Old Town Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Old Town Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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%
23488
21%
74664
11%
23440
47%
23440
24%
46702

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
20%
757
24%
2602
9%
757
40%
757
21%
1558
January11th to 20thNight
25%
737
23%
2393
9%
737
42%
737
19%
1546
January21st to endNight
22%
792
26%
2574
10%
792
42%
792
22%
1558
February1st to 10thNight
25%
720
18%
2340
8%
720
38%
720
20%
1497
February11th to 20thNight
16%
702
20%
2212
4%
700
36%
700
18%
1416
February21st to endNight
17%
592
25%
1776
7%
592
39%
592
20%
1147
March1st to 10thNight
22%
720
24%
2021
9%
720
39%
720
25%
1262
March11th to 20thNight
22%
720
21%
1980
8%
720
35%
720
23%
1310
March21st to endNight
21%
792
21%
2138
7%
792
33%
792
23%
1436
April1st to 10thNight
21%
720
20%
1800
4%
720
32%
720
23%
1223
April11th to 20thNight
32%
711
22%
1775
6%
711
39%
711
31%
1153
April21st to endNight
30%
720
21%
1800
7%
720
36%
720
27%
1213
May1st to 10thNight
34%
616
18%
1696
8%
616
40%
616
24%
1138
May11th to 20thNight
39%
416
18%
1477
10%
416
47%
416
20%
949
May21st to endNight
52%
388
16%
1551
16%
388
56%
388
22%
943
June1st to 10thNight
50%
360
20%
1440
18%
360
59%
360
24%
834
June11th to 20thNight
48%
360
16%
1440
15%
360
55%
360
21%
874
June21st to endNight
52%
360
18%
1440
17%
360
60%
360
25%
815
July1st to 10thNight
57%
350
16%
1400
18%
350
61%
350
22%
852
July11th to 20thNight
66%
415
17%
1459
17%
415
68%
415
28%
841
July21st to endNight
60%
591
18%
1672
12%
558
66%
558
32%
1029
August1st to 10thNight
64%
537
15%
1600
11%
534
66%
534
28%
1040
August11th to 20thNight
56%
622
16%
1686
10%
622
58%
622
26%
1158
August21st to endNight
57%
792
19%
1980
10%
792
58%
792
32%
1317
September1st to 10thNight
53%
720
23%
1800
12%
720
57%
720
31%
1217
September11th to 20thNight
59%
720
29%
1800
20%
720
63%
720
38%
1141
September21st to endNight
43%
720
20%
2056
13%
720
50%
720
24%
1394
October1st to 10thNight
45%
720
20%
2160
16%
720
52%
720
27%
1364
October11th to 20thNight
41%
720
26%
2160
18%
720
53%
720
28%
1302
October21st to endNight
33%
792
28%
2376
15%
792
49%
792
28%
1442
November1st to 10thNight
36%
740
27%
2320
16%
740
51%
740
30%
1346
November11th to 20thNight
33%
760
26%
2470
13%
760
49%
760
26%
1444
November21st to endNight
33%
760
25%
2658
13%
760
49%
760
25%
1495
December1st to 10thNight
25%
760
21%
2660
7%
760
42%
760
18%
1654
December11th to 20thNight
26%
760
22%
3164
9%
759
41%
759
18%
1857
December21st to endNight
28%
826
14%
4788
11%
817
42%
817
11%
2937

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%25%5%35%5%6%8%42%
74696
Night
14%6%25%4345%5%7%44%
75076
TransparencyDay
39%6%12%23%17%3
74406
Night
39%6%11%23%17%4
74885
SeeingDay
19%12%28%24%12%4
13880
Night
18%11%30%29%12%1
23503

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
15%6%35%5%2445%7%43%
1559
11th to 20thDay
16%7%25%5%345%5%7%41%
1656
21st to endDay
15%6%37%6%35%445%42%
1782
February1st to 10thDay
15%7%25%6%45%5%5%7%38%
1620
11th to 20thDay
19%7%3443445%6%41%
1636
21st to endDay
19%7%36%5%33447%39%
1480
March1st to 10thDay
12%6%25%434446%50%
1934
11th to 20thDay
17%5%35%5%35%446%42%
1980
21st to endDay
18%6%36%6%35%45%6%39%
2218
April1st to 10thDay
12%6%25%5%35%5%5%7%44%
2160
11th to 20thDay
13%5%25%5%3445%6%48%
2134
21st to endDay
18%6%24435%5%5%7%41%
2160
May1st to 10thDay
14%7%26%5%35%5%6%9%38%
2278
11th to 20thDay
17%6%35%5%35%7%6%8%36%
2414
21st to endDay
14%5%25%5%35%5%6%8%41%
2725
June1st to 10thDay
11%4245%35%5%7%10%43%
2520
11th to 20thDay
11%5%25%5%35%7%7%9%41%
2520
21st to endDay
9%425%5%35%6%8%10%42%
2520
July1st to 10thDay
9%5%26%5%45%5%8%9%41%
2520
11th to 20thDay
6%3245%36%7%8%12%43%
2448
21st to endDay
9%5%27%5%47%7%8%10%36%
2547
August1st to 10thDay
9%6%36%6%5%7%6%8%9%36%
2327
11th to 20thDay
11%5%25%6%46%7%6%10%38%
2196
21st to endDay
10%425%5%45%7%8%10%40%
2376
September1st to 10thDay
14%5%25%5%4446%8%45%
2160
11th to 20thDay
10%6%3442446%9%48%
2160
21st to endDay
17%8%26%435%6%6%6%38%
1900
October1st to 10thDay
15%6%25%5%2445%7%46%
1800
11th to 20thDay
17%42432435%6%49%
1800
21st to endDay
14%6%25%42445%7%47%
1980
November1st to 10thDay
12%5%23435%447%52%
1754
11th to 20thDay
14%5%2433445%8%50%
1710
21st to endDay
15%5%2443345%6%48%
1520
December1st to 10thDay
15%5%26%5%35%46%7%42%
1520
11th to 20thDay
16%7%25%334447%47%
1910
21st to endDay
17%7%35%5%35%5%6%7%37%
2772
January1st to 10thNight
16%7%24423446%47%
2602
11th to 20thNight
17%6%35%5%3445%6%41%
2393
21st to endNight
15%7%25%334447%46%
2574
February1st to 10thNight
16%7%346%35%45%7%41%
2340
11th to 20thNight
19%7%26%423446%43%
2210
21st to endNight
18%8%25%42335%7%43%
1776
March1st to 10thNight
14%425%4335%46%49%
2021
11th to 20thNight
17%6%25%5%24448%43%
1980
21st to endNight
15%6%36%5%3445%7%42%
2138
April1st to 10thNight
14%7%35%5%35%5%5%6%42%
1800
11th to 20thNight
14%5%35%4235%5%7%48%
1775
21st to endNight
18%5%25%43446%7%43%
1800
May1st to 10thNight
15%6%45%4345%6%8%39%
1696
11th to 20thNight
16%6%35%5%35%5%6%9%38%
1477
21st to endNight
12%6%25%5%246%7%10%40%
1550
June1st to 10thNight
10%425%436%5%8%9%44%
1440
11th to 20thNight
12%5%25%5%36%7%6%10%40%
1440
21st to endNight
9%5%25%6%446%8%10%43%
1440
July1st to 10thNight
8%5%36%6%36%5%8%10%40%
1440
11th to 20thNight
6%426%436%6%6%10%46%
1507
21st to endNight
8%425%5%46%5%9%11%40%
1771
August1st to 10thNight
8%426%5%47%7%7%9%41%
1611
11th to 20thNight
11%6%36%6%35%6%8%7%38%
1686
21st to endNight
9%6%36%5%45%46%9%43%
1980
September1st to 10thNight
13%5%36%435%45%8%44%
1800
11th to 20thNight
9%6%25%5%2345%8%50%
1800
21st to endNight
16%8%26%5%3446%7%39%
2056
October1st to 10thNight
17%6%34433446%46%
2160
11th to 20thNight
16%5%24433346%50%
2160
21st to endNight
15%5%244245%47%49%
2376
November1st to 10thNight
13%424424445%54%
2320
11th to 20thNight
14%7%34423447%50%
2470
21st to endNight
13%4245%235%5%7%49%
2658
December1st to 10thNight
17%8%35%424446%42%
2660
11th to 20thNight
17%5%25%43445%7%43%
3285
21st to endNight
16%7%35%5%35%6%6%7%37%
4884

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
40%5%11%25%15%4
1560
11th to 20thDay
42%5%12%24%15%3
1656
21st to endDay
44%49%24%15%4
1782
February1st to 10thDay
45%5%12%24%12%2
1620
11th to 20thDay
43%48%25%17%3
1645
21st to endDay
46%5%11%18%16%4
1480
March1st to 10thDay
36%5%11%25%20%3
1934
11th to 20thDay
43%410%19%18%6%
1980
21st to endDay
46%5%9%19%17%4
2218
April1st to 10thDay
39%5%11%21%19%6%
2160
11th to 20thDay
36%6%8%22%21%7%
2134
21st to endDay
41%6%11%21%16%4
2160
May1st to 10thDay
42%6%12%21%16%3
2278
11th to 20thDay
44%7%12%21%14%2
2418
21st to endDay
40%8%13%26%12%2
2725
June1st to 10thDay
35%7%14%26%15%2
2520
11th to 20thDay
36%10%13%22%16%2
2520
21st to endDay
33%9%15%24%17%2
2520
July1st to 10thDay
37%10%12%22%16%3
2450
11th to 20thDay
31%9%16%26%16%3
2373
21st to endDay
38%9%14%20%18%1
2405
August1st to 10thDay
40%10%15%23%12%1
2314
11th to 20thDay
39%10%14%22%15%1
2196
21st to endDay
36%8%15%23%14%4
2376
September1st to 10thDay
37%7%14%19%19%4
2160
11th to 20thDay
33%6%12%25%21%4
2160
21st to endDay
44%6%10%19%18%2
1900
October1st to 10thDay
38%5%10%25%19%3
1800
11th to 20thDay
36%5%9%25%22%4
1800
21st to endDay
37%38%26%23%3
1980
November1st to 10thDay
32%411%27%21%4
1754
11th to 20thDay
33%411%25%22%5%
1710
21st to endDay
37%49%27%19%3
1520
December1st to 10thDay
42%5%13%26%12%3
1520
11th to 20thDay
38%5%8%32%13%3
1906
21st to endDay
44%7%11%25%12%1
2772
January1st to 10thNight
39%49%23%19%5%
2602
11th to 20thNight
44%5%11%22%16%2
2393
21st to endNight
39%48%26%21%2
2574
February1st to 10thNight
43%5%11%23%15%2
2340
11th to 20thNight
44%38%22%18%6%
2212
21st to endNight
43%49%22%17%5%
1776
March1st to 10thNight
37%5%10%25%20%3
2021
11th to 20thNight
41%6%11%21%18%4
1980
21st to endNight
42%6%9%21%16%6%
2138
April1st to 10thNight
42%5%9%19%21%5%
1800
11th to 20thNight
36%6%11%21%21%6%
1775
21st to endNight
40%6%10%25%14%5%
1800
May1st to 10thNight
41%7%12%22%14%4
1696
11th to 20thNight
43%7%11%19%16%3
1478
21st to endNight
37%9%17%22%13%2
1551
June1st to 10thNight
34%9%12%26%17%2
1440
11th to 20thNight
37%9%13%24%13%3
1440
21st to endNight
34%8%16%20%19%3
1440
July1st to 10thNight
38%9%16%20%13%4
1400
11th to 20thNight
31%10%15%26%16%2
1459
21st to endNight
31%10%16%26%15%1
1672
August1st to 10thNight
35%11%17%22%15%1
1600
11th to 20thNight
41%10%15%21%13%2
1686
21st to endNight
37%8%14%23%14%3
1980
September1st to 10thNight
38%7%10%22%17%5%
1800
11th to 20thNight
32%7%10%26%22%4
1800
21st to endNight
44%7%9%19%17%4
2056
October1st to 10thNight
40%5%10%23%18%4
2160
11th to 20thNight
36%5%8%26%22%3
2160
21st to endNight
36%5%9%24%22%4
2376
November1st to 10thNight
33%5%9%26%21%6%
2320
11th to 20thNight
36%49%22%22%6%
2470
21st to endNight
34%5%11%26%22%4
2658
December1st to 10thNight
43%5%10%24%15%3
2660
11th to 20thNight
40%410%24%18%4
3288
21st to endNight
44%7%13%22%11%1
4884

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
28%21%33%15%41
200
11th to 20thDay
27%25%31%12%5%
252
21st to endDay
23%28%33%12%5%
264
February1st to 10thDay
27%23%33%12%5%
240
11th to 20thDay
32%20%40%7%1
303
21st to endDay
31%18%32%17%2
346
March1st to 10thDay
23%23%31%20%3
420
11th to 20thDay
28%18%32%15%5%1
420
21st to endDay
25%18%32%18%6%2
462
April1st to 10thDay
21%21%33%18%5%1
420
11th to 20thDay
18%19%33%19%7%4
412
21st to endDay
26%16%30%20%6%1
420
May1st to 10thDay
23%18%28%20%9%2
423
11th to 20thDay
21%14%28%26%8%3
447
21st to endDay
18%7%24%29%19%3
485
June1st to 10thDay
14%8%26%30%16%6%
450
11th to 20thDay
17%7%28%27%16%5%
450
21st to endDay
11%5%29%34%17%4
450
July1st to 10thDay
14%217%37%19%12%
445
11th to 20thDay
5%321%35%29%7%
444
21st to endDay
11%423%34%22%7%
488
August1st to 10thDay
12%420%32%24%9%
446
11th to 20thDay
13%416%33%25%10%
439
21st to endDay
10%322%32%20%13%
495
September1st to 10thDay
17%7%21%25%17%14%
450
11th to 20thDay
13%421%36%17%9%
450
21st to endDay
24%11%23%27%10%5%
450
October1st to 10thDay
22%7%24%25%17%6%
450
11th to 20thDay
17%15%27%23%15%2
450
21st to endDay
19%11%38%20%9%2
495
November1st to 10thDay
16%14%33%24%10%3
406
11th to 20thDay
18%16%34%22%8%2
370
21st to endDay
23%22%29%17%9%1
180
December1st to 10thDay
18%24%37%15%42
180
11th to 20thDay
26%21%29%18%7%
180
21st to endDay
26%17%33%19%5%1
198
January1st to 10thNight
20%17%39%20%3
760
11th to 20thNight
22%14%33%26%5%
737
21st to endNight
18%17%38%25%2
792
February1st to 10thNight
20%16%33%27%3
720
11th to 20thNight
26%20%34%19%1
703
21st to endNight
24%18%36%18%3
592
March1st to 10thNight
19%16%40%23%2
720
11th to 20thNight
23%15%37%19%5%1
720
21st to endNight
19%16%39%22%41
792
April1st to 10thNight
19%20%36%21%4
720
11th to 20thNight
17%14%33%29%6%
711
21st to endNight
23%10%33%26%8%
720
May1st to 10thNight
20%10%31%27%12%
616
11th to 20thNight
19%7%27%37%9%
416
21st to endNight
15%5%22%39%17%2
389
June1st to 10thNight
11%231%35%19%1
360
11th to 20thNight
14%426%39%16%1
360
21st to endNight
11%325%45%17%1
360
July1st to 10thNight
8%320%43%25%2
350
11th to 20thNight
7%315%42%30%3
415
21st to endNight
9%220%41%26%3
591
August1st to 10thNight
10%113%43%31%2
537
11th to 20thNight
14%415%40%26%2
622
21st to endNight
11%319%35%27%4
792
September1st to 10thNight
16%320%30%27%5%
720
11th to 20thNight
11%416%39%25%5%
720
21st to endNight
20%5%24%32%18%2
720
October1st to 10thNight
20%6%22%28%20%5%
720
11th to 20thNight
17%10%26%32%14%1
720
21st to endNight
19%11%33%25%12%1
792
November1st to 10thNight
14%9%34%29%12%2
740
11th to 20thNight
18%13%32%28%8%1
760
21st to endNight
17%14%32%27%9%1
760
December1st to 10thNight
22%13%33%23%8%1
760
11th to 20thNight
18%11%39%26%5%
760
21st to endNight
21%12%32%31%3
836
Page generated at 2024-01-11 22:33:45. Version ac07

Copyright 2024 Attilla Danko


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