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Limber Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Limber Observatory clear sky chart from 2005-11-05 to 2022-09-17.

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
46%
21713
25%
66348
17%
21660
55%
21660
32%
38975

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
38%
1262
29%
3281
13%
1262
48%
1262
32%
2068
January16th to endNight
36%
1171
29%
3328
13%
1171
47%
1171
29%
2049
February1st to 15thNight
32%
987
27%
2960
12%
979
44%
979
28%
1747
February16th to endNight
22%
889
25%
2664
7%
887
37%
887
24%
1648
March1st to 15thNight
26%
826
25%
2858
12%
826
41%
826
22%
1746
March16th to endNight
28%
813
23%
2980
12%
813
42%
813
24%
1717
April1st to 15thNight
25%
762
25%
2787
12%
762
44%
762
24%
1575
April16th to endNight
24%
747
25%
2433
12%
747
40%
747
24%
1532
May1st to 15thNight
28%
758
23%
2269
15%
758
39%
758
28%
1421
May16th to endNight
39%
779
24%
2329
16%
778
52%
778
30%
1428
June1st to 15thNight
58%
760
24%
2287
21%
758
68%
758
47%
1194
June16th to endNight
56%
752
21%
2280
20%
752
62%
752
37%
1328
July1st to 15thNight
69%
732
19%
2195
20%
732
72%
732
37%
1251
July16th to endNight
76%
794
22%
2268
24%
758
80%
758
47%
1179
August1st to 15thNight
81%
739
26%
2413
29%
736
84%
736
49%
1147
August16th to endNight
73%
810
18%
2749
21%
810
74%
810
33%
1554
September1st to 15thNight
68%
762
18%
2795
22%
762
70%
762
26%
1667
September16th to endNight
62%
717
22%
2643
24%
717
64%
717
27%
1555
October1st to 15thNight
67%
718
33%
2628
32%
718
71%
718
36%
1356
October16th to endNight
52%
979
34%
3022
21%
978
60%
978
39%
1621
November1st to 15thNight
52%
1065
28%
3060
17%
1065
58%
1065
33%
1836
November16th to endNight
46%
1266
30%
3291
15%
1266
54%
1266
36%
1990
December1st to 15thNight
42%
1270
30%
3306
16%
1270
49%
1270
34%
2052
December16th to endNight
37%
1355
24%
3522
12%
1355
43%
1355
29%
2314

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
13%5%2442445%6%45%
67335
Night
13%5%23323346%51%
66590
TransparencyDay
38%49%20%17%9%
67048
Night
34%311%20%18%11%
66378
SeeingDay
15%8%23%30%18%3
11867
Night
16%7%25%35%14%1
21718

By Month

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
16%6%34322235%49%
2272
16th to endDay
16%5%24213235%51%
2591
February1st to 15thDay
17%7%2332333448%
2455
16th to endDay
20%6%23313335%45%
2230
March1st to 15thDay
19%7%24323345%43%
2727
16th to endDay
18%5%24323346%47%
2953
April1st to 15thDay
15%5%24423435%47%
2776
16th to endDay
16%6%345%23445%42%
3059
May1st to 15thDay
16%5%35%5%2445%7%38%
3263
16th to endDay
15%5%244345%5%7%39%
3374
June1st to 15thDay
7%3145%35%5%6%8%48%
3315
16th to endDay
11%5%35%6%36%6%7%8%36%
3297
July1st to 15thDay
10%5%25%5%35%45%9%41%
3302
16th to endDay
6%214435%5%6%9%48%
3463
August1st to 15thDay
3212425%46%11%55%
3002
16th to endDay
7%5%15%6%45%5%6%10%41%
3184
September1st to 15thDay
12%6%25%6%45%5%6%7%36%
2793
16th to endDay
10%5%246%445%6%7%42%
2649
October1st to 15thDay
9%5%14425%446%51%
2614
16th to endDay
13%31331234458%
2569
November1st to 15thDay
17%7%25%323345%43%
2434
16th to endDay
14%5%2432333451%
2272
December1st to 15thDay
18%5%24313326%47%
2294
16th to endDay
19%5%24423335%46%
2447
January1st to 15thNight
16%423323235%51%
3279
16th to endNight
17%5%13313346%49%
3327
February1st to 15thNight
17%6%13212235%51%
2961
16th to endNight
18%5%23333336%46%
2665
March1st to 15thNight
18%6%24413345%45%
2859
16th to endNight
17%5%13323335%49%
2978
April1st to 15thNight
13%5%23323345%50%
2790
16th to endNight
18%5%24323345%46%
2436
May1st to 15thNight
14%6%24423347%45%
2269
16th to endNight
13%5%2442345%8%46%
2328
June1st to 15thNight
5%21332335%8%61%
2295
16th to endNight
8%3233245%5%10%50%
2279
July1st to 15thNight
7%4234235%6%9%50%
2293
16th to endNight
5%31222446%9%58%
2383
August1st to 15thNight
321232345%10%62%
2424
16th to endNight
6%4234245%6%10%49%
2750
September1st to 15thNight
8%435%5%35%5%6%8%44%
2795
16th to endNight
10%6%26%42446%7%45%
2644
October1st to 15thNight
9%413213345%57%
2627
16th to endNight
12%412312325%61%
3024
November1st to 15thNight
11%5%14323345%52%
3060
16th to endNight
14%413322346%54%
3291
December1st to 15thNight
16%6%13212236%52%
3306
16th to endNight
18%8%1421333348%
3527

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
39%3316%18%19%
2275
16th to endDay
36%25%14%24%16%
2590
February1st to 15thDay
40%2414%19%17%
2458
16th to endDay
43%25%16%19%12%
2230
March1st to 15thDay
43%37%14%17%12%
2726
16th to endDay
39%27%17%18%14%
2968
April1st to 15thDay
40%36%17%18%13%
2778
16th to endDay
44%35%19%17%9%
3060
May1st to 15thDay
45%49%17%18%5%
3268
16th to endDay
44%48%21%17%3
3376
June1st to 15thDay
33%5%11%24%20%4
3311
16th to endDay
43%6%10%24%13%2
3300
July1st to 15thDay
37%5%15%25%13%1
3154
16th to endDay
29%5%20%31%11%
3294
August1st to 15thDay
22%418%37%15%1
2994
16th to endDay
36%5%18%25%11%1
3186
September1st to 15thDay
43%5%11%21%15%3
2795
16th to endDay
39%5%9%20%17%8%
2648
October1st to 15thDay
33%49%18%22%10%
2616
16th to endDay
30%2417%24%20%
2568
November1st to 15thDay
42%26%20%17%9%
2434
16th to endDay
36%35%16%20%18%
2278
December1st to 15thDay
40%27%17%20%12%
2294
16th to endDay
42%26%14%21%13%
2447
January1st to 15thNight
37%2415%20%20%
3281
16th to endNight
38%2415%21%17%
3328
February1st to 15thNight
37%25%14%20%20%
2969
16th to endNight
41%25%15%19%15%
2665
March1st to 15thNight
42%28%15%17%13%
2858
16th to endNight
38%39%15%17%15%
2988
April1st to 15thNight
37%28%17%17%16%
2787
16th to endNight
42%48%17%15%11%
2437
May1st to 15thNight
39%311%20%15%8%
2273
16th to endNight
36%5%12%27%15%3
2330
June1st to 15thNight
22%415%29%22%4
2287
16th to endNight
31%5%18%28%14%1
2280
July1st to 15thNight
28%7%20%29%12%1
2195
16th to endNight
20%7%27%33%10%1
2268
August1st to 15thNight
19%424%36%13%
2416
16th to endNight
30%6%24%25%10%1
2749
September1st to 15thNight
36%7%16%21%14%4
2795
16th to endNight
36%5%12%20%16%8%
2643
October1st to 15thNight
28%410%25%19%12%
2628
16th to endNight
28%25%16%25%21%
3022
November1st to 15thNight
35%38%20%21%11%
3060
16th to endNight
32%36%17%21%18%
3291
December1st to 15thNight
36%26%18%22%13%
3306
16th to endNight
41%25%14%20%15%
3522

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
24%14%34%20%5%
315
16th to endDay
21%15%33%24%6%
333
February1st to 15thDay
28%18%26%20%5%
315
16th to endDay
30%18%35%12%2
279
March1st to 15thDay
26%21%39%10%2
315
16th to endDay
21%17%41%17%2
336
April1st to 15thDay
19%21%39%17%2
315
16th to endDay
19%17%39%19%3
606
May1st to 15thDay
18%12%37%26%4
836
16th to endDay
19%7%29%33%9%
883
June1st to 15thDay
8%222%45%19%2
866
16th to endDay
11%218%38%24%4
864
July1st to 15thDay
10%111%36%33%5%
845
16th to endDay
5%7%38%40%6%
904
August1st to 15thDay
46%43%36%8%
644
16th to endDay
6%16%39%36%10%
598
September1st to 15thDay
12%9%30%38%9%
360
16th to endDay
9%214%29%36%7%
321
October1st to 15thDay
4218%41%28%4
315
16th to endDay
23%9%20%28%15%2
336
November1st to 15thDay
24%8%31%22%10%2
315
16th to endDay
17%16%34%20%9%1
315
December1st to 15thDay
18%14%31%26%8%
315
16th to endDay
26%13%33%21%4
336
January1st to 15thNight
19%12%25%33%8%
1262
16th to endNight
21%9%28%32%7%
1171
February1st to 15thNight
23%13%28%27%7%
987
16th to endNight
25%12%37%22%1
889
March1st to 15thNight
22%13%34%26%3
826
16th to endNight
19%12%36%27%3
813
April1st to 15thNight
15%14%42%25%2
762
16th to endNight
20%11%42%21%4
749
May1st to 15thNight
17%10%40%27%3
758
16th to endNight
16%6%35%33%8%
779
June1st to 15thNight
5%131%45%15%
760
16th to endNight
8%129%40%18%
752
July1st to 15thNight
6%114%50%24%1
732
16th to endNight
5%111%53%26%2
796
August1st to 15thNight
219%50%34%2
740
16th to endNight
6%18%48%31%3
810
September1st to 15thNight
10%110%40%33%4
762
16th to endNight
12%112%38%31%3
717
October1st to 15thNight
10%214%46%23%2
718
16th to endNight
15%5%23%31%21%2
979
November1st to 15thNight
13%5%23%37%17%1
1065
16th to endNight
17%8%23%34%14%1
1266
December1st to 15thNight
21%7%25%34%10%
1270
16th to endNight
24%9%24%31%8%
1355
Page generated at 2022-09-18 15:32:09. Version ac05

Copyright 2022 A. Danko


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