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 2017-08-12.

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
44%
15729
26%
46551
15%
15684
54%
15684
37%
26163

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
14%
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
35%
585
25%
2025
15%
585
46%
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
74%
527
24%
1575
27%
524
76%
524
41%
868
August16th to endNight
69%
525
23%
1628
23%
525
72%
525
40%
872
September1st to 15thNight
56%
495
24%
1815
24%
495
65%
495
30%
1022
September16th to endNight
57%
492
31%
1815
28%
492
66%
492
36%
903
October1st to 15thNight
47%
566
32%
1886
24%
566
56%
566
34%
1019
October16th to endNight
45%
704
35%
2112
16%
704
59%
704
48%
1033
November1st to 15thNight
42%
856
31%
2256
12%
856
54%
856
46%
1224
November16th to endNight
39%
900
30%
2340
12%
900
51%
900
42%
1334
December1st to 15thNight
36%
900
26%
2340
11%
900
47%
900
37%
1403
December16th to endNight
38%
960
30%
2496
14%
960
49%
960
34%
1557

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%
47424
Night
8%423323347%54%
46747
Cloud CoverDay
9%5%2432445%7%51%
47422
Night
8%423323347%54%
46747
TransparencyDay
31%5%12%26%19%4
47122
Night
28%411%26%21%5%
46552
SeeingDay
10%6%27%33%18%3
5695
Night
10%8%31%35%12%
15732

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%324335%6%5%9%48%
2289
16th to endDay
6%3133246%5%8%53%
2220
September1st to 15thDay
9%5%25%425%447%47%
1815
16th to endDay
7%313324346%58%
1815
October1st to 15thDay
13%412223345%56%
1733
16th to endDay
6%5%23322346%59%
1760
November1st to 15thDay
6%223313446%61%
1600
16th to endDay
10%31221233462%
1620
December1st to 15thDay
12%6%23323445%50%
1620
16th to endDay
11%7%45%423345%47%
1728
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%7%10%52%
1585
16th to endNight
431442445%7%56%
1628
September1st to 15thNight
7%425%5%34347%50%
1815
16th to endNight
6%31432346%7%57%
1815
October1st to 15thNight
10%424223236%56%
1886
16th to endNight
7%21221223369%
2112
November1st to 15thNight
6%313212347%62%
2256
16th to endNight
10%312223335%60%
2340
December1st to 15thNight
9%6%2322335%7%52%
2340
16th to endNight
11%6%24322346%50%
2496

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%336%6%5%9%48%
2289
16th to endDay
6%3143245%5%8%53%
2220
September1st to 15thDay
9%5%25%425%447%47%
1815
16th to endDay
7%313324346%57%
1815
October1st to 15thDay
13%412224345%56%
1733
16th to endDay
6%5%23322345%60%
1760
November1st to 15thDay
5%323313446%61%
1600
16th to endDay
10%31321233462%
1620
December1st to 15thDay
12%6%32323445%50%
1620
16th to endDay
11%7%45%423345%47%
1728
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%9%52%
1585
16th to endNight
43145%2445%7%56%
1628
September1st to 15thNight
7%425%434447%50%
1815
16th to endNight
6%31332345%7%57%
1815
October1st to 15thNight
10%5%23223235%56%
1886
16th to endNight
7%21221223469%
2112
November1st to 15thNight
6%213312347%62%
2256
16th to endNight
10%312223335%60%
2340
December1st to 15thNight
9%6%2322335%7%52%
2340
16th to endNight
10%7%33323336%50%
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
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
28%8%16%24%16%5%
2275
16th to endDay
27%7%13%27%16%7%
2220
September1st to 15thDay
35%6%10%23%14%8%
1815
16th to endDay
26%5%10%29%23%4
1815
October1st to 15thDay
29%49%24%26%5%
1733
16th to endDay
25%48%28%26%5%
1760
November1st to 15thDay
24%49%25%27%9%
1600
16th to endDay
25%49%29%25%6%
1620
December1st to 15thDay
34%5%11%30%16%1
1620
16th to endDay
39%310%26%16%3
1728
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%14%29%16%6%
1575
16th to endNight
25%6%13%26%21%7%
1628
September1st to 15thNight
33%5%10%22%17%10%
1815
16th to endNight
24%5%10%24%28%6%
1815
October1st to 15thNight
31%39%21%25%9%
1886
16th to endNight
20%37%28%32%7%
2112
November1st to 15thNight
22%410%23%29%10%
2256
16th to endNight
26%37%28%25%7%
2340
December1st to 15thNight
30%413%30%19%2
2340
16th to endNight
34%412%26%15%6%
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
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
6%12%44%31%5%
474
16th to endDay
7%216%36%30%6%
388
September1st to 15thDay
4121%55%14%3
90
16th to endDay
11%128%23%22%13%
90
October1st to 15thDay
8%11%21%31%21%6%
90
16th to endDay
5%5%38%27%15%8%
96
November1st to 15thDay
5%327%35%18%8%
90
16th to endDay
21%21%32%17%7%
90
December1st to 15thDay
14%8%41%24%8%2
90
16th to endDay
17%13%38%22%7%
96
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%52%28%1
527
16th to endNight
6%114%43%31%3
525
September1st to 15thNight
9%225%37%22%3
495
16th to endNight
10%5%24%35%22%1
492
October1st to 15thNight
13%5%32%27%19%2
566
16th to endNight
8%8%35%34%12%
704
November1st to 15thNight
8%9%35%32%12%
856
16th to endNight
12%11%33%32%9%
900
December1st to 15thNight
14%10%34%33%6%
900
16th to endNight
14%9%33%36%5%
960
Page generated at 2017-08-13 13:16:32. Version ac04

Copyright 2017 A. Danko


Lake Afton Public Observatory Clear Sky Chart | Charts Home