Huntsville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Huntsville 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
51%
15138
23%
46464
18%
15095
57%
15095
29%
28556

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
28%
720
23%
2327
11%
716
42%
716
21%
1504
January16th to endNight
31%
768
24%
2355
13%
768
41%
768
22%
1547
February1st to 15thNight
32%
704
22%
2112
11%
701
43%
701
27%
1337
February16th to endNight
29%
631
23%
1893
12%
631
38%
631
23%
1254
March1st to 15thNight
32%
720
19%
2151
11%
720
37%
720
22%
1426
March16th to endNight
40%
714
21%
2058
14%
714
46%
714
29%
1299
April1st to 15thNight
43%
539
24%
1797
17%
539
54%
539
32%
1009
April16th to endNight
51%
540
26%
1791
21%
540
60%
540
34%
988
May1st to 15thNight
55%
540
21%
1620
15%
540
61%
540
30%
1016
May16th to endNight
70%
561
21%
1682
18%
561
72%
561
35%
1002
June1st to 15thNight
71%
540
20%
1620
17%
540
74%
540
35%
972
June16th to endNight
79%
540
20%
1546
18%
540
80%
540
39%
891
July1st to 15thNight
73%
510
15%
1476
13%
510
74%
510
28%
966
July16th to endNight
77%
564
19%
1595
18%
531
79%
531
34%
967
August1st to 15thNight
77%
527
19%
1733
22%
524
78%
524
33%
997
August16th to endNight
72%
525
20%
1750
25%
525
72%
525
26%
1087
September1st to 15thNight
67%
566
21%
1721
21%
566
68%
566
31%
1058
September16th to endNight
62%
657
28%
1815
22%
657
64%
657
34%
1104
October1st to 15thNight
59%
660
35%
1815
29%
660
62%
660
38%
1074
October16th to endNight
53%
704
33%
2155
29%
704
59%
704
35%
1226
November1st to 15thNight
52%
700
29%
2276
26%
700
60%
700
34%
1259
November16th to endNight
42%
720
27%
2340
20%
720
53%
720
28%
1385
December1st to 15thNight
37%
720
22%
2340
16%
720
46%
720
22%
1492
December16th to endNight
31%
768
20%
2496
15%
768
39%
768
19%
1696

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%
47477
Night
12%5%2442445%7%45%
46663
TransparencyDay
41%6%11%20%16%3
47178
Night
37%5%10%21%19%5%
46466
SeeingDay
16%6%16%22%22%15%
5114
Night
15%6%21%29%23%4
15140

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%8%25%31435%5%38%
1611
16th to endDay
20%5%34313345%43%
1867
February1st to 15thDay
19%8%35%334335%39%
1750
16th to endDay
19%7%35%5%24345%38%
1580
March1st to 15thDay
17%9%36%5%2345%5%37%
1809
16th to endDay
15%5%25%435%46%7%38%
2176
April1st to 15thDay
14%5%2442345%7%44%
2151
16th to endDay
12%5%25%5%345%5%8%43%
2166
May1st to 15thDay
15%424426%5%5%7%41%
2331
16th to endDay
11%5%35%5%35%5%5%8%41%
2431
June1st to 15thDay
8%4245%47%7%7%10%37%
2340
16th to endDay
6%425%5%26%5%7%11%42%
2399
July1st to 15thDay
9%5%36%6%37%6%8%10%31%
2381
16th to endDay
8%425%6%48%8%8%9%32%
2465
August1st to 15thDay
6%425%6%5%7%7%9%9%35%
2127
16th to endDay
11%5%36%6%46%7%6%9%31%
2100
September1st to 15thDay
11%5%25%5%45%5%7%9%36%
1898
16th to endDay
12%424434447%47%
1815
October1st to 15thDay
10%3145%34345%52%
1815
16th to endDay
12%314313335%55%
1715
November1st to 15thDay
13%5%13324235%54%
1582
16th to endDay
15%5%23423446%47%
1620
December1st to 15thDay
20%6%36%424445%36%
1620
16th to endDay
23%8%345%13345%35%
1728
January1st to 15thNight
18%6%34424335%42%
2327
16th to endNight
17%8%35%424445%40%
2355
February1st to 15thNight
18%6%34313346%44%
2103
16th to endNight
18%6%25%423445%41%
1893
March1st to 15thNight
18%5%25%5%3445%6%39%
2151
16th to endNight
14%5%25%424347%45%
2058
April1st to 15thNight
13%31432335%9%48%
1797
16th to endNight
10%42342335%7%52%
1791
May1st to 15thNight
10%424435%5%5%7%46%
1619
16th to endNight
6%313436%5%6%9%47%
1682
June1st to 15thNight
5%3245%25%5%6%12%45%
1620
16th to endNight
42135%45%5%6%12%49%
1546
July1st to 15thNight
9%325%5%46%6%5%9%41%
1566
16th to endNight
5%3245%25%6%8%13%41%
1703
August1st to 15thNight
5%314435%6%8%10%45%
1744
16th to endNight
8%425%5%46%5%6%8%42%
1750
September1st to 15thNight
7%5%25%5%245%5%8%46%
1721
16th to endNight
9%425%424448%48%
1815
October1st to 15thNight
10%42342344456%
1815
16th to endNight
13%5%23312335%56%
2155
November1st to 15thNight
12%5%22313435%55%
2276
16th to endNight
15%5%24423345%49%
2340
December1st to 15thNight
17%6%24423447%41%
2340
16th to endNight
21%8%44423335%37%
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
47%36%18%20%3
1612
16th to endDay
42%37%23%18%3
1867
February1st to 15thDay
47%36%21%18%2
1752
16th to endDay
47%47%20%16%3
1580
March1st to 15thDay
48%47%16%16%5%
1809
16th to endDay
43%5%14%21%13%1
2177
April1st to 15thDay
38%5%10%22%16%5%
2151
16th to endDay
38%5%9%23%18%3
2166
May1st to 15thDay
42%6%10%22%14%3
2331
16th to endDay
39%7%12%25%13%1
2435
June1st to 15thDay
38%9%14%22%14%1
2340
16th to endDay
34%7%15%20%17%3
2399
July1st to 15thDay
40%10%17%19%8%3
2242
16th to endDay
39%11%18%21%8%
2310
August1st to 15thDay
39%10%15%18%13%1
2114
16th to endDay
45%10%11%19%10%1
2100
September1st to 15thDay
42%8%15%16%12%4
1898
16th to endDay
36%5%10%20%22%5%
1815
October1st to 15thDay
33%5%7%18%26%8%
1815
16th to endDay
32%3419%30%9%
1715
November1st to 15thDay
33%3419%30%8%
1582
16th to endDay
38%36%20%25%5%
1620
December1st to 15thDay
49%46%19%15%4
1620
16th to endDay
51%310%18%13%2
1728
January1st to 15thNight
45%36%20%20%3
2327
16th to endNight
45%37%19%18%5%
2355
February1st to 15thNight
41%39%21%19%5%
2112
16th to endNight
45%36%21%18%4
1893
March1st to 15thNight
45%47%18%17%6%
2151
16th to endNight
39%312%24%18%1
2058
April1st to 15thNight
33%412%22%20%7%
1797
16th to endNight
31%310%25%22%5%
1791
May1st to 15thNight
35%7%11%20%22%2
1620
16th to endNight
30%8%17%24%15%3
1684
June1st to 15thNight
30%8%16%25%17%1
1620
16th to endNight
27%7%17%23%20%3
1546
July1st to 15thNight
35%10%17%20%10%4
1476
16th to endNight
28%10%19%25%14%1
1595
August1st to 15thNight
28%9%19%21%17%3
1733
16th to endNight
36%8%15%23%12%3
1750
September1st to 15thNight
35%7%19%17%15%5%
1721
16th to endNight
33%5%8%20%22%8%
1815
October1st to 15thNight
31%46%21%25%10%
1815
16th to endNight
32%3316%31%12%
2155
November1st to 15thNight
31%35%19%25%13%
2276
16th to endNight
38%36%18%26%7%
2340
December1st to 15thNight
43%48%18%19%5%
2340
16th to endNight
49%48%18%16%3
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
22%23%28%17%6%1
90
16th to endDay
22%23%36%12%4
96
February1st to 15thDay
25%28%30%13%2
90
16th to endDay
25%12%35%20%4
81
March1st to 15thDay
25%24%28%17%5%
99
16th to endDay
20%9%27%27%13%1
288
April1st to 15thDay
17%13%22%28%16%2
270
16th to endDay
17%6%21%30%18%5%
270
May1st to 15thDay
15%9%21%24%15%11%
288
16th to endDay
16%5%12%26%19%18%
331
June1st to 15thDay
10%28%20%28%29%
315
16th to endDay
9%112%25%25%24%
374
July1st to 15thDay
13%110%20%28%26%
346
16th to endDay
11%1314%31%37%
326
August1st to 15thDay
12%18%19%32%26%
297
16th to endDay
16%16%17%35%21%
268
September1st to 15thDay
11%29%19%32%24%
255
16th to endDay
19%10%24%38%6%
254
October1st to 15thDay
12%420%30%24%8%
255
16th to endDay
16%416%33%21%7%
155
November1st to 15thDay
22%10%23%27%15%1
90
16th to endDay
13%20%31%23%10%2
90
December1st to 15thDay
26%14%36%13%8%
90
16th to endDay
27%19%33%15%4
96
January1st to 15thNight
22%13%32%23%7%
720
16th to endNight
20%11%32%30%4
768
February1st to 15thNight
21%10%31%30%5%
704
16th to endNight
23%12%31%29%3
631
March1st to 15thNight
21%10%30%30%6%
720
16th to endNight
14%10%28%30%15%
714
April1st to 15thNight
14%6%30%30%15%1
539
16th to endNight
12%5%26%37%17%1
540
May1st to 15thNight
14%221%32%25%3
540
16th to endNight
8%111%38%34%4
563
June1st to 15thNight
7%19%30%42%9%
540
16th to endNight
5%6%28%49%9%
540
July1st to 15thNight
9%7%28%40%13%
510
16th to endNight
7%6%21%45%18%
564
August1st to 15thNight
6%423%53%11%
527
16th to endNight
10%6%25%46%10%
525
September1st to 15thNight
10%19%28%40%10%
566
16th to endNight
12%112%33%37%2
657
October1st to 15thNight
13%417%29%29%5%
660
16th to endNight
15%6%22%28%24%3
704
November1st to 15thNight
14%7%21%30%22%3
700
16th to endNight
17%10%25%30%15%1
720
December1st to 15thNight
20%10%26%32%9%
720
16th to endNight
26%10%27%27%6%
768
Page generated at 2017-08-13 13:16:18. Version ac04

Copyright 2017 A. Danko


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