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 2017-04-25.

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
37%
15411
21%
45611
13%
15364
46%
15364
27%
28681

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%
525
23%
1750
15%
525
47%
525
28%
1042
May1st to 15thNight
37%
495
19%
1523
11%
494
45%
494
25%
993
May16th to endNight
45%
515
18%
1369
12%
513
49%
513
29%
898
June1st to 15thNight
58%
495
22%
1320
16%
495
63%
495
39%
785
June16th to endNight
62%
495
21%
1320
14%
495
65%
495
43%
773
July1st to 15thNight
64%
465
21%
1240
16%
465
65%
465
39%
754
July16th to endNight
72%
522
22%
1386
20%
489
74%
489
43%
778
August1st to 15thNight
74%
494
25%
1530
28%
491
76%
491
40%
831
August16th to endNight
71%
525
23%
1750
25%
525
74%
525
36%
955
September1st to 15thNight
61%
495
28%
1650
28%
495
65%
495
30%
962
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%41%
46030
Night
13%6%25%424346%45%
45795
TransparencyDay
40%5%12%24%14%2
45717
Night
39%411%24%16%2
45613
SeeingDay
14%9%25%26%18%6%
5210
Night
16%10%29%27%13%1
15411

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
16%6%36%5%35%446%37%
2098
May1st to 15thDay
19%5%35%5%2445%8%35%
2092
16th to endDay
12%5%25%5%35%46%8%38%
2393
June1st to 15thDay
8%425%5%45%5%6%7%44%
2310
16th to endDay
7%323325%5%7%12%45%
2310
July1st to 15thDay
9%3245%35%6%7%10%43%
2310
16th to endDay
5%315%435%6%7%10%45%
2368
August1st to 15thDay
7%325%445%6%8%8%42%
2090
16th to endDay
9%425%435%5%6%8%45%
2100
September1st to 15thDay
15%425%32345%8%44%
1980
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
14%5%35%423347%45%
1750
May1st to 15thNight
17%6%2432445%6%42%
1523
16th to endNight
11%6%25%5%3445%8%43%
1368
June1st to 15thNight
7%4143345%5%9%49%
1320
16th to endNight
7%31233445%9%53%
1320
July1st to 15thNight
9%42432446%8%50%
1320
16th to endNight
43145%245%6%11%50%
1490
August1st to 15thNight
431442446%9%54%
1540
16th to endNight
5%3244245%49%52%
1750
September1st to 15thNight
13%5%14424446%49%
1650
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
47%5%10%23%12%1
2098
May1st to 15thDay
47%6%13%22%10%
2092
16th to endDay
41%7%14%19%13%3
2397
June1st to 15thDay
36%6%14%25%16%1
2310
16th to endDay
29%6%18%25%17%3
2310
July1st to 15thDay
34%7%14%27%12%4
2161
16th to endDay
31%8%16%28%14%1
2209
August1st to 15thDay
34%7%13%25%18%1
2076
16th to endDay
35%7%12%21%17%5%
2100
September1st to 15thDay
38%410%22%19%4
1980
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
38%38%30%15%2
1750
May1st to 15thNight
41%7%13%23%13%1
1524
16th to endNight
38%7%14%19%16%3
1370
June1st to 15thNight
30%415%30%16%2
1320
16th to endNight
27%5%15%26%20%4
1320
July1st to 15thNight
32%412%29%15%5%
1240
16th to endNight
25%5%15%33%17%1
1386
August1st to 15thNight
25%6%13%30%22%2
1530
16th to endNight
28%6%11%25%23%5%
1750
September1st to 15thNight
36%46%23%22%6%
1650
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
23%6%35%23%10%1
250
May1st to 15thDay
17%16%31%21%9%3
272
16th to endDay
17%9%30%26%10%6%
437
June1st to 15thDay
11%428%31%16%6%
420
16th to endDay
8%327%36%18%6%
420
July1st to 15thDay
12%420%32%24%7%
400
16th to endDay
5%216%32%35%7%
445
August1st to 15thDay
9%19%34%32%12%
363
16th to endDay
10%214%25%32%14%
268
September1st to 15thDay
18%39%28%29%10%
255
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
17%8%35%30%7%
525
May1st to 15thNight
17%335%30%10%1
495
16th to endNight
13%427%33%18%2
515
June1st to 15thNight
9%421%42%20%1
495
16th to endNight
8%120%44%21%2
495
July1st to 15thNight
11%113%42%26%4
465
16th to endNight
5%112%40%36%4
522
August1st to 15thNight
5%18%39%40%4
494
16th to endNight
5%112%38%35%5%
525
September1st to 15thNight
14%313%31%29%6%
495
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 2017-04-26 16:21:36. Version ac04

Copyright 2017 A. Danko


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