HAO Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the HAO 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
36%
23415
16%
74836
11%
23366
42%
23366
19%
52495

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%
757
12%
2459
4%
757
25%
757
10%
1941
January11th to 20thNight
14%
724
8%
2352
2%
724
22%
724
8%
1917
January21st to endNight
18%
792
10%
2574
5%
792
25%
792
10%
2036
February1st to 10thNight
21%
720
11%
2340
8%
720
27%
720
12%
1806
February11th to 20thNight
14%
702
10%
2275
5%
700
21%
700
10%
1742
February21st to endNight
16%
592
14%
1761
5%
592
25%
592
12%
1368
March1st to 10thNight
24%
720
18%
1980
9%
720
33%
720
19%
1432
March11th to 20thNight
25%
720
19%
1980
11%
720
33%
720
19%
1418
March21st to endNight
25%
792
18%
2178
9%
792
33%
792
19%
1588
April1st to 10thNight
26%
720
14%
1882
6%
720
31%
720
20%
1391
April11th to 20thNight
32%
711
17%
1775
8%
711
37%
711
26%
1243
April21st to endNight
33%
545
20%
1625
8%
545
41%
545
23%
1098
May1st to 10thNight
39%
540
14%
1620
8%
540
44%
540
20%
1135
May11th to 20thNight
38%
531
15%
1592
10%
531
43%
531
20%
1130
May21st to endNight
59%
450
17%
1613
15%
450
64%
450
28%
927
June1st to 10thNight
55%
360
17%
1440
20%
360
60%
360
23%
856
June11th to 20thNight
53%
360
17%
1440
20%
360
58%
360
22%
865
June21st to endNight
56%
360
19%
1440
22%
360
62%
360
25%
827
July1st to 10thNight
61%
429
14%
1479
15%
429
63%
429
25%
916
July11th to 20thNight
64%
522
18%
1566
15%
522
67%
522
35%
930
July21st to endNight
61%
591
16%
1672
15%
558
63%
558
28%
1065
August1st to 10thNight
61%
537
18%
1600
13%
534
63%
534
28%
1023
August11th to 20thNight
64%
534
20%
1598
16%
534
66%
534
28%
1022
August21st to endNight
61%
707
22%
1895
15%
707
63%
707
35%
1189
September1st to 10thNight
60%
720
25%
1800
15%
720
63%
720
34%
1178
September11th to 20thNight
63%
720
27%
1962
22%
720
66%
720
39%
1171
September21st to endNight
48%
720
23%
1986
18%
720
53%
720
28%
1308
October1st to 10thNight
48%
720
19%
2160
18%
720
51%
720
26%
1379
October11th to 20thNight
36%
720
19%
2160
12%
720
46%
720
24%
1438
October21st to endNight
33%
792
21%
2376
14%
792
41%
792
20%
1658
November1st to 10thNight
40%
740
24%
2271
19%
740
48%
740
27%
1409
November11th to 20thNight
29%
760
19%
2588
13%
760
39%
760
16%
1789
November21st to endNight
26%
760
16%
2660
10%
760
35%
760
14%
1909
December1st to 10thNight
20%
760
9%
2660
6%
760
25%
760
10%
2090
December11th to 20thNight
20%
759
9%
3243
7%
759
26%
759
8%
2466
December21st to endNight
19%
828
7%
4834
6%
817
26%
817
5%
3835

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%10%47%6%35%5%5%7%32%
74574
Night
17%10%47%5%3445%6%34%
75119
TransparencyDay
52%5%11%20%11%1
74294
Night
51%5%11%20%11%2
74918
SeeingDay
23%13%25%21%13%5%
13610
Night
22%11%24%28%13%1
23430

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%15%7%11%7%45%44420%
1706
11th to 20thDay
20%19%7%11%8%43335%17%
1620
21st to endDay
20%17%7%11%7%4343420%
1782
February1st to 10thDay
23%15%6%9%7%34345%20%
1620
11th to 20thDay
19%15%8%10%5%43446%21%
1573
21st to endDay
22%14%410%5%33445%25%
1492
March1st to 10thDay
17%11%5%7%5%3445%6%32%
1980
11th to 20thDay
20%11%5%7%6%35%446%28%
1980
21st to endDay
21%10%5%8%6%345%46%28%
2178
April1st to 10thDay
16%11%46%6%35%5%6%6%31%
2078
11th to 20thDay
16%11%36%6%35%5%5%6%34%
2143
21st to endDay
22%8%36%5%35%45%6%33%
2340
May1st to 10thDay
20%9%37%6%36%5%6%7%30%
2340
11th to 20thDay
22%8%36%6%445%5%6%30%
2301
21st to endDay
13%5%36%6%36%6%7%10%36%
2659
June1st to 10thDay
14%6%35%6%46%6%7%9%35%
2520
11th to 20thDay
14%6%36%6%46%6%7%8%35%
2520
21st to endDay
14%6%35%6%45%6%6%10%36%
2520
July1st to 10thDay
12%6%26%6%46%6%6%9%37%
2431
11th to 20thDay
11%5%36%6%45%6%6%10%37%
2340
21st to endDay
13%6%36%6%47%5%7%9%34%
2547
August1st to 10thDay
12%6%26%5%5%7%7%8%10%32%
2327
11th to 20thDay
13%6%26%6%46%6%7%10%35%
2303
21st to endDay
12%5%36%6%46%6%7%9%38%
2441
September1st to 10thDay
15%5%25%5%35%5%6%7%43%
2160
11th to 20thDay
13%5%345%3446%8%45%
1994
21st to endDay
20%7%36%5%33446%38%
1973
October1st to 10thDay
17%6%36%5%2446%7%39%
1800
11th to 20thDay
19%9%26%5%4445%6%37%
1800
21st to endDay
23%11%36%433346%34%
1980
November1st to 10thDay
12%8%47%5%44446%43%
1805
11th to 20thDay
17%12%47%5%4445%6%33%
1590
21st to endDay
20%14%5%6%5%35%445%29%
1520
December1st to 10thDay
22%16%7%11%6%3443419%
1520
11th to 20thDay
20%18%8%8%5%24346%23%
1910
21st to endDay
24%20%7%9%6%33345%16%
2781
January1st to 10thNight
19%17%6%9%6%446%45%21%
2459
11th to 20thNight
23%16%6%10%7%35%34419%
2352
21st to endNight
19%17%6%10%7%3433423%
2574
February1st to 10thNight
21%15%5%10%6%24445%25%
2340
11th to 20thNight
21%13%5%10%5%45%445%24%
2273
21st to endNight
22%13%5%9%6%34445%25%
1761
March1st to 10thNight
18%10%47%6%3445%5%35%
1980
11th to 20thNight
19%10%5%6%5%2335%6%35%
1980
21st to endNight
19%10%47%5%35%346%34%
2178
April1st to 10thNight
18%11%47%5%34446%35%
1882
11th to 20thNight
16%9%26%5%3446%7%38%
1775
21st to endNight
16%9%35%5%2445%7%38%
1625
May1st to 10thNight
18%7%36%6%45%5%6%7%32%
1620
11th to 20thNight
19%9%45%5%35%45%6%36%
1592
21st to endNight
9%6%34435%5%6%11%44%
1612
June1st to 10thNight
12%5%26%6%35%46%7%45%
1440
11th to 20thNight
12%6%25%5%36%6%7%9%39%
1440
21st to endNight
12%4146%35%5%7%10%42%
1440
July1st to 10thNight
10%5%36%5%35%5%6%9%43%
1523
11th to 20thNight
11%4244346%6%9%48%
1620
21st to endNight
10%5%25%6%36%7%8%10%38%
1771
August1st to 10thNight
8%5%36%6%45%6%7%10%41%
1611
11th to 20thNight
9%6%36%5%35%6%6%7%43%
1598
21st to endNight
10%5%26%5%245%5%7%47%
1895
September1st to 10thNight
12%5%25%5%345%6%7%47%
1800
11th to 20thNight
12%5%244345%5%8%52%
1962
21st to endNight
15%7%345%34448%43%
1986
October1st to 10thNight
16%5%25%5%44447%43%
2160
11th to 20thNight
18%6%26%5%345%5%6%39%
2160
21st to endNight
25%7%35%5%33346%36%
2376
November1st to 10thNight
13%8%36%5%24445%46%
2271
11th to 20thNight
19%11%46%5%345%5%6%33%
2588
21st to endNight
21%13%46%5%34445%31%
2660
December1st to 10thNight
23%16%7%8%5%33345%22%
2660
11th to 20thNight
20%16%7%8%6%34435%25%
3285
21st to endNight
24%17%5%8%7%45%346%17%
4870

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
68%5%10%13%5%
1707
11th to 20thDay
72%310%13%2
1620
21st to endDay
70%39%13%5%1
1782
February1st to 10thDay
68%49%13%5%1
1620
11th to 20thDay
64%49%16%7%
1582
21st to endDay
62%310%15%7%2
1492
March1st to 10thDay
53%312%23%9%1
1980
11th to 20thDay
58%410%17%10%1
1980
21st to endDay
57%49%18%11%2
2178
April1st to 10thDay
53%410%20%11%3
2078
11th to 20thDay
50%411%15%17%3
2143
21st to endDay
52%5%10%21%11%2
2340
May1st to 10thDay
52%5%11%20%9%2
2340
11th to 20thDay
54%6%11%16%11%2
2305
21st to endDay
42%8%17%22%10%1
2659
June1st to 10thDay
45%7%14%23%11%1
2520
11th to 20thDay
44%7%14%23%12%1
2520
21st to endDay
43%6%12%25%13%1
2520
July1st to 10thDay
44%7%12%21%13%3
2365
11th to 20thDay
42%7%13%23%15%1
2271
21st to endDay
44%6%12%23%12%1
2405
August1st to 10thDay
44%8%14%24%9%
2314
11th to 20thDay
42%7%13%26%11%1
2303
21st to endDay
40%6%14%23%13%3
2441
September1st to 10thDay
39%6%12%21%19%3
2160
11th to 20thDay
37%412%30%14%2
1994
21st to endDay
48%410%22%15%1
1973
October1st to 10thDay
44%5%13%22%15%1
1800
11th to 20thDay
49%411%25%11%
1800
21st to endDay
53%39%21%12%1
1980
November1st to 10thDay
43%311%22%16%3
1805
11th to 20thDay
53%310%19%12%2
1590
21st to endDay
58%411%19%8%1
1520
December1st to 10thDay
70%39%13%5%
1520
11th to 20thDay
65%211%16%5%
1906
21st to endDay
72%211%11%4
2781
January1st to 10thNight
65%48%15%6%1
2459
11th to 20thNight
70%410%12%4
2352
21st to endNight
66%49%16%6%1
2574
February1st to 10thNight
63%310%17%6%
2340
11th to 20thNight
63%49%17%8%
2275
21st to endNight
63%38%16%8%2
1761
March1st to 10thNight
52%49%22%12%1
1980
11th to 20thNight
51%410%22%11%2
1980
21st to endNight
53%47%20%13%3
2178
April1st to 10thNight
52%5%8%19%13%2
1882
11th to 20thNight
45%5%11%19%16%4
1775
21st to endNight
45%5%10%25%11%4
1625
May1st to 10thNight
50%6%11%18%12%3
1620
11th to 20thNight
49%6%11%17%14%3
1593
21st to endNight
35%6%19%26%12%2
1613
June1st to 10thNight
38%7%11%27%15%2
1440
11th to 20thNight
40%7%13%25%14%2
1440
21st to endNight
36%7%14%26%16%2
1440
July1st to 10thNight
38%8%12%23%15%4
1479
11th to 20thNight
32%6%16%25%19%1
1566
21st to endNight
38%7%16%23%13%3
1672
August1st to 10thNight
37%9%14%26%15%
1600
11th to 20thNight
37%8%13%24%15%2
1598
21st to endNight
35%6%14%27%14%4
1895
September1st to 10thNight
37%6%9%24%19%5%
1800
11th to 20thNight
31%5%14%27%23%1
1962
21st to endNight
41%5%11%23%20%1
1986
October1st to 10thNight
41%6%11%26%14%3
2160
11th to 20thNight
45%410%25%14%1
2160
21st to endNight
51%39%22%13%2
2376
November1st to 10thNight
40%410%23%18%4
2271
11th to 20thNight
52%48%20%13%2
2588
21st to endNight
56%49%21%8%1
2660
December1st to 10thNight
66%310%15%5%1
2660
11th to 20thNight
64%410%17%4
3288
21st to endNight
70%311%13%3
4870

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
29%27%26%11%6%1
270
11th to 20thDay
34%25%29%9%31
240
21st to endDay
30%31%26%8%31
264
February1st to 10thDay
35%25%30%9%
240
11th to 20thDay
38%25%30%8%
240
21st to endDay
38%18%34%9%1
238
March1st to 10thDay
26%24%27%20%2
420
11th to 20thDay
32%18%30%13%5%1
420
21st to endDay
32%15%27%19%5%1
462
April1st to 10thDay
28%18%27%19%8%1
420
11th to 20thDay
23%17%30%16%9%5%
412
21st to endDay
28%18%27%16%9%2
420
May1st to 10thDay
29%15%27%16%10%3
423
11th to 20thDay
24%11%30%20%10%5%
447
21st to endDay
15%7%25%27%18%8%
485
June1st to 10thDay
14%8%28%30%18%3
450
11th to 20thDay
17%9%26%25%20%4
450
21st to endDay
15%8%26%28%19%4
450
July1st to 10thDay
15%5%20%25%22%13%
445
11th to 20thDay
11%6%21%32%19%10%
444
21st to endDay
17%421%28%20%10%
488
August1st to 10thDay
14%420%28%23%12%
446
11th to 20thDay
16%5%15%28%24%12%
439
21st to endDay
13%7%19%27%21%15%
495
September1st to 10thDay
18%5%18%26%21%11%
450
11th to 20thDay
13%5%15%31%24%13%
450
21st to endDay
24%8%24%23%17%5%
450
October1st to 10thDay
18%7%25%24%20%5%
450
11th to 20thDay
22%14%27%24%10%2
450
21st to endDay
30%14%27%19%9%1
495
November1st to 10thDay
19%13%30%23%11%4
403
11th to 20thDay
30%17%29%14%9%1
212
21st to endDay
28%16%41%12%41
180
December1st to 10thDay
30%23%30%13%31
180
11th to 20thDay
33%22%28%16%2
180
21st to endDay
37%20%26%10%6%
202
January1st to 10thNight
30%19%30%17%4
760
11th to 20thNight
35%14%31%18%3
724
21st to endNight
29%19%28%21%3
792
February1st to 10thNight
30%17%27%24%3
720
11th to 20thNight
30%20%32%17%1
703
21st to endNight
31%16%32%19%3
592
March1st to 10thNight
25%16%30%25%3
720
11th to 20thNight
27%16%28%22%7%1
720
21st to endNight
26%14%30%25%6%1
792
April1st to 10thNight
26%14%30%23%6%
720
11th to 20thNight
21%12%31%26%10%1
711
21st to endNight
21%10%31%30%8%
545
May1st to 10thNight
22%7%24%35%11%1
540
11th to 20thNight
23%8%23%33%12%1
531
21st to endNight
11%322%36%27%1
452
June1st to 10thNight
11%5%19%42%21%1
360
11th to 20thNight
12%423%38%21%1
360
21st to endNight
12%423%38%23%
360
July1st to 10thNight
11%315%40%24%6%
429
11th to 20thNight
11%215%38%30%4
522
21st to endNight
13%314%38%31%2
591
August1st to 10thNight
10%214%40%31%2
537
11th to 20thNight
11%410%38%32%5%
534
21st to endNight
12%415%34%30%4
707
September1st to 10thNight
14%413%35%29%5%
720
11th to 20thNight
13%413%36%30%4
720
21st to endNight
19%6%20%31%21%3
720
October1st to 10thNight
18%7%21%32%20%3
720
11th to 20thNight
23%7%27%31%11%1
720
21st to endNight
28%11%23%29%8%1
792
November1st to 10thNight
18%10%26%33%13%1
740
11th to 20thNight
26%14%26%25%8%1
760
21st to endNight
29%13%28%24%6%1
760
December1st to 10thNight
34%13%28%20%5%
760
11th to 20thNight
28%17%27%23%4
760
21st to endNight
31%14%29%24%2
836
Page generated at 2024-01-08 11:14:17. Version ac07

Copyright 2024 Attilla Danko


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