Hepcat Sky Observatory
Clear Sky Chart
History

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

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
52%
23688
23%
74229
18%
23630
58%
23630
30%
44200

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
36%
950
26%
2458
11%
946
45%
946
31%
1597
January11th to 20thNight
37%
905
24%
2353
10%
905
44%
905
29%
1541
January21st to endNight
36%
990
26%
2574
11%
990
44%
990
28%
1702
February1st to 10thNight
29%
810
21%
2250
8%
810
37%
810
23%
1531
February11th to 20thNight
32%
704
20%
2098
9%
700
40%
700
24%
1345
February21st to endNight
24%
444
23%
1628
9%
444
38%
444
17%
1054
March1st to 10thNight
33%
540
23%
1980
13%
540
45%
540
21%
1240
March11th to 20thNight
36%
540
20%
1980
15%
540
44%
540
21%
1238
March21st to endNight
36%
594
24%
2178
17%
594
47%
594
26%
1246
April1st to 10thNight
36%
540
21%
1980
15%
540
47%
540
22%
1226
April11th to 20thNight
37%
533
22%
1829
15%
533
49%
533
25%
1110
April21st to endNight
40%
540
24%
1800
20%
540
50%
540
26%
1093
May1st to 10thNight
41%
540
21%
1724
17%
540
49%
540
25%
1072
May11th to 20thNight
51%
531
23%
1594
22%
531
55%
531
32%
954
May21st to endNight
62%
583
22%
1745
22%
582
67%
582
35%
1010
June1st to 10thNight
77%
540
22%
1620
24%
540
79%
540
45%
857
June11th to 20thNight
78%
540
22%
1620
26%
540
81%
540
46%
838
June21st to endNight
72%
540
18%
1620
21%
540
73%
540
32%
977
July1st to 10thNight
78%
525
15%
1575
18%
525
79%
525
34%
929
July11th to 20thNight
84%
522
22%
1566
25%
522
85%
522
45%
826
July21st to endNight
85%
591
19%
1673
22%
558
86%
558
41%
915
August1st to 10thNight
90%
537
25%
1601
28%
534
91%
534
58%
748
August11th to 20thNight
85%
534
23%
1667
25%
534
86%
534
41%
904
August21st to endNight
80%
594
18%
2044
20%
594
81%
594
31%
1181
September1st to 10thNight
78%
540
18%
1980
22%
540
79%
540
31%
1088
September11th to 20thNight
69%
540
22%
1980
24%
540
71%
540
26%
1177
September21st to endNight
73%
540
28%
1980
31%
540
75%
540
35%
1026
October1st to 10thNight
76%
616
32%
2056
31%
616
78%
616
43%
1025
October11th to 20thNight
60%
720
33%
2160
23%
720
66%
720
41%
1195
October21st to endNight
54%
792
34%
2376
23%
792
60%
792
39%
1299
November1st to 10thNight
59%
740
28%
2220
22%
740
63%
740
37%
1266
November11th to 20thNight
49%
760
28%
2280
19%
760
55%
760
31%
1366
November21st to endNight
42%
836
27%
2356
16%
836
49%
836
29%
1511
December1st to 10thNight
41%
950
26%
2470
15%
950
47%
950
28%
1686
December11th to 20thNight
36%
949
23%
2884
10%
948
41%
948
22%
1921
December21st to endNight
35%
1038
15%
4330
11%
1026
41%
1026
18%
2506

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%6%35%6%35%5%6%8%41%
74931
Night
13%5%2442445%8%48%
74790
TransparencyDay
40%7%12%18%16%7%
74656
Night
35%6%13%21%17%9%
74585
SeeingDay
12%6%17%26%26%13%
13715
Night
14%6%21%34%23%3
23697

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
19%6%25%42445%5%45%
1707
11th to 20thDay
21%6%35%5%34345%43%
1620
21st to endDay
19%6%35%5%3345%6%43%
1782
February1st to 10thDay
23%8%36%5%2334439%
1724
11th to 20thDay
20%9%35%5%24445%38%
1749
21st to endDay
20%6%35%5%24445%40%
1626
March1st to 10thDay
21%7%36%6%34446%36%
1980
11th to 20thDay
17%8%36%6%3435%6%38%
1980
21st to endDay
16%7%36%5%3445%6%42%
2178
April1st to 10thDay
15%8%38%6%45%446%38%
1980
11th to 20thDay
18%6%25%6%3445%7%39%
2080
21st to endDay
12%5%35%6%3446%7%43%
2160
May1st to 10thDay
10%6%36%7%46%5%6%8%39%
2231
11th to 20thDay
9%6%35%6%36%5%6%8%41%
2302
21st to endDay
9%5%47%8%47%7%7%11%31%
2531
June1st to 10thDay
6%426%5%46%7%6%10%44%
2340
11th to 20thDay
5%3245%47%7%7%12%44%
2340
21st to endDay
6%5%48%8%5%8%9%8%9%30%
2340
July1st to 10thDay
10%436%7%5%6%8%9%10%32%
2340
11th to 20thDay
5%426%7%5%6%9%8%11%36%
2340
21st to endDay
4436%6%36%8%9%13%37%
2546
August1st to 10thDay
32147%47%7%9%13%43%
2328
11th to 20thDay
6%4247%47%7%8%10%42%
2232
21st to endDay
7%426%8%5%7%7%7%9%37%
2305
September1st to 10thDay
6%5%36%6%47%6%6%10%41%
1980
11th to 20thDay
12%6%36%8%5%7%6%6%8%36%
1980
21st to endDay
7%436%6%46%5%6%8%46%
1980
October1st to 10thDay
7%413435%45%7%56%
1886
11th to 20thDay
10%5%345%4435%6%51%
1800
21st to endDay
13%5%24334445%53%
1980
November1st to 10thDay
10%6%35%445%45%7%47%
1858
11th to 20thDay
12%6%35%5%3445%6%48%
1900
21st to endDay
15%7%35%7%34446%42%
1820
December1st to 10thDay
15%7%47%6%2435%7%40%
1710
11th to 20thDay
15%8%36%5%25%35%6%43%
2161
21st to endDay
17%6%35%424346%46%
3135
January1st to 10thNight
19%6%24323347%47%
2458
11th to 20thNight
20%6%24422235%48%
2353
21st to endNight
18%6%34424346%45%
2574
February1st to 10thNight
21%8%36%423346%40%
2250
11th to 20thNight
22%6%34423346%44%
2098
21st to endNight
22%8%34424445%40%
1628
March1st to 10thNight
19%7%25%42345%7%41%
1980
11th to 20thNight
17%7%36%4335%5%7%41%
1980
21st to endNight
14%6%35%423347%49%
2178
April1st to 10thNight
14%7%26%5%35%47%7%41%
1980
11th to 20thNight
18%5%35%42345%7%45%
1829
21st to endNight
13%6%36%434447%46%
1800
May1st to 10thNight
12%6%45%5%345%5%8%42%
1724
11th to 20thNight
11%435%4245%5%9%46%
1593
21st to endNight
7%5%24335%5%6%12%47%
1745
June1st to 10thNight
6%3133245%6%11%56%
1620
11th to 20thNight
43223345%6%12%56%
1620
21st to endNight
6%4246%36%6%9%11%44%
1620
July1st to 10thNight
6%4245%35%6%9%11%47%
1620
11th to 20thNight
42233245%6%13%56%
1620
21st to endNight
32235%35%5%8%11%54%
1772
August1st to 10thNight
211322336%12%65%
1611
11th to 20thNight
33134246%8%13%52%
1667
21st to endNight
5%3146%46%6%7%12%47%
2044
September1st to 10thNight
5%435%5%346%7%11%48%
1980
11th to 20thNight
11%5%35%6%345%6%8%44%
1980
21st to endNight
8%42442345%9%54%
1980
October1st to 10thNight
442342445%7%61%
2056
11th to 20thNight
11%42332335%6%58%
2160
21st to endNight
11%5%24323335%60%
2376
November1st to 10thNight
10%5%2443445%6%54%
2220
11th to 20thNight
13%5%345%2445%6%50%
2280
21st to endNight
17%6%35%424446%45%
2356
December1st to 10thNight
18%7%35%5%24347%42%
2470
11th to 20thNight
17%8%35%5%34445%42%
3036
21st to endNight
16%6%35%423445%47%
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
42%47%15%22%9%
1708
11th to 20thDay
44%46%15%20%11%
1620
21st to endDay
44%36%15%19%13%
1782
February1st to 10thDay
51%45%13%16%12%
1724
11th to 20thDay
50%47%13%17%9%
1759
21st to endDay
48%48%15%14%11%
1626
March1st to 10thDay
51%410%11%18%6%
1980
11th to 20thDay
47%48%12%19%10%
1980
21st to endDay
43%48%16%21%8%
2178
April1st to 10thDay
49%5%7%17%15%8%
1980
11th to 20thDay
46%49%15%18%9%
2080
21st to endDay
39%6%8%19%21%7%
2160
May1st to 10thDay
43%7%10%17%16%8%
2231
11th to 20thDay
39%6%12%22%17%3
2306
21st to endDay
44%9%14%20%13%1
2531
June1st to 10thDay
32%8%19%25%16%1
2340
11th to 20thDay
31%9%19%24%15%2
2340
21st to endDay
46%11%16%19%8%
2340
July1st to 10thDay
41%10%21%22%5%
2276
11th to 20thDay
37%11%22%22%9%
2271
21st to endDay
32%12%24%26%5%1
2405
August1st to 10thDay
29%10%23%28%10%1
2314
11th to 20thDay
34%11%20%24%9%1
2232
21st to endDay
39%12%17%22%8%2
2305
September1st to 10thDay
37%10%14%20%13%5%
1980
11th to 20thDay
44%9%13%16%14%4
1980
21st to endDay
35%6%12%18%18%10%
1980
October1st to 10thDay
27%6%9%24%20%14%
1886
11th to 20thDay
33%5%7%18%20%16%
1800
21st to endDay
33%5%6%14%24%17%
1980
November1st to 10thDay
35%5%10%20%21%10%
1858
11th to 20thDay
38%410%14%22%12%
1900
21st to endDay
45%5%7%15%17%11%
1820
December1st to 10thDay
45%49%18%17%7%
1710
11th to 20thDay
43%5%7%14%22%10%
2159
21st to endDay
41%46%15%23%11%
3135
January1st to 10thNight
39%46%18%20%13%
2458
11th to 20thNight
41%36%17%20%13%
2353
21st to endNight
42%35%16%19%15%
2574
February1st to 10thNight
47%36%12%17%14%
2250
11th to 20thNight
44%48%15%18%12%
2098
21st to endNight
47%5%7%13%15%14%
1628
March1st to 10thNight
43%5%9%16%17%9%
1980
11th to 20thNight
42%6%10%12%19%9%
1980
21st to endNight
37%412%16%20%10%
2178
April1st to 10thNight
42%6%10%18%15%9%
1980
11th to 20thNight
39%5%11%16%16%13%
1829
21st to endNight
39%6%9%20%19%8%
1800
May1st to 10thNight
40%6%11%18%16%9%
1724
11th to 20thNight
33%7%14%25%18%4
1594
21st to endNight
30%7%20%29%12%2
1746
June1st to 10thNight
21%8%20%33%18%
1620
11th to 20thNight
21%6%19%32%17%4
1620
21st to endNight
31%10%20%28%11%1
1620
July1st to 10thNight
29%10%28%27%7%
1575
11th to 20thNight
19%9%31%30%10%
1566
21st to endNight
20%12%29%32%6%
1673
August1st to 10thNight
13%7%30%37%12%1
1601
11th to 20thNight
20%12%29%31%8%1
1667
21st to endNight
28%12%23%28%7%2
2044
September1st to 10thNight
28%9%23%22%13%5%
1980
11th to 20thNight
36%7%15%22%15%5%
1980
21st to endNight
28%6%16%22%18%10%
1980
October1st to 10thNight
23%5%12%28%18%14%
2056
11th to 20thNight
27%6%8%22%23%15%
2160
21st to endNight
29%37%17%23%20%
2376
November1st to 10thNight
31%5%11%22%22%10%
2220
11th to 20thNight
35%5%10%18%20%12%
2280
21st to endNight
41%49%18%18%11%
2356
December1st to 10thNight
44%47%20%15%10%
2470
11th to 20thNight
45%47%11%19%14%
3037
21st to endNight
40%47%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
23%11%34%23%7%1
270
11th to 20thDay
25%8%28%29%10%1
240
21st to endDay
20%14%36%23%6%
264
February1st to 10thDay
29%15%27%23%6%
240
11th to 20thDay
25%19%32%19%5%1
240
21st to endDay
25%18%36%18%3
198
March1st to 10thDay
23%16%33%21%8%
240
11th to 20thDay
16%18%39%20%5%3
240
21st to endDay
20%15%30%23%11%
264
April1st to 10thDay
16%14%38%25%7%
240
11th to 20thDay
25%13%24%25%12%1
358
21st to endDay
13%9%35%28%13%1
420
May1st to 10thDay
13%10%31%29%17%1
494
11th to 20thDay
13%424%34%22%3
625
21st to endDay
9%420%39%23%5%
679
June1st to 10thDay
7%29%32%37%13%
630
11th to 20thDay
7%17%34%37%14%
630
21st to endDay
9%29%26%34%21%
630
July1st to 10thDay
7%35%23%36%26%
621
11th to 20thDay
31318%44%32%
618
21st to endDay
42317%47%27%
684
August1st to 10thDay
31117%47%31%
626
11th to 20thDay
6%1215%44%32%
546
21st to endDay
10%1315%33%38%
424
September1st to 10thDay
6%1121%42%28%
270
11th to 20thDay
10%16%21%41%20%
270
21st to endDay
9%2327%36%22%
270
October1st to 10thDay
7%18%38%35%11%
270
11th to 20thDay
10%5%17%34%23%11%
270
21st to endDay
20%10%22%24%19%6%
297
November1st to 10thDay
12%6%16%40%22%5%
270
11th to 20thDay
15%7%27%34%13%3
270
21st to endDay
16%17%31%23%10%3
270
December1st to 10thDay
15%7%35%26%12%5%
270
11th to 20thDay
20%14%31%27%6%1
270
21st to endDay
19%10%36%25%7%3
297
January1st to 10thNight
22%8%29%31%9%
950
11th to 20thNight
22%9%26%34%8%
905
21st to endNight
21%9%29%34%6%
990
February1st to 10thNight
24%10%30%30%6%
810
11th to 20thNight
25%8%30%30%7%
704
21st to endNight
22%14%36%25%3
444
March1st to 10thNight
24%8%32%32%4
540
11th to 20thNight
18%9%32%33%8%
540
21st to endNight
16%9%35%32%8%1
594
April1st to 10thNight
16%8%34%35%7%
540
11th to 20thNight
21%6%30%31%11%
533
21st to endNight
16%6%32%34%11%
540
May1st to 10thNight
13%9%31%39%9%
540
11th to 20thNight
13%425%41%15%2
531
21st to endNight
7%420%43%24%2
584
June1st to 10thNight
6%29%43%36%3
540
11th to 20thNight
3210%51%33%2
540
21st to endNight
7%29%33%44%7%
540
July1st to 10thNight
5%3435%45%9%
525
11th to 20thNight
41332%52%9%
522
21st to endNight
21435%51%8%
591
August1st to 10thNight
1234%55%8%
537
11th to 20thNight
5%230%56%8%
534
21st to endNight
5%2326%55%11%
594
September1st to 10thNight
5%1426%54%10%
540
11th to 20thNight
13%15%29%48%5%
540
21st to endNight
8%18%32%45%6%
540
October1st to 10thNight
5%111%37%41%6%
616
11th to 20thNight
12%219%38%26%2
720
21st to endNight
12%7%21%35%21%2
792
November1st to 10thNight
11%319%40%24%2
740
11th to 20thNight
16%7%23%36%18%1
760
21st to endNight
18%8%26%33%14%1
836
December1st to 10thNight
21%6%25%33%14%1
950
11th to 20thNight
22%11%26%33%8%1
950
21st to endNight
21%9%29%31%9%1
1045
Page generated at 2024-01-08 10:14:18. Version ac07

Copyright 2024 Attilla Danko


Hepcat Sky Observatory Clear Sky Chart |Charts Home