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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 2017-02-18.

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%
14540
26%
44880
21%
14508
61%
14508
37%
24279

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%
717
18%
2506
16%
716
55%
716
27%
1435
January16th to endNight
44%
768
22%
2514
19%
768
51%
768
27%
1514
February1st to 15thNight
42%
699
20%
2225
18%
697
48%
697
26%
1363
February16th to endNight
47%
588
23%
1763
19%
588
53%
588
29%
1076
March1st to 15thNight
41%
660
17%
1938
13%
660
48%
660
24%
1249
March16th to endNight
41%
704
16%
1854
11%
704
45%
704
28%
1189
April1st to 15thNight
42%
659
18%
1649
9%
659
46%
659
29%
1110
April16th to endNight
49%
660
19%
1650
9%
660
53%
660
39%
992
May1st to 15thNight
51%
524
26%
1514
16%
524
57%
524
42%
783
May16th to endNight
58%
342
18%
1368
19%
342
61%
342
30%
683
June1st to 15thNight
65%
330
28%
1320
31%
330
74%
330
40%
586
June16th to endNight
69%
330
32%
1320
35%
330
80%
330
58%
458
July1st to 15thNight
83%
310
34%
1240
42%
310
88%
310
60%
442
July16th to endNight
78%
397
35%
1349
36%
371
82%
371
59%
522
August1st to 15thNight
77%
564
36%
1547
24%
561
80%
561
63%
732
August16th to endNight
77%
700
41%
1750
24%
700
80%
700
75%
804
September1st to 15thNight
81%
660
43%
1650
28%
660
85%
660
78%
755
September16th to endNight
68%
656
40%
1776
31%
656
75%
656
60%
834
October1st to 15thNight
58%
660
30%
1963
24%
660
68%
660
45%
988
October16th to endNight
61%
704
34%
2131
30%
704
71%
704
49%
1028
November1st to 15thNight
57%
700
27%
2275
26%
700
64%
700
37%
1208
November16th to endNight
47%
720
27%
2370
20%
720
59%
720
34%
1238
December1st to 15thNight
44%
720
18%
2520
14%
720
52%
720
23%
1540
December16th to endNight
36%
768
20%
2688
16%
768
44%
768
18%
1750

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%58%
45297
Night
1324425%45%7%57%
45062
TransparencyDay
26%410%19%23%14%
44973
Night
25%6%11%21%23%12%
44885
SeeingDay
14%22%34%19%7%1
4952
Night
8%11%21%29%23%6%
14550

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
425%6%47%46%8%49%
1432
16th to endDay
36%37%6%35%6%6%8%42%
1709
February1st to 15thDay
15%25%5%35%45%9%48%
1634
16th to endDay
15%5%8%6%46%5%6%6%43%
1470
March1st to 15thDay
6%5%7%7%36%7%5%8%40%
1691
16th to endDay
15%47%5%36%6%6%9%43%
2018
April1st to 15thDay
37%46%5%36%6%5%8%42%
1969
16th to endDay
37%35%324447%54%
1980
May1st to 15thDay
47%23313347%57%
2103
16th to endDay
6%8%25%5%25%447%47%
2391
June1st to 15thDay
4423324347%60%
2310
16th to endDay
112212235%76%
2310
July1st to 15thDay
121213245%74%
2310
16th to endDay
21121322475%
2409
August1st to 15thDay
111221223376%
2072
16th to endDay
11111222282%
2100
September1st to 15thDay
111221223477%
1980
16th to endDay
221212235%73%
1854
October1st to 15thDay
35%24423247%59%
1666
16th to endDay
2324333246%62%
1741
November1st to 15thDay
2424335%6%6%6%53%
1584
16th to endDay
425%425%47%10%52%
1588
December1st to 15thDay
6%47%6%37%5%48%45%
1440
16th to endDay
16%48%6%5%8%5%6%7%41%
1536
January1st to 15thNight
1335%6%36%5%6%10%45%
2506
16th to endNight
16%36%5%46%6%6%7%45%
2514
February1st to 15thNight
1435%5%47%6%6%9%44%
2218
16th to endNight
5%346%37%6%7%9%45%
1763
March1st to 15thNight
5%35%5%37%7%7%9%43%
1938
16th to endNight
5%36%425%6%5%8%50%
1854
April1st to 15thNight
25%35%7%27%6%6%10%42%
1649
16th to endNight
3425%41435%6%57%
1650
May1st to 15thNight
231342435%8%60%
1514
16th to endNight
47%2332445%8%52%
1368
June1st to 15thNight
3213324335%65%
1320
16th to endNight
11111122380%
1320
July1st to 15thNight
11211223477%
1320
16th to endNight
221221122477%
1449
August1st to 15thNight
311211223474%
1556
16th to endNight
111123481%
1750
September1st to 15thNight
121112483%
1650
16th to endNight
22221223475%
1776
October1st to 15thNight
3423322335%64%
1963
16th to endNight
1213223348%66%
2131
November1st to 15thNight
1413325%5%6%9%55%
2275
16th to endNight
1323325%45%10%57%
2370
December1st to 15thNight
1325%5%47%6%6%9%46%
2520
16th to endNight
438%7%49%8%6%8%38%
2688

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
33%7%14%23%16%3
1432
16th to endDay
40%6%10%18%16%8%
1709
February1st to 15thDay
32%8%16%21%16%4
1634
16th to endDay
40%5%12%24%14%1
1470
March1st to 15thDay
41%9%14%15%14%4
1691
16th to endDay
38%8%17%19%12%3
2018
April1st to 15thDay
39%6%15%19%15%2
1969
16th to endDay
32%5%16%24%18%3
1980
May1st to 15thDay
26%312%31%21%3
2103
16th to endDay
36%5%11%24%16%4
2395
June1st to 15thDay
24%5%11%20%24%13%
2310
16th to endDay
12%25%16%40%22%
2310
July1st to 15thDay
12%3411%24%44%
2161
16th to endDay
14%2412%22%43%
2246
August1st to 15thDay
13%3310%26%43%
2056
16th to endDay
10%1212%40%33%
2100
September1st to 15thDay
13%1411%37%31%
1980
16th to endDay
15%25%24%35%16%
1854
October1st to 15thDay
26%27%23%28%11%
1666
16th to endDay
24%311%24%27%8%
1741
November1st to 15thDay
28%6%13%23%20%7%
1584
16th to endDay
27%7%13%25%22%4
1588
December1st to 15thDay
37%8%13%21%16%2
1440
16th to endDay
42%6%13%15%18%3
1536
January1st to 15thNight
32%7%16%20%18%4
2506
16th to endNight
36%5%12%18%16%10%
2514
February1st to 15thNight
34%9%13%23%12%7%
2229
16th to endNight
34%6%15%23%16%3
1763
March1st to 15thNight
33%11%14%18%16%5%
1938
16th to endNight
31%10%18%20%15%3
1854
April1st to 15thNight
36%8%17%22%12%2
1649
16th to endNight
26%7%19%27%16%3
1650
May1st to 15thNight
21%412%30%25%4
1515
16th to endNight
29%416%26%18%4
1368
June1st to 15thNight
20%5%9%22%26%14%
1320
16th to endNight
11%15%19%38%23%
1320
July1st to 15thNight
12%15%10%28%42%
1240
16th to endNight
13%1412%24%43%
1349
August1st to 15thNight
14%2413%26%38%
1547
16th to endNight
8%1214%40%32%
1750
September1st to 15thNight
7%16%12%42%29%
1650
16th to endNight
14%16%24%33%19%
1776
October1st to 15thNight
22%29%29%27%9%
1963
16th to endNight
17%412%25%32%6%
2131
November1st to 15thNight
24%6%13%24%21%8%
2275
16th to endNight
24%6%13%25%25%5%
2370
December1st to 15thNight
31%13%14%19%16%3
2520
16th to endNight
42%8%12%14%17%4
2688

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
35%15%38%5%5%1
60
16th to endDay
23%20%23%20%10%2
237
February1st to 15thDay
18%25%25%21%8%
247
16th to endDay
20%24%30%17%6%1
195
March1st to 15thDay
26%37%21%11%3
210
16th to endDay
18%35%24%16%5%
224
April1st to 15thDay
19%32%29%11%6%
209
16th to endDay
21%27%31%13%4
210
May1st to 15thDay
21%22%35%16%3
228
16th to endDay
22%20%30%15%6%3
266
June1st to 15thDay
11%28%36%18%31
255
16th to endDay
5%18%51%16%34
255
July1st to 15thDay
415%46%24%7%2
245
16th to endDay
314%50%21%5%4
271
August1st to 15thDay
421%45%18%7%2
255
16th to endDay
214%50%19%8%3
268
September1st to 15thDay
5%12%43%29%7%1
255
16th to endDay
9%16%34%30%7%1
255
October1st to 15thDay
12%21%31%21%9%2
255
16th to endDay
16%22%26%24%9%
253
November1st to 15thDay
10%16%16%13%37%5%
90
16th to endDay
16%28%23%20%9%2
85
December1st to 15thDay
25%38%21%10%31
60
16th to endDay
20%18%18%23%14%4
64
January1st to 15thNight
11%9%24%28%16%8%
720
16th to endNight
9%13%27%26%15%7%
768
February1st to 15thNight
10%14%24%26%18%4
704
16th to endNight
13%14%21%27%17%5%
588
March1st to 15thNight
11%20%22%25%15%4
660
16th to endNight
11%21%23%23%18%2
704
April1st to 15thNight
9%16%27%27%16%3
659
16th to endNight
10%12%22%25%20%6%
660
May1st to 15thNight
7%13%23%29%21%4
525
16th to endNight
10%7%20%28%30%2
343
June1st to 15thNight
6%420%40%25%3
330
16th to endNight
2421%39%30%1
330
July1st to 15thNight
119%47%37%2
310
16th to endNight
3111%34%42%6%
397
August1st to 15thNight
4113%40%34%5%
564
16th to endNight
3314%40%34%5%
700
September1st to 15thNight
2211%35%38%8%
660
16th to endNight
47%16%29%30%11%
656
October1st to 15thNight
9%8%18%31%23%9%
660
16th to endNight
7%9%18%27%24%12%
704
November1st to 15thNight
7%10%22%28%24%7%
700
16th to endNight
10%15%23%23%19%6%
720
December1st to 15thNight
10%14%25%28%14%5%
720
16th to endNight
12%18%27%23%12%4
768
Page generated at 2017-02-18 13:04:31. Version ac04

Copyright 2017 A. Danko


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