Far Away Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Far Away Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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%
16215
33%
46919
30%
16172
78%
16172
49%
24309

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
68%
717
29%
2325
29%
716
73%
716
42%
1199
January16th to endNight
64%
768
33%
2304
30%
768
69%
768
38%
1294
February1st to 15thNight
70%
698
33%
2109
34%
698
74%
698
43%
1126
February16th to endNight
60%
632
27%
1895
31%
632
62%
632
30%
1178
March1st to 15thNight
69%
720
29%
2160
32%
720
72%
720
40%
1181
March16th to endNight
73%
768
28%
2037
25%
768
74%
768
43%
1166
April1st to 15thNight
65%
719
26%
1799
18%
719
66%
719
41%
1098
April16th to endNight
72%
720
30%
1800
19%
720
74%
720
50%
1026
May1st to 15thNight
73%
581
29%
1661
21%
581
73%
581
44%
931
May16th to endNight
72%
561
27%
1685
21%
561
73%
561
41%
942
June1st to 15thNight
81%
540
30%
1620
26%
540
81%
540
52%
813
June16th to endNight
93%
540
36%
1620
33%
540
93%
540
78%
637
July1st to 15thNight
92%
510
29%
1530
25%
510
92%
510
64%
674
July16th to endNight
90%
626
31%
1650
24%
588
89%
588
59%
793
August1st to 15thNight
93%
717
37%
1790
24%
713
93%
713
77%
823
August16th to endNight
94%
764
41%
1910
29%
764
94%
764
76%
898
September1st to 15thNight
92%
706
38%
1833
32%
706
92%
706
69%
869
September16th to endNight
89%
656
45%
1815
43%
656
91%
656
73%
790
October1st to 15thNight
79%
660
36%
1815
35%
660
80%
660
54%
934
October16th to endNight
76%
704
36%
2110
37%
704
78%
704
49%
1054
November1st to 15thNight
79%
700
34%
2275
38%
700
81%
700
49%
1069
November16th to endNight
75%
720
34%
2340
37%
720
78%
720
44%
1179
December1st to 15thNight
68%
720
32%
2340
35%
720
70%
720
38%
1255
December16th to endNight
62%
768
31%
2496
31%
768
67%
768
35%
1380

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
5%312213336%65%
47730
Night
6%312323346%62%
47123
TransparencyDay
20%35%15%26%28%
47431
Night
22%36%14%23%29%
46923
SeeingDay
8%7%28%39%12%3
5894
Night
7%17%32%38%11%
16227

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
8%5%14422335%59%
1611
16th to endDay
10%5%23213347%55%
1920
February1st to 15thDay
9%314323335%57%
1751
16th to endDay
14%7%24323347%45%
1579
March1st to 15thDay
7%31331335%8%56%
1800
16th to endDay
6%314323347%58%
2184
April1st to 15thDay
8%423224446%55%
2149
16th to endDay
6%312212236%66%
2160
May1st to 15thDay
5%423313435%62%
2289
16th to endDay
4312213345%65%
2429
June1st to 15thDay
331221222471%
2340
16th to endDay
111112385%
2340
July1st to 15thDay
112322346%69%
2340
16th to endDay
21221346%7%66%
2402
August1st to 15thDay
111211235%77%
2160
16th to endDay
11212345%77%
2292
September1st to 15thDay
1121223478%
2045
16th to endDay
1121123479%
1815
October1st to 15thDay
6%412222345%64%
1815
16th to endDay
6%31331223468%
1757
November1st to 15thDay
5%312222345%66%
1584
16th to endDay
7%313213247%61%
1620
December1st to 15thDay
9%41333345%8%52%
1620
16th to endDay
14%424323235%53%
1728
January1st to 15thNight
7%32332434459%
2325
16th to endNight
11%42342233456%
2304
February1st to 15thNight
8%423222335%59%
2101
16th to endNight
14%6%24424335%47%
1895
March1st to 15thNight
9%5%1331335%7%55%
2160
16th to endNight
7%42332345%8%54%
2037
April1st to 15thNight
9%7%24313347%51%
1799
16th to endNight
6%422322336%62%
1800
May1st to 15thNight
5%5%23424448%56%
1661
16th to endNight
5%6%233225%36%57%
1684
June1st to 15thNight
1412323347%64%
1620
16th to endNight
11223482%
1620
July1st to 15thNight
1132335%8%68%
1620
16th to endNight
2222345%9%64%
1763
August1st to 15thNight
1111227%8%72%
1800
16th to endNight
11112345%77%
1910
September1st to 15thNight
112212245%74%
1833
16th to endNight
21111122481%
1815
October1st to 15thNight
5%212313346%66%
1815
16th to endNight
6%313322345%64%
2110
November1st to 15thNight
422232233467%
2275
16th to endNight
6%412323436%60%
2340
December1st to 15thNight
9%414323347%54%
2340
16th to endNight
13%414312335%55%
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
27%25%12%26%25%
1612
16th to endDay
30%37%13%16%29%
1920
February1st to 15thDay
28%35%13%23%26%
1751
16th to endDay
38%45%15%23%13%
1579
March1st to 15thDay
25%36%20%23%21%
1800
16th to endDay
24%48%23%22%15%
2184
April1st to 15thDay
28%46%22%26%10%
2149
16th to endDay
19%37%22%27%18%
2160
May1st to 15thDay
23%36%20%27%19%
2289
16th to endDay
20%36%22%33%13%
2432
June1st to 15thDay
18%2317%30%27%
2340
16th to endDay
7%126%22%59%
2340
July1st to 15thDay
14%3411%25%40%
2201
16th to endDay
14%49%22%28%20%
2252
August1st to 15thDay
10%1314%33%36%
2146
16th to endDay
10%3311%34%36%
2292
September1st to 15thDay
10%238%35%38%
2045
16th to endDay
10%228%34%41%
1815
October1st to 15thDay
22%2416%27%26%
1815
16th to endDay
20%25%10%20%40%
1757
November1st to 15thDay
20%36%13%20%34%
1584
16th to endDay
23%3412%21%34%
1620
December1st to 15thDay
29%39%14%16%26%
1620
16th to endDay
33%36%14%23%17%
1728
January1st to 15thNight
27%26%12%21%30%
2325
16th to endNight
31%27%10%16%31%
2304
February1st to 15thNight
26%26%14%20%29%
2112
16th to endNight
39%3313%22%16%
1895
March1st to 15thNight
28%36%18%19%23%
2160
16th to endNight
26%5%9%18%23%16%
2037
April1st to 15thNight
31%37%21%22%13%
1799
16th to endNight
24%38%20%22%20%
1800
May1st to 15thNight
26%48%16%22%20%
1662
16th to endNight
28%47%19%26%14%
1685
June1st to 15thNight
19%46%15%29%25%
1620
16th to endNight
6%247%20%58%
1620
July1st to 15thNight
12%2412%25%41%
1530
16th to endNight
15%411%21%28%19%
1650
August1st to 15thNight
8%15%16%37%30%
1790
16th to endNight
8%26%10%32%40%
1910
September1st to 15thNight
12%16%10%29%38%
1833
16th to endNight
10%1310%33%41%
1815
October1st to 15thNight
20%35%17%28%25%
1815
16th to endNight
23%2410%19%40%
2110
November1st to 15thNight
20%3414%19%38%
2275
16th to endNight
24%25%14%18%34%
2340
December1st to 15thNight
29%36%14%19%26%
2340
16th to endNight
31%38%13%21%21%
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
27%417%41%8%
90
16th to endDay
15%12%32%30%7%1
288
February1st to 15thDay
9%11%30%36%10%1
266
16th to endDay
20%12%35%25%5%
238
March1st to 15thDay
11%12%31%27%13%2
270
16th to endDay
7%14%36%26%12%2
288
April1st to 15thDay
12%17%35%23%8%2
269
16th to endDay
7%16%40%26%7%1
270
May1st to 15thDay
14%9%31%35%6%2
288
16th to endDay
11%10%34%32%10%1
330
June1st to 15thDay
4334%39%14%3
315
16th to endDay
123%49%18%6%
315
July1st to 15thDay
2114%54%18%7%
305
16th to endDay
48%59%16%10%
327
August1st to 15thDay
117%58%13%7%
315
16th to endDay
1112%58%17%8%
332
September1st to 15thDay
3226%53%11%4
300
16th to endDay
36%35%41%8%3
255
October1st to 15thDay
6%9%41%30%10%
255
16th to endDay
12%5%34%28%16%2
212
November1st to 15thDay
8%414%28%37%5%
90
16th to endDay
13%6%21%40%16%2
90
December1st to 15thDay
6%318%41%26%3
90
16th to endDay
21%428%34%11%
96
January1st to 15thNight
9%114%41%24%8%
720
16th to endNight
13%210%37%27%7%
768
February1st to 15thNight
11%19%37%30%9%
704
16th to endNight
16%310%38%24%6%
632
March1st to 15thNight
11%38%40%30%5%
720
16th to endNight
8%28%36%34%8%
768
April1st to 15thNight
11%410%39%28%5%
719
16th to endNight
8%211%35%33%8%
720
May1st to 15thNight
8%19%36%35%8%
582
16th to endNight
9%29%32%39%6%
563
June1st to 15thNight
2110%39%41%5%
540
16th to endNight
1234%53%7%
540
July1st to 15thNight
20%64%12%
510
16th to endNight
12114%63%18%
626
August1st to 15thNight
1118%59%18%
717
16th to endNight
110%59%28%
764
September1st to 15thNight
121%56%19%
706
16th to endNight
3429%46%16%
656
October1st to 15thNight
6%16%38%36%11%
660
16th to endNight
9%6%29%36%17%
704
November1st to 15thNight
5%16%37%35%14%
700
16th to endNight
8%18%35%31%14%
720
December1st to 15thNight
13%19%39%27%9%
720
16th to endNight
16%211%38%24%6%
768
Page generated at 2017-09-13 04:39:19. Version ac04

Copyright 2017 A. Danko


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