Astro Birdie Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astro Birdie Observatory clear sky chart from 2005-11-05 to 2018-01-12.

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
50%
15904
24%
48326
17%
15855
56%
15855
31%
28966

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
33%
956
23%
2472
9%
951
41%
951
28%
1625
January16th to endNight
31%
960
26%
2496
9%
960
40%
960
28%
1646
February1st to 15thNight
31%
782
24%
2185
9%
776
41%
776
25%
1415
February16th to endNight
23%
530
25%
1792
10%
530
37%
530
22%
1105
March1st to 15thNight
30%
540
25%
1980
14%
540
42%
540
21%
1231
March16th to endNight
35%
576
22%
2112
15%
576
44%
576
25%
1223
April1st to 15thNight
33%
539
21%
1943
14%
539
46%
539
25%
1140
April16th to endNight
34%
540
22%
1800
16%
540
45%
540
26%
1090
May1st to 15thNight
37%
539
19%
1690
14%
539
45%
539
27%
1039
May16th to endNight
53%
563
24%
1684
21%
561
61%
561
35%
978
June1st to 15thNight
75%
540
19%
1620
21%
540
79%
540
46%
849
June16th to endNight
74%
540
18%
1620
20%
540
77%
540
35%
958
July1st to 15thNight
78%
510
19%
1530
20%
510
80%
510
39%
862
July16th to endNight
82%
564
19%
1594
23%
531
84%
531
38%
911
August1st to 15thNight
89%
539
27%
1610
30%
536
89%
536
55%
771
August16th to endNight
75%
573
16%
1922
18%
573
77%
573
27%
1194
September1st to 15thNight
73%
540
17%
1980
19%
540
75%
540
28%
1149
September16th to endNight
71%
537
28%
1980
30%
537
73%
537
32%
1074
October1st to 15thNight
71%
658
32%
2098
29%
658
74%
658
43%
1062
October16th to endNight
57%
768
37%
2304
25%
768
65%
768
44%
1208
November1st to 15thNight
50%
760
26%
2280
18%
760
56%
760
33%
1344
November16th to endNight
46%
835
32%
2395
20%
835
55%
835
35%
1410
December1st to 15thNight
35%
975
24%
2535
12%
975
42%
975
25%
1751
December16th to endNight
32%
1040
19%
2704
8%
1040
38%
1040
22%
1931

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
12%5%25%5%35%5%5%7%39%
49000
Night
11%5%2442345%8%48%
48527
TransparencyDay
42%6%11%17%15%6%
48700
Night
34%5%13%20%17%9%
48332
SeeingDay
11%418%26%27%11%
5768
Night
14%6%23%32%19%2
15905

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
19%6%24323445%43%
1710
16th to endDay
19%6%24323335%44%
1728
February1st to 15thDay
18%6%34413335%44%
1683
16th to endDay
19%7%25%42233441%
1681
March1st to 15thDay
23%7%25%423345%37%
1980
16th to endDay
16%6%35%434346%41%
2110
April1st to 15thDay
15%7%35%6%2435%5%39%
2004
16th to endDay
13%7%26%5%35%5%5%7%37%
2160
May1st to 15thDay
11%7%36%6%46%5%5%6%34%
2257
16th to endDay
10%5%35%6%46%6%7%10%33%
2430
June1st to 15thDay
5%425%7%48%7%8%9%37%
2340
16th to endDay
6%437%8%5%9%7%8%11%27%
2340
July1st to 15thDay
9%436%7%5%7%7%7%10%31%
2340
16th to endDay
6%437%9%6%9%7%8%9%28%
2466
August1st to 15thDay
42145%47%6%7%10%43%
2340
16th to endDay
8%426%7%5%7%7%8%9%31%
2277
September1st to 15thDay
7%6%26%6%46%6%6%8%37%
1980
16th to endDay
7%425%5%5%6%5%6%8%40%
1980
October1st to 15thDay
8%425%434446%52%
1848
16th to endDay
10%41333233459%
1920
November1st to 15thDay
9%426%435%46%7%44%
1908
16th to endDay
13%5%24424335%50%
1891
December1st to 15thDay
17%8%36%6%34335%37%
1755
16th to endDay
20%10%25%5%23446%35%
1872
January1st to 15thNight
18%7%24312336%45%
2472
16th to endNight
18%6%24322346%45%
2496
February1st to 15thNight
16%7%145%23335%46%
2180
16th to endNight
16%6%25%423335%45%
1792
March1st to 15thNight
20%5%24423246%42%
1980
16th to endNight
11%7%34324346%48%
2112
April1st to 15thNight
10%6%25%5%2446%6%45%
1943
16th to endNight
13%6%2442335%8%45%
1800
May1st to 15thNight
10%5%245%345%6%10%41%
1689
16th to endNight
6%42342346%10%49%
1683
June1st to 15thNight
4123245%6%11%56%
1620
16th to endNight
4224425%6%8%12%46%
1620
July1st to 15thNight
5%42332446%12%51%
1620
16th to endNight
3122425%6%8%13%48%
1702
August1st to 15thNight
211132327%12%61%
1620
16th to endNight
7%2245%446%7%12%42%
1922
September1st to 15thNight
6%5%25%5%35%46%8%46%
1980
16th to endNight
7%415%42346%10%50%
1980
October1st to 15thNight
6%212313438%60%
2098
16th to endNight
9%31321233464%
2304
November1st to 15thNight
10%5%2342435%6%50%
2280
16th to endNight
12%423323335%54%
2395
December1st to 15thNight
17%6%35%424336%40%
2535
16th to endNight
18%10%36%423345%38%
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
42%37%14%21%10%
1711
16th to endDay
42%36%14%19%13%
1728
February1st to 15thDay
43%35%17%17%12%
1684
16th to endDay
46%47%12%18%10%
1681
March1st to 15thDay
48%38%12%19%7%
1980
16th to endDay
45%47%14%21%6%
2112
April1st to 15thDay
45%46%17%16%9%
2004
16th to endDay
44%5%10%16%16%7%
2160
May1st to 15thDay
48%7%9%14%12%7%
2257
16th to endDay
42%9%12%19%13%2
2434
June1st to 15thDay
38%9%14%20%15%1
2340
16th to endDay
47%10%15%17%8%
2340
July1st to 15thDay
43%9%17%19%8%
2201
16th to endDay
45%11%18%18%5%
2311
August1st to 15thDay
32%9%20%27%9%
2326
16th to endDay
44%12%17%17%5%2
2277
September1st to 15thDay
41%8%15%17%11%4
1980
16th to endDay
39%7%12%17%16%7%
1980
October1st to 15thDay
33%5%9%20%15%15%
1848
16th to endDay
28%35%13%30%18%
1920
November1st to 15thDay
37%6%11%17%18%8%
1908
16th to endDay
37%45%13%23%15%
1891
December1st to 15thDay
50%38%14%15%7%
1755
16th to endDay
50%47%15%14%6%
1872
January1st to 15thNight
41%26%16%20%12%
2472
16th to endNight
40%45%15%20%13%
2496
February1st to 15thNight
41%45%14%20%14%
2190
16th to endNight
42%37%15%17%14%
1792
March1st to 15thNight
43%37%14%19%10%
1980
16th to endNight
36%5%12%14%21%8%
2112
April1st to 15thNight
37%5%11%16%17%11%
1943
16th to endNight
38%5%11%18%17%8%
1800
May1st to 15thNight
37%6%13%19%14%8%
1690
16th to endNight
29%7%17%27%14%3
1685
June1st to 15thNight
20%7%20%28%21%1
1620
16th to endNight
26%11%19%29%11%
1620
July1st to 15thNight
24%9%28%28%9%
1530
16th to endNight
21%13%29%30%4
1594
August1st to 15thNight
15%5%27%39%11%
1610
16th to endNight
31%13%24%23%5%1
1922
September1st to 15thNight
32%8%23%19%11%5%
1980
16th to endNight
29%7%15%21%18%8%
1980
October1st to 15thNight
23%411%27%17%14%
2098
16th to endNight
25%25%15%28%22%
2304
November1st to 15thNight
33%413%20%19%8%
2280
16th to endNight
33%37%15%23%16%
2395
December1st to 15thNight
46%48%16%15%8%
2535
16th to endNight
48%46%13%15%10%
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
29%8%29%22%7%2
123
16th to endDay
19%15%41%14%8%
96
February1st to 15thDay
12%18%37%23%7%
90
16th to endDay
18%13%45%16%6%
81
March1st to 15thDay
30%16%33%13%6%
90
16th to endDay
15%11%31%27%14%
96
April1st to 15thDay
13%14%33%24%14%
123
16th to endDay
20%8%30%24%13%2
270
May1st to 15thDay
17%10%37%22%11%1
394
16th to endDay
12%5%29%31%17%3
517
June1st to 15thDay
6%13%40%30%8%
495
16th to endDay
9%111%31%31%14%
495
July1st to 15thDay
6%19%30%34%17%
475
16th to endDay
3424%46%21%
515
August1st to 15thDay
4322%49%19%
493
16th to endDay
13%415%38%26%
317
September1st to 15thDay
48%21%45%19%
135
16th to endDay
45%25%39%25%
135
October1st to 15thDay
211%36%36%14%
135
16th to endDay
16%6%18%23%27%7%
144
November1st to 15thDay
11%226%38%18%1
135
16th to endDay
10%11%33%28%9%7%
135
December1st to 15thDay
26%7%26%23%7%8%
135
16th to endDay
34%17%29%16%2
144
January1st to 15thNight
23%11%28%27%8%
956
16th to endNight
21%13%31%27%5%
960
February1st to 15thNight
21%13%29%29%6%
782
16th to endNight
20%13%39%22%4
530
March1st to 15thNight
24%8%34%28%5%
540
16th to endNight
13%11%36%29%8%
576
April1st to 15thNight
13%9%40%30%6%
539
16th to endNight
18%7%36%27%9%
540
May1st to 15thNight
13%7%36%32%8%
540
16th to endNight
8%230%37%19%1
563
June1st to 15thNight
4114%48%28%2
540
16th to endNight
3112%43%34%4
540
July1st to 15thNight
417%46%32%7%
510
16th to endNight
3438%47%5%
564
August1st to 15thNight
2247%41%6%
539
16th to endNight
7%434%47%6%
573
September1st to 15thNight
7%16%31%44%8%
540
16th to endNight
8%110%31%40%7%
537
October1st to 15thNight
6%214%39%31%5%
658
16th to endNight
10%5%24%32%24%2
768
November1st to 15thNight
10%6%28%32%20%1
760
16th to endNight
16%7%26%30%17%1
835
December1st to 15thNight
22%10%25%28%11%
975
16th to endNight
26%11%26%28%7%
1040
Page generated at 2018-01-12 21:01:26. Version ac04

Copyright 2018 A. Danko


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