SFA Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SFA Observatory clear sky chart from 2005-11-06 to 2024-03-23.

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%
24134
24%
79760
16%
24018
53%
24018
28%
46938

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
28%
947
29%
3984
9%
926
39%
926
20%
2199
January11th to 20thNight
28%
949
27%
3938
9%
930
37%
930
19%
2211
January21st to endNight
26%
1041
17%
4463
8%
1023
36%
1023
16%
2844
February1st to 10thNight
25%
950
22%
2470
6%
950
34%
950
26%
1668
February11th to 20thNight
22%
754
20%
2229
7%
750
32%
750
22%
1463
February21st to endNight
20%
471
24%
1727
10%
471
36%
471
18%
1076
March1st to 10thNight
26%
570
23%
2090
11%
570
40%
570
20%
1311
March11th to 20thNight
28%
570
20%
2090
12%
570
39%
570
18%
1331
March21st to endNight
28%
600
23%
2200
13%
600
41%
600
23%
1302
April1st to 10thNight
27%
540
23%
1949
13%
540
42%
540
24%
1164
April11th to 20thNight
28%
533
23%
1775
13%
533
41%
533
24%
1074
April21st to endNight
32%
540
25%
1800
15%
540
48%
540
28%
1042
May1st to 10thNight
33%
540
20%
1751
15%
540
45%
540
27%
1051
May11th to 20thNight
43%
531
23%
1593
19%
531
51%
531
34%
936
May21st to endNight
51%
584
23%
1746
18%
582
61%
582
33%
1053
June1st to 10thNight
70%
540
19%
1620
19%
540
75%
540
39%
907
June11th to 20thNight
72%
540
23%
1620
25%
540
76%
540
50%
804
June21st to endNight
69%
540
22%
1620
23%
540
72%
540
37%
938
July1st to 10thNight
72%
525
17%
1575
19%
525
75%
525
32%
959
July11th to 20thNight
80%
522
21%
1566
24%
522
83%
522
46%
829
July21st to endNight
80%
591
19%
1673
21%
558
82%
558
39%
939
August1st to 10thNight
86%
537
27%
1601
30%
534
87%
534
54%
761
August11th to 20thNight
80%
534
23%
1693
27%
534
81%
534
37%
938
August21st to endNight
75%
594
19%
1980
22%
594
76%
594
30%
1187
September1st to 10thNight
71%
540
24%
1876
27%
540
73%
540
34%
1033
September11th to 20thNight
68%
540
22%
1980
25%
540
70%
540
29%
1136
September21st to endNight
72%
540
31%
1980
33%
540
74%
540
37%
997
October1st to 10thNight
70%
684
32%
2124
27%
684
74%
684
45%
1088
October11th to 20thNight
54%
720
34%
2160
21%
720
63%
720
38%
1215
October21st to endNight
48%
792
33%
2376
21%
792
56%
792
36%
1350
November1st to 10thNight
52%
740
29%
2220
21%
740
58%
740
37%
1259
November11th to 20thNight
44%
760
28%
2280
18%
760
52%
760
33%
1318
November21st to endNight
36%
835
27%
2355
14%
835
46%
835
27%
1521
December1st to 10thNight
34%
950
26%
2470
12%
950
43%
950
29%
1635
December11th to 20thNight
29%
949
25%
2867
10%
948
38%
948
22%
1880
December21st to endNight
29%
1041
15%
4319
10%
1026
37%
1026
17%
2519

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
13%6%35%5%35%5%5%7%43%
79219
Night
13%6%2442445%7%50%
80724
TransparencyDay
39%7%11%19%18%6%
78944
Night
34%6%11%19%21%9%
80519
SeeingDay
14%9%23%27%21%6%
14129
Night
15%9%25%31%17%2
24147

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
18%10%35%423445%43%
2847
11th to 20thDay
21%6%23312345%49%
2850
21st to endDay
24%9%24422236%42%
3135
February1st to 10thDay
22%8%46%433336%37%
1710
11th to 20thDay
21%9%35%5%3444439%
1853
21st to endDay
21%7%36%43433442%
1727
March1st to 10thDay
20%8%35%5%34346%38%
2090
11th to 20thDay
18%7%35%4345%47%39%
2090
21st to endDay
16%8%35%5%2445%5%42%
2200
April1st to 10thDay
14%6%36%7%3445%7%42%
2008
11th to 20thDay
15%6%45%5%35%6%5%8%39%
2134
21st to endDay
12%5%36%5%345%5%7%45%
2160
May1st to 10thDay
12%6%36%6%36%5%6%7%40%
2204
11th to 20thDay
12%6%36%6%35%5%5%6%42%
2302
21st to endDay
10%5%37%7%46%6%7%11%34%
2531
June1st to 10thDay
7%5%35%7%46%7%7%10%41%
2340
11th to 20thDay
6%335%6%46%6%8%11%44%
2340
21st to endDay
6%436%6%47%7%8%10%39%
2340
July1st to 10thDay
7%6%36%7%5%7%7%8%10%35%
2340
11th to 20thDay
7%425%5%47%6%8%10%43%
2340
21st to endDay
6%436%7%46%6%8%11%40%
2546
August1st to 10thDay
32245%36%6%7%9%52%
2328
11th to 20thDay
5%5%25%6%45%6%9%10%43%
2205
21st to endDay
9%436%7%5%7%7%8%8%37%
2376
September1st to 10thDay
7%5%25%6%36%6%7%8%44%
2079
11th to 20thDay
12%5%36%6%36%5%6%7%41%
1980
21st to endDay
8%4245%345%5%6%53%
1980
October1st to 10thDay
7%41333445%7%60%
1818
11th to 20thDay
12%6%24324446%53%
1800
21st to endDay
15%5%25%323335%54%
1980
November1st to 10thDay
12%6%25%425%45%6%50%
1858
11th to 20thDay
11%6%25%5%2335%5%53%
1900
21st to endDay
18%7%36%433335%45%
1822
December1st to 10thDay
17%6%25%5%33346%45%
1710
11th to 20thDay
18%7%36%434445%41%
2161
21st to endDay
17%8%47%5%24435%41%
3135
January1st to 10thNight
16%7%25%423335%51%
4108
11th to 20thNight
19%6%25%32223452%
4120
21st to endNight
23%11%3431234441%
4532
February1st to 10thNight
17%7%35%5%2435%6%44%
2470
11th to 20thNight
21%8%35%422335%44%
2229
21st to endNight
22%7%24324345%44%
1727
March1st to 10thNight
19%8%245%2345%7%41%
2090
11th to 20thNight
15%7%36%6%35%35%6%41%
2090
21st to endNight
14%6%35%423446%48%
2200
April1st to 10thNight
12%435%5%35%5%5%7%46%
1949
11th to 20thNight
13%436%5%34446%46%
1775
21st to endNight
12%5%25%5%24446%52%
1800
May1st to 10thNight
9%6%35%5%245%5%10%46%
1751
11th to 20thNight
12%6%2432336%8%50%
1593
21st to endNight
8%425%5%3447%11%47%
1745
June1st to 10thNight
5%423425%6%6%11%53%
1620
11th to 20thNight
32223245%6%11%62%
1620
21st to endNight
7%325%435%5%7%10%50%
1620
July1st to 10thNight
5%415%5%46%7%7%11%45%
1620
11th to 20thNight
321342447%10%59%
1620
21st to endNight
42245%35%6%8%13%49%
1772
August1st to 10thNight
311322447%11%63%
1611
11th to 20thNight
3423435%7%7%13%49%
1693
21st to endNight
8%3235%45%7%8%11%45%
1980
September1st to 10thNight
7%5%35%4345%49%52%
1876
11th to 20thNight
11%5%245%3445%7%50%
1980
21st to endNight
7%41442345%7%58%
1980
October1st to 10thNight
5%314324447%62%
2124
11th to 20thNight
11%5%13324345%58%
2160
21st to endNight
15%42332233459%
2376
November1st to 10thNight
12%413433346%57%
2220
11th to 20thNight
11%5%25%42335%6%53%
2280
21st to endNight
16%7%25%5%3445%446%
2355
December1st to 10thNight
17%7%2443445%6%45%
2470
11th to 20thNight
17%8%35%5%24335%46%
3036
21st to endNight
16%8%25%43344448%
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
43%5%6%17%25%5%
2848
11th to 20thDay
38%36%23%25%5%
2850
21st to endDay
46%25%17%20%10%
3135
February1st to 10thDay
50%5%6%13%17%10%
1710
11th to 20thDay
49%46%14%19%8%
1863
21st to endDay
47%5%6%13%18%11%
1727
March1st to 10thDay
48%5%8%13%19%8%
2090
11th to 20thDay
44%7%8%14%20%6%
2090
21st to endDay
44%5%8%15%23%5%
2200
April1st to 10thDay
43%6%9%19%16%7%
2008
11th to 20thDay
42%8%10%16%16%8%
2134
21st to endDay
39%7%9%18%24%5%
2160
May1st to 10thDay
42%8%10%18%16%6%
2204
11th to 20thDay
41%7%11%23%16%2
2306
21st to endDay
42%10%14%20%14%1
2531
June1st to 10thDay
36%10%14%24%13%1
2340
11th to 20thDay
31%10%16%27%14%2
2340
21st to endDay
36%11%15%24%12%2
2340
July1st to 10thDay
40%12%19%21%7%1
2276
11th to 20thDay
31%10%20%25%13%
2271
21st to endDay
33%11%20%26%10%
2405
August1st to 10thDay
25%9%20%31%14%1
2314
11th to 20thDay
32%10%20%25%12%2
2205
21st to endDay
39%11%17%20%11%2
2376
September1st to 10thDay
35%9%15%19%15%8%
2079
11th to 20thDay
39%9%14%15%16%7%
1980
21st to endDay
30%6%11%20%21%12%
1980
October1st to 10thDay
25%6%10%20%24%14%
1818
11th to 20thDay
32%5%7%17%24%15%
1800
21st to endDay
34%45%14%28%14%
1980
November1st to 10thDay
35%5%9%17%24%10%
1858
11th to 20thDay
35%47%18%25%11%
1900
21st to endDay
43%5%6%17%22%7%
1822
December1st to 10thDay
41%5%10%17%19%8%
1710
11th to 20thDay
44%46%15%22%8%
2159
21st to endDay
46%45%13%24%7%
3135
January1st to 10thNight
36%47%17%28%7%
4108
11th to 20thNight
38%45%17%27%10%
4120
21st to endNight
47%46%16%19%10%
4532
February1st to 10thNight
43%47%15%18%13%
2470
11th to 20thNight
45%46%15%20%10%
2229
21st to endNight
44%48%12%18%14%
1727
March1st to 10thNight
44%5%8%15%19%10%
2090
11th to 20thNight
43%7%8%13%21%8%
2090
21st to endNight
38%6%9%16%23%8%
2200
April1st to 10thNight
36%7%11%18%17%10%
1949
11th to 20thNight
38%5%11%18%16%12%
1775
21st to endNight
34%6%10%19%25%7%
1800
May1st to 10thNight
36%7%11%19%19%8%
1751
11th to 20thNight
33%5%14%26%19%3
1594
21st to endNight
32%8%18%25%16%1
1746
June1st to 10thNight
25%9%19%28%18%1
1620
11th to 20thNight
17%8%19%35%19%3
1620
21st to endNight
28%9%16%25%20%2
1620
July1st to 10thNight
29%12%23%26%9%1
1575
11th to 20thNight
18%11%29%26%16%1
1566
21st to endNight
22%12%26%28%11%1
1673
August1st to 10thNight
14%8%26%35%15%2
1601
11th to 20thNight
24%11%22%27%13%3
1693
21st to endNight
30%11%19%23%13%3
1980
September1st to 10thNight
29%7%17%22%17%9%
1876
11th to 20thNight
33%8%15%19%18%8%
1980
21st to endNight
25%6%11%21%25%11%
1980
October1st to 10thNight
23%5%9%24%22%17%
2124
11th to 20thNight
29%5%7%16%26%17%
2160
21st to endNight
30%5%6%15%26%18%
2376
November1st to 10thNight
30%5%9%20%25%12%
2220
11th to 20thNight
31%6%9%18%23%14%
2280
21st to endNight
40%5%7%15%22%11%
2355
December1st to 10thNight
39%5%10%17%19%9%
2470
11th to 20thNight
43%46%12%22%13%
3037
21st to endNight
40%5%7%14%28%8%
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
27%17%37%15%4
270
11th to 20thDay
30%16%34%15%4
270
21st to endDay
27%21%35%15%2
297
February1st to 10thDay
29%22%31%16%2
270
11th to 20thDay
36%21%32%12%
270
21st to endDay
30%24%38%7%
225
March1st to 10thDay
29%21%31%17%2
270
11th to 20thDay
23%26%36%12%3
270
21st to endDay
21%19%40%16%3
270
April1st to 10thDay
22%15%44%16%3
268
11th to 20thDay
23%17%26%24%9%1
412
21st to endDay
17%15%38%21%7%2
420
May1st to 10thDay
16%10%39%28%7%
467
11th to 20thDay
15%9%27%32%15%2
625
21st to endDay
12%8%27%33%15%5%
679
June1st to 10thDay
8%119%38%26%7%
630
11th to 20thDay
6%120%42%24%6%
630
21st to endDay
7%316%35%29%10%
630
July1st to 10thDay
7%113%32%35%11%
621
11th to 20thDay
418%30%45%12%
618
21st to endDay
5%17%35%40%12%
684
August1st to 10thDay
46%30%48%11%
626
11th to 20thDay
6%1431%45%13%
519
21st to endDay
10%27%21%38%21%
495
September1st to 10thDay
5%28%30%41%15%
369
11th to 20thDay
7%214%33%34%10%
270
21st to endDay
11%39%37%31%9%
270
October1st to 10thDay
6%423%40%22%5%
270
11th to 20thDay
12%8%33%30%13%5%
270
21st to endDay
25%11%30%19%11%3
297
November1st to 10thDay
14%7%32%31%14%1
270
11th to 20thDay
15%14%37%26%7%1
270
21st to endDay
24%15%35%19%6%1
270
December1st to 10thDay
17%15%36%21%8%3
270
11th to 20thDay
26%14%35%19%6%
270
21st to endDay
25%20%36%14%41
297
January1st to 10thNight
23%14%32%25%5%
950
11th to 20thNight
25%16%28%25%7%
950
21st to endNight
24%14%33%25%4
1045
February1st to 10thNight
23%15%33%25%3
950
11th to 20thNight
28%15%32%21%3
754
21st to endNight
26%17%35%20%2
471
March1st to 10thNight
25%14%34%23%5%
570
11th to 20thNight
18%17%34%27%5%1
570
21st to endNight
16%13%41%24%6%
600
April1st to 10thNight
15%14%41%23%7%
540
11th to 20thNight
17%13%37%22%11%
533
21st to endNight
15%11%40%24%10%
540
May1st to 10thNight
12%10%40%28%9%
540
11th to 20thNight
13%8%31%33%14%1
531
21st to endNight
10%429%35%19%3
584
June1st to 10thNight
7%215%42%32%3
540
11th to 20thNight
2218%50%25%2
540
21st to endNight
7%116%42%29%6%
540
July1st to 10thNight
6%113%40%35%6%
525
11th to 20thNight
319%39%43%5%
522
21st to endNight
416%44%37%7%
591
August1st to 10thNight
315%47%40%5%
537
11th to 20thNight
5%17%45%36%7%
534
21st to endNight
9%26%35%43%7%
594
September1st to 10thNight
8%18%36%42%6%
540
11th to 20thNight
12%210%29%42%6%
540
21st to endNight
7%311%36%36%7%
540
October1st to 10thNight
7%216%40%30%5%
684
11th to 20thNight
13%6%23%38%17%3
720
21st to endNight
16%7%27%30%18%2
792
November1st to 10thNight
12%6%26%37%18%1
740
11th to 20thNight
12%10%29%38%10%1
760
21st to endNight
19%14%27%27%13%
835
December1st to 10thNight
21%13%29%29%8%
950
11th to 20thNight
23%11%32%29%5%
950
21st to endNight
22%13%30%27%6%
1045
Page generated at 2024-03-19 22:31:06. Version ac07

Copyright © 2024 Attilla Danko.


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