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 2018-03-11.

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%
16254
36%
49047
31%
16218
81%
16218
53%
23467

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%
776
33%
2522
33%
776
77%
776
50%
1185
January16th to endNight
68%
832
36%
2704
34%
832
76%
832
43%
1346
February1st to 15thNight
74%
758
37%
2398
35%
758
82%
758
54%
1099
February16th to endNight
65%
684
38%
1972
33%
684
72%
684
49%
1009
March1st to 15thNight
67%
764
39%
2101
31%
764
75%
764
58%
1020
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%
720
27%
1980
24%
720
80%
720
40%
1170
September16th to endNight
85%
716
44%
1980
34%
716
89%
716
68%
901
October1st to 15thNight
82%
720
40%
2097
32%
720
87%
720
67%
925
October16th to endNight
85%
768
45%
2304
40%
768
88%
768
69%
974
November1st to 15thNight
80%
760
42%
2280
37%
760
84%
760
65%
985
November16th to endNight
71%
780
41%
2460
37%
780
77%
780
53%
1150
December1st to 15thNight
70%
780
37%
2535
37%
780
74%
780
48%
1202
December16th to endNight
66%
832
36%
2704
35%
832
72%
832
43%
1366

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%64%
49575
Night
3212323346%67%
49243
TransparencyDay
20%35%12%26%31%
49270
Night
18%36%14%27%30%
49049
SeeingDay
5%6%20%34%24%8%
5974
Night
4112%40%34%6%
16267

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
4313213347%62%
1746
16th to endDay
5%313322346%62%
1872
February1st to 15thDay
4313213335%66%
1794
16th to endDay
5%313323336%63%
1787
March1st to 15thDay
3212323346%66%
2095
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%37%5%6%6%47%
1980
16th to endDay
31232335%5%69%
1980
October1st to 15thDay
111213245%74%
1862
16th to endDay
11212345%76%
1920
November1st to 15thDay
11212246%74%
1909
16th to endDay
2312213225%71%
1826
December1st to 15thDay
6%213313346%62%
1755
16th to endDay
5%41331345%6%60%
1872
January1st to 15thNight
4313212445%66%
2522
16th to endNight
421432345%5%60%
2704
February1st to 15thNight
3212322335%68%
2387
16th to endNight
4413333345%63%
1972
March1st to 15thNight
3212222345%69%
2101
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
44144345%5%8%53%
1980
16th to endNight
112112245%75%
1980
October1st to 15thNight
11121233477%
2097
16th to endNight
11121222479%
2304
November1st to 15thNight
111212336%74%
2280
16th to endNight
4212313235%68%
2460
December1st to 15thNight
5%313223346%64%
2535
16th to endNight
6%413313346%61%
2704

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
22%25%15%30%24%
1747
16th to endDay
22%3316%27%26%
1872
February1st to 15thDay
20%2412%27%32%
1794
16th to endDay
23%2413%29%26%
1787
March1st to 15thDay
19%237%33%33%
2095
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
34%5%10%16%17%15%
1980
16th to endDay
17%2411%34%28%
1980
October1st to 15thDay
13%35%11%28%37%
1862
16th to endDay
10%2311%29%42%
1920
November1st to 15thDay
12%1314%35%32%
1909
16th to endDay
17%1310%29%36%
1826
December1st to 15thDay
22%2416%32%20%
1755
16th to endDay
23%37%17%32%15%
1872
January1st to 15thNight
20%25%14%31%25%
2522
16th to endNight
24%3415%29%22%
2704
February1st to 15thNight
17%2415%24%33%
2398
16th to endNight
22%25%12%32%24%
1972
March1st to 15thNight
17%2311%30%35%
2101
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%20%13%
1980
16th to endNight
11%35%16%35%28%
1980
October1st to 15thNight
11%25%15%27%37%
2097
16th to endNight
11%1312%26%44%
2304
November1st to 15thNight
12%1317%33%30%
2280
16th to endNight
19%2310%27%36%
2460
December1st to 15thNight
21%2417%31%22%
2535
16th to endNight
25%36%17%29%18%
2704

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%5%20%42%18%1
135
16th to endDay
6%425%39%18%6%
144
February1st to 15thDay
7%8%21%36%21%5%
219
16th to endDay
9%18%30%29%11%1
290
March1st to 15thDay
5%14%30%25%16%7%
312
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
11%8%37%32%9%
315
16th to endDay
5%419%34%27%8%
315
October1st to 15thDay
1320%37%27%10%
197
16th to endDay
116%36%43%10%
144
November1st to 15thDay
37%14%37%32%4
135
16th to endDay
5%425%29%30%3
135
December1st to 15thDay
8%5%20%40%22%2
135
16th to endDay
9%6%29%30%18%6%
144
January1st to 15thNight
6%115%50%24%2
780
16th to endNight
7%216%44%25%2
832
February1st to 15thNight
3213%45%29%4
764
16th to endNight
4323%47%19%
684
March1st to 15thNight
4319%42%26%3
764
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%
720
16th to endNight
28%38%40%8%
716
October1st to 15thNight
112%42%36%6%
720
16th to endNight
19%41%38%8%
768
November1st to 15thNight
3112%41%34%5%
760
16th to endNight
5%116%41%29%5%
780
December1st to 15thNight
7%215%45%25%3
780
16th to endNight
9%315%46%21%5%
832
Page generated at 2018-03-12 10:28:04. Version ac04

Copyright 2018 A. Danko


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