Alapaha River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alapaha River Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
55%
15635
22%
46859
17%
15591
61%
15591
29%
29111

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
35%
719
22%
2327
11%
716
49%
716
24%
1435
January16th to endNight
37%
768
24%
2437
15%
768
48%
768
26%
1502
February1st to 15thNight
40%
704
24%
2107
13%
699
52%
699
29%
1282
February16th to endNight
38%
631
26%
1893
14%
631
51%
631
30%
1166
March1st to 15thNight
46%
720
28%
2010
15%
720
56%
720
35%
1197
March16th to endNight
47%
768
24%
2112
14%
768
54%
768
34%
1272
April1st to 15thNight
50%
718
25%
1976
17%
718
57%
718
37%
1170
April16th to endNight
57%
567
30%
1719
21%
567
65%
567
40%
941
May1st to 15thNight
61%
539
25%
1619
17%
539
68%
539
37%
924
May16th to endNight
68%
561
21%
1682
17%
561
71%
561
34%
1021
June1st to 15thNight
70%
540
13%
1620
11%
540
70%
540
27%
1074
June16th to endNight
75%
540
14%
1620
13%
540
75%
540
24%
1116
July1st to 15thNight
74%
510
13%
1530
12%
510
75%
510
24%
1033
July16th to endNight
75%
564
11%
1595
11%
531
75%
531
25%
1082
August1st to 15thNight
72%
539
11%
1636
11%
536
72%
536
21%
1152
August16th to endNight
66%
618
14%
1955
16%
618
66%
618
18%
1411
September1st to 15thNight
64%
700
14%
1925
13%
700
65%
700
22%
1365
September16th to endNight
57%
657
19%
1815
16%
657
60%
657
24%
1255
October1st to 15thNight
62%
660
31%
1839
27%
660
67%
660
37%
1085
October16th to endNight
60%
704
32%
2112
30%
704
66%
704
39%
1163
November1st to 15thNight
57%
700
31%
2154
26%
700
65%
700
37%
1181
November16th to endNight
47%
720
28%
2340
20%
720
59%
720
35%
1285
December1st to 15thNight
45%
720
24%
2340
18%
720
53%
720
29%
1397
December16th to endNight
43%
768
23%
2496
18%
768
51%
768
23%
1602

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
10%5%25%5%35%5%6%7%41%
47753
Night
9%5%25%435%5%6%8%45%
47064
TransparencyDay
39%7%11%17%16%6%
47454
Night
35%7%11%17%17%9%
46867
SeeingDay
11%314%21%26%21%
5510
Night
11%420%32%25%4
15639

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
13%6%26%5%3436%6%42%
1611
16th to endDay
13%5%35%423445%46%
1785
February1st to 15thDay
14%5%345%33446%44%
1750
16th to endDay
14%6%23423345%48%
1580
March1st to 15thDay
9%5%1443345%7%49%
1949
16th to endDay
11%5%25%424445%47%
2111
April1st to 15thDay
11%5%245%24446%48%
1972
16th to endDay
8%3233245%5%7%53%
2247
May1st to 15thDay
7%324435%5%6%7%48%
2331
16th to endDay
6%5%25%6%46%5%6%9%40%
2431
June1st to 15thDay
9%5%25%6%46%8%7%10%32%
2340
16th to endDay
6%426%6%5%7%8%8%11%31%
2340
July1st to 15thDay
6%6%26%7%6%7%8%9%10%28%
2340
16th to endDay
8%5%27%8%5%8%8%8%10%25%
2465
August1st to 15thDay
9%6%38%8%5%9%7%8%10%20%
2310
16th to endDay
11%7%37%7%48%6%8%8%26%
2233
September1st to 15thDay
8%7%37%7%5%6%7%7%9%30%
1923
16th to endDay
12%7%37%6%46%46%8%33%
1815
October1st to 15thDay
13%5%13323336%52%
1790
16th to endDay
8%324323235%57%
1760
November1st to 15thDay
8%323323345%57%
1702
16th to endDay
11%42342334454%
1620
December1st to 15thDay
14%6%245%23446%44%
1620
16th to endDay
18%7%25%42445%6%37%
1728
January1st to 15thNight
11%6%25%43445%6%43%
2327
16th to endNight
14%5%24324446%45%
2437
February1st to 15thNight
13%5%24423436%48%
2103
16th to endNight
12%4245%24346%48%
1893
March1st to 15thNight
9%415%42435%8%50%
2010
16th to endNight
9%5%24323445%53%
2112
April1st to 15thNight
9%423425%346%52%
1976
16th to endNight
5%31433445%8%55%
1719
May1st to 15thNight
6%31342447%9%51%
1619
16th to endNight
4325%5%35%6%5%9%48%
1682
June1st to 15thNight
8%325%6%35%7%10%12%34%
1620
16th to endNight
5%426%5%48%8%8%10%35%
1620
July1st to 15thNight
5%4247%37%8%10%12%32%
1620
16th to endNight
6%326%5%48%7%9%11%33%
1703
August1st to 15thNight
6%5%26%6%37%8%10%13%29%
1647
16th to endNight
8%6%36%7%5%6%6%8%11%29%
1955
September1st to 15thNight
8%6%37%6%45%6%7%11%32%
1925
16th to endNight
10%6%36%6%45%5%6%9%35%
1815
October1st to 15thNight
10%5%24423345%53%
1839
16th to endNight
8%413323345%57%
2112
November1st to 15thNight
8%423323447%55%
2154
16th to endNight
10%423324347%53%
2340
December1st to 15thNight
12%5%25%425%35%7%46%
2340
16th to endNight
14%7%35%434446%41%
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
41%48%16%18%11%
1612
16th to endDay
38%46%17%22%10%
1785
February1st to 15thDay
41%35%14%23%11%
1752
16th to endDay
37%35%16%24%11%
1580
March1st to 15thDay
33%48%20%23%9%
1949
16th to endDay
37%6%9%17%21%7%
2112
April1st to 15thDay
36%48%19%21%9%
1972
16th to endDay
29%49%25%21%9%
2247
May1st to 15thDay
31%6%12%21%21%7%
2331
16th to endDay
37%7%14%21%14%3
2435
June1st to 15thDay
42%9%17%20%10%
2340
16th to endDay
40%12%17%17%10%1
2340
July1st to 15thDay
44%14%19%15%5%
2201
16th to endDay
47%13%17%17%4
2310
August1st to 15thDay
52%13%17%12%3
2297
16th to endDay
50%10%16%15%5%1
2233
September1st to 15thDay
46%11%13%13%12%2
1923
16th to endDay
47%6%10%14%15%4
1815
October1st to 15thDay
33%48%17%24%11%
1790
16th to endDay
30%3416%29%15%
1760
November1st to 15thDay
28%37%17%25%16%
1702
16th to endDay
33%37%15%24%14%
1620
December1st to 15thDay
40%48%17%19%9%
1620
16th to endDay
46%39%18%13%8%
1728
January1st to 15thNight
39%48%15%21%10%
2327
16th to endNight
39%45%14%23%12%
2437
February1st to 15thNight
36%46%14%21%15%
2112
16th to endNight
36%5%6%15%20%15%
1893
March1st to 15thNight
31%5%9%21%20%11%
2010
16th to endNight
32%5%9%18%23%11%
2112
April1st to 15thNight
31%5%8%19%23%12%
1976
16th to endNight
26%5%12%21%22%10%
1719
May1st to 15thNight
27%7%13%20%20%10%
1620
16th to endNight
31%8%14%24%15%5%
1684
June1st to 15thNight
36%11%21%18%10%1
1620
16th to endNight
38%13%17%18%9%2
1620
July1st to 15thNight
36%13%22%20%5%1
1530
16th to endNight
37%12%24%19%4
1595
August1st to 15thNight
38%16%24%16%3
1636
16th to endNight
45%13%17%16%5%2
1955
September1st to 15thNight
42%12%15%13%13%2
1925
16th to endNight
43%8%13%14%15%5%
1815
October1st to 15thNight
31%49%20%19%14%
1839
16th to endNight
29%36%15%25%19%
2112
November1st to 15thNight
29%37%17%25%16%
2154
16th to endNight
30%48%17%22%17%
2340
December1st to 15thNight
37%412%18%19%8%
2340
16th to endNight
43%48%20%14%9%
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
12%15%30%21%11%10%
90
16th to endDay
16%14%39%19%7%2
96
February1st to 15thDay
12%20%32%25%10%
90
16th to endDay
8%8%39%33%7%2
81
March1st to 15thDay
11%5%31%34%15%1
239
16th to endDay
13%5%24%32%21%2
288
April1st to 15thDay
13%8%21%27%23%5%
270
16th to endDay
7%222%24%28%15%
270
May1st to 15thDay
8%416%32%22%15%
288
16th to endDay
11%15%17%33%30%
331
June1st to 15thDay
13%6%15%32%33%
315
16th to endDay
8%413%33%39%
315
July1st to 15thDay
8%111%28%48%
305
16th to endDay
7%5%10%32%44%
326
August1st to 15thDay
14%15%11%30%37%
313
16th to endDay
10%5%13%28%41%
332
September1st to 15thDay
15%17%17%32%26%
294
16th to endDay
18%9%23%29%18%
254
October1st to 15thDay
16%114%27%30%9%
255
16th to endDay
8%218%31%31%7%
272
November1st to 15thDay
14%121%31%20%9%
210
16th to endDay
35%33%32%16%8%
90
December1st to 15thDay
15%7%31%24%14%6%
90
16th to endDay
31%6%12%28%17%4
96
January1st to 15thNight
15%11%32%29%10%
720
16th to endNight
16%7%34%30%9%
768
February1st to 15thNight
16%8%29%36%9%
704
16th to endNight
15%6%34%37%5%
631
March1st to 15thNight
11%7%30%38%11%
720
16th to endNight
11%6%30%32%17%1
768
April1st to 15thNight
11%6%27%37%17%
718
16th to endNight
6%427%35%23%1
567
May1st to 15thNight
7%223%38%23%3
540
16th to endNight
6%113%35%36%5%
563
June1st to 15thNight
10%7%35%39%7%
540
16th to endNight
7%5%30%43%12%
540
July1st to 15thNight
6%326%43%19%
510
16th to endNight
6%421%52%14%
564
August1st to 15thNight
10%320%54%10%
539
16th to endNight
12%5%23%41%16%
618
September1st to 15thNight
10%17%24%44%11%
700
16th to endNight
14%13%33%35%2
657
October1st to 15thNight
15%113%34%32%3
660
16th to endNight
11%320%35%27%1
704
November1st to 15thNight
10%5%21%38%22%2
700
16th to endNight
11%6%30%33%16%1
720
December1st to 15thNight
15%428%32%16%1
720
16th to endNight
17%7%25%35%14%
768
Page generated at 2017-09-11 19:35:15. Version ac04

Copyright 2017 A. Danko


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