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 2018-11-30.

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
28%
16227
14%
51742
8%
16196
36%
16196
17%
36106

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
14%
780
8%
2716
2%
776
21%
776
7%
2162
January16th to endNight
17%
832
12%
2765
5%
832
25%
832
11%
2125
February1st to 15thNight
14%
763
12%
2482
4%
761
24%
761
11%
1866
February16th to endNight
18%
683
14%
2175
5%
683
30%
683
14%
1569
March1st to 15thNight
16%
780
13%
2184
5%
780
24%
780
15%
1621
March16th to endNight
29%
832
22%
2267
10%
832
39%
832
24%
1515
April1st to 15thNight
22%
778
16%
1946
6%
778
28%
778
19%
1441
April16th to endNight
30%
641
18%
1797
8%
641
38%
641
23%
1223
May1st to 15thNight
36%
443
18%
1613
13%
443
45%
443
20%
1016
May16th to endNight
36%
406
15%
1625
11%
406
50%
406
23%
930
June1st to 15thNight
38%
390
12%
1560
10%
390
49%
390
20%
952
June16th to endNight
42%
390
11%
1560
13%
390
49%
390
21%
941
July1st to 15thNight
50%
370
17%
1480
21%
370
58%
370
31%
768
July16th to endNight
48%
418
15%
1556
13%
396
56%
396
28%
858
August1st to 15thNight
55%
575
16%
1715
11%
572
59%
572
34%
1039
August16th to endNight
53%
705
19%
1947
9%
705
58%
705
36%
1176
September1st to 15thNight
46%
780
19%
1950
9%
780
50%
780
35%
1246
September16th to endNight
47%
777
22%
2156
15%
777
51%
777
30%
1374
October1st to 15thNight
31%
780
16%
2340
10%
780
39%
780
19%
1650
October16th to endNight
19%
832
12%
2518
4%
832
28%
832
13%
1918
November1st to 15thNight
26%
820
17%
2810
13%
820
35%
820
16%
1948
November16th to endNight
20%
840
11%
2938
6%
840
27%
840
10%
2229
December1st to 15thNight
13%
780
7%
2730
2%
780
18%
780
7%
2187
December16th to endNight
10%
832
9%
2912
3%
832
18%
832
7%
2352

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%10%47%6%34446%30%
52568
Night
16%10%47%6%3445%6%32%
51913
Cloud CoverDay
17%10%47%6%34446%30%
52578
Night
16%10%47%5%3445%6%32%
51918
TransparencyDay
53%310%19%10%1
52258
Night
51%311%20%10%1
51742
SeeingDay
24%12%30%19%9%3
6857
Night
22%11%30%23%10%1
16229

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%5%9%6%23335%21%
1552
16th to endDay
14%14%8%13%8%44335%19%
1810
February1st to 15thDay
13%16%6%13%8%3444320%
1710
16th to endDay
16%17%49%6%34335%24%
1584
March1st to 15thDay
16%13%5%7%7%44435%26%
2092
16th to endDay
14%11%46%5%24435%38%
2308
April1st to 15thDay
23%11%45%5%3333430%
2332
16th to endDay
21%8%25%423335%37%
2449
May1st to 15thDay
19%7%36%5%34446%33%
2666
16th to endDay
15%6%25%5%3445%6%37%
2842
June1st to 15thDay
22%7%36%5%35%45%6%29%
2730
16th to endDay
16%6%35%6%35%5%5%9%33%
2730
July1st to 15thDay
13%5%25%5%35%5%5%8%39%
2730
16th to endDay
12%6%36%7%46%5%6%8%33%
2865
August1st to 15thDay
12%7%37%7%46%5%5%7%31%
2487
16th to endDay
14%6%25%5%35%5%6%7%36%
2593
September1st to 15thDay
17%6%25%5%3445%7%37%
2340
16th to endDay
16%6%25%5%2335%7%40%
2132
October1st to 15thDay
24%9%27%5%34445%28%
1950
16th to endDay
29%11%37%5%23445%22%
2057
November1st to 15thDay
20%11%46%5%34445%28%
1708
16th to endDay
22%16%6%9%6%2334419%
1677
December1st to 15thDay
18%21%7%10%7%2332416%
1560
16th to endDay
19%20%8%8%5%3323319%
1664
January1st to 15thNight
20%15%6%9%8%35%335%18%
2716
16th to endNight
14%14%7%9%8%3435%422%
2765
February1st to 15thNight
12%13%6%10%9%35%45%6%21%
2480
16th to endNight
15%12%47%7%34446%27%
2175
March1st to 15thNight
16%12%47%7%3443430%
2172
16th to endNight
14%6%46%5%235%45%41%
2267
April1st to 15thNight
19%10%5%5%6%2344432%
1946
16th to endNight
17%7%25%5%2445%5%38%
1797
May1st to 15thNight
17%6%25%5%345%5%7%36%
1613
16th to endNight
12%5%15%4345%47%44%
1623
June1st to 15thNight
16%6%25%5%2436%8%37%
1560
16th to endNight
13%5%26%445%45%7%40%
1560
July1st to 15thNight
8%425%5%24447%50%
1560
16th to endNight
9%32443446%8%46%
1652
August1st to 15thNight
8%5%25%4245%6%8%46%
1726
16th to endNight
9%4245%2346%7%47%
1947
September1st to 15thNight
13%42442446%8%43%
1950
16th to endNight
17%424324445%46%
2156
October1st to 15thNight
19%7%26%5%4445%6%32%
2340
16th to endNight
23%11%37%5%35%45%5%24%
2518
November1st to 15thNight
19%9%35%5%3445%6%32%
2810
16th to endNight
22%13%47%6%34445%23%
2938
December1st to 15thNight
19%19%6%9%6%34445%16%
2730
16th to endNight
20%16%8%10%5%3334418%
2912

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
19%17%5%10%5%33335%21%
1552
16th to endDay
14%14%8%12%8%35%335%19%
1810
February1st to 15thDay
13%16%7%12%9%4434320%
1710
16th to endDay
16%17%48%6%34335%25%
1584
March1st to 15thDay
16%13%5%7%8%44345%26%
2103
16th to endDay
14%10%46%5%2434438%
2307
April1st to 15thDay
22%11%46%5%24335%30%
2332
16th to endDay
20%9%25%5%23236%37%
2449
May1st to 15thDay
18%8%36%5%34446%34%
2666
16th to endDay
15%6%25%5%35%5%5%6%37%
2842
June1st to 15thDay
22%7%36%5%35%45%7%29%
2730
16th to endDay
15%6%26%5%35%5%5%9%32%
2730
July1st to 15thDay
12%5%35%5%35%45%8%39%
2730
16th to endDay
11%6%26%6%46%5%7%8%33%
2865
August1st to 15thDay
12%6%37%8%36%6%5%8%31%
2487
16th to endDay
14%6%346%35%5%7%7%36%
2593
September1st to 15thDay
16%6%35%5%2445%7%37%
2340
16th to endDay
15%6%25%5%33447%41%
2132
October1st to 15thDay
23%9%36%5%3435%6%28%
1950
16th to endDay
28%11%46%6%24345%22%
2057
November1st to 15thDay
19%10%47%5%3445%5%28%
1708
16th to endDay
22%15%6%8%6%2444419%
1677
December1st to 15thDay
18%21%7%10%7%3332416%
1560
16th to endDay
20%19%8%9%5%3423319%
1664
January1st to 15thNight
20%15%6%9%7%35%345%18%
2716
16th to endNight
14%14%6%9%8%4445%423%
2765
February1st to 15thNight
12%13%5%11%8%35%45%6%22%
2473
16th to endNight
15%12%48%7%35%45%7%26%
2175
March1st to 15thNight
17%13%47%6%3443430%
2184
16th to endNight
13%6%36%5%24446%41%
2267
April1st to 15thNight
19%9%47%6%33345%32%
1946
16th to endNight
17%7%25%5%2445%5%38%
1797
May1st to 15thNight
17%5%25%435%45%7%37%
1613
16th to endNight
11%5%25%5%35%5%48%44%
1623
June1st to 15thNight
15%7%35%5%2436%8%37%
1560
16th to endNight
12%5%25%5%45%45%7%40%
1560
July1st to 15thNight
8%3245%3445%7%50%
1560
16th to endNight
9%42343446%9%46%
1652
August1st to 15thNight
8%5%24425%5%6%8%46%
1726
16th to endNight
8%425%43446%7%47%
1947
September1st to 15thNight
13%425%42346%8%44%
1950
16th to endNight
16%5%23424345%46%
2156
October1st to 15thNight
19%7%36%6%35%347%32%
2340
16th to endNight
22%11%46%5%35%5%5%5%24%
2518
November1st to 15thNight
19%9%35%5%25%45%6%32%
2810
16th to endNight
21%13%47%6%34445%23%
2938
December1st to 15thNight
19%18%6%9%6%33446%16%
2730
16th to endNight
20%16%7%11%6%3334318%
2912

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%29%12%8%
1553
16th to endDay
68%36%11%8%1
1810
February1st to 15thDay
67%39%14%5%
1712
16th to endDay
62%29%12%12%1
1584
March1st to 15thDay
59%213%15%7%1
2103
16th to endDay
48%36%20%16%4
2308
April1st to 15thDay
57%36%17%12%2
2332
16th to endDay
49%26%23%15%2
2449
May1st to 15thDay
51%38%22%13%1
2666
16th to endDay
45%411%22%14%2
2846
June1st to 15thDay
54%310%20%11%
2730
16th to endDay
46%412%22%11%1
2730
July1st to 15thDay
39%410%29%14%1
2581
16th to endDay
46%5%12%23%10%
2699
August1st to 15thDay
49%5%14%20%9%
2474
16th to endDay
43%412%28%9%
2593
September1st to 15thDay
45%411%26%11%
2340
16th to endDay
43%312%29%11%
2132
October1st to 15thDay
56%39%19%10%
1950
16th to endDay
64%310%14%6%
2057
November1st to 15thDay
55%313%16%9%
1708
16th to endDay
67%310%11%5%1
1677
December1st to 15thDay
72%39%10%4
1560
16th to endDay
70%26%13%6%
1664
January1st to 15thNight
68%29%11%6%
2716
16th to endNight
63%27%15%9%
2765
February1st to 15thNight
62%211%16%6%
2482
16th to endNight
56%210%20%9%
2175
March1st to 15thNight
57%210%18%9%1
2184
16th to endNight
44%38%23%17%2
2267
April1st to 15thNight
54%26%21%13%1
1946
16th to endNight
46%39%20%18%2
1797
May1st to 15thNight
45%310%20%16%3
1613
16th to endNight
38%411%25%16%2
1625
June1st to 15thNight
43%313%23%14%
1560
16th to endNight
42%413%25%12%1
1560
July1st to 15thNight
30%410%30%20%2
1480
16th to endNight
33%5%15%30%13%
1556
August1st to 15thNight
32%6%19%28%11%
1715
16th to endNight
33%417%30%13%1
1947
September1st to 15thNight
36%418%26%13%
1950
16th to endNight
39%312%33%10%
2156
October1st to 15thNight
51%310%21%11%
2340
16th to endNight
59%412%16%6%
2518
November1st to 15thNight
51%412%20%9%
2810
16th to endNight
62%312%15%5%
2938
December1st to 15thNight
68%311%12%3
2730
16th to endNight
69%37%11%7%
2912

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
26%20%37%12%3
90
16th to endDay
39%16%31%9%3
130
February1st to 15thDay
34%22%39%3
135
16th to endDay
38%18%30%9%1
165
March1st to 15thDay
28%16%29%20%4
330
16th to endDay
24%15%30%19%7%2
352
April1st to 15thDay
29%17%30%13%8%
330
16th to endDay
27%16%26%17%10%2
319
May1st to 15thDay
28%12%27%19%6%4
348
16th to endDay
20%13%36%18%7%2
395
June1st to 15thDay
24%7%36%21%8%1
375
16th to endDay
18%12%33%23%9%2
375
July1st to 15thDay
16%6%28%27%15%5%
365
16th to endDay
15%7%32%25%14%4
390
August1st to 15thDay
13%431%28%14%7%
358
16th to endDay
19%6%24%25%14%9%
396
September1st to 15thDay
16%6%28%19%17%11%
375
16th to endDay
18%9%26%21%15%8%
374
October1st to 15thDay
28%12%31%15%11%1
375
16th to endDay
36%15%26%16%4
393
November1st to 15thDay
34%10%29%17%6%1
182
16th to endDay
37%19%31%9%
119
December1st to 15thDay
35%20%26%15%2
90
16th to endDay
33%22%35%5%3
96
January1st to 15thNight
30%17%29%16%4
780
16th to endNight
22%15%35%20%5%1
832
February1st to 15thNight
21%19%36%20%2
764
16th to endNight
21%17%35%18%6%
683
March1st to 15thNight
27%16%34%18%3
780
16th to endNight
19%13%32%23%9%1
832
April1st to 15thNight
26%14%30%22%6%
778
16th to endNight
22%12%29%21%12%
641
May1st to 15thNight
21%8%27%27%13%1
443
16th to endNight
15%5%35%31%11%
407
June1st to 15thNight
17%9%28%33%10%1
390
16th to endNight
15%5%28%37%12%
390
July1st to 15thNight
6%5%29%36%19%2
370
16th to endNight
10%231%34%19%
418
August1st to 15thNight
12%221%34%25%2
575
16th to endNight
10%426%31%24%2
705
September1st to 15thNight
15%5%27%26%19%4
780
16th to endNight
19%7%21%27%19%4
777
October1st to 15thNight
24%9%27%23%12%2
780
16th to endNight
31%14%28%19%5%
832
November1st to 15thNight
25%13%28%22%10%1
820
16th to endNight
31%14%27%19%5%1
840
December1st to 15thNight
31%16%33%15%3
780
16th to endNight
29%14%35%16%3
832
Page generated at 2018-12-01 11:35:37. Version ac04

Copyright 2018 A. Danko


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