Sentinel
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sentinel clear sky chart from 2005-11-05 to 2017-12-04.

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%
16130
39%
47871
34%
16092
83%
16092
61%
21510

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
77%
716
35%
2327
36%
716
82%
716
53%
1060
January16th to endNight
70%
768
39%
2484
38%
768
77%
768
49%
1171
February1st to 15thNight
75%
700
41%
2107
40%
698
82%
698
59%
957
February16th to endNight
67%
632
37%
1895
37%
632
72%
632
48%
965
March1st to 15thNight
70%
720
41%
2017
34%
720
79%
720
61%
951
March16th to endNight
76%
768
41%
2112
32%
768
84%
768
66%
967
April1st to 15thNight
64%
719
35%
1978
21%
719
74%
719
62%
930
April16th to endNight
71%
593
48%
1674
31%
593
82%
593
78%
676
May1st to 15thNight
73%
539
41%
1619
30%
539
80%
539
71%
658
May16th to endNight
73%
561
42%
1684
30%
561
80%
561
77%
649
June1st to 15thNight
82%
540
36%
1620
30%
540
85%
540
77%
633
June16th to endNight
88%
540
36%
1620
31%
540
89%
540
77%
639
July1st to 15thNight
86%
510
29%
1530
24%
510
87%
510
59%
711
July16th to endNight
87%
564
33%
1593
29%
531
87%
531
53%
778
August1st to 15thNight
88%
539
35%
1611
30%
536
88%
536
56%
761
August16th to endNight
84%
753
39%
1932
30%
753
85%
753
58%
1004
September1st to 15thNight
83%
720
35%
1980
29%
720
85%
720
59%
976
September16th to endNight
86%
716
49%
1980
41%
716
90%
716
77%
833
October1st to 15thNight
78%
720
45%
2007
34%
720
85%
720
72%
871
October16th to endNight
86%
768
47%
2304
43%
768
90%
768
71%
939
November1st to 15thNight
83%
760
41%
2374
41%
760
86%
760
63%
1018
November16th to endNight
79%
780
43%
2535
45%
780
84%
780
59%
1072
December1st to 15thNight
76%
736
38%
2392
39%
736
80%
736
51%
1102
December16th to endNight
73%
768
38%
2496
40%
768
76%
768
47%
1189

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
212212235%73%
48612
Night
212212235%72%
48072
TransparencyDay
14%2311%24%45%
48307
Night
14%2310%23%45%
47878
SeeingDay
3313%30%34%15%
5852
Night
3111%40%36%5%
16141

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
422323335%68%
1611
16th to endDay
5%312312246%66%
1738
February1st to 15thDay
1212211345%71%
1751
16th to endDay
323312337%66%
1579
March1st to 15thDay
311221235%5%71%
1941
16th to endDay
212112136%75%
2112
April1st to 15thDay
111112347%74%
1970
16th to endDay
11112484%
2281
May1st to 15thDay
111222382%
2331
16th to endDay
11111387%
2429
June1st to 15thDay
11111385%
2340
16th to endDay
1111211284%
2340
July1st to 15thDay
121222435%7%66%
2340
16th to endDay
42145%35%5%6%10%50%
2467
August1st to 15thDay
321242445%7%61%
2340
16th to endDay
22322345%8%64%
2264
September1st to 15thDay
421331335%6%62%
1980
16th to endDay
1111122382%
1980
October1st to 15thDay
1111122383%
1953
16th to endDay
1111232479%
1920
November1st to 15thDay
121121223477%
1813
16th to endDay
412211235%74%
1755
December1st to 15thDay
333312346%65%
1649
16th to endDay
321312335%6%66%
1728
January1st to 15thNight
32332334468%
2327
16th to endNight
5%313212235%66%
2484
February1st to 15thNight
3212212245%71%
2101
16th to endNight
4314323446%61%
1895
March1st to 15thNight
4211112245%72%
2017
16th to endNight
211113236%73%
2112
April1st to 15thNight
2212212235%73%
1978
16th to endNight
11112387%
1674
May1st to 15thNight
1121223479%
1619
16th to endNight
1111111287%
1684
June1st to 15thNight
111122383%
1620
16th to endNight
111111285%
1620
July1st to 15thNight
1221346%7%66%
1620
16th to endNight
2123235%7%12%57%
1701
August1st to 15thNight
112323349%64%
1620
16th to endNight
213313447%65%
1932
September1st to 15thNight
2112323346%68%
1980
16th to endNight
111113383%
1980
October1st to 15thNight
1111212480%
2007
16th to endNight
1111223480%
2304
November1st to 15thNight
2112112235%74%
2374
16th to endNight
3212212235%73%
2535
December1st to 15thNight
3213223346%66%
2392
16th to endNight
4313323335%64%
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
18%2312%30%32%
1612
16th to endDay
19%2316%26%31%
1738
February1st to 15thDay
15%1412%30%34%
1751
16th to endDay
18%2216%30%28%
1579
March1st to 15thDay
14%218%26%46%
1941
16th to endDay
13%227%29%44%
2112
April1st to 15thDay
11%18%30%47%
1970
16th to endDay
7%16%22%61%
2281
May1st to 15thDay
8%116%20%61%
2331
16th to endDay
6%5%21%65%
2432
June1st to 15thDay
7%1215%72%
2340
16th to endDay
9%1127%77%
2340
July1st to 15thDay
16%35%13%20%39%
2201
16th to endDay
25%5%9%25%22%11%
2312
August1st to 15thDay
21%25%18%20%31%
2325
16th to endDay
17%45%14%29%28%
2264
September1st to 15thDay
21%3414%22%33%
1980
16th to endDay
9%115%22%60%
1980
October1st to 15thDay
8%118%24%55%
1953
16th to endDay
10%137%20%55%
1920
November1st to 15thDay
12%1112%26%45%
1813
16th to endDay
14%1211%26%44%
1755
December1st to 15thDay
19%3314%29%28%
1649
16th to endDay
17%36%21%30%21%
1728
January1st to 15thNight
18%2410%25%37%
2327
16th to endNight
21%2212%24%36%
2484
February1st to 15thNight
16%1314%22%40%
2112
16th to endNight
22%3211%24%35%
1895
March1st to 15thNight
15%217%21%51%
2017
16th to endNight
13%128%27%46%
2112
April1st to 15thNight
14%217%26%46%
1978
16th to endNight
6%15%24%61%
1674
May1st to 15thNight
8%116%22%58%
1620
16th to endNight
7%5%19%66%
1685
June1st to 15thNight
7%1215%72%
1620
16th to endNight
8%116%80%
1620
July1st to 15thNight
15%37%13%23%37%
1530
16th to endNight
17%410%24%27%15%
1593
August1st to 15thNight
16%36%19%23%30%
1611
16th to endNight
17%46%14%29%27%
1932
September1st to 15thNight
17%35%14%26%33%
1980
16th to endNight
7%18%21%60%
1980
October1st to 15thNight
10%119%22%55%
2007
16th to endNight
9%129%16%60%
2304
November1st to 15thNight
13%218%29%44%
2374
16th to endNight
15%128%24%48%
2535
December1st to 15thNight
19%2314%26%33%
2392
16th to endNight
22%2416%27%27%
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
13%112%47%20%5%
90
16th to endDay
5%316%31%32%11%
106
February1st to 15thDay
4416%36%31%6%
266
16th to endDay
7%5%24%33%24%3
238
March1st to 15thDay
4421%27%28%12%
270
16th to endDay
17%25%28%23%13%
288
April1st to 15thDay
48%23%27%26%9%
269
16th to endDay
19%30%28%20%9%
270
May1st to 15thDay
18%22%33%24%9%
288
16th to endDay
1416%37%33%6%
330
June1st to 15thDay
2216%39%31%8%
315
16th to endDay
16%38%36%17%
315
July1st to 15thDay
25%26%45%19%
305
16th to endDay
3119%41%33%
327
August1st to 15thDay
2224%39%30%
315
16th to endDay
3321%40%31%
332
September1st to 15thDay
6%6%23%45%17%
315
16th to endDay
2212%30%37%14%
315
October1st to 15thDay
2214%29%38%12%
288
16th to endDay
5%414%48%26%
144
November1st to 15thDay
2111%37%38%8%
135
16th to endDay
7%211%32%36%9%
135
December1st to 15thDay
317%36%42%11%
100
16th to endDay
10%125%36%26%1
96
January1st to 15thNight
3111%46%32%4
720
16th to endNight
8%114%43%28%4
768
February1st to 15thNight
3212%43%33%4
704
16th to endNight
5%217%47%23%3
632
March1st to 15thNight
4219%36%32%4
720
16th to endNight
2314%41%31%6%
768
April1st to 15thNight
3323%41%25%3
719
16th to endNight
1322%44%24%3
593
May1st to 15thNight
221%45%27%2
540
16th to endNight
1219%41%32%1
563
June1st to 15thNight
1113%54%29%
540
16th to endNight
26%47%40%1
540
July1st to 15thNight
16%41%45%4
510
16th to endNight
2235%53%5%
564
August1st to 15thNight
2235%53%5%
539
16th to endNight
4327%52%12%
753
September1st to 15thNight
36%29%51%8%
720
16th to endNight
19%37%43%7%
716
October1st to 15thNight
214%37%40%4
720
16th to endNight
217%36%42%9%
768
November1st to 15thNight
38%43%39%5%
760
16th to endNight
49%38%37%9%
780
December1st to 15thNight
49%44%35%3
736
16th to endNight
6%210%47%28%4
768
Page generated at 2017-12-05 08:19:00. Version ac04

Copyright 2017 A. Danko


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