Timerson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Timerson Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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
29%
14711
12%
46516
8%
14678
34%
14678
15%
34098

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 15thNight
11%
719
6%
2506
3%
716
15%
716
5%
2117
January16th to endNight
11%
768
7%
2535
3%
768
18%
768
6%
2129
February1st to 15thNight
9%
704
7%
2287
1%
701
17%
701
6%
1888
February16th to endNight
16%
631
9%
1962
4%
631
22%
631
9%
1561
March1st to 15thNight
17%
720
11%
2037
5%
720
23%
720
12%
1608
March16th to endNight
24%
768
15%
2073
7%
768
30%
768
18%
1541
April1st to 15thNight
23%
718
12%
1796
4%
718
27%
718
17%
1375
April16th to endNight
33%
672
18%
1752
8%
672
38%
672
26%
1195
May1st to 15thNight
39%
416
16%
1496
12%
416
47%
416
18%
995
May16th to endNight
42%
374
16%
1497
16%
374
51%
374
22%
900
June1st to 15thNight
42%
360
13%
1440
12%
360
51%
360
17%
923
June16th to endNight
46%
360
13%
1440
14%
360
54%
360
22%
852
July1st to 15thNight
57%
340
14%
1360
19%
340
61%
340
26%
760
July16th to endNight
57%
402
15%
1442
16%
378
61%
378
26%
825
August1st to 15thNight
55%
527
15%
1575
10%
524
59%
524
31%
961
August16th to endNight
55%
643
19%
1693
11%
643
58%
643
34%
1068
September1st to 15thNight
50%
660
19%
1650
10%
660
54%
660
30%
1115
September16th to endNight
48%
657
20%
1812
15%
657
50%
657
27%
1196
October1st to 15thNight
34%
660
15%
1980
12%
660
39%
660
18%
1398
October16th to endNight
20%
704
7%
2131
3%
704
25%
704
11%
1690
November1st to 15thNight
25%
700
14%
2324
11%
700
30%
700
14%
1664
November16th to endNight
19%
720
11%
2520
7%
720
25%
720
9%
1925
December1st to 15thNight
12%
720
5%
2520
1%
720
16%
720
6%
2071
December16th to endNight
10%
768
4%
2688
1%
768
14%
768
4%
2341

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%35%45%7%29%
47464
Night
16%10%47%6%34446%30%
46689
Cloud CoverDay
15%9%47%6%35%45%7%29%
47474
Night
16%9%47%6%3445%6%30%
46694
TransparencyDay
53%7%12%16%9%
47155
Night
53%7%12%17%9%1
46516
SeeingDay
21%14%27%20%11%4
5355
Night
21%15%28%23%9%1
14713

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 15thDay
16%13%7%15%11%45%435%13%
1432
16th to endDay
12%15%8%15%10%45%44413%
1688
February1st to 15thDay
15%14%10%14%9%36%44412%
1575
16th to endDay
18%15%412%8%35%445%16%
1510
March1st to 15thDay
16%14%6%11%8%4434420%
1909
16th to endDay
17%11%47%425%447%29%
2151
April1st to 15thDay
20%11%36%5%24435%31%
2152
16th to endDay
16%9%35%423346%38%
2217
May1st to 15thDay
15%8%36%6%35%5%5%6%34%
2454
16th to endDay
13%6%245%35%46%8%38%
2618
June1st to 15thDay
19%6%36%5%2446%7%33%
2520
16th to endDay
12%5%246%35%6%6%10%36%
2520
July1st to 15thDay
9%435%6%35%6%5%8%40%
2520
16th to endDay
11%5%25%7%45%6%7%9%33%
2626
August1st to 15thDay
12%425%7%5%5%6%7%8%33%
2288
16th to endDay
13%6%26%6%45%46%8%35%
2146
September1st to 15thDay
16%6%25%335%5%6%7%38%
1980
16th to endDay
15%7%26%5%34447%38%
1818
October1st to 15thDay
18%8%37%6%24346%34%
1650
16th to endDay
25%10%46%6%3445%5%22%
1741
November1st to 15thDay
14%11%45%6%45%36%6%30%
1533
16th to endDay
19%11%48%5%35%5%5%7%22%
1440
December1st to 15thDay
19%14%7%11%8%25%345%18%
1440
16th to endDay
19%18%8%13%7%33345%12%
1536
January1st to 15thNight
17%15%6%12%8%35%43415%
2506
16th to endNight
14%15%6%12%9%45%445%15%
2535
February1st to 15thNight
14%14%7%12%8%44435%18%
2285
16th to endNight
14%11%5%12%8%36%45%420%
1962
March1st to 15thNight
19%12%6%8%7%34345%24%
2025
16th to endNight
18%9%46%5%34446%32%
2073
April1st to 15thNight
19%9%35%6%45%346%30%
1796
16th to endNight
16%6%25%5%2345%7%40%
1752
May1st to 15thNight
16%7%26%6%34448%35%
1496
16th to endNight
11%5%245%3447%8%42%
1495
June1st to 15thNight
16%6%25%435%5%5%7%38%
1440
16th to endNight
10%425%5%245%6%8%41%
1440
July1st to 15thNight
6%5%26%6%25%5%5%8%47%
1440
16th to endNight
10%314435%5%6%9%45%
1540
August1st to 15thNight
8%415%426%5%6%7%46%
1586
16th to endNight
8%325%434448%48%
1693
September1st to 15thNight
14%5%26%323447%44%
1650
16th to endNight
13%6%16%42445%7%42%
1812
October1st to 15thNight
20%8%25%5%34446%34%
1980
16th to endNight
26%10%46%6%3435%6%22%
2131
November1st to 15thNight
17%10%46%5%235%48%30%
2324
16th to endNight
18%14%46%6%34446%25%
2520
December1st to 15thNight
20%14%6%9%7%35%45%418%
2520
16th to endNight
21%16%7%11%7%35%44412%
2688

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 15thDay
16%13%7%14%11%45%44414%
1432
16th to endDay
12%14%8%14%10%5%6%445%13%
1688
February1st to 15thDay
15%14%10%13%10%36%44412%
1575
16th to endDay
18%15%5%11%9%35%445%16%
1510
March1st to 15thDay
16%13%7%10%8%35%345%20%
1920
16th to endDay
17%11%47%5%245%46%29%
2150
April1st to 15thDay
20%11%46%5%24345%31%
2152
16th to endDay
17%9%26%423446%38%
2217
May1st to 15thDay
15%8%36%5%35%45%7%34%
2454
16th to endDay
14%6%245%35%45%8%38%
2618
June1st to 15thDay
19%6%35%5%245%5%7%33%
2520
16th to endDay
12%425%5%35%6%7%9%36%
2520
July1st to 15thDay
9%426%6%36%5%6%8%40%
2520
16th to endDay
11%5%36%7%46%6%7%9%33%
2626
August1st to 15thDay
11%5%25%6%46%5%8%8%34%
2288
16th to endDay
14%6%26%6%35%5%5%7%35%
2146
September1st to 15thDay
16%6%344335%6%7%38%
1980
16th to endDay
15%5%36%5%34447%38%
1818
October1st to 15thDay
18%8%36%6%3335%6%34%
1650
16th to endDay
24%11%37%6%445%46%22%
1741
November1st to 15thDay
14%11%36%6%4445%6%30%
1533
16th to endDay
18%13%38%6%345%48%22%
1440
December1st to 15thDay
18%16%7%10%7%35%336%18%
1440
16th to endDay
20%18%7%12%8%34335%12%
1536
January1st to 15thNight
17%15%6%12%8%35%5%3416%
2506
16th to endNight
14%15%6%12%9%5%5%5%4416%
2535
February1st to 15thNight
14%13%8%13%7%45%445%17%
2278
16th to endNight
15%11%6%11%8%45%45%5%21%
1962
March1st to 15thNight
20%11%5%9%7%34345%24%
2037
16th to endNight
18%9%36%5%24446%32%
2073
April1st to 15thNight
20%8%36%5%45%44431%
1796
16th to endNight
17%5%25%6%1335%6%41%
1752
May1st to 15thNight
17%6%26%5%4435%8%36%
1496
16th to endNight
11%435%5%2446%9%42%
1495
June1st to 15thNight
17%5%344335%5%8%37%
1440
16th to endNight
9%426%5%345%7%8%41%
1440
July1st to 15thNight
6%425%6%2446%9%46%
1440
16th to endNight
10%3144346%5%9%44%
1540
August1st to 15thNight
8%414426%5%5%9%45%
1586
16th to endNight
9%426%4235%5%8%48%
1693
September1st to 15thNight
14%435%423447%44%
1650
16th to endNight
13%6%25%4235%5%7%43%
1812
October1st to 15thNight
21%7%25%5%34346%34%
1980
16th to endNight
26%10%37%5%35%45%5%23%
2131
November1st to 15thNight
17%10%46%5%245%5%7%30%
2324
16th to endNight
18%14%47%6%34445%25%
2520
December1st to 15thNight
20%13%5%8%7%45%5%4419%
2520
16th to endNight
22%15%8%10%7%35%345%12%
2688

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 15thDay
72%6%7%9%3
1433
16th to endDay
73%6%9%7%2
1688
February1st to 15thDay
74%7%6%8%2
1577
16th to endDay
68%6%9%10%4
1510
March1st to 15thDay
65%6%10%12%4
1920
16th to endDay
54%7%10%17%9%
2151
April1st to 15thDay
55%411%16%10%1
2152
16th to endDay
46%48%19%18%2
2217
May1st to 15thDay
48%7%11%19%11%1
2454
16th to endDay
43%8%14%19%12%1
2622
June1st to 15thDay
48%6%12%19%12%
2520
16th to endDay
41%9%15%21%12%
2520
July1st to 15thDay
38%8%12%23%14%
2371
16th to endDay
44%9%16%19%9%
2461
August1st to 15thDay
43%10%15%19%10%
2275
16th to endDay
44%7%14%22%9%1
2146
September1st to 15thDay
43%7%12%23%11%
1980
16th to endDay
44%7%11%21%14%
1818
October1st to 15thDay
49%6%12%17%11%
1650
16th to endDay
62%7%14%11%3
1741
November1st to 15thDay
52%8%14%15%8%1
1533
16th to endDay
59%8%14%15%2
1440
December1st to 15thDay
67%7%13%9%1
1440
16th to endDay
75%7%9%6%1
1536
January1st to 15thNight
69%8%7%8%5%
2506
16th to endNight
69%7%10%9%3
2535
February1st to 15thNight
67%7%8%11%4
2287
16th to endNight
62%6%12%12%4
1962
March1st to 15thNight
62%5%11%15%4
2037
16th to endNight
52%6%10%16%12%1
2073
April1st to 15thNight
54%6%10%17%10%1
1796
16th to endNight
42%5%10%21%16%2
1752
May1st to 15thNight
46%6%12%17%13%2
1496
16th to endNight
37%8%14%23%14%2
1497
June1st to 15thNight
43%8%13%22%12%
1440
16th to endNight
37%8%13%22%17%1
1440
July1st to 15thNight
33%7%14%23%18%2
1360
16th to endNight
33%8%16%25%13%3
1442
August1st to 15thNight
33%8%17%29%10%
1575
16th to endNight
33%7%13%30%14%1
1693
September1st to 15thNight
39%6%12%24%14%1
1650
16th to endNight
38%7%12%26%13%1
1812
October1st to 15thNight
49%6%11%18%12%
1980
16th to endNight
61%7%14%11%4
2131
November1st to 15thNight
51%7%14%15%8%2
2324
16th to endNight
59%7%13%14%5%
2520
December1st to 15thNight
66%9%12%9%2
2520
16th to endNight
73%7%9%7%1
2688

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 15thDay
16%40%25%8%10%
60
16th to endDay
30%25%31%11%1
89
February1st to 15thDay
30%37%27%4
90
16th to endDay
28%20%33%15%2
169
March1st to 15thDay
26%21%27%17%6%
270
16th to endDay
27%20%28%16%6%1
288
April1st to 15thDay
30%17%32%12%6%1
270
16th to endDay
21%15%25%21%11%3
270
May1st to 15thDay
29%15%22%18%10%3
288
16th to endDay
16%12%35%19%11%3
331
June1st to 15thDay
23%10%27%27%8%1
315
16th to endDay
13%12%35%24%10%2
315
July1st to 15thDay
12%6%26%32%17%4
305
16th to endDay
11%7%30%27%17%5%
326
August1st to 15thDay
14%425%25%20%9%
297
16th to endDay
15%419%23%19%17%
268
September1st to 15thDay
16%8%16%24%20%13%
255
16th to endDay
18%10%21%21%17%10%
254
October1st to 15thDay
22%10%25%21%16%4
255
16th to endDay
30%17%32%14%4
269
November1st to 15thDay
21%12%32%22%9%
187
16th to endDay
21%25%26%23%3
60
December1st to 15thDay
25%28%23%16%5%1
60
16th to endDay
35%31%28%4
64
January1st to 15thNight
25%28%30%13%3
720
16th to endNight
24%22%32%17%2
768
February1st to 15thNight
23%23%37%13%2
704
16th to endNight
23%23%32%17%2
631
March1st to 15thNight
27%21%29%19%2
720
16th to endNight
23%16%32%20%7%
768
April1st to 15thNight
24%16%31%24%2
718
16th to endNight
21%12%29%26%9%
672
May1st to 15thNight
22%7%23%33%11%
416
16th to endNight
11%6%33%31%16%
375
June1st to 15thNight
18%7%25%30%17%
360
16th to endNight
10%5%31%39%11%
360
July1st to 15thNight
7%322%43%22%
340
16th to endNight
9%323%42%17%2
402
August1st to 15thNight
11%125%34%21%4
527
16th to endNight
10%5%22%31%28%2
643
September1st to 15thNight
15%8%20%29%23%2
660
16th to endNight
14%9%21%25%23%4
657
October1st to 15thNight
25%12%23%21%16%1
660
16th to endNight
31%15%29%20%3
704
November1st to 15thNight
23%15%31%21%7%1
700
16th to endNight
26%22%26%16%7%1
720
December1st to 15thNight
30%22%32%12%2
720
16th to endNight
31%22%30%13%2
768
Page generated at 2017-08-13 14:16:22. Version ac04

Copyright 2017 A. Danko


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