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 2019-06-19.

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
48%
17917
26%
53943
18%
17870
56%
17870
33%
31515

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
33%
1050
27%
2717
11%
1045
43%
1045
29%
1737
January16th to endNight
30%
1120
28%
2912
10%
1120
40%
1120
30%
1850
February1st to 15thNight
26%
1030
23%
2678
7%
1026
36%
1026
29%
1738
February16th to endNight
23%
603
26%
2073
10%
603
39%
603
22%
1263
March1st to 15thNight
31%
630
26%
2310
15%
630
45%
630
22%
1376
March16th to endNight
34%
672
22%
2464
14%
672
45%
672
27%
1409
April1st to 15thNight
34%
629
27%
2194
17%
629
50%
629
31%
1184
April16th to endNight
38%
624
24%
2078
17%
624
52%
624
30%
1179
May1st to 15thNight
40%
630
23%
1968
17%
630
52%
630
29%
1208
May16th to endNight
55%
659
24%
1973
21%
657
62%
657
37%
1131
June1st to 15thNight
75%
630
24%
1890
24%
630
79%
630
43%
1015
June16th to endNight
73%
597
24%
1791
26%
597
76%
597
45%
943
July1st to 15thNight
76%
555
20%
1665
22%
555
79%
555
39%
946
July16th to endNight
83%
612
26%
1738
30%
579
86%
579
46%
913
August1st to 15thNight
86%
575
29%
1717
34%
572
86%
572
51%
849
August16th to endNight
74%
621
21%
2063
25%
621
74%
621
31%
1212
September1st to 15thNight
71%
585
23%
2038
27%
585
72%
585
32%
1146
September16th to endNight
72%
582
33%
2145
36%
582
75%
582
37%
1091
October1st to 15thNight
63%
767
31%
2327
25%
767
67%
767
41%
1255
October16th to endNight
52%
832
36%
2496
23%
832
63%
832
42%
1317
November1st to 15thNight
47%
820
27%
2460
19%
820
55%
820
34%
1420
November16th to endNight
40%
924
32%
2604
18%
924
51%
924
33%
1547
December1st to 15thNight
35%
1050
26%
2730
12%
1050
44%
1050
28%
1815
December16th to endNight
30%
1120
21%
2912
9%
1120
38%
1120
26%
1971

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%25%5%3445%6%44%
54776
Night
11%424323347%51%
54138
TransparencyDay
39%5%9%20%18%5%
54476
Night
32%410%21%21%8%
53943
SeeingDay
13%7%21%27%23%6%
7865
Night
14%8%24%31%19%2
17917

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
16%6%2441333448%
1881
16th to endDay
19%6%2231323350%
2016
February1st to 15thDay
20%8%35%5%2222443%
1851
16th to endDay
22%7%25%42333440%
1976
March1st to 15thDay
21%6%24424235%43%
2310
16th to endDay
15%6%36%424346%42%
2462
April1st to 15thDay
14%6%25%424346%46%
2413
16th to endDay
14%4345%3445%7%43%
2487
May1st to 15thDay
16%6%35%5%44346%39%
2640
16th to endDay
9%427%5%45%45%9%40%
2846
June1st to 15thDay
6%415%6%46%6%7%9%42%
2730
16th to endDay
5%425%6%46%6%7%9%40%
2577
July1st to 15thDay
7%5%36%7%47%6%7%9%35%
2535
16th to endDay
8%2245%46%5%8%10%40%
2674
August1st to 15thDay
5%3135%45%6%6%8%49%
2486
16th to endDay
9%426%6%46%6%8%8%35%
2491
September1st to 15thDay
12%5%25%6%3445%7%41%
2249
16th to endDay
9%3245%33447%51%
2145
October1st to 15thDay
13%413323347%51%
1950
16th to endDay
13%41232323458%
2080
November1st to 15thDay
13%6%24423336%48%
2058
16th to endDay
15%5%23313235%52%
2013
December1st to 15thDay
19%8%2422223347%
1890
16th to endDay
18%7%35%5%33335%40%
2016
January1st to 15thNight
15%6%24323326%49%
2717
16th to endNight
17%5%2332333451%
2912
February1st to 15thNight
17%5%24322245%48%
2668
16th to endNight
19%6%24322335%46%
2073
March1st to 15thNight
18%6%24323345%46%
2310
16th to endNight
12%5%35%423447%48%
2464
April1st to 15thNight
9%42332445%7%53%
2194
16th to endNight
10%424423346%52%
2078
May1st to 15thNight
10%5%25%32345%6%48%
1967
16th to endNight
7%3134345%6%9%49%
1971
June1st to 15thNight
32133245%5%8%58%
1890
16th to endNight
431342346%9%57%
1791
July1st to 15thNight
4324425%47%11%49%
1755
16th to endNight
21123345%7%13%53%
1846
August1st to 15thNight
31123125%6%10%60%
1727
16th to endNight
6%414425%5%8%12%44%
2063
September1st to 15thNight
10%31432445%7%51%
2038
16th to endNight
6%41432235%7%57%
2145
October1st to 15thNight
9%313322345%59%
2327
16th to endNight
13%31221223462%
2496
November1st to 15thNight
10%425%423346%53%
2460
16th to endNight
13%5%1431333455%
2604
December1st to 15thNight
16%6%25%422335%46%
2730
16th to endNight
18%7%25%313345%43%
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
41%26%19%22%7%
1882
16th to endDay
39%2420%25%7%
2016
February1st to 15thDay
48%2418%18%7%
1852
16th to endDay
49%3415%20%7%
1976
March1st to 15thDay
45%26%18%19%6%
2310
16th to endDay
43%47%19%21%3
2464
April1st to 15thDay
39%48%20%18%8%
2413
16th to endDay
40%49%19%21%4
2487
May1st to 15thDay
46%5%9%16%17%5%
2640
16th to endDay
40%6%12%22%16%1
2850
June1st to 15thDay
35%7%14%25%16%
2730
16th to endDay
37%7%13%21%18%1
2577
July1st to 15thDay
40%9%15%23%10%
2396
16th to endDay
35%7%18%24%12%
2519
August1st to 15thDay
29%8%15%28%15%2
2472
16th to endDay
41%9%15%21%10%2
2491
September1st to 15thDay
40%6%10%19%15%7%
2249
16th to endDay
32%5%9%21%22%8%
2145
October1st to 15thDay
33%410%18%19%13%
1950
16th to endDay
31%3418%29%13%
2080
November1st to 15thDay
38%38%21%21%6%
2058
16th to endDay
36%35%16%29%9%
2013
December1st to 15thDay
44%27%18%18%8%
1890
16th to endDay
47%26%19%18%4
2016
January1st to 15thNight
38%27%15%26%8%
2717
16th to endNight
38%25%17%25%11%
2912
February1st to 15thNight
39%37%20%19%9%
2678
16th to endNight
41%36%18%20%9%
2073
March1st to 15thNight
40%37%16%20%10%
2310
16th to endNight
36%39%22%22%5%
2464
April1st to 15thNight
29%5%10%22%21%9%
2194
16th to endNight
32%5%8%21%24%6%
2078
May1st to 15thNight
35%6%9%22%16%9%
1968
16th to endNight
29%6%15%26%19%2
1973
June1st to 15thNight
22%7%13%30%22%3
1890
16th to endNight
22%6%13%27%26%4
1791
July1st to 15thNight
27%7%18%29%15%1
1665
16th to endNight
19%8%19%32%17%2
1738
August1st to 15thNight
18%5%17%33%20%4
1717
16th to endNight
30%9%16%24%15%3
2063
September1st to 15thNight
30%7%13%21%18%8%
2038
16th to endNight
26%5%8%22%25%11%
2145
October1st to 15thNight
27%49%22%21%15%
2327
16th to endNight
26%25%18%27%19%
2496
November1st to 15thNight
32%310%18%24%10%
2460
16th to endNight
33%35%15%29%12%
2604
December1st to 15thNight
41%38%17%18%9%
2730
16th to endNight
43%38%18%18%7%
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
20%17%34%22%5%
180
16th to endDay
18%22%34%18%5%
192
February1st to 15thDay
24%22%38%10%4
180
16th to endDay
34%23%33%5%2
159
March1st to 15thDay
22%31%33%11%1
180
16th to endDay
13%22%38%20%5%
192
April1st to 15thDay
21%15%34%18%9%
292
16th to endDay
18%10%32%24%10%2
379
May1st to 15thDay
16%8%35%26%10%2
537
16th to endDay
11%6%29%30%18%4
677
June1st to 15thDay
7%114%38%33%4
645
16th to endDay
6%215%38%28%8%
587
July1st to 15thDay
6%212%35%32%11%
550
16th to endDay
6%17%31%39%13%
595
August1st to 15thDay
7%429%44%12%
549
16th to endDay
13%6%22%42%14%
403
September1st to 15thDay
11%7%18%46%16%
284
16th to endDay
9%17%38%32%10%
180
October1st to 15thDay
9%118%43%17%8%
180
16th to endDay
20%9%25%27%13%3
192
November1st to 15thDay
26%7%34%22%8%
180
16th to endDay
16%15%33%18%12%3
180
December1st to 15thDay
27%14%33%13%8%2
180
16th to endDay
22%21%36%15%21
192
January1st to 15thNight
21%13%27%29%7%
1050
16th to endNight
20%14%32%27%5%
1120
February1st to 15thNight
21%13%35%24%5%
1030
16th to endNight
22%16%35%22%3
603
March1st to 15thNight
22%12%30%28%5%
630
16th to endNight
13%10%38%28%7%
672
April1st to 15thNight
10%14%38%26%9%
629
16th to endNight
12%8%36%28%13%
624
May1st to 15thNight
12%6%36%29%13%1
630
16th to endNight
6%427%37%21%3
659
June1st to 15thNight
4112%38%41%2
630
16th to endNight
412%40%35%6%
597
July1st to 15thNight
49%36%42%6%
555
16th to endNight
216%31%48%10%
612
August1st to 15thNight
4434%46%10%
575
16th to endNight
9%6%32%42%8%
621
September1st to 15thNight
11%18%30%40%7%
585
16th to endNight
8%111%31%41%5%
582
October1st to 15thNight
9%417%37%26%5%
767
16th to endNight
14%6%23%31%21%2
832
November1st to 15thNight
11%7%27%37%14%1
820
16th to endNight
15%12%28%29%13%
924
December1st to 15thNight
20%11%28%31%8%
1050
16th to endNight
23%12%29%27%6%
1120
Page generated at 2019-06-20 07:02:26. Version ac04

Copyright 2019 A. Danko


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