Lake Afton Public Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Afton Public Observatory clear sky chart from 2005-11-05 to 2017-12-20.

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
45%
16242
27%
48075
16%
16197
54%
16197
37%
26946

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
36%
900
30%
2327
13%
895
48%
895
39%
1359
January16th to endNight
37%
960
34%
2496
13%
960
49%
960
43%
1414
February1st to 15thNight
32%
818
23%
2226
9%
814
41%
814
32%
1379
February16th to endNight
33%
632
29%
1894
11%
632
47%
632
33%
1053
March1st to 15thNight
34%
585
25%
2025
15%
585
45%
585
29%
1133
March16th to endNight
31%
576
19%
2112
12%
576
42%
576
24%
1238
April1st to 15thNight
29%
539
22%
1920
13%
539
46%
539
27%
1077
April16th to endNight
32%
540
22%
1620
14%
540
44%
540
28%
985
May1st to 15thNight
35%
539
23%
1620
16%
539
47%
539
31%
958
May16th to endNight
47%
561
19%
1684
16%
561
54%
561
34%
990
June1st to 15thNight
51%
540
19%
1620
11%
540
59%
540
41%
865
June16th to endNight
59%
540
24%
1620
15%
540
66%
540
50%
816
July1st to 15thNight
70%
510
18%
1530
16%
510
73%
510
42%
831
July16th to endNight
74%
564
26%
1594
25%
531
77%
531
46%
830
August1st to 15thNight
75%
539
23%
1610
27%
536
77%
536
41%
886
August16th to endNight
70%
573
26%
1777
27%
573
74%
573
41%
940
September1st to 15thNight
58%
540
24%
1980
23%
540
66%
540
32%
1081
September16th to endNight
55%
537
32%
1980
27%
537
66%
537
36%
991
October1st to 15thNight
47%
618
31%
2058
22%
618
55%
618
34%
1120
October16th to endNight
45%
768
37%
2304
17%
768
59%
768
49%
1115
November1st to 15thNight
42%
929
29%
2449
11%
929
53%
929
45%
1342
November16th to endNight
39%
975
32%
2535
13%
975
52%
975
42%
1450
December1st to 15thNight
37%
975
27%
2535
11%
975
48%
975
38%
1497
December16th to endNight
37%
984
30%
2559
14%
984
49%
984
34%
1596

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
9%5%2442445%7%51%
48767
Night
8%423323447%55%
48271
Cloud CoverDay
9%5%2432445%7%51%
48765
Night
8%423323347%55%
48271
TransparencyDay
31%5%12%26%19%4
48465
Night
28%411%26%21%5%
48076
SeeingDay
10%6%27%32%19%3
6119
Night
10%8%31%35%12%
16245

By Month

Percentage Cloud Cover SW (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
7%6%14322346%57%
1611
16th to endDay
8%5%2432325%8%53%
1728
February1st to 15thDay
7%8%35%423435%51%
1647
16th to endDay
7%6%1332335%7%54%
1580
March1st to 15thDay
10%6%24424446%47%
1935
16th to endDay
15%7%24323445%44%
2112
April1st to 15thDay
12%5%1442435%7%48%
2024
16th to endDay
16%6%246%23345%44%
2340
May1st to 15thDay
11%5%34423446%47%
2331
16th to endDay
11%6%245%345%5%7%42%
2430
June1st to 15thDay
7%324323448%54%
2340
16th to endDay
5%2133145%6%9%56%
2340
July1st to 15thDay
7%3144345%6%10%48%
2340
16th to endDay
4213435%5%6%9%52%
2466
August1st to 15thDay
5%324336%6%5%9%47%
2340
16th to endDay
6%3133245%5%8%53%
2423
September1st to 15thDay
8%425%325%447%50%
1980
16th to endDay
8%313324347%57%
1980
October1st to 15thDay
13%412223345%56%
1890
16th to endDay
6%423322336%60%
1920
November1st to 15thDay
7%313313447%59%
1736
16th to endDay
9%31331233463%
1755
December1st to 15thDay
11%6%23323445%52%
1755
16th to endDay
11%7%45%423345%47%
1764
January1st to 15thNight
7%423323436%57%
2327
16th to endNight
7%323313335%62%
2496
February1st to 15thNight
10%7%35%422346%50%
2216
16th to endNight
8%424323346%56%
1894
March1st to 15thNight
8%7%25%32445%6%51%
2025
16th to endNight
15%5%24422347%47%
2112
April1st to 15thNight
13%31342445%7%49%
1920
16th to endNight
14%5%1332445%6%47%
1620
May1st to 15thNight
13%424313347%50%
1619
16th to endNight
9%3243246%5%11%47%
1683
June1st to 15thNight
5%31331446%10%54%
1620
16th to endNight
41231346%10%60%
1620
July1st to 15thNight
5%2133245%8%9%52%
1620
16th to endNight
431332346%13%53%
1702
August1st to 15thNight
4113425%5%6%10%52%
1620
16th to endNight
431442445%7%57%
1777
September1st to 15thNight
7%425%433347%53%
1980
16th to endNight
6%31332346%7%56%
1980
October1st to 15thNight
10%5%24323235%56%
2058
16th to endNight
6%21221223469%
2304
November1st to 15thNight
6%313312447%61%
2449
16th to endNight
10%312223335%60%
2535
December1st to 15thNight
8%5%2322335%7%53%
2535
16th to endNight
11%6%24322336%50%
2559

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
7%6%13422346%57%
1611
16th to endDay
8%5%2332335%8%53%
1728
February1st to 15thDay
7%7%35%423436%50%
1647
16th to endDay
7%6%1332345%8%54%
1580
March1st to 15thDay
11%5%24334446%47%
1935
16th to endDay
15%8%24313445%44%
2110
April1st to 15thDay
12%5%1432445%7%48%
2024
16th to endDay
16%6%145%23445%44%
2340
May1st to 15thDay
11%6%25%423446%47%
2331
16th to endDay
11%6%25%5%3445%7%42%
2430
June1st to 15thDay
7%324423448%54%
2340
16th to endDay
5%2133145%6%9%56%
2340
July1st to 15thDay
7%3144345%6%9%48%
2340
16th to endDay
5%223425%5%6%9%52%
2466
August1st to 15thDay
5%315%346%6%5%9%47%
2340
16th to endDay
6%3143245%5%8%54%
2423
September1st to 15thDay
9%425%424447%49%
1980
16th to endDay
8%31432435%7%56%
1980
October1st to 15thDay
13%412223345%56%
1890
16th to endDay
6%423322345%61%
1920
November1st to 15thDay
7%313323447%59%
1736
16th to endDay
9%31321233463%
1755
December1st to 15thDay
11%5%23323445%52%
1755
16th to endDay
11%7%45%423345%47%
1764
January1st to 15thNight
7%423323346%57%
2327
16th to endNight
7%324313325%62%
2496
February1st to 15thNight
10%7%25%413346%50%
2216
16th to endNight
8%414314346%56%
1894
March1st to 15thNight
8%7%15%32445%6%50%
2025
16th to endNight
16%5%24423246%48%
2112
April1st to 15thNight
13%41242445%7%49%
1920
16th to endNight
14%5%2442435%6%47%
1620
May1st to 15thNight
13%5%24312346%51%
1619
16th to endNight
9%3143245%5%10%47%
1683
June1st to 15thNight
5%31231446%10%54%
1620
16th to endNight
41231346%10%60%
1620
July1st to 15thNight
5%2233245%7%9%53%
1620
16th to endNight
431232446%12%53%
1702
August1st to 15thNight
4113425%5%7%10%52%
1620
16th to endNight
43145%2446%7%57%
1777
September1st to 15thNight
7%425%434347%53%
1980
16th to endNight
6%31332345%7%56%
1980
October1st to 15thNight
11%5%24323235%56%
2058
16th to endNight
6%21221223469%
2304
November1st to 15thNight
6%313312447%61%
2449
16th to endNight
10%312223335%60%
2535
December1st to 15thNight
9%5%2322335%7%53%
2535
16th to endNight
11%6%24323336%50%
2559

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
28%312%31%21%2
1612
16th to endDay
29%314%30%18%3
1728
February1st to 15thDay
35%5%14%26%14%4
1648
16th to endDay
28%413%28%20%4
1580
March1st to 15thDay
36%410%22%20%4
1935
16th to endDay
40%5%10%24%15%2
2112
April1st to 15thDay
35%413%26%16%3
2024
16th to endDay
41%5%9%27%13%2
2340
May1st to 15thDay
36%6%10%21%22%2
2331
16th to endDay
39%6%13%25%12%2
2434
June1st to 15thDay
27%7%15%25%18%4
2340
16th to endDay
22%6%14%27%22%6%
2340
July1st to 15thDay
29%6%13%28%18%2
2201
16th to endDay
24%8%14%27%20%3
2311
August1st to 15thDay
29%8%16%24%16%4
2326
16th to endDay
27%7%13%27%18%6%
2423
September1st to 15thDay
33%6%10%25%15%8%
1980
16th to endDay
27%5%10%30%21%4
1980
October1st to 15thDay
30%49%23%26%6%
1890
16th to endDay
25%48%27%27%6%
1920
November1st to 15thDay
25%49%25%26%8%
1736
16th to endDay
24%38%29%26%5%
1755
December1st to 15thDay
32%5%11%31%17%1
1755
16th to endDay
39%310%26%16%3
1764
January1st to 15thNight
27%48%30%24%3
2327
16th to endNight
26%310%30%25%4
2496
February1st to 15thNight
35%413%25%16%4
2226
16th to endNight
28%411%27%19%7%
1894
March1st to 15thNight
33%49%23%20%7%
2025
16th to endNight
38%411%25%16%3
2112
April1st to 15thNight
32%6%10%24%22%4
1920
16th to endNight
36%5%13%20%19%4
1620
May1st to 15thNight
34%412%24%19%3
1620
16th to endNight
30%7%20%25%14%2
1685
June1st to 15thNight
24%5%17%28%19%3
1620
16th to endNight
18%6%13%31%23%7%
1620
July1st to 15thNight
23%7%13%27%24%3
1530
16th to endNight
22%5%14%29%24%3
1594
August1st to 15thNight
24%7%15%29%16%6%
1610
16th to endNight
24%6%12%26%22%6%
1777
September1st to 15thNight
31%5%10%25%17%9%
1980
16th to endNight
25%5%10%25%26%6%
1980
October1st to 15thNight
31%38%20%25%9%
2058
16th to endNight
19%37%28%33%8%
2304
November1st to 15thNight
23%411%24%27%9%
2449
16th to endNight
26%37%28%26%7%
2535
December1st to 15thNight
29%413%29%20%3
2535
16th to endNight
34%412%26%15%6%
2559

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
11%11%35%33%6%2
90
16th to endDay
15%10%43%28%11
96
February1st to 15thDay
5%17%50%20%6%
90
16th to endDay
7%11%48%24%7%1
81
March1st to 15thDay
7%17%48%21%4
90
16th to endDay
16%16%33%27%6%
96
April1st to 15thDay
13%13%37%27%8%
143
16th to endDay
21%10%39%20%6%1
450
May1st to 15thDay
12%10%35%27%10%2
468
16th to endDay
15%9%33%26%11%2
517
June1st to 15thDay
8%429%35%20%2
495
16th to endDay
6%224%42%21%3
495
July1st to 15thDay
8%215%41%28%4
475
16th to endDay
5%18%40%35%8%
515
August1st to 15thDay
7%11%43%31%4
493
16th to endDay
6%216%35%31%6%
463
September1st to 15thDay
217%44%29%5%
135
16th to endDay
12%32%24%20%9%
135
October1st to 15thDay
12%10%28%26%17%5%
135
16th to endDay
6%9%37%27%13%5%
144
November1st to 15thDay
13%7%25%32%14%5%
135
16th to endDay
15%21%30%22%10%
135
December1st to 15thDay
10%10%44%24%8%2
135
16th to endDay
16%12%39%24%6%
108
January1st to 15thNight
9%13%36%31%8%
900
16th to endNight
10%10%38%33%7%
960
February1st to 15thNight
13%11%37%34%3
818
16th to endNight
10%14%36%32%5%
632
March1st to 15thNight
12%10%38%31%6%
585
16th to endNight
16%13%36%28%5%
576
April1st to 15thNight
15%12%40%23%7%
539
16th to endNight
16%11%36%27%6%
540
May1st to 15thNight
14%8%36%29%10%1
540
16th to endNight
9%6%31%34%15%2
563
June1st to 15thNight
6%433%36%18%
540
16th to endNight
5%130%45%16%
540
July1st to 15thNight
5%116%53%20%1
510
16th to endNight
6%12%48%29%2
564
August1st to 15thNight
4111%53%28%1
539
16th to endNight
5%114%44%32%2
573
September1st to 15thNight
8%225%37%23%3
540
16th to endNight
9%5%26%35%21%1
537
October1st to 15thNight
13%5%31%27%18%2
618
16th to endNight
8%8%35%34%12%
768
November1st to 15thNight
8%9%36%32%12%
929
16th to endNight
12%11%33%32%9%
975
December1st to 15thNight
13%10%34%33%6%
975
16th to endNight
14%9%33%36%5%
984
Page generated at 2017-12-21 06:04:55. Version ac04

Copyright 2017 A. Danko


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