Sunday Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sunday Creek Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
29%
23259
10%
74869
7%
23219
34%
23219
14%
56777

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
19%
948
7%
2838
4%
946
22%
946
8%
2372
January11th to 20thNight
22%
923
7%
2767
4%
923
25%
923
9%
2260
January21st to endNight
30%
864
10%
2656
6%
864
34%
864
11%
2154
February1st to 10thNight
25%
720
9%
2340
6%
720
29%
720
11%
1851
February11th to 20thNight
23%
703
9%
2274
4%
699
30%
699
12%
1753
February21st to endNight
21%
592
11%
1916
5%
592
28%
592
11%
1486
March1st to 10thNight
24%
720
12%
2027
7%
720
29%
720
14%
1558
March11th to 20thNight
24%
720
13%
1980
6%
720
30%
720
14%
1544
March21st to endNight
30%
792
17%
2178
8%
792
36%
792
21%
1568
April1st to 10thNight
26%
720
13%
1828
7%
720
29%
720
17%
1409
April11th to 20thNight
32%
547
16%
1611
10%
547
35%
547
19%
1158
April21st to endNight
32%
540
15%
1620
8%
540
38%
540
21%
1129
May1st to 10thNight
35%
442
13%
1522
12%
442
40%
442
18%
1045
May11th to 20thNight
35%
354
15%
1416
15%
354
45%
354
16%
944
May21st to endNight
40%
389
11%
1462
11%
388
49%
388
21%
909
June1st to 10thNight
37%
360
9%
1260
8%
360
41%
360
18%
864
June11th to 20thNight
42%
360
11%
1260
9%
360
45%
360
25%
765
June21st to endNight
45%
360
9%
1260
8%
360
47%
360
21%
810
July1st to 10thNight
44%
350
12%
1225
11%
350
50%
350
23%
760
July11th to 20thNight
48%
348
13%
1218
13%
348
53%
348
25%
736
July21st to endNight
54%
398
13%
1398
17%
376
57%
376
22%
880
August1st to 10thNight
48%
537
11%
1600
9%
534
52%
534
24%
1084
August11th to 20thNight
51%
534
14%
1598
9%
534
55%
534
27%
1052
August21st to endNight
42%
594
14%
1782
10%
594
46%
594
21%
1233
September1st to 10thNight
42%
720
14%
1800
7%
720
44%
720
27%
1249
September11th to 20thNight
41%
720
15%
1908
9%
720
44%
720
25%
1321
September21st to endNight
42%
720
15%
2006
11%
720
45%
720
23%
1406
October1st to 10thNight
32%
720
14%
2160
10%
720
38%
720
18%
1588
October11th to 20thNight
23%
720
8%
2160
6%
720
26%
720
11%
1745
October21st to endNight
23%
792
9%
2472
5%
792
29%
792
11%
1975
November1st to 10thNight
22%
740
11%
2592
7%
740
30%
740
12%
1972
November11th to 20thNight
18%
760
8%
2660
5%
760
22%
760
7%
2197
November21st to endNight
17%
760
4%
2660
3%
760
18%
760
6%
2280
December1st to 10thNight
17%
809
6%
2709
2%
809
21%
809
6%
2330
December11th to 20thNight
20%
950
6%
3509
3%
949
23%
949
7%
2904
December21st to endNight
16%
1033
4%
5197
3%
1026
19%
1026
3%
4486

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
17%11%5%8%7%45%5%5%7%27%
74701
Night
17%12%5%9%7%45%5%5%6%27%
75081
TransparencyDay
56%7%11%18%8%1
74392
Night
58%6%11%16%7%1
74925
SeeingDay
21%12%30%24%10%3
14075
Night
23%9%30%29%9%1
23273

By Month

Percentage Cloud Cover NE (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
14%17%8%13%7%5%5%5%5%5%14%
1328
11th to 20thDay
15%16%6%13%9%46%5%37%16%
1288
21st to endDay
11%17%7%12%10%46%46%5%18%
1696
February1st to 10thDay
8%15%7%11%10%5%8%45%6%19%
1620
11th to 20thDay
11%17%7%9%7%45%5%5%7%22%
1573
21st to endDay
11%16%10%10%9%45%345%23%
1338
March1st to 10thDay
13%13%5%11%8%46%5%45%26%
1929
11th to 20thDay
12%13%5%8%8%36%6%46%29%
1980
21st to endDay
16%12%5%7%7%45%335%33%
2178
April1st to 10thDay
19%14%6%9%7%3445%7%24%
2132
11th to 20thDay
20%11%47%6%3445%6%31%
2312
21st to endDay
20%13%46%5%23346%33%
2340
May1st to 10thDay
18%10%36%7%45%45%7%30%
2438
11th to 20thDay
21%9%47%5%34445%33%
2478
21st to endDay
18%8%36%6%35%5%5%8%35%
2811
June1st to 10thDay
19%8%37%6%46%5%6%7%30%
2700
11th to 20thDay
13%7%37%6%46%5%6%7%36%
2700
21st to endDay
17%7%37%7%35%6%6%8%30%
2700
July1st to 10thDay
14%6%36%5%45%5%7%9%36%
2700
11th to 20thDay
13%6%37%6%46%5%6%9%35%
2700
21st to endDay
13%6%36%7%47%5%7%10%32%
2835
August1st to 10thDay
13%7%36%7%5%6%7%6%9%30%
2327
11th to 20thDay
16%7%36%6%36%6%7%7%34%
2303
21st to endDay
16%7%37%6%36%6%6%8%31%
2556
September1st to 10thDay
17%6%37%6%35%5%6%7%35%
2160
11th to 20thDay
20%7%26%5%35%46%6%34%
2048
21st to endDay
22%9%47%5%34447%30%
1953
October1st to 10thDay
20%11%36%6%35%45%6%30%
1800
11th to 20thDay
26%16%5%7%6%34445%20%
1800
21st to endDay
25%17%5%9%7%35%44416%
1882
November1st to 10thDay
21%15%6%8%5%3445%7%21%
1486
11th to 20thDay
18%15%6%12%9%5%7%435%16%
1520
21st to endDay
21%19%8%13%10%3444311%
1520
December1st to 10thDay
15%19%9%12%8%3445%6%15%
1468
11th to 20thDay
17%17%6%10%8%45%5%45%19%
1671
21st to endDay
16%22%9%16%10%3433411%
2431
January1st to 10thNight
15%17%7%13%9%45%6%5%416%
2838
11th to 20thNight
15%17%6%12%7%46%5%5%6%17%
2767
21st to endNight
12%14%5%12%10%6%6%5%6%5%18%
2656
February1st to 10thNight
11%14%6%10%10%6%7%6%5%6%19%
2340
11th to 20thNight
11%15%7%10%9%5%6%446%24%
2273
21st to endNight
10%16%8%12%7%45%6%46%22%
1916
March1st to 10thNight
12%14%6%11%8%46%45%5%26%
2017
11th to 20thNight
16%12%410%8%45%446%26%
1979
21st to endNight
15%12%48%5%35%446%34%
2178
April1st to 10thNight
19%14%6%8%6%3345%6%26%
1828
11th to 20thNight
19%9%38%6%44445%33%
1611
21st to endNight
20%7%46%6%24446%36%
1620
May1st to 10thNight
18%8%47%5%35%46%6%35%
1522
11th to 20thNight
19%6%36%6%45%46%7%33%
1415
21st to endNight
15%7%36%5%25%45%8%41%
1461
June1st to 10thNight
18%8%25%6%46%6%7%7%33%
1260
11th to 20thNight
17%6%245%25%35%8%44%
1260
21st to endNight
15%6%35%6%35%5%6%6%40%
1260
July1st to 10thNight
12%6%246%35%6%6%8%42%
1260
11th to 20thNight
13%5%25%5%35%5%6%9%43%
1260
21st to endNight
10%6%245%46%5%7%9%41%
1480
August1st to 10thNight
11%6%26%6%5%7%5%6%9%37%
1611
11th to 20thNight
14%425%5%35%7%5%8%41%
1598
21st to endNight
17%6%27%6%445%5%6%39%
1782
September1st to 10thNight
14%7%35%5%345%5%7%42%
1800
11th to 20thNight
18%6%37%344446%41%
1908
21st to endNight
18%8%36%4345%5%8%37%
2006
October1st to 10thNight
21%10%37%5%44446%33%
2160
11th to 20thNight
25%14%47%7%35%5%45%22%
2160
21st to endNight
23%14%5%8%7%3445%6%21%
2472
November1st to 10thNight
17%14%6%8%6%45%6%46%25%
2592
11th to 20thNight
19%14%6%12%8%45%445%18%
2660
21st to endNight
22%18%6%10%7%45%35%5%15%
2660
December1st to 10thNight
17%18%7%13%10%5%5%44414%
2709
11th to 20thNight
18%17%5%10%10%45%5%45%16%
3526
21st to endNight
19%20%8%15%9%3433412%
5236

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
71%7%8%12%3
1329
11th to 20thDay
68%48%13%6%
1288
21st to endDay
66%6%7%14%8%
1696
February1st to 10thDay
65%5%11%12%7%
1620
11th to 20thDay
62%5%10%14%8%1
1582
21st to endDay
64%38%17%8%1
1338
March1st to 10thDay
59%6%9%15%10%1
1932
11th to 20thDay
56%5%8%21%9%1
1980
21st to endDay
54%48%18%13%3
2178
April1st to 10thDay
60%6%10%14%10%1
2132
11th to 20thDay
53%5%10%22%9%2
2312
21st to endDay
54%49%16%14%2
2340
May1st to 10thDay
53%7%11%16%12%2
2438
11th to 20thDay
54%5%9%17%14%1
2482
21st to endDay
47%7%12%21%11%1
2811
June1st to 10thDay
52%7%12%21%9%1
2700
11th to 20thDay
46%7%11%21%14%1
2700
21st to endDay
50%8%12%20%8%1
2700
July1st to 10thDay
42%9%15%26%9%
2626
11th to 20thDay
43%8%16%25%9%
2619
21st to endDay
46%9%16%25%4
2677
August1st to 10thDay
49%11%17%19%4
2314
11th to 20thDay
46%10%16%20%7%1
2303
21st to endDay
49%9%14%22%6%
2556
September1st to 10thDay
47%8%15%22%8%
2160
11th to 20thDay
49%8%16%22%5%
2048
21st to endDay
54%7%14%19%5%
1953
October1st to 10thDay
56%7%13%17%7%
1800
11th to 20thDay
67%6%9%13%4
1800
21st to endDay
71%7%9%9%5%
1882
November1st to 10thDay
64%7%14%11%5%
1486
11th to 20thDay
72%5%8%11%31
1520
21st to endDay
78%6%9%6%2
1520
December1st to 10thDay
71%5%11%10%4
1468
11th to 20thDay
66%6%10%17%2
1671
21st to endDay
80%5%6%8%2
2431
January1st to 10thNight
70%6%10%11%3
2838
11th to 20thNight
68%5%8%13%5%
2767
21st to endNight
66%6%7%13%7%1
2656
February1st to 10thNight
64%5%10%13%8%
2340
11th to 20thNight
62%5%12%15%6%
2275
21st to endNight
63%5%9%15%8%1
1916
March1st to 10thNight
61%410%14%9%2
2027
11th to 20thNight
60%5%9%15%9%1
1980
21st to endNight
51%5%10%15%15%4
2178
April1st to 10thNight
58%5%8%17%12%1
1828
11th to 20thNight
54%48%18%14%2
1611
21st to endNight
48%6%11%14%19%2
1620
May1st to 10thNight
49%7%10%20%11%2
1522
11th to 20thNight
48%7%10%19%14%2
1416
21st to endNight
42%6%15%18%16%3
1462
June1st to 10thNight
47%9%11%21%11%2
1260
11th to 20thNight
39%5%13%25%15%2
1260
21st to endNight
43%7%15%20%14%1
1260
July1st to 10thNight
37%10%14%25%14%1
1225
11th to 20thNight
37%8%16%28%11%
1218
21st to endNight
39%10%18%28%5%
1398
August1st to 10thNight
42%9%19%25%6%
1600
11th to 20thNight
38%10%19%25%8%1
1598
21st to endNight
45%9%15%22%8%1
1782
September1st to 10thNight
41%9%18%22%9%2
1800
11th to 20thNight
45%7%18%25%6%
1908
21st to endNight
45%8%17%24%6%
2006
October1st to 10thNight
53%7%13%18%9%1
2160
11th to 20thNight
64%7%11%15%3
2160
21st to endNight
64%6%12%13%5%
2472
November1st to 10thNight
59%8%14%15%4
2592
11th to 20thNight
69%7%10%10%4
2660
21st to endNight
73%7%10%8%2
2660
December1st to 10thNight
74%6%8%9%2
2709
11th to 20thNight
71%5%9%12%3
3525
21st to endNight
78%46%8%3
5236

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
23%16%30%20%9%2
180
11th to 20thDay
18%15%32%25%8%2
168
21st to endDay
21%8%34%27%9%1
258
February1st to 10thDay
20%21%37%17%41
240
11th to 20thDay
20%19%35%22%41
240
21st to endDay
21%23%42%13%1
198
March1st to 10thDay
17%15%42%21%6%
372
11th to 20thDay
20%16%34%22%6%1
420
21st to endDay
24%15%32%23%5%1
462
April1st to 10thDay
23%16%28%23%10%1
420
11th to 20thDay
28%13%24%24%8%3
412
21st to endDay
27%16%27%17%9%3
420
May1st to 10thDay
25%10%33%19%11%2
423
11th to 20thDay
23%13%29%21%10%4
447
21st to endDay
20%11%35%24%9%1
571
June1st to 10thDay
20%12%33%26%9%2
630
11th to 20thDay
16%13%30%27%11%2
630
21st to endDay
17%9%27%30%13%3
630
July1st to 10thDay
13%10%32%29%14%3
621
11th to 20thDay
14%10%30%28%15%3
618
21st to endDay
14%8%27%30%16%5%
586
August1st to 10thDay
15%7%26%27%19%7%
446
11th to 20thDay
16%5%23%30%17%9%
439
21st to endDay
19%9%28%22%12%11%
495
September1st to 10thDay
17%8%29%26%16%4
450
11th to 20thDay
21%10%26%30%11%3
450
21st to endDay
25%12%23%23%16%2
450
October1st to 10thDay
28%10%27%23%10%2
450
11th to 20thDay
32%16%29%18%5%1
450
21st to endDay
32%15%31%18%31
401
November1st to 10thDay
34%16%34%13%2
180
11th to 20thDay
23%21%28%22%5%1
180
21st to endDay
34%21%30%10%42
180
December1st to 10thDay
21%18%32%20%8%1
180
11th to 20thDay
26%15%36%15%7%2
180
21st to endDay
25%15%35%18%5%3
198
January1st to 10thNight
22%10%34%27%6%1
950
11th to 20thNight
25%10%30%27%8%1
923
21st to endNight
20%7%27%33%12%2
864
February1st to 10thNight
19%11%33%30%7%
720
11th to 20thNight
20%10%34%29%6%1
703
21st to endNight
18%14%36%25%7%
592
March1st to 10thNight
20%12%35%27%6%1
720
11th to 20thNight
22%13%34%23%7%
720
21st to endNight
19%12%32%30%7%1
792
April1st to 10thNight
26%12%29%28%5%1
720
11th to 20thNight
24%9%29%29%8%1
547
21st to endNight
24%8%31%29%8%1
540
May1st to 10thNight
20%7%29%37%7%
442
11th to 20thNight
21%7%29%32%9%1
354
21st to endNight
19%9%27%39%6%
389
June1st to 10thNight
23%8%29%33%8%
360
11th to 20thNight
19%6%30%34%12%1
360
21st to endNight
17%6%26%37%13%1
360
July1st to 10thNight
14%335%39%10%
350
11th to 20thNight
15%6%25%40%14%1
348
21st to endNight
12%425%42%16%1
398
August1st to 10thNight
14%425%37%18%2
537
11th to 20thNight
15%322%36%22%2
534
21st to endNight
19%6%26%31%17%2
594
September1st to 10thNight
19%5%28%30%16%2
720
11th to 20thNight
20%7%26%29%17%1
720
21st to endNight
23%7%24%31%14%2
720
October1st to 10thNight
28%8%27%28%9%1
720
11th to 20thNight
30%11%31%20%7%1
720
21st to endNight
32%9%28%26%5%1
792
November1st to 10thNight
24%10%35%25%6%1
740
11th to 20thNight
27%12%32%22%7%1
760
21st to endNight
32%11%30%23%5%
760
December1st to 10thNight
28%9%31%24%6%1
809
11th to 20thNight
27%10%32%23%6%1
950
21st to endNight
30%11%26%23%9%1
1045
Page generated at 2024-01-12 07:31:46. Version ac07

Copyright 2024 Attilla Danko


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