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 2017-09-22.

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%
15767
21%
46951
10%
15729
45%
15729
21%
29980

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
15%
717
23%
2327
6%
716
36%
716
14%
1447
January16th to endNight
15%
768
24%
2496
6%
768
36%
768
15%
1544
February1st to 15thNight
15%
702
23%
2273
7%
701
34%
701
14%
1387
February16th to endNight
12%
631
24%
1869
5%
631
32%
631
17%
1186
March1st to 15thNight
21%
720
25%
1980
9%
720
35%
720
19%
1301
March16th to endNight
21%
768
18%
2112
7%
768
30%
768
18%
1449
April1st to 15thNight
25%
718
20%
1902
5%
718
37%
718
23%
1215
April16th to endNight
31%
618
21%
1698
7%
618
42%
618
22%
1125
May1st to 15thNight
31%
540
16%
1620
6%
540
39%
540
20%
1064
May16th to endNight
40%
561
14%
1684
6%
561
46%
561
19%
1088
June1st to 15thNight
55%
540
14%
1620
11%
540
58%
540
25%
1039
June16th to endNight
55%
540
16%
1620
11%
540
60%
540
27%
1016
July1st to 15thNight
58%
510
11%
1530
8%
510
61%
510
23%
1010
July16th to endNight
60%
564
15%
1595
11%
531
68%
531
29%
992
August1st to 15thNight
55%
539
16%
1609
12%
536
58%
536
24%
1084
August16th to endNight
58%
654
19%
1800
14%
654
61%
654
27%
1206
September1st to 15thNight
55%
720
21%
1932
14%
720
58%
720
29%
1255
September16th to endNight
45%
685
18%
1892
13%
685
51%
685
21%
1307
October1st to 15thNight
42%
660
26%
1947
20%
660
52%
660
25%
1227
October16th to endNight
36%
704
33%
2112
17%
704
55%
704
29%
1198
November1st to 15thNight
33%
700
27%
2157
15%
700
48%
700
25%
1257
November16th to endNight
27%
720
27%
2340
13%
720
45%
720
21%
1370
December1st to 15thNight
20%
720
23%
2340
8%
720
38%
720
14%
1519
December16th to endNight
14%
768
22%
2496
6%
768
33%
768
11%
1694

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%35%5%35%5%5%7%36%
47918
Night
13%5%2442445%7%43%
47144
Cloud CoverDay
14%6%25%5%35%5%5%7%37%
47928
Night
13%5%2442445%7%43%
47148
TransparencyDay
43%7%11%20%14%3
47629
Night
38%6%11%22%16%3
46951
SeeingDay
16%20%19%20%14%8%
5607
Night
14%25%19%21%15%2
15774

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%8%34435%45%6%40%
1611
16th to endDay
14%5%26%5%245%46%42%
1728
February1st to 15thDay
12%8%46%42435%7%40%
1586
16th to endDay
13%6%35%5%3445%7%39%
1603
March1st to 15thDay
13%6%245%2445%6%43%
1969
16th to endDay
18%7%25%5%34446%37%
2112
April1st to 15thDay
11%5%3443345%7%46%
2044
16th to endDay
16%5%35%5%35%45%6%36%
2273
May1st to 15thDay
17%6%35%5%46%5%6%7%31%
2331
16th to endDay
13%5%27%6%46%6%6%8%33%
2431
June1st to 15thDay
10%5%26%7%5%7%6%7%9%32%
2340
16th to endDay
9%5%36%6%46%6%7%9%34%
2340
July1st to 15thDay
12%7%26%7%5%7%7%7%9%26%
2340
16th to endDay
11%6%47%8%5%7%6%8%9%25%
2465
August1st to 15thDay
13%6%28%9%46%7%6%8%25%
2340
16th to endDay
12%5%35%6%46%7%8%10%28%
2388
September1st to 15thDay
16%6%36%5%345%5%8%35%
2025
16th to endDay
22%8%35%5%33445%33%
1881
October1st to 15thDay
16%5%13424345%46%
1683
16th to endDay
15%4245%22236%49%
1760
November1st to 15thDay
10%424424446%51%
1700
16th to endDay
16%5%25%424345%44%
1620
December1st to 15thDay
14%7%25%42446%6%40%
1620
16th to endDay
19%9%25%5%23346%36%
1728
January1st to 15thNight
14%5%245%24347%44%
2327
16th to endNight
13%8%244235%5%5%42%
2496
February1st to 15thNight
13%6%3432435%6%44%
2271
16th to endNight
12%6%25%3345%6%7%40%
1869
March1st to 15thNight
14%6%23325%5%5%7%42%
1968
16th to endNight
14%6%24435%45%7%39%
2112
April1st to 15thNight
10%5%25%43446%8%43%
1902
16th to endNight
15%6%24433448%42%
1698
May1st to 15thNight
15%5%444345%5%8%39%
1620
16th to endNight
11%5%245%25%5%6%10%39%
1682
June1st to 15thNight
8%5%14425%5%8%10%42%
1620
16th to endNight
7%424425%5%6%10%45%
1620
July1st to 15thNight
10%424436%6%6%10%40%
1620
16th to endNight
43245%26%7%8%12%40%
1703
August1st to 15thNight
13%5%26%5%245%7%8%38%
1620
16th to endNight
9%4246%45%5%7%9%38%
1800
September1st to 15thNight
11%5%26%5%245%5%6%45%
1932
16th to endNight
17%5%25%5%3435%6%39%
1892
October1st to 15thNight
14%6%24423446%47%
1947
16th to endNight
11%324413246%53%
2112
November1st to 15thNight
14%413323435%52%
2157
16th to endNight
15%32332445%5%48%
2340
December1st to 15thNight
15%6%35%42435%6%41%
2340
16th to endNight
18%9%35%5%245%47%33%
2496

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%8%2443445%6%40%
1611
16th to endDay
14%5%25%5%24435%43%
1728
February1st to 15thDay
12%8%36%5%2445%6%41%
1586
16th to endDay
13%7%25%5%2445%7%40%
1603
March1st to 15thDay
14%6%25%33435%6%43%
1980
16th to endDay
18%7%26%434346%37%
2111
April1st to 15thDay
12%42442345%7%46%
2044
16th to endDay
16%5%35%5%35%45%7%37%
2273
May1st to 15thDay
18%6%25%5%35%6%6%6%32%
2331
16th to endDay
14%5%26%5%35%6%6%8%33%
2431
June1st to 15thDay
10%5%25%7%46%6%7%9%32%
2340
16th to endDay
10%5%26%6%36%6%8%8%34%
2340
July1st to 15thDay
12%5%36%7%47%7%7%9%26%
2340
16th to endDay
12%6%37%8%5%7%7%8%8%25%
2465
August1st to 15thDay
14%7%27%8%46%6%7%8%25%
2340
16th to endDay
12%5%36%6%46%7%8%10%29%
2388
September1st to 15thDay
17%5%25%4345%5%7%36%
2025
16th to endDay
23%7%25%5%33445%33%
1881
October1st to 15thDay
17%414323345%46%
1683
16th to endDay
16%425%422335%50%
1760
November1st to 15thDay
10%323424446%52%
1700
16th to endDay
15%5%35%5%24345%45%
1620
December1st to 15thDay
15%7%2433445%6%41%
1620
16th to endDay
20%8%24423346%37%
1728
January1st to 15thNight
15%5%23423447%45%
2327
16th to endNight
13%8%244235%5%5%43%
2496
February1st to 15thNight
13%6%2433435%7%45%
2264
16th to endNight
12%6%35%3345%6%7%41%
1869
March1st to 15thNight
15%5%23325%5%5%6%43%
1980
16th to endNight
15%5%24426%45%6%40%
2112
April1st to 15thNight
11%5%2442436%8%44%
1902
16th to endNight
16%5%24424447%42%
1698
May1st to 15thNight
15%6%35%42445%8%39%
1619
16th to endNight
13%415%5%2447%10%39%
1682
June1st to 15thNight
9%424425%6%7%10%42%
1620
16th to endNight
7%4244245%6%10%45%
1620
July1st to 15thNight
11%4245%35%6%6%10%40%
1620
16th to endNight
4334436%7%9%11%40%
1703
August1st to 15thNight
14%425%5%345%7%9%38%
1620
16th to endNight
10%425%6%36%6%6%9%39%
1800
September1st to 15thNight
11%5%26%4235%5%7%43%
1932
16th to endNight
18%6%25%5%34346%39%
1892
October1st to 15thNight
15%5%23423346%47%
1947
16th to endNight
11%413423236%54%
2112
November1st to 15thNight
13%423323336%53%
2157
16th to endNight
16%31332435%6%49%
2340
December1st to 15thNight
16%6%35%42435%5%42%
2340
16th to endNight
19%9%24424447%34%
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
42%6%8%22%16%3
1612
16th to endDay
41%5%7%25%15%4
1728
February1st to 15thDay
42%5%8%21%18%3
1588
16th to endDay
41%5%12%21%15%2
1603
March1st to 15thDay
39%5%9%23%17%5%
1980
16th to endDay
46%6%9%21%12%2
2112
April1st to 15thDay
35%5%11%26%14%6%
2044
16th to endDay
45%6%9%18%15%4
2273
May1st to 15thDay
48%8%14%17%9%1
2331
16th to endDay
44%8%15%21%7%1
2435
June1st to 15thDay
44%9%17%19%8%
2340
16th to endDay
41%10%15%17%12%2
2340
July1st to 15thDay
48%11%14%13%9%2
2201
16th to endDay
47%11%16%16%7%1
2310
August1st to 15thDay
51%10%13%16%7%
2327
16th to endDay
45%10%13%19%8%1
2388
September1st to 15thDay
43%8%11%18%16%2
2025
16th to endDay
51%5%7%18%15%1
1881
October1st to 15thDay
38%5%8%24%17%5%
1683
16th to endDay
37%36%25%19%7%
1760
November1st to 15thDay
32%47%19%27%7%
1700
16th to endDay
39%5%6%22%22%4
1620
December1st to 15thDay
42%6%8%19%18%4
1620
16th to endDay
48%310%17%16%3
1728
January1st to 15thNight
38%6%9%18%20%7%
2327
16th to endNight
39%5%8%23%19%3
2496
February1st to 15thNight
38%5%8%24%19%4
2273
16th to endNight
38%5%12%25%15%2
1869
March1st to 15thNight
39%6%8%26%15%3
1980
16th to endNight
42%7%10%22%14%1
2112
April1st to 15thNight
36%5%12%24%16%5%
1902
16th to endNight
39%6%11%20%15%5%
1698
May1st to 15thNight
43%5%16%21%12%
1620
16th to endNight
37%8%20%23%7%1
1684
June1st to 15thNight
33%11%20%24%9%
1620
16th to endNight
33%9%18%22%15%2
1620
July1st to 15thNight
36%11%16%21%10%3
1530
16th to endNight
30%11%21%24%9%1
1595
August1st to 15thNight
40%9%16%19%13%
1609
16th to endNight
38%8%16%24%9%1
1800
September1st to 15thNight
37%6%15%20%16%3
1932
16th to endNight
45%5%9%18%18%1
1892
October1st to 15thNight
38%5%8%24%19%3
1947
16th to endNight
31%37%28%22%7%
2112
November1st to 15thNight
34%47%18%25%9%
2157
16th to endNight
35%46%24%23%4
2340
December1st to 15thNight
42%6%7%19%18%5%
2340
16th to endNight
48%5%8%17%17%2
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
26%34%24%11%12
90
16th to endDay
17%45%29%7%
96
February1st to 15thDay
23%44%27%31
90
16th to endDay
15%43%29%8%2
104
March1st to 15thDay
14%40%23%16%5%
270
16th to endDay
18%33%26%13%5%1
288
April1st to 15thDay
14%30%21%21%12%
270
16th to endDay
18%21%22%17%13%6%
270
May1st to 15thDay
17%30%23%14%7%5%
288
16th to endDay
19%15%17%20%17%9%
331
June1st to 15thDay
10%16%16%24%20%12%
315
16th to endDay
11%15%21%30%14%6%
315
July1st to 15thDay
13%9%20%26%17%11%
305
16th to endDay
7%13%11%26%24%16%
326
August1st to 15thDay
21%8%15%20%20%14%
313
16th to endDay
10%7%9%27%19%24%
332
September1st to 15thDay
16%8%11%19%25%18%
315
16th to endDay
24%11%12%20%17%12%
278
October1st to 15thDay
21%14%19%22%14%7%
255
16th to endDay
16%20%21%22%15%4
272
November1st to 15thDay
16%22%23%20%13%3
208
16th to endDay
18%30%16%25%8%
90
December1st to 15thDay
21%33%28%11%5%
90
16th to endDay
39%21%26%12%
96
January1st to 15thNight
15%40%25%15%3
720
16th to endNight
15%37%28%17%1
768
February1st to 15thNight
17%38%25%17%1
704
16th to endNight
14%39%31%13%1
631
March1st to 15thNight
17%32%27%19%3
720
16th to endNight
16%31%26%18%6%
768
April1st to 15thNight
14%33%23%21%6%
718
16th to endNight
17%26%19%24%11%
618
May1st to 15thNight
16%24%22%22%12%1
540
16th to endNight
14%21%12%23%23%3
563
June1st to 15thNight
8%18%12%27%28%5%
540
16th to endNight
7%17%12%28%31%3
540
July1st to 15thNight
10%13%9%28%32%5%
510
16th to endNight
5%17%8%21%36%10%
564
August1st to 15thNight
16%10%7%30%29%4
539
16th to endNight
11%9%8%27%36%8%
654
September1st to 15thNight
12%10%11%24%32%7%
720
16th to endNight
21%12%11%25%24%4
685
October1st to 15thNight
16%17%19%23%17%5%
660
16th to endNight
12%21%25%25%13%1
704
November1st to 15thNight
13%27%21%21%13%2
700
16th to endNight
14%32%21%21%9%
720
December1st to 15thNight
17%33%22%20%5%
720
16th to endNight
23%33%25%14%2
768
Page generated at 2017-09-23 06:43:37. Version ac04

Copyright 2017 A. Danko


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