Elkhorn Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Elkhorn Ranch 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
47%
15886
27%
46948
15%
15839
58%
15839
38%
25224

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
38%
849
28%
2455
14%
844
53%
844
43%
1211
January16th to endNight
41%
768
33%
2496
18%
768
60%
768
42%
1149
February1st to 15thNight
32%
703
24%
2263
11%
699
49%
699
36%
1119
February16th to endNight
28%
632
34%
1894
12%
632
51%
632
39%
959
March1st to 15thNight
37%
720
27%
2058
9%
720
52%
720
40%
1095
March16th to endNight
36%
712
28%
2056
13%
712
50%
712
37%
1104
April1st to 15thNight
33%
539
24%
1798
11%
539
48%
539
30%
936
April16th to endNight
32%
540
25%
1800
12%
540
51%
540
29%
961
May1st to 15thNight
42%
540
21%
1680
13%
540
53%
540
30%
967
May16th to endNight
47%
563
22%
1497
11%
561
57%
561
35%
880
June1st to 15thNight
62%
540
26%
1440
18%
540
67%
540
49%
756
June16th to endNight
71%
540
26%
1440
22%
540
74%
540
49%
774
July1st to 15thNight
67%
510
14%
1360
12%
510
68%
510
25%
931
July16th to endNight
74%
564
13%
1543
13%
531
74%
531
23%
1026
August1st to 15thNight
69%
539
13%
1656
14%
536
70%
536
26%
1040
August16th to endNight
73%
573
21%
1910
21%
573
75%
573
27%
1160
September1st to 15thNight
67%
540
25%
1800
22%
540
74%
540
32%
1031
September16th to endNight
67%
548
34%
1860
28%
548
78%
548
46%
880
October1st to 15thNight
50%
660
31%
1980
18%
660
60%
660
42%
1044
October16th to endNight
52%
704
36%
2112
18%
704
66%
704
50%
1012
November1st to 15thNight
47%
842
33%
2242
16%
842
58%
842
51%
1123
November16th to endNight
44%
900
37%
2400
16%
900
58%
900
49%
1208
December1st to 15thNight
29%
900
24%
2520
7%
900
43%
900
39%
1320
December16th to endNight
33%
960
25%
2688
11%
960
45%
960
34%
1538

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
34245%35%5%6%8%50%
47957
Night
341332445%7%59%
47133
TransparencyDay
26%9%14%24%19%4
47643
Night
22%7%15%27%21%5%
46949
SeeingDay
8%19%28%25%13%3
5768
Night
412%30%31%17%2
15887

By Month

Percentage Cloud Cover SW (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
1413425%45%8%59%
1492
16th to endDay
1424323348%60%
1728
February1st to 15thDay
1335%42445%9%56%
1598
16th to endDay
5%25%42445%8%56%
1580
March1st to 15thDay
15%25%32445%8%56%
1899
16th to endDay
35%34435%45%8%50%
2166
April1st to 15thDay
26%345%3445%9%51%
2150
16th to endDay
47%35%5%35%46%7%45%
2160
May1st to 15thDay
5%7%35%5%45%5%6%8%40%
2267
16th to endDay
5%435%436%5%6%8%46%
2616
June1st to 15thDay
3314435%6%7%8%49%
2520
16th to endDay
2213435%6%7%7%55%
2520
July1st to 15thDay
6%5%25%6%5%7%6%7%9%36%
2520
16th to endDay
6%5%35%8%5%7%8%8%8%33%
2515
August1st to 15thDay
8%5%36%8%47%6%7%7%34%
2292
16th to endDay
6%5%25%5%46%6%8%10%39%
2292
September1st to 15thDay
6%435%5%36%5%7%8%43%
2160
16th to endDay
43234245%46%59%
1934
October1st to 15thDay
5%31442445%6%57%
1650
16th to endDay
1313323345%65%
1760
November1st to 15thDay
12232235%6%69%
1605
16th to endDay
1313212236%70%
1557
December1st to 15thDay
15%2431335%8%60%
1440
16th to endDay
142443446%11%51%
1536
January1st to 15thNight
1312313347%67%
2455
16th to endNight
1312213246%69%
2496
February1st to 15thNight
1414212348%63%
2253
16th to endNight
5%13323348%63%
1894
March1st to 15thNight
1423324437%62%
2058
16th to endNight
142332445%5%62%
2056
April1st to 15thNight
35%1432445%8%56%
1798
16th to endNight
46%24324347%55%
1800
May1st to 15thNight
6%6%345%24447%51%
1679
16th to endNight
6%42442445%7%55%
1497
June1st to 15thNight
221322445%7%62%
1440
16th to endNight
212325%6%5%7%60%
1440
July1st to 15thNight
7%427%7%36%6%7%8%39%
1440
16th to endNight
6%4346%47%7%8%12%36%
1650
August1st to 15thNight
4425%6%36%6%7%9%43%
1665
16th to endNight
4425%5%347%8%10%42%
1910
September1st to 15thNight
7%3144346%7%8%49%
1800
16th to endNight
431321236%6%64%
1860
October1st to 15thNight
5%312323446%61%
1980
16th to endNight
3312113347%66%
2112
November1st to 15thNight
1212213347%68%
2242
16th to endNight
2312212236%70%
2400
December1st to 15thNight
2413323347%65%
2520
16th to endNight
142442345%7%57%
2688

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
22%5%21%30%18%
1493
16th to endDay
21%6%17%33%17%3
1728
February1st to 15thDay
22%9%21%30%12%3
1599
16th to endDay
22%8%14%30%20%2
1580
March1st to 15thDay
22%6%14%28%24%2
1899
16th to endDay
27%8%12%29%18%3
2166
April1st to 15thDay
26%8%12%28%18%4
2150
16th to endDay
29%9%13%24%19%2
2160
May1st to 15thDay
35%11%13%22%16%1
2267
16th to endDay
30%10%13%21%19%5%
2620
June1st to 15thDay
25%10%13%16%22%11%
2520
16th to endDay
22%8%10%19%26%13%
2520
July1st to 15thDay
35%14%14%15%13%6%
2371
16th to endDay
37%15%18%18%7%1
2359
August1st to 15thDay
39%14%13%14%13%4
2277
16th to endDay
31%13%15%22%14%3
2292
September1st to 15thDay
31%11%14%19%16%6%
2160
16th to endDay
20%8%11%23%30%4
1934
October1st to 15thDay
24%6%10%27%25%5%
1650
16th to endDay
17%6%10%32%28%4
1760
November1st to 15thDay
13%6%14%25%33%5%
1605
16th to endDay
15%311%36%24%7%
1557
December1st to 15thDay
21%8%21%31%15%1
1440
16th to endDay
25%12%21%25%11%3
1536
January1st to 15thNight
17%5%22%31%21%2
2455
16th to endNight
16%5%16%34%22%4
2496
February1st to 15thNight
20%6%22%31%15%3
2263
16th to endNight
19%5%14%30%25%3
1894
March1st to 15thNight
20%7%15%28%26%2
2058
16th to endNight
21%7%13%31%24%2
2056
April1st to 15thNight
23%8%13%28%22%4
1798
16th to endNight
27%6%14%27%21%3
1800
May1st to 15thNight
31%6%15%23%19%4
1680
16th to endNight
26%8%15%25%17%6%
1498
June1st to 15thNight
17%7%13%22%21%18%
1440
16th to endNight
19%7%11%21%22%17%
1440
July1st to 15thNight
39%11%14%15%10%8%
1360
16th to endNight
34%16%21%18%7%3
1543
August1st to 15thNight
32%13%18%17%11%7%
1656
16th to endNight
29%13%17%21%12%4
1910
September1st to 15thNight
27%10%17%19%17%7%
1800
16th to endNight
18%6%12%26%30%5%
1860
October1st to 15thNight
21%7%11%27%26%6%
1980
16th to endNight
16%5%9%28%34%5%
2112
November1st to 15thNight
14%6%13%27%31%6%
2242
16th to endNight
15%410%35%27%6%
2400
December1st to 15thNight
19%6%21%29%21%1
2520
16th to endNight
23%9%19%28%16%2
2688

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
12%15%33%30%7%1
90
16th to endDay
5%19%38%29%7%
96
February1st to 15thDay
6%28%44%16%3
90
16th to endDay
7%35%27%19%9%
81
March1st to 15thDay
439%32%21%2
189
16th to endDay
6%47%33%9%2
288
April1st to 15thDay
11%40%29%11%5%1
269
16th to endDay
14%46%25%10%2
270
May1st to 15thDay
8%30%33%19%7%
339
16th to endDay
9%20%29%25%12%3
517
June1st to 15thDay
414%26%30%20%4
495
16th to endDay
48%26%30%24%6%
495
July1st to 15thDay
11%5%19%32%24%7%
475
16th to endDay
12%218%35%23%7%
374
August1st to 15thDay
14%5%30%32%15%2
315
16th to endDay
10%9%30%34%11%3
332
September1st to 15thDay
9%12%34%25%13%3
315
16th to endDay
5%16%32%29%13%2
186
October1st to 15thDay
6%14%27%28%16%5%
90
16th to endDay
8%18%23%29%16%3
96
November1st to 15thDay
317%25%34%17%1
90
16th to endDay
436%32%24%11
90
December1st to 15thDay
5%37%40%15%1
90
16th to endDay
5%23%35%32%3
96
January1st to 15thNight
219%36%28%9%2
849
16th to endNight
217%35%31%10%1
768
February1st to 15thNight
316%44%29%5%
704
16th to endNight
220%44%26%5%
632
March1st to 15thNight
216%38%30%10%1
720
16th to endNight
318%37%31%8%
712
April1st to 15thNight
5%20%38%26%8%
539
16th to endNight
9%20%35%24%8%
540
May1st to 15thNight
8%12%30%34%12%1
540
16th to endNight
8%11%25%35%16%2
563
June1st to 15thNight
28%22%41%21%3
540
16th to endNight
2317%40%32%4
540
July1st to 15thNight
8%27%33%41%5%
510
16th to endNight
7%5%26%50%9%
564
August1st to 15thNight
7%18%33%42%7%
539
16th to endNight
6%28%35%40%6%
573
September1st to 15thNight
8%214%39%27%7%
540
16th to endNight
5%418%40%25%6%
548
October1st to 15thNight
6%9%30%34%15%3
660
16th to endNight
5%7%31%34%17%3
704
November1st to 15thNight
212%33%34%13%2
842
16th to endNight
5%16%32%31%13%1
900
December1st to 15thNight
320%43%24%6%
900
16th to endNight
317%40%27%10%
960
Page generated at 2017-09-24 07:15:55. Version ac04

Copyright 2017 A. Danko


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