Lightholder Optics Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lightholder Optics Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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%
15714
27%
48488
21%
15682
62%
15682
38%
26035

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%
777
18%
2716
16%
776
55%
776
27%
1569
January16th to endNight
43%
788
22%
2580
18%
788
51%
788
26%
1568
February1st to 15thNight
42%
699
20%
2225
18%
697
48%
697
26%
1363
February16th to endNight
45%
632
23%
1895
19%
632
52%
632
28%
1176
March1st to 15thNight
44%
720
17%
2114
13%
720
50%
720
26%
1330
March16th to endNight
40%
768
17%
2022
11%
768
45%
768
28%
1293
April1st to 15thNight
41%
719
18%
1799
8%
719
45%
719
29%
1202
April16th to endNight
48%
720
21%
1800
9%
720
53%
720
38%
1087
May1st to 15thNight
52%
571
25%
1651
16%
571
57%
571
43%
848
May16th to endNight
59%
374
22%
1496
23%
374
63%
374
32%
729
June1st to 15thNight
65%
360
26%
1440
30%
360
73%
360
41%
631
June16th to endNight
70%
360
34%
1440
39%
360
81%
360
59%
498
July1st to 15thNight
85%
340
32%
1360
40%
340
89%
340
63%
472
July16th to endNight
79%
430
37%
1466
39%
404
83%
404
60%
566
August1st to 15thNight
77%
616
34%
1689
23%
613
80%
613
62%
807
August16th to endNight
78%
764
42%
1910
25%
764
80%
764
74%
888
September1st to 15thNight
81%
720
41%
1800
26%
720
85%
720
77%
826
September16th to endNight
68%
716
42%
1938
32%
716
75%
716
60%
910
October1st to 15thNight
60%
720
30%
2142
24%
720
70%
720
48%
1051
October16th to endNight
64%
768
37%
2325
34%
768
73%
768
51%
1103
November1st to 15thNight
56%
760
27%
2470
25%
760
62%
760
37%
1295
November16th to endNight
48%
780
28%
2568
21%
780
59%
780
34%
1346
December1st to 15thNight
46%
780
19%
2730
16%
780
54%
780
26%
1604
December16th to endNight
37%
832
21%
2912
17%
832
46%
832
19%
1873

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
2424424446%59%
49050
Night
132442445%7%58%
48670
TransparencyDay
26%5%10%19%23%15%
48726
Night
25%5%11%21%23%12%
48493
SeeingDay
13%21%33%20%9%2
6156
Night
8%11%20%30%23%6%
15724

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
1425%6%46%5%6%8%48%
1552
16th to endDay
36%37%6%35%6%6%8%42%
1746
February1st to 15thDay
15%25%5%35%45%9%48%
1634
16th to endDay
16%5%8%6%46%5%6%6%42%
1579
March1st to 15thDay
5%5%7%7%36%6%5%8%41%
1845
16th to endDay
15%47%5%36%6%6%9%43%
2202
April1st to 15thDay
37%36%5%36%6%5%8%43%
2149
16th to endDay
36%35%324447%54%
2160
May1st to 15thDay
46%23313347%58%
2295
16th to endDay
6%8%25%425%446%49%
2615
June1st to 15thDay
4423323346%61%
2520
16th to endDay
11111223477%
2520
July1st to 15thDay
121213245%75%
2520
16th to endDay
21121322475%
2600
August1st to 15thDay
121231223374%
2260
16th to endDay
11111222380%
2292
September1st to 15thDay
121221223475%
2160
16th to endDay
23221224472%
2022
October1st to 15thDay
25%24423246%62%
1817
16th to endDay
2323333246%64%
1899
November1st to 15thDay
2414335%6%6%6%55%
1719
16th to endDay
425%425%47%10%52%
1720
December1st to 15thDay
5%46%5%36%5%48%47%
1560
16th to endDay
15%48%6%48%5%6%7%40%
1664
January1st to 15thNight
1436%6%36%5%6%10%45%
2716
16th to endNight
16%36%5%46%6%6%7%45%
2580
February1st to 15thNight
1435%5%47%6%6%9%44%
2218
16th to endNight
5%346%37%6%7%9%43%
1895
March1st to 15thNight
435%5%37%6%7%9%46%
2114
16th to endNight
5%36%425%7%5%8%49%
2022
April1st to 15thNight
25%35%7%27%6%6%9%43%
1799
16th to endNight
3425%42435%7%57%
1800
May1st to 15thNight
331332425%8%61%
1651
16th to endNight
46%2431345%8%55%
1496
June1st to 15thNight
3213324335%66%
1440
16th to endNight
11121122380%
1440
July1st to 15thNight
11211222478%
1440
16th to endNight
221221122377%
1566
August1st to 15thNight
311221223474%
1698
16th to endNight
1111123480%
1910
September1st to 15thNight
12111125%82%
1800
16th to endNight
22221222475%
1938
October1st to 15thNight
3322322335%67%
2142
16th to endNight
1213222348%67%
2325
November1st to 15thNight
1412325%5%6%9%56%
2470
16th to endNight
1323325%45%10%56%
2568
December1st to 15thNight
1325%5%36%5%6%10%49%
2730
16th to endNight
5%37%6%49%8%6%8%38%
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
34%7%15%23%16%3
1552
16th to endDay
40%6%10%18%16%8%
1746
February1st to 15thDay
32%8%16%21%16%4
1634
16th to endDay
41%5%11%24%14%2
1579
March1st to 15thDay
40%9%13%16%15%4
1845
16th to endDay
37%9%18%19%11%2
2202
April1st to 15thDay
39%6%16%20%15%2
2149
16th to endDay
31%6%16%24%17%3
2160
May1st to 15thDay
26%312%32%22%3
2295
16th to endDay
35%5%10%24%19%4
2619
June1st to 15thDay
24%5%11%20%25%12%
2520
16th to endDay
12%25%16%37%25%
2520
July1st to 15thDay
11%3410%24%45%
2371
16th to endDay
14%2411%21%45%
2437
August1st to 15thDay
14%3310%27%40%
2244
16th to endDay
10%2212%39%32%
2292
September1st to 15thDay
14%2412%35%29%
2160
16th to endDay
16%25%25%34%14%
2022
October1st to 15thDay
24%27%23%28%14%
1817
16th to endDay
22%311%23%27%11%
1899
November1st to 15thDay
27%6%14%22%21%7%
1719
16th to endDay
26%7%13%26%21%4
1720
December1st to 15thDay
34%8%13%21%18%5%
1560
16th to endDay
42%7%12%15%18%4
1664
January1st to 15thNight
33%7%16%21%17%4
2716
16th to endNight
37%6%12%17%16%10%
2580
February1st to 15thNight
34%9%13%23%12%7%
2229
16th to endNight
35%6%14%22%16%3
1895
March1st to 15thNight
32%11%14%19%17%6%
2114
16th to endNight
31%10%19%21%14%3
2022
April1st to 15thNight
35%8%18%22%12%2
1799
16th to endNight
26%8%18%26%17%3
1800
May1st to 15thNight
21%412%31%25%4
1652
16th to endNight
27%415%27%19%5%
1496
June1st to 15thNight
20%49%23%27%13%
1440
16th to endNight
11%2419%35%26%
1440
July1st to 15thNight
10%149%28%45%
1360
16th to endNight
13%1411%23%45%
1466
August1st to 15thNight
14%2413%26%37%
1689
16th to endNight
9%1314%39%31%
1910
September1st to 15thNight
8%16%13%41%29%
1800
16th to endNight
14%16%25%34%17%
1938
October1st to 15thNight
20%28%27%27%13%
2142
16th to endNight
17%312%24%33%9%
2325
November1st to 15thNight
23%7%14%24%22%8%
2470
16th to endNight
23%7%13%25%24%5%
2568
December1st to 15thNight
29%12%14%19%17%6%
2730
16th to endNight
41%8%11%15%18%5%
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
28%16%28%15%6%3
90
16th to endDay
23%20%23%19%10%2
249
February1st to 15thDay
18%25%25%21%8%
247
16th to endDay
23%23%30%16%5%
238
March1st to 15thDay
22%32%20%12%10%1
270
16th to endDay
19%36%24%13%6%
288
April1st to 15thDay
21%31%28%12%5%
269
16th to endDay
20%30%30%13%4
270
May1st to 15thDay
19%22%32%18%6%1
288
16th to endDay
20%19%29%17%9%4
330
June1st to 15thDay
12%27%33%18%6%1
315
16th to endDay
415%46%21%6%5%
315
July1st to 15thDay
313%46%25%9%2
305
16th to endDay
314%47%22%7%4
327
August1st to 15thDay
419%43%20%8%2
315
16th to endDay
312%45%21%11%4
332
September1st to 15thDay
5%11%44%28%8%1
315
16th to endDay
8%18%35%29%6%1
315
October1st to 15thDay
10%23%29%23%10%2
315
16th to endDay
13%20%23%24%15%3
315
November1st to 15thDay
11%23%18%12%29%3
135
16th to endDay
14%25%25%21%12%1
127
December1st to 15thDay
16%31%22%13%5%11%
90
16th to endDay
15%15%25%22%16%4
96
January1st to 15thNight
11%9%25%28%17%8%
780
16th to endNight
9%13%27%26%15%7%
788
February1st to 15thNight
10%14%24%26%18%4
704
16th to endNight
14%15%21%26%16%5%
632
March1st to 15thNight
12%19%21%24%17%5%
720
16th to endNight
11%21%23%23%17%2
768
April1st to 15thNight
10%16%26%27%15%2
719
16th to endNight
10%13%23%25%20%5%
720
May1st to 15thNight
6%13%22%30%21%4
572
16th to endNight
10%6%20%28%30%3
375
June1st to 15thNight
5%5%19%39%26%3
360
16th to endNight
1420%39%32%2
360
July1st to 15thNight
118%47%38%2
340
16th to endNight
3110%34%42%6%
430
August1st to 15thNight
4113%41%35%4
616
16th to endNight
3313%39%34%5%
764
September1st to 15thNight
2211%37%38%7%
720
16th to endNight
47%16%30%29%10%
716
October1st to 15thNight
8%8%17%33%22%8%
720
16th to endNight
7%8%17%27%27%12%
768
November1st to 15thNight
8%11%22%27%23%7%
760
16th to endNight
11%15%23%24%19%6%
780
December1st to 15thNight
10%13%24%29%14%7%
780
16th to endNight
12%18%27%24%13%4
832
Page generated at 2018-01-21 09:19:31. Version ac04

Copyright 2018 A. Danko


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