Lake Murray Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Murray Observatory clear sky chart from 2005-11-05 to 2018-03-11.

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
47%
16472
23%
49060
15%
16432
55%
16432
28%
30515

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
32%
778
22%
2522
9%
776
48%
776
23%
1537
January16th to endNight
26%
832
26%
2704
14%
832
43%
832
23%
1642
February1st to 15thNight
29%
763
23%
2388
10%
761
44%
761
25%
1473
February16th to endNight
27%
683
27%
2025
10%
683
44%
683
28%
1240
March1st to 15thNight
30%
764
26%
2101
12%
764
42%
764
30%
1303
March16th to endNight
34%
768
21%
2112
10%
768
43%
768
29%
1343
April1st to 15thNight
37%
718
24%
1946
12%
718
48%
718
34%
1175
April16th to endNight
44%
633
26%
1713
14%
633
52%
633
34%
1048
May1st to 15thNight
46%
539
19%
1620
10%
539
53%
539
29%
999
May16th to endNight
60%
561
19%
1683
13%
561
64%
561
30%
1036
June1st to 15thNight
58%
540
15%
1620
12%
540
59%
540
26%
1064
June16th to endNight
66%
540
15%
1620
13%
540
67%
540
27%
1045
July1st to 15thNight
68%
510
11%
1530
9%
510
68%
510
24%
1034
July16th to endNight
68%
564
12%
1595
10%
531
70%
531
26%
1052
August1st to 15thNight
68%
539
15%
1609
15%
536
68%
536
23%
1116
August16th to endNight
65%
663
15%
1839
11%
663
66%
663
24%
1287
September1st to 15thNight
66%
720
20%
1980
17%
720
67%
720
30%
1283
September16th to endNight
57%
717
20%
1980
16%
717
60%
717
27%
1328
October1st to 15thNight
53%
720
29%
2091
25%
720
60%
720
34%
1246
October16th to endNight
52%
768
36%
2304
27%
768
66%
768
39%
1257
November1st to 15thNight
51%
760
30%
2304
23%
760
62%
760
36%
1286
November16th to endNight
43%
780
28%
2535
21%
780
55%
780
31%
1436
December1st to 15thNight
41%
780
25%
2535
16%
780
53%
780
25%
1547
December16th to endNight
33%
832
22%
2704
15%
832
44%
832
21%
1738

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
12%424435%5%5%7%43%
49560
Night
12%42442445%7%45%
49259
TransparencyDay
38%6%11%20%18%5%
49261
Night
37%5%11%19%19%7%
49062
SeeingDay
14%7%22%24%20%9%
6215
Night
14%7%24%30%19%2
16478

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
15%5%24424345%45%
1746
16th to endDay
16%6%24323345%48%
1872
February1st to 15thDay
16%5%2443345%6%44%
1799
16th to endDay
16%5%24314435%47%
1733
March1st to 15thDay
14%3235%23445%50%
2096
16th to endDay
15%434424446%45%
2111
April1st to 15thDay
9%32442446%7%49%
2002
16th to endDay
10%4243345%6%8%46%
2256
May1st to 15thDay
10%3345%35%5%5%7%44%
2331
16th to endDay
10%5%35%5%36%5%6%7%40%
2431
June1st to 15thDay
10%5%15%5%46%5%7%10%38%
2340
16th to endDay
3325%436%6%9%12%40%
2340
July1st to 15thDay
7%5%27%6%48%7%7%10%33%
2340
16th to endDay
6%325%6%47%7%9%11%33%
2465
August1st to 15thDay
11%5%25%6%5%5%7%7%9%33%
2340
16th to endDay
14%425%6%45%6%8%11%30%
2348
September1st to 15thDay
8%5%26%6%445%6%8%42%
1980
16th to endDay
17%6%25%4245%47%40%
1980
October1st to 15thDay
15%5%13322235%53%
1867
16th to endDay
10%41331323460%
1920
November1st to 15thDay
13%423313245%54%
1881
16th to endDay
12%4235%1443451%
1755
December1st to 15thDay
17%7%25%424445%42%
1755
16th to endDay
19%5%25%424446%40%
1872
January1st to 15thNight
13%6%24424445%48%
2522
16th to endNight
16%6%2432334447%
2704
February1st to 15thNight
17%413424335%46%
2380
16th to endNight
13%42442345%6%48%
2025
March1st to 15thNight
12%42443445%7%47%
2101
16th to endNight
12%5%24424446%48%
2112
April1st to 15thNight
11%423424346%52%
1946
16th to endNight
9%2335%25%46%5%50%
1713
May1st to 15thNight
8%425%435%5%7%9%43%
1619
16th to endNight
8%314435%6%7%9%43%
1682
June1st to 15thNight
11%335%6%35%6%6%11%35%
1620
16th to endNight
4436%5%36%7%8%12%37%
1620
July1st to 15thNight
7%5%26%6%47%7%8%12%32%
1620
16th to endNight
5%435%6%36%7%9%12%34%
1703
August1st to 15thNight
9%435%6%47%7%8%11%32%
1620
16th to endNight
12%5%26%6%35%5%7%12%32%
1839
September1st to 15thNight
8%5%24435%5%7%9%42%
1980
16th to endNight
16%426%43445%6%41%
1980
October1st to 15thNight
16%413323336%52%
2091
16th to endNight
8%414323335%58%
2304
November1st to 15thNight
12%413312336%57%
2304
16th to endNight
11%5%24313445%51%
2535
December1st to 15thNight
14%5%24423345%47%
2535
16th to endNight
18%6%25%424446%40%
2704

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
41%48%15%23%6%
1747
16th to endDay
38%36%19%23%8%
1872
February1st to 15thDay
40%48%19%22%5%
1801
16th to endDay
39%46%20%22%6%
1733
March1st to 15thDay
36%37%22%20%10%
2096
16th to endDay
40%410%19%19%4
2112
April1st to 15thDay
33%5%10%20%24%5%
2002
16th to endDay
33%7%9%19%22%7%
2256
May1st to 15thDay
37%6%14%20%19%2
2331
16th to endDay
39%8%14%22%13%1
2435
June1st to 15thDay
39%9%15%23%10%1
2340
16th to endDay
32%11%16%24%13%2
2340
July1st to 15thDay
41%10%17%19%7%3
2201
16th to endDay
37%12%19%20%8%1
2310
August1st to 15thDay
44%9%14%19%11%1
2327
16th to endDay
46%9%16%17%9%1
2348
September1st to 15thDay
39%7%13%18%18%3
1980
16th to endDay
42%6%9%18%16%5%
1980
October1st to 15thDay
35%47%20%24%7%
1867
16th to endDay
30%2419%30%12%
1920
November1st to 15thDay
32%36%20%26%10%
1881
16th to endDay
35%47%17%24%10%
1755
December1st to 15thDay
43%48%17%18%6%
1755
16th to endDay
44%39%19%16%6%
1872
January1st to 15thNight
39%48%15%25%7%
2522
16th to endNight
40%3418%22%10%
2704
February1st to 15thNight
40%26%19%21%9%
2389
16th to endNight
36%48%21%21%7%
2025
March1st to 15thNight
36%49%18%21%10%
2101
16th to endNight
37%5%10%19%20%6%
2112
April1st to 15thNight
33%39%22%23%8%
1946
16th to endNight
32%5%8%21%22%8%
1713
May1st to 15thNight
35%7%14%21%17%3
1620
16th to endNight
33%8%15%24%15%2
1684
June1st to 15thNight
40%7%16%23%10%1
1620
16th to endNight
35%10%16%22%12%2
1620
July1st to 15thNight
40%10%20%16%8%3
1530
16th to endNight
36%12%23%17%8%2
1595
August1st to 15thNight
41%11%16%19%9%1
1609
16th to endNight
42%9%19%18%8%
1839
September1st to 15thNight
36%8%14%20%14%5%
1980
16th to endNight
42%6%11%18%17%4
1980
October1st to 15thNight
34%39%19%24%7%
2091
16th to endNight
28%35%20%27%14%
2304
November1st to 15thNight
30%36%18%27%13%
2304
16th to endNight
33%37%16%25%13%
2535
December1st to 15thNight
39%410%18%19%8%
2535
16th to endNight
44%49%18%16%7%
2704

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
18%19%39%22%
135
16th to endDay
17%28%35%15%2
144
February1st to 15thDay
19%24%46%9%
135
16th to endDay
18%16%36%22%6%
143
March1st to 15thDay
14%16%36%24%8%
312
16th to endDay
14%12%36%21%13%
288
April1st to 15thDay
14%14%27%19%21%2
270
16th to endDay
12%431%23%21%5%
270
May1st to 15thDay
12%9%28%28%14%6%
288
16th to endDay
14%415%24%24%16%
331
June1st to 15thDay
13%213%23%30%16%
315
16th to endDay
7%114%28%27%20%
315
July1st to 15thDay
9%8%31%34%16%
305
16th to endDay
7%19%26%35%19%
326
August1st to 15thDay
16%11%24%32%14%
313
16th to endDay
14%39%24%24%23%
332
September1st to 15thDay
13%212%24%32%13%
315
16th to endDay
23%14%25%25%10%
314
October1st to 15thDay
20%416%33%16%8%
315
16th to endDay
10%8%22%26%24%7%
336
November1st to 15thDay
19%7%23%29%13%7%
299
16th to endDay
5%11%32%30%18%2
135
December1st to 15thDay
25%16%31%19%7%
135
16th to endDay
25%18%37%13%4
144
January1st to 15thNight
17%14%31%28%7%
780
16th to endNight
20%15%33%25%4
832
February1st to 15thNight
20%13%34%28%3
764
16th to endNight
15%12%39%27%4
683
March1st to 15thNight
15%12%38%26%6%
764
16th to endNight
15%10%35%27%10%
768
April1st to 15thNight
14%13%32%27%12%
718
16th to endNight
13%7%29%34%14%
633
May1st to 15thNight
11%431%35%15%1
540
16th to endNight
10%218%38%26%4
563
June1st to 15thNight
12%16%33%30%6%
540
16th to endNight
7%13%37%31%9%
540
July1st to 15thNight
10%8%39%32%8%
510
16th to endNight
6%8%34%42%6%
564
August1st to 15thNight
11%6%34%40%6%
539
16th to endNight
15%8%30%39%5%
663
September1st to 15thNight
11%19%32%38%5%
720
16th to endNight
18%113%32%29%4
717
October1st to 15thNight
19%318%28%25%4
720
16th to endNight
10%7%25%30%23%3
768
November1st to 15thNight
13%5%24%33%19%3
760
16th to endNight
14%8%30%26%18%1
780
December1st to 15thNight
17%10%25%32%12%1
780
16th to endNight
23%11%27%29%7%
832
Page generated at 2018-03-12 13:28:03. Version ac04

Copyright 2018 A. Danko


Lake Murray Observatory Clear Sky Chart |Charts Home