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 2005-11-05 to 2017-10-06.

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
49%
15298
24%
47086
17%
15255
57%
15255
29%
28648

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
25%
720
23%
2327
9%
716
42%
716
21%
1484
January16th to endNight
25%
768
25%
2316
12%
768
38%
768
21%
1523
February1st to 15thNight
29%
704
24%
2112
10%
701
43%
701
27%
1313
February16th to endNight
29%
631
25%
1893
12%
631
40%
631
25%
1207
March1st to 15thNight
30%
720
20%
2160
10%
720
38%
720
24%
1374
March16th to endNight
40%
690
23%
2037
15%
690
47%
690
29%
1244
April1st to 15thNight
41%
539
25%
1797
17%
539
53%
539
31%
1024
April16th to endNight
47%
540
27%
1800
20%
540
59%
540
33%
991
May1st to 15thNight
51%
540
21%
1644
14%
540
58%
540
30%
1016
May16th to endNight
68%
561
23%
1682
18%
561
72%
561
37%
964
June1st to 15thNight
72%
540
19%
1620
16%
540
74%
540
34%
963
June16th to endNight
76%
540
20%
1565
18%
540
77%
540
37%
924
July1st to 15thNight
72%
510
14%
1488
13%
510
73%
510
29%
962
July16th to endNight
74%
564
17%
1626
16%
531
76%
531
30%
1016
August1st to 15thNight
81%
539
19%
1788
22%
536
82%
536
32%
1040
August16th to endNight
73%
573
20%
1910
25%
573
73%
573
26%
1213
September1st to 15thNight
64%
606
20%
1866
19%
606
66%
606
28%
1184
September16th to endNight
66%
717
29%
1980
23%
717
69%
717
38%
1162
October1st to 15thNight
57%
684
33%
1881
26%
684
62%
684
39%
1088
October16th to endNight
53%
704
33%
2142
28%
704
61%
704
36%
1198
November1st to 15thNight
49%
700
30%
2276
24%
700
60%
700
36%
1225
November16th to endNight
39%
720
27%
2340
18%
720
53%
720
28%
1381
December1st to 15thNight
36%
720
23%
2340
15%
720
47%
720
23%
1481
December16th to endNight
29%
768
20%
2496
13%
768
39%
768
19%
1671

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
13%5%25%5%35%5%5%7%41%
48058
Night
12%42443445%7%46%
47288
TransparencyDay
40%6%11%20%17%4
47763
Night
36%5%10%20%20%6%
47088
SeeingDay
15%6%18%23%22%13%
5265
Night
14%7%22%28%22%4
15300

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 15thDay
22%7%24423235%41%
1611
16th to endDay
18%6%2332323446%
1907
February1st to 15thDay
19%8%35%323435%41%
1750
16th to endDay
19%6%34424345%41%
1580
March1st to 15thDay
19%7%35%5%33445%39%
1800
16th to endDay
14%5%25%435%448%40%
2194
April1st to 15thDay
13%5%25%42445%7%45%
2151
16th to endDay
10%425%5%335%5%8%44%
2160
May1st to 15thDay
12%6%25%435%446%42%
2305
16th to endDay
11%425%5%36%5%6%7%40%
2431
June1st to 15thDay
7%425%6%46%6%7%10%37%
2340
16th to endDay
6%425%5%35%6%6%10%43%
2372
July1st to 15thDay
8%437%6%48%6%6%12%31%
2361
16th to endDay
7%426%6%5%8%7%9%10%30%
2429
August1st to 15thDay
7%426%6%46%6%8%11%34%
2160
16th to endDay
12%6%26%7%46%7%7%8%30%
2292
September1st to 15thDay
13%425%5%46%5%5%7%37%
2081
16th to endDay
11%4243235%5%7%47%
1980
October1st to 15thDay
9%424424347%51%
1877
16th to endDay
13%41332233457%
1727
November1st to 15thDay
12%414323345%55%
1582
16th to endDay
17%41332345%5%48%
1620
December1st to 15thDay
21%7%34424435%39%
1620
16th to endDay
25%8%25%423235%36%
1728
January1st to 15thNight
18%6%2342343443%
2327
16th to endNight
17%7%25%434345%41%
2316
February1st to 15thNight
18%6%23322345%46%
2103
16th to endNight
17%5%25%433345%45%
1893
March1st to 15thNight
18%425%433346%43%
2160
16th to endNight
12%5%34324346%48%
2037
April1st to 15thNight
12%31433445%8%49%
1797
16th to endNight
10%42332435%7%52%
1800
May1st to 15thNight
10%425%4345%5%7%46%
1643
16th to endNight
5%324435%46%8%49%
1682
June1st to 15thNight
4314436%6%7%10%46%
1620
16th to endNight
42145%25%5%7%11%48%
1565
July1st to 15thNight
7%425%5%36%7%6%8%41%
1578
16th to endNight
5%3246%45%7%7%11%40%
1736
August1st to 15thNight
4214435%6%7%13%44%
1800
16th to endNight
8%5%25%445%6%7%8%41%
1910
September1st to 15thNight
9%5%245%345%6%8%43%
1866
16th to endNight
7%425%43335%6%53%
1980
October1st to 15thNight
9%413422336%56%
1881
16th to endNight
13%5%2332223458%
2142
November1st to 15thNight
11%413313345%55%
2276
16th to endNight
15%5%1442333449%
2340
December1st to 15thNight
17%6%24333446%42%
2340
16th to endNight
23%6%25%433345%37%
2496

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
47%26%16%21%5%
1612
16th to endDay
42%25%23%20%5%
1907
February1st to 15thDay
44%38%21%17%4
1752
16th to endDay
44%47%16%22%4
1580
March1st to 15thDay
47%48%15%18%5%
1800
16th to endDay
42%5%11%21%17%1
2195
April1st to 15thDay
38%410%21%17%7%
2151
16th to endDay
36%5%9%23%20%3
2160
May1st to 15thDay
40%6%10%20%17%4
2305
16th to endDay
39%7%13%24%12%2
2435
June1st to 15thDay
38%10%13%20%15%1
2340
16th to endDay
34%8%14%22%15%4
2372
July1st to 15thDay
40%11%19%17%7%2
2222
16th to endDay
41%11%18%19%8%
2277
August1st to 15thDay
38%12%15%19%11%2
2148
16th to endDay
47%8%12%20%8%2
2292
September1st to 15thDay
43%6%14%17%12%5%
2081
16th to endDay
35%6%11%21%20%5%
1980
October1st to 15thDay
32%5%8%20%24%8%
1877
16th to endDay
30%35%18%32%10%
1727
November1st to 15thDay
32%26%18%30%9%
1582
16th to endDay
37%45%19%24%8%
1620
December1st to 15thDay
47%47%18%16%5%
1620
16th to endDay
52%28%19%13%3
1728
January1st to 15thNight
43%36%17%23%4
2327
16th to endNight
45%35%18%19%6%
2316
February1st to 15thNight
40%27%21%20%7%
2112
16th to endNight
41%35%21%22%4
1893
March1st to 15thNight
42%39%19%18%6%
2160
16th to endNight
36%5%10%25%20%3
2037
April1st to 15thNight
33%410%23%18%8%
1797
16th to endNight
30%49%24%24%6%
1800
May1st to 15thNight
36%6%12%17%22%4
1644
16th to endNight
28%6%17%26%14%5%
1684
June1st to 15thNight
29%9%16%23%18%2
1620
16th to endNight
27%9%16%23%20%3
1565
July1st to 15thNight
34%11%19%21%8%4
1488
16th to endNight
33%10%20%21%13%
1626
August1st to 15thNight
27%11%18%23%14%3
1788
16th to endNight
37%9%16%21%11%3
1910
September1st to 15thNight
36%8%16%18%13%6%
1866
16th to endNight
30%5%10%22%23%7%
1980
October1st to 15thNight
30%36%22%23%12%
1881
16th to endNight
31%2313%33%14%
2142
November1st to 15thNight
30%26%18%26%14%
2276
16th to endNight
38%25%17%25%10%
2340
December1st to 15thNight
42%47%18%20%5%
2340
16th to endNight
48%37%18%16%5%
2496

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
22%21%33%15%6%1
90
16th to endDay
28%23%36%8%3
96
February1st to 15thDay
28%25%33%11%1
90
16th to endDay
28%17%39%12%2
81
March1st to 15thDay
26%27%33%7%4
90
16th to endDay
20%11%30%22%13%1
284
April1st to 15thDay
17%13%26%22%16%3
270
16th to endDay
14%7%25%27%22%3
270
May1st to 15thDay
18%6%25%25%14%10%
288
16th to endDay
14%420%27%18%15%
331
June1st to 15thDay
11%110%23%29%23%
315
16th to endDay
11%112%23%25%25%
347
July1st to 15thDay
8%10%24%31%23%
326
16th to endDay
9%16%15%32%34%
326
August1st to 15thDay
13%9%23%29%23%
313
16th to endDay
15%17%25%32%18%
332
September1st to 15thDay
13%310%21%33%17%
315
16th to endDay
13%210%28%33%11%
314
October1st to 15thDay
11%320%35%21%6%
278
16th to endDay
17%5%18%32%20%4
143
November1st to 15thDay
24%12%25%22%14%1
90
16th to endDay
13%20%32%22%10%2
90
December1st to 15thDay
26%18%34%15%31
90
16th to endDay
30%19%30%14%41
96
January1st to 15thNight
23%13%34%21%6%
720
16th to endNight
20%14%34%26%3
768
February1st to 15thNight
21%12%33%28%4
704
16th to endNight
21%14%32%28%3
631
March1st to 15thNight
20%13%32%26%6%
720
16th to endNight
14%12%28%28%14%
690
April1st to 15thNight
13%10%32%26%15%1
539
16th to endNight
14%6%27%32%17%1
540
May1st to 15thNight
11%424%30%25%3
540
16th to endNight
7%113%36%34%6%
563
June1st to 15thNight
6%10%31%39%10%
540
16th to endNight
48%25%47%13%
540
July1st to 15thNight
7%16%28%42%12%
510
16th to endNight
6%7%21%44%18%
564
August1st to 15thNight
5%427%48%14%
539
16th to endNight
10%5%28%43%10%
573
September1st to 15thNight
12%112%27%36%10%
606
16th to endNight
9%113%35%34%5%
717
October1st to 15thNight
11%422%28%27%5%
684
16th to endNight
15%7%18%31%23%2
704
November1st to 15thNight
13%7%24%30%19%3
700
16th to endNight
18%10%28%28%13%
720
December1st to 15thNight
21%12%26%30%9%
720
16th to endNight
28%9%28%24%9%
768
Page generated at 2017-10-07 13:07:56. Version ac04

Copyright 2017 A. Danko


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