AACC Astronomy Lab
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AACC Astronomy Lab clear sky chart from 2005-11-06 to 2024-03-01.

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
38%
23595
14%
80175
7%
23501
45%
23501
12%
58762

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 10thNight
18%
750
18%
4338
4%
737
32%
737
7%
2795
January11th to 20thNight
25%
760
21%
3982
5%
740
35%
740
7%
2544
January21st to endNight
22%
829
10%
4451
5%
814
35%
814
7%
3071
February1st to 10thNight
27%
760
14%
2470
6%
760
38%
760
12%
1822
February11th to 20thNight
16%
742
13%
2311
3%
740
29%
740
10%
1744
February21st to endNight
19%
628
16%
1884
4%
628
33%
628
12%
1413
March1st to 10thNight
26%
723
17%
2069
6%
723
38%
723
16%
1502
March11th to 20thNight
26%
720
14%
1980
6%
720
34%
720
12%
1542
March21st to endNight
25%
792
14%
2112
5%
792
33%
792
13%
1656
April1st to 10thNight
24%
720
12%
1800
2%
720
31%
720
13%
1408
April11th to 20thNight
36%
711
16%
1775
5%
711
40%
711
17%
1360
April21st to endNight
34%
720
15%
1800
4%
720
39%
720
17%
1377
May1st to 10thNight
38%
647
13%
1727
5%
647
42%
647
14%
1370
May11th to 20thNight
40%
364
14%
1425
10%
364
46%
364
9%
1090
May21st to endNight
55%
388
12%
1551
12%
388
59%
388
12%
1125
June1st to 10thNight
54%
360
14%
1440
16%
360
58%
360
14%
1022
June11th to 20thNight
53%
360
12%
1440
13%
360
57%
360
12%
1064
June21st to endNight
57%
360
12%
1440
11%
360
63%
360
12%
1047
July1st to 10thNight
61%
350
11%
1400
13%
350
62%
350
11%
1060
July11th to 20thNight
72%
350
11%
1394
14%
350
72%
350
12%
1001
July21st to endNight
65%
591
12%
1672
9%
558
68%
558
17%
1244
August1st to 10thNight
65%
537
12%
1600
9%
534
67%
534
16%
1223
August11th to 20thNight
58%
645
11%
1709
6%
645
60%
645
14%
1368
August21st to endNight
60%
792
9%
1980
5%
792
61%
792
16%
1598
September1st to 10thNight
56%
720
16%
1800
8%
720
60%
720
19%
1401
September11th to 20thNight
62%
720
20%
1800
13%
720
65%
720
20%
1371
September21st to endNight
43%
720
13%
2037
8%
720
48%
720
14%
1588
October1st to 10thNight
44%
720
13%
2160
11%
720
50%
720
15%
1623
October11th to 20thNight
42%
720
16%
2160
11%
720
49%
720
14%
1605
October21st to endNight
36%
792
17%
2376
9%
792
45%
792
13%
1777
November1st to 10thNight
39%
740
17%
2366
10%
740
49%
740
15%
1703
November11th to 20thNight
32%
760
16%
2470
10%
760
40%
760
11%
1857
November21st to endNight
32%
760
13%
2631
8%
760
41%
760
11%
1941
December1st to 10thNight
27%
760
14%
2660
4%
760
40%
760
10%
1975
December11th to 20thNight
24%
760
15%
3171
5%
759
35%
759
9%
2246
December21st to endNight
28%
824
9%
4794
4%
817
38%
817
6%
3229

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
14%5%25%5%345%6%8%44%
78503
Night
15%6%25%5%3445%7%44%
80905
TransparencyDay
26%36%8%16%11%2
78213
Night
27%35%8%16%12%2
80714
SeeingDay
17%8%25%27%17%6%
14034
Night
18%10%28%29%14%2
23626

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 10thDay
16%5%24423347%49%
2517
11th to 20thDay
15%11%46%434446%40%
2817
21st to endDay
18%7%35%435%447%40%
3124
February1st to 10thDay
15%6%25%5%45%46%7%41%
1710
11th to 20thDay
19%6%2443336%6%43%
1755
21st to endDay
18%8%35%5%33447%39%
1570
March1st to 10thDay
12%6%25%5%3445%7%49%
1894
11th to 20thDay
17%5%25%5%34447%43%
1980
21st to endDay
19%5%35%5%34447%40%
2242
April1st to 10thDay
13%5%244345%6%7%45%
2160
11th to 20thDay
12%435%5%2445%7%49%
2134
21st to endDay
17%5%24435%5%6%8%42%
2160
May1st to 10thDay
16%6%245%245%6%9%41%
2248
11th to 20thDay
18%5%24435%6%6%8%38%
2465
21st to endDay
14%5%245%345%6%9%42%
2725
June1st to 10thDay
11%425%435%5%8%10%43%
2520
11th to 20thDay
10%425%5%35%6%7%9%44%
2520
21st to endDay
9%314435%6%7%11%46%
2520
July1st to 10thDay
8%425%6%36%6%7%10%43%
2520
11th to 20thDay
5%2145%36%7%7%12%48%
2514
21st to endDay
9%415%5%37%7%8%12%38%
2547
August1st to 10thDay
8%5%26%6%46%7%8%10%40%
2327
11th to 20thDay
10%425%5%35%6%7%9%44%
2174
21st to endDay
11%4245%346%7%10%44%
2376
September1st to 10thDay
15%5%244245%6%8%46%
2160
11th to 20thDay
12%5%2443445%7%50%
2160
21st to endDay
18%6%25%5%345%6%6%40%
1917
October1st to 10thDay
17%5%2442345%7%48%
1800
11th to 20thDay
19%42332335%6%50%
1800
21st to endDay
15%6%2442345%6%49%
1980
November1st to 10thDay
13%6%13334347%53%
1711
11th to 20thDay
14%5%234345%5%6%49%
1710
21st to endDay
14%5%344345%5%6%48%
1544
December1st to 10thDay
16%6%2443446%7%43%
1520
11th to 20thDay
16%7%34424447%46%
1910
21st to endDay
17%7%25%5%45%446%40%
2772
January1st to 10thNight
16%7%25%5%35%446%44%
4429
11th to 20thNight
19%8%2442345%6%45%
4141
21st to endNight
19%9%35%5%23345%42%
4532
February1st to 10thNight
16%7%35%4345%5%6%41%
2470
11th to 20thNight
19%7%25%434446%44%
2309
21st to endNight
18%8%2442445%6%43%
1884
March1st to 10thNight
13%5%24424446%51%
2069
11th to 20thNight
17%6%25%43446%7%43%
1980
21st to endNight
16%6%35%6%3445%6%42%
2112
April1st to 10thNight
15%7%25%5%3445%7%42%
1800
11th to 20thNight
14%5%25%5%345%6%6%47%
1775
21st to endNight
19%425%33345%7%45%
1800
May1st to 10thNight
16%7%25%5%35%45%8%39%
1727
11th to 20thNight
18%5%26%5%25%5%6%7%38%
1425
21st to endNight
14%6%24435%47%11%41%
1550
June1st to 10thNight
11%435%5%35%45%10%45%
1440
11th to 20thNight
10%5%37%5%35%5%6%10%41%
1440
21st to endNight
11%335%5%35%5%7%11%42%
1440
July1st to 10thNight
9%426%6%5%6%5%8%9%39%
1440
11th to 20thNight
6%3345%45%7%8%10%44%
1442
21st to endNight
8%4345%36%6%7%11%42%
1771
August1st to 10thNight
9%5%25%6%46%6%7%10%41%
1611
11th to 20thNight
9%6%37%6%46%6%7%8%39%
1709
21st to endNight
12%5%35%5%35%6%5%9%43%
1980
September1st to 10thNight
15%6%35%5%3445%7%44%
1800
11th to 20thNight
10%5%25%5%2445%7%50%
1800
21st to endNight
18%7%25%5%3445%7%40%
2037
October1st to 10thNight
20%6%245%24446%44%
2160
11th to 20thNight
17%424423446%50%
2160
21st to endNight
17%5%24434447%48%
2376
November1st to 10thNight
12%6%25%423445%53%
2366
11th to 20thNight
17%5%24424346%49%
2470
21st to endNight
13%4245%2446%7%48%
2631
December1st to 10thNight
18%6%35%5%345%6%6%41%
2660
11th to 20thNight
17%425%5%3445%7%44%
3285
21st to endNight
16%6%35%5%35%5%7%8%38%
4884

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 10thDay
26%25%8%28%12%2
2518
11th to 20thDay
37%25%8%15%12%3
2817
21st to endDay
37%24%11%19%8%1
3124
February1st to 10thDay
26%35%8%19%11%1
1710
11th to 20thDay
28%35%7%17%12%1
1764
21st to endDay
31%34%9%13%10%3
1570
March1st to 10thDay
22%36%8%19%14%1
1894
11th to 20thDay
26%37%9%13%12%4
1980
21st to endDay
31%37%6%14%10%1
2242
April1st to 10thDay
23%37%10%14%11%4
2160
11th to 20thDay
24%36%6%14%14%5%
2134
21st to endDay
26%37%8%13%13%4
2160
May1st to 10thDay
25%39%9%14%12%2
2248
11th to 20thDay
28%40%8%11%11%2
2469
21st to endDay
24%40%8%17%10%1
2725
June1st to 10thDay
21%40%12%16%11%1
2520
11th to 20thDay
25%39%10%16%9%2
2520
21st to endDay
22%40%10%17%11%1
2520
July1st to 10thDay
23%41%9%16%9%2
2450
11th to 20thDay
20%41%10%18%9%2
2439
21st to endDay
24%42%11%13%10%1
2405
August1st to 10thDay
26%40%9%17%8%
2314
11th to 20thDay
25%38%9%15%12%1
2174
21st to endDay
28%39%9%14%7%3
2376
September1st to 10thDay
23%38%8%13%15%4
2160
11th to 20thDay
22%36%7%17%15%3
2160
21st to endDay
29%37%5%12%14%2
1917
October1st to 10thDay
25%36%7%15%15%2
1800
11th to 20thDay
25%37%6%17%14%2
1800
21st to endDay
26%37%5%16%14%1
1980
November1st to 10thDay
18%40%7%21%14%1
1711
11th to 20thDay
23%40%7%14%13%3
1710
21st to endDay
25%40%7%16%12%1
1544
December1st to 10thDay
23%40%10%17%8%1
1520
11th to 20thDay
29%32%6%23%9%1
1906
21st to endDay
34%27%12%18%9%
2772
January1st to 10thNight
32%25%9%22%11%1
4429
11th to 20thNight
31%25%8%20%14%2
4141
21st to endNight
39%23%6%21%11%1
4532
February1st to 10thNight
27%35%7%17%13%1
2470
11th to 20thNight
30%34%6%16%11%3
2311
21st to endNight
28%34%8%14%13%2
1884
March1st to 10thNight
21%36%7%20%14%2
2069
11th to 20thNight
28%37%8%12%11%3
1980
21st to endNight
29%36%7%13%10%4
2112
April1st to 10thNight
28%36%8%12%13%4
1800
11th to 20thNight
25%37%7%13%14%4
1775
21st to endNight
25%36%7%16%11%4
1800
May1st to 10thNight
28%38%7%14%9%3
1727
11th to 20thNight
30%39%6%10%13%2
1426
21st to endNight
22%41%11%14%10%2
1551
June1st to 10thNight
23%38%10%17%12%1
1440
11th to 20thNight
26%38%9%15%9%2
1440
21st to endNight
25%39%10%14%11%2
1440
July1st to 10thNight
26%41%11%14%7%2
1400
11th to 20thNight
22%41%10%15%10%2
1394
21st to endNight
21%40%11%18%10%
1672
August1st to 10thNight
24%40%11%16%9%
1600
11th to 20thNight
30%39%8%14%9%1
1709
21st to endNight
28%39%10%13%7%3
1980
September1st to 10thNight
26%37%6%13%14%5%
1800
11th to 20thNight
23%37%6%16%15%3
1800
21st to endNight
29%37%6%11%13%3
2037
October1st to 10thNight
26%36%6%16%14%2
2160
11th to 20thNight
26%36%7%17%12%2
2160
21st to endNight
25%38%6%15%15%2
2376
November1st to 10thNight
19%40%5%17%16%3
2366
11th to 20thNight
24%40%6%14%12%3
2470
21st to endNight
24%40%7%14%13%2
2631
December1st to 10thNight
24%40%7%16%11%1
2660
11th to 20thNight
28%33%7%15%14%3
3288
21st to endNight
33%28%14%17%8%1
4884

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 10thDay
23%15%37%17%8%1
180
11th to 20thDay
19%23%33%21%3
265
21st to endDay
21%16%39%18%6%1
297
February1st to 10thDay
21%10%44%17%8%
270
11th to 20thDay
28%15%40%14%3
362
21st to endDay
26%12%38%19%5%
382
March1st to 10thDay
16%20%35%22%6%
420
11th to 20thDay
21%15%33%23%7%2
420
21st to endDay
21%12%35%24%6%2
462
April1st to 10thDay
18%12%37%24%7%1
420
11th to 20thDay
15%12%33%24%11%5%
412
21st to endDay
22%10%30%27%10%1
420
May1st to 10thDay
23%8%29%27%11%2
423
11th to 20thDay
21%330%27%14%5%
447
21st to endDay
21%315%27%26%9%
485
June1st to 10thDay
14%421%28%25%9%
450
11th to 20thDay
14%419%31%24%8%
450
21st to endDay
11%316%36%25%8%
450
July1st to 10thDay
11%110%32%31%15%
445
11th to 20thDay
417%39%37%13%
444
21st to endDay
10%112%37%31%9%
488
August1st to 10thDay
11%110%34%33%12%
446
11th to 20thDay
12%111%31%32%12%
439
21st to endDay
11%116%31%27%15%
495
September1st to 10thDay
20%116%22%26%14%
450
11th to 20thDay
14%216%32%25%11%
450
21st to endDay
24%5%19%31%17%4
450
October1st to 10thDay
22%5%16%28%21%9%
450
11th to 20thDay
19%7%25%30%15%4
450
21st to endDay
17%9%32%28%11%3
495
November1st to 10thDay
17%9%32%23%12%6%
385
11th to 20thDay
15%15%34%25%9%2
370
21st to endDay
17%15%30%22%16%1
204
December1st to 10thDay
21%13%34%26%6%2
180
11th to 20thDay
21%16%31%24%9%
180
21st to endDay
24%9%29%28%9%1
198
January1st to 10thNight
19%17%39%21%4
760
11th to 20thNight
23%15%31%25%6%
760
21st to endNight
19%18%35%26%2
836
February1st to 10thNight
19%14%35%28%4
760
11th to 20thNight
24%17%37%20%2
743
21st to endNight
24%14%37%22%3
628
March1st to 10thNight
16%17%37%24%5%
723
11th to 20thNight
20%15%33%24%6%2
720
21st to endNight
19%12%38%25%6%1
792
April1st to 10thNight
20%16%36%22%6%
720
11th to 20thNight
16%11%32%30%10%1
711
21st to endNight
21%8%33%29%9%1
720
May1st to 10thNight
20%8%28%30%13%1
647
11th to 20thNight
18%8%24%34%14%1
364
21st to endNight
14%319%35%26%3
389
June1st to 10thNight
12%323%37%24%2
360
11th to 20thNight
10%5%23%39%22%2
360
21st to endNight
11%218%45%21%3
360
July1st to 10thNight
11%215%37%31%5%
350
11th to 20thNight
5%210%42%37%4
350
21st to endNight
9%116%40%30%4
591
August1st to 10thNight
10%211%42%32%3
537
11th to 20thNight
12%312%35%32%5%
645
21st to endNight
14%213%35%29%8%
792
September1st to 10thNight
17%314%32%28%6%
720
11th to 20thNight
12%214%36%30%6%
720
21st to endNight
20%5%20%33%20%3
720
October1st to 10thNight
22%5%21%26%21%5%
720
11th to 20thNight
19%9%25%29%16%1
720
21st to endNight
20%11%28%25%14%1
792
November1st to 10thNight
15%10%29%30%14%2
740
11th to 20thNight
19%15%28%27%10%
760
21st to endNight
16%14%33%27%9%1
760
December1st to 10thNight
22%15%31%22%9%1
760
11th to 20thNight
18%12%39%25%6%
760
21st to endNight
19%11%35%30%4
836
Page generated at 2024-02-27 06:30:17. Version ac07

Copyright © 2024 Attilla Danko.


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