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 2005-11-05 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
34%
15683
21%
48382
10%
15644
46%
15644
22%
30126

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
19%
762
22%
2607
8%
761
36%
761
17%
1575
January16th to endNight
19%
768
23%
2496
8%
768
38%
768
18%
1540
February1st to 15thNight
21%
703
20%
2287
7%
701
38%
701
17%
1405
February16th to endNight
18%
631
26%
1893
7%
631
40%
631
21%
1159
March1st to 15thNight
25%
720
22%
2034
10%
720
38%
720
22%
1290
March16th to endNight
26%
768
21%
2067
7%
768
38%
768
22%
1382
April1st to 15thNight
26%
718
20%
1796
5%
718
35%
718
26%
1171
April16th to endNight
34%
720
20%
1800
5%
720
41%
720
27%
1171
May1st to 15thNight
32%
557
17%
1637
8%
557
39%
557
19%
1109
May16th to endNight
45%
374
17%
1497
13%
374
55%
374
18%
884
June1st to 15thNight
47%
360
19%
1440
19%
360
56%
360
22%
836
June16th to endNight
49%
360
17%
1440
15%
360
59%
360
21%
824
July1st to 15thNight
52%
340
13%
1360
15%
340
55%
340
18%
850
July16th to endNight
60%
507
17%
1538
14%
474
68%
474
31%
876
August1st to 15thNight
57%
554
18%
1624
13%
551
59%
551
28%
1016
August16th to endNight
59%
764
19%
1910
10%
764
61%
764
30%
1283
September1st to 15thNight
54%
720
24%
1800
14%
720
58%
720
33%
1193
September16th to endNight
51%
717
24%
1959
16%
717
57%
717
28%
1264
October1st to 15thNight
41%
720
22%
2160
18%
720
49%
720
24%
1372
October16th to endNight
35%
768
30%
2304
16%
768
53%
768
29%
1333
November1st to 15thNight
31%
760
23%
2445
12%
760
47%
760
23%
1479
November16th to endNight
27%
780
24%
2646
11%
780
45%
780
20%
1560
December1st to 15thNight
24%
780
18%
2730
5%
780
40%
780
14%
1733
December16th to endNight
19%
832
22%
2912
8%
832
37%
832
16%
1821

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
13%42442445%7%44%
48947
Night
14%5%2442445%7%44%
48564
Cloud CoverDay
13%5%2442445%8%44%
48957
Night
14%5%2442445%7%44%
48568
TransparencyDay
37%5%12%24%16%2
48647
Night
39%5%11%23%17%3
48382
SeeingDay
16%12%20%24%17%7%
6062
Night
15%21%22%25%13%1
15688

By Month

Percentage Cloud Cover NE (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
16%6%2442335%8%42%
1575
16th to endDay
15%6%24435%347%43%
1728
February1st to 15thDay
15%6%2442445%6%42%
1575
16th to endDay
14%8%34423445%42%
1578
March1st to 15thDay
14%6%24424445%45%
1912
16th to endDay
18%5%24424336%42%
2156
April1st to 15thDay
14%425%5%2345%6%45%
2152
16th to endDay
16%42342345%6%45%
2160
May1st to 15thDay
16%5%2442446%8%40%
2323
16th to endDay
13%414435%5%6%9%41%
2618
June1st to 15thDay
11%314425%5%8%9%43%
2520
16th to endDay
9%314435%5%6%10%45%
2520
July1st to 15thDay
8%315%436%6%7%9%41%
2520
16th to endDay
6%2135%36%6%9%11%42%
2520
August1st to 15thDay
10%4245%35%6%7%9%40%
2312
16th to endDay
11%3234245%6%9%45%
2292
September1st to 15thDay
12%4244245%6%7%46%
2160
16th to endDay
14%6%245%34446%44%
1998
October1st to 15thDay
19%42232235%6%47%
1800
16th to endDay
14%5%23413346%50%
1920
November1st to 15thDay
16%6%23323446%46%
1743
16th to endDay
14%5%23323446%47%
1641
December1st to 15thDay
16%5%2442345%6%44%
1560
16th to endDay
18%6%25%324446%40%
1664
January1st to 15thNight
17%424433447%43%
2607
16th to endNight
17%5%2442346%5%44%
2496
February1st to 15thNight
15%5%3442445%5%43%
2285
16th to endNight
15%7%23324346%46%
1893
March1st to 15thNight
16%6%24313447%46%
2022
16th to endNight
16%5%25%425%346%42%
2067
April1st to 15thNight
14%6%15%42445%7%44%
1796
16th to endNight
18%41332345%6%45%
1800
May1st to 15thNight
19%5%245%34348%38%
1637
16th to endNight
13%5%2442446%9%43%
1495
June1st to 15thNight
11%424425%45%9%45%
1440
16th to endNight
8%426%6%345%5%10%42%
1440
July1st to 15thNight
8%5%35%6%5%6%6%7%8%37%
1440
16th to endNight
6%313336%6%7%11%44%
1645
August1st to 15thNight
8%5%25%5%35%5%5%9%44%
1635
16th to endNight
11%4245%35%5%6%8%43%
1910
September1st to 15thNight
11%5%24434446%45%
1800
16th to endNight
13%5%245%2445%8%43%
1959
October1st to 15thNight
19%5%24423335%45%
2160
16th to endNight
14%313323346%52%
2304
November1st to 15thNight
15%5%24323335%49%
2445
16th to endNight
14%5%2442445%6%46%
2646
December1st to 15thNight
17%5%25%5%3446%6%39%
2730
16th to endNight
16%5%25%42445%6%42%
2912

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
16%6%2441335%8%42%
1575
16th to endDay
15%6%24425%347%43%
1728
February1st to 15thDay
15%6%2433446%6%42%
1575
16th to endDay
13%8%3442345%6%42%
1578
March1st to 15thDay
14%5%245%24446%45%
1923
16th to endDay
18%5%345%24336%42%
2155
April1st to 15thDay
14%4245%24446%45%
2152
16th to endDay
16%42332345%6%45%
2160
May1st to 15thDay
16%5%244245%6%8%40%
2323
16th to endDay
13%4134246%6%8%41%
2618
June1st to 15thDay
10%314425%5%8%9%43%
2520
16th to endDay
8%4144345%7%10%45%
2520
July1st to 15thDay
7%3145%36%7%7%10%42%
2520
16th to endDay
6%214426%7%8%13%42%
2520
August1st to 15thDay
10%425%5%35%6%7%9%40%
2312
16th to endDay
10%3144345%7%9%45%
2292
September1st to 15thDay
12%41442446%8%45%
2160
16th to endDay
14%6%245%335%45%44%
1998
October1st to 15thDay
19%41332235%6%48%
1800
16th to endDay
14%5%2332335%6%50%
1920
November1st to 15thDay
15%6%13324347%46%
1743
16th to endDay
14%5%233245%45%47%
1641
December1st to 15thDay
15%5%2432445%6%44%
1560
16th to endDay
18%6%24424446%40%
1664
January1st to 15thNight
16%424433447%43%
2607
16th to endNight
17%6%2442335%5%44%
2496
February1st to 15thNight
14%6%24434445%44%
2278
16th to endNight
15%7%24324346%46%
1893
March1st to 15thNight
15%5%24323447%45%
2034
16th to endNight
16%5%245%2435%6%42%
2067
April1st to 15thNight
14%5%2442345%7%44%
1796
16th to endNight
17%41423345%6%46%
1800
May1st to 15thNight
18%6%245%24447%39%
1636
16th to endNight
12%5%14325%36%9%42%
1495
June1st to 15thNight
11%435%425%45%9%45%
1440
16th to endNight
9%327%5%25%46%10%42%
1440
July1st to 15thNight
8%436%6%5%6%6%6%7%37%
1440
16th to endNight
7%312436%6%7%12%44%
1645
August1st to 15thNight
8%425%5%35%46%9%44%
1635
16th to endNight
11%425%5%25%5%5%7%43%
1910
September1st to 15thNight
11%5%245%2445%6%45%
1800
16th to endNight
13%5%245%2445%8%43%
1959
October1st to 15thNight
19%4235%23345%45%
2160
16th to endNight
14%313323346%52%
2304
November1st to 15thNight
15%5%24313435%49%
2445
16th to endNight
14%42442445%6%45%
2646
December1st to 15thNight
17%5%25%5%3446%6%39%
2730
16th to endNight
16%5%25%42445%6%41%
2912

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
40%314%23%13%4
1576
16th to endDay
41%411%24%13%4
1728
February1st to 15thDay
40%411%26%14%2
1577
16th to endDay
43%310%25%15%1
1578
March1st to 15thDay
39%5%11%24%15%3
1923
16th to endDay
44%310%20%18%2
2156
April1st to 15thDay
38%411%24%17%4
2152
16th to endDay
38%410%19%20%6%
2160
May1st to 15thDay
40%7%13%22%14%2
2323
16th to endDay
37%7%15%24%13%1
2622
June1st to 15thDay
34%9%14%26%14%1
2520
16th to endDay
33%8%15%22%18%1
2520
July1st to 15thDay
35%8%15%23%14%3
2371
16th to endDay
31%8%16%26%14%1
2364
August1st to 15thDay
38%7%13%24%16%1
2299
16th to endDay
33%7%14%24%16%3
2292
September1st to 15thDay
34%5%14%23%19%3
2160
16th to endDay
41%47%23%20%2
1998
October1st to 15thDay
37%310%27%18%3
1800
16th to endDay
35%38%28%22%2
1920
November1st to 15thDay
37%313%22%17%3
1743
16th to endDay
38%38%28%18%3
1641
December1st to 15thDay
39%5%14%25%12%3
1560
16th to endDay
44%311%25%13%
1664
January1st to 15thNight
40%310%21%18%4
2607
16th to endNight
40%410%26%17%1
2496
February1st to 15thNight
40%411%24%16%3
2287
16th to endNight
39%29%25%20%2
1893
March1st to 15thNight
38%411%26%15%2
2034
16th to endNight
42%5%10%20%17%3
2067
April1st to 15thNight
38%411%21%21%3
1796
16th to endNight
38%410%21%19%6%
1800
May1st to 15thNight
45%5%10%21%14%2
1637
16th to endNight
36%8%16%20%15%2
1497
June1st to 15thNight
36%6%12%26%16%1
1440
16th to endNight
36%6%13%23%17%2
1440
July1st to 15thNight
41%7%15%18%12%3
1360
16th to endNight
29%8%16%27%16%1
1538
August1st to 15thNight
35%7%14%23%18%1
1624
16th to endNight
38%7%10%24%16%3
1910
September1st to 15thNight
38%411%22%18%4
1800
16th to endNight
38%5%9%21%21%3
1959
October1st to 15thNight
41%49%23%18%3
2160
16th to endNight
32%48%28%21%3
2304
November1st to 15thNight
37%49%22%18%6%
2445
16th to endNight
37%49%23%20%4
2646
December1st to 15thNight
44%411%22%13%2
2730
16th to endNight
42%5%12%24%13%2
2912

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%13%39%15%8%1
92
16th to endDay
20%17%37%17%6%
96
February1st to 15thDay
25%11%41%15%6%
90
16th to endDay
17%18%39%21%2
237
March1st to 15thDay
18%21%25%24%9%
270
16th to endDay
21%18%27%24%43
288
April1st to 15thDay
15%18%31%22%9%2
270
16th to endDay
20%15%20%24%13%6%
270
May1st to 15thDay
25%18%25%15%10%4
288
16th to endDay
20%10%13%21%24%8%
331
June1st to 15thDay
11%13%17%22%24%11%
315
16th to endDay
10%12%15%33%21%6%
315
July1st to 15thDay
9%7%10%34%31%7%
305
16th to endDay
410%6%34%30%13%
326
August1st to 15thDay
15%6%9%28%27%13%
313
16th to endDay
8%5%9%27%32%16%
332
September1st to 15thDay
12%6%22%20%22%14%
315
16th to endDay
19%8%11%28%22%10%
314
October1st to 15thDay
22%8%14%25%20%7%
315
16th to endDay
13%11%30%25%13%5%
336
November1st to 15thDay
19%15%26%21%11%5%
287
16th to endDay
16%19%31%18%9%4
171
December1st to 15thDay
18%17%27%18%13%3
90
16th to endDay
30%8%34%22%4
96
January1st to 15thNight
15%29%28%20%5%
765
16th to endNight
19%27%29%22%1
768
February1st to 15thNight
16%27%29%23%2
704
16th to endNight
16%27%31%21%2
631
March1st to 15thNight
17%26%27%23%5%
720
16th to endNight
16%24%29%21%6%2
768
April1st to 15thNight
15%25%28%24%4
718
16th to endNight
16%20%24%25%11%1
720
May1st to 15thNight
19%22%19%23%12%1
557
16th to endNight
13%20%14%24%24%2
375
June1st to 15thNight
9%19%16%28%23%2
360
16th to endNight
6%19%14%39%19%1
360
July1st to 15thNight
7%13%13%30%31%2
340
16th to endNight
6%16%11%31%30%4
507
August1st to 15thNight
11%11%10%36%27%2
554
16th to endNight
11%9%8%32%31%6%
764
September1st to 15thNight
11%10%15%28%28%5%
720
16th to endNight
15%10%12%30%24%5%
717
October1st to 15thNight
21%13%17%24%19%3
720
16th to endNight
15%17%28%21%15%1
768
November1st to 15thNight
16%21%24%22%14%1
760
16th to endNight
14%27%25%23%7%
780
December1st to 15thNight
18%26%24%18%10%1
780
16th to endNight
18%26%31%20%3
832
Page generated at 2018-01-12 22:01:36. Version ac04

Copyright 2018 A. Danko


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