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 2019-06-24.

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
56%
18537
18%
54008
14%
18497
61%
18497
24%
35190

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
42%
837
21%
2717
14%
836
52%
836
22%
1713
January16th to endNight
40%
896
22%
2912
16%
896
50%
896
23%
1795
February1st to 15thNight
48%
821
23%
2477
16%
818
57%
818
28%
1494
February16th to endNight
51%
735
27%
2059
16%
735
61%
735
35%
1180
March1st to 15thNight
48%
840
28%
2310
16%
840
59%
840
33%
1330
March16th to endNight
54%
896
24%
2464
16%
896
61%
896
35%
1451
April1st to 15thNight
58%
838
22%
2296
17%
838
62%
838
34%
1350
April16th to endNight
58%
831
25%
2077
14%
831
63%
831
35%
1265
May1st to 15thNight
63%
789
23%
2049
15%
789
65%
789
33%
1279
May16th to endNight
64%
657
18%
1970
13%
657
66%
657
25%
1277
June1st to 15thNight
60%
630
11%
1890
7%
630
62%
630
18%
1355
June16th to endNight
64%
609
9%
1828
8%
609
65%
609
19%
1300
July1st to 15thNight
67%
555
7%
1665
6%
555
67%
555
18%
1200
July16th to endNight
67%
612
8%
1739
8%
579
71%
579
21%
1227
August1st to 15thNight
71%
598
9%
1738
9%
595
71%
595
23%
1168
August16th to endNight
62%
828
6%
2154
5%
828
63%
828
19%
1629
September1st to 15thNight
63%
780
6%
2145
6%
780
63%
780
17%
1649
September16th to endNight
55%
777
8%
2145
6%
777
58%
777
15%
1657
October1st to 15thNight
58%
780
19%
2271
19%
780
60%
780
21%
1544
October16th to endNight
55%
832
21%
2496
17%
832
61%
832
24%
1598
November1st to 15thNight
54%
820
21%
2461
19%
820
58%
820
24%
1595
November16th to endNight
50%
840
24%
2520
18%
840
58%
840
24%
1639
December1st to 15thNight
48%
840
23%
2713
19%
840
56%
840
22%
1739
December16th to endNight
55%
896
22%
2912
19%
896
62%
896
25%
1756

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%37%
54794
Night
8%425%5%35%5%6%9%41%
54217
TransparencyDay
37%11%17%17%12%3
54495
Night
36%10%16%19%12%4
54020
SeeingDay
8%7%10%22%29%22%
8335
Night
8%14%11%22%29%13%
18546

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
11%6%245%346%7%9%37%
1881
16th to endDay
10%424435%47%7%44%
2016
February1st to 15thDay
9%5%14435%45%9%44%
2034
16th to endDay
8%424425%45%8%49%
1986
March1st to 15thDay
5%3145%25%46%9%51%
2310
16th to endDay
7%4245%35%5%5%8%48%
2463
April1st to 15thDay
5%2145%35%6%7%9%48%
2309
16th to endDay
6%3235%35%5%6%8%48%
2488
May1st to 15thDay
6%3245%45%5%6%9%46%
2571
16th to endDay
8%437%5%46%6%7%8%36%
2847
June1st to 15thDay
9%6%36%6%48%8%8%11%25%
2730
16th to endDay
7%5%26%7%5%6%8%8%12%29%
2639
July1st to 15thDay
8%5%37%6%37%8%8%12%27%
2535
16th to endDay
9%5%26%7%47%8%8%12%27%
2673
August1st to 15thDay
5%425%5%36%8%9%14%31%
2451
16th to endDay
9%6%25%8%5%6%7%9%13%25%
2396
September1st to 15thDay
7%5%37%6%5%7%8%10%11%26%
2145
16th to endDay
10%6%37%7%5%8%6%8%10%24%
2145
October1st to 15thDay
10%5%35%6%5%6%7%7%10%30%
2018
16th to endDay
10%5%25%5%345%6%8%42%
2080
November1st to 15thDay
6%5%26%5%36%6%7%8%40%
2057
16th to endDay
9%5%25%6%35%6%5%9%40%
2100
December1st to 15thDay
11%5%36%5%35%5%5%7%39%
1904
16th to endDay
7%425%5%36%7%6%9%41%
2016
January1st to 15thNight
10%5%25%43446%8%43%
2717
16th to endNight
10%436%425%5%6%8%42%
2912
February1st to 15thNight
10%5%23424447%49%
2477
16th to endNight
7%3233245%5%8%54%
2059
March1st to 15thNight
432432446%8%55%
2310
16th to endNight
7%31442446%8%51%
2464
April1st to 15thNight
6%223425%45%8%54%
2296
16th to endNight
6%2134245%6%9%51%
2077
May1st to 15thNight
7%3235%345%6%8%51%
2049
16th to endNight
7%3245%36%6%7%11%40%
1970
June1st to 15thNight
9%6%35%6%48%6%8%13%28%
1890
16th to endNight
6%426%6%47%6%9%12%33%
1828
July1st to 15thNight
9%435%6%46%7%8%10%33%
1755
16th to endNight
5%5%25%6%36%8%7%12%36%
1847
August1st to 15thNight
44145%46%8%10%13%36%
1749
16th to endNight
9%5%35%7%46%7%8%11%30%
2154
September1st to 15thNight
7%5%37%7%5%7%8%8%12%26%
2145
16th to endNight
8%7%29%8%46%7%8%10%25%
2145
October1st to 15thNight
8%6%37%5%35%6%7%10%35%
2271
16th to endNight
11%6%24425%5%6%9%41%
2496
November1st to 15thNight
6%436%6%46%5%5%9%41%
2461
16th to endNight
11%5%24425%5%6%9%41%
2520
December1st to 15thNight
7%5%36%6%345%6%8%41%
2713
16th to endNight
6%325%5%25%5%7%10%44%
2912

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
40%9%9%19%17%4
1882
16th to endDay
36%6%10%19%20%6%
2016
February1st to 15thDay
35%6%11%17%20%8%
2036
16th to endDay
30%7%14%19%21%6%
1986
March1st to 15thDay
28%6%15%26%16%6%
2310
16th to endDay
32%7%14%20%20%5%
2464
April1st to 15thDay
28%9%16%23%18%3
2309
16th to endDay
29%7%12%22%22%5%
2488
May1st to 15thDay
30%9%14%21%18%5%
2571
16th to endDay
39%11%13%19%15%
2851
June1st to 15thDay
45%14%20%16%2
2730
16th to endDay
40%15%25%14%3
2639
July1st to 15thDay
40%17%27%13%
2396
16th to endDay
42%18%23%13%1
2518
August1st to 15thDay
36%18%31%13%
2438
16th to endDay
44%18%24%10%1
2396
September1st to 15thDay
43%18%22%11%2
2145
16th to endDay
46%15%20%12%4
2145
October1st to 15thDay
43%11%13%16%12%3
2018
16th to endDay
36%6%12%14%22%6%
2080
November1st to 15thDay
35%8%13%20%16%4
2057
16th to endDay
39%8%12%17%15%7%
2100
December1st to 15thDay
41%7%12%20%12%4
1904
16th to endDay
33%9%13%23%14%4
2016
January1st to 15thNight
38%7%12%20%15%5%
2717
16th to endNight
38%6%11%22%15%6%
2912
February1st to 15thNight
33%6%12%19%18%8%
2486
16th to endNight
26%6%14%22%22%6%
2059
March1st to 15thNight
26%6%13%28%19%5%
2310
16th to endNight
27%7%15%24%17%7%
2464
April1st to 15thNight
26%8%17%25%17%4
2296
16th to endNight
28%6%13%22%23%5%
2077
May1st to 15thNight
29%8%12%25%18%6%
2050
16th to endNight
34%11%16%22%15%
1972
June1st to 15thNight
43%12%22%17%3
1890
16th to endNight
39%16%23%17%3
1828
July1st to 15thNight
40%17%25%15%1
1665
16th to endNight
35%18%29%15%
1739
August1st to 15thNight
32%17%34%15%
1738
16th to endNight
43%16%26%12%
2154
September1st to 15thNight
44%18%22%12%2
2145
16th to endNight
48%15%17%14%31
2145
October1st to 15thNight
40%10%14%16%13%3
2271
16th to endNight
38%7%10%15%20%7%
2496
November1st to 15thNight
39%7%13%17%17%4
2461
16th to endNight
39%6%10%18%16%7%
2520
December1st to 15thNight
40%7%12%22%11%5%
2713
16th to endNight
32%9%15%24%12%5%
2912

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
17%323%32%16%6%
180
16th to endDay
11%8%27%35%15%1
192
February1st to 15thDay
7%118%34%31%6%
180
16th to endDay
7%8%15%35%26%7%
305
March1st to 15thDay
5%11%23%35%18%4
390
16th to endDay
10%10%18%30%25%5%
416
April1st to 15thDay
38%15%35%30%5%
390
16th to endDay
6%8%11%29%36%7%
379
May1st to 15thDay
8%8%6%32%32%11%
408
16th to endDay
7%7%6%15%37%25%
459
June1st to 15thDay
8%7%312%39%29%
435
16th to endDay
48%17%26%52%
407
July1st to 15thDay
6%5%1324%59%
365
16th to endDay
8%8%18%28%43%
390
August1st to 15thDay
5%5%1432%51%
358
16th to endDay
9%437%25%50%
396
September1st to 15thDay
7%5%49%32%41%
375
16th to endDay
10%4410%31%38%
374
October1st to 15thDay
12%5%8%21%41%11%
375
16th to endDay
10%6%13%32%29%8%
400
November1st to 15thDay
7%8%10%28%32%12%
385
16th to endDay
10%8%15%36%25%3
390
December1st to 15thDay
8%323%34%26%3
194
16th to endDay
7%39%30%40%8%
192
January1st to 15thNight
12%18%19%25%19%3
840
16th to endNight
9%19%23%30%16%
896
February1st to 15thNight
9%17%17%30%21%3
824
16th to endNight
9%15%17%33%22%2
735
March1st to 15thNight
5%18%22%32%18%3
840
16th to endNight
6%16%16%30%26%2
896
April1st to 15thNight
5%16%13%30%28%4
838
16th to endNight
6%15%12%31%29%3
831
May1st to 15thNight
7%15%6%28%35%5%
790
16th to endNight
7%15%316%39%17%
659
June1st to 15thNight
9%14%310%40%21%
630
16th to endNight
6%14%26%32%37%
609
July1st to 15thNight
7%11%15%32%41%
555
16th to endNight
5%15%1436%37%
612
August1st to 15thNight
5%9%15%37%41%
598
16th to endNight
10%7%37%31%38%
828
September1st to 15thNight
10%8%38%36%32%
780
16th to endNight
13%8%311%35%27%
777
October1st to 15thNight
12%8%6%21%40%9%
780
16th to endNight
14%9%12%23%31%9%
832
November1st to 15thNight
8%14%11%28%28%7%
820
16th to endNight
11%16%14%32%21%4
840
December1st to 15thNight
8%17%17%25%25%5%
840
16th to endNight
7%17%13%27%28%5%
896
Page generated at 2019-06-24 20:41:32. Version ac04

Copyright 2019 A. Danko


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