Lookout Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lookout Mountain Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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
53%
15829
30%
46899
17%
15785
65%
15785
47%
23499

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
52%
815
34%
2423
21%
812
66%
812
64%
1032
January16th to endNight
47%
768
36%
2496
22%
768
66%
768
57%
1077
February1st to 15thNight
40%
699
29%
2264
15%
696
58%
696
49%
1066
February16th to endNight
35%
632
38%
1894
15%
632
58%
632
54%
885
March1st to 15thNight
40%
720
31%
2043
13%
720
57%
720
51%
1004
March16th to endNight
40%
722
33%
2066
14%
722
58%
722
50%
1008
April1st to 15thNight
32%
539
28%
1798
10%
539
55%
539
40%
842
April16th to endNight
37%
540
29%
1800
14%
540
58%
540
37%
899
May1st to 15thNight
47%
539
23%
1710
14%
539
59%
539
36%
912
May16th to endNight
50%
563
26%
1497
14%
561
61%
561
43%
825
June1st to 15thNight
59%
540
28%
1440
18%
540
66%
540
56%
713
June16th to endNight
72%
540
27%
1440
21%
540
75%
540
54%
730
July1st to 15thNight
69%
510
14%
1360
11%
510
70%
510
28%
911
July16th to endNight
81%
564
13%
1584
14%
531
83%
531
27%
988
August1st to 15thNight
72%
539
14%
1656
15%
536
73%
536
29%
1017
August16th to endNight
73%
573
19%
1910
21%
573
75%
573
27%
1154
September1st to 15thNight
70%
540
24%
1800
22%
540
75%
540
35%
988
September16th to endNight
71%
542
37%
1802
30%
542
79%
542
52%
817
October1st to 15thNight
58%
660
33%
1980
19%
660
69%
660
53%
963
October16th to endNight
56%
704
38%
2112
20%
704
70%
704
58%
966
November1st to 15thNight
55%
820
38%
2220
20%
820
66%
820
65%
1021
November16th to endNight
51%
900
39%
2396
18%
900
65%
900
62%
1141
December1st to 15thNight
45%
900
30%
2520
11%
900
61%
900
58%
1182
December16th to endNight
44%
960
29%
2688
15%
960
57%
960
50%
1358

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
22133245%6%9%56%
47873
Night
221232345%8%64%
47085
TransparencyDay
22%6%15%26%22%6%
47559
Night
18%6%14%28%24%7%
46901
SeeingDay
7%11%25%31%19%5%
5696
Night
35%32%37%19%2
15837

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
1121435%10%66%
1525
16th to endDay
21232235%7%69%
1728
February1st to 15thDay
21331445%8%64%
1598
16th to endDay
21322336%10%63%
1580
March1st to 15thDay
131332445%8%62%
1914
16th to endDay
132332445%9%59%
2157
April1st to 15thDay
141332435%10%60%
2150
16th to endDay
34134245%6%10%52%
2160
May1st to 15thDay
3423435%5%7%9%49%
2234
16th to endDay
3213425%6%6%8%55%
2616
June1st to 15thDay
2112225%5%6%8%60%
2520
16th to endDay
112335%6%7%8%58%
2520
July1st to 15thDay
43146%47%8%9%10%39%
2520
16th to endDay
43246%5%8%9%9%11%33%
2473
August1st to 15thDay
5%425%6%48%7%8%9%36%
2292
16th to endDay
3424435%6%9%10%44%
2292
September1st to 15thDay
33145%36%6%8%10%45%
2160
16th to endDay
221222345%7%64%
1860
October1st to 15thDay
32132245%47%62%
1650
16th to endDay
1212312345%71%
1760
November1st to 15thDay
1111335%7%73%
1625
16th to endDay
1111335%79%
1563
December1st to 15thDay
22221335%8%68%
1440
16th to endDay
121321347%9%62%
1536
January1st to 15thNight
21112237%76%
2423
16th to endNight
212212347%72%
2496
February1st to 15thNight
31322235%7%67%
2254
16th to endNight
22313247%70%
1894
March1st to 15thNight
1322213346%68%
2043
16th to endNight
1212213347%67%
2066
April1st to 15thNight
221322335%7%66%
1798
16th to endNight
3424322346%63%
1800
May1st to 15thNight
35%2343446%7%55%
1710
16th to endNight
43123235%5%8%60%
1497
June1st to 15thNight
111222447%70%
1440
16th to endNight
1113245%7%10%61%
1440
July1st to 15thNight
3316%6%38%8%8%10%38%
1440
16th to endNight
32135%37%8%8%13%41%
1691
August1st to 15thNight
3325%5%36%6%7%11%45%
1665
16th to endNight
4315%5%35%6%8%10%43%
1910
September1st to 15thNight
5%3144245%7%10%51%
1800
16th to endNight
322212336%70%
1802
October1st to 15thNight
221221335%7%67%
1980
16th to endNight
2212212246%71%
2112
November1st to 15thNight
11113347%74%
2220
16th to endNight
121111133476%
2396
December1st to 15thNight
1221235%7%71%
2520
16th to endNight
1212212349%67%
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
14%5%18%38%23%
1526
16th to endDay
15%415%35%24%4
1728
February1st to 15thDay
19%5%17%35%17%4
1599
16th to endDay
16%5%14%31%28%4
1580
March1st to 15thDay
20%413%29%27%4
1914
16th to endDay
21%6%10%31%25%3
2157
April1st to 15thDay
20%5%11%33%22%7%
2150
16th to endDay
24%5%13%26%23%5%
2160
May1st to 15thDay
28%6%14%26%21%3
2234
16th to endDay
24%7%14%21%22%9%
2620
June1st to 15thDay
19%6%12%19%23%18%
2520
16th to endDay
18%6%11%20%27%16%
2520
July1st to 15thDay
32%10%18%16%12%8%
2371
16th to endDay
35%12%25%16%6%2
2317
August1st to 15thDay
39%10%18%13%11%5%
2277
16th to endDay
30%9%17%23%15%4
2292
September1st to 15thDay
29%8%18%21%16%5%
2160
16th to endDay
17%5%10%26%34%5%
1860
October1st to 15thDay
20%5%9%29%28%6%
1650
16th to endDay
15%39%31%33%6%
1760
November1st to 15thDay
9%314%28%36%7%
1625
16th to endDay
9%39%37%30%8%
1563
December1st to 15thDay
14%5%21%37%17%2
1440
16th to endDay
17%8%21%29%17%4
1536
January1st to 15thNight
10%318%37%27%2
2423
16th to endNight
13%314%36%27%4
2496
February1st to 15thNight
18%415%35%21%5%
2264
16th to endNight
14%411%31%32%5%
1894
March1st to 15thNight
17%312%33%28%4
2043
16th to endNight
16%412%32%28%5%
2066
April1st to 15thNight
18%5%12%31%24%7%
1798
16th to endNight
23%5%11%27%24%8%
1800
May1st to 15thNight
26%6%13%24%23%5%
1711
16th to endNight
22%6%12%26%21%10%
1498
June1st to 15thNight
14%5%12%19%23%24%
1440
16th to endNight
16%6%14%19%24%18%
1440
July1st to 15thNight
36%11%17%15%9%10%
1360
16th to endNight
27%17%24%19%7%3
1584
August1st to 15thNight
30%12%21%16%11%7%
1656
16th to endNight
31%11%19%18%13%4
1910
September1st to 15thNight
27%8%20%20%16%7%
1800
16th to endNight
15%5%9%26%33%8%
1802
October1st to 15thNight
16%6%12%24%32%8%
1980
16th to endNight
15%38%28%37%7%
2112
November1st to 15thNight
9%411%31%33%8%
2220
16th to endNight
12%37%35%32%8%
2396
December1st to 15thNight
12%5%20%37%21%3
2520
16th to endNight
15%7%19%33%21%2
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
12%7%24%37%17%
90
16th to endDay
3240%30%23%
96
February1st to 15thDay
8%7%36%36%10%
90
16th to endDay
8%8%32%34%14%1
81
March1st to 15thDay
10%18%35%26%8%
204
16th to endDay
9%29%36%19%31
288
April1st to 15thDay
14%28%28%18%7%2
269
16th to endDay
16%29%31%17%4
270
May1st to 15thDay
8%18%32%30%7%2
309
16th to endDay
8%11%28%31%15%3
517
June1st to 15thDay
411%26%30%21%5%
495
16th to endDay
15%23%30%30%8%
495
July1st to 15thDay
7%313%32%34%8%
475
16th to endDay
6%413%38%26%11%
332
August1st to 15thDay
9%418%35%23%8%
315
16th to endDay
6%5%21%35%23%7%
332
September1st to 15thDay
47%26%36%18%7%
315
16th to endDay
6%10%18%33%28%2
171
October1st to 15thDay
2426%28%30%7%
90
16th to endDay
7%5%21%32%25%8%
96
November1st to 15thDay
36%17%31%36%4
90
16th to endDay
6%8%45%27%11%
90
December1st to 15thDay
37%45%40%21
90
16th to endDay
6%6%31%47%7%1
96
January1st to 15thNight
15%37%40%13%1
817
16th to endNight
1443%37%11%1
768
February1st to 15thNight
2446%39%7%
704
16th to endNight
18%52%32%5%
632
March1st to 15thNight
38%41%36%9%
720
16th to endNight
211%42%36%6%
722
April1st to 15thNight
414%44%29%6%
539
16th to endNight
5%13%36%34%9%
540
May1st to 15thNight
7%5%32%40%12%1
540
16th to endNight
6%8%29%36%17%1
563
June1st to 15thNight
15%28%40%22%1
540
16th to endNight
318%40%34%1
540
July1st to 15thNight
429%35%42%6%
510
16th to endNight
5%1225%57%6%
564
August1st to 15thNight
328%30%48%5%
539
16th to endNight
5%16%40%38%6%
573
September1st to 15thNight
6%113%43%29%6%
540
16th to endNight
3218%42%29%3
542
October1st to 15thNight
3231%43%17%2
660
16th to endNight
2332%37%19%3
704
November1st to 15thNight
25%34%42%15%
820
16th to endNight
36%35%37%15%1
900
December1st to 15thNight
15%43%38%9%
900
16th to endNight
28%41%35%11%
960
Page generated at 2017-09-18 06:38:27. Version ac04

Copyright 2017 A. Danko


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