9%
900
July1st to 10thNight
45%11%15%24%5%
875
11th to 20thNight
47%10%18%21%4
946
21st to endNight
40%13%23%19%5%
1150
August1st to 10thNight
41%9%20%23%6%
1246
11th to 20thNight
42%11%19%22%5%
1377
21st to endNight
49%10%15%22%3
1687
September1st to 10thNight
42%11%16%24%7%
1736
11th to 20thNight
42%9%18%26%5%
1800
21st to endNight
52%10%13%17%8%1
2056
October1st to 10thNight
50%7%15%19%8%1
2160
11th to 20thNight
50%8%14%22%7%
2288
21st to endNight
53%8%14%20%5%
2772
November1st to 10thNight
62%5%7%20%5%
2642
11th to 20thNight
65%6%9%14%6%
3016
21st to endNight
56%6%11%18%8%1
3040
December1st to 10thNight
59%7%11%15%6%1
3040
11th to 20thNight
57%6%11%16%8%1
3968
21st to endNight
53%8%12%15%11%2
5918

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
10%316%37%24%11%
180
11th to 20thDay
12%324%29%23%9%
180
21st to endDay
15%8%16%38%20%3
198
February1st to 10thDay
9%6%22%43%16%4
180
11th to 20thDay
11%7%22%37%18%4
256
21st to endDay
9%5%25%36%21%4
280
March1st to 10thDay
8%6%24%33%20%10%
386
11th to 20thDay
13%5%21%33%23%5%
420
21st to endDay
16%7%24%26%21%6%
462
April1st to 10thDay
12%9%27%31%16%5%
420
11th to 20thDay
12%10%24%27%22%6%
412
21st to endDay
14%10%28%29%16%2
420
May1st to 10thDay
13%9%30%30%13%4
583
11th to 20thDay
13%8%24%31%20%4
802
21st to endDay
14%6%17%31%25%7%
874
June1st to 10thDay
15%7%22%28%23%5%
810
11th to 20thDay
20%5%19%28%23%6%
810
21st to endDay
11%420%28%26%11%
810
July1st to 10thDay
19%316%27%23%11%
796
11th to 20thDay
12%319%27%26%13%
792
21st to endDay
11%415%32%29%9%
845
August1st to 10thDay
10%418%26%28%13%
626
11th to 20thDay
12%9%29%29%15%7%
484
21st to endDay
19%320%23%21%12%
495
September1st to 10thDay
14%7%24%25%20%8%
450
11th to 20thDay
10%5%20%32%24%8%
450
21st to endDay
15%7%28%26%19%4
450
October1st to 10thDay
17%8%26%33%13%4
450
11th to 20thDay
17%7%26%30%16%4
341
21st to endDay
17%9%21%25%23%5%
198
November1st to 10thDay
24%414%33%19%5%
180
11th to 20thDay
15%312%41%22%7%
180
21st to endDay
12%6%17%41%18%6%
180
December1st to 10thDay
14%6%12%39%24%5%
180
11th to 20thDay
12%319%41%17%8%
180
21st to endDay
8%210%41%27%12%
198
January1st to 10thNight
11%6%18%38%23%5%
1040
11th to 20thNight
15%419%41%17%4
1040
21st to endNight
16%5%21%39%16%2
971
February1st to 10thNight
11%5%23%37%21%2
850
11th to 20thNight
10%8%25%36%20%1
725
21st to endNight
9%420%39%24%4
592
March1st to 10thNight
10%5%21%35%23%7%
720
11th to 20thNight
12%6%25%34%21%2
720
21st to endNight
14%419%32%26%5%
792
April1st to 10thNight
13%8%25%27%22%4
654
11th to 20thNight
10%7%23%34%22%4
448
21st to endNight
19%5%25%33%16%1
360
May1st to 10thNight
15%8%26%31%17%3
360
11th to 20thNight
14%9%23%31%23%1
354
21st to endNight
16%317%31%30%3
389
June1st to 10thNight
16%421%32%25%2
360
11th to 20thNight
16%316%33%29%3
360
21st to endNight
13%318%26%34%7%
360
July1st to 10thNight
18%413%29%32%5%
350
11th to 20thNight
15%317%30%28%7%
348
21st to endNight
12%213%35%32%6%
394
August1st to 10thNight
11%315%28%37%6%
358
11th to 20thNight
14%324%31%24%4
356
21st to endNight
18%115%30%31%5%
499
September1st to 10thNight
15%420%32%24%5%
656
11th to 20thNight
13%419%34%25%6%
720
21st to endNight
19%5%22%33%17%3
720
October1st to 10thNight
19%5%23%36%16%2
720
11th to 20thNight
17%424%38%14%2
720
21st to endNight
17%7%21%33%18%4
792
November1st to 10thNight
20%6%18%32%19%5%
792
11th to 20thNight
16%6%20%36%20%2
1028
21st to endNight
13%5%18%45%16%3
1040
December1st to 10thNight
15%5%16%43%18%3
1040
11th to 20thNight
12%6%21%36%19%6%
1040
21st to endNight
12%315%41%24%5%
1144
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Copyright 2024 Attilla Danko


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