This page made possible by the sponsorship of: Daniel Rodriguez.

Deerlick Astronomy Village
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deerlick Astronomy Village clear sky chart from 2005-11-06 to 2024-01-16.

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
46%
24091
22%
74416
14%
24033
55%
24033
26%
46427

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
23%
760
23%
2459
8%
757
40%
757
20%
1520
January11th to 20thNight
30%
741
25%
2406
13%
741
46%
741
22%
1488
January21st to endNight
24%
792
26%
2574
11%
792
44%
792
22%
1572
February1st to 10thNight
32%
720
24%
2182
12%
720
45%
720
24%
1380
February11th to 20thNight
24%
703
22%
2098
7%
699
39%
699
22%
1346
February21st to endNight
23%
592
23%
1776
9%
592
38%
592
23%
1133
March1st to 10thNight
31%
720
26%
2018
13%
720
43%
720
28%
1261
March11th to 20thNight
32%
720
22%
1980
9%
720
43%
720
27%
1277
March21st to endNight
32%
792
23%
2178
9%
792
43%
792
25%
1393
April1st to 10thNight
36%
720
25%
1980
14%
720
46%
720
31%
1197
April11th to 20thNight
41%
651
26%
1846
14%
651
51%
651
34%
1060
April21st to endNight
49%
540
31%
1620
18%
540
60%
540
36%
916
May1st to 10thNight
50%
540
23%
1620
12%
540
58%
540
35%
924
May11th to 20thNight
54%
531
16%
1592
11%
531
57%
531
26%
1031
May21st to endNight
61%
582
20%
1744
15%
582
63%
582
27%
1123
June1st to 10thNight
62%
540
15%
1620
13%
540
63%
540
24%
1083
June11th to 20thNight
67%
540
16%
1620
12%
540
69%
540
32%
994
June21st to endNight
68%
540
14%
1620
11%
540
70%
540
26%
1060
July1st to 10thNight
66%
525
11%
1575
10%
525
67%
525
23%
1103
July11th to 20thNight
70%
522
11%
1566
11%
522
71%
522
23%
1091
July21st to endNight
74%
591
12%
1672
11%
558
75%
558
26%
1119
August1st to 10thNight
65%
537
12%
1600
11%
534
65%
534
20%
1132
August11th to 20thNight
67%
534
17%
1598
16%
534
68%
534
23%
1097
August21st to endNight
63%
656
13%
2040
13%
656
63%
656
20%
1415
September1st to 10thNight
66%
720
17%
1980
15%
720
67%
720
27%
1335
September11th to 20thNight
59%
720
19%
1980
16%
720
61%
720
27%
1340
September21st to endNight
60%
720
24%
1980
19%
720
65%
720
31%
1263
October1st to 10thNight
58%
720
26%
1980
21%
720
64%
720
36%
1197
October11th to 20thNight
53%
720
31%
2160
25%
720
63%
720
36%
1222
October21st to endNight
48%
792
32%
2376
25%
792
60%
792
35%
1323
November1st to 10thNight
51%
740
29%
2249
24%
740
60%
740
35%
1276
November11th to 20thNight
40%
760
27%
2470
19%
760
53%
760
30%
1412
November21st to endNight
41%
760
26%
2470
17%
760
55%
760
28%
1447
December1st to 10thNight
37%
760
26%
2470
14%
760
52%
760
21%
1540
December11th to 20thNight
36%
759
28%
2907
17%
758
49%
758
22%
1647
December21st to endNight
30%
831
15%
4410
12%
817
42%
817
12%
2710

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%5%25%5%35%5%6%8%42%
74920
Night
12%5%25%5%345%5%8%45%
74882
TransparencyDay
38%8%12%19%18%5%
74643
Night
36%8%11%18%19%7%
74678
SeeingDay
16%9%24%24%19%8%
13987
Night
15%9%23%30%20%3
24099

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%6%35%43435%6%46%
1706
11th to 20thDay
15%7%345%2445%6%45%
1665
21st to endDay
18%6%25%43335%5%46%
1782
February1st to 10thDay
16%6%36%5%345%5%7%40%
1774
11th to 20thDay
20%6%13424445%45%
1748
21st to endDay
18%7%26%424446%42%
1480
March1st to 10thDay
14%5%24424446%51%
1940
11th to 20thDay
18%426%5%335%5%6%43%
1980
21st to endDay
15%5%36%425%5%5%7%43%
2178
April1st to 10thDay
11%435%445%45%6%49%
1980
11th to 20thDay
11%5%25%5%35%45%6%48%
2077
21st to endDay
8%424435%5%6%8%52%
2340
May1st to 10thDay
9%424435%5%5%9%50%
2340
11th to 20thDay
11%6%36%5%5%6%5%6%8%40%
2301
21st to endDay
11%5%35%5%36%5%7%9%41%
2531
June1st to 10thDay
10%5%36%7%46%7%8%9%34%
2340
11th to 20thDay
7%325%6%47%7%7%10%43%
2340
21st to endDay
6%435%6%47%7%9%12%37%
2340
July1st to 10thDay
9%436%9%5%7%8%9%9%31%
2340
11th to 20thDay
8%6%37%7%47%8%9%12%31%
2340
21st to endDay
6%427%7%5%8%8%9%12%30%
2547
August1st to 10thDay
9%6%27%8%5%7%8%9%12%27%
2327
11th to 20thDay
10%5%38%7%5%7%6%9%9%30%
2300
21st to endDay
14%7%36%7%46%7%7%9%29%
2293
September1st to 10thDay
9%6%36%5%46%6%7%8%39%
1980
11th to 20thDay
13%6%36%7%35%5%6%7%41%
1980
21st to endDay
16%6%25%5%3345%6%44%
1980
October1st to 10thDay
15%5%2432345%7%51%
1980
11th to 20thDay
13%424323346%56%
1800
21st to endDay
11%425%43334456%
1980
November1st to 10thDay
12%5%245%24345%54%
1824
11th to 20thDay
14%5%23323346%55%
1710
21st to endDay
14%5%25%4345%5%6%48%
1710
December1st to 10thDay
17%6%35%5%35%5%6%6%38%
1710
11th to 20thDay
17%5%25%43335%6%48%
2153
21st to endDay
20%7%3442345%6%41%
3124
January1st to 10thNight
15%7%25%4245%45%46%
2459
11th to 20thNight
15%7%35%5%3446%7%44%
2406
21st to endNight
16%6%35%42344448%
2574
February1st to 10thNight
16%5%25%435%446%45%
2182
11th to 20thNight
19%6%25%424445%45%
2098
21st to endNight
14%7%35%5%3445%6%44%
1776
March1st to 10thNight
12%6%25%4345%46%50%
2018
11th to 20thNight
15%5%2443445%7%47%
1980
21st to endNight
12%435%5%35%5%47%46%
2178
April1st to 10thNight
10%5%15%5%2445%7%52%
1980
11th to 20thNight
11%5%2342435%8%52%
1846
21st to endNight
9%413435%45%7%56%
1620
May1st to 10thNight
7%4235%345%6%7%54%
1620
11th to 20thNight
9%426%6%47%6%7%9%41%
1592
21st to endNight
10%5%26%6%45%5%7%8%42%
1744
June1st to 10thNight
9%6%35%6%5%5%7%7%13%34%
1620
11th to 20thNight
6%325%6%35%6%7%12%44%
1620
21st to endNight
7%5%25%5%37%8%9%11%38%
1620
July1st to 10thNight
8%5%36%7%46%7%9%12%33%
1620
11th to 20thNight
5%5%37%6%5%8%8%9%13%32%
1620
21st to endNight
6%5%25%5%46%7%10%14%36%
1771
August1st to 10thNight
7%5%47%7%5%7%8%9%11%31%
1611
11th to 20thNight
11%425%6%45%7%9%12%34%
1598
21st to endNight
10%6%36%7%46%7%7%10%33%
2040
September1st to 10thNight
10%5%25%5%45%8%7%10%39%
1980
11th to 20thNight
13%6%25%6%45%5%5%8%42%
1980
21st to endNight
13%6%25%5%3445%6%48%
1980
October1st to 10thNight
13%5%134335%5%6%53%
1980
11th to 20thNight
13%424323346%56%
2160
21st to endNight
11%4145%33446%56%
2376
November1st to 10thNight
11%5%25%423336%57%
2249
11th to 20thNight
14%5%24423446%53%
2470
21st to endNight
14%5%2443445%7%48%
2470
December1st to 10thNight
15%6%35%43445%7%44%
2470
11th to 20thNight
17%5%24323336%51%
3042
21st to endNight
18%8%36%5%345%5%6%37%
4532

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
39%5%8%18%25%4
1707
11th to 20thDay
40%5%7%19%22%6%
1665
21st to endDay
40%36%19%25%7%
1782
February1st to 10thDay
43%5%10%18%16%7%
1774
11th to 20thDay
41%46%20%22%7%
1758
21st to endDay
43%6%8%14%21%9%
1480
March1st to 10thDay
35%5%7%18%23%12%
1940
11th to 20thDay
41%7%10%18%17%7%
1980
21st to endDay
41%6%9%21%18%5%
2178
April1st to 10thDay
35%6%11%19%22%7%
1980
11th to 20thDay
36%6%9%19%21%10%
2077
21st to endDay
28%7%11%26%24%4
2340
May1st to 10thDay
30%7%13%23%22%5%
2340
11th to 20thDay
41%8%16%18%15%1
2305
21st to endDay
36%9%14%22%16%2
2531
June1st to 10thDay
41%11%17%19%11%2
2340
11th to 20thDay
33%11%18%25%12%1
2340
21st to endDay
35%13%19%18%11%4
2340
July1st to 10thDay
41%15%17%16%8%3
2275
11th to 20thDay
40%14%21%16%6%3
2271
21st to endDay
37%16%21%18%7%1
2405
August1st to 10thDay
45%13%18%18%5%1
2314
11th to 20thDay
45%13%16%16%8%2
2300
21st to endDay
47%12%16%15%8%2
2293
September1st to 10thDay
38%11%14%16%16%4
1980
11th to 20thDay
41%8%10%17%21%3
1980
21st to endDay
40%6%11%18%19%6%
1980
October1st to 10thDay
33%5%9%21%25%7%
1980
11th to 20thDay
29%49%23%27%8%
1800
21st to endDay
31%5%5%16%29%12%
1980
November1st to 10thDay
33%5%7%16%26%13%
1824
11th to 20thDay
32%48%21%23%12%
1710
21st to endDay
35%7%7%20%24%7%
1710
December1st to 10thDay
44%7%9%16%17%7%
1710
11th to 20thDay
38%48%17%23%10%
2150
21st to endDay
42%6%9%17%22%4
3124
January1st to 10thNight
39%6%7%18%24%6%
2459
11th to 20thNight
40%47%19%22%7%
2406
21st to endNight
40%45%18%24%10%
2574
February1st to 10thNight
41%49%18%19%9%
2182
11th to 20thNight
41%46%17%22%8%
2099
21st to endNight
40%6%9%15%19%11%
1776
March1st to 10thNight
36%5%8%15%22%13%
2018
11th to 20thNight
37%7%12%15%21%8%
1980
21st to endNight
37%7%9%20%20%7%
2178
April1st to 10thNight
32%6%10%20%22%9%
1980
11th to 20thNight
30%48%24%23%11%
1846
21st to endNight
28%7%11%25%22%7%
1620
May1st to 10thNight
29%7%14%23%21%6%
1620
11th to 20thNight
36%11%15%20%16%2
1593
21st to endNight
36%11%12%21%17%3
1745
June1st to 10thNight
38%12%19%17%12%1
1620
11th to 20thNight
30%12%20%25%12%2
1620
21st to endNight
33%15%20%18%11%4
1620
July1st to 10thNight
38%16%20%14%8%4
1575
11th to 20thNight
37%16%21%18%6%2
1566
21st to endNight
33%15%26%18%6%1
1672
August1st to 10thNight
41%15%19%20%5%
1600
11th to 20thNight
37%15%19%18%9%2
1598
21st to endNight
42%13%19%15%9%2
2040
September1st to 10thNight
36%13%16%16%15%4
1980
11th to 20thNight
40%9%13%15%18%5%
1980
21st to endNight
36%7%11%17%22%6%
1980
October1st to 10thNight
31%7%10%18%27%7%
1980
11th to 20thNight
30%5%9%20%26%10%
2160
21st to endNight
29%47%17%29%14%
2376
November1st to 10thNight
31%5%7%16%27%14%
2249
11th to 20thNight
33%5%7%17%24%14%
2470
21st to endNight
35%5%8%17%25%9%
2470
December1st to 10thNight
39%7%9%19%20%7%
2470
11th to 20thNight
36%48%16%26%9%
3044
21st to endNight
46%6%7%20%18%3
4532

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%22%39%13%3
270
11th to 20thDay
22%20%35%17%5%
255
21st to endDay
25%26%34%10%5%
264
February1st to 10thDay
22%21%37%15%5%
240
11th to 20thDay
35%19%34%11%1
240
21st to endDay
28%21%37%9%5%
198
March1st to 10thDay
20%15%34%24%6%
380
11th to 20thDay
22%16%35%18%8%
420
21st to endDay
19%17%36%20%8%1
462
April1st to 10thDay
19%16%29%25%10%1
420
11th to 20thDay
14%16%30%22%16%2
412
21st to endDay
13%10%30%25%19%4
420
May1st to 10thDay
13%12%33%25%12%5%
423
11th to 20thDay
14%423%30%19%10%
447
21st to endDay
14%7%14%30%24%12%
485
June1st to 10thDay
10%217%31%28%11%
450
11th to 20thDay
8%6%15%26%26%19%
450
21st to endDay
7%218%33%27%14%
450
July1st to 10thDay
10%29%23%34%22%
445
11th to 20thDay
8%210%23%36%20%
444
21st to endDay
6%19%30%36%18%
488
August1st to 10thDay
14%216%26%26%17%
446
11th to 20thDay
10%111%28%31%18%
439
21st to endDay
13%213%26%30%16%
495
September1st to 10thDay
11%411%28%31%15%
450
11th to 20thDay
15%213%28%31%10%
450
21st to endDay
18%414%29%26%8%
450
October1st to 10thDay
18%5%24%26%18%8%
450
11th to 20thDay
13%9%24%26%20%8%
450
21st to endDay
17%9%26%26%17%5%
495
November1st to 10thDay
17%8%28%26%17%3
422
11th to 20thDay
19%16%36%24%5%1
270
21st to endDay
15%15%31%24%14%1
270
December1st to 10thDay
26%16%34%17%7%
270
11th to 20thDay
27%13%38%16%5%1
270
21st to endDay
28%17%33%14%5%2
297
January1st to 10thNight
21%19%33%22%6%
760
11th to 20thNight
21%15%31%26%8%
741
21st to endNight
20%17%35%25%4
792
February1st to 10thNight
19%15%30%31%6%
720
11th to 20thNight
23%16%33%26%3
703
21st to endNight
19%16%37%24%3
592
March1st to 10thNight
14%15%34%32%4
720
11th to 20thNight
17%14%32%27%9%1
720
21st to endNight
15%15%34%27%9%
792
April1st to 10thNight
13%16%32%28%11%
720
11th to 20thNight
15%14%26%29%14%1
651
21st to endNight
10%9%28%37%15%1
540
May1st to 10thNight
8%9%28%38%17%1
540
11th to 20thNight
10%323%37%22%4
531
21st to endNight
12%313%33%34%5%
584
June1st to 10thNight
10%214%40%30%4
540
11th to 20thNight
7%215%33%31%11%
540
21st to endNight
9%212%38%32%7%
540
July1st to 10thNight
10%18%32%39%10%
525
11th to 20thNight
7%18%30%46%9%
522
21st to endNight
7%28%32%45%7%
591
August1st to 10thNight
9%17%35%39%9%
537
11th to 20thNight
14%17%31%40%7%
534
21st to endNight
11%211%29%38%8%
656
September1st to 10thNight
10%210%33%36%9%
720
11th to 20thNight
16%311%27%38%4
720
21st to endNight
16%314%31%33%3
720
October1st to 10thNight
14%419%32%25%6%
720
11th to 20thNight
14%5%23%32%23%4
720
21st to endNight
13%9%24%30%23%2
792
November1st to 10thNight
14%8%23%33%20%3
740
11th to 20thNight
16%11%29%30%13%2
760
21st to endNight
16%10%28%30%15%1
760
December1st to 10thNight
18%15%25%32%9%1
760
11th to 20thNight
20%12%28%29%12%1
760
21st to endNight
25%15%25%28%7%
836
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