Alpenglow Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alpenglow Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
52%
15775
22%
47003
18%
15739
56%
15739
30%
29093

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
44%
716
15%
2327
14%
716
48%
716
20%
1596
January16th to endNight
50%
768
18%
2496
19%
768
51%
768
22%
1662
February1st to 15thNight
47%
700
14%
2288
15%
700
49%
700
21%
1556
February16th to endNight
38%
632
18%
1909
14%
632
45%
632
22%
1309
March1st to 15thNight
45%
720
18%
2016
14%
720
51%
720
26%
1365
March16th to endNight
43%
768
18%
2112
12%
768
47%
768
25%
1455
April1st to 15thNight
43%
647
17%
1872
13%
647
45%
647
25%
1249
April16th to endNight
47%
540
23%
1620
15%
540
52%
540
27%
1038
May1st to 15thNight
50%
539
23%
1619
17%
539
54%
539
32%
955
May16th to endNight
56%
561
19%
1685
17%
561
57%
561
33%
998
June1st to 15thNight
58%
540
22%
1518
19%
540
62%
540
39%
843
June16th to endNight
66%
540
30%
1556
24%
540
74%
540
56%
736
July1st to 15thNight
63%
510
17%
1530
16%
510
66%
510
36%
863
July16th to endNight
69%
564
24%
1593
22%
531
70%
531
40%
883
August1st to 15thNight
65%
539
27%
1611
19%
536
70%
536
41%
863
August16th to endNight
70%
573
37%
1733
30%
573
75%
573
45%
899
September1st to 15thNight
70%
661
29%
1886
23%
661
75%
661
47%
1002
September16th to endNight
71%
656
35%
1815
28%
656
75%
656
51%
955
October1st to 15thNight
57%
660
29%
1925
21%
660
63%
660
37%
1105
October16th to endNight
58%
704
29%
2112
25%
704
62%
704
34%
1242
November1st to 15thNight
51%
700
24%
2275
21%
700
56%
700
29%
1358
November16th to endNight
48%
788
23%
2408
19%
788
52%
788
29%
1466
December1st to 15thNight
42%
900
12%
2520
9%
900
45%
900
24%
1756
December16th to endNight
34%
849
13%
2577
10%
849
38%
849
16%
1939

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%9%36%5%24446%44%
47600
Night
9%9%35%424446%45%
47198
TransparencyDay
39%38%19%18%10%
47295
Night
39%39%21%17%9%
47004
SeeingDay
13%14%34%27%9%1
5425
Night
12%6%19%33%22%4
15786

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
11%15%6%5%6%34446%30%
1611
16th to endDay
10%18%5%8%323246%33%
1728
February1st to 15thDay
13%14%6%9%5%23245%31%
1575
16th to endDay
8%19%7%9%4345%5%6%25%
1563
March1st to 15thDay
6%13%5%7%6%3444436%
1944
16th to endDay
10%15%5%8%5%3445%6%29%
2112
April1st to 15thDay
9%15%47%5%24446%35%
2075
16th to endDay
9%13%36%5%23446%39%
2340
May1st to 15thDay
8%8%36%5%25%46%9%40%
2331
16th to endDay
9%8%37%6%25%5%6%6%38%
2429
June1st to 15thDay
6%6%25%42445%6%51%
2433
16th to endDay
321221222473%
2394
July1st to 15thDay
33245%245%5%7%55%
2340
16th to endDay
5%3245%25%5%5%6%52%
2467
August1st to 15thDay
4314436%5%6%6%53%
2340
16th to endDay
442332445%7%58%
2468
September1st to 15thDay
4314324445%61%
1958
16th to endDay
7%213322345%62%
1815
October1st to 15thDay
9%8%45%433435%47%
1705
16th to endDay
9%8%34413447%48%
1757
November1st to 15thDay
13%11%35%42333445%
1584
16th to endDay
9%13%6%6%5%33326%38%
1537
December1st to 15thDay
14%13%48%7%23345%30%
1440
16th to endDay
13%18%7%9%6%2334425%
1654
January1st to 15thNight
11%14%36%5%23447%36%
2327
16th to endNight
10%15%46%423346%38%
2496
February1st to 15thNight
11%11%47%6%24436%35%
2277
16th to endNight
7%14%5%9%5%35%446%34%
1909
March1st to 15thNight
8%12%6%7%5%33446%38%
2016
16th to endNight
9%13%5%6%4245%5%6%35%
2112
April1st to 15thNight
11%12%46%424345%40%
1872
16th to endNight
9%11%35%434445%42%
1620
May1st to 15thNight
8%6%25%5%245%5%5%48%
1619
16th to endNight
11%6%26%5%2445%6%45%
1684
June1st to 15thNight
7%42442345%6%55%
1518
16th to endNight
221322235%5%68%
1556
July1st to 15thNight
5%435%5%2445%5%51%
1620
16th to endNight
44245%345%6%8%50%
1701
August1st to 15thNight
3315%435%5%5%7%54%
1620
16th to endNight
421443445%8%56%
1733
September1st to 15thNight
4323424335%61%
1886
16th to endNight
7%31321223467%
1815
October1st to 15thNight
8%5%34424335%54%
1925
16th to endNight
8%9%3332345%5%50%
2112
November1st to 15thNight
10%11%24323445%46%
2275
16th to endNight
9%10%44413445%44%
2408
December1st to 15thNight
13%13%46%424345%36%
2520
16th to endNight
16%15%5%10%6%23335%28%
2577

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
53%6%15%17%5%
1612
16th to endDay
52%5%13%16%9%2
1728
February1st to 15thDay
55%411%17%9%1
1575
16th to endDay
56%412%19%6%
1563
March1st to 15thDay
49%314%20%10%1
1944
16th to endDay
52%312%19%7%3
2112
April1st to 15thDay
49%210%21%13%2
2075
16th to endDay
44%29%24%16%1
2340
May1st to 15thDay
38%37%25%19%4
2331
16th to endDay
43%27%22%19%3
2432
June1st to 15thDay
31%3421%28%10%
2433
16th to endDay
17%1211%31%35%
2394
July1st to 15thDay
25%3414%23%28%
2201
16th to endDay
28%4411%22%28%
2312
August1st to 15thDay
26%4417%20%26%
2325
16th to endDay
23%3319%31%19%
2468
September1st to 15thDay
23%4417%30%20%
1958
16th to endDay
23%2423%32%14%
1815
October1st to 15thDay
39%27%26%20%3
1705
16th to endDay
34%39%30%19%1
1757
November1st to 15thDay
43%311%20%17%4
1584
16th to endDay
47%39%25%11%1
1537
December1st to 15thDay
54%416%18%5%
1440
16th to endDay
61%413%14%5%
1654
January1st to 15thNight
47%6%16%20%6%1
2327
16th to endNight
46%414%19%11%2
2496
February1st to 15thNight
48%412%19%13%
2288
16th to endNight
49%311%24%10%
1909
March1st to 15thNight
46%312%23%13%1
2016
16th to endNight
46%410%23%11%3
2112
April1st to 15thNight
46%210%21%16%3
1872
16th to endNight
42%39%23%19%1
1620
May1st to 15thNight
35%37%26%22%5%
1620
16th to endNight
37%19%28%18%4
1685
June1st to 15thNight
28%26%20%30%10%
1518
16th to endNight
17%2110%30%38%
1556
July1st to 15thNight
32%2413%16%30%
1530
16th to endNight
29%35%14%19%27%
1593
August1st to 15thNight
26%36%18%17%27%
1611
16th to endNight
25%2413%33%20%
1733
September1st to 15thNight
24%25%16%26%24%
1886
16th to endNight
23%1419%31%20%
1815
October1st to 15thNight
32%28%27%23%5%
1925
16th to endNight
34%36%25%26%3
2112
November1st to 15thNight
38%39%23%17%6%
2275
16th to endNight
39%212%26%15%3
2408
December1st to 15thNight
48%316%22%8%
2520
16th to endNight
59%312%17%6%
2577

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%7%22%28%14%
90
16th to endDay
23%6%26%27%14%2
96
February1st to 15thDay
27%322%24%18%3
90
16th to endDay
15%22%40%14%4
222
March1st to 15thDay
19%16%35%20%7%
270
16th to endDay
22%24%31%17%3
288
April1st to 15thDay
17%21%31%20%6%2
269
16th to endDay
28%20%27%19%3
270
May1st to 15thDay
13%25%35%20%4
288
16th to endDay
13%15%31%28%9%2
330
June1st to 15thDay
10%14%34%26%11%1
408
16th to endDay
411%35%36%10%2
369
July1st to 15thDay
410%36%35%10%2
305
16th to endDay
5%6%49%29%6%1
327
August1st to 15thDay
8%7%46%27%8%1
315
16th to endDay
5%7%35%37%11%2
332
September1st to 15thDay
6%12%36%30%11%2
294
16th to endDay
8%11%28%37%12%1
255
October1st to 15thDay
8%17%28%27%15%1
145
16th to endDay
17%19%25%25%11%1
96
November1st to 15thDay
17%8%18%26%21%6%
90
16th to endDay
21%21%31%20%42
90
December1st to 15thDay
25%16%35%17%4
90
16th to endDay
15%17%25%30%11%
96
January1st to 15thNight
16%6%23%28%20%5%
720
16th to endNight
16%8%17%31%19%6%
768
February1st to 15thNight
16%6%18%38%17%3
704
16th to endNight
13%10%28%30%15%2
632
March1st to 15thNight
14%8%23%33%15%4
720
16th to endNight
13%11%26%31%14%3
768
April1st to 15thNight
18%11%22%30%14%3
647
16th to endNight
15%8%21%34%16%2
540
May1st to 15thNight
11%5%24%37%18%2
540
16th to endNight
12%5%15%34%25%4
563
June1st to 15thNight
9%9%15%41%21%2
540
16th to endNight
4321%39%26%4
540
July1st to 15thNight
7%312%35%36%4
510
16th to endNight
5%112%37%39%3
564
August1st to 15thNight
6%318%40%30%1
539
16th to endNight
4214%38%34%5%
573
September1st to 15thNight
6%213%38%33%6%
661
16th to endNight
7%412%27%35%12%
656
October1st to 15thNight
10%420%30%27%6%
660
16th to endNight
13%5%16%32%24%6%
704
November1st to 15thNight
14%8%19%27%23%5%
700
16th to endNight
13%9%22%32%16%5%
788
December1st to 15thNight
19%8%25%31%14%1
900
16th to endNight
22%10%22%29%12%1
849
Page generated at 2017-09-11 17:35:30. Version ac04

Copyright 2017 A. Danko


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