Chattanooga
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chattanooga 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
43%
15252
22%
46571
15%
15209
51%
15209
25%
28798

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
22%
720
21%
2327
9%
716
36%
716
18%
1514
January16th to endNight
27%
768
23%
2423
12%
768
39%
768
20%
1584
February1st to 15thNight
25%
704
21%
2112
9%
701
37%
701
21%
1343
February16th to endNight
22%
631
22%
1893
9%
631
33%
631
20%
1251
March1st to 15thNight
29%
720
21%
2106
12%
720
37%
720
21%
1356
March16th to endNight
30%
768
19%
2112
9%
768
37%
768
23%
1374
April1st to 15thNight
38%
560
26%
1818
16%
560
52%
560
30%
1011
April16th to endNight
40%
540
25%
1731
16%
540
52%
540
28%
986
May1st to 15thNight
43%
540
20%
1620
12%
540
51%
540
26%
1008
May16th to endNight
54%
561
20%
1683
12%
561
60%
561
25%
1039
June1st to 15thNight
61%
540
17%
1620
12%
540
65%
540
30%
956
June16th to endNight
64%
540
18%
1620
13%
540
68%
540
33%
937
July1st to 15thNight
64%
510
14%
1530
12%
510
66%
510
29%
953
July16th to endNight
64%
564
18%
1595
14%
531
71%
531
30%
963
August1st to 15thNight
67%
527
20%
1642
19%
524
70%
524
28%
1000
August16th to endNight
63%
525
19%
1750
21%
525
65%
525
24%
1107
September1st to 15thNight
60%
605
19%
1760
16%
605
63%
605
25%
1151
September16th to endNight
56%
657
26%
1815
17%
657
62%
657
30%
1128
October1st to 15thNight
53%
660
34%
1815
26%
660
60%
660
35%
1060
October16th to endNight
49%
704
32%
2147
25%
704
59%
704
34%
1223
November1st to 15thNight
45%
700
30%
2276
24%
700
57%
700
31%
1233
November16th to endNight
33%
720
26%
2340
15%
720
48%
720
23%
1399
December1st to 15thNight
30%
720
22%
2340
12%
720
41%
720
18%
1522
December16th to endNight
26%
768
19%
2496
10%
768
37%
768
15%
1700

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%40%
47401
Night
12%5%2443445%7%45%
46769
TransparencyDay
40%6%11%20%16%3
47102
Night
37%5%11%21%18%4
46572
SeeingDay
14%12%16%21%21%12%
5118
Night
13%19%18%26%18%3
15254

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
20%7%25%5%24345%38%
1611
16th to endDay
17%5%145%24345%44%
1800
February1st to 15thDay
16%7%26%424435%40%
1750
16th to endDay
16%6%25%5%25%45%7%38%
1580
March1st to 15thDay
16%5%35%435%446%39%
1854
16th to endDay
15%5%25%5%35%45%7%38%
2111
April1st to 15thDay
12%4245%245%5%7%43%
2139
16th to endDay
12%425%5%35%447%43%
2228
May1st to 15thDay
13%435%5%34447%42%
2331
16th to endDay
11%4245%37%5%6%10%37%
2431
June1st to 15thDay
6%325%6%47%7%8%10%37%
2340
16th to endDay
5%3146%45%6%7%10%41%
2340
July1st to 15thDay
10%325%6%48%7%8%9%32%
2340
16th to endDay
7%426%7%48%10%7%11%30%
2465
August1st to 15thDay
6%327%7%5%8%7%8%10%33%
2218
16th to endDay
13%6%26%6%5%7%6%7%8%28%
2100
September1st to 15thDay
13%5%26%6%35%5%6%7%35%
1859
16th to endDay
15%4245%24345%46%
1815
October1st to 15thDay
12%324413335%55%
1815
16th to endDay
12%413323445%55%
1724
November1st to 15thDay
11%424424435%53%
1582
16th to endDay
18%4132235%46%46%
1620
December1st to 15thDay
17%7%36%5%33445%37%
1620
16th to endDay
22%8%25%5%2333436%
1728
January1st to 15thNight
18%6%35%334335%41%
2327
16th to endNight
16%7%24435%45%6%39%
2423
February1st to 15thNight
15%7%24433345%45%
2103
16th to endNight
18%5%25%4335%45%40%
1893
March1st to 15thNight
16%5%25%42445%8%41%
2106
16th to endNight
13%6%35%424445%44%
2112
April1st to 15thNight
12%32341345%8%51%
1818
16th to endNight
10%42332345%6%51%
1731
May1st to 15thNight
11%5%13435%45%8%44%
1619
16th to endNight
7%3135%45%5%6%9%46%
1682
June1st to 15thNight
43146%35%5%7%12%46%
1620
16th to endNight
41225%35%5%7%12%49%
1620
July1st to 15thNight
9%423446%6%7%10%40%
1620
16th to endNight
4324436%6%8%13%41%
1703
August1st to 15thNight
5%325%435%6%9%10%43%
1653
16th to endNight
10%425%5%35%5%6%10%39%
1750
September1st to 15thNight
9%415%6%45%5%6%11%38%
1760
16th to endNight
12%42342345%8%47%
1815
October1st to 15thNight
12%313423336%56%
1815
16th to endNight
12%42432333357%
2147
November1st to 15thNight
12%423223336%55%
2276
16th to endNight
15%6%24423235%48%
2340
December1st to 15thNight
16%5%35%5%34445%41%
2340
16th to endNight
22%6%34434346%35%
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
48%37%19%18%2
1612
16th to endDay
42%39%25%16%2
1800
February1st to 15thDay
46%39%21%16%2
1752
16th to endDay
45%310%19%17%3
1580
March1st to 15thDay
45%5%9%19%16%3
1854
16th to endDay
44%5%12%23%12%1
2112
April1st to 15thDay
38%5%11%22%18%3
2139
16th to endDay
39%5%9%22%19%3
2228
May1st to 15thDay
40%6%11%24%15%2
2331
16th to endDay
38%9%14%21%13%2
2435
June1st to 15thDay
35%10%18%23%12%
2340
16th to endDay
32%9%17%21%15%4
2340
July1st to 15thDay
40%12%17%17%8%3
2201
16th to endDay
40%11%18%18%9%1
2310
August1st to 15thDay
38%10%17%19%12%1
2205
16th to endDay
47%9%13%16%10%2
2100
September1st to 15thDay
43%8%12%16%13%4
1859
16th to endDay
37%5%9%19%22%4
1815
October1st to 15thDay
31%47%20%25%9%
1815
16th to endDay
32%36%22%28%6%
1724
November1st to 15thDay
34%36%19%28%7%
1582
16th to endDay
38%36%24%23%3
1620
December1st to 15thDay
49%36%21%15%3
1620
16th to endDay
52%310%18%12%2
1728
January1st to 15thNight
46%38%18%19%3
2327
16th to endNight
45%47%21%17%4
2423
February1st to 15thNight
42%310%22%17%5%
2112
16th to endNight
45%38%23%16%2
1893
March1st to 15thNight
41%49%20%17%6%
2106
16th to endNight
41%411%26%15%1
2112
April1st to 15thNight
31%311%25%21%5%
1818
16th to endNight
32%411%24%21%4
1731
May1st to 15thNight
36%6%14%21%19%2
1620
16th to endNight
32%9%16%24%14%2
1684
June1st to 15thNight
28%9%19%27%12%1
1620
16th to endNight
26%9%20%22%16%4
1620
July1st to 15thNight
33%8%20%20%13%3
1530
16th to endNight
29%10%22%20%13%3
1595
August1st to 15thNight
31%11%17%23%14%2
1642
16th to endNight
38%8%17%20%13%1
1750
September1st to 15thNight
37%9%18%17%12%4
1760
16th to endNight
34%6%9%20%23%5%
1815
October1st to 15thNight
30%48%22%24%9%
1815
16th to endNight
33%2320%28%11%
2147
November1st to 15thNight
31%25%21%27%11%
2276
16th to endNight
39%25%22%24%5%
2340
December1st to 15thNight
44%48%19%18%4
2340
16th to endNight
50%310%17%15%2
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
26%21%18%21%11%1
90
16th to endDay
20%18%46%9%4
96
February1st to 15thDay
16%27%43%11%1
90
16th to endDay
27%12%37%22%1
81
March1st to 15thDay
18%25%27%25%12
144
16th to endDay
16%18%28%23%12%
288
April1st to 15thDay
17%19%20%24%16%1
270
16th to endDay
14%17%19%24%19%4
270
May1st to 15thDay
11%18%26%19%13%10%
288
16th to endDay
17%12%14%19%21%12%
331
June1st to 15thDay
10%10%6%22%26%22%
315
16th to endDay
7%10%12%23%24%21%
315
July1st to 15thDay
11%7%6%25%28%20%
305
16th to endDay
7%10%415%28%33%
326
August1st to 15thDay
13%7%9%22%28%18%
297
16th to endDay
17%7%5%17%30%21%
268
September1st to 15thDay
11%7%6%17%37%19%
255
16th to endDay
17%8%10%22%30%11%
254
October1st to 15thDay
16%6%17%27%24%6%
255
16th to endDay
11%9%20%26%26%6%
214
November1st to 15thDay
20%11%23%25%17%2
90
16th to endDay
16%12%31%21%17%1
90
December1st to 15thDay
24%17%34%16%6%
90
16th to endDay
31%20%27%18%2
96
January1st to 15thNight
20%26%28%20%4
720
16th to endNight
16%23%27%28%3
768
February1st to 15thNight
17%25%28%25%2
704
16th to endNight
18%24%31%22%3
631
March1st to 15thNight
17%26%23%27%5%
720
16th to endNight
15%23%25%24%9%
768
April1st to 15thNight
11%22%25%27%13%
560
16th to endNight
13%20%22%32%11%
540
May1st to 15thNight
11%18%22%28%17%2
540
16th to endNight
10%18%10%28%28%4
563
June1st to 15thNight
417%8%27%34%8%
540
16th to endNight
417%7%25%35%10%
540
July1st to 15thNight
10%12%7%26%35%9%
510
16th to endNight
6%17%6%17%39%14%
564
August1st to 15thNight
9%10%6%25%42%7%
527
16th to endNight
12%9%5%23%40%8%
525
September1st to 15thNight
10%10%8%24%38%7%
605
16th to endNight
16%10%10%26%34%2
657
October1st to 15thNight
13%12%16%27%25%5%
660
16th to endNight
13%13%20%30%20%2
704
November1st to 15thNight
13%19%18%28%17%2
700
16th to endNight
15%23%22%27%10%
720
December1st to 15thNight
17%24%23%25%8%
720
16th to endNight
22%23%23%25%4
768
Page generated at 2017-08-13 14:16:58. Version ac04

Copyright 2017 A. Danko


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