Nashville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nashville clear sky chart from 2005-11-05 to 2017-08-12.

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%
15358
23%
46386
16%
15314
53%
15314
28%
28903

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
27%
900
20%
2506
10%
895
36%
895
22%
1708
January16th to endNight
27%
782
21%
2396
10%
782
38%
782
20%
1622
February1st to 15thNight
26%
704
19%
2112
10%
701
34%
701
20%
1456
February16th to endNight
23%
631
20%
1893
9%
631
32%
631
20%
1300
March1st to 15thNight
31%
720
18%
2160
11%
720
37%
720
21%
1462
March16th to endNight
35%
696
19%
2040
13%
696
41%
696
24%
1346
April1st to 15thNight
39%
539
25%
1797
15%
539
53%
539
30%
1014
April16th to endNight
41%
540
24%
1776
17%
540
52%
540
29%
1047
May1st to 15thNight
42%
540
20%
1620
12%
540
49%
540
27%
1038
May16th to endNight
60%
561
19%
1683
13%
561
63%
561
32%
1026
June1st to 15thNight
71%
540
20%
1548
15%
540
74%
540
39%
898
June16th to endNight
77%
540
24%
1440
18%
540
79%
540
45%
826
July1st to 15thNight
69%
510
17%
1360
13%
510
71%
510
36%
851
July16th to endNight
77%
564
22%
1564
20%
531
79%
531
40%
897
August1st to 15thNight
77%
527
23%
1702
24%
524
78%
524
38%
935
August16th to endNight
75%
525
20%
1750
24%
525
76%
525
32%
1007
September1st to 15thNight
62%
553
23%
1708
23%
553
66%
553
29%
1066
September16th to endNight
61%
657
29%
1815
22%
657
65%
657
36%
1095
October1st to 15thNight
55%
660
34%
1815
26%
660
60%
660
36%
1077
October16th to endNight
48%
704
30%
2192
24%
704
57%
704
33%
1268
November1st to 15thNight
49%
700
31%
2276
26%
700
59%
700
33%
1264
November16th to endNight
40%
720
27%
2340
20%
720
51%
720
29%
1385
December1st to 15thNight
32%
720
20%
2340
15%
720
40%
720
20%
1558
December16th to endNight
30%
825
20%
2553
11%
825
39%
825
20%
1757

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%6%25%5%35%5%5%7%39%
47573
Night
12%5%25%42445%7%44%
46573
TransparencyDay
41%5%10%22%16%3
47263
Night
38%410%22%18%4
46387
SeeingDay
13%7%20%24%21%12%
5421
Night
15%7%23%30%20%3
15360

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
19%6%45%5%35%35%6%34%
1432
16th to endDay
16%7%35%5%23345%40%
1820
February1st to 15thDay
16%9%37%5%2335%6%35%
1750
16th to endDay
15%9%46%5%34447%34%
1580
March1st to 15thDay
17%9%35%5%24346%36%
1800
16th to endDay
14%6%47%7%35%5%5%7%33%
2192
April1st to 15thDay
11%5%2443445%7%44%
2151
16th to endDay
12%5%36%6%25%447%41%
2184
May1st to 15thDay
15%5%35%42445%7%39%
2331
16th to endDay
8%5%35%6%36%6%6%8%38%
2431
June1st to 15thDay
7%3245%46%7%7%9%41%
2406
16th to endDay
4325%6%37%6%7%10%40%
2520
July1st to 15thDay
7%426%7%48%8%7%10%32%
2520
16th to endDay
6%425%7%48%6%9%11%34%
2495
August1st to 15thDay
5%426%7%48%6%7%9%36%
2158
16th to endDay
10%6%16%6%46%6%7%9%33%
2100
September1st to 15thDay
11%6%35%6%35%6%7%8%34%
1909
16th to endDay
11%5%245%34446%48%
1815
October1st to 15thDay
11%5%14423346%51%
1815
16th to endDay
15%314323335%53%
1677
November1st to 15thDay
14%5%13322337%52%
1582
16th to endDay
15%5%24324345%47%
1620
December1st to 15thDay
22%8%35%423346%34%
1620
16th to endDay
19%8%26%5%23345%37%
1665
January1st to 15thNight
17%7%36%424346%38%
2506
16th to endNight
17%8%35%5%33445%37%
2396
February1st to 15thNight
18%8%47%42433437%
2103
16th to endNight
17%8%46%6%3344436%
1893
March1st to 15thNight
16%6%35%436%346%39%
2160
16th to endNight
14%6%45%5%2435%7%40%
2040
April1st to 15thNight
11%5%143235%5%7%49%
1797
16th to endNight
12%42442445%7%46%
1776
May1st to 15thNight
11%5%35%5%3445%6%44%
1619
16th to endNight
5%316%5%35%5%6%11%44%
1682
June1st to 15thNight
5%414435%46%9%49%
1548
16th to endNight
2234346%8%13%49%
1440
July1st to 15thNight
8%425%4246%6%11%43%
1440
16th to endNight
5%223435%5%7%12%47%
1671
August1st to 15thNight
431443446%12%48%
1713
16th to endNight
7%3244345%7%10%45%
1750
September1st to 15thNight
10%5%35%5%35%46%7%45%
1708
16th to endNight
10%42442445%6%51%
1815
October1st to 15thNight
12%414323245%54%
1815
16th to endNight
15%423313236%52%
2192
November1st to 15thNight
12%324323345%53%
2276
16th to endNight
15%434323345%48%
2340
December1st to 15thNight
18%9%35%423445%37%
2340
16th to endNight
21%9%36%323335%36%
2553

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
49%37%21%15%2
1433
16th to endDay
46%39%25%13%1
1820
February1st to 15thDay
50%38%22%12%2
1752
16th to endDay
49%410%20%12%2
1580
March1st to 15thDay
49%38%20%13%4
1800
16th to endDay
49%6%10%21%11%
2193
April1st to 15thDay
38%49%23%19%3
2151
16th to endDay
42%47%24%17%3
2184
May1st to 15thDay
43%5%11%22%16%1
2331
16th to endDay
41%7%14%21%13%2
2435
June1st to 15thDay
34%8%13%23%17%1
2406
16th to endDay
34%7%12%22%18%5%
2520
July1st to 15thDay
41%9%16%18%10%3
2371
16th to endDay
37%8%18%22%10%2
2339
August1st to 15thDay
39%6%15%21%14%2
2145
16th to endDay
42%8%12%19%14%3
2100
September1st to 15thDay
44%7%11%18%14%4
1909
16th to endDay
35%49%21%24%3
1815
October1st to 15thDay
33%47%23%25%5%
1815
16th to endDay
34%36%22%28%5%
1677
November1st to 15thDay
33%26%22%26%7%
1582
16th to endDay
38%36%28%19%3
1620
December1st to 15thDay
50%37%21%14%2
1620
16th to endDay
49%411%21%12%1
1665
January1st to 15thNight
46%37%21%17%2
2506
16th to endNight
48%38%21%15%2
2396
February1st to 15thNight
49%38%21%14%1
2112
16th to endNight
49%37%21%15%2
1893
March1st to 15thNight
46%5%8%17%17%5%
2160
16th to endNight
43%411%26%12%1
2040
April1st to 15thNight
33%310%24%21%5%
1797
16th to endNight
35%48%26%20%3
1776
May1st to 15thNight
40%5%11%23%17%1
1620
16th to endNight
32%8%17%23%16%2
1684
June1st to 15thNight
27%7%16%29%17%1
1548
16th to endNight
23%7%17%30%15%5%
1440
July1st to 15thNight
31%8%16%23%15%5%
1360
16th to endNight
27%6%19%27%15%2
1564
August1st to 15thNight
27%6%17%28%18%2
1702
16th to endNight
31%6%16%23%17%4
1750
September1st to 15thNight
37%5%12%20%17%4
1708
16th to endNight
33%47%19%26%7%
1815
October1st to 15thNight
32%46%20%28%7%
1815
16th to endNight
34%3422%27%7%
2192
November1st to 15thNight
32%35%21%27%10%
2276
16th to endNight
37%28%24%22%4
2340
December1st to 15thNight
47%47%20%15%4
2340
16th to endNight
51%39%19%15%1
2553

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
30%20%30%11%6%2
90
16th to endDay
20%10%54%10%31
96
February1st to 15thDay
25%21%38%11%21
90
16th to endDay
27%24%30%14%2
81
March1st to 15thDay
21%22%44%8%3
90
16th to endDay
14%14%32%23%13%1
288
April1st to 15thDay
13%16%24%31%11%2
270
16th to endDay
17%8%26%26%16%5%
270
May1st to 15thDay
20%11%22%22%12%9%
288
16th to endDay
12%421%25%21%14%
331
June1st to 15thDay
8%313%22%29%21%
381
16th to endDay
6%119%31%24%16%
495
July1st to 15thDay
9%217%31%24%14%
475
16th to endDay
6%27%18%32%31%
355
August1st to 15thDay
9%28%22%35%23%
297
16th to endDay
15%2324%35%18%
268
September1st to 15thDay
11%310%22%30%21%
255
16th to endDay
16%312%26%31%9%
254
October1st to 15thDay
16%323%23%25%7%
255
16th to endDay
19%8%19%35%11%3
126
November1st to 15thDay
17%13%18%34%12%3
90
16th to endDay
21%20%30%25%21
90
December1st to 15thDay
22%17%40%12%7%
90
16th to endDay
19%18%40%17%3
96
January1st to 15thNight
21%16%30%25%5%
900
16th to endNight
21%11%33%30%3
782
February1st to 15thNight
21%13%33%27%3
704
16th to endNight
22%14%34%25%2
631
March1st to 15thNight
20%11%32%28%6%
720
16th to endNight
16%10%31%28%11%1
696
April1st to 15thNight
13%11%33%29%10%1
539
16th to endNight
14%9%30%33%10%
540
May1st to 15thNight
13%6%30%29%18%1
540
16th to endNight
7%220%35%29%4
563
June1st to 15thNight
7%211%41%31%5%
540
16th to endNight
411%35%42%6%
540
July1st to 15thNight
9%10%33%37%7%
510
16th to endNight
6%7%25%48%11%
564
August1st to 15thNight
5%6%29%49%7%
527
16th to endNight
8%1436%39%9%
525
September1st to 15thNight
10%311%26%39%7%
553
16th to endNight
12%214%30%36%3
657
October1st to 15thNight
13%5%17%28%28%6%
660
16th to endNight
18%5%23%31%20%1
704
November1st to 15thNight
14%8%22%30%21%3
700
16th to endNight
18%10%27%30%12%
720
December1st to 15thNight
25%8%28%27%8%1
720
16th to endNight
24%10%30%28%6%
825
Page generated at 2017-08-13 13:16:41. Version ac04

Copyright 2017 A. Danko


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