Green Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Green Valley clear sky chart from 2005-11-05 to 2017-08-12.

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
77%
15461
36%
46522
32%
15423
82%
15423
55%
21832

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
77%
718
34%
2327
37%
716
81%
716
53%
1055
January16th to endNight
69%
768
35%
2496
34%
768
76%
768
43%
1266
February1st to 15thNight
75%
698
38%
2187
37%
698
82%
698
58%
970
February16th to endNight
67%
632
40%
1832
36%
632
74%
632
52%
900
March1st to 15thNight
69%
720
41%
1980
33%
720
77%
720
61%
947
March16th to endNight
76%
768
39%
2112
30%
768
82%
768
63%
993
April1st to 15thNight
70%
690
36%
1949
26%
690
77%
690
57%
928
April16th to endNight
73%
540
45%
1792
40%
540
83%
540
71%
665
May1st to 15thNight
74%
539
42%
1619
32%
539
82%
539
74%
637
May16th to endNight
78%
561
43%
1684
34%
561
85%
561
77%
648
June1st to 15thNight
85%
540
35%
1620
31%
540
86%
540
71%
662
June16th to endNight
87%
540
31%
1620
27%
540
88%
540
63%
713
July1st to 15thNight
85%
510
19%
1530
16%
510
85%
510
39%
838
July16th to endNight
81%
564
17%
1593
14%
531
80%
531
31%
987
August1st to 15thNight
87%
527
25%
1575
23%
524
87%
524
42%
843
August16th to endNight
82%
558
27%
1732
28%
558
82%
558
40%
949
September1st to 15thNight
80%
660
30%
1815
27%
660
81%
660
44%
1045
September16th to endNight
88%
656
43%
1815
36%
656
91%
656
68%
838
October1st to 15thNight
80%
660
42%
1913
32%
660
86%
660
68%
834
October16th to endNight
87%
704
44%
2112
39%
704
91%
704
71%
883
November1st to 15thNight
82%
700
44%
2100
40%
700
86%
700
70%
871
November16th to endNight
72%
720
39%
2283
37%
720
77%
720
52%
1064
December1st to 15thNight
75%
720
39%
2340
39%
720
79%
720
52%
1040
December16th to endNight
68%
768
35%
2496
36%
768
72%
768
44%
1256

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
3213324446%64%
47440
Night
2212213346%68%
46724
TransparencyDay
20%35%11%25%33%
47135
Night
17%35%14%27%31%
46530
SeeingDay
5%7%19%31%25%10%
5279
Night
3211%37%37%7%
15472

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 15thDay
211333335%6%64%
1611
16th to endDay
4313323346%63%
1728
February1st to 15thDay
4312213335%68%
1667
16th to endDay
4223214335%64%
1640
March1st to 15thDay
2212213446%68%
1980
16th to endDay
22221233475%
2112
April1st to 15thDay
212212346%72%
1997
16th to endDay
11111111383%
2166
May1st to 15thDay
1111235%79%
2331
16th to endDay
111212383%
2429
June1st to 15thDay
11112235%79%
2340
16th to endDay
122213345%71%
2340
July1st to 15thDay
4325%7%48%8%7%9%39%
2340
16th to endDay
7%5%28%7%5%8%7%8%9%27%
2467
August1st to 15thDay
6%5%25%6%38%8%8%8%36%
2290
16th to endDay
43246%47%5%7%9%44%
2115
September1st to 15thDay
6%425%6%36%6%5%7%46%
1815
16th to endDay
322223445%68%
1815
October1st to 15thDay
11221223475%
1716
16th to endDay
11212235%77%
1760
November1st to 15thDay
111112236%77%
1759
16th to endDay
31121333472%
1674
December1st to 15thDay
5%213222437%64%
1620
16th to endDay
5%21321346%6%62%
1728
January1st to 15thNight
3212312346%68%
2327
16th to endNight
5%2134245%46%60%
2496
February1st to 15thNight
222222346%69%
2182
16th to endNight
2313313447%64%
1832
March1st to 15thNight
2112212246%71%
1980
16th to endNight
2111213335%73%
2112
April1st to 15thNight
1112323235%72%
1949
16th to endNight
2111111384%
1792
May1st to 15thNight
111235%80%
1619
16th to endNight
1122385%
1684
June1st to 15thNight
21111125%81%
1620
16th to endNight
1112212435%73%
1620
July1st to 15thNight
1213436%6%7%13%49%
1620
16th to endNight
33235%37%7%11%16%34%
1701
August1st to 15thNight
2213335%5%8%10%54%
1584
16th to endNight
42144345%7%11%50%
1732
September1st to 15thNight
432442347%7%55%
1815
16th to endNight
112213335%74%
1815
October1st to 15thNight
11121223478%
1913
16th to endNight
121213480%
2112
November1st to 15thNight
12112245%77%
2100
16th to endNight
4213323235%69%
2283
December1st to 15thNight
4212212347%67%
2340
16th to endNight
5%313324346%62%
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
20%3413%27%30%
1612
16th to endDay
22%3218%26%27%
1728
February1st to 15thDay
19%1213%28%34%
1667
16th to endDay
22%2314%29%27%
1640
March1st to 15thDay
18%128%32%37%
1980
16th to endDay
14%129%33%37%
2112
April1st to 15thDay
14%117%38%36%
1997
16th to endDay
9%117%27%52%
2166
May1st to 15thDay
9%118%25%53%
2331
16th to endDay
8%25%28%53%
2432
June1st to 15thDay
9%11424%59%
2340
16th to endDay
16%226%19%52%
2340
July1st to 15thDay
35%8%13%14%15%13%
2201
16th to endDay
47%9%18%17%5%1
2312
August1st to 15thDay
38%9%13%13%16%9%
2275
16th to endDay
33%7%13%20%14%10%
2115
September1st to 15thDay
35%47%18%18%16%
1815
16th to endDay
18%4311%32%30%
1815
October1st to 15thDay
13%2412%30%37%
1716
16th to endDay
9%1310%29%45%
1760
November1st to 15thDay
11%2211%36%37%
1759
16th to endDay
16%1311%28%38%
1674
December1st to 15thDay
21%3316%32%23%
1620
16th to endDay
21%36%18%32%18%
1728
January1st to 15thNight
18%2414%29%30%
2327
16th to endNight
25%3415%29%22%
2496
February1st to 15thNight
16%1417%25%33%
2193
16th to endNight
20%2313%34%24%
1832
March1st to 15thNight
16%1111%30%38%
1980
16th to endNight
14%1411%33%34%
2112
April1st to 15thNight
17%1210%35%33%
1949
16th to endNight
9%118%28%52%
1792
May1st to 15thNight
7%128%30%49%
1620
16th to endNight
6%117%29%53%
1685
June1st to 15thNight
10%115%22%59%
1620
16th to endNight
13%235%21%53%
1620
July1st to 15thNight
23%9%18%16%16%15%
1530
16th to endNight
31%11%25%21%8%1
1593
August1st to 15thNight
21%9%16%22%18%11%
1575
16th to endNight
25%7%17%18%19%11%
1732
September1st to 15thNight
26%6%10%21%20%14%
1815
16th to endNight
11%2315%36%30%
1815
October1st to 15thNight
11%2416%28%36%
1913
16th to endNight
10%1312%25%46%
2112
November1st to 15thNight
10%1215%34%34%
2100
16th to endNight
19%2210%27%37%
2283
December1st to 15thNight
18%1418%32%25%
2340
16th to endNight
24%36%18%28%19%
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
8%7%18%37%25%1
90
16th to endDay
5%8%16%34%25%10%
96
February1st to 15thDay
5%9%16%37%28%3
182
16th to endDay
6%18%31%27%12%2
238
March1st to 15thDay
415%26%28%15%8%
270
16th to endDay
315%29%29%14%7%
288
April1st to 15thDay
313%33%26%15%6%
269
16th to endDay
217%32%29%11%5%
270
May1st to 15thDay
215%31%29%13%7%
288
16th to endDay
18%29%37%18%3
330
June1st to 15thDay
3424%41%19%6%
315
16th to endDay
211%41%29%13%
315
July1st to 15thDay
5%7%37%33%14%
305
16th to endDay
11%16%22%32%25%
327
August1st to 15thDay
7%25%24%39%21%
300
16th to endDay
5%5%25%44%19%
268
September1st to 15thDay
13%18%34%34%8%
255
16th to endDay
7%314%31%31%10%
255
October1st to 15thDay
17%20%30%26%13%
156
16th to endDay
214%16%45%20%
96
November1st to 15thDay
26%18%28%36%6%
90
16th to endDay
18%24%33%28%3
90
December1st to 15thDay
4215%24%43%10%
90
16th to endDay
10%5%30%30%22%1
96
January1st to 15thNight
4211%45%32%4
720
16th to endNight
6%213%43%28%4
768
February1st to 15thNight
3212%44%30%5%
704
16th to endNight
45%19%47%20%2
632
March1st to 15thNight
2320%41%27%4
720
16th to endNight
2314%43%30%5%
768
April1st to 15thNight
3417%48%24%1
690
16th to endNight
1320%45%25%3
540
May1st to 15thNight
319%42%30%3
540
16th to endNight
216%43%33%2
563
June1st to 15thNight
217%46%39%3
540
16th to endNight
1335%53%5%
540
July1st to 15thNight
11323%60%9%
510
16th to endNight
5%112%61%17%
564
August1st to 15thNight
3112%63%19%
527
16th to endNight
4117%58%17%
558
September1st to 15thNight
5%223%52%15%
660
16th to endNight
25%34%46%10%
656
October1st to 15thNight
1212%38%36%8%
660
16th to endNight
17%35%43%11%
704
November1st to 15thNight
112%39%37%7%
700
16th to endNight
4214%39%31%7%
720
December1st to 15thNight
6%410%42%29%7%
720
16th to endNight
7%314%43%24%6%
768
Page generated at 2017-08-13 11:16:40. Version ac04

Copyright 2017 A. Danko


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