Lewis Smith Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lewis Smith Lake Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
48%
23443
23%
74343
17%
23388
56%
23388
27%
45659

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 10thNight
25%
760
22%
2459
10%
757
40%
757
21%
1564
January11th to 20thNight
26%
744
22%
2344
10%
744
39%
744
17%
1619
January21st to endNight
25%
792
29%
2376
13%
792
40%
792
24%
1511
February1st to 10thNight
27%
720
24%
2160
11%
720
40%
720
24%
1403
February11th to 20thNight
25%
703
20%
2098
8%
699
35%
699
21%
1394
February21st to endNight
24%
592
22%
1776
9%
592
35%
592
20%
1218
March1st to 10thNight
31%
720
23%
2160
12%
720
39%
720
25%
1334
March11th to 20thNight
31%
720
19%
2075
10%
720
39%
720
24%
1373
March21st to endNight
33%
676
23%
2062
12%
676
44%
676
25%
1307
April1st to 10thNight
39%
540
26%
1800
17%
540
51%
540
29%
1048
April11th to 20thNight
39%
533
27%
1775
18%
533
53%
533
28%
1032
April21st to endNight
47%
540
26%
1800
20%
540
58%
540
32%
991
May1st to 10thNight
52%
540
24%
1656
16%
540
59%
540
35%
958
May11th to 20thNight
53%
531
20%
1592
14%
531
58%
531
30%
989
May21st to endNight
70%
582
21%
1744
18%
582
73%
582
35%
1030
June1st to 10thNight
65%
540
19%
1620
16%
540
67%
540
29%
1016
June11th to 20thNight
77%
540
21%
1620
18%
540
79%
540
42%
899
June21st to endNight
71%
540
20%
1538
16%
540
73%
540
34%
938
July1st to 10thNight
72%
525
14%
1511
13%
525
73%
525
28%
997
July11th to 20thNight
75%
522
16%
1566
14%
522
77%
522
30%
975
July21st to endNight
70%
591
16%
1719
15%
558
71%
558
27%
1114
August1st to 10thNight
83%
537
17%
1778
19%
534
83%
534
32%
1023
August11th to 20thNight
73%
534
16%
1776
19%
534
74%
534
26%
1116
August21st to endNight
70%
594
20%
1980
25%
594
70%
594
25%
1257
September1st to 10thNight
69%
548
23%
1808
25%
548
71%
548
30%
1076
September11th to 20thNight
62%
720
23%
1980
20%
720
64%
720
30%
1268
September21st to endNight
65%
720
30%
1980
22%
720
70%
720
40%
1140
October1st to 10thNight
60%
720
33%
1980
25%
720
65%
720
42%
1121
October11th to 20thNight
51%
720
33%
1988
23%
720
60%
720
36%
1181
October21st to endNight
50%
792
30%
2506
27%
792
56%
792
31%
1450
November1st to 10thNight
53%
740
29%
2406
25%
740
62%
740
34%
1322
November11th to 20thNight
41%
760
29%
2470
19%
760
56%
760
33%
1380
November21st to endNight
39%
760
26%
2470
17%
760
52%
760
27%
1487
December1st to 10thNight
33%
760
24%
2470
15%
760
45%
760
21%
1601
December11th to 20thNight
33%
759
24%
2899
16%
758
43%
758
20%
1734
December21st to endNight
27%
828
14%
4401
12%
817
39%
817
11%
2793

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%6%25%5%35%5%5%7%42%
74927
Night
13%5%25%43445%7%46%
74829
TransparencyDay
40%7%11%20%18%4
74654
Night
37%6%10%20%20%6%
74622
SeeingDay
17%10%22%23%19%9%
13473
Night
15%8%22%29%21%4
23454

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 10thDay
22%8%25%323346%42%
1706
11th to 20thDay
22%9%35%433335%39%
1742
21st to endDay
18%7%2433344448%
1980
February1st to 10thDay
21%9%35%4235%36%39%
1800
11th to 20thDay
24%7%25%5%3444439%
1748
21st to endDay
24%8%44433445%38%
1480
March1st to 10thDay
16%7%36%5%33446%44%
1800
11th to 20thDay
20%6%45%5%45%446%37%
1883
21st to endDay
15%6%36%6%35%5%5%7%39%
2308
April1st to 10thDay
13%5%25%5%345%5%7%47%
2160
11th to 20thDay
15%6%25%43445%6%46%
2134
21st to endDay
10%5%246%345%5%9%47%
2160
May1st to 10thDay
13%5%24445%446%47%
2300
11th to 20thDay
11%7%25%5%36%5%6%7%42%
2301
21st to endDay
10%425%6%45%6%6%9%43%
2531
June1st to 10thDay
10%6%25%6%5%6%6%7%10%37%
2340
11th to 20thDay
5%325%6%46%7%8%10%44%
2340
21st to endDay
8%5%26%5%46%6%7%9%42%
2390
July1st to 10thDay
8%5%37%7%49%7%7%11%31%
2373
11th to 20thDay
9%5%36%5%5%8%7%8%12%32%
2340
21st to endDay
7%436%6%5%8%8%9%11%32%
2493
August1st to 10thDay
7%5%26%6%5%6%7%9%11%35%
2148
11th to 20thDay
10%5%27%7%5%6%6%8%10%34%
2125
21st to endDay
13%6%26%7%46%6%6%8%35%
2376
September1st to 10thDay
11%426%5%46%6%6%8%41%
2132
11th to 20thDay
13%6%25%5%45%6%6%7%43%
1980
21st to endDay
11%425%4235%5%6%52%
1980
October1st to 10thDay
10%42442435%6%55%
1980
11th to 20thDay
11%4244245%47%53%
1968
21st to endDay
14%424433446%53%
1850
November1st to 10thDay
12%424423345%56%
1672
11th to 20thDay
15%424435%346%52%
1710
21st to endDay
17%5%245%235%6%5%45%
1710
December1st to 10thDay
23%8%344245%5%6%37%
1710
11th to 20thDay
19%7%25%434435%43%
2153
21st to endDay
19%10%46%5%34446%35%
3124
January1st to 10thNight
20%6%245%34435%44%
2459
11th to 20thNight
21%8%5%6%5%34445%36%
2344
21st to endNight
17%8%35%434445%44%
2376
February1st to 10thNight
21%7%35%32335%5%43%
2160
11th to 20thNight
22%7%35%43333443%
2098
21st to endNight
23%6%245%3445%6%37%
1776
March1st to 10thNight
17%425%43335%6%46%
2160
11th to 20thNight
17%5%35%5%3445%8%41%
2075
21st to endNight
15%6%35%5%345%5%6%44%
2062
April1st to 10thNight
11%425%435%5%6%7%48%
1800
11th to 20thNight
15%5%23424447%50%
1775
21st to endNight
11%42443445%8%52%
1800
May1st to 10thNight
10%425%434448%52%
1656
11th to 20thNight
10%5%26%5%35%5%6%9%45%
1592
21st to endNight
7%3245%45%6%7%10%47%
1744
June1st to 10thNight
7%5%26%6%46%6%7%9%43%
1620
11th to 20thNight
4313435%5%6%12%53%
1620
21st to endNight
7%325%6%35%5%6%10%48%
1538
July1st to 10thNight
9%5%35%6%46%7%7%10%40%
1556
11th to 20thNight
6%425%6%46%7%8%9%44%
1620
21st to endNight
7%5%35%6%46%7%8%11%39%
1820
August1st to 10thNight
42245%46%7%8%13%45%
1790
11th to 20thNight
8%426%5%35%7%7%11%43%
1776
21st to endNight
11%6%35%5%46%6%6%7%43%
1980
September1st to 10thNight
8%4245%345%7%8%49%
1808
11th to 20thNight
11%6%25%5%3446%8%45%
1980
21st to endNight
7%425%43345%6%56%
1980
October1st to 10thNight
9%414423336%60%
1980
11th to 20thNight
11%5%3442345%6%53%
1988
21st to endNight
16%6%24323235%55%
2506
November1st to 10thNight
11%424324445%56%
2406
11th to 20thNight
13%6%2442345%5%54%
2470
21st to endNight
16%6%24434446%47%
2470
December1st to 10thNight
20%6%25%43445%7%40%
2470
11th to 20thNight
18%6%24433345%47%
3042
21st to endNight
20%7%36%5%435%6%7%32%
4532

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 10thDay
45%37%19%21%5%
1707
11th to 20thDay
49%36%20%18%4
1742
21st to endDay
40%35%24%23%5%
1980
February1st to 10thDay
47%48%18%20%4
1800
11th to 20thDay
49%45%19%18%5%
1758
21st to endDay
49%47%13%21%6%
1480
March1st to 10thDay
42%48%15%20%10%
1800
11th to 20thDay
48%6%9%15%17%5%
1883
21st to endDay
44%5%10%22%17%2
2308
April1st to 10thDay
36%5%11%22%18%7%
2160
11th to 20thDay
39%47%21%23%6%
2134
21st to endDay
34%6%10%26%22%3
2160
May1st to 10thDay
37%5%11%23%19%4
2300
11th to 20thDay
38%9%13%23%15%2
2305
21st to endDay
37%8%14%24%16%2
2531
June1st to 10thDay
41%10%13%18%17%1
2340
11th to 20thDay
32%10%16%25%15%3
2340
21st to endDay
36%10%16%22%12%4
2390
July1st to 10thDay
41%12%19%18%9%2
2308
11th to 20thDay
41%12%21%16%8%2
2271
21st to endDay
39%13%19%19%9%
2354
August1st to 10thDay
35%14%19%24%8%1
2136
11th to 20thDay
42%11%14%19%11%2
2125
21st to endDay
44%9%13%20%10%4
2376
September1st to 10thDay
38%9%14%19%16%5%
2132
11th to 20thDay
40%7%12%16%20%5%
1980
21st to endDay
32%6%11%22%22%8%
1980
October1st to 10thDay
30%6%8%22%26%8%
1980
11th to 20thDay
30%5%8%22%26%9%
1968
21st to endDay
34%35%18%31%9%
1850
November1st to 10thDay
32%47%18%28%10%
1672
11th to 20thDay
36%45%21%25%10%
1710
21st to endDay
40%5%6%18%24%7%
1710
December1st to 10thDay
49%5%7%15%19%5%
1710
11th to 20thDay
46%36%19%21%5%
2150
21st to endDay
50%48%19%17%2
3124
January1st to 10thNight
44%46%20%21%4
2459
11th to 20thNight
51%46%18%17%4
2344
21st to endNight
42%46%20%23%6%
2376
February1st to 10thNight
44%37%20%20%5%
2160
11th to 20thNight
46%36%18%19%7%
2099
21st to endNight
47%5%6%16%18%8%
1776
March1st to 10thNight
40%37%17%21%11%
2160
11th to 20thNight
42%6%11%18%18%5%
2075
21st to endNight
41%5%8%24%19%4
2062
April1st to 10thNight
35%5%11%23%19%6%
1800
11th to 20thNight
35%5%6%21%22%12%
1775
21st to endNight
31%5%11%26%22%5%
1800
May1st to 10thNight
31%6%12%22%25%4
1656
11th to 20thNight
36%7%17%21%17%3
1593
21st to endNight
28%10%16%26%17%4
1745
June1st to 10thNight
35%9%14%20%19%2
1620
11th to 20thNight
23%9%18%29%18%4
1620
21st to endNight
31%9%16%22%18%4
1538
July1st to 10thNight
37%10%20%20%9%3
1511
11th to 20thNight
31%12%23%21%12%2
1566
21st to endNight
35%12%20%21%11%1
1719
August1st to 10thNight
27%12%23%28%10%1
1778
11th to 20thNight
33%13%19%18%12%4
1776
21st to endNight
38%10%15%21%12%5%
1980
September1st to 10thNight
32%9%16%20%17%6%
1808
11th to 20thNight
36%8%11%18%22%5%
1980
21st to endNight
28%6%10%21%25%9%
1980
October1st to 10thNight
28%47%24%26%12%
1980
11th to 20thNight
32%47%21%24%12%
1988
21st to endNight
35%35%16%31%10%
2506
November1st to 10thNight
31%47%19%26%14%
2406
11th to 20thNight
33%37%18%27%12%
2470
21st to endNight
39%36%20%24%8%
2470
December1st to 10thNight
45%5%8%18%21%4
2470
11th to 20thNight
40%46%18%26%5%
3044
21st to endNight
48%5%7%20%17%2
4532

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 10thDay
29%23%32%14%3
270
11th to 20thDay
33%18%30%12%6%
257
21st to endDay
24%23%37%13%3
264
February1st to 10thDay
28%22%33%13%4
240
11th to 20thDay
38%21%30%10%1
240
21st to endDay
36%20%34%9%1
198
March1st to 10thDay
24%20%37%15%31
240
11th to 20thDay
27%18%33%15%5%1
323
21st to endDay
24%17%31%19%8%
462
April1st to 10thDay
21%15%27%23%12%2
420
11th to 20thDay
17%17%29%21%13%2
412
21st to endDay
16%11%32%25%14%1
420
May1st to 10thDay
17%8%28%25%17%5%
423
11th to 20thDay
11%6%27%27%19%10%
447
21st to endDay
12%5%20%29%20%15%
485
June1st to 10thDay
14%417%28%25%13%
450
11th to 20thDay
6%316%28%26%21%
450
21st to endDay
11%315%27%27%17%
500
July1st to 10thDay
8%29%27%31%23%
478
11th to 20thDay
8%39%20%32%29%
444
21st to endDay
8%310%20%37%23%
488
August1st to 10thDay
9%212%24%30%23%
446
11th to 20thDay
10%29%31%32%15%
439
21st to endDay
15%39%22%32%19%
495
September1st to 10thDay
10%311%29%36%11%
450
11th to 20thDay
11%6%12%22%36%14%
450
21st to endDay
12%316%28%30%10%
450
October1st to 10thDay
11%6%21%31%22%9%
450
11th to 20thDay
14%9%26%34%15%2
438
21st to endDay
20%12%24%30%12%2
297
November1st to 10thDay
20%8%31%26%11%3
270
11th to 20thDay
15%16%39%22%7%1
270
21st to endDay
18%18%32%22%9%1
270
December1st to 10thDay
32%15%31%16%5%1
270
11th to 20thDay
26%21%30%15%7%1
270
21st to endDay
27%20%33%16%31
297
January1st to 10thNight
24%14%35%23%4
760
11th to 20thNight
25%16%29%24%7%
744
21st to endNight
21%16%35%24%3
792
February1st to 10thNight
24%12%33%28%4
720
11th to 20thNight
26%14%31%26%3
703
21st to endNight
27%16%31%24%2
592
March1st to 10thNight
19%15%32%29%5%
720
11th to 20thNight
18%14%33%26%8%1
720
21st to endNight
18%12%32%27%11%
676
April1st to 10thNight
12%14%32%28%14%
540
11th to 20thNight
17%9%31%27%14%2
533
21st to endNight
14%9%26%34%15%2
540
May1st to 10thNight
10%6%26%33%23%2
540
11th to 20thNight
10%5%23%31%28%4
531
21st to endNight
8%211%36%36%7%
584
June1st to 10thNight
7%212%36%36%7%
540
11th to 20thNight
4110%31%39%15%
540
21st to endNight
6%210%28%45%9%
540
July1st to 10thNight
8%16%28%43%14%
525
11th to 20thNight
6%17%25%44%19%
522
21st to endNight
7%19%24%45%15%
591
August1st to 10thNight
4427%50%15%
537
11th to 20thNight
9%7%31%43%10%
534
21st to endNight
12%36%29%41%10%
594
September1st to 10thNight
9%110%29%43%8%
548
11th to 20thNight
12%412%30%36%7%
720
21st to endNight
9%215%35%35%4
720
October1st to 10thNight
11%421%29%30%6%
720
11th to 20thNight
13%7%24%34%21%2
720
21st to endNight
18%8%19%35%18%2
792
November1st to 10thNight
13%7%21%35%20%3
740
11th to 20thNight
15%10%30%32%12%1
760
21st to endNight
19%9%29%30%11%1
760
December1st to 10thNight
23%13%26%30%8%
760
11th to 20thNight
23%12%28%27%9%
760
21st to endNight
27%10%30%26%7%
836
Page generated at 2024-01-13 18:28:33. Version ac07

Copyright 2024 Attilla Danko


Lewis Smith Lake Observatory Clear Sky Chart |Charts Home