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 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
51%
15890
23%
48794
18%
15847
57%
15847
29%
29987

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%
780
23%
2522
12%
776
42%
776
21%
1624
January16th to endNight
32%
832
25%
2551
14%
832
43%
832
23%
1645
February1st to 15thNight
31%
764
21%
2292
11%
761
41%
761
25%
1478
February16th to endNight
29%
659
22%
1977
12%
659
37%
659
22%
1320
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%
539
19%
1771
21%
536
78%
536
32%
1026
August16th to endNight
71%
573
21%
1910
26%
573
71%
573
26%
1194
September1st to 15thNight
66%
618
20%
1878
20%
618
68%
618
30%
1156
September16th to endNight
64%
717
29%
1980
25%
717
66%
717
36%
1181
October1st to 15thNight
60%
720
34%
1980
28%
720
63%
720
38%
1169
October16th to endNight
53%
768
34%
2352
30%
768
60%
768
36%
1329
November1st to 15thNight
51%
760
28%
2471
25%
760
59%
760
32%
1405
November16th to endNight
45%
780
29%
2535
22%
780
55%
780
30%
1471
December1st to 15thNight
37%
780
23%
2535
16%
780
46%
780
22%
1611
December16th to endNight
31%
832
19%
2704
15%
832
39%
832
19%
1842

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%
49427
Night
12%5%2442445%7%45%
48993
TransparencyDay
41%6%10%20%16%3
49128
Night
37%5%10%21%19%5%
48796
SeeingDay
16%7%17%22%21%14%
5767
Night
15%6%21%29%23%4
15892

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%26%32435%5%39%
1746
16th to endDay
20%5%34323345%44%
2023
February1st to 15thDay
20%8%35%334335%38%
1900
16th to endDay
19%6%35%5%24346%37%
1643
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%7%5%7%7%9%9%34%
2175
16th to endDay
11%5%36%6%46%7%6%9%31%
2292
September1st to 15thDay
12%5%25%5%45%5%6%8%37%
2070
16th to endDay
11%42443445%7%48%
1980
October1st to 15thDay
10%3145%34345%53%
1980
16th to endDay
12%31432333456%
1870
November1st to 15thDay
13%5%13314335%53%
1717
16th to endDay
14%5%23423446%48%
1755
December1st to 15thDay
19%6%36%423445%37%
1755
16th to endDay
24%8%35%5%12345%34%
1872
January1st to 15thNight
18%6%34424335%42%
2522
16th to endNight
16%7%25%423445%42%
2551
February1st to 15thNight
20%6%34313346%42%
2283
16th to endNight
18%6%25%424446%40%
1977
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%
1782
16th to endNight
8%425%5%46%5%6%8%41%
1910
September1st to 15thNight
8%5%26%5%245%5%7%46%
1878
16th to endNight
8%425%424448%51%
1980
October1st to 15thNight
10%42342344456%
1980
16th to endNight
13%5%13312335%57%
2352
November1st to 15thNight
12%5%23323435%53%
2471
16th to endNight
14%5%24423345%51%
2535
December1st to 15thNight
17%6%24423447%41%
2535
16th to endNight
20%8%44423446%36%
2704

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%19%20%3
1747
16th to endDay
42%37%23%19%4
2023
February1st to 15thDay
49%36%20%17%2
1902
16th to endDay
47%47%20%16%3
1643
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%17%13%1
2162
16th to endDay
46%10%11%19%10%1
2292
September1st to 15thDay
42%8%14%17%12%4
2070
16th to endDay
34%6%11%22%21%4
1980
October1st to 15thDay
33%5%7%19%25%7%
1980
16th to endDay
31%3418%30%10%
1870
November1st to 15thDay
35%35%18%29%7%
1717
16th to endDay
37%36%20%26%6%
1755
December1st to 15thDay
48%45%20%15%4
1755
16th to endDay
52%310%19%12%2
1872
January1st to 15thNight
45%37%20%19%3
2522
16th to endNight
44%37%20%19%5%
2551
February1st to 15thNight
43%28%20%18%5%
2292
16th to endNight
45%47%21%17%4
1977
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%10%19%21%16%3
1771
16th to endNight
37%8%14%23%12%2
1910
September1st to 15thNight
35%6%17%18%16%5%
1878
16th to endNight
32%5%9%23%22%7%
1980
October1st to 15thNight
30%46%23%25%9%
1980
16th to endNight
32%2316%31%12%
2352
November1st to 15thNight
33%46%19%24%12%
2471
16th to endNight
36%36%17%27%8%
2535
December1st to 15thNight
43%48%19%19%4
2535
16th to endNight
49%49%18%15%3
2704

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
18%24%34%16%5%
135
16th to endDay
21%23%32%14%6%1
144
February1st to 15thDay
28%23%32%14%1
135
16th to endDay
26%11%41%18%4
100
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
13%7%19%33%25%
313
16th to endDay
15%18%20%32%21%
332
September1st to 15thDay
14%28%20%31%22%
315
16th to endDay
16%9%24%38%10%
314
October1st to 15thDay
13%321%29%24%8%
315
16th to endDay
14%9%17%32%20%5%
208
November1st to 15thDay
20%7%28%29%12%
135
16th to endDay
11%14%28%28%14%2
135
December1st to 15thDay
25%13%37%14%10%
135
16th to endDay
31%18%33%13%2
144
January1st to 15thNight
21%13%32%24%7%
780
16th to endNight
19%12%31%30%5%
832
February1st to 15thNight
24%9%30%29%5%
764
16th to endNight
22%12%32%29%3
659
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%5%23%53%11%
539
16th to endNight
10%6%26%46%9%
573
September1st to 15thNight
11%9%28%39%10%
618
16th to endNight
11%112%31%40%3
717
October1st to 15thNight
13%317%30%30%4
720
16th to endNight
14%6%22%29%24%3
768
November1st to 15thNight
14%6%22%31%21%3
760
16th to endNight
16%10%24%30%17%1
780
December1st to 15thNight
20%11%26%32%9%
780
16th to endNight
26%11%27%28%6%
832
Page generated at 2018-02-23 10:21:30. Version ac04

Copyright 2018 A. Danko


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