Green Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Green Valley clear sky chart from 2005-11-06 to 2024-03-18.

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
74%
24227
36%
79584
31%
24146
80%
24146
50%
36887

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 10thNight
71%
750
42%
3976
34%
736
78%
736
37%
1479
January11th to 20thNight
71%
748
48%
3878
36%
740
80%
740
48%
1215
January21st to endNight
63%
828
24%
4286
33%
814
73%
814
26%
2178
February1st to 10thNight
70%
760
37%
2409
35%
760
78%
760
52%
1124
February11th to 20thNight
61%
740
35%
2219
29%
740
72%
740
49%
1103
February21st to endNight
58%
628
38%
1784
29%
628
68%
628
50%
910
March1st to 10thNight
60%
760
40%
2090
27%
760
72%
760
54%
1055
March11th to 20thNight
68%
752
40%
2068
29%
752
76%
752
59%
1013
March21st to endNight
69%
792
37%
2178
27%
792
77%
792
58%
1063
April1st to 10thNight
70%
720
39%
1980
27%
720
79%
720
65%
904
April11th to 20thNight
64%
582
41%
1826
32%
582
76%
582
61%
773
April21st to endNight
72%
540
46%
1789
41%
540
82%
540
70%
670
May1st to 10thNight
70%
540
43%
1620
32%
540
79%
540
69%
658
May11th to 20thNight
78%
531
43%
1594
36%
531
83%
531
73%
642
May21st to endNight
76%
582
44%
1746
34%
582
84%
582
80%
660
June1st to 10thNight
84%
540
37%
1620
32%
540
85%
540
66%
687
June11th to 20thNight
84%
540
39%
1620
32%
540
87%
540
77%
629
June21st to endNight
84%
540
29%
1620
25%
540
85%
540
56%
756
July1st to 10thNight
84%
525
22%
1575
19%
525
84%
525
43%
831
July11th to 20thNight
79%
522
18%
1566
15%
522
79%
522
31%
964
July21st to endNight
78%
591
15%
1674
13%
558
77%
558
27%
1087
August1st to 10thNight
84%
537
23%
1602
20%
534
84%
534
41%
865
August11th to 20thNight
81%
534
26%
1606
26%
534
81%
534
40%
882
August21st to endNight
81%
648
27%
2034
28%
648
81%
648
37%
1139
September1st to 10thNight
79%
720
29%
1980
27%
720
80%
720
43%
1143
September11th to 20thNight
88%
720
41%
1980
35%
720
89%
720
61%
974
September21st to endNight
82%
720
39%
1980
30%
720
86%
720
61%
963
October1st to 10thNight
79%
720
40%
2049
32%
720
85%
720
67%
925
October11th to 20thNight
81%
720
44%
2160
36%
720
88%
720
70%
901
October21st to endNight
83%
792
46%
2376
40%
792
88%
792
73%
967
November1st to 10thNight
80%
740
45%
2220
39%
740
85%
740
68%
940
November11th to 20thNight
79%
760
43%
2284
38%
760
84%
760
62%
1005
November21st to endNight
65%
760
38%
2470
34%
760
72%
760
47%
1186
December1st to 10thNight
72%
760
39%
2470
38%
760
77%
760
50%
1146
December11th to 20thNight
65%
760
33%
2941
34%
759
72%
759
35%
1550
December21st to endNight
63%
825
24%
4314
34%
817
70%
817
30%
1900

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
331332445%6%65%
79173
Night
3313323447%67%
80685
TransparencyDay
21%35%12%26%33%
78900
Night
19%35%14%28%31%
80480
SeeingDay
5%6%18%31%27%13%
14029
Night
4314%41%33%6%
24274

By Month

Percentage Cloud Cover SW (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 10thDay
4433324346%65%
2858
11th to 20thDay
4312323445%68%
2860
21st to endDay
6%4234245%6%8%57%
3146
February1st to 10thDay
5%413323336%67%
1768
11th to 20thDay
5%323324445%64%
1850
21st to endDay
6%423323336%67%
1668
March1st to 10thDay
3313424447%64%
2090
11th to 20thDay
4313322346%69%
2058
21st to endDay
2212323435%73%
2178
April1st to 10thDay
1112323347%74%
1980
11th to 20thDay
321121122480%
2081
21st to endDay
1112212225%83%
2166
May1st to 10thDay
1112222335%80%
2340
11th to 20thDay
112222235%79%
2301
21st to endDay
111211212386%
2530
June1st to 10thDay
2212212247%76%
2340
11th to 20thDay
11111223483%
2340
21st to endDay
2213434445%67%
2340
July1st to 10thDay
3325%6%47%7%6%8%48%
2340
11th to 20thDay
6%427%7%6%8%8%8%10%34%
2340
21st to endDay
8%6%27%7%5%8%8%8%10%29%
2545
August1st to 10thDay
6%5%246%47%8%8%9%42%
2328
11th to 20thDay
4425%7%48%7%8%10%42%
2295
21st to endDay
43246%47%6%8%9%48%
2318
September1st to 10thDay
6%426%5%45%6%5%8%49%
1980
11th to 20thDay
321232445%6%66%
1980
21st to endDay
3212223445%70%
1980
October1st to 10thDay
121222335%5%75%
1908
11th to 20thDay
211312235%80%
1800
21st to endDay
111312346%78%
1980
November1st to 10thDay
2111222347%75%
1859
11th to 20thDay
2212224346%73%
1891
21st to endDay
431332445%5%66%
1710
December1st to 10thDay
5%31333345%7%63%
1710
11th to 20thDay
5%425%5%245%6%6%54%
2169
21st to endDay
6%31343445%6%62%
3146
January1st to 10thNight
4413323445%67%
4097
11th to 20thNight
3212213335%76%
4110
21st to endNight
10%5%24424448%53%
4521
February1st to 10thNight
3413323445%68%
2409
11th to 20thNight
4413323446%65%
2218
21st to endNight
3314423347%64%
1784
March1st to 10thNight
321342345%7%66%
2090
11th to 20thNight
3212213346%72%
2068
21st to endNight
3212323447%68%
2178
April1st to 10thNight
1212223336%75%
1980
11th to 20thNight
121232223379%
1826
21st to endNight
211121222483%
1789
May1st to 10thNight
111121233480%
1620
11th to 20thNight
1112212246%80%
1594
21st to endNight
1111122388%
1746
June1st to 10thNight
3112222236%76%
1620
11th to 20thNight
112212225%83%
1620
21st to endNight
22143235%35%69%
1620
July1st to 10thNight
2224435%6%6%9%56%
1620
11th to 20thNight
34245%47%8%10%16%37%
1620
21st to endNight
4325%8%5%7%8%11%16%32%
1773
August1st to 10thNight
2324435%6%7%11%54%
1611
11th to 20thNight
42246%35%5%7%11%49%
1606
21st to endNight
43245%45%6%8%11%48%
2034
September1st to 10thNight
6%4244345%7%8%54%
1980
11th to 20thNight
2213323346%71%
1980
21st to endNight
2212323346%71%
1980
October1st to 10thNight
122313336%76%
2049
11th to 20thNight
1112212235%80%
2160
21st to endNight
1111212235%82%
2376
November1st to 10thNight
2112212346%77%
2220
11th to 20thNight
2212313346%74%
2284
21st to endNight
431332335%6%65%
2470
December1st to 10thNight
5%31332345%6%66%
2470
11th to 20thNight
5%4245%34346%58%
3041
21st to endNight
5%4244345%5%5%60%
4521

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 10thDay
22%3311%32%30%
2859
11th to 20thDay
21%3313%35%25%
2860
21st to endDay
27%3417%33%17%
3146
February1st to 10thDay
20%3311%24%38%
1768
11th to 20thDay
24%3314%26%31%
1860
21st to endDay
22%2310%28%35%
1668
March1st to 10thDay
22%229%32%33%
2090
11th to 20thDay
19%239%29%38%
2058
21st to endDay
15%3210%36%34%
2178
April1st to 10thDay
12%227%37%40%
1980
11th to 20thDay
11%216%28%52%
2084
21st to endDay
9%127%31%50%
2166
May1st to 10thDay
10%227%23%56%
2340
11th to 20thDay
10%129%25%52%
2304
21st to endDay
7%11425%61%
2530
June1st to 10thDay
11%116%26%54%
2340
11th to 20thDay
8%11319%67%
2340
21st to endDay
19%449%19%46%
2340
July1st to 10thDay
30%7%9%14%18%22%
2276
11th to 20thDay
40%9%17%21%8%4
2271
21st to endDay
45%10%18%17%8%2
2404
August1st to 10thDay
34%9%14%14%18%11%
2313
11th to 20thDay
34%7%15%18%17%10%
2295
21st to endDay
31%8%11%21%16%13%
2318
September1st to 10thDay
34%48%17%18%19%
1980
11th to 20thDay
18%4414%27%33%
1980
21st to endDay
17%4414%33%30%
1980
October1st to 10thDay
13%35%15%29%36%
1908
11th to 20thDay
10%229%32%45%
1800
21st to endDay
10%2211%27%47%
1980
November1st to 10thDay
12%3211%37%36%
1859
11th to 20thDay
15%2312%30%39%
1891
21st to endDay
22%3413%25%33%
1710
December1st to 10thDay
22%4316%28%28%
1710
11th to 20thDay
30%3414%28%20%
2168
21st to endDay
24%3313%38%19%
3146
January1st to 10thNight
19%3212%39%24%
4097
11th to 20thNight
13%2218%41%23%
4110
21st to endNight
33%26%17%28%14%
4521
February1st to 10thNight
19%2414%22%39%
2409
11th to 20thNight
22%25%15%27%29%
2219
21st to endNight
23%2311%29%33%
1784
March1st to 10thNight
19%3212%32%31%
2090
11th to 20thNight
17%2212%26%40%
2068
21st to endNight
17%25%12%35%29%
2178
April1st to 10thNight
14%2211%35%38%
1980
11th to 20thNight
14%128%27%49%
1826
21st to endNight
9%118%31%49%
1789
May1st to 10thNight
10%237%26%52%
1620
11th to 20thNight
9%229%26%51%
1595
21st to endNight
6%115%28%59%
1746
June1st to 10thNight
12%226%25%54%
1620
11th to 20thNight
8%115%19%68%
1620
21st to endNight
16%447%19%49%
1620
July1st to 10thNight
23%7%14%14%15%27%
1575
11th to 20thNight
32%10%19%23%12%4
1566
21st to endNight
36%11%24%18%9%2
1674
August1st to 10thNight
23%9%15%22%18%13%
1602
11th to 20thNight
27%6%19%19%18%11%
1606
21st to endNight
27%8%14%19%20%12%
2034
September1st to 10thNight
26%6%10%23%17%18%
1980
11th to 20thNight
16%3414%31%32%
1980
21st to endNight
15%3415%34%29%
1980
October1st to 10thNight
12%25%17%27%36%
2049
11th to 20thNight
10%3312%27%46%
2160
21st to endNight
9%2311%29%46%
2376
November1st to 10thNight
11%2213%37%35%
2220
11th to 20thNight
14%2314%30%37%
2284
21st to endNight
21%4312%29%31%
2470
December1st to 10thNight
21%2419%27%28%
2470
11th to 20thNight
30%25%14%27%21%
3041
21st to endNight
26%3413%32%22%
4521

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 10thDay
6%7%22%35%26%3
270
11th to 20thDay
8%5%17%40%25%6%
270
21st to endDay
28%21%37%25%6%
297
February1st to 10thDay
7%8%20%34%25%5%
328
11th to 20thDay
10%12%30%33%14%1
455
21st to endDay
9%16%34%29%10%2
382
March1st to 10thDay
5%15%28%35%14%3
460
11th to 20thDay
7%12%24%30%19%7%
449
21st to endDay
5%16%29%33%13%4
462
April1st to 10thDay
19%31%31%20%8%
420
11th to 20thDay
412%32%30%17%6%
412
21st to endDay
212%30%27%19%9%
420
May1st to 10thDay
213%27%29%18%10%
423
11th to 20thDay
27%25%35%24%7%
448
21st to endDay
27%28%35%21%7%
485
June1st to 10thDay
3419%42%24%9%
450
11th to 20thDay
1418%39%27%12%
450
21st to endDay
2212%37%32%13%
450
July1st to 10thDay
326%32%36%22%
446
11th to 20thDay
6%17%21%36%29%
444
21st to endDay
10%1416%38%30%
487
August1st to 10thDay
5%1319%40%31%
447
11th to 20thDay
5%25%19%39%30%
437
21st to endDay
5%1318%40%34%
495
September1st to 10thDay
8%28%31%34%16%
450
11th to 20thDay
5%9%30%40%16%
450
21st to endDay
4415%28%32%17%
450
October1st to 10thDay
26%17%30%29%17%
378
11th to 20thDay
3311%27%40%15%
270
21st to endDay
1213%31%36%15%
297
November1st to 10thDay
46%16%35%31%8%
270
11th to 20thDay
2311%39%38%7%
270
21st to endDay
5%7%22%36%23%6%
270
December1st to 10thDay
7%5%15%37%31%6%
270
11th to 20thDay
6%420%43%24%3
270
21st to endDay
11%6%24%35%20%4
297
January1st to 10thNight
5%316%47%26%3
760
11th to 20thNight
5%316%47%25%4
760
21st to endNight
7%419%44%23%3
836
February1st to 10thNight
45%17%46%24%5%
760
11th to 20thNight
5%5%24%46%18%2
744
21st to endNight
47%26%45%15%1
628
March1st to 10thNight
35%28%47%17%1
760
11th to 20thNight
45%20%40%26%5%
752
21st to endNight
35%18%47%24%3
792
April1st to 10thNight
2221%49%24%2
720
11th to 20thNight
3426%46%20%1
582
21st to endNight
2421%49%22%2
540
May1st to 10thNight
1422%47%24%1
540
11th to 20thNight
1117%48%30%3
531
21st to endNight
1318%49%27%2
584
June1st to 10thNight
317%51%35%2
540
11th to 20thNight
1111%48%39%1
540
21st to endNight
215%40%46%7%
540
July1st to 10thNight
12432%55%6%
525
11th to 20thNight
41318%64%10%
522
21st to endNight
5%2219%56%16%
591
August1st to 10thNight
31217%60%18%
537
11th to 20thNight
32221%61%11%
534
21st to endNight
5%1218%60%15%
648
September1st to 10thNight
6%1425%51%13%
720
11th to 20thNight
31335%51%8%
720
21st to endNight
319%38%42%7%
720
October1st to 10thNight
1113%43%36%5%
720
11th to 20thNight
2211%43%35%6%
720
21st to endNight
1211%41%36%9%
792
November1st to 10thNight
2213%44%33%7%
740
11th to 20thNight
3213%43%36%4
760
21st to endNight
5%321%44%22%5%
760
December1st to 10thNight
6%413%48%24%5%
760
11th to 20thNight
7%418%47%21%3
760
21st to endNight
7%5%19%43%22%5%
836
Page generated at 2024-03-15 11:01:44. Version ac07

Copyright © 2024 Attilla Danko.


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