Estrella Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Estrella Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
78%
15677
38%
46967
34%
15638
82%
15638
56%
21857

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
75%
718
34%
2327
36%
716
79%
716
47%
1121
January16th to endNight
69%
768
37%
2496
36%
768
77%
768
43%
1250
February1st to 15thNight
73%
699
37%
2174
37%
698
81%
698
54%
1007
February16th to endNight
70%
632
37%
1889
38%
632
74%
632
45%
980
March1st to 15thNight
72%
720
41%
1980
35%
720
77%
720
60%
942
March16th to endNight
77%
768
41%
2112
32%
768
84%
768
64%
981
April1st to 15thNight
71%
713
34%
1972
24%
713
77%
713
57%
963
April16th to endNight
69%
540
46%
1686
37%
540
79%
540
71%
647
May1st to 15thNight
75%
539
40%
1619
32%
539
81%
539
66%
675
May16th to endNight
78%
561
41%
1684
32%
561
83%
561
73%
670
June1st to 15thNight
84%
540
36%
1620
30%
540
86%
540
74%
645
June16th to endNight
88%
540
36%
1620
30%
540
89%
540
75%
643
July1st to 15thNight
82%
510
27%
1530
23%
510
83%
510
52%
752
July16th to endNight
82%
564
29%
1593
25%
531
83%
531
43%
864
August1st to 15thNight
85%
539
32%
1611
27%
536
85%
536
49%
809
August16th to endNight
81%
651
35%
1871
31%
651
82%
651
47%
993
September1st to 15thNight
80%
720
34%
1980
29%
720
82%
720
53%
1016
September16th to endNight
83%
683
44%
1890
35%
683
88%
683
68%
852
October1st to 15thNight
81%
660
43%
1886
37%
660
85%
660
66%
840
October16th to endNight
85%
704
45%
2112
40%
704
89%
704
68%
884
November1st to 15thNight
84%
700
43%
2139
42%
700
88%
700
67%
895
November16th to endNight
78%
720
41%
2340
42%
720
83%
720
56%
1034
December1st to 15thNight
75%
720
38%
2340
40%
720
79%
720
48%
1111
December16th to endNight
72%
768
37%
2496
39%
768
75%
768
42%
1283

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
3212212346%70%
47909
Night
3212213346%69%
47165
TransparencyDay
16%1311%25%41%
47604
Night
17%1210%23%43%
46971
SeeingDay
5%418%33%28%10%
5489
Night
419%42%36%4
15687

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
5%213222345%66%
1611
16th to endDay
7%313212236%65%
1728
February1st to 15thDay
3413211237%67%
1685
16th to endDay
7%413313327%61%
1583
March1st to 15thDay
4211313345%68%
1980
16th to endDay
311231333471%
2112
April1st to 15thDay
2111113347%70%
1974
16th to endDay
1111122480%
2271
May1st to 15thDay
111111135%80%
2331
16th to endDay
2111111482%
2429
June1st to 15thDay
1111112482%
2340
16th to endDay
11122483%
2340
July1st to 15thDay
22133235%6%9%60%
2340
16th to endDay
5%3145%35%5%7%10%46%
2467
August1st to 15thDay
32123145%6%9%57%
2340
16th to endDay
311232335%9%62%
2327
September1st to 15thDay
3213323447%63%
1980
16th to endDay
2111122481%
1882
October1st to 15thDay
21121323476%
1744
16th to endDay
112111235%79%
1760
November1st to 15thDay
21211224377%
1717
16th to endDay
421221124473%
1620
December1st to 15thDay
6%313323435%63%
1620
16th to endDay
7%413324345%59%
1728
January1st to 15thNight
5%31322423465%
2327
16th to endNight
9%213313335%62%
2496
February1st to 15thNight
4313212335%68%
2165
16th to endNight
6%313423336%62%
1889
March1st to 15thNight
4213211345%70%
1980
16th to endNight
312112336%73%
2112
April1st to 15thNight
3112213336%68%
1972
16th to endNight
211122383%
1686
May1st to 15thNight
11211345%76%
1619
16th to endNight
211112284%
1684
June1st to 15thNight
1112225%81%
1620
16th to endNight
111222482%
1620
July1st to 15thNight
1213325%5%6%10%57%
1620
16th to endNight
3313436%5%7%11%48%
1701
August1st to 15thNight
221243448%10%55%
1620
16th to endNight
1114426%5%7%7%56%
1871
September1st to 15thNight
2233245%5%8%60%
1980
16th to endNight
11121233377%
1890
October1st to 15thNight
212212136%74%
1886
16th to endNight
12111123478%
2112
November1st to 15thNight
21112336%75%
2139
16th to endNight
421222222472%
2340
December1st to 15thNight
7%212223336%64%
2340
16th to endNight
8%313423235%59%
2496

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
21%415%28%28%
1612
16th to endDay
22%1216%25%30%
1728
February1st to 15thDay
19%1417%28%29%
1685
16th to endDay
23%2115%31%25%
1583
March1st to 15thDay
18%118%31%38%
1980
16th to endDay
18%118%33%37%
2112
April1st to 15thDay
14%18%34%39%
1974
16th to endDay
10%17%25%55%
2271
May1st to 15thDay
9%17%24%56%
2331
16th to endDay
9%5%22%60%
2432
June1st to 15thDay
8%1215%71%
2340
16th to endDay
7%1310%76%
2340
July1st to 15thDay
19%27%15%19%35%
2201
16th to endDay
28%410%24%20%11%
2312
August1st to 15thDay
20%37%18%19%30%
2325
16th to endDay
18%35%17%28%26%
2327
September1st to 15thDay
21%2413%24%33%
1980
16th to endDay
10%6%27%55%
1882
October1st to 15thDay
13%129%27%45%
1744
16th to endDay
10%137%28%48%
1760
November1st to 15thDay
12%111%31%41%
1717
16th to endDay
16%110%27%42%
1620
December1st to 15thDay
24%1415%28%24%
1620
16th to endDay
25%2422%28%16%
1728
January1st to 15thNight
23%1311%24%35%
2327
16th to endNight
26%1112%26%31%
2496
February1st to 15thNight
19%1314%24%35%
2176
16th to endNight
25%1112%27%30%
1889
March1st to 15thNight
16%118%25%46%
1980
16th to endNight
14%117%31%43%
2112
April1st to 15thNight
17%216%28%44%
1972
16th to endNight
8%115%21%62%
1686
May1st to 15thNight
10%115%24%55%
1620
16th to endNight
9%16%16%66%
1685
June1st to 15thNight
8%1313%72%
1620
16th to endNight
8%1136%79%
1620
July1st to 15thNight
20%37%16%15%36%
1530
16th to endNight
26%410%20%21%16%
1593
August1st to 15thNight
21%37%19%17%30%
1611
16th to endNight
24%36%13%23%28%
1871
September1st to 15thNight
19%36%18%20%31%
1980
16th to endNight
11%25%20%59%
1890
October1st to 15thNight
13%1110%23%50%
1886
16th to endNight
11%118%17%58%
2112
November1st to 15thNight
12%119%27%48%
2139
16th to endNight
18%119%23%46%
2340
December1st to 15thNight
22%1214%27%31%
2340
16th to endNight
27%1415%29%21%
2496

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
23%17%35%21%2
90
16th to endDay
11%311%32%27%14%
96
February1st to 15thDay
45%17%36%31%5%
200
16th to endDay
11%6%29%31%17%3
238
March1st to 15thDay
6%7%24%28%20%12%
270
16th to endDay
410%28%25%23%7%
288
April1st to 15thDay
8%10%24%30%17%8%
269
16th to endDay
6%12%34%30%13%4
270
May1st to 15thDay
310%28%34%17%5%
288
16th to endDay
3327%38%21%5%
330
June1st to 15thDay
1225%38%25%5%
315
16th to endDay
112%39%34%10%
315
July1st to 15thDay
1110%42%35%9%
305
16th to endDay
4427%37%24%
327
August1st to 15thDay
3435%38%18%
315
16th to endDay
15%32%43%16%
332
September1st to 15thDay
6%211%35%34%10%
315
16th to endDay
5%120%32%30%9%
280
October1st to 15thDay
4419%28%27%15%
184
16th to endDay
4326%51%15%
96
November1st to 15thDay
1112%30%37%17%
90
16th to endDay
8%214%38%30%5%
90
December1st to 15thDay
48%34%40%12%
90
16th to endDay
17%19%29%31%2
96
January1st to 15thNight
6%8%50%29%4
720
16th to endNight
10%110%47%26%2
768
February1st to 15thNight
5%111%47%30%3
704
16th to endNight
8%112%54%21%2
632
March1st to 15thNight
4214%47%27%3
720
16th to endNight
4310%45%32%4
768
April1st to 15thNight
4413%47%27%2
713
16th to endNight
25%21%44%23%2
540
May1st to 15thNight
15%14%45%30%2
540
16th to endNight
2213%42%35%1
563
June1st to 15thNight
219%54%30%1
540
16th to endNight
16%43%45%2
540
July1st to 15thNight
16%35%51%4
510
16th to endNight
4322%58%10%
564
August1st to 15thNight
2225%57%11%
539
16th to endNight
25%24%56%10%
651
September1st to 15thNight
327%28%50%7%
720
16th to endNight
219%38%41%6%
683
October1st to 15thNight
317%46%37%3
660
16th to endNight
116%40%41%7%
704
November1st to 15thNight
317%44%39%5%
700
16th to endNight
49%45%35%4
720
December1st to 15thNight
8%8%45%35%1
720
16th to endNight
10%16%49%28%3
768
Page generated at 2017-09-23 03:43:38. Version ac04

Copyright 2017 A. Danko


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