NF/ Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NF/ Observatory clear sky chart from 2005-11-06 to 2024-02-10.

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
59%
23576
33%
79096
23%
23479
70%
23479
43%
37711

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
53%
754
37%
3994
26%
736
68%
736
31%
1587
January11th to 20thNight
53%
755
44%
3905
26%
740
68%
740
41%
1303
January21st to endNight
47%
828
24%
4268
24%
814
66%
814
25%
2145
February1st to 10thNight
51%
758
35%
2463
24%
758
68%
758
47%
1131
February11th to 20thNight
44%
700
33%
2155
20%
700
60%
700
44%
1062
February21st to endNight
35%
592
40%
1643
18%
592
56%
592
47%
819
March1st to 10thNight
42%
720
39%
1980
17%
720
61%
720
49%
986
March11th to 20thNight
50%
720
37%
1980
19%
720
65%
720
51%
978
March21st to endNight
42%
792
38%
2178
14%
792
62%
792
52%
1064
April1st to 10thNight
42%
594
40%
1854
16%
594
67%
594
57%
778
April11th to 20thNight
40%
533
40%
1777
20%
533
68%
533
53%
716
April21st to endNight
41%
540
42%
1800
22%
540
69%
540
54%
705
May1st to 10thNight
50%
540
36%
1800
24%
540
69%
540
57%
731
May11th to 20thNight
57%
531
33%
1645
23%
531
70%
531
53%
754
May21st to endNight
55%
584
38%
1746
21%
582
71%
582
63%
739
June1st to 10thNight
64%
540
30%
1620
24%
540
70%
540
51%
778
June11th to 20thNight
67%
540
32%
1620
23%
540
75%
540
61%
710
June21st to endNight
67%
540
20%
1620
16%
540
69%
540
38%
898
July1st to 10thNight
73%
525
20%
1575
17%
525
74%
525
35%
908
July11th to 20thNight
74%
522
16%
1566
14%
522
74%
522
25%
1034
July21st to endNight
73%
591
14%
1674
13%
558
72%
558
28%
1071
August1st to 10thNight
75%
537
15%
1602
15%
534
75%
534
30%
980
August11th to 20thNight
74%
534
21%
1770
23%
534
75%
534
27%
1087
August21st to endNight
75%
594
21%
1980
24%
594
76%
594
28%
1193
September1st to 10thNight
73%
540
26%
1800
28%
540
74%
540
32%
1024
September11th to 20thNight
78%
613
35%
1873
32%
613
80%
613
44%
986
September21st to endNight
74%
720
33%
2029
24%
720
79%
720
54%
1024
October1st to 10thNight
68%
720
33%
2160
24%
720
74%
720
49%
1084
October11th to 20thNight
70%
720
41%
2160
28%
720
79%
720
63%
939
October21st to endNight
68%
792
44%
2376
30%
792
79%
792
65%
1014
November1st to 10thNight
70%
740
43%
2220
31%
740
79%
740
64%
949
November11th to 20thNight
66%
760
42%
2280
30%
760
77%
760
59%
1010
November21st to endNight
53%
760
41%
2280
27%
760
66%
760
44%
1135
December1st to 10thNight
58%
760
38%
2465
30%
760
68%
760
46%
1171
December11th to 20thNight
50%
758
32%
2916
23%
758
64%
758
35%
1460
December21st to endNight
51%
829
23%
4322
27%
817
64%
817
30%
1758

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
44244345%5%7%60%
78851
Night
431342445%7%62%
80188
TransparencyDay
21%5%8%15%28%23%
78578
Night
20%5%8%16%29%22%
79982
SeeingDay
7%13%27%30%18%5%
13473
Night
5%7%23%37%23%4
23608

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
34245%3445%461%
2858
11th to 20thDay
341322345%6%67%
2860
21st to endDay
8%6%243335%6%8%51%
3146
February1st to 10thDay
34234235%45%65%
1701
11th to 20thDay
6%4234235%45%62%
1692
21st to endDay
36%2322334368%
1610
March1st to 10thDay
45%24334446%60%
1980
11th to 20thDay
5%41332335%5%67%
1980
21st to endDay
221232446%7%67%
2178
April1st to 10thDay
2212323446%70%
2105
11th to 20thDay
2312212335%76%
2131
21st to endDay
2212312335%76%
2160
May1st to 10thDay
2212323246%73%
2160
11th to 20thDay
322322445%6%68%
2246
21st to endDay
2212212335%78%
2530
June1st to 10thDay
321232435%8%66%
2340
11th to 20thDay
3212212346%74%
2340
21st to endDay
4325%435%6%7%7%55%
2340
July1st to 10thDay
6%425%6%5%6%8%6%9%42%
2340
11th to 20thDay
5%5%26%7%6%7%8%8%12%34%
2340
21st to endDay
7%6%46%7%5%8%9%8%12%29%
2545
August1st to 10thDay
7%436%6%47%7%9%11%37%
2328
11th to 20thDay
6%5%36%7%47%7%9%9%38%
2128
21st to endDay
6%437%6%5%7%6%8%9%40%
2376
September1st to 10thDay
10%5%35%5%35%6%6%8%44%
2160
11th to 20thDay
7%4133346%6%7%56%
2082
21st to endDay
5%213324447%65%
1931
October1st to 10thDay
6%2123235%5%6%64%
1800
11th to 20thDay
431332333472%
1800
21st to endDay
3212222235%76%
1980
November1st to 10thDay
2212323336%72%
1859
11th to 20thDay
3313323345%71%
1900
21st to endDay
5%5%2432445%6%60%
1900
December1st to 10thDay
5%323324447%63%
1710
11th to 20thDay
6%7%26%5%34437%54%
2169
21st to endDay
35%223235%5%6%63%
3146
January1st to 10thNight
46%2442345%7%60%
4097
11th to 20thNight
321232333474%
4110
21st to endNight
8%7%25%4235%6%8%50%
4521
February1st to 10thNight
331332445%6%65%
2463
11th to 20thNight
6%424323446%63%
2155
21st to endNight
341323335%468%
1643
March1st to 10thNight
33133135%5%8%64%
1980
11th to 20thNight
4323323346%69%
1980
21st to endNight
3312323346%69%
2178
April1st to 10thNight
221222345%6%72%
1854
11th to 20thNight
3213222345%74%
1777
21st to endNight
1112313345%76%
1800
May1st to 10thNight
3212313345%74%
1800
11th to 20thNight
321231435%6%69%
1645
21st to endNight
2212312335%76%
1746
June1st to 10thNight
321243345%7%64%
1620
11th to 20thNight
2113223346%72%
1620
21st to endNight
43246%45%6%7%8%50%
1620
July1st to 10thNight
5%325%5%36%6%8%12%45%
1620
11th to 20thNight
4336%7%5%9%9%10%12%33%
1620
21st to endNight
45%36%7%5%6%7%9%14%35%
1773
August1st to 10thNight
4435%5%36%7%10%13%39%
1611
11th to 20thNight
4426%7%47%7%10%13%36%
1770
21st to endNight
4425%7%47%8%9%11%39%
1980
September1st to 10thNight
7%4245%45%6%7%9%47%
1800
11th to 20thNight
6%31443445%8%59%
1873
21st to endNight
5%312324346%68%
2029
October1st to 10thNight
5%31332445%5%64%
2160
11th to 20thNight
331221233476%
2160
21st to endNight
3212212235%78%
2376
November1st to 10thNight
3212213347%73%
2220
11th to 20thNight
2312322245%73%
2280
21st to endNight
6%424223347%63%
2280
December1st to 10thNight
6%31233345%7%63%
2465
11th to 20thNight
4425%5%25%5%5%8%55%
3041
21st to endNight
6%41432345%6%62%
4521

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
22%36%13%39%18%
2859
11th to 20thDay
16%46%21%37%17%
2860
21st to endDay
26%5%7%22%28%12%
3146
February1st to 10thDay
19%46%15%27%30%
1701
11th to 20thDay
23%46%13%28%26%
1702
21st to endDay
20%2310%30%34%
1610
March1st to 10thDay
23%36%11%31%26%
1980
11th to 20thDay
19%35%13%31%30%
1980
21st to endDay
15%36%15%37%25%
2178
April1st to 10thDay
14%25%12%38%29%
2105
11th to 20thDay
12%1410%33%40%
2134
21st to endDay
11%25%11%35%36%
2160
May1st to 10thDay
12%25%11%28%42%
2160
11th to 20thDay
16%47%12%30%31%
2249
21st to endDay
10%249%29%45%
2530
June1st to 10thDay
16%35%11%31%34%
2340
11th to 20thDay
12%348%23%51%
2340
21st to endDay
23%6%10%13%19%28%
2340
July1st to 10thDay
32%9%13%15%16%16%
2276
11th to 20thDay
34%12%17%21%10%6%
2271
21st to endDay
42%13%20%15%9%1
2404
August1st to 10thDay
33%12%17%21%13%4
2313
11th to 20thDay
34%10%15%18%19%4
2128
21st to endDay
34%10%14%18%18%6%
2376
September1st to 10thDay
34%7%10%18%19%12%
2160
11th to 20thDay
23%6%8%17%29%16%
2082
21st to endDay
18%5%7%18%33%21%
1931
October1st to 10thDay
19%49%16%26%26%
1800
11th to 20thDay
17%3410%32%35%
1800
21st to endDay
13%2415%37%30%
1980
November1st to 10thDay
15%26%18%33%27%
1859
11th to 20thDay
17%3417%32%28%
1900
21st to endDay
25%36%15%31%20%
1900
December1st to 10thDay
20%46%22%29%19%
1710
11th to 20thDay
31%46%19%24%15%
2168
21st to endDay
19%48%15%35%20%
3146
January1st to 10thNight
21%46%14%39%15%
4097
11th to 20thNight
15%25%20%43%14%
4110
21st to endNight
31%46%20%28%11%
4521
February1st to 10thNight
17%5%6%17%27%28%
2463
11th to 20thNight
21%36%16%28%25%
2155
21st to endNight
18%35%12%30%31%
1643
March1st to 10thNight
17%46%15%31%27%
1980
11th to 20thNight
18%3413%34%28%
1980
21st to endNight
17%25%16%37%23%
2178
April1st to 10thNight
13%26%15%40%25%
1854
11th to 20thNight
13%2411%33%37%
1777
21st to endNight
11%3415%36%31%
1800
May1st to 10thNight
13%2310%31%41%
1800
11th to 20thNight
16%47%13%26%33%
1646
21st to endNight
12%25%9%28%45%
1746
June1st to 10thNight
18%5%6%10%27%34%
1620
11th to 20thNight
13%35%8%23%48%
1620
21st to endNight
27%6%11%12%16%27%
1620
July1st to 10thNight
28%9%15%19%16%13%
1575
11th to 20thNight
34%15%16%20%9%5%
1566
21st to endNight
35%11%26%18%8%3
1674
August1st to 10thNight
30%12%21%22%10%5%
1602
11th to 20thNight
34%10%19%16%14%6%
1770
21st to endNight
32%11%17%22%15%3
1980
September1st to 10thNight
29%9%13%18%17%13%
1800
11th to 20thNight
22%7%10%18%25%17%
1873
21st to endNight
18%48%17%34%19%
2029
October1st to 10thNight
20%5%8%15%27%25%
2160
11th to 20thNight
13%2414%31%36%
2160
21st to endNight
12%2418%32%33%
2376
November1st to 10thNight
12%26%16%37%27%
2220
11th to 20thNight
14%2419%31%29%
2280
21st to endNight
22%45%16%32%22%
2280
December1st to 10thNight
20%47%21%27%21%
2465
11th to 20thNight
25%49%18%25%18%
3041
21st to endNight
23%36%17%30%22%
4521

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
14%16%33%26%11%
270
11th to 20thDay
12%15%30%28%12%4
270
21st to endDay
6%15%35%28%13%3
297
February1st to 10thDay
6%20%30%27%13%4
267
11th to 20thDay
15%20%32%27%7%
240
21st to endDay
16%36%28%15%5%1
328
March1st to 10thDay
13%27%35%19%5%1
420
11th to 20thDay
13%21%32%24%8%2
420
21st to endDay
9%36%35%13%5%1
462
April1st to 10thDay
6%26%39%22%5%1
420
11th to 20thDay
8%30%37%17%6%1
412
21st to endDay
10%23%41%19%7%1
420
May1st to 10thDay
5%20%42%24%9%
423
11th to 20thDay
216%37%34%8%2
448
21st to endDay
317%40%30%9%1
485
June1st to 10thDay
47%35%37%15%1
450
11th to 20thDay
38%34%35%17%2
450
21st to endDay
6%326%41%21%4
450
July1st to 10thDay
7%211%42%29%9%
446
11th to 20thDay
5%7%31%43%14%
444
21st to endDay
5%19%24%43%18%
487
August1st to 10thDay
6%17%33%38%15%
447
11th to 20thDay
7%211%39%28%13%
437
21st to endDay
5%110%31%40%13%
495
September1st to 10thDay
11%215%37%28%7%
450
11th to 20thDay
5%120%43%24%7%
450
21st to endDay
5%6%25%38%22%4
401
October1st to 10thDay
8%10%26%30%20%7%
270
11th to 20thDay
9%11%22%36%19%4
270
21st to endDay
6%11%22%32%23%6%
297
November1st to 10thDay
415%31%33%13%3
270
11th to 20thDay
5%9%25%37%20%3
270
21st to endDay
10%17%28%31%12%1
270
December1st to 10thDay
7%16%27%31%17%1
270
11th to 20thDay
8%19%33%28%10%2
270
21st to endDay
13%20%31%28%5%1
297
January1st to 10thNight
7%9%26%37%17%4
760
11th to 20thNight
6%9%28%37%17%4
760
21st to endNight
9%10%27%34%17%2
836
February1st to 10thNight
411%32%35%16%3
758
11th to 20thNight
8%13%32%36%11%1
704
21st to endNight
7%17%36%30%9%1
592
March1st to 10thNight
5%15%35%33%12%1
720
11th to 20thNight
5%12%29%37%15%3
720
21st to endNight
5%14%35%32%13%1
792
April1st to 10thNight
311%41%35%9%1
594
11th to 20thNight
315%40%29%12%1
533
21st to endNight
414%38%33%10%2
540
May1st to 10thNight
39%35%42%9%1
540
11th to 20thNight
36%28%47%15%1
531
21st to endNight
25%34%45%14%1
584
June1st to 10thNight
4423%49%19%1
540
11th to 20thNight
3322%50%20%2
540
21st to endNight
4318%42%31%3
540
July1st to 10thNight
6%9%39%38%8%
525
11th to 20thNight
5%428%53%11%
522
21st to endNight
6%16%23%51%13%
591
August1st to 10thNight
5%323%55%14%
537
11th to 20thNight
318%28%51%10%
534
21st to endNight
416%29%52%8%
594
September1st to 10thNight
7%17%35%46%4
540
11th to 20thNight
6%18%42%38%5%
613
21st to endNight
4214%42%33%5%
720
October1st to 10thNight
5%219%46%25%3
720
11th to 20thNight
4319%46%23%4
720
21st to endNight
4421%39%25%7%
792
November1st to 10thNight
4419%42%24%7%
740
11th to 20thNight
35%21%44%23%4
760
21st to endNight
7%10%24%34%20%5%
760
December1st to 10thNight
7%8%23%39%18%5%
760
11th to 20thNight
6%9%29%38%16%3
760
21st to endNight
9%12%24%39%14%3
836
Page generated at 2024-02-07 04:11:56. Version ac07

Copyright 2024 Attilla Danko


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