Astroknip's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astroknip's Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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
29%
22567
13%
74749
8%
22525
36%
22525
16%
53422

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
15%
760
8%
2649
2%
757
22%
757
7%
2143
January11th to 20thNight
17%
732
9%
2560
5%
732
23%
732
8%
2041
January21st to endNight
23%
792
13%
2701
8%
792
31%
792
13%
1964
February1st to 10thNight
16%
720
9%
2340
2%
720
24%
720
10%
1823
February11th to 20thNight
17%
702
13%
2271
5%
700
27%
700
13%
1670
February21st to endNight
24%
592
15%
1776
7%
592
33%
592
14%
1321
March1st to 10thNight
20%
720
14%
2160
8%
720
29%
720
14%
1614
March11th to 20thNight
21%
720
16%
1979
6%
720
31%
720
17%
1427
March21st to endNight
28%
792
21%
2062
9%
792
36%
792
20%
1467
April1st to 10thNight
23%
720
15%
1800
4%
720
29%
720
19%
1340
April11th to 20thNight
25%
711
17%
1775
5%
711
31%
711
21%
1286
April21st to endNight
28%
609
16%
1689
7%
609
35%
609
19%
1222
May1st to 10thNight
33%
360
16%
1440
12%
360
42%
360
16%
944
May11th to 20thNight
33%
354
21%
1416
15%
354
49%
354
18%
876
May21st to endNight
36%
389
13%
1551
10%
388
48%
388
22%
920
June1st to 10thNight
39%
360
10%
1440
11%
360
47%
360
17%
961
June11th to 20thNight
40%
360
12%
1440
15%
360
48%
360
20%
872
June21st to endNight
37%
360
11%
1440
13%
360
44%
360
17%
940
July1st to 10thNight
49%
350
14%
1400
18%
350
57%
350
25%
795
July11th to 20thNight
51%
348
15%
1392
23%
348
57%
348
25%
810
July21st to endNight
52%
394
15%
1486
17%
372
57%
372
23%
867
August1st to 10thNight
51%
389
16%
1453
14%
387
57%
387
23%
889
August11th to 20thNight
56%
541
17%
1605
13%
541
59%
541
30%
1026
August21st to endNight
47%
792
18%
1980
8%
792
50%
792
32%
1309
September1st to 10thNight
46%
720
17%
1800
8%
720
50%
720
31%
1212
September11th to 20thNight
50%
720
22%
1800
13%
720
54%
720
34%
1172
September21st to endNight
42%
720
21%
2036
14%
720
47%
720
26%
1347
October1st to 10thNight
34%
720
16%
2160
11%
720
42%
720
20%
1487
October11th to 20thNight
26%
720
14%
2160
8%
720
35%
720
16%
1581
October21st to endNight
25%
792
13%
2520
7%
792
34%
792
13%
1886
November1st to 10thNight
27%
740
15%
2407
9%
740
35%
740
16%
1681
November11th to 20thNight
21%
760
15%
2650
9%
760
31%
760
13%
1903
November21st to endNight
19%
760
9%
2660
4%
760
26%
760
10%
2037
December1st to 10thNight
19%
760
7%
2660
3%
760
24%
760
7%
2176
December11th to 20thNight
17%
759
12%
3243
6%
759
25%
759
8%
2456
December21st to endNight
14%
829
5%
4848
2%
817
21%
817
4%
3957

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%8%47%6%35%5%5%7%33%
74730
Night
18%10%47%6%3445%6%32%
75002
TransparencyDay
50%7%12%20%10%1
74435
Night
52%6%11%19%10%1
74831
SeeingDay
22%15%30%21%9%3
13357
Night
22%12%30%26%9%1
22576

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
16%16%6%11%7%35%5%45%21%
1517
11th to 20thDay
19%14%6%10%7%45%44424%
1456
21st to endDay
13%14%410%7%45%6%6%5%26%
1652
February1st to 10thDay
14%14%5%12%7%5%5%5%5%5%24%
1620
11th to 20thDay
13%15%5%8%6%35%5%5%6%29%
1577
21st to endDay
18%13%48%8%346%6%5%24%
1480
March1st to 10thDay
15%9%5%8%8%46%6%5%5%29%
1797
11th to 20thDay
15%11%47%6%46%5%5%6%32%
1976
21st to endDay
18%8%46%6%3445%6%37%
2294
April1st to 10thDay
22%9%46%5%3445%7%32%
2160
11th to 20thDay
20%8%36%5%34446%37%
2134
21st to endDay
22%9%46%6%4445%5%31%
2285
May1st to 10thDay
20%7%36%5%35%5%5%6%35%
2520
11th to 20thDay
15%7%36%5%45%5%47%40%
2478
21st to endDay
15%6%26%6%35%5%6%6%38%
2725
June1st to 10thDay
20%6%47%7%36%6%5%7%30%
2520
11th to 20thDay
14%5%25%6%46%5%6%9%38%
2520
21st to endDay
18%6%36%6%36%6%7%7%31%
2520
July1st to 10thDay
11%5%35%5%36%6%6%9%41%
2520
11th to 20thDay
12%6%26%6%45%5%6%9%40%
2520
21st to endDay
11%5%35%5%46%6%7%9%40%
2744
August1st to 10thDay
10%5%37%5%45%6%7%9%39%
2471
11th to 20thDay
11%6%26%6%35%6%6%9%40%
2277
21st to endDay
13%5%25%5%45%5%6%9%41%
2376
September1st to 10thDay
13%5%35%445%5%6%8%42%
2160
11th to 20thDay
12%5%345%3445%9%46%
2160
21st to endDay
17%5%25%5%4446%8%39%
1921
October1st to 10thDay
20%8%35%5%345%6%6%35%
1800
11th to 20thDay
22%7%37%6%45%5%5%7%28%
1800
21st to endDay
26%7%37%6%35%5%46%27%
1835
November1st to 10thDay
16%7%36%6%46%5%6%7%34%
1671
11th to 20thDay
20%10%47%5%46%5%6%6%27%
1526
21st to endDay
21%12%5%8%8%5%6%446%20%
1520
December1st to 10thDay
22%15%5%9%7%446%5%6%17%
1520
11th to 20thDay
21%13%5%8%7%45%5%5%6%23%
1906
21st to endDay
28%17%6%9%6%3333319%
2772
January1st to 10thNight
17%16%7%11%8%445%45%19%
2649
11th to 20thNight
18%16%7%9%8%35%44422%
2560
21st to endNight
12%14%6%9%7%345%47%29%
2701
February1st to 10thNight
15%13%5%12%8%5%6%5%45%23%
2340
11th to 20thNight
14%12%6%9%8%4445%6%29%
2269
21st to endNight
17%11%5%7%6%35%5%5%6%28%
1776
March1st to 10thNight
16%12%5%8%7%45%445%29%
2150
11th to 20thNight
17%10%5%8%7%34445%34%
1979
21st to endNight
18%8%37%5%3345%5%39%
2062
April1st to 10thNight
21%9%46%5%345%5%6%33%
1800
11th to 20thNight
19%7%36%6%335%5%5%36%
1775
21st to endNight
21%8%46%6%25%45%6%33%
1689
May1st to 10thNight
20%6%35%5%35%5%5%7%36%
1440
11th to 20thNight
17%8%345%345%47%39%
1415
21st to endNight
13%6%35%5%3446%8%44%
1550
June1st to 10thNight
16%7%25%7%45%7%6%8%33%
1440
11th to 20thNight
14%5%26%5%3346%8%42%
1440
21st to endNight
17%6%35%5%36%5%6%8%36%
1440
July1st to 10thNight
11%4346%35%6%5%8%45%
1440
11th to 20thNight
11%6%35%425%6%6%9%43%
1440
21st to endNight
9%5%25%6%35%6%6%8%44%
1574
August1st to 10thNight
9%7%36%5%346%6%9%42%
1463
11th to 20thNight
10%6%26%5%445%6%7%45%
1605
21st to endNight
11%5%26%6%45%5%5%8%44%
1980
September1st to 10thNight
12%5%35%5%45%46%6%46%
1800
11th to 20thNight
14%5%2443346%6%49%
1800
21st to endNight
17%5%36%5%34346%43%
2036
October1st to 10thNight
18%8%26%5%3445%6%37%
2160
11th to 20thNight
21%9%26%7%35%46%6%31%
2160
21st to endNight
23%9%46%6%35%45%7%27%
2520
November1st to 10thNight
20%9%45%6%3445%7%34%
2407
11th to 20thNight
18%10%47%7%45%5%5%6%29%
2650
21st to endNight
21%12%49%7%4445%7%24%
2660
December1st to 10thNight
22%15%5%9%7%46%5%5%5%17%
2660
11th to 20thNight
22%14%48%7%3443427%
3288
21st to endNight
30%17%5%8%6%3433418%
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
66%7%9%14%5%
1518
11th to 20thDay
65%5%8%11%10%1
1456
21st to endDay
59%7%12%13%8%1
1652
February1st to 10thDay
61%6%10%17%42
1620
11th to 20thDay
56%6%12%17%8%1
1586
21st to endDay
60%6%10%14%9%1
1480
March1st to 10thDay
55%6%11%17%10%1
1800
11th to 20thDay
53%5%12%16%11%3
1976
21st to endDay
48%6%9%18%14%5%
2294
April1st to 10thDay
53%48%20%12%3
2160
11th to 20thDay
50%48%22%15%2
2134
21st to endDay
54%5%8%14%14%4
2285
May1st to 10thDay
49%6%8%19%14%4
2520
11th to 20thDay
44%7%8%22%16%3
2482
21st to endDay
44%8%13%20%13%2
2725
June1st to 10thDay
53%7%10%18%12%1
2520
11th to 20thDay
41%8%11%24%13%3
2520
21st to endDay
48%9%13%19%10%1
2520
July1st to 10thDay
37%8%14%26%14%1
2450
11th to 20thDay
38%8%16%26%11%
2445
21st to endDay
39%11%15%25%10%
2591
August1st to 10thDay
40%10%15%25%10%
2457
11th to 20thDay
39%9%16%25%10%1
2277
21st to endDay
39%7%15%27%11%1
2376
September1st to 10thDay
39%8%15%27%12%
2160
11th to 20thDay
36%8%13%31%12%1
2160
21st to endDay
43%7%15%26%8%
1921
October1st to 10thDay
49%6%12%22%10%1
1800
11th to 20thDay
55%8%15%15%6%1
1800
21st to endDay
59%6%12%14%8%
1835
November1st to 10thDay
47%8%15%21%6%1
1671
11th to 20thDay
57%6%13%14%8%1
1526
21st to endDay
64%7%12%10%6%
1520
December1st to 10thDay
68%8%12%10%31
1520
11th to 20thDay
62%8%12%13%4
1906
21st to endDay
72%47%14%3
2772
January1st to 10thNight
68%6%10%12%5%
2649
11th to 20thNight
66%5%9%11%8%1
2560
21st to endNight
56%6%9%18%11%1
2701
February1st to 10thNight
63%5%10%14%6%1
2340
11th to 20thNight
57%5%11%19%8%1
2271
21st to endNight
56%6%9%18%10%1
1776
March1st to 10thNight
57%6%10%16%10%2
2160
11th to 20thNight
53%311%18%12%2
1980
21st to endNight
48%5%7%19%16%4
2062
April1st to 10thNight
52%5%8%18%14%2
1800
11th to 20thNight
49%6%8%21%16%1
1775
21st to endNight
52%5%8%16%15%4
1689
May1st to 10thNight
47%6%7%19%15%5%
1440
11th to 20thNight
44%5%8%22%18%3
1416
21st to endNight
37%8%15%19%18%2
1551
June1st to 10thNight
47%8%12%22%9%1
1440
11th to 20thNight
40%8%10%23%17%2
1440
21st to endNight
45%8%13%20%13%1
1440
July1st to 10thNight
35%7%13%27%17%2
1400
11th to 20thNight
36%7%14%30%13%
1392
21st to endNight
36%8%15%26%14%
1486
August1st to 10thNight
37%10%17%22%13%1
1453
11th to 20thNight
37%8%16%28%11%
1605
21st to endNight
36%8%16%29%11%
1980
September1st to 10thNight
38%8%11%29%14%1
1800
11th to 20thNight
34%7%13%34%9%1
1800
21st to endNight
41%7%11%30%10%
2036
October1st to 10thNight
46%7%11%22%13%1
2160
11th to 20thNight
53%7%11%20%8%
2160
21st to endNight
57%6%13%15%8%
2520
November1st to 10thNight
51%6%14%21%9%1
2407
11th to 20thNight
55%6%12%17%9%1
2650
21st to endNight
60%7%13%15%5%
2660
December1st to 10thNight
67%8%10%12%3
2660
11th to 20thNight
61%5%10%16%7%1
3288
21st to endNight
72%47%13%3
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
24%19%30%22%4
180
11th to 20thDay
28%18%35%14%5%1
164
21st to endDay
22%19%33%20%5%
206
February1st to 10thDay
33%23%33%11%
240
11th to 20thDay
27%24%39%9%1
244
21st to endDay
29%21%31%16%2
346
March1st to 10thDay
25%17%34%18%5%
420
11th to 20thDay
26%18%34%18%31
420
21st to endDay
29%21%26%15%8%1
462
April1st to 10thDay
28%20%30%16%5%1
420
11th to 20thDay
30%20%22%16%11%1
412
21st to endDay
32%18%27%15%6%1
420
May1st to 10thDay
23%15%32%20%7%2
423
11th to 20thDay
18%18%34%20%8%3
447
21st to endDay
17%15%33%22%11%1
485
June1st to 10thDay
26%9%34%22%8%2
450
11th to 20thDay
17%14%29%26%11%3
450
21st to endDay
17%14%32%23%11%3
450
July1st to 10thDay
12%7%28%34%15%4
445
11th to 20thDay
12%8%32%29%16%3
444
21st to endDay
13%8%30%31%15%4
488
August1st to 10thDay
15%7%28%29%17%4
446
11th to 20thDay
12%8%25%29%18%8%
439
21st to endDay
14%12%29%25%13%8%
495
September1st to 10thDay
16%11%30%19%16%9%
450
11th to 20thDay
13%9%27%24%17%10%
450
21st to endDay
17%11%30%22%14%5%
450
October1st to 10thDay
25%14%24%21%12%5%
450
11th to 20thDay
25%18%29%20%6%2
450
21st to endDay
31%14%27%22%5%
422
November1st to 10thDay
23%18%30%19%7%1
365
11th to 20thDay
29%20%32%11%6%1
186
21st to endDay
26%18%37%14%31
180
December1st to 10thDay
29%16%37%16%2
180
11th to 20thDay
28%27%31%12%21
180
21st to endDay
32%20%34%12%21
198
January1st to 10thNight
25%17%33%21%4
760
11th to 20thNight
27%17%30%20%5%1
732
21st to endNight
19%12%38%26%5%1
792
February1st to 10thNight
24%14%37%20%3
720
11th to 20thNight
22%17%39%19%4
703
21st to endNight
25%18%29%24%4
592
March1st to 10thNight
23%15%36%23%3
720
11th to 20thNight
23%19%32%21%5%
720
21st to endNight
23%16%27%26%8%
792
April1st to 10thNight
26%14%31%23%5%
720
11th to 20thNight
25%15%30%22%8%
711
21st to endNight
26%14%28%24%7%1
609
May1st to 10thNight
24%8%29%29%9%1
360
11th to 20thNight
22%11%28%30%9%
354
21st to endNight
15%7%39%25%13%
389
June1st to 10thNight
19%5%32%36%9%
360
11th to 20thNight
15%8%28%34%13%1
360
21st to endNight
19%5%32%30%14%1
360
July1st to 10thNight
9%5%30%41%15%
350
11th to 20thNight
13%426%42%15%1
348
21st to endNight
9%428%42%14%2
394
August1st to 10thNight
11%325%39%21%1
389
11th to 20thNight
13%221%37%24%2
541
21st to endNight
13%7%26%34%19%2
792
September1st to 10thNight
14%6%29%32%17%1
720
11th to 20thNight
17%7%21%32%20%3
720
21st to endNight
18%9%25%26%19%2
720
October1st to 10thNight
21%10%29%25%14%1
720
11th to 20thNight
25%13%29%25%8%1
720
21st to endNight
27%14%28%26%6%
792
November1st to 10thNight
27%13%28%23%9%1
740
11th to 20thNight
24%17%33%17%9%1
760
21st to endNight
30%16%26%22%6%
760
December1st to 10thNight
30%15%31%21%3
760
11th to 20thNight
28%16%31%20%5%1
760
21st to endNight
33%15%30%18%4
836
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