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 2017-12-20.

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%
15226
12%
48080
8%
15193
34%
15193
15%
35141

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
15%
631
9%
1962
4%
631
21%
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
39%
672
26%
1195
May1st to 15thNight
38%
416
16%
1496
12%
416
46%
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
56%
340
14%
1360
19%
340
61%
340
26%
760
July16th to endNight
57%
402
14%
1442
16%
378
61%
378
26%
825
August1st to 15thNight
54%
539
15%
1609
10%
536
58%
536
31%
986
August16th to endNight
57%
702
21%
1848
12%
702
60%
702
36%
1153
September1st to 15thNight
50%
720
18%
1800
10%
720
53%
720
29%
1222
September16th to endNight
50%
717
22%
1977
17%
717
53%
717
29%
1282
October1st to 15thNight
35%
720
14%
2160
12%
720
39%
720
19%
1519
October16th to endNight
20%
768
9%
2325
5%
768
26%
768
12%
1805
November1st to 15thNight
25%
760
13%
2523
10%
760
30%
760
14%
1823
November16th to endNight
19%
780
11%
2730
7%
780
25%
780
10%
2068
December1st to 15thNight
12%
780
6%
2730
1%
780
17%
780
6%
2220
December16th to endNight
10%
788
4%
2755
1%
788
14%
788
4%
2394

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%6%29%
48768
Night
16%10%47%6%3445%6%30%
48253
Cloud CoverDay
15%9%47%6%35%45%7%30%
48778
Night
16%9%47%6%3445%6%30%
48258
TransparencyDay
52%7%12%17%9%
48459
Night
52%7%12%17%9%1
48080
SeeingDay
20%14%27%20%11%4
5786
Night
21%15%28%23%10%1
15228

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
11%425%7%5%5%6%7%8%34%
2340
16th to endDay
12%5%26%6%45%5%6%7%35%
2342
September1st to 15thDay
16%6%25%3345%5%7%39%
2160
16th to endDay
14%6%26%5%34447%39%
1983
October1st to 15thDay
18%8%36%6%34346%34%
1800
16th to endDay
24%10%46%6%3445%5%23%
1899
November1st to 15thDay
14%12%46%6%45%36%6%29%
1664
16th to endDay
19%12%48%6%345%5%7%23%
1560
December1st to 15thDay
18%14%6%11%8%35%345%18%
1560
16th to endDay
19%18%8%13%7%34345%12%
1568
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
7%415%426%5%6%7%46%
1620
16th to endNight
8%325%42445%8%49%
1848
September1st to 15thNight
14%5%26%324447%43%
1800
16th to endNight
12%6%15%42345%7%44%
1977
October1st to 15thNight
19%8%25%5%34446%35%
2160
16th to endNight
25%10%46%5%34346%24%
2325
November1st to 15thNight
18%10%47%5%235%48%29%
2523
16th to endNight
18%14%46%6%3445%6%25%
2730
December1st to 15thNight
19%14%6%9%6%35%45%5%19%
2730
16th to endNight
21%16%7%11%7%3444413%
2755

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%
2340
16th to endDay
13%6%16%6%45%5%5%7%36%
2342
September1st to 15thDay
15%6%344345%6%7%39%
2160
16th to endDay
14%5%25%5%3445%7%39%
1983
October1st to 15thDay
18%7%36%5%4435%5%34%
1800
16th to endDay
23%10%37%6%445%46%23%
1899
November1st to 15thDay
14%12%46%6%4445%6%29%
1664
16th to endDay
17%13%38%5%35%45%8%22%
1560
December1st to 15thDay
17%15%7%10%8%35%345%18%
1560
16th to endDay
20%18%7%12%8%34345%12%
1568
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%415%426%5%5%9%45%
1620
16th to endNight
8%425%4245%5%8%49%
1848
September1st to 15thNight
14%435%423447%44%
1800
16th to endNight
12%5%25%4235%5%7%44%
1977
October1st to 15thNight
20%7%25%5%34346%35%
2160
16th to endNight
25%10%37%5%24446%25%
2325
November1st to 15thNight
17%10%46%5%245%5%7%29%
2523
16th to endNight
18%14%46%6%3445%6%26%
2730
December1st to 15thNight
20%13%5%8%7%35%5%45%19%
2730
16th to endNight
22%15%7%10%7%35%345%12%
2755

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
42%10%15%19%10%
2327
16th to endDay
43%7%15%22%10%1
2342
September1st to 15thDay
42%7%13%23%12%1
2160
16th to endDay
43%7%11%22%14%
1983
October1st to 15thDay
49%6%12%18%12%
1800
16th to endDay
60%7%14%12%3
1899
November1st to 15thDay
53%7%14%14%8%1
1664
16th to endDay
59%8%14%15%2
1560
December1st to 15thDay
67%7%12%9%1
1560
16th to endDay
75%7%9%6%1
1568
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%
1609
16th to endNight
31%7%13%30%14%1
1848
September1st to 15thNight
39%7%13%23%14%2
1800
16th to endNight
36%7%12%26%15%1
1977
October1st to 15thNight
49%6%11%19%13%
2160
16th to endNight
59%7%14%13%4
2325
November1st to 15thNight
52%7%13%15%7%2
2523
16th to endNight
58%7%13%15%5%
2730
December1st to 15thNight
65%8%13%9%2
2730
16th to endNight
73%8%9%7%1
2755

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%428%24%19%8%
313
16th to endDay
13%6%23%24%18%14%
332
September1st to 15thDay
16%9%18%23%20%11%
315
16th to endDay
15%10%19%21%19%13%
314
October1st to 15thDay
22%10%26%20%13%5%
315
16th to endDay
27%19%30%16%6%
331
November1st to 15thDay
24%12%30%22%9%
228
16th to endDay
23%30%26%17%2
90
December1st to 15thDay
23%25%28%15%5%1
90
16th to endDay
38%29%25%6%
72
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%126%34%21%4
539
16th to endNight
9%5%21%32%27%1
702
September1st to 15thNight
15%8%20%29%23%2
720
16th to endNight
13%9%20%23%26%6%
717
October1st to 15thNight
25%11%23%22%15%1
720
16th to endNight
30%14%30%20%3
768
November1st to 15thNight
23%15%30%21%7%1
760
16th to endNight
25%22%27%16%7%1
780
December1st to 15thNight
29%21%32%13%2
780
16th to endNight
30%23%30%13%2
788
Page generated at 2017-12-21 07:04:52. Version ac04

Copyright 2017 A. Danko


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