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Tralfamadore Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tralfamadore Observatory clear sky chart from 2005-11-05 to 2017-10-16.

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
66%
15659
37%
47154
27%
15621
76%
15621
61%
20221

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
58%
718
31%
2506
23%
716
73%
716
52%
1029
January16th to endNight
54%
768
35%
2470
25%
768
68%
768
45%
1152
February1st to 15thNight
57%
700
36%
2103
27%
697
71%
697
54%
967
February16th to endNight
53%
632
35%
1895
27%
632
68%
632
53%
882
March1st to 15thNight
52%
720
31%
2160
20%
720
69%
720
54%
982
March16th to endNight
53%
768
36%
2010
19%
768
66%
768
56%
977
April1st to 15thNight
51%
719
35%
1799
14%
719
62%
719
57%
882
April16th to endNight
54%
720
40%
1800
15%
720
66%
720
68%
831
May1st to 15thNight
58%
566
36%
1646
21%
566
66%
566
68%
673
May16th to endNight
61%
561
35%
1684
23%
561
70%
561
64%
685
June1st to 15thNight
70%
363
36%
1443
35%
363
82%
363
67%
473
June16th to endNight
81%
360
41%
1440
44%
360
90%
360
78%
428
July1st to 15thNight
91%
340
35%
1360
42%
340
93%
340
64%
466
July16th to endNight
88%
471
39%
1504
38%
442
89%
442
64%
596
August1st to 15thNight
85%
717
37%
1790
24%
713
87%
713
81%
803
August16th to endNight
89%
764
45%
1910
29%
764
90%
764
82%
851
September1st to 15thNight
86%
720
43%
1825
29%
720
90%
720
78%
825
September16th to endNight
82%
716
48%
1980
40%
716
90%
716
81%
800
October1st to 15thNight
71%
720
40%
2013
32%
720
80%
720
66%
890
October16th to endNight
72%
708
44%
2182
39%
708
83%
708
66%
877
November1st to 15thNight
69%
700
38%
2275
33%
700
82%
700
64%
901
November16th to endNight
65%
720
39%
2340
34%
720
76%
720
58%
969
December1st to 15thNight
59%
720
34%
2340
23%
720
73%
720
50%
1030
December16th to endNight
50%
768
32%
2679
22%
768
66%
768
39%
1252

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
111212346%74%
48260
Night
11112236%76%
47345
TransparencyDay
11%47%17%28%30%
47940
Night
10%47%20%31%25%
47165
SeeingDay
5%18%38%25%8%2
5915
Night
26%22%32%27%8%
15668

By Month

Percentage Cloud Cover SW (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
11111235%8%71%
1432
16th to endDay
3213214346%65%
1749
February1st to 15thDay
11121335%8%69%
1751
16th to endDay
13121235%9%68%
1579
March1st to 15thDay
1123349%71%
1800
16th to endDay
2121236%9%69%
2212
April1st to 15thDay
1211223446%70%
2149
16th to endDay
11112237%76%
2160
May1st to 15thDay
111212246%75%
2302
16th to endDay
1212322336%69%
2429
June1st to 15thDay
11111346%77%
2514
16th to endDay
11222384%
2520
July1st to 15thDay
212223345%71%
2520
16th to endDay
1112314446%67%
2558
August1st to 15thDay
11111122381%
2160
16th to endDay
111223381%
2292
September1st to 15thDay
121343476%
2133
16th to endDay
11221384%
1980
October1st to 15thDay
21121222479%
1944
16th to endDay
111111335%77%
1710
November1st to 15thDay
12111245%78%
1584
16th to endDay
111112246%76%
1620
December1st to 15thDay
112112349%70%
1620
16th to endDay
11221236%9%68%
1542
January1st to 15thNight
11212348%71%
2506
16th to endNight
2312312246%69%
2470
February1st to 15thNight
12223449%69%
2101
16th to endNight
11121335%7%70%
1895
March1st to 15thNight
1121236%8%70%
2160
16th to endNight
1111235%10%69%
2010
April1st to 15thNight
1111212248%73%
1799
16th to endNight
1111226%81%
1800
May1st to 15thNight
111237%79%
1646
16th to endNight
111111135%80%
1684
June1st to 15thNight
11237%80%
1443
16th to endNight
111289%
1440
July1st to 15thNight
111224479%
1440
16th to endNight
11121223478%
1607
August1st to 15thNight
111122484%
1800
16th to endNight
1122484%
1910
September1st to 15thNight
111123483%
1825
16th to endNight
1122486%
1980
October1st to 15thNight
11111223379%
2013
16th to endNight
11111146%80%
2182
November1st to 15thNight
111111235%79%
2275
16th to endNight
1122237%76%
2340
December1st to 15thNight
11213348%70%
2340
16th to endNight
22213438%69%
2679

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
11%6%12%27%31%10%
1432
16th to endDay
20%49%24%25%16%
1749
February1st to 15thDay
13%5%9%29%27%14%
1751
16th to endDay
14%5%12%24%31%11%
1579
March1st to 15thDay
11%5%9%28%28%16%
1800
16th to endDay
12%5%14%26%27%14%
2212
April1st to 15thDay
15%5%8%23%32%15%
2149
16th to endDay
9%39%25%35%17%
2160
May1st to 15thDay
10%46%19%38%21%
2302
16th to endDay
14%5%5%17%39%18%
2432
June1st to 15thDay
7%36%11%29%42%
2514
16th to endDay
6%12419%65%
2520
July1st to 15thDay
14%35%6%13%56%
2371
16th to endDay
15%6%410%17%46%
2398
August1st to 15thDay
8%236%18%60%
2146
16th to endDay
7%236%26%52%
2292
September1st to 15thDay
9%449%22%49%
2133
16th to endDay
6%2211%38%38%
1980
October1st to 15thDay
10%3314%36%31%
1944
16th to endDay
10%3415%39%26%
1710
November1st to 15thDay
9%48%23%34%18%
1584
16th to endDay
10%37%25%34%19%
1620
December1st to 15thDay
12%7%14%27%26%12%
1620
16th to endDay
15%7%13%27%21%14%
1542
January1st to 15thNight
11%5%11%27%30%12%
2506
16th to endNight
17%410%20%29%16%
2470
February1st to 15thNight
14%310%28%27%14%
2112
16th to endNight
13%5%10%27%33%9%
1895
March1st to 15thNight
13%49%27%27%17%
2160
16th to endNight
12%411%31%30%8%
2010
April1st to 15thNight
12%211%25%35%12%
1799
16th to endNight
7%35%30%37%15%
1800
May1st to 15thNight
6%38%24%39%16%
1647
16th to endNight
8%36%27%35%18%
1685
June1st to 15thNight
6%35%16%31%37%
1443
16th to endNight
4117%23%61%
1440
July1st to 15thNight
8%329%16%58%
1360
16th to endNight
11%25%10%21%48%
1504
August1st to 15thNight
6%149%23%54%
1790
16th to endNight
5%228%32%48%
1910
September1st to 15thNight
6%3310%25%51%
1825
16th to endNight
41212%38%40%
1980
October1st to 15thNight
10%3316%38%27%
2013
16th to endNight
7%3416%42%25%
2182
November1st to 15thNight
9%310%19%38%18%
2275
16th to endNight
11%37%23%35%18%
2340
December1st to 15thNight
13%5%14%27%28%10%
2340
16th to endNight
15%9%12%26%21%13%
2679

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
11%30%40%8%10%
60
16th to endDay
11%25%30%20%8%3
229
February1st to 15thDay
5%23%32%25%10%1
266
16th to endDay
13%24%39%17%5%1
238
March1st to 15thDay
9%23%37%17%9%2
270
16th to endDay
7%28%44%14%4
288
April1st to 15thDay
12%32%34%13%5%1
269
16th to endDay
9%35%38%11%31
270
May1st to 15thDay
424%43%19%5%1
288
16th to endDay
6%23%36%23%6%2
330
June1st to 15thDay
5%16%40%28%7%1
315
16th to endDay
115%38%28%11%4
315
July1st to 15thDay
26%38%35%12%4
305
16th to endDay
17%36%37%10%6%
327
August1st to 15thDay
312%42%30%6%4
315
16th to endDay
5%40%33%11%7%
332
September1st to 15thDay
210%40%34%10%1
315
16th to endDay
311%42%32%9%
315
October1st to 15thDay
5%18%40%26%7%
315
16th to endDay
5%18%33%32%7%1
218
November1st to 15thDay
313%13%32%31%6%
90
16th to endDay
414%37%31%12%
90
December1st to 15thDay
413%46%27%7%
90
16th to endDay
9%15%36%24%10%3
65
January1st to 15thNight
17%28%29%21%10%
720
16th to endNight
5%10%26%30%21%5%
768
February1st to 15thNight
17%29%30%22%7%
704
16th to endNight
311%29%30%20%4
632
March1st to 15thNight
28%34%29%17%7%
720
16th to endNight
211%31%30%19%4
768
April1st to 15thNight
313%29%31%17%4
719
16th to endNight
111%31%29%22%5%
720
May1st to 15thNight
28%30%34%20%4
567
16th to endNight
29%25%36%24%2
563
June1st to 15thNight
224%40%27%4
363
16th to endNight
16%49%28%4
360
July1st to 15thNight
2444%42%6%
340
16th to endNight
15%38%46%7%
471
August1st to 15thNight
110%40%37%9%
717
16th to endNight
7%34%43%13%
764
September1st to 15thNight
19%29%47%11%
720
16th to endNight
312%34%36%13%
716
October1st to 15thNight
15%20%35%26%11%
720
16th to endNight
17%16%28%31%13%
708
November1st to 15thNight
15%21%28%32%11%
700
16th to endNight
18%21%31%27%8%
720
December1st to 15thNight
36%27%32%21%7%
720
16th to endNight
312%31%27%19%5%
768
Page generated at 2017-10-17 13:35:27. Version ac04

Copyright 2017 A. Danko


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