Coronach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Coronach clear sky chart from 2005-11-06 to 2024-02-05.

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%
24577
15%
79869
9%
24494
44%
24494
23%
50663

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
30%
935
14%
4556
6%
926
38%
926
13%
2812
January11th to 20thNight
28%
947
15%
4382
7%
930
36%
930
12%
3030
January21st to endNight
25%
1037
8%
4653
5%
1023
32%
1023
12%
2818
February1st to 10thNight
29%
824
12%
2484
6%
824
37%
824
17%
1787
February11th to 20thNight
28%
700
13%
2273
8%
700
34%
700
16%
1619
February21st to endNight
40%
592
18%
1817
10%
592
48%
592
22%
1242
March1st to 10thNight
32%
720
12%
2160
6%
720
38%
720
19%
1533
March11th to 20thNight
36%
720
18%
2032
10%
720
42%
720
23%
1398
March21st to endNight
38%
654
13%
2040
10%
654
42%
654
19%
1445
April1st to 10thNight
39%
540
17%
1800
13%
540
47%
540
24%
1135
April11th to 20thNight
31%
533
13%
1777
7%
533
40%
533
21%
1196
April21st to endNight
37%
540
16%
1500
10%
540
41%
540
27%
996
May1st to 10thNight
47%
540
16%
1440
9%
540
50%
540
31%
941
May11th to 20thNight
46%
531
15%
1418
9%
531
48%
531
31%
920
May21st to endNight
43%
584
9%
1552
5%
582
45%
582
25%
1077
June1st to 10thNight
47%
510
8%
1410
5%
510
49%
510
32%
882
June11th to 20thNight
46%
360
8%
1260
7%
360
50%
360
26%
745
June21st to endNight
54%
360
9%
1260
8%
360
59%
360
32%
682
July1st to 10thNight
60%
350
10%
1225
9%
350
64%
350
38%
601
July11th to 20thNight
53%
479
13%
1349
7%
479
57%
479
43%
739
July21st to endNight
59%
591
21%
1488
11%
558
63%
558
53%
769
August1st to 10thNight
63%
537
21%
1424
14%
534
67%
534
46%
796
August11th to 20thNight
61%
534
26%
1497
17%
534
68%
534
49%
787
August21st to endNight
59%
594
26%
1928
20%
594
67%
594
42%
986
September1st to 10thNight
56%
540
22%
1800
20%
540
64%
540
37%
959
September11th to 20thNight
54%
540
25%
1800
23%
540
62%
540
33%
991
September21st to endNight
46%
596
24%
2022
18%
596
56%
596
30%
1169
October1st to 10thNight
42%
720
20%
2160
12%
720
49%
720
27%
1362
October11th to 20thNight
37%
725
22%
2165
11%
725
45%
725
27%
1320
October21st to endNight
29%
990
18%
2574
5%
990
37%
990
24%
1794
November1st to 10thNight
29%
925
17%
2508
7%
925
36%
925
21%
1783
November11th to 20thNight
28%
950
16%
2660
7%
950
36%
950
20%
1867
November21st to endNight
25%
950
14%
2660
4%
950
34%
950
21%
1853
December1st to 10thNight
29%
950
11%
2711
5%
950
34%
950
18%
1964
December11th to 20thNight
26%
948
14%
3281
5%
948
34%
948
14%
2370
December21st to endNight
27%
1031
12%
4803
6%
1026
35%
1026
16%
2295

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
9%8%37%6%45%5%6%8%39%
78146
Night
7%8%47%6%45%5%6%8%41%
80688
TransparencyDay
41%7%15%23%11%2
77840
Night
40%7%16%24%12%2
80515
SeeingDay
12%11%31%29%14%3
14923
Night
11%10%33%34%11%1
24623

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 10thDay
6%10%5%8%8%6%9%7%7%8%27%
2346
11th to 20thDay
36%39%12%7%10%13%9%8%20%
2540
21st to endDay
49%39%7%36%46%8%40%
2794
February1st to 10thDay
6%11%6%13%8%5%7%6%7%8%24%
1588
11th to 20thDay
6%12%5%9%10%6%7%7%7%6%24%
1575
21st to endDay
5%10%5%11%9%47%7%7%8%26%
1438
March1st to 10thDay
8%12%7%12%8%45%5%7%8%24%
1800
11th to 20thDay
7%10%6%8%7%47%46%8%34%
1926
21st to endDay
8%12%5%9%8%45%6%6%8%30%
2315
April1st to 10thDay
8%7%47%6%45%6%6%9%40%
2160
11th to 20thDay
13%13%5%8%6%45%5%6%8%27%
2131
21st to endDay
14%9%47%7%45%45%6%36%
2454
May1st to 10thDay
13%7%36%6%45%5%6%8%37%
2520
11th to 20thDay
11%7%36%7%45%6%6%8%38%
2478
21st to endDay
18%8%46%6%45%6%6%8%31%
2724
June1st to 10thDay
14%6%25%5%36%6%6%8%39%
2546
11th to 20thDay
14%6%36%6%35%5%6%8%37%
2700
21st to endDay
7%425%6%45%6%7%8%45%
2700
July1st to 10thDay
6%3245%45%6%6%8%51%
2700
11th to 20thDay
5%413436%5%5%8%56%
2561
21st to endDay
5%31333446%7%59%
2742
August1st to 10thDay
7%4145%25%5%6%8%53%
2507
11th to 20thDay
7%4245%2346%9%53%
2401
21st to endDay
9%4243335%5%7%56%
2426
September1st to 10thDay
11%5%34425%5%5%6%50%
2160
11th to 20thDay
13%6%3443335%6%49%
2160
21st to endDay
13%8%24434347%47%
1935
October1st to 10thDay
15%9%36%4235%36%44%
1800
11th to 20thDay
10%6%47%6%345%5%8%42%
1775
21st to endDay
8%10%49%5%35%46%7%38%
1782
November1st to 10thDay
10%12%6%9%5%35%45%6%36%
1566
11th to 20thDay
5%9%5%10%7%46%5%7%6%37%
1520
21st to endDay
8%9%6%8%6%46%6%5%8%34%
1520
December1st to 10thDay
6%12%6%10%9%5%8%7%5%7%26%
1456
11th to 20thDay
5%10%5%11%8%46%5%7%7%32%
1830
21st to endDay
5%7%37%5%345%5%8%47%
2570
January1st to 10thNight
38%410%8%5%6%6%8%9%33%
4596
11th to 20thNight
35%411%11%7%9%9%8%8%26%
4430
21st to endNight
310%5%9%6%35%5%6%8%40%
4873
February1st to 10thNight
6%10%6%9%8%46%6%8%8%28%
2484
11th to 20thNight
411%410%9%46%6%7%9%28%
2272
21st to endNight
5%8%5%10%7%5%6%5%6%7%35%
1817
March1st to 10thNight
6%9%5%9%9%45%5%6%9%31%
2160
11th to 20thNight
7%9%47%7%45%6%5%8%37%
2032
21st to endNight
8%9%5%9%9%46%6%5%7%32%
2040
April1st to 10thNight
8%7%36%7%35%5%8%8%41%
1800
11th to 20thNight
12%11%37%435%5%7%7%35%
1777
21st to endNight
11%9%35%5%35%46%8%40%
1500
May1st to 10thNight
10%8%26%5%35%6%7%7%42%
1440
11th to 20thNight
10%7%25%435%47%7%44%
1417
21st to endNight
14%7%35%5%35%5%5%10%37%
1552
June1st to 10thNight
13%4245%3446%8%47%
1410
11th to 20thNight
12%5%16%435%35%8%47%
1260
21st to endNight
7%42443446%10%53%
1260
July1st to 10thNight
5%3133345%5%10%56%
1260
11th to 20thNight
6%225%4245%6%9%56%
1394
21st to endNight
43133245%6%8%62%
1576
August1st to 10thNight
43135%245%47%61%
1432
11th to 20thNight
5%31332445%8%62%
1497
21st to endNight
7%41332345%7%60%
1928
September1st to 10thNight
8%4245%3346%7%57%
1800
11th to 20thNight
10%42442445%7%53%
1800
21st to endNight
12%5%24434447%51%
2022
October1st to 10thNight
13%6%36%434347%47%
2160
11th to 20thNight
8%8%45%6%2445%7%47%
2165
21st to endNight
9%10%47%6%25%5%6%8%38%
2574
November1st to 10thNight
12%12%46%5%35%5%5%8%35%
2508
11th to 20thNight
5%9%5%9%8%46%5%7%7%34%
2660
21st to endNight
6%9%5%9%7%46%5%5%8%36%
2660
December1st to 10thNight
6%10%410%10%5%7%5%6%8%30%
2711
11th to 20thNight
5%10%6%10%8%5%6%6%6%8%30%
3353
21st to endNight
47%36%6%3445%7%51%
5068

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
51%10%16%19%5%
2346
11th to 20thDay
54%9%15%16%5%1
2540
21st to endDay
42%7%17%30%5%
2794
February1st to 10thDay
56%5%12%17%10%
1588
11th to 20thDay
57%7%12%14%9%1
1584
21st to endDay
52%9%15%14%9%1
1438
March1st to 10thDay
56%9%16%15%5%
1800
11th to 20thDay
47%8%17%22%7%
1926
21st to endDay
50%9%18%17%6%
2315
April1st to 10thDay
40%8%17%22%12%1
2160
11th to 20thDay
53%8%15%17%7%
2134
21st to endDay
49%6%14%23%8%
2454
May1st to 10thDay
44%7%12%25%11%2
2520
11th to 20thDay
42%7%13%27%10%
2482
21st to endDay
49%8%14%20%7%
2724
June1st to 10thDay
40%8%18%23%10%1
2546
11th to 20thDay
43%9%17%20%10%2
2700
21st to endDay
34%10%17%29%10%1
2700
July1st to 10thDay
27%8%17%31%15%2
2626
11th to 20thDay
25%6%16%27%22%4
2483
21st to endDay
23%7%12%32%23%3
2590
August1st to 10thDay
28%7%16%30%16%3
2491
11th to 20thDay
27%6%18%30%16%3
2401
21st to endDay
27%6%13%31%21%3
2426
September1st to 10thDay
33%6%13%27%17%3
2160
11th to 20thDay
35%6%15%27%13%4
2160
21st to endDay
37%5%12%28%16%2
1935
October1st to 10thDay
42%5%15%24%12%2
1800
11th to 20thDay
39%6%15%25%13%1
1775
21st to endDay
44%7%18%23%8%1
1782
November1st to 10thDay
50%5%14%21%9%2
1566
11th to 20thDay
44%8%20%19%8%1
1520
21st to endDay
46%8%22%18%6%1
1520
December1st to 10thDay
55%8%15%15%6%1
1456
11th to 20thDay
48%9%24%13%5%
1828
21st to endDay
35%5%11%27%15%7%
2570
January1st to 10thNight
43%8%21%20%7%1
4596
11th to 20thNight
51%7%16%19%6%1
4430
21st to endNight
42%8%21%23%6%
4873
February1st to 10thNight
50%7%15%19%9%1
2484
11th to 20thNight
50%8%15%16%9%1
2273
21st to endNight
46%6%13%21%13%1
1817
March1st to 10thNight
48%8%17%21%6%
2160
11th to 20thNight
44%7%14%25%9%
2032
21st to endNight
50%7%17%17%9%
2040
April1st to 10thNight
39%7%15%24%13%1
1800
11th to 20thNight
45%7%15%20%12%1
1777
21st to endNight
41%6%15%26%11%
1500
May1st to 10thNight
38%6%14%26%15%1
1440
11th to 20thNight
36%7%14%27%15%1
1418
21st to endNight
43%8%16%23%9%1
1552
June1st to 10thNight
34%7%19%25%12%2
1410
11th to 20thNight
37%6%18%24%13%2
1260
21st to endNight
28%8%19%30%12%2
1260
July1st to 10thNight
22%8%17%34%17%3
1225
11th to 20thNight
23%7%18%29%20%3
1349
21st to endNight
18%5%15%33%25%5%
1488
August1st to 10thNight
23%7%16%33%19%3
1424
11th to 20thNight
20%6%16%36%20%3
1497
21st to endNight
23%6%11%30%25%5%
1928
September1st to 10thNight
26%6%12%31%20%5%
1800
11th to 20thNight
30%6%14%25%21%3
1800
21st to endNight
33%6%11%30%19%1
2022
October1st to 10thNight
38%6%14%24%15%2
2160
11th to 20thNight
37%5%15%29%13%2
2165
21st to endNight
43%8%15%23%10%2
2574
November1st to 10thNight
47%7%13%20%10%2
2508
11th to 20thNight
46%8%18%20%7%1
2660
21st to endNight
46%6%19%21%7%
2660
December1st to 10thNight
51%7%16%18%7%1
2711
11th to 20thNight
49%9%16%19%6%1
3354
21st to endNight
32%5%13%26%18%5%
5068

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
11%14%30%31%11%3
216
11th to 20thDay
10%14%34%29%10%3
270
21st to endDay
9%15%35%31%9%
297
February1st to 10thDay
14%12%42%27%5%1
252
11th to 20thDay
16%6%41%27%8%1
240
21st to endDay
8%9%33%37%13%1
198
March1st to 10thDay
16%12%38%27%6%1
240
11th to 20thDay
10%16%35%24%12%2
366
21st to endDay
13%15%35%23%12%3
462
April1st to 10thDay
12%17%41%25%5%
420
11th to 20thDay
20%17%33%21%8%1
412
21st to endDay
18%12%30%26%14%1
566
May1st to 10thDay
14%8%27%29%18%4
603
11th to 20thDay
16%11%22%27%18%6%
625
21st to endDay
17%11%26%26%15%6%
679
June1st to 10thDay
14%12%26%28%17%3
630
11th to 20thDay
15%14%32%25%11%3
630
21st to endDay
8%9%25%34%21%3
630
July1st to 10thDay
6%5%28%38%18%4
621
11th to 20thDay
6%8%32%34%16%3
618
21st to endDay
5%8%25%36%21%4
684
August1st to 10thDay
9%7%23%36%19%6%
626
11th to 20thDay
9%7%24%30%24%6%
539
21st to endDay
7%7%27%38%16%4
495
September1st to 10thDay
12%9%32%32%11%3
450
11th to 20thDay
16%10%27%29%17%1
450
21st to endDay
19%11%28%27%12%3
283
October1st to 10thDay
20%6%31%23%17%3
270
11th to 20thDay
10%10%44%20%12%4
270
21st to endDay
13%19%40%20%7%2
297
November1st to 10thDay
16%14%36%23%10%1
270
11th to 20thDay
10%16%34%30%9%1
270
21st to endDay
10%14%39%26%10%1
270
December1st to 10thDay
9%13%44%24%8%2
270
11th to 20thDay
13%14%43%21%8%1
270
21st to endDay
11%8%41%26%10%3
234
January1st to 10thNight
8%14%39%28%10%1
950
11th to 20thNight
10%16%36%30%8%1
950
21st to endNight
10%13%40%28%10%
1045
February1st to 10thNight
11%12%34%31%12%1
824
11th to 20thNight
10%11%41%27%9%1
704
21st to endNight
8%7%35%32%16%3
592
March1st to 10thNight
9%12%34%33%11%1
720
11th to 20thNight
12%10%35%32%9%2
720
21st to endNight
13%7%30%36%11%2
654
April1st to 10thNight
11%10%33%38%8%
540
11th to 20thNight
17%8%39%29%7%
533
21st to endNight
15%8%35%35%7%
540
May1st to 10thNight
12%7%29%38%14%1
540
11th to 20thNight
14%6%28%34%17%1
531
21st to endNight
17%8%24%32%17%1
584
June1st to 10thNight
13%7%28%37%13%1
510
11th to 20thNight
15%6%28%41%10%1
360
21st to endNight
8%8%26%42%14%1
360
July1st to 10thNight
10%322%49%15%1
350
11th to 20thNight
6%5%32%44%12%
479
21st to endNight
3330%46%16%1
591
August1st to 10thNight
5%424%50%14%2
537
11th to 20thNight
5%426%43%22%1
534
21st to endNight
10%424%42%19%1
594
September1st to 10thNight
9%426%44%15%2
540
11th to 20thNight
10%5%25%43%15%1
540
21st to endNight
12%9%29%39%11%1
596
October1st to 10thNight
16%9%27%33%15%1
720
11th to 20thNight
13%12%29%33%11%2
725
21st to endNight
13%12%39%28%8%
990
November1st to 10thNight
18%11%35%29%6%1
925
11th to 20thNight
9%14%40%26%10%1
950
21st to endNight
10%14%41%28%7%1
950
December1st to 10thNight
12%10%37%29%11%1
950
11th to 20thNight
10%14%38%29%8%1
950
21st to endNight
11%10%39%27%11%1
1045
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