Star
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Star clear sky chart from 2005-11-06 to 2024-02-15.

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
49%
23793
22%
79518
17%
23684
56%
23684
27%
47935

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
28%
945
22%
3997
8%
926
39%
926
18%
2399
January11th to 20thNight
28%
949
27%
3941
9%
930
37%
930
17%
2294
January21st to endNight
25%
946
18%
4285
9%
929
37%
929
15%
2698
February1st to 10thNight
28%
760
23%
2280
10%
760
38%
760
22%
1519
February11th to 20thNight
28%
722
21%
2154
10%
719
36%
719
23%
1391
February21st to endNight
18%
592
20%
1776
7%
592
29%
592
18%
1234
March1st to 10thNight
32%
680
23%
2120
12%
680
41%
680
26%
1316
March11th to 20thNight
30%
540
19%
1980
13%
540
40%
540
21%
1252
March21st to endNight
33%
594
24%
2062
15%
594
45%
594
26%
1193
April1st to 10thNight
37%
540
25%
1800
17%
540
49%
540
26%
1081
April11th to 20thNight
36%
533
24%
1775
16%
533
49%
533
28%
1043
April21st to endNight
46%
540
28%
1800
22%
540
58%
540
36%
963
May1st to 10thNight
52%
540
25%
1800
19%
540
63%
540
36%
971
May11th to 20thNight
55%
531
19%
1769
19%
531
60%
531
31%
1026
May21st to endNight
67%
584
21%
1823
20%
582
71%
582
35%
1064
June1st to 10thNight
66%
540
18%
1512
16%
540
68%
540
30%
976
June11th to 20thNight
78%
540
21%
1440
19%
540
79%
540
41%
862
June21st to endNight
73%
540
20%
1455
18%
540
74%
540
36%
905
July1st to 10thNight
74%
525
14%
1575
15%
525
75%
525
29%
1004
July11th to 20thNight
75%
522
15%
1566
17%
522
76%
522
28%
990
July21st to endNight
79%
591
15%
1787
18%
558
80%
558
31%
1084
August1st to 10thNight
84%
537
14%
1778
18%
534
84%
534
33%
1013
August11th to 20thNight
74%
534
17%
1776
19%
534
75%
534
26%
1110
August21st to endNight
70%
594
18%
1980
21%
594
70%
594
25%
1279
September1st to 10thNight
72%
540
23%
1800
25%
540
74%
540
27%
1114
September11th to 20thNight
69%
576
25%
1836
25%
576
70%
576
31%
1107
September21st to endNight
68%
720
29%
1980
25%
720
69%
720
39%
1168
October1st to 10thNight
67%
720
30%
2063
24%
720
70%
720
44%
1116
October11th to 20thNight
55%
720
33%
2160
25%
720
62%
720
36%
1229
October21st to endNight
51%
792
31%
2376
25%
792
57%
792
35%
1373
November1st to 10thNight
57%
740
31%
2224
24%
740
64%
740
38%
1221
November11th to 20thNight
46%
760
29%
2470
23%
760
56%
760
33%
1374
November21st to endNight
41%
760
26%
2470
19%
760
51%
760
29%
1452
December1st to 10thNight
36%
760
24%
2470
16%
760
47%
760
24%
1549
December11th to 20thNight
33%
758
23%
2903
15%
758
43%
758
20%
1806
December21st to endNight
27%
1028
13%
4535
9%
1015
34%
1015
14%
2759

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%6%35%6%35%5%6%7%42%
78647
Night
13%6%2443445%7%47%
80433
TransparencyDay
40%8%11%18%18%6%
78379
Night
36%7%11%18%20%8%
80222
SeeingDay
14%9%21%25%22%10%
13939
Night
14%8%23%30%21%4
23812

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%13%25%423446%41%
2847
11th to 20thDay
16%6%25%423346%48%
2850
21st to endDay
23%9%34423445%41%
3272
February1st to 10thDay
17%10%45%5%33345%40%
1900
11th to 20thDay
21%7%35%5%33345%41%
1788
21st to endDay
18%8%47%5%34445%39%
1480
March1st to 10thDay
17%7%27%5%34447%40%
1854
11th to 20thDay
16%6%36%6%35%5%5%7%37%
1980
21st to endDay
12%7%36%5%45%5%5%6%42%
2292
April1st to 10thDay
11%6%25%5%35%5%6%6%45%
2160
11th to 20thDay
15%6%36%5%3435%7%42%
2134
21st to endDay
8%5%26%5%35%5%6%8%47%
2160
May1st to 10thDay
11%5%25%6%36%5%5%7%44%
2160
11th to 20thDay
9%6%36%6%46%6%6%7%42%
2124
21st to endDay
8%5%26%6%46%6%7%9%41%
2448
June1st to 10thDay
10%5%26%8%47%7%7%10%35%
2442
11th to 20thDay
5%436%7%47%7%8%10%39%
2520
21st to endDay
7%427%7%49%7%8%9%36%
2497
July1st to 10thDay
7%5%37%8%5%8%8%9%9%31%
2340
11th to 20thDay
8%5%27%8%5%8%8%9%11%30%
2340
21st to endDay
8%436%8%5%8%7%9%10%31%
2423
August1st to 10thDay
5%5%26%7%49%7%8%10%38%
2148
11th to 20thDay
8%6%37%8%47%7%7%10%32%
2125
21st to endDay
12%5%36%6%46%6%7%9%35%
2376
September1st to 10thDay
8%5%25%7%5%6%7%6%8%40%
2160
11th to 20thDay
13%6%35%6%35%5%5%7%43%
2104
21st to endDay
11%42442445%8%53%
1980
October1st to 10thDay
7%4145%2445%6%56%
1891
11th to 20thDay
10%425%423447%53%
1800
21st to endDay
13%5%24423345%56%
1980
November1st to 10thDay
10%425%424446%55%
1852
11th to 20thDay
12%7%24423445%53%
1710
21st to endDay
16%6%25%424345%48%
1710
December1st to 10thDay
16%8%35%42445%7%43%
1710
11th to 20thDay
14%10%46%6%34335%42%
2153
21st to endDay
15%6%35%5%345%5%7%42%
2937
January1st to 10thNight
17%11%24324445%44%
4108
11th to 20thNight
17%7%35%42333449%
4120
21st to endNight
26%9%3431323443%
4373
February1st to 10thNight
16%9%45%5%33446%41%
2280
11th to 20thNight
21%7%33423345%45%
2153
21st to endNight
21%8%35%5%3435%6%37%
1776
March1st to 10thNight
15%8%2443345%6%46%
2120
11th to 20thNight
14%5%46%5%35%5%6%8%40%
1980
21st to endNight
13%425%5%345%5%8%47%
2062
April1st to 10thNight
12%5%25%5%35%46%7%47%
1800
11th to 20thNight
13%5%2443446%9%46%
1775
21st to endNight
7%434435%45%9%53%
1800
May1st to 10thNight
8%42442446%10%53%
1800
11th to 20thNight
7%5%35%435%5%6%10%47%
1769
21st to endNight
6%425%435%5%8%11%48%
1823
June1st to 10thNight
7%5%35%6%35%6%6%11%42%
1512
11th to 20thNight
33335%35%7%6%11%51%
1440
21st to endNight
5%4245%35%6%8%12%45%
1455
July1st to 10thNight
5%436%6%36%48%12%43%
1620
11th to 20thNight
5%325%6%35%7%8%12%43%
1620
21st to endNight
4325%5%46%6%8%13%44%
1892
August1st to 10thNight
32245%35%8%8%13%47%
1790
11th to 20thNight
6%5%25%5%36%5%8%12%43%
1776
21st to endNight
10%435%6%45%5%6%10%42%
1980
September1st to 10thNight
7%435%5%46%6%6%8%45%
1800
11th to 20thNight
8%6%25%5%35%5%6%7%48%
1836
21st to endNight
8%425%43445%8%53%
1980
October1st to 10thNight
6%2145%2335%6%61%
2063
11th to 20thNight
10%5%24424446%55%
2160
21st to endNight
14%6%2442333456%
2376
November1st to 10thNight
11%42332335%6%58%
2224
11th to 20thNight
12%5%24424445%54%
2470
21st to endNight
14%6%2443435%6%49%
2470
December1st to 10thNight
17%7%35%5%2445%6%44%
2470
11th to 20thNight
15%7%35%5%34345%45%
3042
21st to endNight
18%11%25%5%33336%41%
4718

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
44%4418%24%6%
2848
11th to 20thDay
36%5%7%22%23%7%
2850
21st to endDay
47%46%14%23%7%
3272
February1st to 10thDay
48%5%7%14%16%10%
1900
11th to 20thDay
45%5%6%16%20%8%
1798
21st to endDay
47%6%8%13%17%9%
1480
March1st to 10thDay
45%5%8%14%18%9%
1854
11th to 20thDay
46%6%9%14%18%7%
1980
21st to endDay
40%6%10%18%20%5%
2292
April1st to 10thDay
37%6%11%20%18%7%
2160
11th to 20thDay
42%5%8%17%21%7%
2134
21st to endDay
33%8%10%22%24%3
2160
May1st to 10thDay
39%7%11%18%21%5%
2160
11th to 20thDay
39%8%14%23%14%1
2128
21st to endDay
37%9%16%22%15%1
2448
June1st to 10thDay
42%11%14%20%11%2
2442
11th to 20thDay
37%11%16%21%12%3
2520
21st to endDay
39%13%17%19%11%1
2497
July1st to 10thDay
45%13%18%16%7%1
2276
11th to 20thDay
41%17%21%14%5%1
2271
21st to endDay
42%13%17%18%8%1
2288
August1st to 10thDay
37%12%22%20%8%
2136
11th to 20thDay
43%14%16%16%8%3
2125
21st to endDay
44%11%15%16%10%4
2376
September1st to 10thDay
38%12%14%16%15%5%
2160
11th to 20thDay
40%9%10%14%19%8%
2104
21st to endDay
31%6%12%23%19%9%
1980
October1st to 10thDay
28%6%10%19%26%11%
1891
11th to 20thDay
31%5%7%17%27%12%
1800
21st to endDay
31%46%16%30%13%
1980
November1st to 10thDay
32%6%6%16%29%11%
1852
11th to 20thDay
34%47%15%27%14%
1710
21st to endDay
38%48%17%23%10%
1710
December1st to 10thDay
41%7%9%17%18%9%
1710
11th to 20thDay
46%47%13%24%7%
2150
21st to endDay
39%6%8%20%24%3
2937
January1st to 10thNight
42%46%14%25%9%
4108
11th to 20thNight
39%5%6%18%21%11%
4120
21st to endNight
47%3416%23%6%
4373
February1st to 10thNight
45%5%7%15%19%9%
2280
11th to 20thNight
43%46%15%22%9%
2154
21st to endNight
49%5%7%12%15%12%
1776
March1st to 10thNight
38%6%8%16%21%12%
2120
11th to 20thNight
41%7%12%15%17%7%
1980
21st to endNight
35%6%11%19%23%6%
2062
April1st to 10thNight
35%8%11%19%19%9%
1800
11th to 20thNight
34%6%11%21%20%9%
1775
21st to endNight
27%6%11%23%27%6%
1800
May1st to 10thNight
27%7%11%26%22%7%
1800
11th to 20thNight
31%9%17%23%18%2
1770
21st to endNight
28%9%18%23%19%2
1824
June1st to 10thNight
35%10%16%23%14%1
1512
11th to 20thNight
24%11%20%28%13%3
1440
21st to endNight
29%11%22%23%14%2
1455
July1st to 10thNight
32%13%23%22%7%3
1575
11th to 20thNight
29%16%26%20%7%2
1566
21st to endNight
28%14%26%22%8%1
1787
August1st to 10thNight
24%13%29%24%10%
1778
11th to 20thNight
32%14%21%19%11%3
1776
21st to endNight
37%12%19%16%13%4
1980
September1st to 10thNight
34%11%15%18%16%6%
1800
11th to 20thNight
33%8%14%17%18%9%
1836
21st to endNight
29%6%11%24%19%10%
1980
October1st to 10thNight
24%6%11%19%24%16%
2063
11th to 20thNight
30%6%6%17%26%15%
2160
21st to endNight
32%46%15%25%17%
2376
November1st to 10thNight
27%5%8%17%28%14%
2224
11th to 20thNight
32%5%7%15%27%15%
2470
21st to endNight
36%49%19%20%12%
2470
December1st to 10thNight
41%5%10%17%20%7%
2470
11th to 20thNight
42%5%7%12%26%8%
3044
21st to endNight
45%47%17%23%5%
4718

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
25%24%33%14%31
270
11th to 20thDay
26%19%36%13%6%1
270
21st to endDay
27%21%35%13%3
297
February1st to 10thDay
26%24%32%11%6%1
270
11th to 20thDay
36%17%33%12%2
252
21st to endDay
21%27%42%8%1
198
March1st to 10thDay
28%18%35%15%5%
240
11th to 20thDay
26%26%29%15%3
240
21st to endDay
24%16%30%25%5%
378
April1st to 10thDay
16%15%35%23%10%
420
11th to 20thDay
21%14%29%23%11%2
412
21st to endDay
11%12%33%30%13%1
420
May1st to 10thDay
13%11%29%28%15%4
423
11th to 20thDay
11%426%27%22%10%
447
21st to endDay
7%422%31%25%11%
485
June1st to 10thDay
14%312%34%27%11%
552
11th to 20thDay
6%313%36%32%10%
630
21st to endDay
7%213%29%33%15%
630
July1st to 10thDay
5%28%33%36%16%
621
11th to 20thDay
6%25%22%43%22%
618
21st to endDay
7%29%23%40%20%
561
August1st to 10thDay
6%16%22%39%26%
446
11th to 20thDay
8%25%23%39%23%
439
21st to endDay
13%37%23%29%25%
495
September1st to 10thDay
8%110%27%36%17%
450
11th to 20thDay
12%311%21%36%18%
450
21st to endDay
11%412%29%32%12%
450
October1st to 10thDay
9%6%19%37%18%11%
361
11th to 20thDay
10%6%27%30%20%6%
270
21st to endDay
21%9%25%29%11%4
297
November1st to 10thDay
15%9%27%34%11%4
270
11th to 20thDay
16%14%35%24%10%1
270
21st to endDay
15%19%35%16%13%2
270
December1st to 10thDay
24%14%35%19%7%1
270
11th to 20thDay
21%16%37%20%6%1
270
21st to endDay
24%18%34%16%9%
297
January1st to 10thNight
24%15%30%26%5%
950
11th to 20thNight
23%15%30%25%7%
950
21st to endNight
24%16%32%25%3
951
February1st to 10thNight
22%14%33%27%4
760
11th to 20thNight
26%15%29%25%4
722
21st to endNight
26%18%34%20%2
592
March1st to 10thNight
20%15%31%30%5%
680
11th to 20thNight
15%13%38%27%7%1
540
21st to endNight
15%10%39%27%9%
594
April1st to 10thNight
15%11%34%28%11%1
540
11th to 20thNight
15%11%34%27%12%1
533
21st to endNight
8%9%34%36%14%
540
May1st to 10thNight
10%5%30%38%16%1
540
11th to 20thNight
9%324%39%21%3
531
21st to endNight
5%318%34%32%7%
584
June1st to 10thNight
9%212%40%31%6%
540
11th to 20thNight
318%37%41%9%
540
21st to endNight
6%210%29%41%13%
540
July1st to 10thNight
5%16%29%46%13%
525
11th to 20thNight
6%15%24%47%18%
522
21st to endNight
5%16%27%47%15%
591
August1st to 10thNight
25%24%49%20%
537
11th to 20thNight
6%25%26%46%14%
534
21st to endNight
11%26%23%39%19%
594
September1st to 10thNight
7%18%29%46%8%
540
11th to 20thNight
9%311%28%42%7%
576
21st to endNight
10%112%36%36%6%
720
October1st to 10thNight
7%218%36%32%7%
720
11th to 20thNight
12%6%22%34%23%3
720
21st to endNight
16%7%22%32%20%3
792
November1st to 10thNight
14%6%19%39%19%3
740
11th to 20thNight
14%9%28%35%15%1
760
21st to endNight
17%8%30%30%14%1
760
December1st to 10thNight
20%11%28%31%10%
760
11th to 20thNight
21%9%31%30%9%
760
21st to endNight
24%14%30%26%6%
1034
Page generated at 2024-02-12 05:35:34. Version ac07

Copyright 2024 Attilla Danko


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