Albert L. Ruppel Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Albert L. Ruppel Observatory clear sky chart from 2005-11-05 to 2018-03-11.

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
38%
16612
22%
49112
13%
16565
46%
16565
27%
30837

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
22%
975
19%
2687
7%
970
32%
970
22%
1831
January16th to endNight
21%
1040
21%
2704
6%
1040
31%
1040
24%
1841
February1st to 15thNight
21%
912
15%
2440
4%
909
28%
909
19%
1739
February16th to endNight
19%
683
20%
2049
6%
683
29%
683
21%
1351
March1st to 15thNight
20%
687
17%
2215
7%
687
31%
687
19%
1483
March16th to endNight
25%
576
14%
2040
8%
576
34%
576
16%
1383
April1st to 15thNight
27%
539
21%
1797
11%
539
43%
539
25%
1079
April16th to endNight
34%
540
23%
1800
15%
540
47%
540
27%
1092
May1st to 15thNight
38%
540
18%
1662
11%
539
47%
539
25%
1068
May16th to endNight
46%
563
20%
1497
13%
561
50%
561
30%
965
June1st to 15thNight
60%
540
22%
1440
15%
540
64%
540
41%
837
June16th to endNight
60%
540
23%
1440
15%
540
65%
540
44%
836
July1st to 15thNight
65%
510
19%
1360
15%
510
66%
510
40%
818
July16th to endNight
71%
564
24%
1506
21%
531
75%
531
43%
839
August1st to 15thNight
73%
539
23%
1670
26%
536
75%
536
39%
923
August16th to endNight
71%
573
24%
1910
27%
573
75%
573
37%
1029
September1st to 15thNight
62%
540
27%
1800
27%
540
65%
540
30%
1037
September16th to endNight
60%
656
33%
1928
25%
656
67%
656
36%
1103
October1st to 15thNight
47%
720
28%
2160
19%
720
55%
720
35%
1238
October16th to endNight
31%
768
28%
2307
15%
768
44%
768
32%
1347
November1st to 15thNight
35%
760
27%
2471
16%
760
49%
760
29%
1399
November16th to endNight
28%
832
25%
2587
13%
832
41%
832
26%
1570
December1st to 15thNight
25%
975
17%
2730
6%
975
35%
975
21%
1909
December16th to endNight
20%
1040
17%
2912
5%
1040
30%
1040
17%
2120

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%6%25%43445%7%42%
49519
Night
13%6%25%424346%45%
49296
TransparencyDay
40%5%12%24%15%2
49206
Night
39%410%24%17%3
49114
SeeingDay
14%9%25%26%17%5%
6406
Night
16%10%29%27%13%1
16612

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
12%9%48%6%24445%36%
1581
16th to endDay
11%9%46%43445%6%40%
1872
February1st to 15thDay
15%8%47%5%2445%5%35%
1751
16th to endDay
14%10%37%5%34346%36%
1710
March1st to 15thDay
17%7%45%5%24346%38%
1991
16th to endDay
17%10%47%6%35%445%30%
2182
April1st to 15thDay
13%6%25%5%25%45%5%42%
2151
16th to endDay
17%6%26%5%35%446%36%
2160
May1st to 15thDay
18%5%25%5%2445%7%36%
2283
16th to endDay
12%5%25%5%35%5%6%8%39%
2617
June1st to 15thDay
8%4245%45%5%6%7%46%
2520
16th to endDay
6%323325%5%7%12%46%
2520
July1st to 15thDay
9%324435%5%7%10%44%
2520
16th to endDay
5%315%435%6%7%9%46%
2555
August1st to 15thDay
8%425%5%45%6%7%8%42%
2280
16th to endDay
8%425%435%5%6%8%45%
2292
September1st to 15thDay
14%41432335%8%46%
2160
16th to endDay
9%424424448%50%
2016
October1st to 15thDay
14%5%24423246%48%
1800
16th to endDay
12%414423345%52%
1915
November1st to 15thDay
13%5%23423346%50%
1717
16th to endDay
17%7%25%324335%44%
1702
December1st to 15thDay
15%9%36%424445%39%
1560
16th to endDay
16%12%36%42335%5%35%
1664
January1st to 15thNight
15%6%37%5%34345%40%
2687
16th to endNight
11%10%36%434346%41%
2704
February1st to 15thNight
14%10%46%5%24445%36%
2431
16th to endNight
16%8%37%5%23235%42%
2049
March1st to 15thNight
19%9%35%433335%39%
2215
16th to endNight
18%8%26%425%45%7%34%
2040
April1st to 15thNight
12%5%35%5%24446%46%
1797
16th to endNight
15%6%35%423347%44%
1800
May1st to 15thNight
16%6%2432445%6%43%
1662
16th to endNight
10%5%245%3445%8%45%
1496
June1st to 15thNight
6%31433445%8%52%
1440
16th to endNight
6%312335%35%9%54%
1440
July1st to 15thNight
9%42332446%9%50%
1440
16th to endNight
32145%245%6%11%51%
1610
August1st to 15thNight
5%31442446%8%53%
1680
16th to endNight
5%3244245%49%53%
1910
September1st to 15thNight
12%41442435%6%50%
1800
16th to endNight
8%424333337%54%
1928
October1st to 15thNight
10%5%23323436%53%
2160
16th to endNight
14%6%14213335%53%
2307
November1st to 15thNight
12%5%23323346%52%
2471
16th to endNight
16%6%33313346%47%
2587
December1st to 15thNight
18%9%345%24345%36%
2730
16th to endNight
18%11%37%424345%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
48%49%23%12%1
1582
16th to endDay
43%414%25%10%1
1872
February1st to 15thDay
49%411%23%9%1
1753
16th to endDay
48%410%22%12%1
1710
March1st to 15thDay
48%310%20%14%2
1991
16th to endDay
54%5%13%17%8%
2184
April1st to 15thDay
41%5%9%23%17%2
2151
16th to endDay
48%5%10%22%12%1
2160
May1st to 15thDay
45%6%12%23%10%
2283
16th to endDay
41%7%13%19%14%3
2621
June1st to 15thDay
34%6%14%25%18%1
2520
16th to endDay
28%6%18%25%18%3
2520
July1st to 15thDay
33%6%13%27%13%4
2371
16th to endDay
30%7%15%28%15%1
2396
August1st to 15thDay
35%7%12%25%18%1
2266
16th to endDay
34%7%13%22%18%4
2292
September1st to 15thDay
36%410%24%20%4
2160
16th to endDay
32%48%30%21%2
2016
October1st to 15thDay
37%39%25%19%4
1800
16th to endDay
33%39%30%19%3
1915
November1st to 15thDay
34%311%24%20%5%
1717
16th to endDay
42%29%28%14%1
1702
December1st to 15thDay
47%412%23%12%
1560
16th to endDay
50%312%20%10%1
1664
January1st to 15thNight
46%39%23%15%1
2687
16th to endNight
44%312%24%13%
2704
February1st to 15thNight
49%410%20%13%1
2440
16th to endNight
46%312%21%14%1
2049
March1st to 15thNight
48%39%21%13%3
2215
16th to endNight
49%5%12%22%9%
2040
April1st to 15thNight
37%410%25%18%3
1797
16th to endNight
40%38%29%15%2
1800
May1st to 15thNight
40%6%12%24%15%1
1663
16th to endNight
36%7%14%20%16%3
1498
June1st to 15thNight
29%414%29%20%2
1440
16th to endNight
26%5%14%27%21%5%
1440
July1st to 15thNight
31%412%30%15%5%
1360
16th to endNight
25%6%15%32%18%1
1506
August1st to 15thNight
27%6%13%29%22%2
1670
16th to endNight
27%6%11%24%24%5%
1910
September1st to 15thNight
35%37%23%22%6%
1800
16th to endNight
30%5%7%26%26%3
1928
October1st to 15thNight
32%39%24%23%6%
2160
16th to endNight
35%28%27%21%4
2307
November1st to 15thNight
33%310%23%21%7%
2471
16th to endNight
39%39%27%19%1
2587
December1st to 15thNight
49%410%21%13%
2730
16th to endNight
53%411%19%10%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%19%39%12%2
135
16th to endDay
12%29%38%18%1
144
February1st to 15thDay
20%20%40%15%2
135
16th to endDay
31%25%28%12%2
120
March1st to 15thDay
23%23%39%9%2
121
16th to endDay
23%19%36%16%3
168
April1st to 15thDay
18%14%33%20%12%
270
16th to endDay
25%8%34%21%9%1
270
May1st to 15thDay
17%16%30%22%10%3
336
16th to endDay
16%10%32%27%9%5%
517
June1st to 15thDay
10%425%33%18%6%
495
16th to endDay
7%5%29%35%16%5%
495
July1st to 15thDay
11%419%32%25%6%
475
16th to endDay
5%216%31%37%6%
515
August1st to 15thDay
10%19%33%31%11%
433
16th to endDay
9%215%28%32%12%
332
September1st to 15thDay
15%5%10%27%28%12%
315
16th to endDay
10%414%28%27%13%
302
October1st to 15thDay
15%14%20%36%9%2
135
16th to endDay
11%18%34%23%11%
144
November1st to 15thDay
15%6%29%27%14%6%
135
16th to endDay
28%17%27%18%6%1
135
December1st to 15thDay
9%31%33%17%43
135
16th to endDay
20%24%43%10%
144
January1st to 15thNight
20%18%36%19%4
975
16th to endNight
16%18%38%22%2
1040
February1st to 15thNight
20%18%36%22%2
912
16th to endNight
20%17%38%20%2
683
March1st to 15thNight
24%13%38%19%3
687
16th to endNight
23%11%35%22%7%
576
April1st to 15thNight
15%16%37%22%8%
539
16th to endNight
18%8%35%29%7%
540
May1st to 15thNight
17%433%30%11%1
540
16th to endNight
12%428%34%17%1
563
June1st to 15thNight
8%321%42%22%1
540
16th to endNight
8%122%45%19%2
540
July1st to 15thNight
11%113%42%27%3
510
16th to endNight
4112%40%36%4
564
August1st to 15thNight
6%18%38%39%4
539
16th to endNight
5%113%38%35%4
573
September1st to 15thNight
13%313%30%30%7%
540
16th to endNight
9%5%17%30%29%6%
656
October1st to 15thNight
12%6%27%29%19%3
720
16th to endNight
18%10%37%24%8%
768
November1st to 15thNight
15%13%33%25%12%
760
16th to endNight
20%13%35%22%6%
832
December1st to 15thNight
25%14%32%22%4
975
16th to endNight
24%13%36%22%2
1040
Page generated at 2018-03-12 12:28:01. Version ac04

Copyright 2018 A. Danko


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