Star Corral Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Star Corral Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
46%
15810
27%
47110
17%
15764
55%
15764
36%
26807

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%
899
29%
2327
12%
895
44%
895
36%
1385
January16th to endNight
35%
960
31%
2496
12%
960
46%
960
39%
1471
February1st to 15thNight
32%
870
23%
2278
8%
866
41%
866
33%
1401
February16th to endNight
29%
602
28%
1864
10%
602
44%
602
30%
1072
March1st to 15thNight
34%
540
23%
1980
14%
540
45%
540
24%
1166
March16th to endNight
32%
576
21%
2112
15%
576
43%
576
26%
1211
April1st to 15thNight
30%
539
23%
1905
13%
539
46%
539
29%
1064
April16th to endNight
33%
540
23%
1711
14%
540
47%
540
30%
1012
May1st to 15thNight
39%
539
22%
1620
16%
539
49%
539
28%
1010
May16th to endNight
48%
563
22%
1684
17%
561
58%
561
32%
1004
June1st to 15thNight
64%
540
22%
1620
18%
540
69%
540
41%
860
June16th to endNight
67%
540
25%
1620
20%
540
73%
540
48%
830
July1st to 15thNight
71%
510
19%
1530
19%
510
73%
510
39%
855
July16th to endNight
83%
564
30%
1594
35%
531
85%
531
50%
795
August1st to 15thNight
82%
539
28%
1610
33%
536
83%
536
47%
838
August16th to endNight
77%
573
27%
1810
32%
573
79%
573
40%
973
September1st to 15thNight
65%
540
26%
1938
29%
540
68%
540
35%
1023
September16th to endNight
65%
537
33%
1980
31%
537
72%
537
36%
993
October1st to 15thNight
49%
636
29%
2004
21%
636
56%
636
36%
1120
October16th to endNight
48%
704
35%
2112
19%
704
59%
704
44%
1082
November1st to 15thNight
44%
739
33%
2139
16%
739
57%
739
42%
1136
November16th to endNight
36%
900
30%
2340
14%
900
45%
900
37%
1413
December1st to 15thNight
34%
900
25%
2340
11%
900
43%
900
32%
1481
December16th to endNight
34%
960
27%
2496
11%
960
44%
960
31%
1612

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
12%5%2442445%7%48%
48081
Night
10%423323346%54%
47306
TransparencyDay
35%5%11%24%18%4
47781
Night
30%410%25%22%6%
47111
SeeingDay
12%5%22%29%24%6%
5825
Night
12%7%29%33%15%1
15812

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
10%7%24422236%53%
1611
16th to endDay
12%425%323245%53%
1728
February1st to 15thDay
12%7%45%5%22335%47%
1593
16th to endDay
14%6%24423345%47%
1610
March1st to 15thDay
16%6%24424345%45%
1980
16th to endDay
19%8%35%323345%40%
2110
April1st to 15thDay
14%5%245%24345%46%
2041
16th to endDay
18%6%25%423345%41%
2246
May1st to 15thDay
18%5%26%5%3444440%
2331
16th to endDay
11%6%26%5%346%6%9%38%
2430
June1st to 15thDay
9%4235%25%46%8%47%
2340
16th to endDay
7%2134245%6%9%50%
2340
July1st to 15thDay
9%3245%36%7%6%9%41%
2340
16th to endDay
5%223425%5%6%10%50%
2466
August1st to 15thDay
5%314425%6%7%10%48%
2340
16th to endDay
5%4144345%5%10%49%
2390
September1st to 15thDay
13%42443445%7%46%
2019
16th to endDay
10%3133235%5%8%52%
1980
October1st to 15thDay
14%5%13312335%54%
1742
16th to endDay
10%322213235%61%
1760
November1st to 15thDay
10%32231325%6%57%
1716
16th to endDay
14%413213236%54%
1620
December1st to 15thDay
17%5%25%423236%47%
1620
16th to endDay
15%7%34423235%46%
1728
January1st to 15thNight
13%42232333456%
2327
16th to endNight
9%423313346%57%
2496
February1st to 15thNight
12%7%23323345%52%
2268
16th to endNight
11%5%24323346%52%
1864
March1st to 15thNight
13%424424435%48%
1980
16th to endNight
16%32432335%6%49%
2112
April1st to 15thNight
13%323413336%53%
1905
16th to endNight
14%5%24423246%49%
1711
May1st to 15thNight
13%424334446%48%
1619
16th to endNight
10%32432446%10%46%
1683
June1st to 15thNight
5%2133245%5%7%58%
1620
16th to endNight
321221346%10%60%
1620
July1st to 15thNight
5%21442447%11%50%
1620
16th to endNight
421231345%10%60%
1702
August1st to 15thNight
312325%5%6%10%56%
1620
16th to endNight
4224425%46%8%55%
1810
September1st to 15thNight
10%414312346%54%
1938
16th to endNight
8%312423436%58%
1980
October1st to 15thNight
11%324323437%53%
2004
16th to endNight
8%312213235%64%
2112
November1st to 15thNight
8%323312335%62%
2139
16th to endNight
12%5%2322333457%
2340
December1st to 15thNight
15%5%24423335%50%
2340
16th to endNight
15%7%24323345%48%
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
34%38%27%23%2
1612
16th to endDay
34%28%29%20%3
1728
February1st to 15thDay
40%313%24%14%4
1594
16th to endDay
38%38%27%16%5%
1610
March1st to 15thDay
40%48%23%17%5%
1980
16th to endDay
46%411%21%14%2
2112
April1st to 15thDay
39%5%12%22%15%4
2041
16th to endDay
44%5%8%20%17%2
2246
May1st to 15thDay
46%48%18%19%2
2331
16th to endDay
39%9%14%22%14%
2434
June1st to 15thDay
34%6%13%25%18%1
2340
16th to endDay
28%7%14%25%19%4
2340
July1st to 15thDay
33%9%13%27%15%
2201
16th to endDay
24%8%16%30%18%1
2311
August1st to 15thDay
27%8%15%23%20%5%
2326
16th to endDay
29%7%15%25%16%5%
2390
September1st to 15thDay
35%7%10%20%17%8%
2019
16th to endDay
28%6%11%25%22%5%
1980
October1st to 15thDay
33%410%23%21%6%
1742
16th to endDay
25%48%28%25%7%
1760
November1st to 15thDay
26%39%28%23%7%
1716
16th to endDay
32%28%23%26%5%
1620
December1st to 15thDay
40%29%27%17%1
1620
16th to endDay
40%39%24%17%5%
1728
January1st to 15thNight
30%38%27%25%4
2327
16th to endNight
29%38%28%23%6%
2496
February1st to 15thNight
35%39%27%19%4
2278
16th to endNight
33%49%26%21%5%
1864
March1st to 15thNight
38%5%10%18%20%7%
1980
16th to endNight
35%412%25%18%2
2112
April1st to 15thNight
33%410%21%22%7%
1905
16th to endNight
36%39%24%20%5%
1711
May1st to 15thNight
37%6%10%18%22%5%
1620
16th to endNight
32%7%15%26%16%1
1685
June1st to 15thNight
23%7%13%33%20%2
1620
16th to endNight
19%6%13%30%23%5%
1620
July1st to 15thNight
26%6%13%30%20%2
1530
16th to endNight
18%5%11%34%24%4
1594
August1st to 15thNight
20%7%14%29%21%6%
1610
16th to endNight
25%6%12%27%20%7%
1810
September1st to 15thNight
30%311%22%20%11%
1938
16th to endNight
26%48%27%26%6%
1980
October1st to 15thNight
31%311%20%23%9%
2004
16th to endNight
23%36%25%30%10%
2112
November1st to 15thNight
25%38%25%27%9%
2139
16th to endNight
31%36%21%28%7%
2340
December1st to 15thNight
36%311%24%20%3
2340
16th to endNight
38%39%21%20%5%
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
20%13%38%21%6%
90
16th to endDay
7%8%46%29%7%1
96
February1st to 15thDay
12%13%46%24%3
90
16th to endDay
13%13%46%23%2
81
March1st to 15thDay
18%22%42%14%2
90
16th to endDay
11%15%35%29%8%
96
April1st to 15thDay
13%11%36%28%8%
160
16th to endDay
24%12%32%19%8%1
356
May1st to 15thDay
17%11%31%27%9%2
468
16th to endDay
17%6%32%26%12%3
517
June1st to 15thDay
9%320%37%24%4
495
16th to endDay
6%117%36%31%5%
495
July1st to 15thDay
10%14%37%29%7%
475
16th to endDay
5%427%45%16%
515
August1st to 15thDay
6%7%32%45%7%
493
16th to endDay
9%19%33%38%8%
430
September1st to 15thDay
6%10%25%41%15%
174
16th to endDay
11%13%32%26%15%
135
October1st to 15thDay
11%328%26%19%10%
107
16th to endDay
9%427%42%11%5%
96
November1st to 15thDay
13%225%25%30%3
90
16th to endDay
30%13%28%22%41
90
December1st to 15thDay
20%6%41%21%7%3
90
16th to endDay
23%9%40%20%5%
96
January1st to 15thNight
14%13%34%31%5%
900
16th to endNight
11%12%38%31%5%
960
February1st to 15thNight
16%12%34%31%4
870
16th to endNight
11%12%42%27%5%
602
March1st to 15thNight
17%8%35%34%3
540
16th to endNight
16%8%38%28%7%
576
April1st to 15thNight
13%10%42%27%5%
539
16th to endNight
16%7%39%27%7%
540
May1st to 15thNight
13%6%36%32%10%
540
16th to endNight
11%330%34%16%1
563
June1st to 15thNight
5%220%45%23%2
540
16th to endNight
3220%46%24%1
540
July1st to 15thNight
6%14%47%29%2
510
16th to endNight
35%37%49%3
564
August1st to 15thNight
218%42%41%3
539
16th to endNight
5%19%39%39%3
573
September1st to 15thNight
13%113%37%32%1
540
16th to endNight
10%117%37%28%4
537
October1st to 15thNight
13%329%30%19%3
636
16th to endNight
9%7%31%34%14%1
704
November1st to 15thNight
9%9%33%32%14%
739
16th to endNight
14%11%35%28%9%
900
December1st to 15thNight
18%11%32%30%6%
900
16th to endNight
19%10%33%30%7%
960
Page generated at 2017-10-07 13:07:54. Version ac04

Copyright 2017 A. Danko


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