Jack Observing site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jack Observing site clear sky chart from 2005-11-05 to 2017-09-23.

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
55%
15557
34%
46970
22%
15516
68%
15516
49%
22255

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
48%
720
33%
2327
22%
716
64%
716
44%
1097
January16th to endNight
47%
768
37%
2496
24%
768
66%
768
44%
1190
February1st to 15thNight
49%
700
33%
2244
23%
700
64%
700
47%
1047
February16th to endNight
37%
632
39%
1862
21%
632
60%
632
45%
873
March1st to 15thNight
46%
720
38%
1980
20%
720
63%
720
50%
961
March16th to endNight
45%
768
36%
2112
17%
768
62%
768
52%
1013
April1st to 15thNight
37%
668
31%
1927
12%
668
54%
668
42%
941
April16th to endNight
40%
540
40%
1722
19%
540
63%
540
51%
709
May1st to 15thNight
46%
540
36%
1619
19%
539
62%
539
57%
705
May16th to endNight
45%
561
35%
1684
19%
561
58%
561
56%
719
June1st to 15thNight
51%
540
33%
1620
20%
540
62%
540
64%
673
June16th to endNight
68%
540
33%
1620
25%
540
75%
540
64%
701
July1st to 15thNight
73%
510
19%
1530
14%
510
76%
510
39%
852
July16th to endNight
72%
564
17%
1593
13%
531
74%
531
31%
964
August1st to 15thNight
78%
539
25%
1611
22%
536
79%
536
42%
853
August16th to endNight
78%
573
30%
1815
28%
573
81%
573
42%
952
September1st to 15thNight
75%
714
30%
1974
23%
714
80%
714
49%
1057
September16th to endNight
69%
688
43%
1903
25%
688
82%
688
66%
839
October1st to 15thNight
56%
660
40%
1922
23%
660
70%
660
62%
841
October16th to endNight
64%
704
42%
2112
28%
704
76%
704
59%
935
November1st to 15thNight
60%
700
39%
2121
25%
700
73%
700
55%
949
November16th to endNight
53%
720
40%
2340
28%
720
69%
720
53%
983
December1st to 15thNight
51%
720
34%
2340
24%
720
66%
720
42%
1114
December16th to endNight
42%
768
33%
2496
22%
768
58%
768
37%
1287

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
221332445%7%62%
47935
Night
121221335%7%67%
47166
TransparencyDay
22%47%18%29%17%
47630
Night
16%48%21%30%18%
46972
SeeingDay
6%15%26%30%16%4
5388
Night
310%26%32%21%4
15563

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
141332335%6%64%
1611
16th to endDay
2312313346%65%
1728
February1st to 15thDay
1315%223237%65%
1616
16th to endDay
1222235%5%8%65%
1609
March1st to 15thDay
21231345%7%66%
1980
16th to endDay
1112414346%67%
2112
April1st to 15thDay
11222435%8%66%
2021
16th to endDay
1212212246%71%
2237
May1st to 15thDay
2112213237%71%
2331
16th to endDay
2213313445%67%
2429
June1st to 15thDay
11111222479%
2340
16th to endDay
232343374%
2340
July1st to 15thDay
4325%7%47%9%6%8%41%
2340
16th to endDay
5%5%36%8%49%8%10%9%28%
2467
August1st to 15thDay
6%426%7%5%7%7%7%8%37%
2340
16th to endDay
33146%47%6%8%9%44%
2387
September1st to 15thDay
42146%45%6%6%8%47%
1983
16th to endDay
112223335%73%
1893
October1st to 15thDay
11221343472%
1708
16th to endDay
222212235%74%
1760
November1st to 15thDay
111222347%72%
1735
16th to endDay
2212222335%73%
1620
December1st to 15thDay
23133225%5%8%62%
1620
16th to endDay
13144245%6%7%58%
1728
January1st to 15thNight
131322335%7%66%
2327
16th to endNight
2212412446%66%
2496
February1st to 15thNight
1211213447%69%
2233
16th to endNight
1221445%8%67%
1862
March1st to 15thNight
21222235%8%68%
1980
16th to endNight
111121335%6%71%
2112
April1st to 15thNight
111231345%6%68%
1927
16th to endNight
11212235%77%
1722
May1st to 15thNight
111222247%72%
1619
16th to endNight
12111222478%
1684
June1st to 15thNight
1111112125%79%
1620
16th to endNight
1221223378%
1620
July1st to 15thNight
22135%35%6%8%10%50%
1620
16th to endNight
3325%5%47%8%8%10%40%
1701
August1st to 15thNight
3234345%6%10%55%
1620
16th to endNight
1213425%6%8%10%53%
1815
September1st to 15thNight
121432446%8%58%
1974
16th to endNight
11111123479%
1903
October1st to 15thNight
111112245%75%
1922
16th to endNight
12122122477%
2112
November1st to 15thNight
11122235%6%71%
2121
16th to endNight
1111212335%74%
2340
December1st to 15thNight
121232345%7%65%
2340
16th to endNight
24133235%5%8%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
23%37%25%33%7%
1612
16th to endDay
21%38%21%35%9%
1728
February1st to 15thDay
21%38%26%24%15%
1616
16th to endDay
19%48%23%32%11%
1609
March1st to 15thDay
18%3421%38%13%
1980
16th to endDay
19%2422%37%12%
2112
April1st to 15thDay
17%3420%37%15%
2021
16th to endDay
17%25%17%39%18%
2237
May1st to 15thDay
15%25%20%34%21%
2331
16th to endDay
18%36%12%38%20%
2432
June1st to 15thDay
11%139%30%44%
2340
16th to endDay
15%227%24%46%
2340
July1st to 15thDay
35%8%10%15%10%19%
2201
16th to endDay
44%11%18%15%9%1
2312
August1st to 15thDay
40%7%11%15%15%9%
2325
16th to endDay
34%8%13%16%20%7%
2387
September1st to 15thDay
32%7%9%15%19%14%
1983
16th to endDay
15%4215%37%24%
1893
October1st to 15thDay
15%35%18%32%24%
1708
16th to endDay
15%3416%43%18%
1760
November1st to 15thDay
14%3425%36%15%
1735
16th to endDay
15%25%19%35%20%
1620
December1st to 15thDay
21%5%11%26%26%8%
1620
16th to endDay
23%7%9%28%24%5%
1728
January1st to 15thNight
18%47%26%35%8%
2327
16th to endNight
19%47%21%35%10%
2496
February1st to 15thNight
17%48%25%26%18%
2244
16th to endNight
14%48%24%32%15%
1862
March1st to 15thNight
15%35%23%38%14%
1980
16th to endNight
14%37%24%36%14%
2112
April1st to 15thNight
18%35%21%34%17%
1927
16th to endNight
11%2420%39%21%
1722
May1st to 15thNight
13%16%24%30%24%
1620
16th to endNight
12%25%15%41%22%
1685
June1st to 15thNight
11%127%29%48%
1620
16th to endNight
12%226%21%54%
1620
July1st to 15thNight
26%7%14%16%15%20%
1530
16th to endNight
32%9%20%22%11%3
1593
August1st to 15thNight
22%7%16%20%19%13%
1611
16th to endNight
22%7%17%21%20%10%
1815
September1st to 15thNight
20%6%13%22%22%15%
1974
16th to endNight
9%2317%38%28%
1903
October1st to 15thNight
11%26%23%27%27%
1922
16th to endNight
13%25%15%38%25%
2112
November1st to 15thNight
13%36%24%34%16%
2121
16th to endNight
14%2420%34%23%
2340
December1st to 15thNight
18%5%9%23%30%12%
2340
16th to endNight
22%6%11%26%26%6%
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
8%25%34%21%7%2
90
16th to endDay
6%26%25%21%16%4
96
February1st to 15thDay
5%19%27%32%10%4
131
16th to endDay
10%36%23%21%5%2
238
March1st to 15thDay
5%27%32%22%9%2
270
16th to endDay
7%25%34%20%9%1
288
April1st to 15thDay
6%25%35%18%9%3
269
16th to endDay
8%30%35%17%7%1
270
May1st to 15thDay
5%23%35%26%8%1
288
16th to endDay
5%20%31%29%10%2
330
June1st to 15thDay
414%40%24%12%4
315
16th to endDay
2430%36%22%3
315
July1st to 15thDay
8%221%45%18%3
305
16th to endDay
7%313%36%27%11%
327
August1st to 15thDay
8%19%40%31%8%
315
16th to endDay
5%115%37%32%8%
332
September1st to 15thDay
7%6%20%36%22%6%
315
16th to endDay
5%15%22%30%20%5%
284
October1st to 15thDay
416%29%29%15%4
148
16th to endDay
13%7%26%27%22%3
96
November1st to 15thDay
48%21%41%17%6%
90
16th to endDay
430%21%35%8%
90
December1st to 15thDay
6%21%22%28%17%3
90
16th to endDay
7%23%26%33%7%2
96
January1st to 15thNight
5%12%30%27%19%5%
720
16th to endNight
314%31%30%16%4
768
February1st to 15thNight
311%32%31%17%3
704
16th to endNight
222%36%23%12%2
632
March1st to 15thNight
218%30%29%15%3
720
16th to endNight
216%32%32%13%1
768
April1st to 15thNight
224%32%28%11%1
668
16th to endNight
220%35%28%10%2
540
May1st to 15thNight
211%36%35%12%1
540
16th to endNight
313%35%27%18%1
563
June1st to 15thNight
27%36%40%12%1
540
16th to endNight
1224%49%20%1
540
July1st to 15thNight
412%48%31%2
510
16th to endNight
6%9%36%40%6%
564
August1st to 15thNight
47%32%44%10%
539
16th to endNight
219%35%39%10%
573
September1st to 15thNight
3112%33%41%7%
714
16th to endNight
26%19%31%32%7%
688
October1st to 15thNight
28%30%32%19%6%
660
16th to endNight
36%22%33%26%6%
704
November1st to 15thNight
29%26%33%22%6%
700
16th to endNight
313%27%27%20%7%
720
December1st to 15thNight
412%28%30%20%3
720
16th to endNight
5%16%32%27%13%4
768
Page generated at 2017-09-24 06:15:52. Version ac04

Copyright 2017 A. Danko


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