Silent Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Silent Lake clear sky chart from 2005-11-05 to 2017-09-19.

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%
14711
14%
46901
8%
14680
36%
14680
17%
32784

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
13%
720
7%
2506
2%
716
20%
716
7%
2018
January16th to endNight
18%
768
13%
2553
5%
768
27%
768
11%
1952
February1st to 15thNight
15%
703
11%
2287
4%
701
23%
701
11%
1724
February16th to endNight
19%
631
15%
2009
5%
631
32%
631
14%
1444
March1st to 15thNight
17%
720
14%
2016
6%
720
24%
720
15%
1491
March16th to endNight
29%
768
21%
2093
10%
768
38%
768
24%
1406
April1st to 15thNight
22%
718
16%
1796
5%
718
28%
718
20%
1332
April16th to endNight
30%
600
19%
1680
8%
600
38%
600
24%
1141
May1st to 15thNight
36%
409
17%
1489
13%
409
45%
409
20%
947
May16th to endNight
37%
374
15%
1497
11%
374
49%
374
22%
874
June1st to 15thNight
36%
360
10%
1440
8%
360
48%
360
19%
895
June16th to endNight
43%
360
10%
1440
12%
360
49%
360
21%
877
July1st to 15thNight
50%
340
15%
1360
20%
340
57%
340
29%
727
July16th to endNight
49%
385
15%
1427
13%
363
57%
363
28%
788
August1st to 15thNight
56%
539
16%
1609
11%
536
61%
536
35%
964
August16th to endNight
53%
651
20%
1797
10%
651
59%
651
37%
1071
September1st to 15thNight
45%
720
18%
1800
8%
720
49%
720
34%
1159
September16th to endNight
47%
673
22%
1864
14%
673
51%
673
30%
1198
October1st to 15thNight
31%
660
17%
1980
11%
660
39%
660
19%
1386
October16th to endNight
19%
704
11%
2130
4%
704
27%
704
12%
1638
November1st to 15thNight
28%
700
18%
2400
14%
700
36%
700
17%
1641
November16th to endNight
20%
720
12%
2520
7%
720
27%
720
11%
1904
December1st to 15thNight
13%
720
6%
2520
2%
720
18%
720
7%
2022
December16th to endNight
11%
768
9%
2688
3%
768
17%
768
7%
2185

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
18%10%47%6%34446%30%
47922
Night
16%10%46%6%3445%6%32%
47072
Cloud CoverDay
17%10%47%6%34446%30%
47932
Night
16%10%47%6%3445%6%32%
47077
TransparencyDay
54%310%20%10%1
47612
Night
52%311%20%10%
46901
SeeingDay
23%11%29%20%10%4
5384
Night
22%11%30%23%10%1
14713

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 15thDay
19%18%6%8%6%23335%21%
1432
16th to endDay
14%14%8%12%8%44335%19%
1671
February1st to 15thDay
13%16%6%13%8%45%44420%
1575
16th to endDay
16%17%49%6%34335%24%
1464
March1st to 15thDay
16%11%5%7%8%44435%27%
1930
16th to endDay
14%11%36%5%24435%37%
2130
April1st to 15thDay
22%11%45%5%2333431%
2152
16th to endDay
21%9%25%423346%37%
2290
May1st to 15thDay
19%8%36%5%34446%32%
2460
16th to endDay
16%6%25%5%35%5%5%6%36%
2618
June1st to 15thDay
23%7%36%5%35%45%7%28%
2520
16th to endDay
16%6%35%6%35%5%5%9%32%
2520
July1st to 15thDay
14%5%25%5%35%5%6%8%36%
2520
16th to endDay
11%6%36%7%46%5%6%9%33%
2642
August1st to 15thDay
12%6%36%7%46%5%5%7%32%
2340
16th to endDay
14%6%25%5%35%5%6%7%36%
2393
September1st to 15thDay
17%6%25%42445%7%38%
2160
16th to endDay
16%6%26%5%3335%6%40%
1840
October1st to 15thDay
23%8%26%5%34445%30%
1650
16th to endDay
30%11%37%5%2444421%
1741
November1st to 15thDay
18%10%36%5%34445%31%
1458
16th to endDay
23%15%6%9%6%2434419%
1440
December1st to 15thDay
19%21%7%11%7%2332416%
1440
16th to endDay
20%20%9%9%5%2423318%
1536
January1st to 15thNight
20%16%6%9%8%35%33417%
2506
16th to endNight
13%14%7%9%8%35%35%423%
2553
February1st to 15thNight
12%13%6%10%9%35%45%6%21%
2285
16th to endNight
15%12%47%7%345%46%27%
2009
March1st to 15thNight
17%11%47%7%3443431%
2004
16th to endNight
14%7%46%5%225%45%40%
2093
April1st to 15thNight
19%10%5%5%6%2344432%
1796
16th to endNight
16%7%25%5%2446%5%37%
1680
May1st to 15thNight
19%6%25%5%245%5%7%35%
1489
16th to endNight
12%5%15%5%35%5%5%7%43%
1495
June1st to 15thNight
16%6%25%6%2436%8%36%
1440
16th to endNight
13%5%26%5%45%45%6%40%
1440
July1st to 15thNight
8%425%5%2445%7%48%
1440
16th to endNight
9%3234445%6%8%46%
1523
August1st to 15thNight
8%5%244245%6%8%47%
1620
16th to endNight
9%4245%3446%8%49%
1797
September1st to 15thNight
13%5%245%2446%8%43%
1800
16th to endNight
18%424324445%45%
1864
October1st to 15thNight
19%7%26%5%4445%6%32%
1980
16th to endNight
23%11%47%5%35%45%5%23%
2130
November1st to 15thNight
17%8%35%5%3445%6%33%
2400
16th to endNight
22%13%47%6%34445%23%
2520
December1st to 15thNight
19%19%6%9%5%24445%16%
2520
16th to endNight
21%16%8%10%5%2334417%
2688

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
20%18%5%9%5%33335%22%
1432
16th to endDay
14%14%8%11%8%35%435%20%
1671
February1st to 15thDay
13%16%6%12%9%4434420%
1575
16th to endDay
15%17%48%7%4433425%
1464
March1st to 15thDay
17%11%5%7%8%44345%26%
1941
16th to endDay
14%10%46%5%2434438%
2129
April1st to 15thDay
22%11%45%5%24335%31%
2152
16th to endDay
20%9%25%5%23336%37%
2290
May1st to 15thDay
19%8%46%5%34446%32%
2460
16th to endDay
15%7%25%5%35%5%5%6%36%
2618
June1st to 15thDay
22%7%36%5%35%45%7%28%
2520
16th to endDay
15%6%26%5%35%5%5%10%31%
2520
July1st to 15thDay
13%6%35%5%35%5%6%9%36%
2520
16th to endDay
11%6%26%6%46%5%7%8%33%
2642
August1st to 15thDay
12%6%27%8%36%6%5%8%32%
2340
16th to endDay
13%6%346%35%5%7%7%36%
2393
September1st to 15thDay
17%6%35%5%2345%7%38%
2160
16th to endDay
16%6%26%5%33346%40%
1840
October1st to 15thDay
22%9%36%5%33446%30%
1650
16th to endDay
30%11%46%6%24345%21%
1741
November1st to 15thDay
17%9%47%5%3445%5%31%
1458
16th to endDay
22%15%6%8%5%3444419%
1440
December1st to 15thDay
19%21%6%10%7%3332415%
1440
16th to endDay
21%19%8%10%5%3323318%
1536
January1st to 15thNight
20%15%7%9%7%35%345%17%
2506
16th to endNight
13%14%6%9%8%4445%423%
2553
February1st to 15thNight
12%13%6%10%8%35%446%22%
2278
16th to endNight
15%12%47%7%25%45%7%26%
2009
March1st to 15thNight
17%12%47%6%3444431%
2016
16th to endNight
14%7%46%5%23446%40%
2093
April1st to 15thNight
19%9%47%6%33445%33%
1796
16th to endNight
16%7%25%5%2445%6%38%
1680
May1st to 15thNight
18%6%26%42445%7%36%
1489
16th to endNight
11%5%25%5%35%5%47%42%
1495
June1st to 15thNight
15%7%35%5%2437%8%36%
1440
16th to endNight
12%5%25%5%45%45%7%39%
1440
July1st to 15thNight
9%335%5%3445%8%48%
1440
16th to endNight
9%42343446%8%46%
1523
August1st to 15thNight
8%5%14425%5%5%8%47%
1620
16th to endNight
8%425%43446%7%49%
1797
September1st to 15thNight
13%425%42346%8%43%
1800
16th to endNight
17%5%23324345%46%
1864
October1st to 15thNight
19%7%25%6%34347%32%
1980
16th to endNight
22%11%46%5%345%5%5%23%
2130
November1st to 15thNight
17%8%36%6%25%45%6%33%
2400
16th to endNight
21%13%46%6%35%445%23%
2520
December1st to 15thNight
19%19%6%9%5%33446%16%
2520
16th to endNight
21%16%8%11%5%3344418%
2688

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
66%210%12%7%
1433
16th to endDay
67%37%11%8%1
1671
February1st to 15thDay
67%39%13%5%
1577
16th to endDay
62%28%13%12%
1464
March1st to 15thDay
58%214%15%7%1
1941
16th to endDay
49%37%19%16%4
2130
April1st to 15thDay
56%36%18%12%2
2152
16th to endDay
49%26%23%15%2
2290
May1st to 15thDay
52%38%20%13%1
2460
16th to endDay
46%411%21%13%1
2622
June1st to 15thDay
54%310%20%9%
2520
16th to endDay
47%413%22%11%1
2520
July1st to 15thDay
42%5%10%28%13%
2371
16th to endDay
46%5%12%24%10%
2476
August1st to 15thDay
48%5%14%21%10%
2327
16th to endDay
43%412%28%9%
2393
September1st to 15thDay
44%311%27%11%
2160
16th to endDay
44%312%29%10%
1840
October1st to 15thDay
54%39%19%11%
1650
16th to endDay
65%310%13%5%
1741
November1st to 15thDay
53%313%18%9%
1458
16th to endDay
66%39%12%5%1
1440
December1st to 15thDay
72%310%10%3
1440
16th to endDay
71%26%12%5%
1536
January1st to 15thNight
69%29%11%5%
2506
16th to endNight
63%27%16%9%
2553
February1st to 15thNight
62%212%15%6%
2287
16th to endNight
56%210%20%9%
2009
March1st to 15thNight
56%210%18%9%1
2016
16th to endNight
44%38%22%17%2
2093
April1st to 15thNight
53%26%21%12%2
1796
16th to endNight
45%39%22%16%2
1680
May1st to 15thNight
46%310%19%16%3
1489
16th to endNight
39%411%25%15%2
1497
June1st to 15thNight
45%313%23%13%
1440
16th to endNight
42%414%25%12%
1440
July1st to 15thNight
32%5%11%31%19%
1360
16th to endNight
33%6%16%30%13%
1427
August1st to 15thNight
31%6%19%29%12%
1609
16th to endNight
32%417%32%12%1
1797
September1st to 15thNight
37%418%27%11%1
1800
16th to endNight
40%312%33%10%
1864
October1st to 15thNight
51%311%22%11%
1980
16th to endNight
60%5%12%15%6%
2130
November1st to 15thNight
50%413%21%9%
2400
16th to endNight
62%311%17%4
2520
December1st to 15thNight
68%312%12%3
2520
16th to endNight
70%37%11%6%
2688

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
28%18%35%15%3
60
16th to endDay
39%14%33%9%3
87
February1st to 15thDay
33%23%40%3
90
16th to endDay
37%15%33%11%2
123
March1st to 15thDay
26%16%31%20%5%
270
16th to endDay
25%14%31%16%9%2
288
April1st to 15thDay
27%16%32%15%8%
270
16th to endDay
28%17%25%16%10%2
270
May1st to 15thDay
30%11%24%19%7%5%
288
16th to endDay
21%15%33%18%8%3
331
June1st to 15thDay
25%7%34%20%9%1
315
16th to endDay
17%12%32%24%10%3
315
July1st to 15thDay
19%6%27%26%14%5%
305
16th to endDay
14%8%31%26%14%4
326
August1st to 15thDay
13%329%29%15%7%
313
16th to endDay
18%6%24%25%15%10%
332
September1st to 15thDay
16%6%27%20%17%12%
315
16th to endDay
19%7%26%23%13%9%
266
October1st to 15thDay
23%12%29%18%12%2
255
16th to endDay
37%12%27%18%4
269
November1st to 15thDay
23%10%32%22%8%2
112
16th to endDay
40%15%30%13%1
60
December1st to 15thDay
33%21%25%18%1
60
16th to endDay
39%28%28%31
64
January1st to 15thNight
30%18%29%15%4
720
16th to endNight
21%14%35%21%5%1
768
February1st to 15thNight
22%19%35%19%2
704
16th to endNight
22%17%35%18%6%
631
March1st to 15thNight
26%16%34%18%3
720
16th to endNight
19%13%32%22%10%1
768
April1st to 15thNight
26%14%31%21%5%
718
16th to endNight
21%13%30%22%11%1
600
May1st to 15thNight
22%7%26%26%13%1
409
16th to endNight
15%5%34%31%11%
375
June1st to 15thNight
17%9%29%32%10%1
360
16th to endNight
15%5%27%39%11%
360
July1st to 15thNight
7%6%28%37%18%2
340
16th to endNight
9%331%35%19%1
385
August1st to 15thNight
11%221%35%25%3
539
16th to endNight
9%426%32%25%2
651
September1st to 15thNight
16%5%27%27%19%4
720
16th to endNight
20%6%21%27%20%3
673
October1st to 15thNight
24%10%27%23%12%1
660
16th to endNight
30%14%27%20%5%
704
November1st to 15thNight
22%13%29%23%10%1
700
16th to endNight
31%13%27%19%6%1
720
December1st to 15thNight
31%16%32%14%3
720
16th to endNight
30%13%35%15%31
768
Page generated at 2017-09-20 04:49:53. Version ac04

Copyright 2017 A. Danko


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