This page made possible by the sponsorship of: David McDavid.

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 2019-09-17.

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%
17979
25%
54884
17%
17935
55%
17935
32%
32108

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%
1046
28%
2717
13%
1045
47%
1045
31%
1734
January16th to endNight
37%
973
29%
2765
13%
973
48%
973
28%
1697
February1st to 15thNight
32%
824
27%
2467
12%
818
44%
818
27%
1469
February16th to endNight
21%
736
25%
2206
6%
736
37%
736
25%
1342
March1st to 15thNight
28%
684
27%
2364
13%
684
44%
684
25%
1414
March16th to endNight
29%
672
22%
2464
13%
672
41%
672
24%
1435
April1st to 15thNight
27%
629
25%
2307
13%
629
45%
629
26%
1290
April16th to endNight
26%
624
25%
2031
12%
624
43%
624
26%
1251
May1st to 15thNight
30%
629
23%
1890
15%
629
41%
629
28%
1178
May16th to endNight
39%
658
24%
1972
15%
657
53%
657
33%
1177
June1st to 15thNight
57%
630
24%
1890
20%
630
67%
630
48%
970
June16th to endNight
57%
630
21%
1890
20%
630
64%
630
39%
1086
July1st to 15thNight
69%
600
19%
1800
18%
600
73%
600
37%
1026
July16th to endNight
78%
660
24%
1882
26%
627
82%
627
46%
979
August1st to 15thNight
83%
620
28%
2003
33%
617
85%
617
51%
937
August16th to endNight
73%
669
19%
2272
22%
669
76%
669
34%
1262
September1st to 15thNight
69%
630
18%
2310
21%
630
71%
630
28%
1358
September16th to endNight
61%
585
22%
2158
23%
585
64%
585
25%
1302
October1st to 15thNight
66%
585
33%
2145
32%
585
70%
585
36%
1104
October16th to endNight
54%
799
35%
2463
23%
799
63%
799
43%
1278
November1st to 15thNight
49%
876
27%
2516
16%
876
55%
876
32%
1517
November16th to endNight
47%
1050
31%
2730
15%
1050
55%
1050
38%
1625
December1st to 15thNight
38%
1050
30%
2730
15%
1050
46%
1050
31%
1735
December16th to endNight
35%
1120
23%
2912
11%
1120
41%
1120
27%
1942

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
14%5%24424446%44%
55795
Night
12%423323347%51%
55085
Cloud CoverDay
13%5%24424447%44%
55793
Night
12%423323347%51%
55085
TransparencyDay
39%49%20%17%8%
55493
Night
33%411%21%18%11%
54890
SeeingDay
15%7%23%31%19%3
7969
Night
16%7%25%34%14%1
17985

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
17%6%2432233448%
1881
16th to endDay
16%5%13213336%51%
2174
February1st to 15thDay
17%7%24323335%45%
2050
16th to endDay
18%6%24223435%45%
1840
March1st to 15thDay
20%6%2442344443%
2254
16th to endDay
19%5%2432335%5%45%
2464
April1st to 15thDay
15%5%24413336%46%
2301
16th to endDay
16%6%25%5%2435%5%43%
2528
May1st to 15thDay
18%5%35%42445%7%37%
2721
16th to endDay
16%6%24434447%38%
2846
June1st to 15thDay
7%4145%36%5%6%8%46%
2730
16th to endDay
11%6%25%5%46%6%6%8%35%
2730
July1st to 15thDay
10%6%25%5%36%46%9%40%
2730
16th to endDay
8%2245%35%46%8%46%
2882
August1st to 15thDay
321233445%12%54%
2526
16th to endDay
8%425%6%345%5%9%41%
2634
September1st to 15thDay
13%6%25%6%35%5%6%7%36%
2310
16th to endDay
12%6%25%5%35%5%5%7%39%
2156
October1st to 15thDay
10%5%24325%446%49%
2145
16th to endDay
13%31332334459%
2098
November1st to 15thDay
18%7%25%433345%42%
1999
16th to endDay
14%5%2432333453%
1890
December1st to 15thDay
21%6%24313336%43%
1890
16th to endDay
20%6%24323235%45%
2016
January1st to 15thNight
17%424223335%50%
2717
16th to endNight
16%5%14313245%49%
2765
February1st to 15thNight
16%7%14212245%51%
2462
16th to endNight
16%5%13423336%47%
2206
March1st to 15thNight
17%6%24313346%47%
2364
16th to endNight
18%5%23323345%48%
2464
April1st to 15thNight
13%5%23423345%51%
2307
16th to endNight
16%425%323445%48%
2031
May1st to 15thNight
14%6%24423347%45%
1889
16th to endNight
12%42432335%9%48%
1971
June1st to 15thNight
423313349%62%
1890
16th to endNight
7%31332446%9%52%
1890
July1st to 15thNight
6%313425%5%6%9%50%
1890
16th to endNight
5%31322445%9%58%
1990
August1st to 15thNight
321231235%9%63%
2013
16th to endNight
6%3143245%6%11%50%
2272
September1st to 15thNight
9%435%5%25%5%5%9%45%
2310
16th to endNight
11%5%36%42445%7%43%
2158
October1st to 15thNight
9%314213347%56%
2145
16th to endNight
10%312222235%63%
2463
November1st to 15thNight
11%5%24423346%51%
2516
16th to endNight
14%412212246%56%
2730
December1st to 15thNight
19%5%13212336%49%
2730
16th to endNight
19%8%1422333446%
2912

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
17%6%34312335%48%
1881
16th to endDay
16%5%13213335%51%
2174
February1st to 15thDay
17%7%23423335%45%
2050
16th to endDay
18%6%33314345%45%
1840
March1st to 15thDay
19%6%24313345%43%
2254
16th to endDay
19%5%24323346%45%
2462
April1st to 15thDay
15%6%24423446%46%
2301
16th to endDay
15%7%345%23345%44%
2528
May1st to 15thDay
17%5%35%5%2445%7%37%
2721
16th to endDay
16%6%245%345%5%7%38%
2846
June1st to 15thDay
7%315%5%36%5%6%8%46%
2730
16th to endDay
11%5%35%6%36%6%6%9%34%
2730
July1st to 15thDay
11%5%25%5%45%45%9%40%
2730
16th to endDay
7%2245%35%5%6%8%47%
2882
August1st to 15thDay
3212425%46%11%55%
2526
16th to endDay
8%5%15%6%45%5%6%10%41%
2634
September1st to 15thDay
12%6%25%6%45%5%5%7%36%
2310
16th to endDay
11%5%25%6%45%5%6%7%39%
2156
October1st to 15thDay
10%5%15%425%446%49%
2145
16th to endDay
12%31332234459%
2098
November1st to 15thDay
18%7%25%323345%42%
1999
16th to endDay
14%6%2422332353%
1890
December1st to 15thDay
21%6%24313326%43%
1890
16th to endDay
20%5%24423335%45%
2016
January1st to 15thNight
17%423323335%50%
2717
16th to endNight
16%5%13313346%49%
2765
February1st to 15thNight
16%6%23212235%51%
2462
16th to endNight
16%5%23433336%47%
2206
March1st to 15thNight
16%6%24313345%47%
2364
16th to endNight
17%5%23323346%48%
2464
April1st to 15thNight
12%5%23323345%51%
2307
16th to endNight
15%5%25%323345%48%
2031
May1st to 15thNight
13%6%24423347%45%
1889
16th to endNight
11%5%1332345%9%48%
1971
June1st to 15thNight
321322335%9%62%
1890
16th to endNight
7%3233245%5%10%52%
1890
July1st to 15thNight
6%3134245%7%10%50%
1890
16th to endNight
5%31222445%9%58%
1990
August1st to 15thNight
311222235%10%63%
2013
16th to endNight
6%3234245%6%10%50%
2272
September1st to 15thNight
8%435%435%5%6%8%45%
2310
16th to endNight
11%5%26%5%2446%7%43%
2158
October1st to 15thNight
9%31421345%6%57%
2145
16th to endNight
10%412312325%63%
2463
November1st to 15thNight
11%5%24323346%51%
2516
16th to endNight
13%313222346%56%
2730
December1st to 15thNight
18%6%13312336%49%
2730
16th to endNight
18%8%1421333446%
2912

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
40%3318%18%15%
1882
16th to endDay
36%26%16%24%14%
2174
February1st to 15thDay
42%25%14%18%16%
2051
16th to endDay
42%25%16%20%12%
1840
March1st to 15thDay
43%37%15%16%13%
2254
16th to endDay
41%38%18%17%11%
2464
April1st to 15thDay
39%37%17%18%12%
2301
16th to endDay
43%35%18%17%10%
2528
May1st to 15thDay
46%49%15%17%5%
2721
16th to endDay
45%49%20%15%3
2850
June1st to 15thDay
34%5%12%23%19%4
2730
16th to endDay
44%6%11%22%13%2
2730
July1st to 15thDay
38%6%16%24%12%1
2591
16th to endDay
30%6%18%32%11%
2727
August1st to 15thDay
22%5%17%38%15%1
2512
16th to endDay
37%6%17%25%11%2
2634
September1st to 15thDay
44%5%11%20%15%3
2310
16th to endDay
42%5%9%19%15%7%
2156
October1st to 15thDay
35%410%19%20%9%
2145
16th to endDay
29%3417%26%19%
2098
November1st to 15thDay
44%36%20%14%10%
1999
16th to endDay
36%35%14%21%19%
1890
December1st to 15thDay
44%26%17%18%10%
1890
16th to endDay
43%26%14%22%10%
2016
January1st to 15thNight
38%25%17%19%18%
2717
16th to endNight
38%2415%22%16%
2765
February1st to 15thNight
37%25%14%19%19%
2472
16th to endNight
39%25%15%20%15%
2206
March1st to 15thNight
39%38%16%17%14%
2364
16th to endNight
39%310%16%18%11%
2464
April1st to 15thNight
36%29%17%18%15%
2307
16th to endNight
39%49%18%16%12%
2031
May1st to 15thNight
38%411%20%15%9%
1890
16th to endNight
33%5%13%29%13%4
1973
June1st to 15thNight
21%5%15%30%23%4
1890
16th to endNight
28%5%19%29%13%2
1890
July1st to 15thNight
26%8%22%28%11%1
1800
16th to endNight
20%7%25%34%11%1
1882
August1st to 15thNight
17%5%22%40%13%
2003
16th to endNight
28%7%24%26%10%2
2272
September1st to 15thNight
35%7%16%21%15%4
2310
16th to endNight
38%6%13%19%14%7%
2158
October1st to 15thNight
27%412%26%17%11%
2145
16th to endNight
26%25%16%27%21%
2463
November1st to 15thNight
35%38%20%18%12%
2516
16th to endNight
31%36%17%21%20%
2730
December1st to 15thNight
38%26%18%22%11%
2730
16th to endNight
42%25%14%21%13%
2912

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
23%12%37%20%6%
180
16th to endDay
21%13%33%23%7%
192
February1st to 15thDay
28%21%23%22%3
180
16th to endDay
31%17%40%8%1
159
March1st to 15thDay
27%21%39%9%2
180
16th to endDay
15%11%45%23%2
192
April1st to 15thDay
16%17%43%18%3
180
16th to endDay
17%14%42%21%3
420
May1st to 15thDay
20%11%37%25%4
618
16th to endDay
20%9%30%29%9%
677
June1st to 15thDay
8%120%47%19%2
645
16th to endDay
13%218%40%21%3
645
July1st to 15thDay
10%214%37%30%5%
625
16th to endDay
6%6%37%42%6%
675
August1st to 15thDay
45%43%37%8%
471
16th to endDay
8%16%41%33%7%
418
September1st to 15thDay
12%18%28%44%5%
225
16th to endDay
16%18%31%33%7%
183
October1st to 15thDay
5%118%37%28%7%
180
16th to endDay
26%6%20%29%15%2
192
November1st to 15thDay
33%10%25%21%9%
180
16th to endDay
21%13%34%17%8%3
180
December1st to 15thDay
23%14%29%20%10%2
180
16th to endDay
32%13%31%18%3
192
January1st to 15thNight
20%11%25%32%9%
1050
16th to endNight
20%11%26%32%8%
973
February1st to 15thNight
23%13%27%27%7%
824
16th to endNight
23%13%38%21%2
736
March1st to 15thNight
21%10%36%27%4
684
16th to endNight
20%9%37%28%3
672
April1st to 15thNight
16%11%42%27%3
629
16th to endNight
18%11%42%22%5%
624
May1st to 15thNight
18%9%39%29%3
630
16th to endNight
13%5%37%32%9%
659
June1st to 15thNight
4132%46%14%1
630
16th to endNight
9%126%43%17%1
630
July1st to 15thNight
6%114%50%24%2
600
16th to endNight
6%17%56%26%2
660
August1st to 15thNight
217%51%33%3
620
16th to endNight
8%17%49%29%3
669
September1st to 15thNight
11%28%39%33%5%
630
16th to endNight
13%210%37%31%4
585
October1st to 15thNight
10%115%43%25%3
585
16th to endNight
13%423%32%23%3
799
November1st to 15thNight
14%7%24%32%18%1
876
16th to endNight
17%8%24%33%15%1
1050
December1st to 15thNight
24%9%24%30%11%
1050
16th to endNight
25%10%24%30%9%
1120
Page generated at 2019-09-17 20:12:17. Version ac04

Copyright 2019 A. Danko


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