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Lake Ahern Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Ahern Observatory clear sky chart from 2005-11-05 to 2017-10-16.

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
61%
16199
18%
47242
15%
16159
65%
16159
27%
30792

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
47%
717
18%
2327
13%
716
55%
716
24%
1471
January16th to endNight
46%
768
23%
2496
17%
768
55%
768
28%
1530
February1st to 15thNight
48%
701
23%
2106
16%
698
57%
698
33%
1245
February16th to endNight
50%
631
26%
1778
15%
631
61%
631
37%
1037
March1st to 15thNight
56%
720
29%
1980
18%
720
65%
720
40%
1134
March16th to endNight
60%
768
23%
2112
19%
768
64%
768
39%
1254
April1st to 15thNight
63%
718
22%
1973
19%
718
66%
718
41%
1141
April16th to endNight
66%
720
25%
1800
16%
720
69%
720
41%
1104
May1st to 15thNight
71%
656
23%
1736
17%
656
73%
656
39%
1052
May16th to endNight
74%
561
18%
1682
14%
561
75%
561
29%
1082
June1st to 15thNight
67%
540
12%
1620
10%
540
67%
540
21%
1151
June16th to endNight
73%
540
9%
1620
8%
540
73%
540
21%
1164
July1st to 15thNight
73%
510
6%
1530
5%
510
73%
510
19%
1123
July16th to endNight
76%
564
9%
1595
9%
531
77%
531
22%
1115
August1st to 15thNight
80%
548
8%
1618
8%
545
80%
545
25%
1110
August16th to endNight
66%
764
7%
2000
6%
764
66%
764
19%
1513
September1st to 15thNight
64%
720
6%
1980
5%
720
64%
720
15%
1523
September16th to endNight
62%
717
8%
1980
8%
717
62%
717
15%
1565
October1st to 15thNight
64%
720
20%
2089
21%
720
66%
720
25%
1411
October16th to endNight
60%
708
22%
2123
19%
708
64%
708
27%
1352
November1st to 15thNight
60%
700
25%
2101
22%
700
65%
700
30%
1314
November16th to endNight
53%
720
25%
2160
20%
720
60%
720
27%
1382
December1st to 15thNight
55%
720
22%
2340
21%
720
60%
720
24%
1493
December16th to endNight
57%
768
20%
2496
19%
768
62%
768
27%
1526

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
8%5%36%6%46%6%7%9%34%
48152
Night
7%425%5%35%5%7%9%41%
47451
TransparencyDay
40%10%16%16%12%3
47853
Night
36%9%16%19%12%4
47254
SeeingDay
9%111%23%28%25%
6032
Night
9%215%28%32%11%
16208

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
12%5%25%6%35%7%6%8%36%
1611
16th to endDay
10%43442445%8%46%
1728
February1st to 15thDay
9%6%26%5%25%45%6%44%
1744
16th to endDay
8%5%25%5%345%6%7%45%
1694
March1st to 15thDay
6%425%5%35%36%8%48%
1980
16th to endDay
7%4245%35%7%6%8%43%
2111
April1st to 15thDay
5%325%6%25%5%6%10%44%
1972
16th to endDay
6%325%5%46%6%6%9%42%
2160
May1st to 15thDay
6%4245%35%6%6%9%45%
2221
16th to endDay
8%436%7%5%8%7%6%8%32%
2431
June1st to 15thDay
11%6%37%6%5%7%7%8%11%23%
2340
16th to endDay
7%5%36%8%5%7%10%8%11%24%
2340
July1st to 15thDay
9%6%37%8%5%8%7%9%11%23%
2340
16th to endDay
9%5%47%7%5%8%9%8%9%23%
2465
August1st to 15thDay
5%436%7%5%9%9%10%11%25%
2318
16th to endDay
11%6%38%9%5%7%7%7%10%21%
2196
September1st to 15thDay
7%5%38%9%5%8%7%8%10%23%
1980
16th to endDay
9%7%48%8%6%8%8%8%10%18%
1980
October1st to 15thDay
9%6%27%8%5%7%6%8%9%28%
1869
16th to endDay
11%5%245%45%5%6%9%38%
1770
November1st to 15thDay
5%436%6%36%6%7%9%41%
1757
16th to endDay
9%5%36%7%36%5%6%9%37%
1797
December1st to 15thDay
11%5%46%6%35%5%6%8%36%
1620
16th to endDay
8%5%35%5%36%6%8%8%39%
1728
January1st to 15thNight
9%5%35%5%35%5%6%8%40%
2327
16th to endNight
10%5%25%425%46%7%44%
2496
February1st to 15thNight
10%5%24423346%51%
2106
16th to endNight
7%31432346%8%51%
1778
March1st to 15thNight
5%214425%45%7%55%
1980
16th to endNight
5%324435%5%6%8%51%
2112
April1st to 15thNight
5%32432446%8%54%
1973
16th to endNight
5%3134345%5%9%52%
1800
May1st to 15thNight
5%314425%45%8%53%
1736
16th to endNight
6%324435%7%8%12%40%
1682
June1st to 15thNight
9%7%36%5%37%7%8%13%28%
1620
16th to endNight
5%5%27%7%47%6%8%12%31%
1620
July1st to 15thNight
7%5%36%6%5%6%7%9%10%31%
1620
16th to endNight
6%425%6%37%6%8%13%34%
1703
August1st to 15thNight
4325%5%47%8%11%12%35%
1629
16th to endNight
8%6%36%7%47%7%8%11%28%
2000
September1st to 15thNight
7%5%37%8%47%8%8%11%26%
1980
16th to endNight
9%7%39%8%5%7%7%8%10%22%
1980
October1st to 15thNight
8%6%27%5%35%6%7%8%38%
2089
16th to endNight
10%6%25%425%46%9%41%
2123
November1st to 15thNight
6%436%5%45%45%7%45%
2101
16th to endNight
8%5%25%5%35%5%5%9%41%
2160
December1st to 15thNight
8%435%7%35%5%7%8%40%
2340
16th to endNight
7%435%5%36%5%7%9%41%
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%7%11%18%15%5%
1612
16th to endDay
36%48%18%22%8%
1728
February1st to 15thDay
36%410%16%21%10%
1746
16th to endDay
34%6%13%17%20%7%
1694
March1st to 15thDay
30%6%13%26%17%5%
1980
16th to endDay
32%8%14%18%20%5%
2112
April1st to 15thDay
30%8%15%22%18%4
1972
16th to endDay
33%7%13%19%20%5%
2160
May1st to 15thDay
31%7%13%22%18%6%
2221
16th to endDay
41%11%13%19%12%1
2435
June1st to 15thDay
46%12%20%16%3
2340
16th to endDay
44%15%23%12%3
2340
July1st to 15thDay
45%17%23%11%1
2201
16th to endDay
46%15%23%12%1
2310
August1st to 15thDay
39%18%30%10%
2305
16th to endDay
47%17%23%9%1
2196
September1st to 15thDay
47%16%20%11%2
1980
16th to endDay
51%14%19%9%4
1980
October1st to 15thDay
45%9%13%15%13%3
1869
16th to endDay
39%5%12%14%22%6%
1770
November1st to 15thDay
33%6%11%22%19%6%
1757
16th to endDay
40%6%11%15%16%9%
1797
December1st to 15thDay
43%6%12%18%14%4
1620
16th to endDay
36%7%16%19%13%6%
1728
January1st to 15thNight
39%7%13%19%14%6%
2327
16th to endNight
37%5%10%21%16%8%
2496
February1st to 15thNight
33%410%18%20%12%
2115
16th to endNight
28%6%14%20%21%7%
1778
March1st to 15thNight
26%6%12%29%19%5%
1980
16th to endNight
27%7%14%23%18%8%
2112
April1st to 15thNight
26%7%16%24%18%6%
1973
16th to endNight
27%7%14%22%21%5%
1800
May1st to 15thNight
29%7%13%24%18%7%
1737
16th to endNight
32%13%17%21%14%
1684
June1st to 15thNight
44%11%20%18%4
1620
16th to endNight
41%14%22%17%3
1620
July1st to 15thNight
42%16%24%14%1
1530
16th to endNight
36%17%27%16%
1595
August1st to 15thNight
32%18%34%13%
1618
16th to endNight
44%16%25%12%
2000
September1st to 15thNight
45%19%19%12%3
1980
16th to endNight
51%15%16%11%31
1980
October1st to 15thNight
41%9%12%17%15%4
2089
16th to endNight
38%7%10%16%20%7%
2123
November1st to 15thNight
36%6%11%18%19%5%
2101
16th to endNight
39%6%10%17%16%9%
2160
December1st to 15thNight
39%7%12%22%11%5%
2340
16th to endNight
36%7%16%19%12%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
21%425%25%17%5%
90
16th to endDay
14%12%31%18%20%2
96
February1st to 15thDay
4432%34%16%7%
90
16th to endDay
11%426%39%16%1
195
March1st to 15thDay
9%423%38%19%4
270
16th to endDay
9%320%29%30%6%
288
April1st to 15thDay
4223%33%26%8%
270
16th to endDay
6%114%31%32%14%
270
May1st to 15thDay
7%10%32%29%18%
288
16th to endDay
8%16%20%32%30%
331
June1st to 15thDay
13%420%25%35%
315
16th to endDay
5%211%29%50%
315
July1st to 15thDay
5%1431%55%
305
16th to endDay
8%311%28%47%
326
August1st to 15thDay
6%210%30%49%
313
16th to endDay
12%39%25%48%
332
September1st to 15thDay
10%15%13%27%42%
315
16th to endDay
11%411%36%35%
314
October1st to 15thDay
14%9%26%35%12%
315
16th to endDay
10%118%27%32%9%
276
November1st to 15thDay
4115%36%30%11%
265
16th to endDay
10%123%33%25%5%
267
December1st to 15thDay
11%423%42%16%2
90
16th to endDay
7%413%33%37%4
96
January1st to 15thNight
13%6%25%28%21%4
720
16th to endNight
11%6%27%36%16%
768
February1st to 15thNight
11%5%27%37%16%1
704
16th to endNight
10%329%39%16%
631
March1st to 15thNight
6%428%40%18%2
720
16th to endNight
6%322%38%26%2
768
April1st to 15thNight
5%221%40%26%2
718
16th to endNight
7%217%42%27%3
720
May1st to 15thNight
8%110%41%34%3
657
16th to endNight
6%8%26%43%14%
563
June1st to 15thNight
13%1419%44%17%
540
16th to endNight
6%312%43%32%
540
July1st to 15thNight
8%29%44%33%
510
16th to endNight
6%117%45%37%
564
August1st to 15thNight
428%47%37%
548
16th to endNight
11%411%41%30%
764
September1st to 15thNight
10%415%43%25%
720
16th to endNight
14%1416%42%21%
717
October1st to 15thNight
11%18%27%41%9%
720
16th to endNight
14%213%25%34%8%
708
November1st to 15thNight
7%218%35%28%7%
700
16th to endNight
10%324%34%24%3
720
December1st to 15thNight
9%419%35%26%4
720
16th to endNight
8%422%33%28%3
768
Page generated at 2017-10-17 16:35:31. Version ac04

Copyright 2017 A. Danko


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