808.5 Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the 808.5 Observatory clear sky chart from 2005-11-05 to 2017-09-16.

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%
15811
22%
46886
14%
15774
55%
15774
28%
29562

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
32%
717
22%
2327
10%
716
47%
716
23%
1427
January16th to endNight
28%
768
25%
2496
12%
768
45%
768
25%
1520
February1st to 15thNight
28%
701
21%
2256
10%
701
43%
701
26%
1372
February16th to endNight
26%
631
28%
1848
11%
631
43%
631
29%
1132
March1st to 15thNight
33%
720
26%
1980
13%
720
44%
720
32%
1208
March16th to endNight
37%
768
20%
2112
10%
768
44%
768
26%
1386
April1st to 15thNight
41%
718
23%
1910
10%
718
49%
718
34%
1186
April16th to endNight
44%
660
23%
1740
11%
660
50%
660
32%
1099
May1st to 15thNight
47%
540
18%
1620
9%
540
54%
540
28%
1025
May16th to endNight
60%
561
17%
1684
13%
561
62%
561
28%
1066
June1st to 15thNight
60%
540
15%
1620
13%
540
62%
540
25%
1109
June16th to endNight
66%
540
15%
1620
12%
540
67%
540
26%
1073
July1st to 15thNight
69%
510
11%
1530
9%
510
70%
510
24%
1046
July16th to endNight
70%
564
14%
1595
12%
531
71%
531
25%
1073
August1st to 15thNight
67%
539
15%
1609
14%
536
67%
536
24%
1082
August16th to endNight
65%
681
17%
1827
13%
681
66%
681
26%
1280
September1st to 15thNight
68%
720
21%
1942
18%
720
69%
720
33%
1254
September16th to endNight
50%
661
16%
1826
13%
661
54%
661
23%
1297
October1st to 15thNight
52%
660
29%
1947
28%
660
59%
660
32%
1165
October16th to endNight
51%
704
33%
2112
24%
704
64%
704
37%
1181
November1st to 15thNight
49%
700
29%
2109
21%
700
59%
700
37%
1183
November16th to endNight
45%
720
27%
2340
20%
720
56%
720
29%
1362
December1st to 15thNight
41%
720
23%
2340
16%
720
51%
720
25%
1443
December16th to endNight
35%
768
23%
2496
16%
768
45%
768
22%
1593

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%2443445%7%43%
47870
Night
12%5%2442445%7%45%
47085
TransparencyDay
38%7%11%20%18%4
47571
Night
37%6%11%19%18%6%
46888
SeeingDay
15%5%20%24%22%10%
5654
Night
15%6%23%31%20%2
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
16%6%35%323336%43%
1611
16th to endDay
13%6%34323445%48%
1728
February1st to 15thDay
15%5%24413445%47%
1602
16th to endDay
15%5%24424336%47%
1623
March1st to 15thDay
14%414323346%50%
1980
16th to endDay
16%5%243145%47%43%
2111
April1st to 15thDay
11%41332445%8%50%
2038
16th to endDay
14%424424445%47%
2229
May1st to 15thDay
11%5%25%5%25%5%6%7%41%
2331
16th to endDay
10%5%25%5%45%45%7%43%
2431
June1st to 15thDay
9%425%5%35%6%6%10%39%
2340
16th to endDay
6%415%5%46%6%7%10%40%
2340
July1st to 15thDay
9%5%26%6%46%6%7%11%32%
2340
16th to endDay
6%5%247%47%8%8%11%33%
2465
August1st to 15thDay
12%6%25%5%5%7%6%8%10%30%
2340
16th to endDay
11%6%25%5%46%7%6%9%32%
2363
September1st to 15thDay
9%425%44445%9%44%
2015
16th to endDay
21%6%2443445%6%37%
1824
October1st to 15thDay
17%5%1331224354%
1683
16th to endDay
12%223423345%57%
1760
November1st to 15thDay
13%323212245%56%
1748
16th to endDay
13%5%24423445%50%
1620
December1st to 15thDay
15%6%3442335%7%44%
1620
16th to endDay
20%5%2342335%6%41%
1728
January1st to 15thNight
15%5%24324345%47%
2327
16th to endNight
17%6%23323335%47%
2496
February1st to 15thNight
15%5%24432445%47%
2249
16th to endNight
13%5%24323446%48%
1848
March1st to 15thNight
13%42431335%7%49%
1980
16th to endNight
14%5%24434446%43%
2112
April1st to 15thNight
10%5%13424347%50%
1910
16th to endNight
11%42442345%7%48%
1740
May1st to 15thNight
10%5%25%5%25%5%49%43%
1619
16th to endNight
10%3244346%6%8%43%
1682
June1st to 15thNight
10%427%6%46%6%7%9%35%
1620
16th to endNight
5%425%7%36%6%8%12%37%
1620
July1st to 15thNight
7%436%6%46%6%8%13%32%
1620
16th to endNight
5%336%6%46%7%8%11%34%
1703
August1st to 15thNight
9%5%25%6%35%7%8%12%33%
1620
16th to endNight
8%5%27%6%35%5%8%10%35%
1827
September1st to 15thNight
10%3244245%6%8%46%
1942
16th to endNight
19%7%25%43445%5%36%
1826
October1st to 15thNight
17%413212335%52%
1947
16th to endNight
10%42242234457%
2112
November1st to 15thNight
12%413312237%55%
2109
16th to endNight
13%423424346%50%
2340
December1st to 15thNight
14%7%24433345%45%
2340
16th to endNight
19%6%24423336%42%
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
42%5%7%16%21%5%
1612
16th to endDay
37%47%20%22%8%
1728
February1st to 15thDay
37%49%20%22%5%
1604
16th to endDay
38%38%24%20%4
1623
March1st to 15thDay
35%48%22%22%5%
1980
16th to endDay
39%6%11%20%18%3
2112
April1st to 15thDay
31%411%23%23%5%
2038
16th to endDay
37%6%9%17%21%7%
2229
May1st to 15thDay
38%8%13%20%16%2
2331
16th to endDay
38%9%13%22%14%1
2435
June1st to 15thDay
37%9%15%23%11%
2340
16th to endDay
34%10%15%21%14%2
2340
July1st to 15thDay
41%12%16%18%8%2
2201
16th to endDay
38%13%17%19%9%1
2310
August1st to 15thDay
44%11%16%16%10%1
2327
16th to endDay
43%11%15%17%10%1
2363
September1st to 15thDay
36%8%13%20%17%3
2015
16th to endDay
46%6%9%16%16%5%
1824
October1st to 15thDay
34%47%23%25%4
1683
16th to endDay
30%36%20%29%9%
1760
November1st to 15thDay
29%38%18%30%9%
1748
16th to endDay
35%49%19%23%7%
1620
December1st to 15thDay
39%5%9%21%18%4
1620
16th to endDay
43%5%9%18%17%6%
1728
January1st to 15thNight
39%5%8%15%24%7%
2327
16th to endNight
39%36%20%22%7%
2496
February1st to 15thNight
38%48%18%23%6%
2258
16th to endNight
35%49%22%22%5%
1848
March1st to 15thNight
34%410%20%22%7%
1980
16th to endNight
40%5%11%18%18%5%
2112
April1st to 15thNight
33%5%9%21%23%6%
1910
16th to endNight
34%7%10%19%20%8%
1740
May1st to 15thNight
37%7%14%21%16%3
1620
16th to endNight
34%10%14%25%13%1
1684
June1st to 15thNight
42%9%15%21%9%1
1620
16th to endNight
36%12%16%19%11%3
1620
July1st to 15thNight
39%11%18%18%8%3
1530
16th to endNight
36%13%18%18%10%2
1595
August1st to 15thNight
39%11%19%18%9%1
1609
16th to endNight
40%11%17%21%8%
1827
September1st to 15thNight
33%9%15%19%15%5%
1942
16th to endNight
46%7%11%13%17%4
1826
October1st to 15thNight
35%310%19%24%6%
1947
16th to endNight
30%37%19%26%12%
2112
November1st to 15thNight
31%27%15%28%14%
2109
16th to endNight
34%5%6%19%25%9%
2340
December1st to 15thNight
40%49%19%19%7%
2340
16th to endNight
43%310%17%18%6%
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
27%14%30%23%4
90
16th to endDay
15%26%42%13%11
96
February1st to 15thDay
14%21%54%7%2
90
16th to endDay
12%14%47%20%4
124
March1st to 15thDay
13%11%37%28%9%
270
16th to endDay
18%11%28%29%11%
288
April1st to 15thDay
16%11%25%24%17%3
270
16th to endDay
17%425%27%18%7%
270
May1st to 15thDay
13%6%29%25%17%6%
288
16th to endDay
16%314%22%28%15%
331
June1st to 15thDay
13%214%26%29%13%
315
16th to endDay
11%14%25%32%15%
315
July1st to 15thDay
8%11%25%35%17%
305
16th to endDay
8%5%25%38%20%
326
August1st to 15thDay
18%19%20%28%20%
313
16th to endDay
13%17%26%28%22%
332
September1st to 15thDay
12%112%26%27%19%
315
16th to endDay
27%317%21%20%9%
257
October1st to 15thDay
22%319%26%22%5%
255
16th to endDay
12%423%27%23%9%
272
November1st to 15thDay
19%5%21%26%20%5%
256
16th to endDay
7%13%21%34%22%1
90
December1st to 15thDay
22%8%41%18%8%
90
16th to endDay
27%14%34%14%9%
96
January1st to 15thNight
18%13%30%30%7%
720
16th to endNight
19%10%37%27%3
768
February1st to 15thNight
18%10%38%29%2
704
16th to endNight
15%13%39%26%3
631
March1st to 15thNight
15%9%38%29%6%
720
16th to endNight
17%9%31%31%10%
768
April1st to 15thNight
13%12%30%31%12%
718
16th to endNight
15%7%27%33%16%
660
May1st to 15thNight
13%6%26%35%17%
540
16th to endNight
12%215%36%30%2
563
June1st to 15thNight
10%213%40%28%5%
540
16th to endNight
7%113%34%36%7%
540
July1st to 15thNight
7%8%40%36%5%
510
16th to endNight
7%18%28%45%8%
564
August1st to 15thNight
11%8%28%45%5%
539
16th to endNight
11%17%28%42%8%
681
September1st to 15thNight
11%18%32%40%6%
720
16th to endNight
23%216%27%27%3
661
October1st to 15thNight
19%320%26%25%4
660
16th to endNight
13%6%25%28%22%3
704
November1st to 15thNight
14%5%26%32%17%3
700
16th to endNight
15%10%26%31%15%1
720
December1st to 15thNight
17%9%25%35%10%
720
16th to endNight
22%10%26%31%8%
768
Page generated at 2017-09-17 12:05:46. Version ac04

Copyright 2017 A. Danko


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