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 2018-02-22.

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%
16130
23%
48740
17%
16086
53%
16086
28%
30376

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%
975
19%
2716
9%
970
36%
970
22%
1849
January16th to endNight
28%
847
21%
2595
11%
847
38%
847
21%
1736
February1st to 15thNight
26%
764
18%
2292
9%
761
34%
761
20%
1599
February16th to endNight
22%
659
20%
1977
9%
659
31%
659
19%
1370
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
76%
539
22%
1740
23%
536
77%
536
37%
969
August16th to endNight
75%
573
21%
1910
25%
573
76%
573
31%
1108
September1st to 15thNight
62%
604
22%
1864
21%
604
65%
604
29%
1162
September16th to endNight
64%
717
31%
1980
24%
717
67%
717
38%
1167
October1st to 15thNight
56%
720
33%
1980
25%
720
61%
720
36%
1174
October16th to endNight
48%
768
31%
2391
25%
768
57%
768
33%
1377
November1st to 15thNight
48%
760
30%
2471
26%
760
57%
760
32%
1399
November16th to endNight
42%
780
28%
2535
22%
780
53%
780
30%
1473
December1st to 15thNight
33%
780
21%
2535
15%
780
41%
780
20%
1682
December16th to endNight
29%
894
19%
2766
11%
894
38%
894
19%
1906

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%
49498
Night
12%5%25%42445%7%44%
48927
TransparencyDay
41%5%10%22%16%3
49188
Night
38%410%22%18%4
48741
SeeingDay
14%8%20%24%20%11%
6072
Night
15%7%23%30%20%3
16132

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%35%5%35%346%34%
1552
16th to endDay
16%7%35%5%23345%41%
1972
February1st to 15thDay
16%9%37%5%3335%6%34%
1900
16th to endDay
16%9%46%5%34447%33%
1643
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%
2206
16th to endDay
10%6%25%6%46%6%7%9%33%
2292
September1st to 15thDay
12%6%35%6%35%5%7%8%35%
2082
16th to endDay
10%4245%24447%50%
1980
October1st to 15thDay
12%5%2442335%6%50%
1980
16th to endDay
14%414323335%53%
1830
November1st to 15thDay
14%5%23322337%50%
1717
16th to endDay
14%5%24324345%49%
1755
December1st to 15thDay
21%9%34423346%35%
1755
16th to endDay
20%9%36%5%23345%36%
1804
January1st to 15thNight
17%7%36%424345%39%
2716
16th to endNight
17%8%35%5%33345%38%
2595
February1st to 15thNight
19%8%47%42434436%
2283
16th to endNight
16%8%46%6%33445%35%
1977
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
5%325%43446%12%47%
1751
16th to endNight
7%3245%35%5%7%10%44%
1910
September1st to 15thNight
11%435%43445%6%45%
1864
16th to endNight
9%42342445%6%53%
1980
October1st to 15thNight
11%414423345%53%
1980
16th to endNight
15%423313336%52%
2391
November1st to 15thNight
12%424323346%51%
2471
16th to endNight
14%434323345%50%
2535
December1st to 15thNight
17%9%35%423445%38%
2535
16th to endNight
21%9%36%324345%36%
2766

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
50%36%21%15%2
1553
16th to endDay
45%38%25%14%1
1972
February1st to 15thDay
51%38%22%11%2
1902
16th to endDay
50%310%20%12%2
1643
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
2193
16th to endDay
41%8%12%19%14%2
2292
September1st to 15thDay
43%6%11%20%14%3
2082
16th to endDay
33%410%24%23%3
1980
October1st to 15thDay
33%47%24%23%5%
1980
16th to endDay
34%36%21%29%5%
1830
November1st to 15thDay
35%26%22%25%7%
1717
16th to endDay
37%35%28%21%3
1755
December1st to 15thDay
49%38%21%14%2
1755
16th to endDay
50%311%20%11%1
1804
January1st to 15thNight
46%38%21%17%2
2716
16th to endNight
47%37%21%16%2
2595
February1st to 15thNight
50%38%21%13%1
2292
16th to endNight
50%37%20%14%2
1977
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
28%6%17%27%18%2
1740
16th to endNight
32%6%15%24%17%3
1910
September1st to 15thNight
38%5%11%22%17%4
1864
16th to endNight
31%49%21%26%6%
1980
October1st to 15thNight
32%46%21%27%7%
1980
16th to endNight
33%3422%27%7%
2391
November1st to 15thNight
34%35%21%25%9%
2471
16th to endNight
36%28%23%24%4
2535
December1st to 15thNight
47%47%20%16%3
2535
16th to endNight
50%39%19%14%1
2766

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
26%22%34%8%6%2
135
16th to endDay
20%12%47%12%5%1
144
February1st to 15thDay
26%20%35%14%2
135
16th to endDay
32%22%31%13%2
100
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
10%17%22%34%22%
313
16th to endDay
13%37%25%32%17%
332
September1st to 15thDay
15%211%21%29%19%
315
16th to endDay
13%312%25%33%11%
314
October1st to 15thDay
16%321%24%26%6%
315
16th to endDay
16%10%24%31%11%4
177
November1st to 15thDay
21%13%22%29%10%2
135
16th to endDay
17%14%30%26%9%1
135
December1st to 15thDay
19%20%38%12%8%
135
16th to endDay
26%22%33%15%2
144
January1st to 15thNight
21%16%29%25%5%
975
16th to endNight
21%11%32%30%4
847
February1st to 15thNight
22%13%32%26%4
764
16th to endNight
23%15%34%24%2
659
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%7%29%48%7%
539
16th to endNight
8%1436%40%8%
573
September1st to 15thNight
12%212%26%38%6%
604
16th to endNight
11%113%29%38%4
717
October1st to 15thNight
13%5%17%29%28%5%
720
16th to endNight
17%5%23%30%20%1
768
November1st to 15thNight
14%8%23%30%20%2
760
16th to endNight
17%9%26%31%13%
780
December1st to 15thNight
23%9%27%28%8%1
780
16th to endNight
24%11%30%28%5%
894
Page generated at 2018-02-23 10:21:28. Version ac04

Copyright 2018 A. Danko


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