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 2018-02-14.

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
78%
16192
37%
48763
33%
16154
82%
16154
55%
22852

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
78%
778
34%
2522
37%
776
81%
776
52%
1155
January16th to endNight
71%
832
36%
2704
36%
832
78%
832
45%
1342
February1st to 15thNight
75%
754
38%
2362
36%
754
83%
754
58%
1044
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%
539
25%
1611
23%
536
87%
536
42%
863
August16th to endNight
83%
609
30%
1890
30%
609
83%
609
41%
1020
September1st to 15thNight
81%
720
29%
1980
26%
720
81%
720
43%
1145
September16th to endNight
87%
716
46%
1980
37%
716
91%
716
70%
901
October1st to 15thNight
80%
720
41%
2087
32%
720
86%
720
70%
897
October16th to endNight
87%
768
46%
2304
41%
768
91%
768
71%
958
November1st to 15thNight
82%
760
43%
2280
39%
760
86%
760
67%
968
November16th to endNight
73%
780
41%
2473
40%
780
78%
780
53%
1140
December1st to 15thNight
73%
780
38%
2535
39%
780
78%
780
51%
1153
December16th to endNight
69%
832
36%
2704
37%
832
73%
832
45%
1348

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
3213324346%65%
49301
Night
2212213346%68%
48965
TransparencyDay
20%35%11%26%33%
48996
Night
17%35%14%27%32%
48771
SeeingDay
5%6%18%30%26%11%
5900
Night
3211%37%37%7%
16203

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
221332336%6%63%
1746
16th to endDay
4312313346%64%
1872
February1st to 15thDay
4212213335%69%
1792
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%37%
2340
16th to endDay
33246%36%5%7%9%46%
2308
September1st to 15thDay
6%425%6%36%5%5%7%47%
1980
16th to endDay
322223345%70%
1980
October1st to 15thDay
11221223476%
1872
16th to endDay
11212235%78%
1920
November1st to 15thDay
111112246%74%
1909
16th to endDay
32221333472%
1813
December1st to 15thDay
5%213322436%63%
1755
16th to endDay
5%21321346%6%62%
1872
January1st to 15thNight
3213312345%67%
2522
16th to endNight
4213314445%62%
2704
February1st to 15thNight
222212346%70%
2357
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%6%8%10%54%
1620
16th to endNight
42144345%7%11%51%
1890
September1st to 15thNight
432442447%7%54%
1980
16th to endNight
111212235%76%
1980
October1st to 15thNight
11111222479%
2087
16th to endNight
111213480%
2304
November1st to 15thNight
112112345%74%
2280
16th to endNight
3212323235%69%
2473
December1st to 15thNight
5%212212347%66%
2535
16th to endNight
5%313323345%63%
2704

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%28%28%
1747
16th to endDay
21%2217%26%28%
1872
February1st to 15thDay
19%1213%28%34%
1792
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
37%9%12%13%17%8%
2325
16th to endDay
32%7%12%19%15%13%
2308
September1st to 15thDay
34%38%17%19%16%
1980
16th to endDay
16%4310%33%31%
1980
October1st to 15thDay
12%2411%30%38%
1872
16th to endDay
10%1310%28%45%
1920
November1st to 15thDay
12%2213%35%34%
1909
16th to endDay
16%1311%28%39%
1813
December1st to 15thDay
22%3316%31%23%
1755
16th to endDay
22%36%17%31%19%
1872
January1st to 15thNight
18%2414%30%28%
2522
16th to endNight
23%3315%29%24%
2704
February1st to 15thNight
16%1417%24%35%
2368
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%
1611
16th to endNight
24%7%16%18%21%12%
1890
September1st to 15thNight
26%6%10%21%20%14%
1980
16th to endNight
11%2314%37%30%
1980
October1st to 15thNight
10%2415%28%38%
2087
16th to endNight
9%1312%26%46%
2304
November1st to 15thNight
11%1217%33%32%
2280
16th to endNight
18%239%28%37%
2473
December1st to 15thNight
20%1417%31%24%
2535
16th to endNight
24%26%17%28%21%
2704

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
7%5%16%34%31%4
135
16th to endDay
46%15%34%27%11%
144
February1st to 15thDay
49%16%32%29%7%
229
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
6%25%24%39%21%
315
16th to endDay
5%422%43%23%
332
September1st to 15thDay
12%17%33%33%10%
315
16th to endDay
6%316%32%30%9%
315
October1st to 15thDay
15%18%30%28%14%
207
16th to endDay
213%16%47%20%
144
November1st to 15thDay
4414%27%41%7%
135
16th to endDay
5%16%32%34%9%
135
December1st to 15thDay
8%214%31%35%7%
135
16th to endDay
9%323%25%27%10%
144
January1st to 15thNight
4211%45%32%4
780
16th to endNight
6%213%44%28%4
832
February1st to 15thNight
3213%42%31%6%
760
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
2113%63%18%
539
16th to endNight
4116%59%17%
609
September1st to 15thNight
5%225%51%15%
720
16th to endNight
26%36%44%9%
716
October1st to 15thNight
1212%37%37%8%
720
16th to endNight
17%34%44%11%
768
November1st to 15thNight
111%40%38%7%
760
16th to endNight
4213%38%33%8%
780
December1st to 15thNight
6%411%43%28%6%
780
16th to endNight
7%214%41%26%6%
832
Page generated at 2018-02-15 08:58:40. Version ac04

Copyright 2018 A. Danko


Green Valley Clear Sky Chart |Charts Home