Fenton Hill Observtory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fenton Hill Observtory clear sky chart from 2005-11-05 to 2018-03-11.

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
52%
16460
29%
49135
18%
16416
62%
16416
37%
26672

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
54%
792
32%
2534
24%
788
66%
788
43%
1232
January16th to endNight
49%
832
35%
2704
25%
832
63%
832
40%
1327
February1st to 15thNight
42%
761
28%
2441
19%
760
53%
760
36%
1274
February16th to endNight
35%
684
35%
2050
17%
684
54%
684
33%
1118
March1st to 15thNight
43%
764
32%
2134
16%
764
56%
764
37%
1178
March16th to endNight
42%
738
32%
2082
15%
738
56%
738
41%
1088
April1st to 15thNight
32%
539
28%
1798
13%
539
52%
539
28%
954
April16th to endNight
34%
540
32%
1800
16%
540
56%
540
30%
901
May1st to 15thNight
40%
540
24%
1769
13%
539
55%
539
32%
946
May16th to endNight
43%
563
30%
1556
14%
561
58%
561
39%
855
June1st to 15thNight
55%
540
27%
1440
15%
540
63%
540
47%
764
June16th to endNight
62%
540
25%
1440
17%
540
67%
540
46%
784
July1st to 15thNight
67%
510
12%
1457
9%
510
68%
510
24%
995
July16th to endNight
72%
564
14%
1593
14%
531
73%
531
25%
1054
August1st to 15thNight
73%
539
15%
1677
15%
536
73%
536
27%
1060
August16th to endNight
70%
573
20%
1910
22%
573
73%
573
28%
1157
September1st to 15thNight
64%
540
22%
1800
23%
540
67%
540
26%
1128
September16th to endNight
66%
600
34%
1950
26%
600
75%
600
44%
972
October1st to 15thNight
54%
720
33%
2160
20%
720
63%
720
44%
1111
October16th to endNight
61%
768
39%
2304
24%
768
72%
768
49%
1122
November1st to 15thNight
60%
823
37%
2343
23%
823
68%
823
54%
1111
November16th to endNight
55%
975
38%
2551
22%
975
64%
975
48%
1345
December1st to 15thNight
46%
975
29%
2730
16%
975
56%
975
39%
1494
December16th to endNight
40%
1040
28%
2912
17%
1040
50%
1040
33%
1702

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
45%245%3445%7%52%
49482
Night
442342445%6%56%
49330
TransparencyDay
28%5%9%20%24%10%
49177
Night
25%5%10%20%25%12%
49137
SeeingDay
12%16%29%25%13%2
6090
Night
9%10%23%33%20%3
16463

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
2423433445%60%
1745
16th to endDay
47%24212325%61%
1872
February1st to 15thDay
28%46%422245%54%
1751
16th to endDay
38%35%425%45%7%50%
1710
March1st to 15thDay
36%35%5%24446%52%
2059
16th to endDay
36%25%5%23445%55%
2142
April1st to 15thDay
36%25%5%34448%52%
2150
16th to endDay
46%35%424445%53%
2160
May1st to 15thDay
45%245%35%36%6%52%
2178
16th to endDay
431342345%5%59%
2554
June1st to 15thDay
32134245%5%6%60%
2520
16th to endDay
121332446%8%60%
2520
July1st to 15thDay
45%37%7%46%7%8%9%36%
2411
16th to endDay
5%436%8%5%7%8%10%11%28%
2467
August1st to 15thDay
6%5%38%8%46%7%8%9%30%
2274
16th to endDay
6%5%26%6%45%6%7%10%38%
2292
September1st to 15thDay
9%5%25%6%45%6%7%7%39%
2160
16th to endDay
5%313423445%60%
2007
October1st to 15thDay
7%213423335%61%
1800
16th to endDay
331332223468%
1920
November1st to 15thDay
321332325%7%63%
1831
16th to endDay
35%13322335%64%
1735
December1st to 15thDay
37%243135%4458%
1560
16th to endDay
311%35%434347%48%
1664
January1st to 15thNight
25%13323345%63%
2534
16th to endNight
5%5%22223336%61%
2704
February1st to 15thNight
37%24323345%58%
2431
16th to endNight
47%23424446%55%
2050
March1st to 15thNight
36%23433435%58%
2134
16th to endNight
441332245%5%62%
2082
April1st to 15thNight
45%34423347%55%
1798
16th to endNight
45%24324246%60%
1800
May1st to 15thNight
5%423425%446%55%
1769
16th to endNight
4213426%445%59%
1556
June1st to 15thNight
221441445%6%62%
1440
16th to endNight
1114425%5%5%8%58%
1440
July1st to 15thNight
35%26%7%48%7%8%9%35%
1545
16th to endNight
3325%8%5%8%7%10%11%32%
1701
August1st to 15thNight
3325%6%37%6%9%10%39%
1686
16th to endNight
5%435%446%6%9%11%38%
1910
September1st to 15thNight
6%4247%46%6%7%8%39%
1800
16th to endNight
5%213433447%61%
1950
October1st to 15thNight
5%313312345%63%
2160
16th to endNight
32332333469%
2304
November1st to 15thNight
2212323336%67%
2343
16th to endNight
342321333466%
2551
December1st to 15thNight
46%14423336%58%
2730
16th to endNight
48%35%424347%51%
2912

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
23%5%7%31%29%3
1746
16th to endDay
26%38%26%26%8%
1872
February1st to 15thDay
30%310%25%19%9%
1752
16th to endDay
30%47%19%27%10%
1710
March1st to 15thDay
29%46%20%30%9%
2059
16th to endDay
28%37%21%30%9%
2142
April1st to 15thDay
28%5%8%22%25%10%
2150
16th to endDay
29%38%18%27%12%
2160
May1st to 15thDay
30%48%17%29%9%
2178
16th to endDay
25%5%9%17%27%14%
2557
June1st to 15thDay
22%5%8%14%23%26%
2520
16th to endDay
19%5%9%16%25%24%
2520
July1st to 15thDay
38%9%14%13%13%11%
2271
16th to endDay
40%12%20%18%6%
2312
August1st to 15thDay
44%9%13%16%10%4
2259
16th to endDay
36%9%13%19%15%5%
2292
September1st to 15thDay
36%8%13%19%16%6%
2160
16th to endDay
23%48%19%30%13%
2007
October1st to 15thDay
25%36%19%30%15%
1800
16th to endDay
19%37%20%36%13%
1920
November1st to 15thDay
18%39%24%32%11%
1831
16th to endDay
21%25%24%33%12%
1735
December1st to 15thDay
26%5%10%29%21%6%
1560
16th to endDay
32%5%12%25%20%3
1664
January1st to 15thNight
21%39%26%30%7%
2534
16th to endNight
23%38%23%31%10%
2704
February1st to 15thNight
26%310%26%21%10%
2441
16th to endNight
26%45%20%30%11%
2050
March1st to 15thNight
25%5%5%24%29%9%
2134
16th to endNight
21%37%21%34%10%
2082
April1st to 15thNight
27%5%7%23%24%12%
1798
16th to endNight
23%46%20%30%13%
1800
May1st to 15thNight
27%49%18%28%10%
1770
16th to endNight
23%5%9%17%26%17%
1557
June1st to 15thNight
20%5%10%13%21%28%
1440
16th to endNight
22%5%11%13%18%28%
1440
July1st to 15thNight
39%12%15%12%7%12%
1457
16th to endNight
37%12%21%19%8%
1593
August1st to 15thNight
32%12%19%16%11%7%
1677
16th to endNight
33%10%17%20%12%6%
1910
September1st to 15thNight
37%8%14%16%13%9%
1800
16th to endNight
22%49%15%29%17%
1950
October1st to 15thNight
22%46%17%28%19%
2160
16th to endNight
18%45%17%36%17%
2304
November1st to 15thNight
16%28%25%36%11%
2343
16th to endNight
20%25%21%34%15%
2551
December1st to 15thNight
25%310%28%23%8%
2730
16th to endNight
30%5%10%25%24%4
2912

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
12%22%31%22%11%
135
16th to endDay
10%22%26%22%17%1
144
February1st to 15thDay
10%22%32%27%6%
135
16th to endDay
24%27%26%14%7%
120
March1st to 15thDay
13%27%39%14%4
276
16th to endDay
15%37%30%11%4
288
April1st to 15thDay
18%31%33%10%3
269
16th to endDay
19%39%29%10%1
270
May1st to 15thDay
14%30%39%12%2
288
16th to endDay
10%23%32%21%10%1
455
June1st to 15thDay
7%12%30%27%20%
495
16th to endDay
35%26%35%24%4
495
July1st to 15thDay
10%126%32%24%4
375
16th to endDay
12%113%37%28%6%
327
August1st to 15thDay
13%223%38%19%3
315
16th to endDay
11%321%42%17%3
332
September1st to 15thDay
11%5%30%37%12%2
315
16th to endDay
10%12%35%28%10%2
228
October1st to 15thDay
11%19%31%21%12%4
135
16th to endDay
12%11%29%24%16%4
144
November1st to 15thDay
11%15%37%23%12%
135
16th to endDay
17%23%27%20%10%
135
December1st to 15thDay
10%24%25%31%5%2
135
16th to endDay
20%20%29%23%5%
144
January1st to 15thNight
8%8%24%36%17%4
792
16th to endNight
10%11%24%33%16%3
832
February1st to 15thNight
11%11%30%32%11%2
764
16th to endNight
13%17%30%30%7%
684
March1st to 15thNight
8%17%25%33%13%1
764
16th to endNight
10%14%30%30%13%
738
April1st to 15thNight
13%19%30%28%7%
539
16th to endNight
11%20%29%27%10%
540
May1st to 15thNight
10%15%29%32%10%
540
16th to endNight
6%12%31%30%17%1
563
June1st to 15thNight
47%28%39%18%1
540
16th to endNight
3423%37%30%1
540
July1st to 15thNight
8%111%36%37%4
510
16th to endNight
5%7%26%51%8%
564
August1st to 15thNight
6%7%30%44%9%
539
16th to endNight
8%9%31%41%7%
573
September1st to 15thNight
9%214%35%33%5%
540
16th to endNight
8%318%37%29%3
600
October1st to 15thNight
8%5%29%36%17%3
720
16th to endNight
7%7%20%35%22%6%
768
November1st to 15thNight
5%10%21%35%24%2
823
16th to endNight
9%11%19%32%21%4
975
December1st to 15thNight
11%13%26%33%13%1
975
16th to endNight
12%13%29%30%12%1
1040
Page generated at 2018-03-12 11:28:04. Version ac04

Copyright 2018 A. Danko


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