Elk Horn Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elk Horn Observatory clear sky chart from 2005-11-05 to 2019-06-10.

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
34%
18076
21%
53876
10%
18038
46%
18038
21%
34513

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
16%
837
23%
2717
6%
836
36%
836
14%
1698
January16th to endNight
18%
896
24%
2912
8%
896
38%
896
16%
1781
February1st to 15thNight
17%
822
22%
2661
8%
821
34%
821
14%
1664
February16th to endNight
13%
735
22%
2177
5%
735
31%
735
16%
1427
March1st to 15thNight
19%
840
25%
2310
8%
840
34%
840
18%
1525
March16th to endNight
22%
896
18%
2464
7%
896
31%
896
18%
1678
April1st to 15thNight
25%
838
20%
2220
5%
838
37%
838
22%
1439
April16th to endNight
31%
712
20%
1958
7%
712
41%
712
22%
1287
May1st to 15thNight
35%
630
17%
1890
7%
630
43%
630
21%
1226
May16th to endNight
41%
657
14%
1972
7%
657
46%
657
20%
1285
June1st to 15thNight
55%
612
16%
1836
12%
612
59%
612
26%
1171
June16th to endNight
56%
585
16%
1755
11%
585
61%
585
28%
1098
July1st to 15thNight
60%
555
13%
1665
11%
555
63%
555
25%
1082
July16th to endNight
60%
612
14%
1739
10%
579
67%
579
27%
1111
August1st to 15thNight
56%
575
16%
1715
12%
572
59%
572
24%
1157
August16th to endNight
59%
709
18%
1951
14%
709
62%
709
28%
1298
September1st to 15thNight
55%
780
20%
2093
14%
780
58%
780
28%
1383
September16th to endNight
47%
777
19%
2145
13%
777
52%
777
21%
1487
October1st to 15thNight
44%
780
25%
2301
20%
780
53%
780
24%
1465
October16th to endNight
35%
832
32%
2496
18%
832
54%
832
30%
1414
November1st to 15thNight
32%
820
25%
2527
15%
820
46%
820
23%
1540
November16th to endNight
29%
840
27%
2730
14%
840
46%
840
22%
1561
December1st to 15thNight
20%
840
23%
2730
8%
840
39%
840
14%
1771
December16th to endNight
15%
896
21%
2912
5%
896
33%
896
11%
1965

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
14%6%25%5%35%5%5%7%36%
54622
Night
13%6%2442445%7%42%
54069
Cloud CoverDay
15%6%25%5%35%5%5%7%37%
54632
Night
13%5%2442445%7%42%
54073
TransparencyDay
43%7%11%20%13%3
54333
Night
38%6%11%22%16%3
53876
SeeingDay
18%20%20%19%12%7%
7869
Night
15%24%19%22%15%2
18083

By Month

Percentage Cloud Cover NE (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
14%9%24434446%40%
1881
16th to endDay
14%6%25%5%245%36%43%
2016
February1st to 15thDay
13%8%36%5%2445%6%38%
1858
16th to endDay
16%7%35%5%3445%7%37%
1867
March1st to 15thDay
15%7%245%2445%6%42%
2299
16th to endDay
17%7%25%5%34446%38%
2464
April1st to 15thDay
12%6%25%43345%7%44%
2386
16th to endDay
15%5%35%5%35%45%7%37%
2619
May1st to 15thDay
17%6%26%5%45%5%5%6%32%
2721
16th to endDay
14%5%26%6%36%6%6%9%32%
2847
June1st to 15thDay
11%5%35%7%5%7%5%7%9%32%
2652
16th to endDay
9%5%26%6%46%6%8%9%34%
2535
July1st to 15thDay
11%6%26%7%5%7%7%7%9%27%
2535
16th to endDay
11%6%47%9%5%7%6%7%8%24%
2673
August1st to 15thDay
13%6%28%9%46%7%6%8%25%
2487
16th to endDay
12%5%35%6%46%7%7%10%29%
2588
September1st to 15thDay
16%6%36%5%345%5%8%34%
2194
16th to endDay
22%7%35%5%34445%33%
2145
October1st to 15thDay
17%5%14424445%44%
1989
16th to endDay
14%424423236%50%
2080
November1st to 15thDay
14%5%24324446%47%
1990
16th to endDay
14%425%424445%46%
1890
December1st to 15thDay
15%8%35%5%2446%6%38%
1890
16th to endDay
20%8%25%5%2335%6%36%
2016
January1st to 15thNight
14%5%245%24346%44%
2717
16th to endNight
13%8%244235%5%6%43%
2912
February1st to 15thNight
14%7%3442445%6%42%
2659
16th to endNight
14%7%35%3345%6%7%38%
2177
March1st to 15thNight
14%6%23325%5%5%7%42%
2298
16th to endNight
14%6%24435%5%5%7%39%
2464
April1st to 15thNight
11%6%25%43446%8%42%
2220
16th to endNight
15%6%24433448%42%
1958
May1st to 15thNight
14%6%344235%5%8%40%
1890
16th to endNight
12%5%25%6%2446%9%39%
1970
June1st to 15thNight
9%5%14425%6%8%10%41%
1836
16th to endNight
7%424425%5%6%10%45%
1755
July1st to 15thNight
10%424436%5%5%10%42%
1755
16th to endNight
44246%26%7%8%12%38%
1847
August1st to 15thNight
13%5%26%5%245%7%8%38%
1726
16th to endNight
9%4246%45%5%7%9%39%
1951
September1st to 15thNight
11%6%26%5%2446%6%43%
2093
16th to endNight
17%6%25%5%3435%6%39%
2145
October1st to 15thNight
14%6%24424446%45%
2301
16th to endNight
12%324423246%53%
2496
November1st to 15thNight
15%5%24323435%48%
2527
16th to endNight
13%42332445%6%49%
2730
December1st to 15thNight
15%7%35%42435%6%40%
2730
16th to endNight
18%9%345%245%5%8%32%
2912

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
14%9%24434446%41%
1881
16th to endDay
14%6%25%424436%43%
2016
February1st to 15thDay
13%9%26%5%3445%6%39%
1858
16th to endDay
16%7%25%5%2435%7%37%
1867
March1st to 15thDay
15%6%2443435%6%42%
2310
16th to endDay
17%7%25%424347%38%
2463
April1st to 15thDay
13%5%3442345%7%44%
2386
16th to endDay
15%6%25%5%35%45%7%37%
2619
May1st to 15thDay
17%6%25%5%45%6%6%6%33%
2721
16th to endDay
15%5%26%5%35%6%6%8%32%
2847
June1st to 15thDay
11%6%25%7%46%6%7%9%32%
2652
16th to endDay
10%5%26%6%36%6%8%9%34%
2535
July1st to 15thDay
12%5%36%7%47%7%7%9%28%
2535
16th to endDay
12%6%37%8%5%7%7%8%8%25%
2673
August1st to 15thDay
14%7%27%8%46%6%7%8%25%
2487
16th to endDay
12%6%36%6%46%7%8%9%30%
2588
September1st to 15thDay
17%5%25%5%345%6%7%35%
2194
16th to endDay
23%7%25%6%33445%32%
2145
October1st to 15thDay
17%41443335%5%44%
1989
16th to endDay
15%424322336%51%
2080
November1st to 15thDay
14%424424446%47%
1990
16th to endDay
14%5%35%424345%47%
1890
December1st to 15thDay
15%8%25%43345%7%39%
1890
16th to endDay
20%8%245%2325%7%36%
2016
January1st to 15thNight
15%6%235%23446%45%
2717
16th to endNight
13%8%24423445%44%
2912
February1st to 15thNight
14%7%2433435%7%43%
2652
16th to endNight
14%7%35%3345%6%7%39%
2177
March1st to 15thNight
15%6%23325%5%5%6%43%
2310
16th to endNight
15%5%24435%45%7%40%
2464
April1st to 15thNight
11%6%25%43446%8%42%
2220
16th to endNight
16%5%24424447%43%
1958
May1st to 15thNight
14%6%3442445%8%40%
1889
16th to endNight
14%5%16%5%2446%10%39%
1970
June1st to 15thNight
10%423325%6%8%10%41%
1836
16th to endNight
7%4244345%6%10%45%
1755
July1st to 15thNight
10%424435%6%6%9%42%
1755
16th to endNight
5%434436%7%9%11%39%
1847
August1st to 15thNight
14%4245%345%6%9%38%
1726
16th to endNight
9%425%5%36%6%6%9%40%
1951
September1st to 15thNight
12%5%26%5%335%5%7%42%
2093
16th to endNight
18%6%25%5%34446%39%
2145
October1st to 15thNight
14%6%2442435%6%45%
2301
16th to endNight
11%414423236%54%
2496
November1st to 15thNight
15%5%24323336%49%
2527
16th to endNight
14%31332445%6%49%
2730
December1st to 15thNight
16%7%35%32435%6%41%
2730
16th to endNight
19%9%2442445%8%33%
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
42%6%8%21%16%4
1882
16th to endDay
40%47%25%16%4
2016
February1st to 15thDay
44%5%8%20%17%3
1860
16th to endDay
45%5%11%19%14%2
1867
March1st to 15thDay
40%5%9%21%17%5%
2310
16th to endDay
45%6%9%22%14%2
2464
April1st to 15thDay
37%6%11%26%13%5%
2386
16th to endDay
44%7%10%19%14%4
2619
May1st to 15thDay
47%8%14%18%9%1
2721
16th to endDay
45%8%15%21%7%1
2851
June1st to 15thDay
44%9%16%19%8%
2652
16th to endDay
40%10%15%18%12%1
2535
July1st to 15thDay
47%11%14%14%9%2
2396
16th to endDay
48%11%15%15%6%
2518
August1st to 15thDay
51%10%13%16%7%
2474
16th to endDay
44%11%14%18%9%1
2588
September1st to 15thDay
43%8%12%17%14%2
2194
16th to endDay
52%5%7%18%15%1
2145
October1st to 15thDay
40%5%8%23%16%5%
1989
16th to endDay
35%36%27%20%6%
2080
November1st to 15thDay
37%5%7%18%24%6%
1990
16th to endDay
37%5%7%21%24%4
1890
December1st to 15thDay
43%6%8%19%17%4
1890
16th to endDay
48%410%18%15%3
2016
January1st to 15thNight
38%6%9%18%19%7%
2717
16th to endNight
39%5%8%23%20%3
2912
February1st to 15thNight
40%5%8%24%17%3
2661
16th to endNight
41%5%12%23%13%3
2177
March1st to 15thNight
39%6%7%24%17%4
2310
16th to endNight
41%7%10%23%14%2
2464
April1st to 15thNight
37%5%13%23%15%4
2220
16th to endNight
39%6%11%20%17%4
1958
May1st to 15thNight
41%6%16%23%12%1
1890
16th to endNight
38%8%19%24%6%1
1972
June1st to 15thNight
33%10%20%24%9%1
1836
16th to endNight
33%9%18%23%14%1
1755
July1st to 15thNight
35%10%16%22%11%3
1665
16th to endNight
32%12%20%23%9%1
1739
August1st to 15thNight
40%9%16%19%13%
1715
16th to endNight
37%8%17%25%9%1
1951
September1st to 15thNight
38%7%15%19%14%3
2093
16th to endNight
46%5%9%19%17%1
2145
October1st to 15thNight
39%5%9%23%18%3
2301
16th to endNight
31%36%27%23%6%
2496
November1st to 15thNight
37%48%18%22%8%
2527
16th to endNight
33%47%23%25%4
2730
December1st to 15thNight
43%6%7%21%16%4
2730
16th to endNight
47%5%9%18%16%2
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
25%35%27%10%11
180
16th to endDay
20%43%26%9%
192
February1st to 15thDay
23%36%30%7%1
180
16th to endDay
28%31%31%6%2
186
March1st to 15thDay
20%40%23%12%3
390
16th to endDay
18%35%25%14%5%1
416
April1st to 15thDay
18%29%23%18%9%
390
16th to endDay
19%21%25%18%10%4
379
May1st to 15thDay
17%25%23%17%10%5%
408
16th to endDay
20%12%19%22%16%8%
459
June1st to 15thDay
12%13%19%26%17%10%
411
16th to endDay
10%14%21%29%16%7%
375
July1st to 15thDay
12%7%18%27%20%12%
365
16th to endDay
10%12%13%26%22%14%
390
August1st to 15thDay
21%7%15%20%19%15%
358
16th to endDay
12%7%9%27%20%23%
396
September1st to 15thDay
17%8%10%18%25%19%
375
16th to endDay
26%9%12%24%16%10%
374
October1st to 15thDay
21%12%17%23%17%7%
375
16th to endDay
16%21%24%20%14%2
400
November1st to 15thDay
24%19%25%17%10%2
318
16th to endDay
13%31%21%26%6%1
180
December1st to 15thDay
28%26%32%9%3
180
16th to endDay
34%23%30%10%
192
January1st to 15thNight
16%39%24%16%3
840
16th to endNight
16%35%27%18%2
896
February1st to 15thNight
18%35%24%18%2
824
16th to endNight
17%35%31%14%1
735
March1st to 15thNight
18%32%26%19%2
840
16th to endNight
16%31%25%19%6%
896
April1st to 15thNight
15%31%24%22%6%
838
16th to endNight
17%25%20%24%10%
712
May1st to 15thNight
16%21%21%23%15%1
630
16th to endNight
16%18%12%25%23%3
659
June1st to 15thNight
10%16%13%26%28%5%
612
16th to endNight
7%15%12%28%31%3
585
July1st to 15thNight
10%12%9%27%34%6%
555
16th to endNight
7%16%8%22%35%9%
612
August1st to 15thNight
17%9%7%29%30%5%
575
16th to endNight
10%8%7%26%36%9%
709
September1st to 15thNight
12%10%11%22%32%9%
780
16th to endNight
22%10%10%25%25%4
777
October1st to 15thNight
17%15%17%23%21%5%
780
16th to endNight
13%20%26%24%14%1
832
November1st to 15thNight
17%24%21%21%13%1
820
16th to endNight
13%31%22%22%10%
840
December1st to 15thNight
18%31%23%20%5%
840
16th to endNight
23%32%24%16%2
896
Page generated at 2019-06-10 19:29:47. Version ac04

Copyright 2019 A. Danko


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