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 2018-03-21.

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
77%
16977
33%
49241
30%
16934
78%
16934
49%
25510

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
67%
777
29%
2520
29%
776
72%
776
40%
1317
January16th to endNight
65%
832
34%
2496
32%
832
70%
832
39%
1378
February1st to 15thNight
71%
758
33%
2289
34%
758
74%
758
43%
1219
February16th to endNight
61%
684
29%
2051
32%
684
63%
684
31%
1255
March1st to 15thNight
68%
780
27%
2340
30%
780
71%
780
39%
1305
March16th to endNight
73%
792
28%
2103
25%
792
75%
792
43%
1212
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
91%
720
37%
1871
31%
720
92%
720
68%
896
September16th to endNight
89%
716
46%
1980
44%
716
90%
716
71%
872
October1st to 15thNight
80%
720
35%
1980
34%
720
81%
720
56%
1005
October16th to endNight
77%
768
38%
2302
39%
768
79%
768
50%
1141
November1st to 15thNight
78%
760
33%
2470
37%
760
80%
760
47%
1193
November16th to endNight
75%
780
35%
2535
38%
780
78%
780
44%
1277
December1st to 15thNight
69%
780
32%
2535
35%
780
71%
780
39%
1330
December16th to endNight
64%
832
33%
2704
33%
832
68%
832
36%
1475

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%312213346%65%
49597
Night
6%312323346%62%
49445
TransparencyDay
20%35%15%26%28%
49298
Night
23%36%14%23%29%
49245
SeeingDay
8%7%27%39%14%4
6574
Night
7%17%33%38%11%
16989

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%58%
1746
16th to endDay
10%423213347%56%
2080
February1st to 15thDay
8%313323336%59%
1901
16th to endDay
13%7%24324346%45%
1709
March1st to 15thDay
7%32332345%8%55%
1950
16th to endDay
6%31442335%7%58%
2245
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
1121223477%
2088
16th to endDay
11121123479%
1980
October1st to 15thDay
5%312212335%66%
1980
16th to endDay
5%31331223469%
1916
November1st to 15thDay
5%313323345%63%
1719
16th to endDay
7%413213247%61%
1755
December1st to 15thDay
8%413333348%54%
1755
16th to endDay
12%424323235%54%
1872
January1st to 15thNight
8%323324345%57%
2520
16th to endNight
10%423422335%57%
2496
February1st to 15thNight
8%423212345%59%
2281
16th to endNight
14%5%24324335%48%
2051
March1st to 15thNight
9%5%1331435%7%53%
2340
16th to endNight
6%42332345%9%53%
2103
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
112213345%73%
1871
16th to endNight
21121123479%
1980
October1st to 15thNight
5%212213346%67%
1980
16th to endNight
6%313322345%65%
2302
November1st to 15thNight
4322323435%64%
2470
16th to endNight
5%413323346%59%
2535
December1st to 15thNight
9%41331335%7%55%
2535
16th to endNight
12%413312335%56%
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
28%35%13%26%23%
1747
16th to endDay
28%37%14%17%28%
2080
February1st to 15thDay
27%35%13%23%27%
1901
16th to endDay
38%45%14%23%13%
1709
March1st to 15thDay
26%46%20%22%20%
1950
16th to endDay
25%49%23%22%15%
2245
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%339%35%37%
2088
16th to endDay
10%128%35%40%
1980
October1st to 15thDay
20%2415%28%28%
1980
16th to endDay
19%2411%20%41%
1916
November1st to 15thDay
22%36%14%20%32%
1719
16th to endDay
23%3412%22%34%
1755
December1st to 15thDay
27%28%14%16%29%
1755
16th to endDay
32%36%14%24%18%
1872
January1st to 15thNight
28%25%13%21%28%
2520
16th to endNight
30%26%11%17%31%
2496
February1st to 15thNight
26%36%13%21%29%
2292
16th to endNight
38%3313%24%16%
2051
March1st to 15thNight
30%36%18%19%21%
2340
16th to endNight
27%5%9%18%23%16%
2103
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
13%16%10%30%38%
1871
16th to endNight
11%129%34%40%
1980
October1st to 15thNight
19%25%16%28%27%
1980
16th to endNight
22%249%18%42%
2302
November1st to 15thNight
21%3415%19%35%
2470
16th to endNight
25%25%13%18%34%
2535
December1st to 15thNight
28%36%14%18%28%
2535
16th to endNight
30%37%12%23%22%
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
24%214%39%15%2
135
16th to endDay
13%10%29%30%13%2
352
February1st to 15thDay
7%9%28%35%14%3
326
16th to endDay
19%13%32%26%7%
290
March1st to 15thDay
11%12%33%28%12%2
330
16th to endDay
7%14%35%27%12%2
311
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
3126%53%11%3
315
16th to endDay
46%33%39%12%3
315
October1st to 15thDay
5%7%37%33%14%
315
16th to endDay
10%431%27%21%3
270
November1st to 15thDay
11%417%34%29%3
135
16th to endDay
13%5%17%37%21%5%
135
December1st to 15thDay
5%417%42%27%3
135
16th to endDay
14%224%32%20%4
144
January1st to 15thNight
9%113%41%25%7%
780
16th to endNight
13%210%38%28%6%
832
February1st to 15thNight
10%19%37%31%9%
764
16th to endNight
15%310%39%24%6%
684
March1st to 15thNight
12%28%42%29%5%
780
16th to endNight
8%38%37%34%8%
792
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
122%55%18%
720
16th to endNight
3430%45%16%
716
October1st to 15thNight
6%6%37%38%10%
720
16th to endNight
8%6%29%36%17%
768
November1st to 15thNight
6%16%39%33%12%
760
16th to endNight
8%18%35%31%13%
780
December1st to 15thNight
12%19%40%27%8%
780
16th to endNight
15%211%38%25%7%
832
Page generated at 2018-03-22 08:34:23. Version ac04

Copyright 2018 A. Danko


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