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 2005-11-06 to 2024-01-27.

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
47%
24049
26%
74388
18%
23987
55%
23987
32%
43322

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 10thNight
30%
950
27%
2458
10%
946
42%
946
30%
1570
January11th to 20thNight
27%
950
25%
2470
8%
950
37%
950
27%
1611
January21st to endNight
27%
1025
28%
2665
9%
1025
38%
1025
28%
1720
February1st to 10thNight
25%
900
23%
2340
6%
900
35%
900
28%
1527
February11th to 20thNight
22%
767
21%
2162
7%
763
32%
763
25%
1425
February21st to endNight
22%
444
27%
1628
11%
444
39%
444
20%
983
March1st to 10thNight
30%
540
25%
1980
13%
540
44%
540
22%
1192
March11th to 20thNight
30%
540
22%
1980
13%
540
43%
540
21%
1204
March21st to endNight
30%
594
24%
2178
14%
594
44%
594
26%
1260
April1st to 10thNight
31%
540
26%
1925
16%
540
47%
540
29%
1058
April11th to 20thNight
35%
533
26%
1775
18%
533
49%
533
26%
1048
April21st to endNight
36%
540
27%
1800
17%
540
52%
540
31%
1001
May1st to 10thNight
40%
540
23%
1720
17%
540
53%
540
29%
1036
May11th to 20thNight
47%
531
22%
1594
19%
531
55%
531
34%
944
May21st to endNight
52%
584
23%
1746
18%
582
61%
582
33%
1043
June1st to 10thNight
73%
540
22%
1620
23%
540
77%
540
41%
886
June11th to 20thNight
70%
540
24%
1620
25%
540
74%
540
45%
845
June21st to endNight
75%
540
26%
1620
28%
540
78%
540
45%
861
July1st to 10thNight
74%
525
21%
1575
22%
525
77%
525
37%
918
July11th to 20thNight
84%
522
27%
1566
31%
522
86%
522
51%
784
July21st to endNight
81%
591
25%
1673
29%
558
83%
558
44%
891
August1st to 10thNight
84%
537
28%
1601
32%
534
85%
534
51%
789
August11th to 20thNight
75%
534
26%
1679
30%
534
76%
534
37%
937
August21st to endNight
77%
594
22%
1980
27%
594
77%
594
34%
1116
September1st to 10thNight
75%
540
25%
1831
29%
540
76%
540
36%
994
September11th to 20thNight
71%
540
27%
1980
31%
540
73%
540
32%
1084
September21st to endNight
72%
540
34%
1980
36%
540
76%
540
42%
939
October1st to 10thNight
69%
702
34%
2142
27%
702
73%
702
48%
1068
October11th to 20thNight
51%
720
35%
2160
21%
720
61%
720
38%
1183
October21st to endNight
45%
792
32%
2376
21%
792
55%
792
35%
1357
November1st to 10thNight
51%
740
30%
2220
21%
740
59%
740
38%
1245
November11th to 20thNight
42%
760
30%
2280
18%
760
53%
760
34%
1297
November21st to endNight
35%
874
29%
2394
15%
874
45%
874
29%
1514
December1st to 10thNight
35%
950
27%
2470
11%
950
46%
950
29%
1612
December11th to 20thNight
31%
948
26%
2873
11%
948
39%
948
24%
1846
December21st to endNight
29%
1042
16%
4327
9%
1026
39%
1026
19%
2534

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%7%45%
75116
Night
12%5%2442345%7%52%
74961
TransparencyDay
38%5%10%21%19%6%
74840
Night
33%5%10%21%22%9%
74757
SeeingDay
14%9%23%27%21%6%
14081
Night
15%9%25%31%18%2
24054

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 10thDay
17%8%25%423235%49%
1707
11th to 20thDay
20%5%2431434448%
1710
21st to endDay
21%7%2342224449%
1836
February1st to 10thDay
21%8%35%5%3332440%
1620
11th to 20thDay
22%8%36%6%2334440%
1698
21st to endDay
25%8%2442334441%
1628
March1st to 10thDay
19%7%35%5%24346%42%
1980
11th to 20thDay
20%7%35%424346%42%
1980
21st to endDay
18%6%36%5%34346%42%
2178
April1st to 10thDay
14%6%36%5%34446%45%
2034
11th to 20thDay
16%6%35%43445%7%42%
2134
21st to endDay
14%435%6%3446%7%44%
2160
May1st to 10thDay
17%6%445%3335%7%43%
2236
11th to 20thDay
13%437%6%45%5%6%8%42%
2302
21st to endDay
12%5%37%6%46%5%6%9%37%
2531
June1st to 10thDay
7%425%6%46%7%7%10%42%
2340
11th to 20thDay
6%425%6%46%6%7%10%45%
2340
21st to endDay
5%325%6%46%6%6%9%47%
2340
July1st to 10thDay
8%5%37%7%47%7%8%10%33%
2340
11th to 20thDay
6%3246%46%5%7%11%48%
2340
21st to endDay
8%325%5%46%6%7%11%43%
2546
August1st to 10thDay
43146%46%6%7%9%50%
2328
11th to 20thDay
8%425%5%45%6%6%8%47%
2222
21st to endDay
8%426%6%46%6%9%9%40%
2376
September1st to 10thDay
10%5%25%5%35%45%8%49%
2124
11th to 20thDay
12%436%6%5%445%8%44%
1980
21st to endDay
9%31443445%7%56%
1980
October1st to 10thDay
8%31342335%8%59%
1800
11th to 20thDay
15%5%14323445%53%
1800
21st to endDay
17%5%2342323453%
1980
November1st to 10thDay
13%5%35%423346%52%
1858
11th to 20thDay
11%5%245%23447%53%
1900
21st to endDay
20%6%34423335%47%
1782
December1st to 10thDay
17%8%25%42334448%
1710
11th to 20thDay
15%8%46%5%33345%45%
2161
21st to endDay
17%8%36%433345%43%
3135
January1st to 10thNight
17%6%24323336%51%
2458
11th to 20thNight
19%6%34423335%49%
2470
21st to endNight
19%7%3342334449%
2665
February1st to 10thNight
18%6%25%423245%48%
2340
11th to 20thNight
22%7%24423235%45%
2161
21st to endNight
20%6%25%422445%46%
1628
March1st to 10thNight
19%7%24433446%45%
1980
11th to 20thNight
17%6%35%4245%45%45%
1980
21st to endNight
14%6%34433447%48%
2178
April1st to 10thNight
11%42443446%7%52%
1925
11th to 20thNight
12%6%2442445%7%49%
1775
21st to endNight
11%5%25%433447%53%
1800
May1st to 10thNight
9%5%35%4345%5%8%49%
1720
11th to 20thNight
12%425%3335%6%7%51%
1593
21st to endNight
9%4245%345%6%9%48%
1745
June1st to 10thNight
4324425%5%6%9%56%
1620
11th to 20thNight
432343345%8%61%
1620
21st to endNight
5%3134245%7%10%57%
1620
July1st to 10thNight
5%335%5%35%5%8%12%47%
1620
11th to 20thNight
321333446%11%60%
1620
21st to endNight
3223435%5%7%12%53%
1772
August1st to 10thNight
31123246%6%10%62%
1611
11th to 20thNight
6%3244246%6%9%51%
1679
21st to endNight
6%415%435%6%8%11%47%
1980
September1st to 10thNight
8%41443445%7%56%
1831
11th to 20thNight
9%42442446%8%52%
1980
21st to endNight
7%31432245%7%62%
1980
October1st to 10thNight
6%32333235%6%64%
2142
11th to 20thNight
12%41332334460%
2160
21st to endNight
16%5%23312335%57%
2376
November1st to 10thNight
11%5%24423345%57%
2220
11th to 20thNight
9%426%5%23345%56%
2280
21st to endNight
15%7%25%423345%50%
2394
December1st to 10thNight
15%6%35%5%23346%48%
2470
11th to 20thNight
15%6%25%5%2444448%
3036
21st to endNight
17%8%25%423345%49%
4532

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 10thDay
41%37%19%23%7%
1708
11th to 20thDay
40%35%24%22%6%
1710
21st to endDay
42%25%17%27%8%
1836
February1st to 10thDay
50%35%16%17%9%
1620
11th to 20thDay
49%35%18%19%7%
1707
21st to endDay
48%35%12%22%9%
1628
March1st to 10thDay
45%46%16%19%10%
1980
11th to 20thDay
45%47%19%20%6%
1980
21st to endDay
44%47%19%22%4
2178
April1st to 10thDay
41%48%22%17%8%
2034
11th to 20thDay
41%6%8%18%19%8%
2134
21st to endDay
39%5%10%20%22%4
2160
May1st to 10thDay
43%48%22%18%5%
2236
11th to 20thDay
40%7%12%23%15%2
2306
21st to endDay
43%7%12%22%14%1
2531
June1st to 10thDay
35%8%15%26%15%1
2340
11th to 20thDay
34%7%16%24%17%2
2340
21st to endDay
31%7%13%27%19%3
2340
July1st to 10thDay
43%10%17%21%9%1
2276
11th to 20thDay
28%9%19%26%16%1
2271
21st to endDay
32%8%18%30%12%
2405
August1st to 10thDay
28%8%17%31%15%1
2314
11th to 20thDay
33%8%15%26%16%2
2222
21st to endDay
36%9%15%25%13%2
2376
September1st to 10thDay
34%6%11%21%19%9%
2124
11th to 20thDay
38%7%11%17%19%7%
1980
21st to endDay
28%6%9%22%25%11%
1980
October1st to 10thDay
25%412%22%24%13%
1800
11th to 20thDay
34%45%17%25%15%
1800
21st to endDay
37%35%18%25%12%
1980
November1st to 10thDay
35%47%20%24%10%
1858
11th to 20thDay
33%47%19%26%10%
1900
21st to endDay
42%45%15%24%9%
1782
December1st to 10thDay
41%37%20%20%8%
1710
11th to 20thDay
43%45%15%25%8%
2159
21st to endDay
44%35%18%24%6%
3135
January1st to 10thNight
38%46%16%27%10%
2458
11th to 20thNight
41%38%18%23%7%
2470
21st to endNight
40%35%15%26%11%
2665
February1st to 10thNight
41%37%20%19%11%
2340
11th to 20thNight
44%35%18%22%8%
2162
21st to endNight
42%37%15%20%14%
1628
March1st to 10thNight
41%5%7%15%20%13%
1980
11th to 20thNight
42%47%17%21%8%
1980
21st to endNight
37%49%20%23%6%
2178
April1st to 10thNight
32%5%11%22%19%10%
1925
11th to 20thNight
36%5%8%19%20%11%
1775
21st to endNight
32%5%9%25%26%4
1800
May1st to 10thNight
34%7%9%23%17%10%
1720
11th to 20thNight
32%6%14%27%17%4
1594
21st to endNight
33%7%14%25%19%2
1746
June1st to 10thNight
24%8%15%30%20%3
1620
11th to 20thNight
22%6%14%32%22%4
1620
21st to endNight
22%7%14%27%26%4
1620
July1st to 10thNight
29%8%19%29%14%2
1575
11th to 20thNight
17%7%19%34%20%3
1566
21st to endNight
21%9%19%34%16%1
1673
August1st to 10thNight
16%8%19%34%21%2
1601
11th to 20thNight
27%8%15%27%18%5%
1679
21st to endNight
28%9%16%27%18%3
1980
September1st to 10thNight
27%8%13%21%22%9%
1831
11th to 20thNight
30%6%11%22%22%9%
1980
21st to endNight
22%5%10%21%28%13%
1980
October1st to 10thNight
22%49%26%23%17%
2142
11th to 20thNight
29%36%15%27%20%
2160
21st to endNight
32%35%17%25%16%
2376
November1st to 10thNight
30%49%17%28%13%
2220
11th to 20thNight
31%48%17%27%13%
2280
21st to endNight
38%45%18%25%10%
2394
December1st to 10thNight
39%5%9%18%21%9%
2470
11th to 20thNight
41%46%15%24%11%
3037
21st to endNight
40%36%18%25%7%
4532

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 10thDay
26%18%34%18%4
270
11th to 20thDay
27%19%34%17%3
270
21st to endDay
25%24%35%13%4
282
February1st to 10thDay
28%19%38%10%41
240
11th to 20thDay
33%24%32%10%1
240
21st to endDay
38%24%32%5%2
198
March1st to 10thDay
24%23%35%15%3
240
11th to 20thDay
26%26%35%10%3
240
21st to endDay
21%24%36%15%3
264
April1st to 10thDay
21%16%39%18%5%
294
11th to 20thDay
24%15%32%20%10%
412
21st to endDay
18%15%35%23%7%2
420
May1st to 10thDay
18%10%37%27%7%1
499
11th to 20thDay
15%6%31%29%16%3
625
21st to endDay
12%6%27%34%17%4
679
June1st to 10thDay
8%317%35%31%6%
630
11th to 20thDay
6%316%42%28%5%
630
21st to endDay
7%217%37%28%10%
630
July1st to 10thDay
7%215%34%33%10%
621
11th to 20thDay
417%38%39%10%
618
21st to endDay
5%210%34%37%13%
684
August1st to 10thDay
5%18%28%46%12%
626
11th to 20thDay
10%18%30%42%9%
536
21st to endDay
11%16%23%41%19%
495
September1st to 10thDay
9%17%27%42%14%
414
11th to 20thDay
5%411%30%37%13%
270
21st to endDay
11%5%10%39%27%9%
270
October1st to 10thDay
6%422%41%22%4
270
11th to 20thDay
14%7%32%32%10%4
270
21st to endDay
26%13%28%22%10%1
297
November1st to 10thDay
19%6%33%31%10%1
270
11th to 20thDay
15%12%40%24%8%1
270
21st to endDay
23%19%28%20%8%1
270
December1st to 10thDay
20%16%37%17%8%2
270
11th to 20thDay
25%19%34%17%41
270
21st to endDay
21%22%39%14%31
297
January1st to 10thNight
22%15%31%27%6%
950
11th to 20thNight
24%14%31%25%6%
950
21st to endNight
22%15%34%26%4
1025
February1st to 10thNight
22%14%36%23%5%
900
11th to 20thNight
28%13%35%20%3
767
21st to endNight
23%20%33%22%2
444
March1st to 10thNight
23%12%31%28%5%
540
11th to 20thNight
20%13%33%29%5%1
540
21st to endNight
17%12%39%25%7%
594
April1st to 10thNight
13%14%40%27%7%
540
11th to 20thNight
15%14%33%27%11%
533
21st to endNight
14%10%37%27%11%1
540
May1st to 10thNight
10%9%36%33%11%1
540
11th to 20thNight
12%5%31%33%17%2
531
21st to endNight
9%428%36%21%3
584
June1st to 10thNight
5%213%39%39%3
540
11th to 20thNight
5%215%43%32%2
540
21st to endNight
5%12%41%35%7%
540
July1st to 10thNight
5%19%36%43%6%
525
11th to 20thNight
417%37%46%6%
522
21st to endNight
318%37%41%10%
591
August1st to 10thNight
317%38%43%7%
537
11th to 20thNight
8%7%41%37%6%
534
21st to endNight
6%17%36%42%9%
594
September1st to 10thNight
9%18%32%43%7%
540
11th to 20thNight
9%110%34%42%4
540
21st to endNight
8%311%37%36%5%
540
October1st to 10thNight
7%215%42%29%5%
702
11th to 20thNight
13%7%24%36%18%1
720
21st to endNight
18%8%26%29%17%2
792
November1st to 10thNight
12%5%27%39%15%1
740
11th to 20thNight
11%11%30%37%10%1
760
21st to endNight
18%14%30%26%11%1
874
December1st to 10thNight
19%13%30%32%7%
950
11th to 20thNight
22%11%31%30%7%
950
21st to endNight
23%14%30%27%6%
1045
Page generated at 2024-01-24 08:37:31. Version ac07

Copyright 2024 Attilla Danko


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