Double AA Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Double AA 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
41%
16148
26%
48360
17%
16104
51%
16104
40%
26096

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%
954
27%
2472
11%
951
42%
951
40%
1420
January16th to endNight
33%
960
31%
2496
11%
960
46%
960
43%
1416
February1st to 15thNight
29%
744
25%
2152
10%
740
41%
740
36%
1218
February16th to endNight
21%
632
27%
1894
8%
632
36%
632
34%
1034
March1st to 15thNight
25%
561
25%
2001
13%
561
38%
561
27%
1121
March16th to endNight
29%
576
23%
2112
14%
576
42%
576
30%
1150
April1st to 15thNight
24%
539
21%
1977
11%
539
40%
539
30%
1059
April16th to endNight
26%
540
23%
1660
12%
540
41%
540
36%
907
May1st to 15thNight
27%
540
23%
1620
12%
540
43%
540
34%
943
May16th to endNight
39%
562
23%
1684
16%
561
51%
561
41%
930
June1st to 15thNight
51%
540
21%
1620
17%
540
59%
540
50%
805
June16th to endNight
58%
540
23%
1620
22%
540
63%
540
52%
801
July1st to 15thNight
67%
510
21%
1530
22%
510
70%
510
44%
813
July16th to endNight
71%
564
26%
1594
30%
531
77%
531
55%
749
August1st to 15thNight
79%
539
34%
1610
40%
536
80%
536
56%
760
August16th to endNight
72%
573
27%
1881
32%
573
74%
573
43%
957
September1st to 15thNight
59%
540
23%
1980
26%
540
62%
540
32%
1070
September16th to endNight
66%
537
29%
1980
30%
537
70%
537
39%
961
October1st to 15thNight
49%
597
33%
2037
26%
597
57%
597
42%
1016
October16th to endNight
46%
768
33%
2304
18%
768
56%
768
51%
1121
November1st to 15thNight
41%
842
27%
2362
13%
842
51%
842
46%
1242
November16th to endNight
30%
975
29%
2535
12%
975
41%
975
42%
1446
December1st to 15thNight
32%
975
27%
2535
11%
975
41%
975
40%
1492
December16th to endNight
26%
1040
23%
2704
9%
1040
36%
1040
35%
1665

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
21%313323345%47%
48976
Night
20%313212345%51%
48556
Cloud CoverDay
8%423324447%54%
48974
Night
7%313323347%59%
48556
TransparencyDay
30%5%10%23%23%7%
48674
Night
26%49%22%25%11%
48361
SeeingDay
9%5%23%32%22%6%
5985
Night
9%7%31%34%14%1
16151

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
24%413212125%50%
1710
16th to endDay
23%2332332450%
1728
February1st to 15thDay
23%41421222447%
1720
16th to endDay
26%5%1221113348%
1580
March1st to 15thDay
28%413313345%39%
1959
16th to endDay
24%5%1231333445%
2112
April1st to 15thDay
26%312212335%47%
1971
16th to endDay
24%413322335%45%
2295
May1st to 15thDay
26%42332233442%
2331
16th to endDay
23%3144245%5%7%37%
2430
June1st to 15thDay
21%213424445%45%
2340
16th to endDay
19%12322347%50%
2340
July1st to 15thDay
20%2134245%5%7%41%
2340
16th to endDay
20%1123245%48%45%
2466
August1st to 15thDay
11%2134345%7%7%50%
2340
16th to endDay
13%3135%245%5%8%45%
2318
September1st to 15thDay
19%313324447%46%
1980
16th to endDay
17%213313446%49%
1980
October1st to 15thDay
16%313222245%55%
1911
16th to endDay
13%21221223363%
1920
November1st to 15thDay
19%313212345%52%
1823
16th to endDay
22%3331122454%
1755
December1st to 15thDay
25%5%2441133442%
1755
16th to endDay
26%5%23312245%42%
1872
January1st to 15thNight
23%31232233449%
2472
16th to endNight
22%21221123356%
2496
February1st to 15thNight
23%41331122449%
2142
16th to endNight
23%41221212452%
1894
March1st to 15thNight
27%41332233343%
2001
16th to endNight
22%313312335%49%
2112
April1st to 15thNight
23%312322335%47%
1977
16th to endNight
23%213322235%48%
1660
May1st to 15thNight
23%213312335%49%
1619
16th to endNight
21%11221335%7%49%
1683
June1st to 15thNight
19%1221235%9%50%
1620
16th to endNight
18%11111347%56%
1620
July1st to 15thNight
19%21332335%8%48%
1620
16th to endNight
18%12212247%55%
1702
August1st to 15thNight
11%1221235%9%60%
1620
16th to endNight
12%21332245%10%51%
1881
September1st to 15thNight
17%41442235%5%49%
1980
16th to endNight
15%212223447%52%
1980
October1st to 15thNight
16%32212245%56%
2037
16th to endNight
14%2221123463%
2304
November1st to 15thNight
18%21321233456%
2362
16th to endNight
23%31231223451%
2535
December1st to 15thNight
25%412312235%45%
2535
16th to endNight
24%5%13222235%44%
2704

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
10%5%24312136%58%
1710
16th to endDay
10%323323335%58%
1728
February1st to 15thDay
10%425%212335%57%
1720
16th to endDay
13%6%2321223456%
1580
March1st to 15thDay
12%5%2432445%6%47%
1959
16th to endDay
11%6%24324345%50%
2110
April1st to 15thDay
10%423213346%56%
1971
16th to endDay
9%424324347%53%
2295
May1st to 15thDay
11%6%2442345%5%49%
2331
16th to endDay
8%435%5%35%5%6%8%44%
2430
June1st to 15thDay
5%313435%5%5%7%53%
2340
16th to endDay
4323425%45%8%56%
2340
July1st to 15thDay
5%324435%6%6%10%45%
2340
16th to endDay
4112435%5%6%10%53%
2466
August1st to 15thDay
2213435%6%7%8%54%
2340
16th to endDay
5%3146%25%5%6%9%49%
2318
September1st to 15thDay
12%32342445%8%48%
1980
16th to endDay
9%21331445%6%55%
1980
October1st to 15thDay
8%313323346%59%
1911
16th to endDay
5%21221223469%
1920
November1st to 15thDay
7%313222336%61%
1823
16th to endDay
8%31321223464%
1755
December1st to 15thDay
11%5%24322335%53%
1755
16th to endDay
14%6%3341225%6%49%
1872
January1st to 15thNight
8%413323345%58%
2472
16th to endNight
7%32332333462%
2496
February1st to 15thNight
9%5%24312335%58%
2142
16th to endNight
10%413322235%59%
1894
March1st to 15thNight
11%424323445%52%
2001
16th to endNight
8%5%13323346%55%
2112
April1st to 15thNight
7%42332345%7%54%
1977
16th to endNight
7%313323347%57%
1660
May1st to 15thNight
9%323423446%54%
1619
16th to endNight
5%11332446%8%57%
1683
June1st to 15thNight
311231336%11%60%
1620
16th to endNight
32132133410%64%
1620
July1st to 15thNight
321432447%10%54%
1620
16th to endNight
111232335%9%65%
1702
August1st to 15thNight
21321336%10%63%
1620
16th to endNight
42134235%6%11%54%
1881
September1st to 15thNight
10%41442335%6%52%
1980
16th to endNight
7%31332335%6%59%
1980
October1st to 15thNight
8%313212346%62%
2037
16th to endNight
6%21221223470%
2304
November1st to 15thNight
5%212223345%64%
2362
16th to endNight
9%313312335%62%
2535
December1st to 15thNight
10%5%13312336%57%
2535
16th to endNight
12%7%24223236%52%
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
30%28%21%29%7%
1711
16th to endDay
29%35%21%30%8%
1728
February1st to 15thDay
31%46%22%27%8%
1721
16th to endDay
32%26%20%26%11%
1580
March1st to 15thDay
35%5%9%18%20%9%
1959
16th to endDay
36%5%9%21%20%6%
2112
April1st to 15thDay
30%410%24%18%11%
1971
16th to endDay
32%5%9%22%22%7%
2295
May1st to 15thDay
37%6%9%18%21%6%
2331
16th to endDay
37%7%13%20%18%2
2434
June1st to 15thDay
29%5%14%24%22%3
2340
16th to endDay
26%6%13%26%22%4
2340
July1st to 15thDay
30%8%15%27%16%1
2201
16th to endDay
22%7%16%27%24%1
2311
August1st to 15thDay
23%8%14%25%24%3
2326
16th to endDay
29%7%13%28%16%4
2318
September1st to 15thDay
33%5%11%22%19%8%
1980
16th to endDay
28%5%8%25%22%9%
1980
October1st to 15thDay
26%410%22%23%12%
1911
16th to endDay
20%37%22%30%16%
1920
November1st to 15thDay
25%49%23%27%9%
1823
16th to endDay
25%26%20%31%13%
1755
December1st to 15thDay
34%27%23%25%6%
1755
16th to endDay
36%27%22%24%6%
1872
January1st to 15thNight
27%36%19%31%11%
2472
16th to endNight
26%26%18%32%13%
2496
February1st to 15thNight
31%27%21%24%13%
2152
16th to endNight
28%37%22%24%14%
1894
March1st to 15thNight
33%46%17%22%13%
2001
16th to endNight
30%6%11%22%23%6%
2112
April1st to 15thNight
29%6%10%19%19%14%
1977
16th to endNight
27%5%10%21%23%10%
1660
May1st to 15thNight
30%5%12%16%24%9%
1620
16th to endNight
24%7%15%27%21%4
1685
June1st to 15thNight
18%5%13%34%20%6%
1620
16th to endNight
17%5%13%27%28%7%
1620
July1st to 15thNight
23%6%11%32%22%3
1530
16th to endNight
16%416%28%30%3
1594
August1st to 15thNight
15%412%29%30%7%
1610
16th to endNight
23%5%11%28%23%6%
1881
September1st to 15thNight
30%5%11%20%22%9%
1980
16th to endNight
24%5%8%23%27%11%
1980
October1st to 15thNight
24%410%23%21%16%
2037
16th to endNight
19%26%18%31%21%
2304
November1st to 15thNight
21%410%23%25%15%
2362
16th to endNight
27%35%17%32%14%
2535
December1st to 15thNight
29%38%22%24%11%
2535
16th to endNight
34%27%20%25%9%
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
17%9%31%33%5%1
123
16th to endDay
9%9%47%23%8%1
96
February1st to 15thDay
6%11%48%24%8%
90
16th to endDay
12%9%50%20%6%
81
March1st to 15thDay
16%21%34%24%3
90
16th to endDay
8%14%39%29%6%2
96
April1st to 15thDay
17%14%26%34%6%
90
16th to endDay
11%15%41%21%7%1
405
May1st to 15thDay
13%10%40%26%8%1
468
16th to endDay
12%8%35%24%16%3
517
June1st to 15thDay
7%220%42%22%5%
495
16th to endDay
6%313%39%28%9%
495
July1st to 15thDay
5%113%40%31%8%
475
16th to endDay
4429%46%14%
515
August1st to 15thDay
46%37%40%9%
493
16th to endDay
8%110%37%33%8%
358
September1st to 15thDay
4226%47%19%
135
16th to endDay
9%5%39%30%14%
135
October1st to 15thDay
2221%35%27%10%
135
16th to endDay
8%8%24%38%18%2
144
November1st to 15thDay
17%5%28%31%12%5%
135
16th to endDay
14%12%40%22%8%
135
December1st to 15thDay
12%6%41%27%11%
135
16th to endDay
16%13%37%30%1
144
January1st to 15thNight
10%12%35%32%8%
956
16th to endNight
9%11%37%34%6%
960
February1st to 15thNight
12%12%38%31%5%
744
16th to endNight
14%15%43%23%2
632
March1st to 15thNight
12%12%40%30%4
561
16th to endNight
10%12%42%28%5%
576
April1st to 15thNight
10%12%47%26%3
539
16th to endNight
10%10%46%25%7%
540
May1st to 15thNight
11%8%43%26%8%1
540
16th to endNight
6%338%33%16%1
563
June1st to 15thNight
328%44%21%1
540
16th to endNight
3120%48%23%2
540
July1st to 15thNight
5%13%48%30%1
510
16th to endNight
36%46%39%3
564
August1st to 15thNight
25%52%34%4
539
16th to endNight
6%7%46%34%4
573
September1st to 15thNight
12%112%40%31%2
540
16th to endNight
8%13%43%29%3
537
October1st to 15thNight
11%228%34%20%2
597
16th to endNight
7%7%34%35%13%1
768
November1st to 15thNight
7%8%33%34%13%1
842
16th to endNight
11%10%38%28%10%
975
December1st to 15thNight
13%10%35%32%7%
975
16th to endNight
15%10%40%25%7%
1040
Page generated at 2018-01-12 21:01:33. Version ac04

Copyright 2018 A. Danko


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