Swan Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Swan Lake Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
52%
15682
23%
47445
17%
15640
59%
15640
29%
29135

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
30%
720
23%
2327
11%
716
45%
716
23%
1421
January16th to endNight
30%
768
25%
2441
12%
768
45%
768
23%
1536
February1st to 15thNight
35%
703
26%
2112
11%
701
49%
701
28%
1293
February16th to endNight
28%
631
24%
1893
10%
631
41%
631
27%
1167
March1st to 15thNight
36%
720
24%
2061
12%
720
46%
720
30%
1270
March16th to endNight
43%
768
22%
2112
12%
768
51%
768
32%
1301
April1st to 15thNight
45%
644
25%
1902
18%
644
53%
644
35%
1098
April16th to endNight
49%
540
25%
1706
17%
540
58%
540
33%
978
May1st to 15thNight
53%
540
21%
1620
14%
540
59%
540
31%
997
May16th to endNight
65%
561
22%
1682
17%
561
68%
561
32%
1026
June1st to 15thNight
73%
540
17%
1620
15%
540
75%
540
30%
1029
June16th to endNight
78%
540
16%
1620
14%
540
79%
540
34%
971
July1st to 15thNight
72%
510
12%
1530
12%
510
72%
510
29%
1010
July16th to endNight
77%
564
15%
1595
13%
531
78%
531
29%
1028
August1st to 15thNight
73%
539
18%
1647
19%
536
73%
536
27%
1088
August16th to endNight
68%
573
18%
1910
20%
573
69%
573
22%
1280
September1st to 15thNight
66%
708
19%
1968
18%
708
67%
708
28%
1309
September16th to endNight
64%
717
25%
1980
21%
717
67%
717
31%
1261
October1st to 15thNight
60%
720
30%
1986
24%
720
65%
720
37%
1184
October16th to endNight
55%
768
35%
2303
29%
768
66%
768
39%
1270
November1st to 15thNight
54%
700
32%
2254
28%
700
64%
700
38%
1188
November16th to endNight
44%
720
27%
2340
19%
720
57%
720
30%
1343
December1st to 15thNight
42%
720
24%
2340
18%
720
51%
720
27%
1417
December16th to endNight
35%
768
20%
2496
15%
768
43%
768
20%
1670

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
12%5%245%35%5%5%7%42%
48300
Night
11%42442445%7%46%
47644
TransparencyDay
38%7%11%19%17%4
48001
Night
35%6%11%19%19%6%
47447
SeeingDay
14%415%21%23%18%
5565
Night
13%5%21%29%24%4
15685

By Month

Percentage Cloud Cover SE (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
16%5%24334446%43%
1611
16th to endDay
17%6%24324446%43%
1782
February1st to 15thDay
15%5%25%424447%44%
1750
16th to endDay
17%5%23424445%43%
1580
March1st to 15thDay
15%426%5%23447%43%
1899
16th to endDay
15%5%14424447%43%
2111
April1st to 15thDay
12%5%345%2435%7%46%
2055
16th to endDay
9%42443445%7%49%
2253
May1st to 15thDay
10%6%25%43445%6%46%
2331
16th to endDay
9%5%25%5%246%7%9%42%
2431
June1st to 15thDay
7%426%6%36%7%7%11%36%
2340
16th to endDay
42135%45%6%7%12%44%
2340
July1st to 15thDay
10%426%6%48%6%8%11%31%
2340
16th to endDay
5%425%6%5%7%8%8%11%33%
2465
August1st to 15thDay
8%6%25%7%5%7%7%9%9%31%
2299
16th to endDay
13%6%35%6%46%6%7%10%28%
2289
September1st to 15thDay
13%5%25%5%35%5%6%8%37%
1980
16th to endDay
15%424434446%46%
1980
October1st to 15thDay
14%414313345%54%
1974
16th to endDay
11%31332333459%
1920
November1st to 15thDay
12%313323335%55%
1602
16th to endDay
13%5%24323345%48%
1620
December1st to 15thDay
16%6%2442446%5%42%
1620
16th to endDay
22%7%34433335%36%
1728
January1st to 15thNight
16%5%35%323347%44%
2327
16th to endNight
17%6%23424346%44%
2441
February1st to 15thNight
14%414434446%47%
2103
16th to endNight
16%425%323346%47%
1893
March1st to 15thNight
13%423424446%48%
2061
16th to endNight
11%6%13323348%49%
2112
April1st to 15thNight
11%423313448%51%
1902
16th to endNight
9%415%4245%47%51%
1706
May1st to 15thNight
8%4245%25%47%6%47%
1619
16th to endNight
7%32443446%8%48%
1682
June1st to 15thNight
7%4135%346%8%11%41%
1620
16th to endNight
32145%35%6%8%12%44%
1620
July1st to 15thNight
6%4246%27%6%7%12%37%
1620
16th to endNight
5%225%5%47%8%10%12%37%
1703
August1st to 15thNight
6%335%5%46%7%7%10%38%
1658
16th to endNight
11%425%5%35%6%6%11%35%
1910
September1st to 15thNight
8%425%6%35%5%8%9%40%
1968
16th to endNight
12%5%1442445%6%47%
1980
October1st to 15thNight
11%424323445%54%
1986
16th to endNight
9%31332333460%
2303
November1st to 15thNight
12%313312236%58%
2254
16th to endNight
13%423324335%51%
2340
December1st to 15thNight
14%5%2432435%7%46%
2340
16th to endNight
19%6%35%42445%5%38%
2496

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
40%49%15%25%4
1612
16th to endDay
41%46%18%20%7%
1782
February1st to 15thDay
40%49%18%22%4
1752
16th to endDay
41%5%6%19%19%6%
1580
March1st to 15thDay
40%410%18%19%5%
1899
16th to endDay
39%6%11%20%17%3
2112
April1st to 15thDay
37%5%9%20%20%6%
2055
16th to endDay
33%5%10%22%23%4
2253
May1st to 15thDay
36%8%12%19%19%3
2331
16th to endDay
35%9%13%25%14%2
2435
June1st to 15thDay
38%11%17%22%8%1
2340
16th to endDay
30%10%17%24%14%2
2340
July1st to 15thDay
41%13%18%18%5%2
2201
16th to endDay
39%13%17%19%7%1
2310
August1st to 15thDay
43%12%17%18%7%1
2286
16th to endDay
48%11%14%14%9%
2289
September1st to 15thDay
42%9%12%15%15%2
1980
16th to endDay
38%411%21%20%3
1980
October1st to 15thDay
32%410%19%25%7%
1974
16th to endDay
30%36%16%31%11%
1920
November1st to 15thDay
32%36%16%30%10%
1602
16th to endDay
37%47%16%25%8%
1620
December1st to 15thDay
42%5%7%21%15%7%
1620
16th to endDay
50%38%17%13%6%
1728
January1st to 15thNight
40%37%19%23%5%
2327
16th to endNight
41%45%18%21%9%
2441
February1st to 15thNight
38%36%19%20%11%
2112
16th to endNight
39%36%19%23%7%
1893
March1st to 15thNight
36%410%20%19%9%
2061
16th to endNight
33%6%10%21%21%5%
2112
April1st to 15thNight
31%5%9%24%21%8%
1902
16th to endNight
32%5%11%21%20%9%
1706
May1st to 15thNight
34%7%13%19%21%3
1620
16th to endNight
31%9%13%25%15%3
1684
June1st to 15thNight
32%12%19%25%10%
1620
16th to endNight
29%10%21%21%15%2
1620
July1st to 15thNight
35%11%22%20%7%2
1530
16th to endNight
31%13%22%19%10%2
1595
August1st to 15thNight
36%11%15%24%10%1
1647
16th to endNight
39%12%17%17%12%1
1910
September1st to 15thNight
36%10%14%17%14%4
1968
16th to endNight
35%8%11%20%18%5%
1980
October1st to 15thNight
31%5%11%18%25%7%
1986
16th to endNight
28%4415%32%14%
2303
November1st to 15thNight
29%25%17%30%14%
2254
16th to endNight
34%46%16%27%10%
2340
December1st to 15thNight
38%410%20%18%8%
2340
16th to endNight
46%5%8%15%18%5%
2496

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
21%13%32%18%10%4
90
16th to endDay
16%20%41%14%6%
96
February1st to 15thDay
12%23%37%21%5%
90
16th to endDay
20%13%37%24%3
81
March1st to 15thDay
16%11%30%30%8%1
189
16th to endDay
16%7%27%29%16%1
288
April1st to 15thDay
16%12%24%18%24%4
270
16th to endDay
11%421%28%24%9%
270
May1st to 15thDay
13%7%22%21%17%17%
288
16th to endDay
13%213%22%27%19%
331
June1st to 15thDay
11%7%19%26%34%
315
16th to endDay
8%6%23%23%35%
315
July1st to 15thDay
8%416%27%41%
305
16th to endDay
6%415%30%42%
326
August1st to 15thDay
13%6%19%28%31%
313
16th to endDay
18%317%32%27%
332
September1st to 15thDay
16%110%14%29%26%
315
16th to endDay
17%8%22%35%14%
314
October1st to 15thDay
20%114%28%22%12%
315
16th to endDay
13%5%16%25%30%9%
336
November1st to 15thDay
29%6%19%23%16%5%
110
16th to endDay
11%11%21%28%21%6%
90
December1st to 15thDay
25%5%37%17%12%1
90
16th to endDay
31%14%23%20%8%1
96
January1st to 15thNight
20%13%30%26%8%
720
16th to endNight
20%11%32%29%5%
768
February1st to 15thNight
16%11%31%33%5%
704
16th to endNight
18%10%39%27%4
631
March1st to 15thNight
17%8%34%31%8%
720
16th to endNight
14%8%29%30%16%
768
April1st to 15thNight
14%7%29%29%17%
644
16th to endNight
11%327%30%23%2
540
May1st to 15thNight
10%424%30%26%4
540
16th to endNight
9%112%32%36%6%
563
June1st to 15thNight
7%16%32%40%11%
540
16th to endNight
47%30%44%13%
540
July1st to 15thNight
9%322%47%16%
510
16th to endNight
5%423%50%15%
564
August1st to 15thNight
8%423%48%13%
539
16th to endNight
12%1425%45%10%
573
September1st to 15thNight
11%7%24%46%10%
708
16th to endNight
16%19%30%37%4
717
October1st to 15thNight
13%118%31%27%6%
720
16th to endNight
10%5%22%31%25%4
768
November1st to 15thNight
14%422%33%23%2
700
16th to endNight
15%9%26%31%15%
720
December1st to 15thNight
14%8%29%34%12%1
720
16th to endNight
23%8%28%30%9%
768
Page generated at 2017-11-01 17:23:33. Version ac04

Copyright 2017 A. Danko


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