Timerson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Timerson Observatory 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
27%
22922
12%
74984
7%
22877
33%
22877
14%
55151

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
9%
759
6%
2649
3%
757
14%
757
5%
2244
January11th to 20thNight
13%
760
5%
2627
3%
760
16%
760
5%
2260
January21st to endNight
11%
820
7%
2664
3%
820
17%
820
6%
2236
February1st to 10thNight
9%
720
8%
2340
1%
720
17%
720
6%
1901
February11th to 20thNight
10%
703
8%
2275
2%
700
17%
700
7%
1835
February21st to endNight
13%
592
9%
1791
4%
592
19%
592
9%
1427
March1st to 10thNight
16%
720
10%
2066
4%
720
22%
720
11%
1638
March11th to 20thNight
20%
720
14%
1980
6%
720
28%
720
15%
1494
March21st to endNight
21%
792
15%
2120
6%
792
27%
792
17%
1589
April1st to 10thNight
19%
720
12%
1800
3%
720
25%
720
17%
1376
April11th to 20thNight
26%
711
14%
1775
5%
711
30%
711
20%
1320
April21st to endNight
30%
649
16%
1729
7%
649
35%
649
21%
1236
May1st to 10thNight
35%
445
14%
1525
10%
445
40%
445
16%
1060
May11th to 20thNight
38%
354
19%
1416
16%
354
49%
354
20%
867
May21st to endNight
42%
388
16%
1551
14%
388
52%
388
23%
908
June1st to 10thNight
42%
360
14%
1440
14%
360
52%
360
18%
909
June11th to 20thNight
44%
360
14%
1440
16%
360
52%
360
21%
850
June21st to endNight
43%
360
15%
1440
15%
360
54%
360
21%
871
July1st to 10thNight
58%
350
15%
1400
19%
350
64%
350
25%
784
July11th to 20thNight
55%
348
17%
1392
23%
348
60%
348
25%
782
July21st to endNight
52%
432
17%
1522
16%
408
56%
408
26%
898
August1st to 10thNight
54%
537
17%
1600
12%
534
57%
534
31%
977
August11th to 20thNight
54%
534
17%
1598
12%
534
57%
534
27%
1040
August21st to endNight
52%
787
20%
1975
10%
787
55%
787
34%
1266
September1st to 10thNight
49%
720
17%
1800
7%
720
52%
720
30%
1215
September11th to 20thNight
51%
720
22%
1800
15%
720
53%
720
32%
1198
September21st to endNight
43%
720
19%
2061
15%
720
46%
720
25%
1381
October1st to 10thNight
34%
720
13%
2160
10%
720
38%
720
18%
1537
October11th to 20thNight
26%
720
12%
2160
7%
720
34%
720
17%
1541
October21st to endNight
17%
792
11%
2407
4%
792
26%
792
12%
1884
November1st to 10thNight
26%
740
15%
2407
11%
740
32%
740
15%
1697
November11th to 20thNight
18%
760
13%
2640
8%
760
25%
760
12%
1938
November21st to endNight
17%
760
9%
2660
5%
760
23%
760
9%
2050
December1st to 10thNight
11%
760
5%
2660
2%
760
15%
760
6%
2176
December11th to 20thNight
13%
759
5%
3252
1%
759
19%
759
5%
2620
December21st to endNight
9%
830
3%
4862
1%
817
13%
817
2%
4146

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
16%10%48%7%45%5%5%7%30%
74827
Night
17%11%48%7%35%5%5%7%29%
75216
TransparencyDay
52%8%12%17%9%1
74535
Night
53%8%12%17%8%1
75042
SeeingDay
22%17%30%19%9%3
13515
Night
22%16%30%23%9%1
22931

By Month

Percentage Cloud Cover NE (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
13%16%9%14%10%47%5%4415%
1517
11th to 20thDay
17%18%7%14%11%44445%12%
1552
21st to endDay
13%16%8%15%12%5%5%445%12%
1836
February1st to 10thDay
16%15%8%15%10%46%45%414%
1620
11th to 20thDay
14%15%9%16%8%46%445%15%
1573
21st to endDay
20%15%413%9%45%445%17%
1464
March1st to 10thDay
15%12%8%14%9%45%35%5%20%
1887
11th to 20thDay
15%15%6%8%6%45%5%45%27%
1980
21st to endDay
20%13%48%5%34346%29%
2234
April1st to 10thDay
17%13%5%8%6%3445%6%30%
2160
11th to 20thDay
19%9%35%5%3445%6%36%
2134
21st to endDay
20%11%46%5%34446%32%
2245
May1st to 10thDay
16%10%47%6%35%5%5%6%33%
2434
11th to 20thDay
15%7%25%6%45%5%5%8%37%
2478
21st to endDay
12%6%36%6%45%46%9%40%
2725
June1st to 10thDay
17%6%36%6%35%46%8%36%
2520
11th to 20thDay
14%5%35%5%35%6%7%9%38%
2520
21st to endDay
13%5%35%7%45%6%6%9%37%
2520
July1st to 10thDay
9%5%36%5%35%6%5%8%43%
2520
11th to 20thDay
11%5%35%6%46%6%7%9%38%
2520
21st to endDay
11%5%35%8%46%7%7%9%35%
2703
August1st to 10thDay
11%5%25%6%5%6%7%7%8%38%
2327
11th to 20thDay
12%5%36%8%5%6%6%8%8%32%
2290
21st to endDay
14%6%26%5%45%6%6%9%36%
2376
September1st to 10thDay
14%7%36%5%35%5%6%8%39%
2160
11th to 20thDay
14%6%25%4445%5%8%42%
2160
21st to endDay
15%7%26%7%45%5%5%7%36%
1895
October1st to 10thDay
18%8%36%7%35%5%5%6%34%
1800
11th to 20thDay
19%10%47%7%45%45%6%29%
1800
21st to endDay
26%12%47%6%4445%5%23%
1949
November1st to 10thDay
14%12%47%7%45%45%6%32%
1671
11th to 20thDay
14%14%6%8%7%45%46%8%25%
1539
21st to endDay
20%15%5%8%7%345%5%6%21%
1520
December1st to 10thDay
20%16%8%11%8%35%445%16%
1520
11th to 20thDay
18%16%7%14%7%25%45%417%
1906
21st to endDay
26%20%6%12%7%3443411%
2772
January1st to 10thNight
16%16%7%14%9%46%5%45%15%
2649
11th to 20thNight
18%17%7%12%10%4445%5%14%
2627
21st to endNight
13%15%7%13%11%5%6%5%45%15%
2664
February1st to 10thNight
17%14%7%12%8%45%446%19%
2340
11th to 20thNight
15%13%6%13%9%47%45%5%20%
2273
21st to endNight
17%11%6%14%8%45%45%5%22%
1791
March1st to 10thNight
15%14%7%9%8%45%5%45%23%
2056
11th to 20thNight
18%13%6%8%6%345%5%6%29%
1979
21st to endNight
18%10%5%8%7%34446%32%
2120
April1st to 10thNight
19%10%5%7%7%45%45%6%30%
1800
11th to 20thNight
18%9%36%6%45%447%34%
1775
21st to endNight
18%8%37%6%345%5%8%33%
1729
May1st to 10thNight
18%9%37%6%35%45%8%32%
1525
11th to 20thNight
12%6%26%5%345%6%10%40%
1415
21st to endNight
10%5%35%5%35%47%8%45%
1550
June1st to 10thNight
15%6%345%35%5%7%8%38%
1440
11th to 20thNight
12%6%25%5%35%6%5%8%42%
1440
21st to endNight
9%5%36%6%35%47%9%42%
1440
July1st to 10thNight
5%6%26%6%36%5%5%8%48%
1440
11th to 20thNight
11%425%5%3445%8%48%
1440
21st to endNight
12%5%35%426%5%6%9%43%
1612
August1st to 10thNight
8%6%25%5%35%5%5%9%47%
1611
11th to 20thNight
11%6%26%6%36%6%6%7%42%
1598
21st to endNight
9%5%26%5%345%6%9%46%
1975
September1st to 10thNight
14%5%36%33445%8%45%
1800
11th to 20thNight
13%6%26%5%335%48%45%
1800
21st to endNight
14%7%26%5%25%5%6%8%39%
2061
October1st to 10thNight
19%8%26%6%35%5%5%6%35%
2160
11th to 20thNight
20%8%36%6%445%5%7%32%
2160
21st to endNight
25%11%47%6%3435%6%25%
2407
November1st to 10thNight
17%11%47%5%345%47%34%
2407
11th to 20thNight
16%11%47%7%445%5%8%28%
2640
21st to endNight
18%16%5%7%7%3445%7%24%
2660
December1st to 10thNight
19%15%7%8%7%46%5%5%5%19%
2660
11th to 20thNight
19%15%6%11%7%34445%20%
3288
21st to endNight
30%16%6%8%6%3445%5%12%
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
71%7%9%10%3
1518
11th to 20thDay
75%7%8%7%2
1552
21st to endDay
73%7%10%7%2
1836
February1st to 10thDay
72%8%8%8%3
1620
11th to 20thDay
71%7%8%11%3
1582
21st to endDay
68%7%9%11%5%1
1464
March1st to 10thDay
64%8%11%13%31
1890
11th to 20thDay
59%7%10%14%10%1
1980
21st to endDay
56%6%9%16%10%2
2234
April1st to 10thDay
55%6%11%17%10%1
2160
11th to 20thDay
49%6%11%19%14%1
2134
21st to endDay
52%6%9%17%14%2
2245
May1st to 10thDay
51%7%11%18%11%2
2434
11th to 20thDay
44%8%12%21%13%2
2482
21st to endDay
41%9%15%22%13%1
2725
June1st to 10thDay
44%8%12%19%16%1
2520
11th to 20thDay
40%9%14%23%13%1
2520
21st to endDay
41%9%15%20%14%1
2520
July1st to 10thDay
37%8%13%26%14%2
2450
11th to 20thDay
38%10%17%22%12%1
2445
21st to endDay
42%11%14%21%11%1
2552
August1st to 10thDay
38%11%16%22%12%1
2314
11th to 20thDay
44%11%16%20%9%
2290
21st to endDay
42%9%13%23%11%1
2376
September1st to 10thDay
40%9%14%26%10%1
2160
11th to 20thDay
39%8%13%24%16%1
2160
21st to endDay
46%8%11%22%12%1
1895
October1st to 10thDay
47%9%14%17%12%1
1800
11th to 20thDay
53%8%14%17%7%
1800
21st to endDay
62%8%11%13%6%1
1949
November1st to 10thDay
52%9%12%16%10%2
1671
11th to 20thDay
56%8%14%15%6%1
1539
21st to endDay
61%9%14%14%2
1520
December1st to 10thDay
69%9%11%10%2
1520
11th to 20thDay
68%8%13%7%3
1906
21st to endDay
76%7%9%7%1
2772
January1st to 10thNight
70%8%8%9%4
2649
11th to 20thNight
71%9%10%7%3
2627
21st to endNight
69%8%10%9%31
2664
February1st to 10thNight
66%8%10%12%5%
2340
11th to 20thNight
64%7%11%13%41
2275
21st to endNight
60%9%12%12%6%
1791
March1st to 10thNight
61%7%12%15%5%
2066
11th to 20thNight
55%6%11%19%8%1
1980
21st to endNight
54%6%10%17%12%2
2120
April1st to 10thNight
54%7%11%19%8%1
1800
11th to 20thNight
50%7%10%16%15%1
1775
21st to endNight
47%7%10%20%12%3
1729
May1st to 10thNight
50%7%11%16%13%2
1525
11th to 20thNight
40%8%13%22%14%3
1416
21st to endNight
35%9%16%22%15%2
1551
June1st to 10thNight
41%9%12%21%15%1
1440
11th to 20thNight
37%8%15%21%16%2
1440
21st to endNight
36%10%11%26%15%1
1440
July1st to 10thNight
32%9%15%22%18%3
1400
11th to 20thNight
34%8%13%29%16%1
1392
21st to endNight
34%9%17%24%15%2
1522
August1st to 10thNight
33%9%15%30%12%1
1600
11th to 20thNight
38%9%16%29%9%
1598
21st to endNight
32%10%16%28%13%2
1975
September1st to 10thNight
38%8%14%25%12%2
1800
11th to 20thNight
36%8%13%26%16%1
1800
21st to endNight
40%9%14%24%12%1
2061
October1st to 10thNight
49%8%12%18%12%1
2160
11th to 20thNight
49%8%15%18%9%1
2160
21st to endNight
60%7%13%12%7%1
2407
November1st to 10thNight
49%8%12%19%8%2
2407
11th to 20thNight
52%10%14%15%7%2
2640
21st to endNight
57%10%15%14%3
2660
December1st to 10thNight
65%10%14%10%2
2660
11th to 20thNight
65%8%11%11%3
3288
21st to endNight
72%10%9%8%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%26%32%9%6%
180
11th to 20thDay
33%29%27%10%11
195
21st to endDay
24%30%31%12%3
282
February1st to 10thDay
34%31%30%5%
240
11th to 20thDay
35%27%35%4
240
21st to endDay
36%23%27%12%1
330
March1st to 10thDay
25%24%33%15%3
420
11th to 20thDay
29%25%30%13%4
420
21st to endDay
34%21%26%14%41
462
April1st to 10thDay
29%20%34%12%41
420
11th to 20thDay
31%21%24%15%7%3
412
21st to endDay
30%19%28%16%6%1
420
May1st to 10thDay
25%19%31%15%8%2
423
11th to 20thDay
18%15%34%23%8%2
447
21st to endDay
16%13%31%24%13%4
485
June1st to 10thDay
20%15%30%27%6%2
450
11th to 20thDay
16%12%34%26%10%2
450
21st to endDay
13%15%37%24%10%2
450
July1st to 10thDay
12%8%26%31%20%4
445
11th to 20thDay
12%8%28%29%19%4
444
21st to endDay
10%9%36%29%12%3
488
August1st to 10thDay
11%7%29%29%19%6%
446
11th to 20thDay
14%6%31%24%16%8%
439
21st to endDay
13%11%29%25%14%7%
495
September1st to 10thDay
16%12%24%26%14%8%
450
11th to 20thDay
13%10%26%24%18%9%
450
21st to endDay
17%14%29%22%14%4
450
October1st to 10thDay
21%15%30%17%13%4
450
11th to 20thDay
24%18%32%18%6%2
450
21st to endDay
31%20%30%15%4
480
November1st to 10thDay
25%19%29%19%7%1
365
11th to 20thDay
28%25%29%15%4
199
21st to endDay
33%25%28%13%1
180
December1st to 10thDay
29%22%32%12%41
180
11th to 20thDay
34%24%28%12%2
180
21st to endDay
35%24%31%10%1
198
January1st to 10thNight
26%28%30%13%3
760
11th to 20thNight
27%24%30%16%21
760
21st to endNight
22%23%35%17%3
820
February1st to 10thNight
28%23%35%13%1
720
11th to 20thNight
23%26%34%14%2
703
21st to endNight
27%23%33%15%2
592
March1st to 10thNight
26%21%33%18%2
720
11th to 20thNight
28%19%30%19%4
720
21st to endNight
26%15%34%19%6%1
792
April1st to 10thNight
25%17%34%21%3
720
11th to 20thNight
23%18%30%23%6%1
711
21st to endNight
23%14%29%25%9%
649
May1st to 10thNight
25%9%25%30%11%1
445
11th to 20thNight
17%7%33%34%8%1
354
21st to endNight
10%8%34%31%17%1
389
June1st to 10thNight
16%7%28%33%15%1
360
11th to 20thNight
14%9%28%34%15%
360
21st to endNight
9%7%33%40%9%1
360
July1st to 10thNight
7%423%45%21%1
350
11th to 20thNight
11%322%41%21%1
348
21st to endNight
11%5%26%41%15%2
432
August1st to 10thNight
12%424%35%21%3
537
11th to 20thNight
11%5%21%36%24%3
534
21st to endNight
9%7%25%34%23%1
787
September1st to 10thNight
15%8%23%30%21%3
720
11th to 20thNight
14%9%21%29%23%5%
720
21st to endNight
15%12%24%27%19%3
720
October1st to 10thNight
23%11%27%20%17%2
720
11th to 20thNight
24%16%30%23%6%
720
21st to endNight
30%16%32%20%2
792
November1st to 10thNight
24%16%31%22%7%
740
11th to 20thNight
22%21%33%16%6%2
760
21st to endNight
26%23%29%17%5%
760
December1st to 10thNight
29%23%33%13%3
760
11th to 20thNight
27%23%31%16%3
760
21st to endNight
33%24%30%13%1
836
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Copyright 2024 Attilla Danko


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