This page made possible by the sponsorship of: Kevin Wigell.

Darling Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Darling Hill Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
25%
22893
12%
74798
8%
22846
31%
22846
13%
56281

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
8%
760
6%
2649
3%
757
12%
757
4%
2271
January11th to 20thNight
12%
740
6%
2588
4%
740
15%
740
5%
2226
January21st to endNight
12%
792
7%
2587
3%
792
17%
792
6%
2215
February1st to 10thNight
9%
720
7%
2340
1%
720
15%
720
5%
1968
February11th to 20thNight
8%
703
7%
2243
2%
700
14%
700
6%
1899
February21st to endNight
11%
592
9%
1776
5%
592
17%
592
8%
1461
March1st to 10thNight
14%
720
10%
2120
4%
720
21%
720
10%
1690
March11th to 20thNight
18%
720
12%
1980
5%
720
25%
720
12%
1551
March21st to endNight
18%
792
14%
2084
6%
792
24%
792
14%
1622
April1st to 10thNight
18%
720
11%
1800
2%
720
23%
720
14%
1401
April11th to 20thNight
24%
711
14%
1775
5%
711
28%
711
19%
1336
April21st to endNight
26%
716
14%
1796
5%
716
31%
716
19%
1334
May1st to 10thNight
33%
400
15%
1480
12%
400
38%
400
15%
1046
May11th to 20thNight
36%
354
19%
1416
18%
354
45%
354
18%
890
May21st to endNight
40%
388
15%
1551
15%
388
48%
388
19%
973
June1st to 10thNight
41%
360
15%
1440
15%
360
51%
360
18%
922
June11th to 20thNight
41%
360
14%
1440
17%
360
48%
360
18%
909
June21st to endNight
43%
360
16%
1440
17%
360
52%
360
21%
897
July1st to 10thNight
55%
350
14%
1400
19%
350
59%
350
23%
818
July11th to 20thNight
55%
348
17%
1392
22%
348
59%
348
25%
785
July21st to endNight
51%
394
17%
1486
18%
372
55%
372
22%
890
August1st to 10thNight
51%
519
16%
1583
13%
517
55%
517
28%
990
August11th to 20thNight
51%
577
15%
1641
10%
577
52%
577
25%
1127
August21st to endNight
49%
792
18%
1980
9%
792
51%
792
30%
1338
September1st to 10thNight
42%
720
16%
1800
7%
720
45%
720
28%
1234
September11th to 20thNight
50%
720
24%
1800
15%
720
54%
720
33%
1182
September21st to endNight
41%
720
19%
2038
15%
720
45%
720
22%
1417
October1st to 10thNight
32%
720
13%
2160
10%
720
37%
720
17%
1564
October11th to 20thNight
24%
720
13%
2160
6%
720
32%
720
15%
1574
October21st to endNight
14%
792
10%
2449
5%
792
21%
792
10%
1966
November1st to 10thNight
22%
740
15%
2407
10%
740
30%
740
14%
1732
November11th to 20thNight
15%
760
14%
2575
9%
760
23%
760
10%
1933
November21st to endNight
16%
760
9%
2660
5%
760
23%
760
8%
2104
December1st to 10thNight
11%
760
5%
2660
2%
760
15%
760
4%
2252
December11th to 20thNight
11%
759
6%
3259
2%
759
15%
759
4%
2691
December21st to endNight
8%
834
3%
4843
1%
817
12%
817
2%
4073

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
17%12%5%8%6%45%5%5%7%28%
74744
Night
16%12%5%9%7%35%45%6%28%
75039
TransparencyDay
56%6%11%17%9%1
74449
Night
58%6%10%17%8%1
74868
SeeingDay
26%18%29%17%8%3
13553
Night
25%18%26%22%8%1
22897

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 10thDay
10%20%10%13%8%5%6%45%414%
1517
11th to 20thDay
15%20%8%15%9%5%5%44411%
1478
21st to endDay
11%17%9%13%11%5%5%5%45%14%
1768
February1st to 10thDay
15%16%8%17%11%6%5%44312%
1620
11th to 20thDay
13%16%9%17%11%45%43414%
1605
21st to endDay
18%17%6%14%11%4443317%
1480
March1st to 10thDay
14%15%7%15%9%345%4420%
1834
11th to 20thDay
16%17%8%9%6%3433426%
1980
21st to endDay
19%13%6%9%7%24346%27%
2272
April1st to 10thDay
16%16%6%9%5%335%36%28%
2160
11th to 20thDay
16%13%46%5%34446%35%
2134
21st to endDay
20%15%46%5%3335%6%31%
2179
May1st to 10thDay
19%11%47%6%4445%6%31%
2479
11th to 20thDay
17%9%36%5%36%5%5%7%34%
2478
21st to endDay
15%7%36%5%35%5%6%9%37%
2725
June1st to 10thDay
20%7%36%5%345%6%7%33%
2520
11th to 20thDay
18%6%25%5%45%5%6%10%34%
2520
21st to endDay
16%7%36%5%45%5%6%10%33%
2520
July1st to 10thDay
13%5%35%6%36%6%7%9%37%
2520
11th to 20thDay
13%6%36%6%45%6%6%10%36%
2520
21st to endDay
14%6%36%6%46%7%7%9%34%
2744
August1st to 10thDay
13%5%26%6%5%6%6%7%10%34%
2341
11th to 20thDay
15%7%37%7%5%6%6%6%8%31%
2241
21st to endDay
16%7%37%6%45%5%7%8%33%
2376
September1st to 10thDay
18%6%25%6%35%6%6%7%37%
2160
11th to 20thDay
17%7%26%5%34447%42%
2160
21st to endDay
16%8%36%6%35%5%6%6%35%
1918
October1st to 10thDay
21%9%35%6%35%5%5%8%31%
1800
11th to 20thDay
20%11%35%6%346%5%7%29%
1800
21st to endDay
27%17%37%5%345%45%22%
1905
November1st to 10thDay
14%14%37%6%36%5%46%31%
1671
11th to 20thDay
16%17%5%9%6%35%45%424%
1601
21st to endDay
17%21%6%10%6%35%345%19%
1520
December1st to 10thDay
17%23%10%12%5%34445%14%
1520
11th to 20thDay
19%18%9%12%6%3323419%
1906
21st to endDay
23%21%9%10%7%3445%411%
2772
January1st to 10thNight
14%18%8%15%9%5%6%43413%
2649
11th to 20thNight
15%17%9%15%9%5%45%4413%
2588
21st to endNight
10%15%7%14%13%7%7%44413%
2587
February1st to 10thNight
14%17%8%15%9%45%44416%
2340
11th to 20thNight
13%15%7%15%12%5%6%445%15%
2241
21st to endNight
18%13%7%16%9%34345%18%
1776
March1st to 10thNight
14%14%9%13%9%35%345%21%
2110
11th to 20thNight
14%16%7%10%8%33445%26%
1979
21st to endNight
18%15%5%8%6%34445%28%
2084
April1st to 10thNight
17%14%6%8%6%445%45%28%
1800
11th to 20thNight
18%12%37%5%4445%5%33%
1775
21st to endNight
19%12%5%5%5%3445%5%33%
1796
May1st to 10thNight
21%9%37%5%3445%6%32%
1480
11th to 20thNight
13%7%35%5%36%6%6%8%39%
1415
21st to endNight
13%5%36%6%346%6%8%41%
1550
June1st to 10thNight
18%5%46%5%35%46%7%37%
1440
11th to 20thNight
17%6%25%5%345%6%9%38%
1440
21st to endNight
14%6%36%5%345%5%8%42%
1440
July1st to 10thNight
8%5%25%6%36%5%7%9%43%
1440
11th to 20thNight
11%425%6%346%6%8%45%
1440
21st to endNight
12%6%25%435%5%6%10%42%
1574
August1st to 10thNight
11%5%25%6%35%5%7%8%44%
1593
11th to 20thNight
12%6%27%6%46%6%6%6%39%
1641
21st to endNight
13%7%35%5%245%5%8%44%
1980
September1st to 10thNight
15%6%25%6%35%5%5%7%42%
1800
11th to 20thNight
15%6%35%42345%7%46%
1800
21st to endNight
17%8%245%35%5%6%6%38%
2038
October1st to 10thNight
21%8%36%5%35%5%5%6%32%
2160
11th to 20thNight
21%10%25%6%35%5%5%7%32%
2160
21st to endNight
28%15%46%7%23445%23%
2449
November1st to 10thNight
13%15%48%6%3445%6%33%
2407
11th to 20thNight
18%16%5%9%5%34446%26%
2575
21st to endNight
15%18%8%9%6%35%35%5%22%
2660
December1st to 10thNight
18%21%9%11%7%25%435%15%
2660
11th to 20thNight
19%17%8%12%7%35%43418%
3288
21st to endNight
24%18%10%11%6%33345%14%
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
74%48%10%4
1518
11th to 20thDay
78%5%7%6%41
1478
21st to endDay
73%410%8%5%1
1768
February1st to 10thDay
78%47%9%3
1620
11th to 20thDay
76%46%10%3
1614
21st to endDay
73%48%10%5%
1480
March1st to 10thDay
68%5%11%11%41
1837
11th to 20thDay
64%48%14%10%1
1980
21st to endDay
60%47%16%12%2
2272
April1st to 10thDay
59%48%18%9%2
2160
11th to 20thDay
51%5%11%20%12%1
2134
21st to endDay
55%49%19%11%2
2179
May1st to 10thDay
55%5%9%19%10%2
2479
11th to 20thDay
49%6%10%21%12%2
2482
21st to endDay
45%8%15%21%11%1
2725
June1st to 10thDay
50%7%11%19%13%1
2520
11th to 20thDay
46%7%12%23%11%1
2520
21st to endDay
47%7%14%21%10%1
2520
July1st to 10thDay
43%7%11%25%12%1
2450
11th to 20thDay
42%9%16%25%8%1
2445
21st to endDay
46%8%13%22%11%1
2591
August1st to 10thDay
44%8%14%22%11%1
2327
11th to 20thDay
49%8%13%22%7%
2241
21st to endDay
48%7%11%23%11%1
2376
September1st to 10thDay
46%6%12%25%11%1
2160
11th to 20thDay
44%410%24%17%1
2160
21st to endDay
48%7%9%24%11%1
1918
October1st to 10thDay
52%6%10%19%12%1
1800
11th to 20thDay
54%6%13%19%7%1
1800
21st to endDay
65%6%10%11%7%1
1905
November1st to 10thDay
53%6%12%17%11%2
1671
11th to 20thDay
62%5%10%14%6%2
1601
21st to endDay
67%6%12%12%3
1520
December1st to 10thDay
74%6%8%9%3
1520
11th to 20thDay
71%413%9%3
1906
21st to endDay
76%6%6%9%2
2772
January1st to 10thNight
76%48%8%4
2649
11th to 20thNight
75%5%8%8%4
2588
21st to endNight
74%47%9%41
2587
February1st to 10thNight
73%5%8%10%5%
2340
11th to 20thNight
73%5%7%11%4
2243
21st to endNight
68%5%9%11%6%1
1776
March1st to 10thNight
66%311%14%5%
2120
11th to 20thNight
62%49%17%8%1
1980
21st to endNight
60%47%15%11%2
2084
April1st to 10thNight
59%6%11%16%8%2
1800
11th to 20thNight
54%49%18%14%1
1775
21st to endNight
53%5%9%18%13%3
1796
May1st to 10thNight
53%7%8%17%13%2
1480
11th to 20thNight
42%8%11%23%13%2
1416
21st to endNight
42%7%15%22%11%2
1551
June1st to 10thNight
46%6%12%23%13%1
1440
11th to 20thNight
44%6%13%21%14%2
1440
21st to endNight
41%8%9%29%13%1
1440
July1st to 10thNight
36%8%14%24%15%3
1400
11th to 20thNight
35%7%15%30%13%1
1392
21st to endNight
38%8%13%24%15%2
1486
August1st to 10thNight
37%8%15%28%11%1
1583
11th to 20thNight
43%8%15%26%8%
1641
21st to endNight
38%8%15%26%12%2
1980
September1st to 10thNight
42%6%13%24%13%2
1800
11th to 20thNight
38%5%11%29%16%1
1800
21st to endNight
45%8%11%24%12%1
2038
October1st to 10thNight
53%6%10%19%11%
2160
11th to 20thNight
52%7%13%17%9%1
2160
21st to endNight
65%6%10%12%7%1
2449
November1st to 10thNight
53%7%10%17%12%2
2407
11th to 20thNight
60%410%16%6%3
2575
21st to endNight
65%6%12%14%4
2660
December1st to 10thNight
74%5%10%9%2
2660
11th to 20thNight
71%6%8%11%4
3288
21st to endNight
74%6%8%10%2
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
31%28%28%10%3
180
11th to 20thDay
36%29%25%7%11
170
21st to endDay
25%33%32%9%1
258
February1st to 10thDay
40%31%25%4
240
11th to 20thDay
39%31%28%3
272
21st to endDay
41%22%25%10%1
346
March1st to 10thDay
32%25%31%10%3
420
11th to 20thDay
34%24%27%12%3
420
21st to endDay
36%23%26%12%31
462
April1st to 10thDay
33%23%28%11%5%
420
11th to 20thDay
28%28%22%11%8%3
412
21st to endDay
35%17%28%14%5%1
420
May1st to 10thDay
29%20%29%13%7%2
423
11th to 20thDay
24%15%32%19%8%2
447
21st to endDay
18%15%32%22%11%3
485
June1st to 10thDay
26%13%30%22%8%1
450
11th to 20thDay
18%15%32%24%9%2
450
21st to endDay
18%19%32%22%7%2
450
July1st to 10thDay
16%9%29%28%14%4
445
11th to 20thDay
14%8%32%27%14%3
444
21st to endDay
15%9%39%24%10%3
488
August1st to 10thDay
13%10%29%27%14%7%
446
11th to 20thDay
18%10%27%25%12%8%
439
21st to endDay
15%13%29%23%13%7%
495
September1st to 10thDay
20%11%25%23%14%7%
450
11th to 20thDay
17%11%28%21%15%8%
450
21st to endDay
19%17%28%20%12%4
450
October1st to 10thDay
26%15%25%16%14%5%
450
11th to 20thDay
28%21%28%16%6%1
450
21st to endDay
40%17%26%14%3
457
November1st to 10thDay
27%24%22%20%7%1
365
11th to 20thDay
36%25%24%13%21
261
21st to endDay
38%24%31%7%
180
December1st to 10thDay
39%22%29%7%21
180
11th to 20thDay
36%29%27%8%1
180
21st to endDay
34%28%32%5%1
198
January1st to 10thNight
29%30%28%11%21
760
11th to 20thNight
30%25%27%15%3
740
21st to endNight
23%26%32%17%2
792
February1st to 10thNight
31%26%30%14%
720
11th to 20thNight
28%28%30%12%2
703
21st to endNight
32%24%27%13%3
592
March1st to 10thNight
27%24%30%17%2
720
11th to 20thNight
29%23%26%19%3
720
21st to endNight
30%20%26%16%7%1
792
April1st to 10thNight
28%21%29%19%3
720
11th to 20thNight
29%19%25%21%7%1
711
21st to endNight
29%13%27%24%6%
716
May1st to 10thNight
24%13%24%29%9%1
400
11th to 20thNight
17%12%32%31%8%1
354
21st to endNight
13%10%31%33%14%1
389
June1st to 10thNight
20%8%24%34%13%1
360
11th to 20thNight
18%11%23%34%15%
360
21st to endNight
15%7%28%41%9%1
360
July1st to 10thNight
10%324%44%17%2
350
11th to 20thNight
12%421%42%20%2
348
21st to endNight
14%6%25%40%14%1
394
August1st to 10thNight
15%5%25%34%20%1
519
11th to 20thNight
16%5%19%33%23%3
577
21st to endNight
15%6%24%34%19%2
792
September1st to 10thNight
17%9%25%31%15%3
720
11th to 20thNight
18%8%18%32%20%4
720
21st to endNight
19%14%23%26%16%3
720
October1st to 10thNight
26%13%23%20%17%1
720
11th to 20thNight
29%15%28%21%6%
720
21st to endNight
38%16%27%16%3
792
November1st to 10thNight
26%18%29%19%7%
740
11th to 20thNight
32%22%26%14%5%1
760
21st to endNight
27%26%26%16%4
760
December1st to 10thNight
35%26%23%13%3
760
11th to 20thNight
32%24%26%14%3
760
21st to endNight
32%29%26%11%2
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