Garvey Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Garvey Ranch Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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%
16050
34%
47289
31%
16003
80%
16003
51%
23600

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
72%
716
28%
2470
29%
716
78%
716
43%
1189
January16th to endNight
66%
768
35%
2332
32%
768
73%
768
43%
1235
February1st to 15thNight
72%
697
35%
2101
35%
696
77%
696
49%
1061
February16th to endNight
64%
632
28%
1895
28%
632
69%
632
37%
1083
March1st to 15thNight
72%
720
31%
2160
32%
720
77%
720
49%
1086
March16th to endNight
72%
768
29%
2004
24%
768
75%
768
49%
1107
April1st to 15thNight
66%
719
28%
1799
18%
719
70%
719
50%
1021
April16th to endNight
71%
720
31%
1800
17%
720
74%
720
54%
977
May1st to 15thNight
71%
620
28%
1700
19%
620
72%
620
49%
932
May16th to endNight
73%
561
29%
1685
23%
561
74%
561
53%
837
June1st to 15thNight
78%
477
28%
1557
26%
477
79%
477
50%
748
June16th to endNight
88%
360
34%
1440
42%
360
88%
360
49%
582
July1st to 15thNight
90%
340
33%
1360
40%
340
90%
340
50%
544
July16th to endNight
87%
639
30%
1659
24%
597
88%
597
54%
850
August1st to 15thNight
86%
717
34%
1790
22%
713
86%
713
61%
920
August16th to endNight
90%
764
41%
1910
29%
764
90%
764
66%
959
September1st to 15thNight
86%
720
38%
1830
31%
720
86%
720
63%
925
September16th to endNight
89%
716
44%
1980
43%
716
90%
716
69%
884
October1st to 15thNight
81%
720
36%
1992
35%
720
83%
720
58%
988
October16th to endNight
81%
768
41%
2329
44%
768
83%
768
54%
1108
November1st to 15thNight
82%
700
36%
2275
39%
700
86%
700
58%
989
November16th to endNight
78%
720
37%
2340
40%
720
82%
720
52%
1084
December1st to 15thNight
70%
720
34%
2340
33%
720
76%
720
41%
1200
December16th to endNight
63%
768
33%
2541
31%
768
70%
768
40%
1291

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
4312212236%68%
48433
Night
5%312212236%66%
47494
TransparencyDay
19%25%18%28%25%
48126
Night
21%26%18%26%24%
47301
SeeingDay
6%7%28%38%14%4
6115
Night
6%28%34%38%9%
16064

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
7%313322236%62%
1465
16th to endDay
10%413213435%59%
1887
February1st to 15thDay
6%313313345%63%
1751
16th to endDay
12%413323337%54%
1579
March1st to 15thDay
431231345%7%61%
1800
16th to endDay
431331335%10%58%
2217
April1st to 15thDay
5%413213348%61%
2149
16th to endDay
4312212236%69%
2160
May1st to 15thDay
4412223336%65%
2250
16th to endDay
4423212336%65%
2429
June1st to 15thDay
6%5%23112236%64%
2399
16th to endDay
12111112480%
2520
July1st to 15thDay
2312112237%70%
2520
16th to endDay
1211112347%71%
2388
August1st to 15thDay
11111112480%
2160
16th to endDay
11112235%78%
2292
September1st to 15thDay
11111135%79%
2130
16th to endDay
1211123479%
1980
October1st to 15thDay
5%212212235%70%
1965
16th to endDay
321212345%71%
1891
November1st to 15thDay
23222223472%
1584
16th to endDay
5%213213336%66%
1620
December1st to 15thDay
7%31231335%9%58%
1620
16th to endDay
11%312312337%59%
1677
January1st to 15thNight
6%413223335%63%
2470
16th to endNight
10%31321232462%
2332
February1st to 15thNight
6%413312335%64%
2101
16th to endNight
12%324223445%54%
1895
March1st to 15thNight
5%31321235%9%62%
2160
16th to endNight
431231345%8%60%
2004
April1st to 15thNight
7%414213225%63%
1799
16th to endNight
3422212236%68%
1800
May1st to 15thNight
5%6%23212247%62%
1700
16th to endNight
36%2212237%67%
1684
June1st to 15thNight
35%12212248%64%
1557
16th to endNight
1412112237%72%
1440
July1st to 15thNight
2311212247%70%
1440
16th to endNight
32122133410%63%
1775
August1st to 15thNight
2312211247%71%
1800
16th to endNight
12212337%73%
1910
September1st to 15thNight
331221225%74%
1830
16th to endNight
12111236%78%
1980
October1st to 15thNight
2212322335%70%
1992
16th to endNight
4312212235%70%
2329
November1st to 15thNight
2212212235%73%
2275
16th to endNight
331221235%5%66%
2340
December1st to 15thNight
7%214323337%60%
2340
16th to endNight
11%31321223462%
2541

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
25%25%13%23%29%
1465
16th to endDay
28%26%16%18%28%
1887
February1st to 15thDay
24%2416%27%25%
1751
16th to endDay
30%26%21%28%10%
1579
March1st to 15thDay
21%29%22%22%21%
1800
16th to endDay
22%311%26%20%15%
2217
April1st to 15thDay
22%29%26%25%12%
2149
16th to endDay
17%18%25%27%18%
2160
May1st to 15thDay
21%28%22%28%16%
2250
16th to endDay
21%26%29%29%9%
2432
June1st to 15thDay
24%26%17%31%18%
2399
16th to endDay
13%128%36%38%
2520
July1st to 15thDay
17%2211%27%37%
2371
16th to endDay
15%27%21%32%20%
2241
August1st to 15thDay
11%115%37%33%
2146
16th to endDay
9%2113%40%31%
2292
September1st to 15thDay
11%1214%34%35%
2130
16th to endDay
10%1117%34%34%
1980
October1st to 15thDay
18%2320%26%28%
1965
16th to endDay
15%2415%21%40%
1891
November1st to 15thDay
17%16%16%22%35%
1584
16th to endDay
20%26%13%24%32%
1620
December1st to 15thDay
25%39%17%19%25%
1620
16th to endDay
26%39%17%21%22%
1677
January1st to 15thNight
25%16%13%22%29%
2470
16th to endNight
27%26%16%16%31%
2332
February1st to 15thNight
23%16%17%22%28%
2112
16th to endNight
33%26%17%24%15%
1895
March1st to 15thNight
22%27%23%23%20%
2160
16th to endNight
24%311%24%20%14%
2004
April1st to 15thNight
25%210%26%22%13%
1799
16th to endNight
21%29%26%22%17%
1800
May1st to 15thNight
25%210%23%24%13%
1701
16th to endNight
20%210%30%24%10%
1685
June1st to 15thNight
21%210%19%34%11%
1557
16th to endNight
18%1312%35%28%
1440
July1st to 15thNight
17%1212%33%31%
1360
16th to endNight
20%36%24%28%16%
1659
August1st to 15thNight
18%1113%41%23%
1790
16th to endNight
14%2113%42%26%
1910
September1st to 15thNight
16%2310%36%30%
1830
16th to endNight
12%1118%34%32%
1980
October1st to 15thNight
18%2419%29%25%
1992
16th to endNight
19%2313%22%38%
2329
November1st to 15thNight
16%15%16%22%37%
2275
16th to endNight
20%16%18%20%33%
2340
December1st to 15thNight
27%27%16%20%25%
2340
16th to endNight
27%28%15%24%21%
2541

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%434%32%11%
93
16th to endDay
12%8%32%32%11%2
283
February1st to 15thDay
11%9%27%30%18%2
266
16th to endDay
13%19%28%28%8%
238
March1st to 15thDay
7%12%30%27%17%3
270
16th to endDay
5%15%35%30%9%2
288
April1st to 15thDay
9%16%41%21%6%4
269
16th to endDay
5%19%43%25%33
270
May1st to 15thDay
9%13%34%30%9%2
288
16th to endDay
6%9%39%30%12%1
330
June1st to 15thDay
8%8%26%42%11%2
315
16th to endDay
1222%46%17%9%
315
July1st to 15thDay
2117%51%21%6%
305
16th to endDay
1112%51%23%9%
327
August1st to 15thDay
4118%55%14%5%
315
16th to endDay
316%53%18%7%
332
September1st to 15thDay
4227%48%12%4
315
16th to endDay
2434%38%12%7%
315
October1st to 15thDay
5%9%31%35%15%2
315
16th to endDay
5%5%26%36%18%7%
309
November1st to 15thDay
35%8%27%35%18%
90
16th to endDay
4425%37%24%3
90
December1st to 15thDay
5%120%42%28%2
90
16th to endDay
14%6%19%36%20%1
87
January1st to 15thNight
7%11%44%29%6%
720
16th to endNight
12%211%37%30%5%
768
February1st to 15thNight
7%29%40%31%7%
704
16th to endNight
13%112%41%25%4
632
March1st to 15thNight
5%213%46%25%6%
720
16th to endNight
5%311%42%30%5%
768
April1st to 15thNight
8%412%41%28%4
719
16th to endNight
45%12%40%31%6%
720
May1st to 15thNight
9%112%38%32%5%
621
16th to endNight
6%312%41%31%4
563
June1st to 15thNight
429%36%41%5%
477
16th to endNight
3325%59%7%
360
July1st to 15thNight
39%71%13%
340
16th to endNight
41117%57%18%
639
August1st to 15thNight
32221%54%15%
717
16th to endNight
3116%54%23%
764
September1st to 15thNight
5%225%47%18%
720
16th to endNight
4229%50%12%
716
October1st to 15thNight
416%37%41%8%
720
16th to endNight
7%15%29%41%14%
768
November1st to 15thNight
316%38%37%13%
700
16th to endNight
5%18%35%37%11%
720
December1st to 15thNight
8%310%39%33%6%
720
16th to endNight
13%313%39%24%5%
768
Page generated at 2017-11-01 14:23:42. Version ac04

Copyright 2017 A. Danko


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