HVAG SkyTour
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the HVAG SkyTour clear sky chart from 2005-11-06 to 2024-01-27.

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
36%
24025
16%
74648
10%
23970
42%
23970
20%
52102

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
14%
892
11%
2591
3%
889
22%
889
11%
2064
January11th to 20thNight
13%
760
8%
2470
4%
760
18%
760
8%
2032
January21st to endNight
16%
820
11%
2664
5%
820
23%
820
10%
2103
February1st to 10thNight
16%
720
8%
2340
4%
720
22%
720
10%
1860
February11th to 20thNight
18%
702
11%
2149
5%
700
24%
700
12%
1630
February21st to endNight
14%
592
13%
1776
3%
592
24%
592
13%
1350
March1st to 10thNight
24%
720
15%
2084
8%
720
31%
720
17%
1540
March11th to 20thNight
28%
720
19%
1980
9%
720
36%
720
22%
1364
March21st to endNight
29%
792
17%
2178
10%
792
36%
792
21%
1551
April1st to 10thNight
27%
680
14%
1940
6%
680
34%
680
20%
1360
April11th to 20thNight
30%
533
20%
1620
9%
533
39%
533
21%
1101
April21st to endNight
30%
540
17%
1620
6%
540
39%
540
22%
1114
May1st to 10thNight
33%
540
11%
1620
5%
540
37%
540
17%
1179
May11th to 20thNight
40%
531
16%
1592
10%
531
45%
531
23%
1079
May21st to endNight
56%
582
16%
1745
12%
582
60%
582
31%
1055
June1st to 10thNight
52%
540
15%
1620
12%
540
56%
540
30%
1008
June11th to 20thNight
57%
540
17%
1456
12%
540
62%
540
34%
910
June21st to endNight
56%
540
19%
1440
14%
540
61%
540
35%
902
July1st to 10thNight
64%
525
17%
1400
16%
525
65%
525
35%
882
July11th to 20thNight
64%
522
20%
1506
17%
522
67%
522
38%
877
July21st to endNight
65%
591
19%
1672
15%
558
69%
558
35%
990
August1st to 10thNight
70%
537
21%
1600
19%
534
71%
534
35%
936
August11th to 20thNight
66%
534
22%
1598
19%
534
68%
534
34%
964
August21st to endNight
67%
594
23%
1786
20%
594
69%
594
36%
1037
September1st to 10thNight
59%
686
22%
1946
16%
686
63%
686
33%
1199
September11th to 20thNight
65%
720
29%
1980
22%
720
69%
720
38%
1173
September21st to endNight
51%
720
24%
1980
19%
720
56%
720
31%
1270
October1st to 10thNight
47%
720
21%
2042
17%
720
51%
720
30%
1304
October11th to 20thNight
32%
720
19%
2160
13%
720
41%
720
22%
1457
October21st to endNight
27%
792
19%
2452
12%
792
36%
792
18%
1697
November1st to 10thNight
33%
740
21%
2406
15%
740
42%
740
25%
1514
November11th to 20thNight
23%
760
19%
2470
9%
760
34%
760
17%
1704
November21st to endNight
24%
760
15%
2486
10%
760
32%
760
14%
1822
December1st to 10thNight
17%
760
9%
2660
5%
760
23%
760
10%
2066
December11th to 20thNight
18%
759
11%
3102
4%
758
27%
758
10%
2281
December21st to endNight
15%
841
5%
4517
3%
828
21%
828
4%
3727

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
15%9%47%6%45%5%5%7%32%
75066
Night
15%10%47%6%345%5%7%34%
74923
TransparencyDay
51%5%11%20%11%1
74781
Night
50%5%11%21%12%2
74728
SeeingDay
18%10%27%24%14%6%
14140
Night
19%10%28%29%13%2
24036

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
17%14%8%12%9%5%5%44416%
1557
11th to 20thDay
17%18%8%13%7%5%6%43414%
1710
21st to endDay
15%17%9%12%9%44445%16%
1836
February1st to 10thDay
18%16%7%11%8%35%5%4420%
1620
11th to 20thDay
15%12%6%12%9%5%5%5%46%21%
1695
21st to endDay
17%13%6%10%7%4445%6%25%
1480
March1st to 10thDay
18%13%7%9%7%34447%25%
1874
11th to 20thDay
16%13%5%8%6%35%446%28%
1980
21st to endDay
21%12%410%7%34447%24%
2178
April1st to 10thDay
15%11%48%6%35%5%6%7%30%
2034
11th to 20thDay
17%10%36%5%35%5%6%7%34%
2289
21st to endDay
20%8%36%5%3445%6%34%
2340
May1st to 10thDay
16%9%38%6%45%5%5%8%32%
2340
11th to 20thDay
19%7%37%6%45%5%5%7%33%
2301
21st to endDay
10%426%6%45%6%7%8%41%
2531
June1st to 10thDay
14%6%36%6%35%5%6%8%38%
2340
11th to 20thDay
11%6%35%6%45%6%6%9%39%
2498
21st to endDay
11%4346%46%5%7%9%40%
2520
July1st to 10thDay
9%5%36%5%45%5%6%8%43%
2520
11th to 20thDay
9%5%35%5%35%5%7%10%44%
2400
21st to endDay
9%5%26%5%45%5%6%10%42%
2547
August1st to 10thDay
8%425%6%36%6%7%9%43%
2327
11th to 20thDay
10%426%6%36%7%7%11%37%
2303
21st to endDay
10%6%25%5%45%5%6%9%43%
2566
September1st to 10thDay
15%5%245%35%45%8%44%
1994
11th to 20thDay
10%6%26%5%35%5%6%8%44%
1980
21st to endDay
16%6%36%6%3445%6%41%
1980
October1st to 10thDay
14%7%37%5%3447%6%40%
1917
11th to 20thDay
18%6%36%5%45%5%5%7%36%
1800
21st to endDay
19%11%46%6%45%5%5%7%28%
1903
November1st to 10thDay
11%9%46%5%3446%8%39%
1672
11th to 20thDay
17%13%46%5%35%446%33%
1710
21st to endDay
18%13%5%9%6%45%5%46%26%
1687
December1st to 10thDay
18%16%8%10%7%35%446%19%
1520
11th to 20thDay
15%14%7%11%7%445%6%6%20%
2033
21st to endDay
22%21%8%11%6%45%44412%
3084
January1st to 10thNight
18%16%6%9%7%445%5%422%
2591
11th to 20thNight
17%19%6%12%8%44445%18%
2470
21st to endNight
17%16%7%12%7%35%34422%
2664
February1st to 10thNight
20%13%6%10%6%445%5%5%22%
2340
11th to 20thNight
15%13%6%10%7%35%5%5%5%25%
2148
21st to endNight
20%13%5%10%7%34446%26%
1776
March1st to 10thNight
16%10%6%8%7%45%445%32%
2084
11th to 20thNight
14%9%36%5%35%46%7%37%
1980
21st to endNight
18%11%46%6%3345%7%33%
2178
April1st to 10thNight
14%10%47%5%46%5%5%7%34%
1940
11th to 20thNight
15%8%36%6%445%5%7%36%
1620
21st to endNight
16%9%36%6%35%5%47%36%
1620
May1st to 10thNight
18%9%37%7%36%45%8%29%
1620
11th to 20thNight
18%7%35%5%345%6%8%37%
1592
21st to endNight
10%6%24436%6%6%10%43%
1744
June1st to 10thNight
10%5%35%5%35%5%6%8%45%
1620
11th to 20thNight
8%425%5%36%5%7%9%44%
1456
21st to endNight
11%5%24435%5%7%9%45%
1440
July1st to 10thNight
9%4245%346%6%7%48%
1440
11th to 20thNight
8%3236%346%6%10%50%
1556
21st to endNight
7%4345%45%5%6%10%48%
1771
August1st to 10thNight
6%3245%45%6%6%9%49%
1611
11th to 20thNight
9%5%26%5%35%47%8%47%
1598
21st to endNight
6%425%6%35%5%6%8%49%
1786
September1st to 10thNight
10%6%25%5%3345%7%49%
1946
11th to 20thNight
10%425%434447%53%
1980
21st to endNight
13%5%36%5%3446%6%45%
1980
October1st to 10thNight
13%6%26%5%3445%7%44%
2042
11th to 20thNight
18%9%36%5%43446%38%
2160
21st to endNight
22%7%36%5%3345%7%33%
2452
November1st to 10thNight
15%8%36%5%3345%7%41%
2406
11th to 20thNight
15%11%5%7%6%4445%6%34%
2470
21st to endNight
19%12%5%8%6%3445%6%27%
2486
December1st to 10thNight
17%16%6%10%6%35%45%6%22%
2660
11th to 20thNight
18%15%5%9%6%345%5%6%25%
3153
21st to endNight
24%18%8%9%7%44445%13%
4543

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
71%5%9%12%4
1558
11th to 20thDay
74%5%10%9%2
1710
21st to endDay
73%48%11%41
1836
February1st to 10thDay
68%49%13%5%1
1620
11th to 20thDay
65%5%8%15%6%1
1705
21st to endDay
62%312%14%7%1
1480
March1st to 10thDay
61%311%18%6%
1874
11th to 20thDay
58%5%10%17%9%1
1980
21st to endDay
61%49%19%6%1
2178
April1st to 10thDay
53%6%12%18%11%1
2034
11th to 20thDay
50%5%12%18%13%2
2289
21st to endDay
51%411%21%11%2
2340
May1st to 10thDay
51%5%12%20%10%1
2340
11th to 20thDay
50%6%11%18%12%2
2305
21st to endDay
40%7%13%26%13%2
2531
June1st to 10thDay
43%5%11%26%12%2
2340
11th to 20thDay
40%7%14%22%15%2
2498
21st to endDay
39%7%14%21%15%4
2520
July1st to 10thDay
39%6%11%24%18%3
2451
11th to 20thDay
34%6%13%28%16%2
2327
21st to endDay
36%6%14%27%15%3
2405
August1st to 10thDay
36%7%14%28%14%1
2314
11th to 20thDay
38%7%16%26%11%2
2303
21st to endDay
37%6%12%23%18%3
2566
September1st to 10thDay
39%5%14%21%17%3
1994
11th to 20thDay
38%5%12%26%17%2
1980
21st to endDay
44%410%23%18%1
1980
October1st to 10thDay
43%6%10%23%16%1
1917
11th to 20thDay
47%412%23%13%2
1800
21st to endDay
55%5%12%17%10%1
1903
November1st to 10thDay
44%5%11%23%16%1
1672
11th to 20thDay
53%411%20%11%1
1710
21st to endDay
59%412%18%7%
1687
December1st to 10thDay
70%310%14%4
1520
11th to 20thDay
64%49%19%4
2030
21st to endDay
79%38%7%3
3084
January1st to 10thNight
65%48%15%7%
2591
11th to 20thNight
70%410%12%4
2470
21st to endNight
67%39%15%6%1
2664
February1st to 10thNight
65%5%9%14%6%1
2340
11th to 20thNight
61%49%17%8%1
2149
21st to endNight
62%39%16%8%2
1776
March1st to 10thNight
56%49%21%9%1
2084
11th to 20thNight
46%5%10%22%13%3
1980
21st to endNight
52%49%25%9%1
2178
April1st to 10thNight
49%5%12%18%14%2
1940
11th to 20thNight
47%5%10%18%17%3
1620
21st to endNight
48%5%10%22%13%3
1620
May1st to 10thNight
54%5%11%17%11%3
1620
11th to 20thNight
45%7%11%18%18%2
1593
21st to endNight
34%7%15%27%15%3
1745
June1st to 10thNight
37%6%11%27%16%4
1620
11th to 20thNight
34%7%15%25%17%3
1456
21st to endNight
35%5%14%26%16%3
1440
July1st to 10thNight
35%6%11%25%19%5%
1400
11th to 20thNight
30%6%14%28%20%2
1506
21st to endNight
32%6%15%26%17%4
1672
August1st to 10thNight
31%7%12%31%18%2
1600
11th to 20thNight
34%5%15%30%14%2
1598
21st to endNight
31%6%14%24%21%4
1786
September1st to 10thNight
35%6%13%25%16%5%
1946
11th to 20thNight
31%5%11%28%23%2
1980
21st to endNight
39%411%24%20%2
1980
October1st to 10thNight
39%412%23%19%2
2042
11th to 20thNight
48%39%23%15%1
2160
21st to endNight
51%410%22%11%2
2452
November1st to 10thNight
43%412%24%16%2
2406
11th to 20thNight
52%410%21%12%2
2470
21st to endNight
58%412%19%7%
2486
December1st to 10thNight
64%410%14%7%
2660
11th to 20thNight
60%412%20%4
3155
21st to endNight
74%411%9%2
4543

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%18%33%19%5%1
270
11th to 20thDay
26%18%39%13%4
270
21st to endDay
28%17%33%18%5%
282
February1st to 10thDay
35%16%36%13%
240
11th to 20thDay
25%18%36%17%3
240
21st to endDay
23%26%41%10%1
198
March1st to 10thDay
23%16%36%20%5%
314
11th to 20thDay
24%14%36%20%42
420
21st to endDay
29%16%29%20%5%1
462
April1st to 10thDay
21%15%30%24%9%1
420
11th to 20thDay
22%17%27%20%10%4
412
21st to endDay
25%12%30%22%9%1
420
May1st to 10thDay
27%10%31%21%9%3
423
11th to 20thDay
21%8%28%26%11%5%
447
21st to endDay
13%6%23%30%19%9%
485
June1st to 10thDay
15%6%21%36%16%4
450
11th to 20thDay
13%6%28%26%22%5%
608
21st to endDay
14%7%27%28%18%5%
630
July1st to 10thDay
9%5%18%32%22%14%
621
11th to 20thDay
11%322%30%22%12%
500
21st to endDay
11%5%19%28%26%11%
488
August1st to 10thDay
11%316%29%26%15%
446
11th to 20thDay
13%318%29%25%13%
439
21st to endDay
9%5%19%27%25%15%
495
September1st to 10thDay
15%5%19%25%24%13%
450
11th to 20thDay
9%417%23%30%17%
450
21st to endDay
18%10%23%22%19%8%
450
October1st to 10thDay
14%8%26%23%21%8%
450
11th to 20thDay
16%16%33%24%9%1
450
21st to endDay
25%17%35%19%41
418
November1st to 10thDay
16%13%37%19%12%3
270
11th to 20thDay
26%16%32%17%8%1
270
21st to endDay
26%16%37%19%3
259
December1st to 10thDay
20%17%40%15%7%2
180
11th to 20thDay
22%20%36%19%3
216
21st to endDay
31%17%35%14%3
297
January1st to 10thNight
26%17%34%18%5%
893
11th to 20thNight
28%15%35%17%31
760
21st to endNight
23%15%37%22%31
820
February1st to 10thNight
27%14%35%22%3
720
11th to 20thNight
25%13%36%23%3
703
21st to endNight
28%15%37%17%3
592
March1st to 10thNight
21%13%35%24%7%
720
11th to 20thNight
19%15%34%26%5%1
720
21st to endNight
23%12%30%27%8%
792
April1st to 10thNight
21%13%34%25%6%
680
11th to 20thNight
18%13%34%23%10%2
533
21st to endNight
21%7%36%26%8%1
540
May1st to 10thNight
21%9%29%31%9%1
540
11th to 20thNight
21%5%27%32%13%2
531
21st to endNight
12%321%39%21%4
584
June1st to 10thNight
11%425%42%18%
540
11th to 20thNight
10%323%43%19%1
540
21st to endNight
11%421%41%21%1
540
July1st to 10thNight
11%313%38%32%3
525
11th to 20thNight
10%217%41%26%4
522
21st to endNight
10%215%42%29%2
591
August1st to 10thNight
8%211%45%29%5%
537
11th to 20thNight
11%212%39%31%5%
534
21st to endNight
8%214%37%34%5%
594
September1st to 10thNight
13%415%35%28%5%
686
11th to 20thNight
10%314%36%32%5%
720
21st to endNight
14%6%21%34%23%3
720
October1st to 10thNight
15%6%24%33%19%3
720
11th to 20thNight
22%11%30%27%8%2
720
21st to endNight
24%15%30%25%5%
792
November1st to 10thNight
19%11%32%26%11%1
740
11th to 20thNight
22%15%34%21%7%1
760
21st to endNight
26%13%33%23%6%
760
December1st to 10thNight
24%18%33%20%5%
760
11th to 20thNight
26%15%35%21%4
760
21st to endNight
29%16%32%20%3
847
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