Green Acres Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Green Acres Observatory clear sky chart from 2005-11-05 to 2017-03-21.

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
68%
14788
30%
45264
26%
14751
73%
14751
46%
22989

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
62%
716
19%
2449
21%
716
65%
716
31%
1398
January16th to endNight
62%
768
24%
2496
25%
768
64%
768
30%
1492
February1st to 15thNight
59%
698
25%
2248
25%
698
63%
698
31%
1327
February16th to endNight
56%
632
26%
1895
24%
632
62%
632
34%
1133
March1st to 15thNight
58%
720
20%
2064
19%
720
60%
720
31%
1282
March16th to endNight
55%
728
22%
1946
16%
728
61%
728
37%
1186
April1st to 15thNight
52%
659
25%
1649
11%
659
58%
659
40%
1020
April16th to endNight
61%
660
26%
1650
12%
660
66%
660
53%
895
May1st to 15thNight
66%
571
33%
1561
21%
571
72%
571
65%
727
May16th to endNight
65%
343
30%
1368
27%
342
75%
342
54%
517
June1st to 15thNight
65%
330
33%
1320
31%
330
78%
330
60%
464
June16th to endNight
80%
330
37%
1320
44%
330
87%
330
77%
401
July1st to 15thNight
86%
310
38%
1240
46%
310
90%
310
77%
368
July16th to endNight
84%
484
36%
1429
33%
451
86%
451
69%
574
August1st to 15thNight
84%
551
42%
1534
29%
548
87%
548
83%
611
August16th to endNight
86%
700
44%
1750
26%
700
88%
700
85%
764
September1st to 15thNight
87%
660
45%
1650
31%
660
90%
660
84%
725
September16th to endNight
80%
656
47%
1774
39%
656
86%
656
78%
752
October1st to 15thNight
74%
660
33%
1980
32%
660
80%
660
56%
929
October16th to endNight
77%
704
38%
2112
40%
704
81%
704
56%
991
November1st to 15thNight
72%
700
31%
2242
32%
700
76%
700
48%
1085
November16th to endNight
67%
720
27%
2379
27%
720
71%
720
39%
1237
December1st to 15thNight
63%
720
21%
2520
20%
720
68%
720
28%
1496
December16th to endNight
53%
768
22%
2688
20%
768
59%
768
26%
1615

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
6%313212335%65%
45594
Night
8%212212235%64%
45449
TransparencyDay
22%48%19%24%20%
45277
Night
22%39%20%24%19%
45265
SeeingDay
8%417%29%27%12%
5195
Night
9%215%38%30%4
14799

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
14%7%25%42345%8%41%
1486
16th to endDay
16%8%36%435%445%38%
1728
February1st to 15thDay
16%6%35%423447%42%
1613
16th to endDay
16%4245%2445%7%42%
1579
March1st to 15thDay
12%425%425%5%5%9%43%
1893
16th to endDay
10%5%24425%5%5%7%46%
2048
April1st to 15thDay
11%42432345%7%50%
1969
16th to endDay
6%212212345%66%
1980
May1st to 15thDay
322112345%73%
2053
16th to endDay
3111312346%69%
2391
June1st to 15thDay
2212212235%74%
2310
16th to endDay
11111386%
2310
July1st to 15thDay
112388%
2310
16th to endDay
11221384%
2323
August1st to 15thDay
111289%
2087
16th to endDay
11111387%
2100
September1st to 15thDay
111388%
1980
16th to endDay
2111113479%
1853
October1st to 15thDay
312212245%72%
1650
16th to endDay
5%213322346%64%
1760
November1st to 15thDay
7%31331335%7%56%
1617
16th to endDay
11%6%35%423347%47%
1578
December1st to 15thDay
15%7%36%5%24335%41%
1440
16th to endDay
18%6%25%324437%38%
1536
January1st to 15thNight
13%5%24323348%48%
2449
16th to endNight
16%424323347%47%
2496
February1st to 15thNight
15%42332435%7%47%
2237
16th to endNight
16%31332235%7%50%
1895
March1st to 15thNight
14%425%423336%50%
2064
16th to endNight
12%412323448%50%
1946
April1st to 15thNight
10%32332445%7%52%
1649
16th to endNight
4212213335%67%
1650
May1st to 15thNight
212212136%74%
1561
16th to endNight
311112236%73%
1368
June1st to 15thNight
21111113479%
1320
16th to endNight
11111287%
1320
July1st to 15thNight
1122385%
1320
16th to endNight
11111221382%
1536
August1st to 15thNight
1112287%
1543
16th to endNight
1112387%
1750
September1st to 15thNight
1111288%
1650
16th to endNight
111111484%
1774
October1st to 15thNight
6%1121323470%
1980
16th to endNight
4112212335%71%
2112
November1st to 15thNight
8%312212246%64%
2242
16th to endNight
9%31332235%6%57%
2379
December1st to 15thNight
15%423314446%48%
2520
16th to endNight
18%423423346%46%
2688

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
41%8%12%16%18%2
1486
16th to endDay
47%6%7%16%15%5%
1728
February1st to 15thDay
40%6%12%24%12%3
1613
16th to endDay
39%6%12%25%14%1
1579
March1st to 15thDay
34%7%13%23%16%3
1893
16th to endDay
35%6%16%20%17%3
2048
April1st to 15thDay
33%5%12%25%17%5%
1969
16th to endDay
19%412%27%28%7%
1980
May1st to 15thDay
13%38%25%35%13%
2053
16th to endDay
16%410%28%28%11%
2395
June1st to 15thDay
14%37%23%26%24%
2310
16th to endDay
6%1213%33%42%
2310
July1st to 15thDay
437%24%59%
2161
16th to endDay
7%138%25%53%
2167
August1st to 15thDay
6%18%29%52%
2071
16th to endDay
5%28%36%45%
2100
September1st to 15thDay
41310%33%46%
1980
16th to endDay
9%1422%37%25%
1853
October1st to 15thDay
14%39%25%26%21%
1650
16th to endDay
21%38%24%28%13%
1760
November1st to 15thDay
26%414%30%21%2
1617
16th to endDay
35%7%13%23%16%2
1578
December1st to 15thDay
46%5%11%18%15%2
1440
16th to endDay
45%5%13%17%13%3
1536
January1st to 15thNight
33%5%12%24%18%5%
2449
16th to endNight
36%5%12%17%16%11%
2496
February1st to 15thNight
35%410%25%17%6%
2248
16th to endNight
33%5%11%27%18%2
1895
March1st to 15thNight
35%5%11%20%18%7%
2064
16th to endNight
31%6%12%21%20%8%
1946
April1st to 15thNight
29%6%14%24%18%6%
1649
16th to endNight
19%414%21%30%9%
1650
May1st to 15thNight
13%28%23%32%19%
1562
16th to endNight
13%311%30%29%11%
1368
June1st to 15thNight
10%310%22%28%24%
1320
16th to endNight
5%212%29%48%
1320
July1st to 15thNight
5%137%20%61%
1240
16th to endNight
9%237%22%54%
1429
August1st to 15thNight
5%112%26%52%
1534
16th to endNight
5%19%32%49%
1750
September1st to 15thNight
5%38%30%51%
1650
16th to endNight
8%319%39%29%
1774
October1st to 15thNight
16%38%22%27%21%
1980
16th to endNight
16%37%23%29%19%
2112
November1st to 15thNight
21%211%29%25%8%
2242
16th to endNight
26%410%26%25%6%
2379
December1st to 15thNight
36%5%12%20%18%6%
2520
16th to endNight
38%5%13%19%16%5%
2688

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
22%423%21%15%12%
114
16th to endDay
20%417%19%19%19%
256
February1st to 15thDay
20%5%14%18%24%15%
243
16th to endDay
18%6%18%25%20%10%
238
March1st to 15thDay
15%7%20%23%21%11%
270
16th to endDay
11%6%22%30%18%10%
245
April1st to 15thDay
14%10%27%25%12%9%
209
16th to endDay
5%10%25%33%14%9%
210
May1st to 15thDay
6%8%26%31%19%7%
228
16th to endDay
6%7%19%25%31%8%
266
June1st to 15thDay
5%6%22%41%18%5%
255
16th to endDay
221%36%29%9%
255
July1st to 15thDay
10%33%40%14%
245
16th to endDay
6%33%45%14%
271
August1st to 15thDay
112%36%40%9%
255
16th to endDay
10%37%38%12%
268
September1st to 15thDay
9%32%40%15%
255
16th to endDay
3312%31%30%17%
255
October1st to 15thDay
5%5%19%29%25%15%
255
16th to endDay
8%317%27%26%17%
272
November1st to 15thDay
8%39%17%30%30%
123
16th to endDay
7%7%13%38%31%2
83
December1st to 15thDay
30%323%23%20%
60
16th to endDay
14%110%35%29%7%
64
January1st to 15thNight
15%111%32%30%7%
720
16th to endNight
18%210%30%29%8%
768
February1st to 15thNight
15%314%33%28%4
704
16th to endNight
17%318%33%22%4
632
March1st to 15thNight
16%314%32%28%4
720
16th to endNight
15%221%33%25%2
728
April1st to 15thNight
11%426%33%21%1
659
16th to endNight
5%424%35%25%3
660
May1st to 15thNight
3125%42%23%2
572
16th to endNight
4324%41%24%
343
June1st to 15thNight
3326%45%21%
330
16th to endNight
16%52%28%1
330
July1st to 15thNight
19%60%27%
310
16th to endNight
18%46%39%2
484
August1st to 15thNight
12%47%36%2
551
16th to endNight
10%47%38%2
700
September1st to 15thNight
28%44%40%3
660
16th to endNight
213%37%38%7%
656
October1st to 15thNight
6%113%36%34%6%
660
16th to endNight
5%111%35%34%11%
704
November1st to 15thNight
9%113%34%35%7%
700
16th to endNight
10%112%36%31%7%
720
December1st to 15thNight
16%111%39%25%5%
720
16th to endNight
20%415%33%23%3
768
Page generated at 2017-03-21 23:42:27. Version ac04

Copyright 2017 A. Danko


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