Fieldon Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fieldon Hill Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
41%
15880
21%
46922
14%
15834
49%
15834
28%
29368

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
26%
899
19%
2497
8%
895
35%
895
23%
1678
January16th to endNight
22%
960
19%
2496
6%
960
31%
960
23%
1755
February1st to 15thNight
24%
846
14%
2255
4%
843
30%
843
20%
1631
February16th to endNight
25%
631
21%
1893
7%
631
36%
631
24%
1215
March1st to 15thNight
24%
651
18%
2091
9%
651
33%
651
20%
1399
March16th to endNight
29%
576
14%
2037
9%
576
37%
576
17%
1395
April1st to 15thNight
31%
539
21%
1797
11%
539
46%
539
26%
1076
April16th to endNight
38%
540
22%
1800
16%
540
49%
540
26%
1116
May1st to 15thNight
42%
540
18%
1635
12%
539
50%
539
25%
1037
May16th to endNight
50%
563
21%
1497
13%
561
55%
561
34%
949
June1st to 15thNight
63%
540
21%
1440
14%
540
67%
540
44%
827
June16th to endNight
61%
540
22%
1440
15%
540
65%
540
42%
847
July1st to 15thNight
69%
510
20%
1360
16%
510
70%
510
41%
802
July16th to endNight
74%
564
25%
1485
22%
531
77%
531
45%
818
August1st to 15thNight
77%
539
23%
1661
26%
536
78%
536
41%
889
August16th to endNight
72%
573
25%
1910
29%
573
75%
573
38%
1010
September1st to 15thNight
63%
540
28%
1800
29%
540
67%
540
33%
1003
September16th to endNight
61%
625
34%
1838
25%
625
68%
625
39%
1006
October1st to 15thNight
51%
660
29%
1980
21%
660
58%
660
37%
1109
October16th to endNight
36%
704
25%
2126
16%
704
45%
704
30%
1278
November1st to 15thNight
38%
700
28%
2276
17%
700
52%
700
32%
1258
November16th to endNight
31%
780
22%
2400
13%
780
42%
780
27%
1476
December1st to 15thNight
26%
900
15%
2520
7%
900
34%
900
20%
1813
December16th to endNight
22%
960
15%
2688
5%
960
31%
960
17%
1981

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
12%6%35%43445%7%42%
47962
Night
13%6%25%424346%45%
47104
TransparencyDay
40%412%24%14%2
47647
Night
39%311%25%17%3
46924
SeeingDay
12%6%23%28%21%7%
5911
Night
15%7%28%31%14%1
15881

By Month

Percentage Cloud Cover SE (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
13%7%5%9%6%24345%35%
1438
16th to endDay
13%9%47%6%34345%36%
1728
February1st to 15thDay
15%7%5%7%43445%7%34%
1606
16th to endDay
13%10%37%434446%37%
1580
March1st to 15thDay
15%11%36%5%34345%36%
1878
16th to endDay
18%9%37%5%36%446%30%
2185
April1st to 15thDay
16%6%25%424446%41%
2151
16th to endDay
17%7%35%6%34446%37%
2160
May1st to 15thDay
18%5%35%5%245%5%8%35%
2311
16th to endDay
11%435%5%35%5%5%7%41%
2617
June1st to 15thDay
8%4245%345%6%9%45%
2520
16th to endDay
7%323435%5%8%9%45%
2520
July1st to 15thDay
8%324435%5%6%11%45%
2520
16th to endDay
5%2245%26%5%7%10%47%
2578
August1st to 15thDay
7%425%6%35%5%7%8%43%
2286
16th to endDay
8%4245%35%5%7%8%43%
2292
September1st to 15thDay
12%5%2332445%6%47%
2160
16th to endDay
8%42443345%8%50%
1921
October1st to 15thDay
14%5%14323335%50%
1650
16th to endDay
15%42332233453%
1746
November1st to 15thDay
14%423313346%50%
1582
16th to endDay
17%8%35%323346%41%
1557
December1st to 15thDay
16%9%47%424346%35%
1440
16th to endDay
18%10%46%424347%33%
1536
January1st to 15thNight
14%7%36%6%34445%39%
2497
16th to endNight
12%10%46%5%23345%38%
2496
February1st to 15thNight
13%11%46%6%24445%34%
2246
16th to endNight
15%7%36%422245%43%
1893
March1st to 15thNight
20%8%25%43433439%
2091
16th to endNight
18%8%35%435%46%6%32%
2037
April1st to 15thNight
12%6%235%24446%46%
1797
16th to endNight
16%6%25%324246%44%
1800
May1st to 15thNight
16%5%2442435%7%41%
1635
16th to endNight
10%425%5%245%48%46%
1496
June1st to 15thNight
6%32332446%7%53%
1440
16th to endNight
7%314325%46%10%49%
1440
July1st to 15thNight
8%3245%24449%51%
1440
16th to endNight
43144245%6%10%52%
1587
August1st to 15thNight
6%213325%46%8%54%
1671
16th to endNight
5%31443435%8%53%
1910
September1st to 15thNight
10%5%1442335%5%52%
1800
16th to endNight
8%423423347%56%
1838
October1st to 15thNight
10%31342345%6%53%
1980
16th to endNight
15%6%1332334451%
2126
November1st to 15thNight
10%5%23322245%54%
2276
16th to endNight
15%7%33323446%45%
2400
December1st to 15thNight
20%9%36%5%23345%32%
2520
16th to endNight
20%11%46%5%2433432%
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
50%49%21%12%
1439
16th to endDay
48%314%24%7%
1728
February1st to 15thDay
49%313%24%9%
1608
16th to endDay
46%313%22%12%1
1580
March1st to 15thDay
50%310%23%11%1
1878
16th to endDay
52%415%18%8%
2187
April1st to 15thDay
43%39%24%16%1
2151
16th to endDay
48%311%22%13%1
2160
May1st to 15thDay
45%6%12%25%10%
2311
16th to endDay
40%6%14%20%15%2
2621
June1st to 15thDay
33%5%14%25%18%1
2520
16th to endDay
31%6%16%25%17%3
2520
July1st to 15thDay
33%5%13%29%14%3
2371
16th to endDay
27%5%17%31%16%1
2417
August1st to 15thDay
35%5%12%26%17%1
2272
16th to endDay
35%5%13%22%17%5%
2292
September1st to 15thDay
35%38%26%20%4
2160
16th to endDay
32%49%32%18%2
1921
October1st to 15thDay
36%29%26%20%4
1650
16th to endDay
35%29%29%19%2
1746
November1st to 15thDay
34%312%22%22%5%
1582
16th to endDay
44%311%27%12%1
1557
December1st to 15thDay
50%314%22%8%
1440
16th to endDay
51%311%21%8%2
1536
January1st to 15thNight
46%39%25%14%
2497
16th to endNight
47%412%24%10%
2496
February1st to 15thNight
51%310%20%12%1
2255
16th to endNight
43%212%26%12%1
1893
March1st to 15thNight
49%29%23%13%2
2091
16th to endNight
50%412%22%9%
2037
April1st to 15thNight
38%310%25%18%3
1797
16th to endNight
41%39%26%16%3
1800
May1st to 15thNight
41%413%22%16%
1636
16th to endNight
36%5%15%21%18%3
1498
June1st to 15thNight
26%5%14%29%21%2
1440
16th to endNight
29%413%26%19%6%
1440
July1st to 15thNight
30%411%32%17%4
1360
16th to endNight
25%416%32%19%1
1485
August1st to 15thNight
27%414%28%22%2
1661
16th to endNight
27%411%25%24%5%
1910
September1st to 15thNight
33%38%23%23%8%
1800
16th to endNight
28%38%29%27%3
1838
October1st to 15thNight
30%310%25%23%5%
1980
16th to endNight
36%37%26%20%4
2126
November1st to 15thNight
31%310%25%21%7%
2276
16th to endNight
40%210%28%17%1
2400
December1st to 15thNight
53%211%20%10%
2520
16th to endNight
55%310%18%10%1
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
27%10%43%15%21
90
16th to endDay
9%19%50%17%3
96
February1st to 15thDay
14%16%40%24%4
90
16th to endDay
8%17%38%30%4
81
March1st to 15thDay
23%15%41%14%5%
90
16th to endDay
20%12%36%22%7%
171
April1st to 15thDay
17%12%31%23%14%
270
16th to endDay
22%6%29%26%13%1
270
May1st to 15thDay
16%10%29%26%13%3
348
16th to endDay
15%5%30%28%12%7%
517
June1st to 15thDay
9%320%34%22%9%
495
16th to endDay
9%427%34%18%6%
495
July1st to 15thDay
10%213%33%30%9%
475
16th to endDay
5%111%30%36%14%
515
August1st to 15thDay
8%110%32%29%16%
439
16th to endDay
8%211%28%36%11%
332
September1st to 15thDay
11%314%26%30%13%
315
16th to endDay
11%5%12%28%30%10%
270
October1st to 15thDay
10%11%22%32%16%7%
90
16th to endDay
15%7%25%38%13%
96
November1st to 15thDay
5%5%27%25%26%8%
90
16th to endDay
34%15%31%12%42
90
December1st to 15thDay
13%13%40%24%5%3
90
16th to endDay
25%14%47%8%4
96
January1st to 15thNight
17%13%38%24%6%
900
16th to endNight
17%14%40%25%2
960
February1st to 15thNight
17%13%36%28%3
846
16th to endNight
20%11%36%28%3
631
March1st to 15thNight
23%11%35%24%5%
651
16th to endNight
21%8%33%28%7%
576
April1st to 15thNight
14%13%36%26%9%
539
16th to endNight
18%5%33%31%9%
540
May1st to 15thNight
16%6%27%36%11%1
540
16th to endNight
10%325%39%19%1
563
June1st to 15thNight
7%219%46%22%1
540
16th to endNight
7%121%43%23%2
540
July1st to 15thNight
9%18%46%30%3
510
16th to endNight
417%39%40%5%
564
August1st to 15thNight
8%5%39%40%4
539
16th to endNight
6%10%39%37%5%
573
September1st to 15thNight
11%212%34%30%7%
540
16th to endNight
10%415%30%32%6%
625
October1st to 15thNight
13%5%23%31%22%3
660
16th to endNight
19%8%32%29%8%
704
November1st to 15thNight
13%9%34%29%12%1
700
16th to endNight
19%11%35%26%7%
780
December1st to 15thNight
24%10%33%24%5%
900
16th to endNight
26%9%34%25%3
960
Page generated at 2017-09-23 05:43:37. Version ac04

Copyright 2017 A. Danko


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