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East Fork Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the East Fork Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
49%
15584
26%
46946
18%
15537
57%
15537
33%
27222

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
32%
900
27%
2327
11%
895
42%
895
30%
1472
January16th to endNight
28%
960
28%
2496
10%
960
39%
960
30%
1588
February1st to 15thNight
28%
880
24%
2288
7%
876
38%
876
32%
1439
February16th to endNight
24%
519
29%
1781
11%
519
42%
519
26%
1029
March1st to 15thNight
31%
540
26%
1980
14%
540
45%
540
23%
1169
March16th to endNight
34%
576
22%
2112
15%
576
44%
576
26%
1225
April1st to 15thNight
34%
539
25%
1880
16%
539
50%
539
31%
1005
April16th to endNight
38%
540
24%
1800
17%
540
51%
540
29%
1042
May1st to 15thNight
38%
540
22%
1686
14%
540
51%
540
28%
1041
May16th to endNight
55%
563
24%
1685
21%
561
61%
561
34%
990
June1st to 15thNight
77%
540
23%
1620
23%
540
81%
540
43%
868
June16th to endNight
74%
540
25%
1620
27%
540
76%
540
43%
866
July1st to 15thNight
75%
510
21%
1530
23%
510
78%
510
38%
876
July16th to endNight
84%
564
27%
1594
31%
531
86%
531
46%
838
August1st to 15thNight
86%
539
30%
1610
34%
536
86%
536
51%
791
August16th to endNight
73%
573
21%
1904
26%
573
73%
573
29%
1143
September1st to 15thNight
72%
540
24%
1881
27%
540
73%
540
34%
1026
September16th to endNight
73%
516
34%
1903
37%
516
76%
516
39%
941
October1st to 15thNight
61%
649
32%
1969
25%
649
65%
649
41%
1055
October16th to endNight
54%
704
37%
2112
24%
704
64%
704
43%
1095
November1st to 15thNight
50%
700
29%
2100
20%
700
58%
700
37%
1167
November16th to endNight
38%
792
32%
2232
18%
792
48%
792
32%
1353
December1st to 15thNight
36%
900
25%
2340
12%
900
43%
900
28%
1544
December16th to endNight
31%
960
22%
2496
9%
960
40%
960
28%
1659

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
13%5%245%3445%6%44%
47959
Night
11%424323347%52%
47141
TransparencyDay
39%5%9%20%19%5%
47659
Night
32%410%21%22%9%
46946
SeeingDay
11%6%19%28%26%7%
5620
Night
13%8%24%30%20%2
15584

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
17%5%2441332450%
1611
16th to endDay
20%6%1231324449%
1728
February1st to 15thDay
19%7%25%5%2221445%
1580
16th to endDay
19%6%2442333445%
1697
March1st to 15thDay
22%5%24324235%43%
1980
16th to endDay
16%7%36%424345%41%
2110
April1st to 15thDay
13%5%25%424346%47%
2067
16th to endDay
14%435%5%3445%7%41%
2160
May1st to 15thDay
16%6%46%5%43446%38%
2262
16th to endDay
11%437%5%45%46%9%38%
2430
June1st to 15thDay
6%315%5%36%6%7%9%42%
2340
16th to endDay
5%425%7%46%6%6%9%40%
2340
July1st to 15thDay
7%5%36%7%47%6%7%9%34%
2340
16th to endDay
9%2245%46%6%8%9%39%
2466
August1st to 15thDay
5%3135%35%6%6%8%49%
2340
16th to endDay
10%5%27%6%46%6%8%9%33%
2298
September1st to 15thDay
11%5%245%3445%8%44%
2076
16th to endDay
9%314433446%54%
1893
October1st to 15thDay
13%413423347%51%
1650
16th to endDay
13%41231223460%
1760
November1st to 15thDay
11%5%24423336%51%
1758
16th to endDay
17%5%2331223451%
1725
December1st to 15thDay
19%8%2422223446%
1620
16th to endDay
19%7%34422335%43%
1728
January1st to 15thNight
16%6%24312225%51%
2327
16th to endNight
18%5%2332323351%
2496
February1st to 15thNight
15%5%2431224452%
2278
16th to endNight
17%5%13312335%51%
1781
March1st to 15thNight
18%6%23322345%46%
1980
16th to endNight
12%5%35%423446%48%
2112
April1st to 15thNight
8%31332435%7%53%
1880
16th to endNight
10%5%25%423436%51%
1800
May1st to 15thNight
11%435%32345%6%48%
1685
16th to endNight
7%3134345%6%10%47%
1683
June1st to 15thNight
321332445%8%59%
1620
16th to endNight
432341346%9%55%
1620
July1st to 15thNight
5%32442447%11%48%
1620
16th to endNight
21123345%7%12%54%
1702
August1st to 15thNight
31122125%6%10%61%
1620
16th to endNight
7%414435%5%8%12%42%
1904
September1st to 15thNight
10%31432445%7%53%
1881
16th to endNight
6%314322347%59%
1903
October1st to 15thNight
8%313332345%59%
1969
16th to endNight
12%31121223464%
2112
November1st to 15thNight
8%424423346%56%
2100
16th to endNight
15%5%2431323453%
2232
December1st to 15thNight
16%5%25%422335%46%
2340
16th to endNight
17%7%24312345%45%
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
40%25%19%23%7%
1612
16th to endDay
40%2419%25%7%
1728
February1st to 15thDay
45%2418%20%7%
1581
16th to endDay
44%35%17%22%8%
1697
March1st to 15thDay
45%27%18%19%7%
1980
16th to endDay
44%47%18%21%3
2112
April1st to 15thDay
38%48%21%18%8%
2067
16th to endDay
41%48%19%20%5%
2160
May1st to 15thDay
47%5%8%14%18%6%
2262
16th to endDay
42%6%12%21%15%1
2434
June1st to 15thDay
35%7%13%26%16%
2340
16th to endDay
37%7%13%21%18%2
2340
July1st to 15thDay
40%9%15%23%11%
2201
16th to endDay
36%7%19%23%12%
2311
August1st to 15thDay
28%8%16%28%15%2
2326
16th to endDay
43%9%14%20%9%2
2298
September1st to 15thDay
38%6%10%20%15%8%
2076
16th to endDay
30%49%22%23%9%
1893
October1st to 15thDay
33%49%16%21%14%
1650
16th to endDay
29%3419%30%13%
1760
November1st to 15thDay
35%37%22%23%7%
1758
16th to endDay
37%3415%29%9%
1725
December1st to 15thDay
44%27%18%19%7%
1620
16th to endDay
45%27%19%19%5%
1728
January1st to 15thNight
37%26%15%27%9%
2327
16th to endNight
38%25%17%24%11%
2496
February1st to 15thNight
36%36%21%21%10%
2288
16th to endNight
37%26%20%21%10%
1781
March1st to 15thNight
40%38%18%19%10%
1980
16th to endNight
37%49%21%22%5%
2112
April1st to 15thNight
29%411%22%21%10%
1880
16th to endNight
34%5%9%21%23%6%
1800
May1st to 15thNight
36%7%9%19%17%10%
1686
16th to endNight
30%7%15%25%17%3
1685
June1st to 15thNight
21%8%12%31%22%3
1620
16th to endNight
23%6%14%25%25%4
1620
July1st to 15thNight
27%7%16%30%15%1
1530
16th to endNight
19%8%20%32%16%2
1594
August1st to 15thNight
17%5%16%34%20%4
1610
16th to endNight
32%10%16%23%14%3
1904
September1st to 15thNight
29%6%13%22%19%9%
1881
16th to endNight
25%48%23%25%12%
1903
October1st to 15thNight
27%38%20%22%17%
1969
16th to endNight
25%2418%28%20%
2112
November1st to 15thNight
29%310%19%26%11%
2100
16th to endNight
35%3413%29%12%
2232
December1st to 15thNight
41%38%19%18%8%
2340
16th to endNight
41%39%17%19%7%
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
14%17%36%27%3
90
16th to endDay
18%28%33%12%7%
96
February1st to 15thDay
14%23%42%15%4
90
16th to endDay
17%22%46%9%3
81
March1st to 15thDay
23%27%35%10%3
90
16th to endDay
10%19%30%31%8%
96
April1st to 15thDay
18%11%37%20%11%
186
16th to endDay
19%11%32%21%12%2
270
May1st to 15thDay
15%11%37%24%9%2
399
16th to endDay
13%6%29%29%17%3
517
June1st to 15thDay
7%113%36%35%5%
495
16th to endDay
6%213%37%29%10%
495
July1st to 15thDay
7%213%36%32%7%
475
16th to endDay
6%15%29%42%14%
515
August1st to 15thDay
7%5%28%44%13%
493
16th to endDay
15%5%23%41%13%
338
September1st to 15thDay
7%6%20%49%16%
231
16th to endDay
28%39%36%11%
111
October1st to 15thDay
2217%56%12%8%
90
16th to endDay
18%7%14%35%19%4
96
November1st to 15thDay
21%231%32%12%1
90
16th to endDay
24%15%31%16%8%3
90
December1st to 15thDay
28%12%33%13%10%2
90
16th to endDay
21%23%34%15%22
96
January1st to 15thNight
20%14%27%29%7%
900
16th to endNight
20%14%33%26%4
960
February1st to 15thNight
19%13%35%25%6%
880
16th to endNight
21%15%36%23%3
519
March1st to 15thNight
22%11%31%30%5%
540
16th to endNight
14%10%38%28%7%
576
April1st to 15thNight
9%14%39%26%9%
539
16th to endNight
12%8%36%28%13%
540
May1st to 15thNight
12%7%37%28%12%1
540
16th to endNight
7%427%38%20%2
563
June1st to 15thNight
3111%39%41%2
540
16th to endNight
5%10%38%37%7%
540
July1st to 15thNight
49%38%42%4
510
16th to endNight
21430%49%10%
564
August1st to 15thNight
4433%46%10%
539
16th to endNight
10%6%31%42%8%
573
September1st to 15thNight
11%18%30%41%6%
540
16th to endNight
6%112%31%42%4
516
October1st to 15thNight
9%418%36%26%5%
649
16th to endNight
13%6%23%30%23%2
704
November1st to 15thNight
9%7%26%38%15%2
700
16th to endNight
17%12%28%27%12%
792
December1st to 15thNight
19%11%28%32%8%
900
16th to endNight
22%13%29%27%7%
960
Page generated at 2017-09-24 08:15:55. Version ac04

Copyright 2017 A. Danko


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