Huntsville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Huntsville clear sky chart from 2005-11-06 to 2024-02-05.

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
28%
22804
11%
80047
8%
22714
33%
22714
13%
60239

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
11%
832
5%
4545
2%
816
16%
816
3%
3848
January11th to 20thNight
11%
756
5%
4341
3%
740
16%
740
3%
3713
January21st to endNight
21%
831
6%
4526
7%
814
26%
814
5%
3855
February1st to 10thNight
15%
739
7%
2399
3%
739
20%
739
8%
1972
February11th to 20thNight
16%
701
13%
2275
5%
700
26%
700
10%
1756
February21st to endNight
18%
592
10%
1914
4%
592
25%
592
9%
1528
March1st to 10thNight
19%
720
15%
1980
7%
720
25%
720
16%
1465
March11th to 20thNight
20%
720
15%
1980
7%
720
28%
720
17%
1467
March21st to endNight
28%
792
17%
2178
8%
792
35%
792
21%
1535
April1st to 10thNight
22%
720
13%
1814
5%
720
26%
720
17%
1396
April11th to 20thNight
28%
638
19%
1702
8%
638
34%
638
21%
1223
April21st to endNight
28%
540
15%
1620
8%
540
34%
540
16%
1195
May1st to 10thNight
37%
482
16%
1562
12%
482
43%
482
22%
1017
May11th to 20thNight
36%
354
20%
1416
18%
354
48%
354
20%
855
May21st to endNight
40%
388
13%
1551
11%
388
50%
388
22%
897
June1st to 10thNight
36%
360
9%
1440
10%
360
42%
360
16%
943
June11th to 20thNight
47%
360
15%
1262
17%
360
54%
360
24%
763
June21st to endNight
42%
360
11%
1260
10%
360
48%
360
20%
813
July1st to 10thNight
55%
350
17%
1225
19%
350
61%
350
31%
688
July11th to 20thNight
49%
348
16%
1349
20%
348
55%
348
24%
787
July21st to endNight
54%
463
15%
1552
16%
438
57%
438
25%
928
August1st to 10thNight
54%
537
16%
1600
13%
534
58%
534
29%
997
August11th to 20thNight
59%
534
16%
1598
12%
534
63%
534
28%
1032
August21st to endNight
45%
657
16%
1845
8%
657
50%
657
26%
1234
September1st to 10thNight
46%
720
15%
1800
6%
720
49%
720
31%
1202
September11th to 20thNight
46%
720
20%
1877
12%
720
49%
720
31%
1227
September21st to endNight
43%
720
21%
2029
14%
720
48%
720
25%
1375
October1st to 10thNight
32%
720
15%
2160
10%
720
39%
720
18%
1531
October11th to 20thNight
22%
720
10%
2160
5%
720
29%
720
12%
1694
October21st to endNight
16%
792
10%
2376
6%
792
21%
792
9%
1945
November1st to 10thNight
26%
740
13%
2558
11%
740
32%
740
14%
1858
November11th to 20thNight
19%
760
12%
2660
7%
760
27%
760
10%
2017
November21st to endNight
16%
760
7%
2660
4%
760
20%
760
7%
2195
December1st to 10thNight
11%
760
5%
2660
3%
760
15%
760
5%
2307
December11th to 20thNight
12%
760
8%
3280
3%
759
19%
759
6%
2748
December21st to endNight
10%
858
4%
4893
1%
847
14%
847
3%
4233

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
18%12%5%8%6%3445%6%30%
78493
Night
17%14%5%8%6%34446%28%
80284
TransparencyDay
55%6%10%18%9%1
78196
Night
58%7%10%16%9%1
80117
SeeingDay
24%16%30%20%8%3
13825
Night
24%13%29%24%9%1
22832

By Month

Percentage Cloud Cover NE (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
16%22%13%13%6%3223318%
2361
11th to 20thDay
11%17%10%15%12%5%434314%
2598
21st to endDay
18%22%10%11%7%3323416%
3124
February1st to 10thDay
13%19%8%14%10%3443418%
1656
11th to 20thDay
14%16%7%12%6%34345%24%
1573
21st to endDay
17%18%7%11%7%4444420%
1340
March1st to 10thDay
15%14%5%9%7%45%5%5%5%27%
1977
11th to 20thDay
12%14%5%10%8%445%5%5%27%
1980
21st to endDay
18%10%5%7%6%34445%35%
2178
April1st to 10thDay
20%14%5%7%5%4445%6%27%
2146
11th to 20thDay
21%11%46%434445%35%
2222
21st to endDay
21%13%37%5%33435%33%
2340
May1st to 10thDay
19%8%37%6%3445%8%33%
2398
11th to 20thDay
18%8%36%5%3445%6%37%
2478
21st to endDay
15%6%25%6%35%5%5%7%40%
2725
June1st to 10thDay
21%7%35%6%345%5%7%34%
2520
11th to 20thDay
15%6%36%5%35%5%6%8%37%
2692
21st to endDay
20%7%36%5%45%5%6%7%34%
2700
July1st to 10thDay
14%4345%35%5%6%8%42%
2700
11th to 20thDay
13%6%36%5%45%46%9%39%
2561
21st to endDay
14%6%35%5%46%5%6%9%37%
2672
August1st to 10thDay
14%6%36%6%45%5%6%8%38%
2327
11th to 20thDay
15%6%36%6%45%5%6%8%38%
2303
21st to endDay
15%6%36%5%35%7%7%7%36%
2492
September1st to 10thDay
16%7%25%5%35%6%5%7%39%
2160
11th to 20thDay
17%6%35%5%35%45%8%40%
2080
21st to endDay
20%9%36%5%45%45%6%34%
1929
October1st to 10thDay
22%7%37%6%35%447%32%
1800
11th to 20thDay
28%12%36%6%35%5%5%6%21%
1800
21st to endDay
33%11%5%9%5%34345%20%
1980
November1st to 10thDay
19%14%47%6%3445%7%27%
1516
11th to 20thDay
19%18%6%9%5%46%445%21%
1520
21st to endDay
22%21%7%8%7%35%34415%
1520
December1st to 10thDay
19%25%8%10%5%3343416%
1520
11th to 20thDay
19%24%6%10%6%3333419%
1906
21st to endDay
24%23%8%11%6%3333313%
2699
January1st to 10thNight
17%22%11%13%7%3444413%
4560
11th to 20thNight
13%17%7%16%12%45%5%45%12%
4348
21st to endNight
16%20%9%12%7%5%433316%
4532
February1st to 10thNight
13%18%7%12%9%45%5%45%18%
2399
11th to 20thNight
13%16%7%12%7%4443425%
2273
21st to endNight
16%17%8%11%7%4444422%
1914
March1st to 10thNight
14%11%6%9%7%34446%32%
1970
11th to 20thNight
14%12%6%8%7%3445%5%31%
1979
21st to endNight
15%11%38%6%3345%6%37%
2178
April1st to 10thNight
22%13%46%44445%5%29%
1814
11th to 20thNight
19%10%5%5%6%24446%36%
1702
21st to endNight
20%9%37%7%35%446%31%
1620
May1st to 10thNight
19%6%16%5%35%5%6%8%37%
1562
11th to 20thNight
15%8%25%42445%7%42%
1415
21st to endNight
11%5%245%25%5%7%10%43%
1550
June1st to 10thNight
16%8%46%6%35%5%6%7%36%
1440
11th to 20thNight
13%6%3443446%9%44%
1262
21st to endNight
15%7%35%6%25%6%7%8%37%
1260
July1st to 10thNight
10%5%3442445%9%50%
1260
11th to 20thNight
14%6%345%335%6%6%45%
1394
21st to endNight
11%6%24436%5%7%8%45%
1643
August1st to 10thNight
12%6%25%4345%5%7%47%
1611
11th to 20thNight
11%6%25%435%5%6%8%45%
1598
21st to endNight
16%7%25%5%345%5%7%41%
1845
September1st to 10thNight
12%5%25%5%245%6%8%44%
1800
11th to 20thNight
14%6%244345%5%8%45%
1877
21st to endNight
18%7%26%5%34346%41%
2029
October1st to 10thNight
20%8%45%5%35%5%5%6%35%
2160
11th to 20thNight
27%10%37%6%3445%6%25%
2160
21st to endNight
28%13%5%8%6%3444323%
2376
November1st to 10thNight
22%13%46%5%3335%5%30%
2558
11th to 20thNight
19%15%5%6%6%45%447%25%
2660
21st to endNight
22%19%5%8%7%34445%17%
2660
December1st to 10thNight
20%23%8%10%6%3444413%
2660
11th to 20thNight
19%23%7%11%6%3343417%
3288
21st to endNight
24%22%7%12%7%3433412%
4927

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
74%48%9%5%
2362
11th to 20thDay
76%46%8%5%1
2598
21st to endDay
74%5%6%8%6%1
3124
February1st to 10thDay
72%46%11%5%1
1656
11th to 20thDay
63%5%10%11%9%2
1582
21st to endDay
69%48%12%7%
1340
March1st to 10thDay
57%7%13%12%10%1
1980
11th to 20thDay
58%5%9%16%9%2
1980
21st to endDay
52%5%9%17%14%4
2178
April1st to 10thDay
58%6%9%16%9%2
2146
11th to 20thDay
52%6%8%22%12%1
2222
21st to endDay
55%5%8%17%12%3
2340
May1st to 10thDay
50%5%10%20%12%3
2398
11th to 20thDay
47%6%9%23%14%1
2482
21st to endDay
42%8%13%20%13%3
2725
June1st to 10thDay
50%7%10%21%13%
2520
11th to 20thDay
44%7%11%22%15%1
2692
21st to endDay
48%7%13%20%10%1
2700
July1st to 10thDay
37%8%13%27%14%1
2626
11th to 20thDay
41%8%13%27%11%1
2483
21st to endDay
43%8%12%27%10%
2523
August1st to 10thDay
43%9%14%22%11%1
2314
11th to 20thDay
43%9%15%24%8%1
2303
21st to endDay
44%10%14%22%10%1
2492
September1st to 10thDay
43%8%13%25%11%1
2160
11th to 20thDay
42%7%13%27%10%1
2080
21st to endDay
51%6%11%25%7%
1929
October1st to 10thDay
52%8%12%18%10%1
1800
11th to 20thDay
64%8%10%12%6%1
1800
21st to endDay
68%5%9%12%6%
1980
November1st to 10thDay
56%8%13%17%5%
1516
11th to 20thDay
66%7%9%12%5%1
1520
21st to endDay
73%6%9%9%31
1520
December1st to 10thDay
73%6%9%9%41
1520
11th to 20thDay
71%5%6%9%7%1
1906
21st to endDay
78%4411%3
2699
January1st to 10thNight
76%5%7%9%3
4560
11th to 20thNight
73%9%7%7%41
4348
21st to endNight
73%6%6%8%6%1
4532
February1st to 10thNight
68%7%9%11%5%1
2399
11th to 20thNight
63%49%16%7%1
2275
21st to endNight
67%48%14%6%1
1914
March1st to 10thNight
54%5%12%14%12%2
1980
11th to 20thNight
54%5%11%17%11%2
1980
21st to endNight
49%5%9%20%14%3
2178
April1st to 10thNight
56%5%9%17%10%2
1814
11th to 20thNight
49%6%6%23%15%2
1702
21st to endNight
54%6%8%14%15%2
1620
May1st to 10thNight
44%5%12%20%15%3
1562
11th to 20thNight
41%6%10%22%19%2
1416
21st to endNight
35%9%15%22%16%3
1551
June1st to 10thNight
46%8%10%21%13%2
1440
11th to 20thNight
37%7%12%24%19%
1262
21st to endNight
43%8%16%21%11%1
1260
July1st to 10thNight
30%8%14%27%19%2
1225
11th to 20thNight
36%7%13%30%13%1
1349
21st to endNight
36%8%14%28%13%1
1552
August1st to 10thNight
35%8%17%27%12%1
1600
11th to 20thNight
35%10%18%24%11%1
1598
21st to endNight
41%8%14%26%10%1
1845
September1st to 10thNight
37%8%17%24%13%1
1800
11th to 20thNight
37%7%15%30%11%
1877
21st to endNight
44%6%13%28%9%
2029
October1st to 10thNight
49%8%12%18%13%
2160
11th to 20thNight
59%9%11%17%5%
2160
21st to endNight
67%6%7%11%8%
2376
November1st to 10thNight
55%6%13%20%6%
2558
11th to 20thNight
59%7%12%14%6%1
2660
21st to endNight
69%7%10%11%3
2660
December1st to 10thNight
75%7%7%8%4
2660
11th to 20thNight
71%6%7%10%5%
3288
21st to endNight
77%5%6%9%3
4927

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
21%26%33%12%7%1
180
11th to 20thDay
24%20%36%15%41
204
21st to endDay
30%13%35%16%6%
297
February1st to 10thDay
29%31%33%5%21
252
11th to 20thDay
30%24%37%8%1
240
21st to endDay
36%29%29%6%
206
March1st to 10thDay
25%21%35%16%2
420
11th to 20thDay
23%22%34%15%5%1
420
21st to endDay
30%15%32%17%5%1
462
April1st to 10thDay
27%21%29%16%6%1
420
11th to 20thDay
33%20%21%14%9%3
412
21st to endDay
31%15%33%15%6%1
420
May1st to 10thDay
26%16%28%21%5%4
423
11th to 20thDay
21%17%31%17%10%4
447
21st to endDay
20%18%29%20%10%3
485
June1st to 10thDay
22%14%33%24%5%2
450
11th to 20thDay
18%15%30%25%10%2
622
21st to endDay
21%13%35%20%9%2
630
July1st to 10thDay
13%10%33%31%11%2
621
11th to 20thDay
17%11%28%28%13%4
482
21st to endDay
15%11%32%28%10%5%
488
August1st to 10thDay
17%7%28%30%13%6%
446
11th to 20thDay
17%5%26%29%15%9%
439
21st to endDay
18%11%28%24%14%5%
495
September1st to 10thDay
17%10%31%23%13%6%
450
11th to 20thDay
17%9%26%25%17%5%
450
21st to endDay
22%15%24%25%11%2
450
October1st to 10thDay
26%15%25%18%12%4
450
11th to 20thDay
30%18%32%15%41
450
21st to endDay
36%19%28%14%3
495
November1st to 10thDay
32%20%30%16%1
201
11th to 20thDay
29%24%31%10%5%
180
21st to endDay
34%23%35%6%11
180
December1st to 10thDay
31%22%34%11%21
180
11th to 20thDay
37%26%22%12%31
180
21st to endDay
33%26%27%11%12
198
January1st to 10thNight
29%17%33%17%4
840
11th to 20thNight
31%16%31%17%4
760
21st to endNight
21%12%36%23%8%1
836
February1st to 10thNight
24%20%34%18%4
739
11th to 20thNight
23%16%35%20%5%
703
21st to endNight
25%22%28%21%4
592
March1st to 10thNight
23%17%34%22%4
720
11th to 20thNight
22%19%34%20%5%1
720
21st to endNight
22%13%30%27%8%
792
April1st to 10thNight
28%14%31%23%5%
720
11th to 20thNight
25%13%28%23%10%1
638
21st to endNight
24%11%28%25%10%1
540
May1st to 10thNight
23%6%26%33%12%1
482
11th to 20thNight
20%10%31%30%9%
354
21st to endNight
11%7%36%35%10%1
389
June1st to 10thNight
17%8%32%32%9%1
360
11th to 20thNight
16%9%24%38%13%
360
21st to endNight
18%8%24%36%14%
360
July1st to 10thNight
11%6%22%44%18%1
350
11th to 20thNight
14%7%24%37%18%1
348
21st to endNight
10%5%22%42%19%1
463
August1st to 10thNight
15%418%36%25%2
537
11th to 20thNight
12%5%17%39%23%3
534
21st to endNight
20%7%24%28%20%2
657
September1st to 10thNight
16%6%27%32%17%3
720
11th to 20thNight
16%7%26%28%19%3
720
21st to endNight
22%9%22%27%18%2
720
October1st to 10thNight
24%13%26%23%13%1
720
11th to 20thNight
31%11%30%20%7%1
720
21st to endNight
36%13%31%16%4
792
November1st to 10thNight
31%11%27%24%7%1
740
11th to 20thNight
27%19%28%18%7%
760
21st to endNight
35%15%26%19%5%
760
December1st to 10thNight
32%19%30%15%4
760
11th to 20thNight
29%19%34%13%41
760
21st to endNight
34%15%30%18%3
866
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