Swan River
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Swan River clear sky chart from 2005-11-06 to 2024-09-29.

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
35%
25432
10%
93788
7%
25240
41%
25240
16%
63663

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
27%
937
7%
4716
4%
926
33%
926
7%
3705
January11th to 20thNight
24%
939
6%
4568
4%
929
29%
929
7%
3697
January21st to endNight
24%
1035
7%
4822
3%
1023
29%
1023
8%
3493
February1st to 10thNight
33%
950
11%
2660
4%
950
39%
950
17%
2021
February11th to 20thNight
36%
892
15%
2491
8%
891
41%
891
21%
1781
February21st to endNight
38%
628
15%
1884
8%
628
43%
628
21%
1314
March1st to 10thNight
39%
753
15%
3595
7%
744
43%
744
13%
2323
March11th to 20thNight
36%
672
14%
3534
9%
657
45%
657
12%
2370
March21st to endNight
41%
616
12%
3218
16%
605
46%
605
15%
1783
April1st to 10thNight
43%
570
17%
1900
16%
570
51%
570
23%
1217
April11th to 20thNight
35%
563
13%
1703
9%
563
40%
563
20%
1190
April21st to endNight
34%
570
13%
1665
6%
570
39%
570
24%
1116
May1st to 10thNight
37%
569
10%
2471
6%
559
40%
559
14%
1682
May11th to 20thNight
37%
555
6%
2211
5%
541
41%
541
18%
1490
May21st to endNight
40%
608
3%
2401
4%
593
43%
593
17%
1536
June1st to 10thNight
42%
570
0%
1330
1%
570
42%
570
28%
949
June11th to 20thNight
43%
403
0%
1163
0%
403
43%
403
22%
812
June21st to endNight
47%
380
0%
1140
0%
380
47%
380
22%
788
July1st to 10thNight
55%
387
0%
1875
0%
385
55%
385
21%
1097
July11th to 20thNight
49%
536
2%
1955
3%
533
50%
533
29%
1058
July21st to endNight
57%
613
6%
2399
6%
569
60%
569
30%
1169
August1st to 10thNight
57%
556
11%
2401
5%
545
61%
545
24%
1386
August11th to 20thNight
58%
549
13%
2349
9%
543
62%
543
26%
1305
August21st to endNight
48%
618
12%
2916
13%
605
54%
605
19%
1728
September1st to 10thNight
49%
570
20%
1898
18%
570
57%
570
30%
1101
September11th to 20thNight
45%
570
17%
2021
17%
570
51%
570
23%
1255
September21st to endNight
44%
567
21%
2079
18%
567
53%
567
25%
1220
October1st to 10thNight
38%
611
17%
2051
12%
611
44%
611
21%
1363
October11th to 20thNight
35%
900
17%
2340
9%
900
39%
900
22%
1698
October21st to endNight
28%
990
14%
2574
5%
990
34%
990
18%
1931
November1st to 10thNight
24%
925
11%
2478
3%
925
29%
925
12%
2012
November11th to 20thNight
23%
950
8%
2850
3%
950
28%
950
12%
2215
November21st to endNight
21%
950
9%
2850
3%
950
26%
950
12%
2241
December1st to 10thNight
24%
950
9%
2850
3%
950
31%
950
12%
2216
December11th to 20thNight
22%
950
10%
3465
4%
949
29%
949
8%
2656
December21st to endNight
30%
1030
9%
4965
8%
1026
36%
1026
12%
2745

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%38%5%5%5%46%7%37%
102296
Night
9%10%49%6%5%5%45%7%35%
96056
TransparencyDay
44%8%16%24%7%1
102044
Night
47%8%15%22%8%1
95956
SeeingDay
15%11%30%28%13%3
16221
Night
14%7%31%33%13%1
25596

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
416%8%14%7%6%7%5%6%6%20%
2219
11th to 20thDay
410%417%11%8%8%6%5%6%20%
2330
21st to endDay
7%14%5%9%7%5%6%46%6%30%
2794
February1st to 10thDay
7%11%5%10%7%7%8%5%6%8%27%
1520
11th to 20thDay
5%9%49%7%7%7%5%5%9%33%
1593
21st to endDay
5%9%5%11%8%7%6%5%6%7%30%
1570
March1st to 10thDay
8%10%5%10%6%5%446%7%34%
3130
11th to 20thDay
8%9%5%11%6%5%5%46%7%34%
3311
21st to endDay
6%9%37%5%45%47%8%42%
4058
April1st to 10thDay
9%9%48%6%45%5%6%7%37%
2280
11th to 20thDay
13%11%411%6%5%5%45%7%29%
2428
21st to endDay
10%9%37%5%5%5%5%5%7%38%
2513
May1st to 10thDay
16%10%37%44447%7%35%
4430
11th to 20thDay
16%9%37%5%4445%6%36%
4668
21st to endDay
18%10%38%5%4446%7%31%
5173
June1st to 10thDay
18%7%36%5%45%46%7%34%
2850
11th to 20thDay
20%6%27%5%5%5%46%7%32%
3011
21st to endDay
15%6%36%5%5%6%47%8%35%
3040
July1st to 10thDay
12%5%25%445%5%7%10%41%
5003
11th to 20thDay
9%5%2434447%9%49%
4750
21st to endDay
7%5%25%445%5%7%8%48%
4915
August1st to 10thDay
11%426%445%5%7%9%42%
4412
11th to 20thDay
10%5%26%45%5%46%9%45%
4264
21st to endDay
13%6%26%44446%8%44%
4532
September1st to 10thDay
13%6%26%44446%8%44%
2280
11th to 20thDay
14%8%36%44446%8%41%
2158
21st to endDay
11%8%26%44435%8%44%
2068
October1st to 10thDay
18%12%37%44335%6%36%
1887
11th to 20thDay
13%13%37%5%45%346%36%
1620
21st to endDay
14%16%6%10%6%4435%5%26%
1782
November1st to 10thDay
16%21%5%9%5%44345%25%
1596
11th to 20thDay
8%17%5%13%7%6%5%35%6%26%
1330
21st to endDay
9%15%7%11%7%5%5%35%6%27%
1330
December1st to 10thDay
6%12%412%9%8%7%5%6%7%24%
1330
11th to 20thDay
10%16%6%15%8%6%5%45%5%21%
1679
21st to endDay
47%39%6%4435%6%48%
2442
January1st to 10thNight
5%14%8%16%9%7%7%6%7%5%18%
4737
11th to 20thNight
410%5%19%12%9%9%5%46%17%
4574
21st to endNight
5%14%7%13%7%7%5%45%6%27%
4873
February1st to 10thNight
8%12%411%6%7%8%5%6%6%27%
2660
11th to 20thNight
410%411%7%7%7%5%6%7%32%
2490
21st to endNight
411%5%13%8%5%5%36%8%33%
1884
March1st to 10thNight
7%12%5%8%5%6%5%45%8%34%
3734
11th to 20thNight
7%11%5%12%7%5%5%36%7%32%
3652
21st to endNight
6%8%46%5%5%5%46%7%45%
3580
April1st to 10thNight
7%8%39%6%5%6%46%6%41%
1900
11th to 20thNight
14%9%49%6%5%445%7%33%
1703
21st to endNight
13%8%28%5%5%5%5%5%7%39%
1665
May1st to 10thNight
19%11%36%44445%6%34%
2540
11th to 20thNight
12%10%37%6%5%6%37%7%34%
2238
21st to endNight
18%8%25%44436%7%38%
2414
June1st to 10thNight
16%8%26%45%445%7%40%
1330
11th to 20thNight
20%5%36%445%5%6%7%35%
1163
21st to endNight
13%7%36%6%6%6%45%6%39%
1140
July1st to 10thNight
10%426%5%5%5%5%7%11%42%
1954
11th to 20thNight
8%32444446%9%53%
2220
21st to endNight
6%32434337%9%57%
2633
August1st to 10thNight
14%5%25%34445%8%47%
2528
11th to 20thNight
9%425%44447%9%49%
2575
21st to endNight
16%6%25%43335%7%46%
3135
September1st to 10thNight
9%6%15%5%3345%8%50%
1898
11th to 20thNight
16%7%25%43435%6%45%
2021
21st to endNight
12%6%25%44445%8%46%
2079
October1st to 10thNight
17%11%36%433347%39%
2051
11th to 20thNight
13%14%37%5%45%45%5%36%
2340
21st to endNight
14%16%49%5%5%4345%32%
2574
November1st to 10thNight
13%17%6%11%7%5%5%345%24%
2478
11th to 20thNight
10%16%6%12%7%5%445%6%25%
2850
21st to endNight
10%14%6%12%8%5%5%45%6%25%
2850
December1st to 10thNight
7%13%5%12%11%6%5%45%7%24%
2850
11th to 20thNight
8%15%6%15%8%5%6%46%6%22%
3518
21st to endNight
5%9%49%6%4435%6%45%
5225

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
60%10%13%15%3
2219
11th to 20thDay
63%6%11%17%3
2352
21st to endDay
50%10%14%21%4
2794
February1st to 10thDay
52%10%14%17%8%
1520
11th to 20thDay
45%9%13%22%10%
1601
21st to endDay
49%8%13%20%10%
1570
March1st to 10thDay
48%7%14%22%9%
3130
11th to 20thDay
46%10%17%20%7%1
3313
21st to endDay
36%7%14%28%14%
4058
April1st to 10thDay
44%8%15%20%13%1
2280
11th to 20thDay
54%7%11%16%9%2
2428
21st to endDay
42%8%15%25%9%1
2513
May1st to 10thDay
45%9%12%26%8%
4430
11th to 20thDay
46%7%12%23%10%1
4672
21st to endDay
50%8%11%23%6%
5173
June1st to 10thDay
48%8%13%21%8%1
2850
11th to 20thDay
51%8%14%18%9%
3011
21st to endDay
45%11%16%22%6%
3040
July1st to 10thDay
37%9%24%24%5%
4925
11th to 20thDay
30%8%20%37%5%
4669
21st to endDay
31%8%24%29%7%1
4760
August1st to 10thDay
36%9%22%26%7%
4396
11th to 20thDay
34%9%19%33%5%
4306
21st to endDay
37%7%23%27%7%
4531
September1st to 10thDay
37%9%17%26%10%1
2280
11th to 20thDay
41%8%16%27%7%
2158
21st to endDay
39%8%15%27%11%
2068
October1st to 10thDay
50%7%16%21%5%1
1887
11th to 20thDay
50%7%11%24%7%
1620
21st to endDay
59%8%13%16%5%
1782
November1st to 10thDay
62%6%10%16%5%
1596
11th to 20thDay
58%9%15%12%5%
1330
21st to endDay
58%8%14%16%4
1330
December1st to 10thDay
54%11%14%16%5%
1330
11th to 20thDay
62%9%14%12%3
1680
21st to endDay
35%8%13%25%15%5%
2442
January1st to 10thNight
62%10%12%13%3
4737
11th to 20thNight
66%8%10%12%4
4614
21st to endNight
55%10%13%17%5%
4873
February1st to 10thNight
53%10%12%16%9%1
2660
11th to 20thNight
48%7%14%20%10%
2492
21st to endNight
48%7%16%22%9%
1884
March1st to 10thNight
47%7%16%23%6%1
3734
11th to 20thNight
48%9%11%19%12%1
3652
21st to endNight
34%8%10%31%17%
3580
April1st to 10thNight
42%7%13%21%16%2
1900
11th to 20thNight
49%7%13%19%10%3
1703
21st to endNight
42%8%15%23%9%2
1665
May1st to 10thNight
48%8%11%20%11%1
2540
11th to 20thNight
46%8%13%19%12%2
2238
21st to endNight
42%10%16%22%9%
2414
June1st to 10thNight
42%8%14%24%11%1
1330
11th to 20thNight
45%9%17%17%10%2
1163
21st to endNight
44%9%18%20%8%
1140
July1st to 10thNight
36%9%27%23%5%
1923
11th to 20thNight
26%8%21%38%6%
2178
21st to endNight
24%8%27%32%9%
2550
August1st to 10thNight
34%8%20%29%10%
2520
11th to 20thNight
31%5%23%33%7%
2599
21st to endNight
38%6%19%30%7%
3135
September1st to 10thNight
31%8%16%32%11%2
1898
11th to 20thNight
40%8%14%30%8%
2021
21st to endNight
37%6%14%31%10%2
2079
October1st to 10thNight
45%7%18%24%5%1
2051
11th to 20thNight
48%7%9%27%8%
2340
21st to endNight
54%6%14%21%5%
2574
November1st to 10thNight
61%9%11%14%5%1
2478
11th to 20thNight
58%9%16%14%3
2850
21st to endNight
59%8%14%14%4
2850
December1st to 10thNight
57%9%12%16%5%
2850
11th to 20thNight
58%10%13%13%6%
3516
21st to endNight
38%7%13%21%16%4
5225

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
11%13%33%30%13%
270
11th to 20thDay
9%7%40%33%9%1
270
21st to endDay
13%8%32%35%10%2
297
February1st to 10thDay
12%11%34%30%14%
270
11th to 20thDay
7%10%36%29%15%3
270
21st to endDay
6%9%39%30%15%2
225
March1st to 10thDay
16%9%30%30%11%3
270
11th to 20thDay
9%13%37%29%9%2
270
21st to endDay
15%13%31%29%10%2
438
April1st to 10thDay
12%12%37%28%11%1
460
11th to 20thDay
17%13%30%25%14%1
626
21st to endDay
13%14%32%29%11%1
650
May1st to 10thDay
19%13%28%29%11%1
653
11th to 20thDay
17%14%27%25%15%2
675
21st to endDay
19%11%27%25%14%3
734
June1st to 10thDay
20%13%29%23%11%4
680
11th to 20thDay
20%14%28%23%11%4
680
21st to endDay
18%9%28%27%14%5%
680
July1st to 10thDay
11%9%26%30%19%5%
671
11th to 20thDay
11%10%29%29%16%5%
668
21st to endDay
10%9%24%28%21%7%
739
August1st to 10thDay
11%9%28%28%18%4
676
11th to 20thDay
14%7%24%28%19%8%
665
21st to endDay
18%8%27%29%17%2
748
September1st to 10thDay
15%15%33%28%7%2
490
11th to 20thDay
20%13%31%25%8%3
368
21st to endDay
16%10%34%26%13%1
294
October1st to 10thDay
24%10%27%25%11%3
270
11th to 20thDay
20%13%36%22%9%1
270
21st to endDay
23%11%33%22%9%2
297
November1st to 10thDay
27%10%30%26%6%1
270
11th to 20thDay
16%11%37%26%8%1
270
21st to endDay
17%11%40%21%9%1
270
December1st to 10thDay
9%10%36%32%13%1
270
11th to 20thDay
14%13%39%28%6%
270
21st to endDay
9%5%26%39%17%3
297
January1st to 10thNight
12%9%37%31%10%1
950
11th to 20thNight
12%7%38%31%11%2
950
21st to endNight
14%9%35%32%9%1
1045
February1st to 10thNight
11%7%33%35%14%1
950
11th to 20thNight
8%8%35%33%15%2
896
21st to endNight
7%7%31%37%17%1
628
March1st to 10thNight
15%6%26%40%13%1
760
11th to 20thNight
11%8%34%33%12%1
677
21st to endNight
12%7%29%31%18%3
627
April1st to 10thNight
10%5%31%35%18%2
570
11th to 20thNight
17%6%32%31%13%1
563
21st to endNight
14%8%36%33%8%1
570
May1st to 10thNight
19%7%29%32%12%1
570
11th to 20thNight
15%9%32%30%13%1
561
21st to endNight
22%8%24%33%12%1
617
June1st to 10thNight
18%7%28%33%13%1
570
11th to 20thNight
20%427%33%14%1
403
21st to endNight
12%7%26%38%17%1
380
July1st to 10thNight
9%6%25%41%19%1
397
11th to 20thNight
9%6%28%36%19%2
552
21st to endNight
8%5%24%38%21%4
624
August1st to 10thNight
9%6%23%39%21%2
567
11th to 20thNight
13%320%35%26%3
564
21st to endNight
17%426%39%14%1
627
September1st to 10thNight
12%6%28%37%17%1
570
11th to 20thNight
18%7%24%38%13%1
570
21st to endNight
12%6%29%41%11%1
567
October1st to 10thNight
21%7%27%33%10%1
611
11th to 20thNight
20%9%27%32%11%1
900
21st to endNight
21%8%30%29%10%1
990
November1st to 10thNight
20%10%32%28%8%1
925
11th to 20thNight
17%8%37%27%9%2
950
21st to endNight
16%13%35%27%8%1
950
December1st to 10thNight
11%9%36%28%13%4
950
11th to 20thNight
16%9%33%29%11%2
950
21st to endNight
12%6%28%37%14%3
1045
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