Vestavia Hills Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vestavia Hills Observatory clear sky chart from 2005-11-05 to 2017-05-01.

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
50%
14828
24%
45678
18%
14785
58%
14785
29%
27744

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
30%
720
24%
2327
12%
716
45%
716
24%
1445
January16th to endNight
28%
768
26%
2307
11%
768
42%
768
23%
1521
February1st to 15thNight
31%
704
25%
2112
10%
701
45%
701
27%
1310
February16th to endNight
29%
631
25%
1893
12%
631
41%
631
27%
1193
March1st to 15thNight
34%
720
21%
2155
12%
720
41%
720
27%
1363
March16th to endNight
40%
705
24%
2049
13%
705
48%
705
30%
1245
April1st to 15thNight
43%
539
25%
1797
18%
539
53%
539
31%
1026
April16th to endNight
49%
540
27%
1800
21%
540
60%
540
33%
978
May1st to 15thNight
51%
498
23%
1520
15%
498
59%
498
30%
948
May16th to endNight
71%
513
24%
1538
20%
513
74%
513
36%
880
June1st to 15thNight
75%
495
18%
1485
16%
495
75%
495
33%
873
June16th to endNight
80%
495
20%
1485
18%
495
81%
495
38%
849
July1st to 15thNight
70%
465
14%
1395
12%
465
72%
465
26%
923
July16th to endNight
75%
522
15%
1502
15%
489
77%
489
29%
963
August1st to 15thNight
78%
494
18%
1638
22%
491
78%
491
32%
961
August16th to endNight
72%
525
18%
1750
23%
525
72%
525
25%
1132
September1st to 15thNight
65%
565
21%
1720
21%
565
66%
565
26%
1111
September16th to endNight
66%
657
27%
1815
22%
657
69%
657
36%
1092
October1st to 15thNight
60%
660
35%
1815
27%
660
66%
660
42%
1031
October16th to endNight
54%
704
34%
2123
29%
704
62%
704
37%
1193
November1st to 15thNight
53%
700
30%
2276
25%
700
63%
700
36%
1217
November16th to endNight
42%
720
27%
2340
20%
720
54%
720
30%
1359
December1st to 15thNight
38%
720
22%
2340
17%
720
47%
720
25%
1456
December16th to endNight
30%
768
20%
2496
15%
768
39%
768
20%
1675

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%5%25%5%35%5%5%7%41%
46068
Night
11%42442445%7%46%
45881
TransparencyDay
40%6%10%19%17%4
45773
Night
35%5%10%19%20%7%
45680
SeeingDay
13%5%19%23%22%14%
4612
Night
13%6%22%29%22%4
14830

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%25%323345%42%
1611
16th to endDay
17%6%25%323335%45%
1914
February1st to 15thDay
16%8%35%424336%42%
1750
16th to endDay
20%6%24424435%41%
1580
March1st to 15thDay
16%7%36%5%24346%40%
1803
16th to endDay
14%6%35%42445%7%42%
2183
April1st to 15thDay
12%425%42445%7%44%
2151
16th to endDay
9%325%5%4445%7%46%
2160
May1st to 15thDay
12%5%245%25%5%5%8%42%
2111
16th to endDay
8%425%5%345%5%9%43%
2223
June1st to 15thDay
7%5%25%447%6%8%11%35%
2145
16th to endDay
43235%36%5%8%12%44%
2145
July1st to 15thDay
10%426%7%5%7%7%9%11%26%
2145
16th to endDay
7%5%35%7%5%7%9%9%10%28%
2244
August1st to 15thDay
8%4246%48%7%7%11%33%
1980
16th to endDay
12%5%36%7%5%7%7%8%8%26%
2100
September1st to 15thDay
12%5%25%7%36%7%6%8%35%
1898
16th to endDay
13%5%24434446%45%
1815
October1st to 15thDay
10%424434347%51%
1815
16th to endDay
11%32431233458%
1745
November1st to 15thDay
13%5%23213235%55%
1582
16th to endDay
14%5%23324346%48%
1620
December1st to 15thDay
19%7%34433336%40%
1620
16th to endDay
21%9%35%433235%35%
1728
January1st to 15thNight
15%6%2432445%445%
2327
16th to endNight
17%6%35%424445%41%
2307
February1st to 15thNight
16%6%14323246%46%
2103
16th to endNight
17%5%24423345%46%
1893
March1st to 15thNight
16%6%24323447%43%
2155
16th to endNight
12%42432435%7%48%
2049
April1st to 15thNight
11%32442445%7%49%
1797
16th to endNight
9%314424346%54%
1800
May1st to 15thNight
9%425%5%25%5%5%9%44%
1519
16th to endNight
4214435%6%6%9%50%
1538
June1st to 15thNight
3323446%6%9%11%43%
1485
16th to endNight
32135%35%6%8%12%47%
1485
July1st to 15thNight
7%426%6%37%7%8%9%37%
1485
16th to endNight
5%425%7%46%6%7%11%40%
1613
August1st to 15thNight
5%215%425%6%8%12%44%
1650
16th to endNight
8%425%5%37%6%7%9%38%
1750
September1st to 15thNight
9%426%6%46%5%5%9%40%
1720
16th to endNight
8%4245%2435%6%50%
1815
October1st to 15thNight
8%413322346%58%
1815
16th to endNight
11%5%1332333358%
2123
November1st to 15thNight
11%41322335%5%56%
2276
16th to endNight
11%6%14424335%51%
2340
December1st to 15thNight
15%7%25%423346%43%
2340
16th to endNight
21%6%35%43435%5%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
44%36%15%24%5%
1612
16th to endDay
41%35%20%21%7%
1914
February1st to 15thDay
45%26%23%18%4
1752
16th to endDay
45%46%14%23%5%
1580
March1st to 15thDay
45%49%15%20%5%
1803
16th to endDay
41%5%11%20%18%2
2184
April1st to 15thDay
37%6%9%20%18%7%
2151
16th to endDay
35%6%8%22%23%2
2160
May1st to 15thDay
39%6%11%19%18%3
2111
16th to endDay
36%7%14%24%13%3
2227
June1st to 15thDay
38%10%16%21%11%1
2145
16th to endDay
29%9%16%24%16%4
2145
July1st to 15thDay
43%12%16%17%7%1
2006
16th to endDay
43%13%18%15%8%
2092
August1st to 15thDay
39%11%16%17%10%3
1968
16th to endDay
49%10%13%15%9%2
2100
September1st to 15thDay
43%10%12%17%10%5%
1898
16th to endDay
38%6%8%20%19%6%
1815
October1st to 15thDay
32%49%18%23%10%
1815
16th to endDay
31%3415%34%11%
1745
November1st to 15thDay
33%25%17%30%10%
1582
16th to endDay
36%37%17%25%9%
1620
December1st to 15thDay
46%37%18%16%6%
1620
16th to endDay
53%27%18%13%4
1728
January1st to 15thNight
40%46%18%25%5%
2327
16th to endNight
44%3417%21%7%
2307
February1st to 15thNight
39%36%21%20%9%
2112
16th to endNight
39%45%18%24%6%
1893
March1st to 15thNight
39%49%18%20%7%
2155
16th to endNight
35%49%24%21%4
2049
April1st to 15thNight
33%49%22%20%9%
1797
16th to endNight
29%5%10%23%23%7%
1800
May1st to 15thNight
35%7%11%19%21%4
1520
16th to endNight
26%9%15%27%15%5%
1540
June1st to 15thNight
28%10%18%24%16%1
1485
16th to endNight
25%9%17%24%19%3
1485
July1st to 15thNight
36%11%19%20%9%3
1395
16th to endNight
33%11%21%21%10%
1502
August1st to 15thNight
28%11%19%22%14%4
1638
16th to endNight
38%9%16%18%12%3
1750
September1st to 15thNight
38%8%16%17%13%5%
1720
16th to endNight
32%5%10%21%22%7%
1815
October1st to 15thNight
27%5%7%21%24%14%
1815
16th to endNight
31%3412%31%16%
2123
November1st to 15thNight
29%36%17%28%15%
2276
16th to endNight
35%36%17%25%12%
2340
December1st to 15thNight
41%49%18%21%5%
2340
16th to endNight
49%37%17%16%5%
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
21%16%32%25%31
90
16th to endDay
22%22%43%7%21
96
February1st to 15thDay
20%25%37%15%1
90
16th to endDay
28%9%39%22%
81
March1st to 15thDay
26%17%38%11%41
93
16th to endDay
19%5%34%23%15%1
288
April1st to 15thDay
17%8%31%24%17%
270
16th to endDay
10%7%26%28%21%5%
270
May1st to 15thDay
12%5%25%26%18%10%
229
16th to endDay
13%214%22%27%20%
267
June1st to 15thDay
12%7%25%27%26%
255
16th to endDay
217%21%32%35%
255
July1st to 15thDay
6%19%24%30%28%
245
16th to endDay
8%17%14%29%38%
270
August1st to 15thDay
10%16%20%30%29%
253
16th to endDay
11%5%26%32%24%
268
September1st to 15thDay
12%17%23%32%22%
255
16th to endDay
12%212%29%32%9%
254
October1st to 15thDay
12%420%28%28%4
255
16th to endDay
15%318%33%23%5%
162
November1st to 15thDay
18%14%27%27%10%1
90
16th to endDay
16%10%41%20%11%1
90
December1st to 15thDay
25%14%34%18%5%1
90
16th to endDay
31%13%33%16%5%
96
January1st to 15thNight
19%12%35%24%7%
720
16th to endNight
20%12%34%26%5%
768
February1st to 15thNight
20%10%34%29%5%
704
16th to endNight
19%11%36%29%3
631
March1st to 15thNight
19%10%33%28%8%
720
16th to endNight
14%9%31%29%14%
705
April1st to 15thNight
11%8%33%28%16%1
539
16th to endNight
11%7%27%34%17%2
540
May1st to 15thNight
9%428%29%23%4
498
16th to endNight
6%113%34%37%6%
515
June1st to 15thNight
7%6%35%40%9%
495
16th to endNight
216%24%48%17%
495
July1st to 15thNight
8%6%27%44%13%
465
16th to endNight
6%6%21%45%19%
522
August1st to 15thNight
7%423%50%13%
494
16th to endNight
10%6%27%42%12%
525
September1st to 15thNight
10%19%26%40%10%
565
16th to endNight
9%112%35%36%4
657
October1st to 15thNight
10%320%33%26%4
660
16th to endNight
12%5%21%30%24%4
704
November1st to 15thNight
13%6%23%33%20%4
700
16th to endNight
14%10%29%32%13%1
720
December1st to 15thNight
20%9%26%32%10%1
720
16th to endNight
25%10%29%25%8%
768
Page generated at 2017-05-02 07:43:35. Version ac04

Copyright 2017 A. Danko


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