This page made possible by the sponsorship of: David & Wendee Levy
(Jarnac Observatory).

Jarnac Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jarnac Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
76%
15526
35%
46826
31%
15490
81%
15490
53%
22430

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
72%
716
32%
2327
33%
716
76%
716
51%
1083
January16th to endNight
67%
768
35%
2496
33%
768
75%
768
41%
1273
February1st to 15thNight
73%
698
36%
2210
35%
698
81%
698
54%
1014
February16th to endNight
65%
632
39%
1822
34%
632
73%
632
51%
915
March1st to 15thNight
67%
720
40%
1980
32%
720
74%
720
58%
957
March16th to endNight
73%
768
39%
2112
28%
768
81%
768
62%
999
April1st to 15thNight
68%
678
35%
1937
26%
678
76%
678
57%
922
April16th to endNight
71%
540
45%
1800
38%
540
82%
540
69%
671
May1st to 15thNight
73%
539
40%
1627
31%
539
82%
539
74%
638
May16th to endNight
81%
561
43%
1684
35%
561
86%
561
72%
676
June1st to 15thNight
85%
540
35%
1620
30%
540
86%
540
69%
670
June16th to endNight
86%
540
31%
1620
26%
540
87%
540
58%
746
July1st to 15thNight
84%
510
18%
1530
17%
510
84%
510
37%
869
July16th to endNight
80%
564
15%
1593
13%
531
80%
531
29%
1005
August1st to 15thNight
85%
539
23%
1611
22%
536
85%
536
38%
908
August16th to endNight
83%
585
29%
1876
30%
585
83%
585
37%
1031
September1st to 15thNight
79%
700
27%
1925
23%
700
79%
700
40%
1144
September16th to endNight
85%
656
41%
1815
32%
656
89%
656
66%
838
October1st to 15thNight
81%
660
41%
1922
33%
660
86%
660
66%
859
October16th to endNight
84%
704
43%
2112
39%
704
87%
704
68%
901
November1st to 15thNight
79%
700
43%
2100
38%
700
85%
700
68%
886
November16th to endNight
70%
720
39%
2271
35%
720
76%
720
52%
1065
December1st to 15thNight
72%
720
37%
2340
39%
720
75%
720
50%
1089
December16th to endNight
65%
768
34%
2496
33%
768
71%
768
42%
1271

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
3213323446%63%
47796
Night
3212323346%66%
47022
TransparencyDay
20%36%12%26%30%
47491
Night
18%36%14%27%30%
46828
SeeingDay
5%7%20%34%23%8%
5373
Night
4112%39%35%6%
15539

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
4213213347%64%
1611
16th to endDay
5%313323346%60%
1728
February1st to 15thDay
4313213335%66%
1652
16th to endDay
4313323336%63%
1651
March1st to 15thDay
3212323346%67%
1980
16th to endDay
222212335%74%
2112
April1st to 15thDay
212223345%71%
2009
16th to endDay
1111112482%
2160
May1st to 15thDay
11221123478%
2320
16th to endDay
111223382%
2429
June1st to 15thDay
111112235%78%
2340
16th to endDay
112324346%69%
2340
July1st to 15thDay
3325%6%47%7%10%9%40%
2340
16th to endDay
6%5%27%8%48%7%8%10%28%
2467
August1st to 15thDay
5%325%8%46%8%7%8%38%
2340
16th to endDay
33145%36%7%7%9%46%
2320
September1st to 15thDay
5%315%6%47%5%6%6%46%
1922
16th to endDay
311232335%5%67%
1815
October1st to 15thDay
1111213245%72%
1707
16th to endDay
11212245%76%
1760
November1st to 15thDay
11212236%76%
1759
16th to endDay
2312313225%70%
1686
December1st to 15thDay
5%213313346%63%
1620
16th to endDay
5%31332345%7%60%
1728
January1st to 15thNight
4313212345%67%
2327
16th to endNight
5%31432445%5%58%
2496
February1st to 15thNight
2212223345%68%
2199
16th to endNight
4312323345%63%
1822
March1st to 15thNight
3212222245%70%
1980
16th to endNight
2211213245%72%
2112
April1st to 15thNight
2212223335%70%
1937
16th to endNight
1111112482%
1800
May1st to 15thNight
1112246%79%
1627
16th to endNight
121212384%
1684
June1st to 15thNight
2112235%79%
1620
16th to endNight
112223345%71%
1620
July1st to 15thNight
11145%36%8%8%12%46%
1620
16th to endNight
22246%36%8%11%16%32%
1701
August1st to 15thNight
1113435%5%7%10%53%
1620
16th to endNight
32144246%7%10%50%
1876
September1st to 15thNight
5%4144345%5%8%52%
1925
16th to endNight
112212345%73%
1815
October1st to 15thNight
11121333476%
1922
16th to endNight
111121222478%
2112
November1st to 15thNight
111212235%76%
2100
16th to endNight
4312313235%68%
2271
December1st to 15thNight
5%212213346%65%
2340
16th to endNight
6%413323346%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%25%15%29%25%
1612
16th to endDay
23%3317%27%24%
1728
February1st to 15thDay
20%2312%28%32%
1652
16th to endDay
22%2414%30%26%
1651
March1st to 15thDay
18%237%33%34%
1980
16th to endDay
14%228%35%35%
2112
April1st to 15thDay
14%127%38%35%
2009
16th to endDay
9%117%28%51%
2160
May1st to 15thDay
10%128%25%50%
2320
16th to endDay
9%126%29%50%
2432
June1st to 15thDay
10%126%22%57%
2340
16th to endDay
16%338%19%48%
2340
July1st to 15thDay
32%10%15%13%14%14%
2201
16th to endDay
44%12%18%17%6%1
2312
August1st to 15thDay
40%8%12%14%16%6%
2325
16th to endDay
31%8%12%16%17%12%
2320
September1st to 15thDay
35%5%10%16%16%15%
1922
16th to endDay
18%35%11%33%27%
1815
October1st to 15thDay
14%35%12%27%36%
1707
16th to endDay
10%2311%30%41%
1760
November1st to 15thDay
11%1312%36%35%
1759
16th to endDay
18%2411%28%35%
1686
December1st to 15thDay
21%2416%33%20%
1620
16th to endDay
22%38%18%32%14%
1728
January1st to 15thNight
20%25%13%30%27%
2327
16th to endNight
25%3416%28%20%
2496
February1st to 15thNight
17%25%15%25%32%
2210
16th to endNight
21%2412%34%23%
1822
March1st to 15thNight
17%2311%30%35%
1980
16th to endNight
15%1412%33%33%
2112
April1st to 15thNight
17%129%37%30%
1937
16th to endNight
9%117%29%50%
1800
May1st to 15thNight
7%138%30%47%
1628
16th to endNight
8%217%28%51%
1685
June1st to 15thNight
9%22421%59%
1620
16th to endNight
15%336%20%50%
1620
July1st to 15thNight
24%11%17%17%15%13%
1530
16th to endNight
32%12%25%21%6%1
1593
August1st to 15thNight
23%10%15%20%20%9%
1611
16th to endNight
25%8%16%18%18%12%
1876
September1st to 15thNight
28%6%11%20%19%12%
1925
16th to endNight
12%35%16%34%27%
1815
October1st to 15thNight
11%35%16%26%35%
1922
16th to endNight
11%1312%25%44%
2112
November1st to 15thNight
11%1316%33%33%
2100
16th to endNight
19%2311%26%36%
2271
December1st to 15thNight
19%2417%32%22%
2340
16th to endNight
25%36%18%29%16%
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%6%26%46%5%1
90
16th to endDay
7%5%21%42%17%5%
96
February1st to 15thDay
7%9%22%39%19%1
167
16th to endDay
9%19%30%27%11%1
238
March1st to 15thDay
5%15%30%24%16%7%
270
16th to endDay
417%29%27%15%5%
288
April1st to 15thDay
315%31%29%15%4
269
16th to endDay
419%32%28%9%4
270
May1st to 15thDay
213%36%28%13%5%
288
16th to endDay
26%30%40%16%4
330
June1st to 15thDay
3324%41%18%8%
315
16th to endDay
310%46%27%11%
315
July1st to 15thDay
39%41%31%12%
305
16th to endDay
11%17%28%30%20%
327
August1st to 15thDay
7%5%27%42%16%
315
16th to endDay
45%33%40%15%
332
September1st to 15thDay
12%8%37%31%9%
294
16th to endDay
6%319%33%27%9%
255
October1st to 15thDay
1422%38%22%10%
147
16th to endDay
21337%46%9%
96
November1st to 15thDay
311%17%37%25%4
90
16th to endDay
7%6%34%28%22%
90
December1st to 15thDay
6%314%44%27%3
90
16th to endDay
10%8%38%34%8%
96
January1st to 15thNight
6%115%50%23%2
720
16th to endNight
8%215%44%25%2
768
February1st to 15thNight
3314%46%28%4
704
16th to endNight
4223%47%21%
632
March1st to 15thNight
3320%41%26%3
720
16th to endNight
3216%42%30%4
768
April1st to 15thNight
3319%49%21%2
678
16th to endNight
3321%45%22%3
540
May1st to 15thNight
221%42%30%2
540
16th to endNight
313%45%34%3
563
June1st to 15thNight
29%47%36%3
540
16th to endNight
15%35%51%4
540
July1st to 15thNight
2327%57%8%
510
16th to endNight
3218%58%17%
564
August1st to 15thNight
2116%61%17%
539
16th to endNight
5%118%58%15%
585
September1st to 15thNight
6%5%23%50%13%
700
16th to endNight
37%36%42%9%
656
October1st to 15thNight
113%42%35%6%
660
16th to endNight
19%40%38%8%
704
November1st to 15thNight
3113%42%33%6%
700
16th to endNight
5%217%42%27%5%
720
December1st to 15thNight
7%213%45%26%3
720
16th to endNight
9%315%47%19%4
768
Page generated at 2017-09-11 16:35:22. Version ac04

Copyright 2017 A. Danko


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