GradyLand Heaven Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the GradyLand Heaven Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
54%
16139
18%
46983
13%
16099
59%
16099
23%
30896

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
40%
717
18%
2327
11%
716
50%
716
20%
1486
January16th to endNight
39%
768
22%
2496
16%
768
50%
768
23%
1532
February1st to 15thNight
44%
701
23%
2115
15%
698
55%
698
27%
1259
February16th to endNight
46%
631
26%
1767
14%
631
57%
631
31%
1036
March1st to 15thNight
45%
720
28%
1980
16%
720
57%
720
32%
1156
March16th to endNight
52%
768
23%
2112
16%
768
59%
768
33%
1261
April1st to 15thNight
55%
718
22%
1967
17%
718
60%
718
34%
1144
April16th to endNight
56%
720
25%
1800
14%
720
61%
720
33%
1110
May1st to 15thNight
62%
676
23%
1756
15%
676
65%
676
34%
1076
May16th to endNight
63%
561
18%
1682
12%
561
65%
561
24%
1094
June1st to 15thNight
57%
540
11%
1620
7%
540
59%
540
17%
1166
June16th to endNight
63%
540
10%
1620
8%
540
64%
540
18%
1154
July1st to 15thNight
65%
510
7%
1530
5%
510
65%
510
17%
1116
July16th to endNight
65%
564
9%
1595
8%
531
70%
531
21%
1126
August1st to 15thNight
70%
560
8%
1630
7%
557
70%
557
22%
1112
August16th to endNight
60%
764
6%
1988
5%
764
61%
764
18%
1511
September1st to 15thNight
62%
720
6%
1980
6%
720
62%
720
17%
1524
September16th to endNight
52%
689
8%
1903
5%
689
55%
689
13%
1511
October1st to 15thNight
57%
660
20%
1921
19%
660
59%
660
22%
1290
October16th to endNight
54%
704
21%
2112
17%
704
60%
704
23%
1360
November1st to 15thNight
51%
700
23%
2101
21%
700
56%
700
25%
1349
November16th to endNight
46%
720
23%
2160
16%
720
55%
720
22%
1427
December1st to 15thNight
45%
720
21%
2325
18%
720
53%
720
19%
1542
December16th to endNight
51%
768
20%
2496
16%
768
59%
768
23%
1554

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
8%5%25%6%46%6%7%10%36%
47906
Night
8%425%5%35%5%6%9%40%
47192
TransparencyDay
38%11%16%17%12%3
47607
Night
37%10%16%19%12%4
46995
SeeingDay
8%9%9%19%28%24%
5964
Night
9%16%10%21%28%13%
16148

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
12%6%245%346%7%9%35%
1611
16th to endDay
10%43443447%7%45%
1728
February1st to 15thDay
10%5%14435%45%7%46%
1736
16th to endDay
9%424425%45%7%48%
1706
March1st to 15thDay
6%3145%25%46%9%49%
1980
16th to endDay
7%4245%35%5%5%8%47%
2111
April1st to 15thDay
5%2146%35%5%7%9%48%
1978
16th to endDay
6%4235%36%6%6%8%46%
2160
May1st to 15thDay
6%3135%35%5%6%9%48%
2203
16th to endDay
8%436%5%47%6%8%9%34%
2431
June1st to 15thDay
10%7%36%6%47%8%8%11%25%
2340
16th to endDay
7%426%8%5%7%7%9%11%29%
2340
July1st to 15thDay
8%5%37%6%37%8%9%12%26%
2340
16th to endDay
9%426%7%47%8%8%12%27%
2465
August1st to 15thDay
5%5%26%6%36%9%9%14%29%
2307
16th to endDay
9%7%36%8%5%6%6%9%12%25%
2211
September1st to 15thDay
7%5%27%6%47%8%9%11%27%
1980
16th to endDay
11%6%47%7%5%8%7%8%10%21%
1894
October1st to 15thDay
10%5%35%6%5%6%7%6%9%32%
1708
16th to endDay
11%5%25%5%245%5%8%41%
1760
November1st to 15thDay
6%5%26%5%36%6%7%8%41%
1757
16th to endDay
9%5%25%6%35%6%6%9%38%
1800
December1st to 15thDay
12%5%36%5%36%6%5%7%36%
1632
16th to endDay
8%425%5%36%7%6%8%40%
1728
January1st to 15thNight
10%6%25%5%35%46%9%40%
2327
16th to endNight
10%5%36%425%5%6%8%42%
2496
February1st to 15thNight
11%5%24423446%50%
2115
16th to endNight
8%3243245%5%8%52%
1767
March1st to 15thNight
5%325%42445%8%53%
1980
16th to endNight
7%31442447%8%50%
2112
April1st to 15thNight
5%223425%45%8%55%
1967
16th to endNight
7%3144246%6%9%49%
1800
May1st to 15thNight
6%3134345%5%8%52%
1756
16th to endNight
7%3245%36%7%7%12%38%
1682
June1st to 15thNight
10%6%35%6%48%6%8%12%27%
1620
16th to endNight
7%326%6%47%6%9%12%33%
1620
July1st to 15thNight
9%435%6%46%7%8%10%32%
1620
16th to endNight
5%5%25%6%36%8%7%11%36%
1703
August1st to 15thNight
44145%45%8%10%13%35%
1641
16th to endNight
10%5%36%7%46%7%7%11%29%
1988
September1st to 15thNight
7%6%37%8%47%7%8%11%26%
1980
16th to endNight
9%8%310%8%5%7%7%8%9%22%
1903
October1st to 15thNight
9%6%37%5%35%5%6%9%36%
1921
16th to endNight
11%6%25%425%5%6%9%40%
2112
November1st to 15thNight
6%436%6%36%5%48%42%
2101
16th to endNight
12%5%24425%5%6%9%39%
2160
December1st to 15thNight
8%5%36%6%45%5%7%7%38%
2325
16th to endNight
7%425%5%26%5%7%10%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%9%10%18%15%4
1612
16th to endDay
35%6%9%18%21%7%
1728
February1st to 15thDay
34%6%9%17%22%9%
1738
16th to endDay
33%8%14%17%19%7%
1706
March1st to 15thDay
30%6%13%27%16%5%
1980
16th to endDay
32%7%15%19%19%5%
2112
April1st to 15thDay
29%9%15%22%19%3
1978
16th to endDay
31%7%13%20%21%4
2160
May1st to 15thDay
29%8%13%23%18%6%
2203
16th to endDay
38%12%15%19%12%
2435
June1st to 15thDay
47%13%17%17%3
2340
16th to endDay
42%14%24%15%3
2340
July1st to 15thDay
42%18%25%12%
2201
16th to endDay
42%17%23%14%1
2310
August1st to 15thDay
37%18%30%12%
2294
16th to endDay
46%18%23%10%1
2211
September1st to 15thDay
44%17%23%12%3
1980
16th to endDay
50%15%17%10%4
1894
October1st to 15thDay
42%11%12%15%13%3
1708
16th to endDay
38%6%12%14%23%5%
1760
November1st to 15thDay
36%7%11%21%18%5%
1757
16th to endDay
40%8%11%14%15%9%
1800
December1st to 15thDay
44%7%11%18%13%4
1632
16th to endDay
35%10%12%21%14%5%
1728
January1st to 15thNight
39%8%13%19%14%5%
2327
16th to endNight
37%5%11%21%15%7%
2496
February1st to 15thNight
33%5%10%18%21%10%
2124
16th to endNight
28%7%15%22%20%6%
1767
March1st to 15thNight
28%6%10%29%19%5%
1980
16th to endNight
28%8%15%22%18%7%
2112
April1st to 15thNight
26%7%16%24%19%5%
1967
16th to endNight
30%6%15%21%21%4
1800
May1st to 15thNight
28%8%11%26%18%7%
1757
16th to endNight
34%12%17%22%12%
1684
June1st to 15thNight
45%11%20%17%4
1620
16th to endNight
39%16%21%18%3
1620
July1st to 15thNight
42%16%23%15%1
1530
16th to endNight
36%18%28%15%
1595
August1st to 15thNight
33%17%34%13%
1630
16th to endNight
45%16%26%12%
1988
September1st to 15thNight
45%18%21%12%2
1980
16th to endNight
52%14%15%12%31
1903
October1st to 15thNight
40%9%14%16%14%3
1921
16th to endNight
39%7%10%14%20%6%
2112
November1st to 15thNight
38%7%10%18%19%5%
2101
16th to endNight
41%6%9%17%16%8%
2160
December1st to 15thNight
43%7%11%21%11%4
2325
16th to endNight
34%9%15%20%13%6%
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%321%27%17%8%
90
16th to endDay
14%12%23%26%19%3
96
February1st to 15thDay
4227%30%27%7%
90
16th to endDay
10%12%18%37%19%
207
March1st to 15thDay
7%15%20%34%17%5%
270
16th to endDay
8%13%17%28%25%6%
288
April1st to 15thDay
312%14%34%29%5%
270
16th to endDay
6%11%9%28%35%8%
270
May1st to 15thDay
5%11%6%29%31%14%
288
16th to endDay
6%9%6%13%34%29%
331
June1st to 15thDay
9%10%411%34%29%
315
16th to endDay
310%17%25%51%
315
July1st to 15thDay
6%6%1323%59%
305
16th to endDay
7%9%17%28%44%
326
August1st to 15thDay
6%5%1331%50%
313
16th to endDay
10%5%37%25%47%
332
September1st to 15thDay
7%6%410%30%40%
315
16th to endDay
13%5%5%10%28%37%
283
October1st to 15thDay
12%6%8%21%36%13%
255
16th to endDay
10%8%12%30%29%8%
272
November1st to 15thDay
6%11%10%27%30%13%
265
16th to endDay
10%11%17%30%24%5%
270
December1st to 15thDay
10%219%32%31%2
102
16th to endDay
9%39%22%45%9%
96
January1st to 15thNight
12%21%19%23%19%3
720
16th to endNight
9%22%22%27%17%
768
February1st to 15thNight
9%20%18%30%18%2
704
16th to endNight
9%17%19%33%18%
631
March1st to 15thNight
5%20%21%30%17%4
720
16th to endNight
5%19%16%28%26%2
768
April1st to 15thNight
5%19%13%29%27%4
718
16th to endNight
6%17%11%30%30%3
720
May1st to 15thNight
7%17%6%27%35%5%
677
16th to endNight
6%17%317%36%18%
563
June1st to 15thNight
10%16%310%37%21%
540
16th to endNight
5%16%26%33%34%
540
July1st to 15thNight
7%12%16%32%39%
510
16th to endNight
5%16%1436%36%
564
August1st to 15thNight
5%9%15%36%41%
560
16th to endNight
11%8%38%31%36%
764
September1st to 15thNight
11%8%39%35%31%
720
16th to endNight
14%9%312%33%26%
689
October1st to 15thNight
13%10%6%21%39%9%
660
16th to endNight
14%10%11%21%32%8%
704
November1st to 15thNight
8%16%12%29%25%7%
700
16th to endNight
12%18%15%28%20%4
720
December1st to 15thNight
9%19%15%25%25%5%
720
16th to endNight
7%20%13%25%27%5%
768
Page generated at 2017-09-24 09:15:58. Version ac04

Copyright 2017 A. Danko


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