Salvador Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salvador Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
38%
14885
14%
47110
10%
14849
43%
14849
19%
32745

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
16%
719
8%
2491
3%
716
23%
716
9%
1966
January16th to endNight
20%
768
10%
2496
5%
768
27%
768
11%
1954
February1st to 15thNight
17%
702
9%
2287
3%
701
26%
701
11%
1770
February16th to endNight
23%
631
12%
2018
5%
631
33%
631
14%
1487
March1st to 15thNight
25%
720
14%
1980
7%
720
32%
720
17%
1485
March16th to endNight
35%
768
20%
2112
11%
768
42%
768
25%
1433
April1st to 15thNight
34%
718
15%
1809
5%
718
40%
718
24%
1313
April16th to endNight
44%
576
19%
1656
9%
576
50%
576
28%
1088
May1st to 15thNight
50%
474
16%
1554
13%
474
55%
474
24%
1009
May16th to endNight
57%
374
17%
1497
19%
374
63%
374
26%
828
June1st to 15thNight
52%
360
12%
1440
13%
360
59%
360
21%
850
June16th to endNight
59%
360
12%
1440
19%
360
62%
360
24%
841
July1st to 15thNight
70%
340
16%
1360
25%
340
73%
340
34%
687
July16th to endNight
65%
470
16%
1505
18%
441
67%
441
30%
867
August1st to 15thNight
67%
539
17%
1609
14%
536
70%
536
35%
945
August16th to endNight
64%
633
23%
1779
15%
633
67%
633
37%
1062
September1st to 15thNight
57%
720
20%
1800
10%
720
61%
720
34%
1181
September16th to endNight
58%
717
23%
2007
17%
717
61%
717
33%
1246
October1st to 15thNight
43%
684
17%
2051
16%
684
48%
684
22%
1406
October16th to endNight
26%
704
11%
2112
6%
704
33%
704
15%
1581
November1st to 15thNight
37%
700
18%
2379
16%
700
43%
700
18%
1619
November16th to endNight
29%
720
10%
2520
7%
720
34%
720
12%
1891
December1st to 15thNight
17%
720
6%
2520
3%
720
20%
720
9%
2011
December16th to endNight
15%
768
6%
2688
2%
768
20%
768
7%
2225

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
14%7%36%6%35%5%5%7%34%
48086
Night
15%7%36%5%3445%6%36%
47288
Cloud CoverDay
14%7%36%5%35%5%5%8%34%
48096
Night
15%7%36%5%3445%6%35%
47293
TransparencyDay
47%8%14%19%9%1
47783
Night
47%7%13%19%10%1
47110
SeeingDay
16%424%30%17%6%
5438
Night
19%6%28%29%13%2
14889

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
17%12%5%6%6%35%45%6%25%
1447
16th to endDay
13%14%6%11%8%45%5%5%6%19%
1728
February1st to 15thDay
14%13%5%10%8%45%435%22%
1575
16th to endDay
16%12%48%6%35%445%28%
1452
March1st to 15thDay
15%8%47%8%46%45%6%28%
1969
16th to endDay
15%7%36%5%24446%37%
2112
April1st to 15thDay
20%8%45%5%3445%6%30%
2138
16th to endDay
17%7%25%5%34446%38%
2315
May1st to 15thDay
13%6%36%6%35%45%7%35%
2395
16th to endDay
11%425%5%26%46%7%41%
2618
June1st to 15thDay
14%5%25%5%35%46%9%35%
2520
16th to endDay
11%4245%36%6%6%10%37%
2520
July1st to 15thDay
7%3146%36%6%6%9%43%
2520
16th to endDay
9%425%5%36%7%6%10%37%
2558
August1st to 15thDay
8%426%6%46%5%6%9%40%
2340
16th to endDay
9%5%25%5%35%5%6%8%42%
2411
September1st to 15thDay
14%415%435%46%6%42%
2160
16th to endDay
12%435%5%3435%7%43%
1950
October1st to 15thDay
17%7%26%6%35%446%35%
1707
16th to endDay
23%9%47%6%3445%5%26%
1760
November1st to 15thDay
13%7%37%6%36%35%8%33%
1475
16th to endDay
18%9%49%6%35%5%5%8%23%
1440
December1st to 15thDay
18%13%5%9%7%35%46%7%19%
1440
16th to endDay
20%11%5%8%7%36%5%5%6%18%
1536
January1st to 15thNight
20%13%48%6%2445%5%23%
2491
16th to endNight
14%12%5%8%7%5%5%446%24%
2496
February1st to 15thNight
14%14%5%7%6%35%45%6%25%
2285
16th to endNight
15%9%47%7%45%446%30%
2018
March1st to 15thNight
17%8%47%7%34345%32%
1968
16th to endNight
14%7%36%424335%43%
2112
April1st to 15thNight
18%6%36%425%35%6%36%
1809
16th to endNight
11%6%35%5%2436%6%43%
1656
May1st to 15thNight
15%425%5%346%6%7%39%
1554
16th to endNight
12%32442346%7%49%
1495
June1st to 15thNight
12%5%24445%45%8%41%
1440
16th to endNight
11%5%245%35%46%8%43%
1440
July1st to 15thNight
5%31442336%8%55%
1440
16th to endNight
8%213435%5%6%9%49%
1608
August1st to 15thNight
6%42442446%8%50%
1620
16th to endNight
8%41443445%6%52%
1779
September1st to 15thNight
12%4243245%5%6%47%
1800
16th to endNight
12%42432345%7%48%
2007
October1st to 15thNight
17%5%27%42445%6%38%
2051
16th to endNight
21%8%45%5%3445%7%28%
2112
November1st to 15thNight
16%5%26%6%25%45%6%36%
2379
16th to endNight
20%9%36%435%5%6%7%26%
2520
December1st to 15thNight
21%12%5%7%6%35%5%5%5%22%
2520
16th to endNight
21%11%5%7%7%46%5%47%18%
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
17%11%5%7%7%35%45%5%24%
1447
16th to endDay
13%13%6%11%8%45%5%5%6%18%
1728
February1st to 15thDay
14%13%5%10%8%45%446%22%
1575
16th to endDay
17%11%48%6%435%5%6%27%
1452
March1st to 15thDay
16%8%38%6%45%5%5%7%28%
1980
16th to endDay
15%7%35%5%34346%37%
2111
April1st to 15thDay
20%7%36%5%3445%7%31%
2138
16th to endDay
17%6%25%434346%39%
2315
May1st to 15thDay
13%6%35%6%4445%8%36%
2395
16th to endDay
11%435%5%345%6%8%42%
2618
June1st to 15thDay
14%5%25%5%35%5%6%9%36%
2520
16th to endDay
11%424435%6%7%11%39%
2520
July1st to 15thDay
7%3245%36%6%7%9%44%
2520
16th to endDay
8%424445%6%8%10%39%
2558
August1st to 15thDay
7%425%6%35%5%7%9%42%
2340
16th to endDay
8%5%244346%6%8%45%
2411
September1st to 15thDay
13%5%144345%6%7%42%
2160
16th to endDay
11%5%245%345%47%44%
1950
October1st to 15thDay
17%7%26%5%35%446%36%
1707
16th to endDay
22%9%37%6%3345%6%26%
1760
November1st to 15thDay
13%8%37%6%35%46%8%32%
1475
16th to endDay
18%10%29%7%345%5%7%24%
1440
December1st to 15thDay
18%14%48%7%45%5%5%7%18%
1440
16th to endDay
21%11%6%8%6%35%5%7%7%17%
1536
January1st to 15thNight
21%13%48%5%24445%22%
2491
16th to endNight
15%11%6%8%7%46%5%46%23%
2496
February1st to 15thNight
14%14%5%8%6%345%5%6%24%
2278
16th to endNight
15%9%48%7%45%45%6%29%
2018
March1st to 15thNight
18%9%47%7%34345%31%
1980
16th to endNight
15%6%36%42443443%
2112
April1st to 15thNight
18%6%36%5%34446%36%
1809
16th to endNight
12%5%25%43445%6%43%
1656
May1st to 15thNight
15%325%5%35%5%6%7%38%
1554
16th to endNight
12%32432345%7%49%
1495
June1st to 15thNight
12%5%24435%5%5%9%41%
1440
16th to endNight
11%4245%3446%9%43%
1440
July1st to 15thNight
5%31442445%9%55%
1440
16th to endNight
8%3244245%5%9%48%
1608
August1st to 15thNight
6%415%4245%7%8%50%
1620
16th to endNight
7%42433445%6%53%
1779
September1st to 15thNight
11%4143345%5%7%47%
1800
16th to endNight
12%4244225%46%49%
2007
October1st to 15thNight
17%6%26%42445%6%38%
2051
16th to endNight
22%9%35%5%3445%6%29%
2112
November1st to 15thNight
16%5%26%6%35%45%6%36%
2379
16th to endNight
21%8%36%5%25%5%6%7%27%
2520
December1st to 15thNight
21%13%46%5%45%45%5%22%
2520
16th to endNight
22%12%5%8%7%45%5%5%6%16%
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
60%8%13%12%4
1448
16th to endDay
64%9%10%9%4
1728
February1st to 15thDay
63%7%11%14%1
1577
16th to endDay
56%7%13%15%6%
1452
March1st to 15thDay
54%8%12%16%7%
1980
16th to endDay
47%5%11%18%14%1
2112
April1st to 15thDay
52%6%11%18%10%
2138
16th to endDay
45%5%11%20%14%2
2315
May1st to 15thDay
45%7%12%21%13%
2395
16th to endDay
38%8%15%21%13%2
2622
June1st to 15thDay
42%8%14%22%12%
2520
16th to endDay
36%9%18%21%12%
2520
July1st to 15thDay
33%9%15%24%15%1
2371
16th to endDay
38%10%15%24%10%1
2399
August1st to 15thDay
36%9%16%22%13%1
2327
16th to endDay
35%8%17%27%11%
2411
September1st to 15thDay
38%9%14%25%11%
2160
16th to endDay
38%8%13%28%10%
1950
October1st to 15thDay
48%6%13%21%8%1
1707
16th to endDay
58%7%16%12%4
1760
November1st to 15thDay
48%9%16%17%7%1
1475
16th to endDay
58%9%14%13%4
1440
December1st to 15thDay
64%10%14%9%1
1440
16th to endDay
64%9%12%10%2
1536
January1st to 15thNight
62%7%12%11%4
2491
16th to endNight
60%8%12%13%4
2496
February1st to 15thNight
59%8%11%16%3
2287
16th to endNight
54%7%12%17%6%
2018
March1st to 15thNight
55%5%12%19%6%
1980
16th to endNight
44%49%22%15%2
2112
April1st to 15thNight
49%5%10%19%14%
1809
16th to endNight
39%6%12%20%17%3
1656
May1st to 15thNight
41%7%12%21%14%2
1554
16th to endNight
33%7%14%25%15%3
1497
June1st to 15thNight
39%6%13%23%15%1
1440
16th to endNight
38%5%13%23%17%1
1440
July1st to 15thNight
25%7%13%26%24%2
1360
16th to endNight
30%9%14%25%17%3
1505
August1st to 15thNight
29%8%18%27%14%1
1609
16th to endNight
30%6%12%32%16%1
1779
September1st to 15thNight
34%8%14%25%15%1
1800
16th to endNight
33%7%12%31%14%
2007
October1st to 15thNight
44%8%11%22%13%
2051
16th to endNight
54%7%14%15%6%
2112
November1st to 15thNight
46%7%12%18%12%1
2379
16th to endNight
54%9%16%14%4
2520
December1st to 15thNight
62%9%12%12%3
2520
16th to endNight
66%9%11%9%2
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
19%15%41%15%6%1
63
16th to endDay
30%8%35%23%2
96
February1st to 15thDay
18%8%54%17%
90
16th to endDay
20%12%40%20%4
101
March1st to 15thDay
23%8%37%22%7%
270
16th to endDay
21%435%27%8%2
288
April1st to 15thDay
22%7%30%30%7%1
270
16th to endDay
20%5%30%24%15%4
270
May1st to 15thDay
19%321%32%15%7%
288
16th to endDay
12%122%37%20%5%
331
June1st to 15thDay
18%418%37%20%1
315
16th to endDay
14%121%37%20%4
315
July1st to 15thDay
10%15%36%27%9%
305
16th to endDay
9%16%40%23%9%
326
August1st to 15thDay
7%115%34%29%12%
313
16th to endDay
13%113%26%29%14%
332
September1st to 15thDay
10%314%28%28%14%
315
16th to endDay
13%316%28%19%18%
314
October1st to 15thDay
17%227%26%18%6%
278
16th to endDay
26%9%31%23%8%
272
November1st to 15thDay
14%8%21%40%12%1
102
16th to endDay
16%15%33%26%8%
60
December1st to 15thDay
13%18%38%25%5%
60
16th to endDay
21%17%48%12%
64
January1st to 15thNight
27%14%35%17%4
720
16th to endNight
20%8%37%26%5%
768
February1st to 15thNight
21%13%39%21%4
704
16th to endNight
20%10%36%25%6%
631
March1st to 15thNight
24%8%35%27%4
720
16th to endNight
18%7%33%27%11%1
768
April1st to 15thNight
20%7%31%32%8%
718
16th to endNight
14%5%30%33%13%1
576
May1st to 15thNight
17%222%36%18%2
474
16th to endNight
13%120%40%22%2
375
June1st to 15thNight
14%322%38%20%
360
16th to endNight
11%118%43%23%1
360
July1st to 15thNight
6%113%47%26%3
340
16th to endNight
8%115%42%28%3
470
August1st to 15thNight
8%11%42%31%4
539
16th to endNight
9%217%34%31%5%
633
September1st to 15thNight
13%319%30%25%6%
720
16th to endNight
14%317%29%26%8%
717
October1st to 15thNight
21%424%28%17%2
684
16th to endNight
24%7%33%26%6%
704
November1st to 15thNight
19%6%30%28%12%1
700
16th to endNight
24%10%29%26%8%1
720
December1st to 15thNight
30%10%37%18%3
720
16th to endNight
26%9%38%21%2
768
Page generated at 2017-10-07 14:07:45. Version ac04

Copyright 2017 A. Danko


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