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 2017-09-10.

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
38%
15819
22%
46808
13%
15772
46%
15772
27%
29324

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%
900
20%
2479
7%
895
32%
895
22%
1678
January16th to endNight
20%
960
20%
2496
5%
960
30%
960
23%
1713
February1st to 15thNight
21%
841
15%
2249
4%
838
28%
838
19%
1601
February16th to endNight
19%
631
20%
1893
6%
631
30%
631
22%
1226
March1st to 15thNight
21%
645
18%
2085
7%
645
31%
645
19%
1395
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%
525
26%
1750
27%
525
66%
525
30%
1007
September16th to endNight
59%
601
31%
1767
23%
601
66%
601
35%
1022
October1st to 15thNight
48%
660
30%
1980
20%
660
56%
660
36%
1116
October16th to endNight
31%
704
26%
2115
14%
704
43%
704
31%
1243
November1st to 15thNight
36%
700
28%
2276
16%
700
51%
700
31%
1243
November16th to endNight
27%
768
22%
2388
12%
768
39%
768
25%
1467
December1st to 15thNight
23%
900
16%
2520
6%
900
33%
900
20%
1789
December16th to endNight
20%
960
17%
2688
5%
960
30%
960
17%
1955

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%
47823
Night
13%6%25%424346%45%
46992
TransparencyDay
40%5%12%24%15%2
47510
Night
39%411%24%17%3
46810
SeeingDay
14%9%25%26%18%5%
5842
Night
16%10%29%27%13%1
15819

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%24446%37%
1459
16th to endDay
12%9%46%5%34445%39%
1728
February1st to 15thDay
15%7%47%5%2445%5%36%
1612
16th to endDay
12%9%37%5%34346%38%
1580
March1st to 15thDay
17%8%45%5%24346%38%
1884
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%
2097
16th to endDay
9%424424449%48%
1848
October1st to 15thDay
14%5%24423246%50%
1650
16th to endDay
12%413423345%53%
1756
November1st to 15thDay
12%5%13323346%51%
1582
16th to endDay
18%7%25%324335%42%
1571
December1st to 15thDay
17%10%36%424445%37%
1440
16th to endDay
16%12%36%42335%5%35%
1536
January1st to 15thNight
15%6%36%5%34345%41%
2479
16th to endNight
12%10%36%434346%40%
2496
February1st to 15thNight
14%10%46%5%25%445%36%
2240
16th to endNight
13%8%37%5%23335%43%
1893
March1st to 15thNight
19%8%35%423335%39%
2085
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%
1750
16th to endNight
9%424333336%54%
1767
October1st to 15thNight
10%5%13323437%54%
1980
16th to endNight
14%6%2422323453%
2115
November1st to 15thNight
11%423323346%55%
2276
16th to endNight
17%7%33313345%46%
2388
December1st to 15thNight
20%9%345%24345%34%
2520
16th to endNight
19%11%37%424345%33%
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
47%410%23%12%1
1460
16th to endDay
45%414%25%9%1
1728
February1st to 15thDay
48%5%12%23%9%1
1614
16th to endDay
46%411%23%11%1
1580
March1st to 15thDay
48%310%21%13%1
1884
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%19%3
2097
16th to endDay
33%5%8%29%20%2
1848
October1st to 15thDay
35%49%26%20%5%
1650
16th to endDay
33%310%30%19%3
1756
November1st to 15thDay
33%311%24%21%6%
1582
16th to endDay
43%310%27%13%1
1571
December1st to 15thDay
49%412%22%10%
1440
16th to endDay
50%312%21%10%1
1536
January1st to 15thNight
45%39%23%15%1
2479
16th to endNight
45%313%23%13%
2496
February1st to 15thNight
49%49%21%13%1
2249
16th to endNight
44%313%23%14%1
1893
March1st to 15thNight
48%39%22%13%2
2085
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%47%23%22%6%
1750
16th to endNight
31%5%7%25%25%4
1767
October1st to 15thNight
30%39%25%23%6%
1980
16th to endNight
36%28%27%20%4
2115
November1st to 15thNight
31%311%23%22%7%
2276
16th to endNight
40%29%26%18%1
2388
December1st to 15thNight
50%410%21%12%
2520
16th to endNight
53%410%19%10%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
31%21%38%6%11
90
16th to endDay
15%32%39%11%1
96
February1st to 15thDay
17%24%41%13%3
90
16th to endDay
19%27%34%16%2
81
March1st to 15thDay
25%23%38%8%21
90
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%28%28%11%
294
16th to endDay
12%6%16%26%23%14%
243
October1st to 15thDay
10%14%23%35%12%4
90
16th to endDay
14%13%34%27%10%
96
November1st to 15thDay
8%6%26%28%18%10%
90
16th to endDay
36%23%21%10%6%2
90
December1st to 15thDay
13%24%36%17%34
90
16th to endDay
22%26%40%9%1
96
January1st to 15thNight
20%18%36%19%4
900
16th to endNight
17%19%38%21%3
960
February1st to 15thNight
20%19%34%23%2
841
16th to endNight
18%17%40%21%2
631
March1st to 15thNight
24%13%37%19%4
645
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%314%31%30%6%
525
16th to endNight
10%6%17%29%28%7%
601
October1st to 15thNight
12%6%27%28%20%4
660
16th to endNight
19%10%36%25%7%
704
November1st to 15thNight
13%13%33%25%13%
700
16th to endNight
21%13%35%22%6%
768
December1st to 15thNight
26%14%32%21%4
900
16th to endNight
25%14%35%22%2
960
Page generated at 2017-09-11 18:35:26. Version ac04

Copyright 2017 A. Danko


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