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 2018-02-13.

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%
16676
19%
48734
15%
16636
65%
16636
27%
31652

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
45%
777
18%
2522
12%
776
54%
776
24%
1598
January16th to endNight
46%
832
24%
2704
18%
832
55%
832
27%
1655
February1st to 15thNight
50%
750
22%
2251
16%
747
58%
747
33%
1339
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
59%
768
22%
2304
20%
768
64%
768
27%
1471
November1st to 15thNight
61%
760
23%
2281
21%
760
66%
760
30%
1427
November16th to endNight
56%
780
26%
2340
22%
780
62%
780
28%
1485
December1st to 15thNight
56%
780
22%
2535
21%
780
62%
780
25%
1581
December16th to endNight
60%
832
22%
2704
22%
832
64%
832
29%
1617

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%
49280
Night
7%425%5%35%5%7%9%41%
48943
TransparencyDay
39%10%16%16%12%3
48981
Night
36%9%16%19%12%4
48746
SeeingDay
9%112%24%27%24%
6434
Night
9%215%28%31%11%
16685

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%6%26%6%35%6%6%7%36%
1746
16th to endDay
9%5%34435%448%45%
1872
February1st to 15thDay
8%6%26%5%25%5%5%7%43%
1864
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
10%5%245%45%5%6%9%38%
1920
November1st to 15thDay
5%436%6%36%6%6%9%41%
1907
16th to endDay
8%5%36%7%36%5%5%9%39%
1947
December1st to 15thDay
10%5%36%5%35%5%6%8%38%
1755
16th to endDay
7%4345%36%6%7%9%40%
1872
January1st to 15thNight
10%6%25%5%35%46%8%40%
2522
16th to endNight
10%5%25%425%46%7%44%
2704
February1st to 15thNight
10%5%2442345%6%50%
2251
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%42446%8%41%
2304
November1st to 15thNight
6%436%5%45%45%7%45%
2281
16th to endNight
8%425%5%35%5%5%9%42%
2340
December1st to 15thNight
7%435%6%35%5%6%8%42%
2535
16th to endNight
6%425%5%36%5%7%9%43%
2704

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
41%7%10%18%16%5%
1747
16th to endDay
37%48%19%22%8%
1872
February1st to 15thDay
36%5%12%16%20%9%
1866
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
38%5%11%14%22%8%
1920
November1st to 15thDay
33%7%12%22%18%5%
1907
16th to endDay
39%6%11%16%16%8%
1947
December1st to 15thDay
41%7%12%20%13%5%
1755
16th to endDay
34%7%17%20%13%6%
1872
January1st to 15thNight
40%6%12%19%14%6%
2522
16th to endNight
37%5%10%22%15%8%
2704
February1st to 15thNight
33%5%11%18%19%11%
2260
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%15%19%8%
2304
November1st to 15thNight
36%6%12%19%18%5%
2281
16th to endNight
37%7%10%19%17%8%
2340
December1st to 15thNight
37%7%13%22%11%7%
2535
16th to endNight
34%7%16%22%12%6%
2704

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
22%432%24%12%3
135
16th to endDay
10%9%35%27%15%1
144
February1st to 15thDay
3328%41%15%6%
126
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%119%32%28%7%
336
November1st to 15thDay
4114%38%29%10%
325
16th to endDay
10%120%38%24%4
327
December1st to 15thDay
8%5%22%41%20%2
135
16th to endDay
6%211%37%35%6%
144
January1st to 15thNight
14%6%25%29%20%3
780
16th to endNight
11%6%28%37%16%
832
February1st to 15thNight
11%5%26%37%18%1
753
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%214%27%32%7%
768
November1st to 15thNight
7%218%35%29%7%
760
16th to endNight
9%322%36%25%2
780
December1st to 15thNight
9%419%34%28%4
780
16th to endNight
7%320%33%29%4
832
Page generated at 2018-02-13 20:46:03. Version ac04

Copyright 2018 A. Danko


Lake Ahern Observatory Clear Sky Chart |Charts Home