Louisville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Louisville 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
50%
24173
22%
74435
15%
24117
57%
24117
27%
46565

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
26%
760
23%
2459
10%
757
43%
757
24%
1505
January11th to 20thNight
34%
744
25%
2417
15%
744
49%
744
24%
1486
January21st to endNight
27%
792
25%
2574
11%
792
44%
792
24%
1581
February1st to 10thNight
35%
720
24%
2192
13%
720
46%
720
27%
1362
February11th to 20thNight
29%
703
23%
2098
9%
699
44%
699
27%
1325
February21st to endNight
29%
592
24%
1776
11%
592
43%
592
25%
1139
March1st to 10thNight
39%
720
28%
1992
15%
720
51%
720
32%
1228
March11th to 20thNight
38%
720
23%
1980
10%
720
48%
720
30%
1250
March21st to endNight
36%
792
22%
2178
10%
792
47%
792
30%
1360
April1st to 10thNight
42%
720
25%
1980
15%
720
51%
720
34%
1197
April11th to 20thNight
43%
701
25%
1883
15%
701
51%
701
35%
1137
April21st to endNight
55%
540
31%
1620
20%
540
64%
540
38%
919
May1st to 10thNight
52%
540
26%
1620
14%
540
61%
540
38%
900
May11th to 20thNight
59%
531
15%
1592
9%
531
63%
531
27%
1039
May21st to endNight
64%
582
20%
1744
14%
582
67%
582
28%
1120
June1st to 10thNight
63%
540
14%
1620
12%
540
64%
540
23%
1109
June11th to 20thNight
69%
540
14%
1620
11%
540
70%
540
29%
1026
June21st to endNight
68%
540
12%
1620
9%
540
70%
540
25%
1087
July1st to 10thNight
71%
525
12%
1575
10%
525
72%
525
23%
1090
July11th to 20thNight
72%
522
10%
1566
8%
522
72%
522
22%
1100
July21st to endNight
72%
591
13%
1672
11%
558
72%
558
25%
1132
August1st to 10thNight
71%
537
12%
1600
12%
534
71%
534
19%
1171
August11th to 20thNight
66%
534
15%
1598
13%
534
66%
534
21%
1125
August21st to endNight
61%
687
13%
2052
12%
687
62%
687
19%
1459
September1st to 10thNight
70%
720
15%
1980
14%
720
70%
720
26%
1342
September11th to 20thNight
60%
720
18%
1980
16%
720
62%
720
27%
1334
September21st to endNight
59%
720
22%
1980
18%
720
63%
720
29%
1297
October1st to 10thNight
60%
720
27%
1993
24%
720
65%
720
35%
1219
October11th to 20thNight
57%
720
31%
2160
28%
720
65%
720
38%
1209
October21st to endNight
54%
792
33%
2376
28%
792
64%
792
37%
1340
November1st to 10thNight
53%
740
29%
2221
24%
740
61%
740
36%
1257
November11th to 20thNight
44%
760
27%
2451
20%
760
55%
760
31%
1424
November21st to endNight
46%
760
27%
2470
20%
760
57%
760
30%
1445
December1st to 10thNight
40%
760
27%
2470
16%
760
54%
760
26%
1491
December11th to 20thNight
39%
759
26%
2913
17%
758
50%
758
23%
1681
December21st to endNight
35%
829
15%
4413
16%
817
44%
817
13%
2679

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
11%5%25%5%35%5%6%8%43%
74928
Night
12%5%25%5%35%5%6%8%45%
74892
TransparencyDay
38%8%12%18%18%6%
74651
Night
37%7%11%17%20%8%
74688
SeeingDay
13%7%21%24%21%13%
14064
Night
14%6%23%32%22%3
24183

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
14%5%345%44447%48%
1706
11th to 20thDay
14%7%25%434447%47%
1671
21st to endDay
17%6%34424446%46%
1782
February1st to 10thDay
15%7%36%435%5%6%7%40%
1766
11th to 20thDay
18%5%2443435%7%45%
1748
21st to endDay
17%6%35%5%24447%43%
1480
March1st to 10thDay
13%5%25%424346%53%
1966
11th to 20thDay
14%5%25%5%3445%7%45%
1980
21st to endDay
13%6%35%5%35%45%7%45%
2178
April1st to 10thDay
11%5%25%4345%5%6%50%
1980
11th to 20thDay
12%5%34435%5%6%6%48%
2038
21st to endDay
6%42343446%8%56%
2340
May1st to 10thDay
7%425%5%3445%9%51%
2340
11th to 20thDay
10%5%25%6%45%5%6%9%42%
2301
21st to endDay
10%5%25%6%36%6%8%9%39%
2531
June1st to 10thDay
9%6%26%6%47%7%8%9%35%
2340
11th to 20thDay
5%426%5%47%7%8%12%40%
2340
21st to endDay
5%6%26%7%47%7%9%11%36%
2340
July1st to 10thDay
7%6%37%8%5%7%7%8%11%33%
2340
11th to 20thDay
7%5%36%8%48%7%9%12%31%
2340
21st to endDay
6%5%37%8%5%8%8%10%12%31%
2547
August1st to 10thDay
7%5%36%7%5%8%9%9%12%28%
2327
11th to 20thDay
9%6%37%7%48%8%7%11%30%
2303
21st to endDay
12%7%37%8%47%7%7%9%29%
2280
September1st to 10thDay
7%5%26%7%46%7%7%8%39%
1980
11th to 20thDay
12%5%26%6%35%6%7%8%41%
1980
21st to endDay
16%7%26%5%35%446%43%
1980
October1st to 10thDay
12%5%25%5%235%46%51%
1964
11th to 20thDay
10%41442335%6%57%
1800
21st to endDay
11%3145%34345%57%
1980
November1st to 10thDay
12%5%25%4335%45%52%
1857
11th to 20thDay
14%6%24322345%56%
1726
21st to endDay
15%5%344235%5%7%46%
1710
December1st to 10thDay
15%6%45%5%345%5%7%42%
1710
11th to 20thDay
16%6%24434346%48%
2153
21st to endDay
18%9%26%434346%41%
3124
January1st to 10thNight
15%6%345%2435%6%46%
2459
11th to 20thNight
15%6%35%435%45%6%46%
2417
21st to endNight
17%6%345%24445%46%
2574
February1st to 10thNight
15%6%35%5%3345%6%44%
2192
11th to 20thNight
19%5%2442325%6%47%
2098
21st to endNight
13%6%35%5%445%6%6%43%
1776
March1st to 10thNight
10%5%36%5%35%447%50%
1992
11th to 20thNight
14%42343446%7%49%
1980
21st to endNight
10%435%5%35%5%5%7%48%
2178
April1st to 10thNight
11%4235%3445%8%51%
1980
11th to 20thNight
12%5%25%32445%8%50%
1883
21st to endNight
8%313435%5%6%7%55%
1620
May1st to 10thNight
7%4235%3347%8%54%
1620
11th to 20thNight
7%425%6%47%7%8%10%40%
1592
21st to endNight
10%5%35%5%35%6%6%8%43%
1744
June1st to 10thNight
10%6%36%6%5%6%7%7%11%33%
1620
11th to 20thNight
5%5%35%6%37%5%7%11%42%
1620
21st to endNight
7%5%36%6%37%8%10%12%34%
1620
July1st to 10thNight
8%5%26%5%5%6%8%9%12%33%
1620
11th to 20thNight
6%6%26%8%47%8%9%12%31%
1620
21st to endNight
5%426%7%48%7%9%12%34%
1771
August1st to 10thNight
7%5%26%8%5%8%8%10%13%29%
1611
11th to 20thNight
10%6%25%7%46%7%8%14%30%
1598
21st to endNight
11%7%47%6%46%6%7%10%33%
2052
September1st to 10thNight
10%5%26%5%36%7%8%11%37%
1980
11th to 20thNight
10%6%36%7%45%5%6%8%40%
1980
21st to endNight
12%6%26%5%35%5%48%44%
1980
October1st to 10thNight
11%5%25%433446%52%
1993
11th to 20thNight
12%424423345%57%
2160
21st to endNight
9%5%245%24345%56%
2376
November1st to 10thNight
12%42442335%5%56%
2221
11th to 20thNight
14%6%24334346%52%
2451
21st to endNight
13%5%25%5%2445%6%50%
2470
December1st to 10thNight
14%6%25%42346%7%46%
2470
11th to 20thNight
17%5%25%423345%50%
3042
21st to endNight
18%8%36%5%3445%6%38%
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
38%48%19%26%4
1707
11th to 20thDay
38%48%17%24%8%
1671
21st to endDay
41%35%17%26%8%
1782
February1st to 10thDay
42%5%8%18%19%7%
1766
11th to 20thDay
39%5%6%19%25%7%
1758
21st to endDay
41%6%9%15%20%10%
1480
March1st to 10thDay
34%47%18%22%14%
1966
11th to 20thDay
39%5%12%18%18%8%
1980
21st to endDay
39%6%10%20%20%6%
2178
April1st to 10thDay
35%5%10%20%21%9%
1980
11th to 20thDay
34%6%9%20%20%11%
2038
21st to endDay
26%6%11%25%26%5%
2340
May1st to 10thDay
29%6%11%23%24%6%
2340
11th to 20thDay
35%10%16%21%15%2
2305
21st to endDay
37%10%13%21%17%2
2531
June1st to 10thDay
40%11%16%19%12%2
2340
11th to 20thDay
33%11%17%24%14%1
2340
21st to endDay
37%12%20%17%12%2
2340
July1st to 10thDay
40%12%20%17%7%4
2275
11th to 20thDay
40%14%23%15%6%2
2271
21st to endDay
38%15%22%19%5%1
2405
August1st to 10thDay
43%14%18%19%6%
2314
11th to 20thDay
44%14%18%16%7%1
2303
21st to endDay
47%13%16%14%9%1
2280
September1st to 10thDay
39%10%16%16%15%4
1980
11th to 20thDay
40%8%11%18%19%5%
1980
21st to endDay
42%6%9%17%19%6%
1980
October1st to 10thDay
34%410%19%22%10%
1964
11th to 20thDay
29%48%24%26%9%
1800
21st to endDay
30%46%14%30%16%
1980
November1st to 10thDay
33%5%8%15%24%15%
1857
11th to 20thDay
33%37%20%24%14%
1726
21st to endDay
37%5%9%19%21%9%
1710
December1st to 10thDay
41%7%10%15%21%7%
1710
11th to 20thDay
39%35%18%26%9%
2150
21st to endDay
45%48%17%23%4
3124
January1st to 10thNight
40%47%19%24%7%
2459
11th to 20thNight
40%5%7%17%23%8%
2417
21st to endNight
41%35%15%25%11%
2574
February1st to 10thNight
40%49%17%20%10%
2192
11th to 20thNight
40%47%16%22%10%
2099
21st to endNight
40%6%8%17%17%13%
1776
March1st to 10thNight
35%5%8%16%23%13%
1992
11th to 20thNight
35%7%12%17%20%9%
1980
21st to endNight
34%7%11%19%20%9%
2178
April1st to 10thNight
33%5%10%19%22%11%
1980
11th to 20thNight
32%5%7%21%23%11%
1883
21st to endNight
27%7%11%23%24%8%
1620
May1st to 10thNight
26%7%12%26%21%8%
1620
11th to 20thNight
35%11%17%17%17%3
1593
21st to endNight
36%10%11%20%20%3
1745
June1st to 10thNight
40%12%17%19%11%
1620
11th to 20thNight
34%10%18%24%12%1
1620
21st to endNight
35%15%20%16%10%3
1620
July1st to 10thNight
38%15%20%16%8%3
1575
11th to 20thNight
39%16%23%15%6%1
1566
21st to endNight
36%14%23%20%6%1
1672
August1st to 10thNight
40%19%16%20%5%
1600
11th to 20thNight
41%14%19%18%7%1
1598
21st to endNight
43%14%17%16%9%1
2052
September1st to 10thNight
38%12%17%15%13%5%
1980
11th to 20thNight
40%8%14%15%17%5%
1980
21st to endNight
39%7%13%16%19%6%
1980
October1st to 10thNight
34%5%10%17%25%9%
1993
11th to 20thNight
30%48%19%28%11%
2160
21st to endNight
31%46%17%28%15%
2376
November1st to 10thNight
31%48%15%25%16%
2221
11th to 20thNight
35%47%15%24%15%
2451
21st to endNight
36%48%18%24%10%
2470
December1st to 10thNight
36%7%10%18%22%7%
2470
11th to 20thNight
38%47%15%26%10%
3044
21st to endNight
46%47%16%23%4
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
15%21%40%20%3
270
11th to 20thDay
18%19%33%22%7%2
257
21st to endDay
22%20%40%13%5%
264
February1st to 10thDay
16%19%40%18%7%
240
11th to 20thDay
27%13%37%21%3
240
21st to endDay
21%18%37%18%5%1
198
March1st to 10thDay
16%14%32%25%13%1
406
11th to 20thDay
17%12%39%23%9%
420
21st to endDay
17%14%33%25%10%1
462
April1st to 10thDay
15%15%25%30%13%1
420
11th to 20thDay
13%12%28%22%19%6%
412
21st to endDay
8%10%24%29%22%7%
420
May1st to 10thDay
7%11%26%31%16%9%
423
11th to 20thDay
10%317%29%25%16%
447
21st to endDay
14%213%24%27%19%
485
June1st to 10thDay
13%212%25%29%19%
450
11th to 20thDay
6%313%21%27%30%
450
21st to endDay
7%211%28%30%23%
450
July1st to 10thDay
7%27%17%33%33%
445
11th to 20thDay
8%2418%37%32%
444
21st to endDay
5%17%24%33%31%
488
August1st to 10thDay
10%19%27%30%23%
446
11th to 20thDay
9%35%18%33%31%
439
21st to endDay
13%18%21%31%26%
495
September1st to 10thDay
9%38%23%36%20%
450
11th to 20thDay
14%212%26%31%14%
450
21st to endDay
17%311%27%25%17%
450
October1st to 10thDay
15%320%31%20%11%
450
11th to 20thDay
10%5%20%29%25%12%
450
21st to endDay
13%6%23%29%24%5%
495
November1st to 10thDay
17%5%25%26%21%6%
455
11th to 20thDay
17%10%36%26%9%2
286
21st to endDay
11%16%27%27%16%2
270
December1st to 10thDay
19%15%33%23%9%1
270
11th to 20thDay
20%16%34%21%6%3
270
21st to endDay
29%12%31%21%6%2
297
January1st to 10thNight
19%12%37%26%6%
760
11th to 20thNight
18%10%33%30%9%
744
21st to endNight
19%10%40%28%3
792
February1st to 10thNight
17%11%31%33%8%
720
11th to 20thNight
20%10%36%30%4
703
21st to endNight
16%12%39%29%4
592
March1st to 10thNight
13%9%34%37%7%
720
11th to 20thNight
14%11%33%32%9%1
720
21st to endNight
11%11%37%29%12%
792
April1st to 10thNight
13%10%30%34%12%1
720
11th to 20thNight
13%10%28%31%17%1
701
21st to endNight
9%5%26%41%18%1
540
May1st to 10thNight
8%5%29%39%18%1
540
11th to 20thNight
9%321%40%23%4
531
21st to endNight
11%312%33%38%4
584
June1st to 10thNight
12%212%36%33%4
540
11th to 20thNight
7%311%35%34%11%
540
21st to endNight
7%210%35%38%8%
540
July1st to 10thNight
9%26%27%46%10%
525
11th to 20thNight
8%16%27%47%11%
522
21st to endNight
7%16%33%44%9%
591
August1st to 10thNight
8%16%29%45%11%
537
11th to 20thNight
12%17%29%43%7%
534
21st to endNight
13%27%26%43%9%
687
September1st to 10thNight
10%37%30%42%8%
720
11th to 20thNight
13%212%28%41%4
720
21st to endNight
15%313%33%32%5%
720
October1st to 10thNight
14%217%38%24%6%
720
11th to 20thNight
15%320%33%25%4
720
21st to endNight
11%5%23%36%23%1
792
November1st to 10thNight
14%5%21%34%21%3
740
11th to 20thNight
16%10%26%33%13%2
760
21st to endNight
15%6%27%34%16%1
760
December1st to 10thNight
15%9%29%35%10%2
760
11th to 20thNight
18%8%29%31%13%1
760
21st to endNight
24%9%26%31%9%
836
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