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 2005-11-06 to 2024-01-11.

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
45%
24316
21%
74354
14%
24266
54%
24266
26%
46850

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 10thNight
28%
758
22%
2459
8%
757
44%
757
22%
1515
January11th to 20thNight
30%
724
24%
2352
11%
724
46%
724
22%
1466
January21st to endNight
28%
792
28%
2574
14%
792
47%
792
26%
1541
February1st to 10thNight
30%
720
20%
2340
11%
720
42%
720
25%
1462
February11th to 20thNight
20%
700
22%
2138
8%
699
36%
699
23%
1393
February21st to endNight
25%
592
26%
1709
10%
592
40%
592
25%
1093
March1st to 10thNight
31%
720
26%
1980
14%
720
42%
720
31%
1220
March11th to 20thNight
29%
720
21%
1980
10%
720
39%
720
26%
1287
March21st to endNight
32%
792
19%
2178
8%
792
40%
792
23%
1466
April1st to 10thNight
35%
720
24%
1971
10%
720
46%
720
31%
1208
April11th to 20thNight
40%
711
24%
1775
9%
711
48%
711
36%
1120
April21st to endNight
45%
630
25%
1710
13%
630
51%
630
33%
1057
May1st to 10thNight
45%
540
19%
1620
9%
540
50%
540
30%
974
May11th to 20thNight
46%
531
15%
1593
8%
531
50%
531
23%
1086
May21st to endNight
63%
582
17%
1745
13%
582
64%
582
26%
1125
June1st to 10thNight
56%
540
15%
1620
12%
540
58%
540
24%
1110
June11th to 20thNight
60%
540
13%
1620
11%
540
62%
540
24%
1094
June21st to endNight
64%
540
13%
1620
10%
540
65%
540
24%
1081
July1st to 10thNight
67%
525
11%
1575
10%
525
67%
525
23%
1091
July11th to 20thNight
74%
522
12%
1566
10%
522
75%
522
26%
1046
July21st to endNight
66%
591
13%
1672
11%
558
68%
558
24%
1147
August1st to 10thNight
64%
537
12%
1600
12%
534
65%
534
23%
1103
August11th to 20thNight
61%
534
15%
1598
13%
534
62%
534
21%
1125
August21st to endNight
64%
756
15%
1944
11%
756
65%
756
25%
1389
September1st to 10thNight
68%
720
21%
1923
17%
720
69%
720
32%
1261
September11th to 20thNight
62%
720
21%
1980
18%
720
63%
720
29%
1319
September21st to endNight
53%
720
18%
1980
14%
720
58%
720
25%
1367
October1st to 10thNight
56%
720
25%
2106
23%
720
62%
720
33%
1274
October11th to 20thNight
50%
720
30%
2160
25%
720
60%
720
33%
1249
October21st to endNight
50%
792
31%
2376
23%
792
62%
792
36%
1338
November1st to 10thNight
49%
740
28%
2221
21%
740
58%
740
34%
1298
November11th to 20thNight
41%
760
27%
2388
19%
760
52%
760
30%
1373
November21st to endNight
44%
760
27%
2470
20%
760
56%
760
29%
1452
December1st to 10thNight
34%
760
23%
2470
12%
760
47%
760
21%
1597
December11th to 20thNight
39%
759
27%
2933
19%
758
50%
758
24%
1684
December21st to endNight
33%
828
16%
4408
14%
817
45%
817
14%
2439

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
13%5%25%5%35%5%6%8%43%
74916
Night
14%6%25%5%345%5%7%44%
74794
TransparencyDay
38%8%12%20%18%4
74639
Night
38%7%11%19%19%6%
74590
SeeingDay
16%9%24%24%19%8%
14190
Night
16%8%24%31%19%2
24332

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 10thDay
17%5%35%434336%46%
1706
11th to 20thDay
16%7%45%43445%6%44%
1620
21st to endDay
15%7%25%324445%49%
1782
February1st to 10thDay
16%6%36%4245%5%6%42%
1620
11th to 20thDay
20%5%24424445%46%
1706
21st to endDay
19%7%35%5%35%445%40%
1545
March1st to 10thDay
15%5%2432335%6%52%
1980
11th to 20thDay
16%6%25%435%45%8%41%
1980
21st to endDay
16%7%26%425%6%5%7%41%
2178
April1st to 10thDay
11%5%244345%6%8%51%
1988
11th to 20thDay
13%5%25%43445%7%47%
2134
21st to endDay
13%4245%25%5%5%6%50%
2263
May1st to 10thDay
9%5%25%5%46%5%7%7%46%
2340
11th to 20thDay
13%5%25%5%35%7%6%8%41%
2301
21st to endDay
10%6%36%6%46%5%6%9%40%
2531
June1st to 10thDay
10%426%6%36%7%7%12%38%
2340
11th to 20thDay
9%425%6%45%6%7%10%41%
2340
21st to endDay
6%425%7%47%7%8%10%39%
2340
July1st to 10thDay
8%5%36%7%46%7%8%12%34%
2340
11th to 20thDay
9%5%27%6%47%8%8%12%33%
2340
21st to endDay
6%5%36%8%5%6%8%8%10%35%
2547
August1st to 10thDay
11%6%26%6%5%7%7%8%11%31%
2327
11th to 20thDay
12%6%26%8%5%7%6%8%10%29%
2303
21st to endDay
10%7%35%5%5%7%6%6%10%36%
2394
September1st to 10thDay
8%426%5%46%6%6%9%43%
2033
11th to 20thDay
12%6%25%5%445%6%8%43%
1980
21st to endDay
19%6%245%345%5%6%41%
1980
October1st to 10thDay
14%6%25%422346%52%
1854
11th to 20thDay
13%424323445%56%
1800
21st to endDay
13%424423345%56%
1980
November1st to 10thDay
14%424323346%57%
1857
11th to 20thDay
13%5%2432335%6%53%
1790
21st to endDay
15%5%2442445%6%50%
1710
December1st to 10thDay
18%7%35%43446%7%39%
1710
11th to 20thDay
16%424313347%52%
2153
21st to endDay
18%6%35%434446%44%
3124
January1st to 10thNight
18%6%245%34345%47%
2459
11th to 20thNight
15%6%35%4345%5%6%45%
2352
21st to endNight
17%6%34433345%49%
2574
February1st to 10thNight
16%6%36%43345%5%45%
2340
11th to 20thNight
21%6%34423446%43%
2138
21st to endNight
16%7%2443345%6%45%
1709
March1st to 10thNight
14%6%3442335%6%50%
1980
11th to 20thNight
16%6%35%43446%8%42%
1980
21st to endNight
15%6%25%5%45%5%5%6%42%
2178
April1st to 10thNight
11%6%2443445%7%50%
1971
11th to 20thNight
11%5%245%34447%52%
1775
21st to endNight
12%425%5%2446%7%50%
1710
May1st to 10thNight
10%6%25%4245%5%8%48%
1620
11th to 20thNight
13%6%37%6%45%6%6%8%36%
1592
21st to endNight
11%5%25%5%446%7%9%41%
1744
June1st to 10thNight
10%6%28%6%46%6%7%9%36%
1620
11th to 20thNight
11%5%26%7%36%7%8%11%35%
1620
21st to endNight
7%5%26%6%47%6%9%13%35%
1620
July1st to 10thNight
7%6%47%7%5%6%7%8%13%32%
1620
11th to 20thNight
7%5%35%6%46%7%9%12%36%
1620
21st to endNight
5%5%38%7%5%6%8%8%12%33%
1771
August1st to 10thNight
11%5%35%6%36%7%9%12%31%
1611
11th to 20thNight
10%7%37%7%46%6%7%9%33%
1598
21st to endNight
9%6%27%7%5%6%7%8%10%33%
1944
September1st to 10thNight
9%425%6%35%5%7%9%45%
1923
11th to 20thNight
13%6%35%5%345%6%7%43%
1980
21st to endNight
18%5%25%445%5%6%5%39%
1980
October1st to 10thNight
14%5%24424446%52%
2106
11th to 20thNight
14%5%2432235%5%54%
2160
21st to endNight
12%6%23423445%57%
2376
November1st to 10thNight
13%6%24423236%54%
2221
11th to 20thNight
13%6%24423447%51%
2388
21st to endNight
14%42443445%7%49%
2470
December1st to 10thNight
17%8%35%5%34446%42%
2470
11th to 20thNight
17%6%24422235%51%
3042
21st to endNight
19%5%25%5%2445%6%44%
4532

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 10thDay
41%48%19%22%5%
1707
11th to 20thDay
42%5%7%17%22%5%
1620
21st to endDay
38%46%21%24%7%
1782
February1st to 10thDay
41%6%10%21%18%5%
1620
11th to 20thDay
41%48%19%23%6%
1716
21st to endDay
47%5%7%17%18%7%
1545
March1st to 10thDay
35%39%21%25%8%
1980
11th to 20thDay
42%6%11%19%16%6%
1980
21st to endDay
42%7%11%19%19%3
2178
April1st to 10thDay
31%6%10%21%27%6%
1988
11th to 20thDay
36%5%9%19%21%9%
2134
21st to endDay
34%6%11%23%22%5%
2263
May1st to 10thDay
35%8%13%22%19%3
2340
11th to 20thDay
39%11%14%18%15%2
2305
21st to endDay
38%11%13%22%15%1
2531
June1st to 10thDay
38%11%13%25%12%1
2340
11th to 20thDay
36%10%18%21%14%1
2340
21st to endDay
35%12%15%21%14%2
2340
July1st to 10thDay
39%13%18%17%10%3
2275
11th to 20thDay
40%13%22%17%7%1
2271
21st to endDay
38%13%18%21%8%1
2405
August1st to 10thDay
43%12%18%19%8%1
2314
11th to 20thDay
45%13%16%16%9%1
2303
21st to endDay
41%12%16%18%9%3
2394
September1st to 10thDay
35%10%15%19%18%3
2033
11th to 20thDay
38%8%12%18%20%4
1980
21st to endDay
44%6%9%19%17%5%
1980
October1st to 10thDay
34%5%8%21%26%5%
1854
11th to 20thDay
31%5%8%25%23%8%
1800
21st to endDay
32%47%21%27%10%
1980
November1st to 10thDay
31%47%20%29%10%
1857
11th to 20thDay
31%410%20%27%8%
1790
21st to endDay
36%49%21%22%8%
1710
December1st to 10thDay
44%6%9%19%18%4
1710
11th to 20thDay
33%46%21%28%8%
2150
21st to endDay
40%6%9%22%20%3
3124
January1st to 10thNight
40%5%9%16%24%7%
2459
11th to 20thNight
40%6%8%17%22%6%
2352
21st to endNight
39%35%20%26%7%
2574
February1st to 10thNight
41%5%9%19%20%7%
2340
11th to 20thNight
43%47%16%22%7%
2139
21st to endNight
40%5%10%19%19%7%
1709
March1st to 10thNight
36%48%18%23%11%
1980
11th to 20thNight
40%5%12%16%20%7%
1980
21st to endNight
43%7%10%18%18%4
2178
April1st to 10thNight
34%5%10%20%25%7%
1971
11th to 20thNight
32%6%11%20%22%9%
1775
21st to endNight
32%8%10%24%22%5%
1710
May1st to 10thNight
33%8%15%23%18%4
1620
11th to 20thNight
43%9%13%19%15%1
1593
21st to endNight
35%12%15%24%12%2
1745
June1st to 10thNight
41%10%14%21%11%2
1620
11th to 20thNight
40%11%17%20%11%1
1620
21st to endNight
36%14%18%18%11%3
1620
July1st to 10thNight
41%13%20%16%8%3
1575
11th to 20thNight
36%13%23%19%7%2
1566
21st to endNight
38%14%21%18%9%1
1672
August1st to 10thNight
40%13%22%18%6%1
1600
11th to 20thNight
45%10%19%15%9%2
1598
21st to endNight
40%13%16%22%7%2
1944
September1st to 10thNight
34%10%14%20%15%6%
1923
11th to 20thNight
38%9%14%17%19%3
1980
21st to endNight
43%8%10%16%17%5%
1980
October1st to 10thNight
34%6%10%19%25%6%
2106
11th to 20thNight
33%5%8%23%23%9%
2160
21st to endNight
30%48%20%27%11%
2376
November1st to 10thNight
33%47%17%26%13%
2221
11th to 20thNight
34%47%17%25%13%
2388
21st to endNight
35%5%6%20%27%8%
2470
December1st to 10thNight
45%5%9%17%19%6%
2470
11th to 20thNight
37%48%17%24%9%
3044
21st to endNight
40%5%9%20%23%3
4532

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 10thDay
22%20%38%17%3
270
11th to 20thDay
24%20%32%18%6%
240
21st to endDay
20%24%36%16%3
264
February1st to 10thDay
22%20%40%12%6%
240
11th to 20thDay
34%15%40%9%2
240
21st to endDay
22%26%30%17%4
263
March1st to 10thDay
20%16%35%21%8%
420
11th to 20thDay
21%17%38%18%5%
420
21st to endDay
21%15%34%21%7%1
462
April1st to 10thDay
18%17%31%22%10%2
420
11th to 20thDay
14%17%30%21%15%3
412
21st to endDay
16%10%30%25%15%4
420
May1st to 10thDay
11%12%35%22%16%4
423
11th to 20thDay
14%5%21%28%23%8%
447
21st to endDay
14%418%26%27%12%
485
June1st to 10thDay
11%418%31%28%9%
450
11th to 20thDay
12%5%18%23%30%12%
450
21st to endDay
8%215%33%30%11%
450
July1st to 10thDay
8%211%22%38%19%
445
11th to 20thDay
10%19%27%34%19%
444
21st to endDay
7%110%29%38%15%
488
August1st to 10thDay
15%313%23%26%18%
446
11th to 20thDay
13%38%28%30%19%
439
21st to endDay
13%211%27%29%20%
495
September1st to 10thDay
10%210%34%27%18%
450
11th to 20thDay
14%413%26%29%13%
450
21st to endDay
21%419%26%24%6%
450
October1st to 10thDay
17%5%20%25%24%8%
450
11th to 20thDay
14%8%24%26%22%7%
450
21st to endDay
16%6%28%27%18%5%
495
November1st to 10thDay
19%6%26%30%16%4
455
11th to 20thDay
17%14%32%25%11%1
350
21st to endDay
13%12%37%24%13%2
270
December1st to 10thDay
23%14%37%19%7%
270
11th to 20thDay
21%11%34%24%9%1
270
21st to endDay
24%17%35%16%6%3
297
January1st to 10thNight
21%14%33%27%6%
760
11th to 20thNight
19%13%33%28%6%
724
21st to endNight
20%10%38%28%4
792
February1st to 10thNight
18%11%37%29%5%
720
11th to 20thNight
25%11%39%22%2
703
21st to endNight
20%17%34%24%4
592
March1st to 10thNight
17%10%37%31%5%
720
11th to 20thNight
18%13%36%24%8%1
720
21st to endNight
18%12%33%29%7%
792
April1st to 10thNight
15%13%33%29%9%1
720
11th to 20thNight
14%13%29%29%14%
711
21st to endNight
14%7%28%38%13%
630
May1st to 10thNight
11%10%29%36%13%
540
11th to 20thNight
15%5%22%36%21%1
531
21st to endNight
13%312%39%31%2
584
June1st to 10thNight
11%217%40%25%4
540
11th to 20thNight
13%314%34%29%6%
540
21st to endNight
9%115%37%33%5%
540
July1st to 10thNight
8%28%35%38%8%
525
11th to 20thNight
8%27%34%40%8%
522
21st to endNight
7%210%33%42%5%
591
August1st to 10thNight
11%29%29%42%6%
537
11th to 20thNight
13%310%30%38%7%
534
21st to endNight
11%210%28%41%8%
756
September1st to 10thNight
11%110%31%41%6%
720
11th to 20thNight
15%213%28%36%5%
720
21st to endNight
20%415%33%25%3
720
October1st to 10thNight
16%419%27%28%6%
720
11th to 20thNight
16%6%23%30%22%2
720
21st to endNight
14%7%24%31%21%2
792
November1st to 10thNight
16%6%25%32%18%3
740
11th to 20thNight
15%11%30%32%11%1
760
21st to endNight
16%9%27%34%14%1
760
December1st to 10thNight
19%12%29%33%7%
760
11th to 20thNight
20%8%27%35%10%
760
21st to endNight
24%13%24%30%9%
836
Page generated at 2024-01-08 11:14:18. Version ac07

Copyright 2024 Attilla Danko


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