BAO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the BAO clear sky chart from 2005-11-05 to 2017-10-31.

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
48%
15917
22%
47418
15%
15876
56%
15876
27%
29857

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
33%
719
24%
2327
13%
716
48%
716
23%
1408
January16th to endNight
29%
768
25%
2496
12%
768
46%
768
25%
1495
February1st to 15thNight
29%
703
23%
2223
10%
701
46%
701
27%
1332
February16th to endNight
23%
631
27%
1879
10%
631
41%
631
26%
1171
March1st to 15thNight
36%
720
26%
1980
14%
720
46%
720
31%
1231
March16th to endNight
37%
768
20%
2112
10%
768
45%
768
26%
1366
April1st to 15thNight
40%
718
23%
1937
11%
718
49%
718
33%
1192
April16th to endNight
47%
612
25%
1692
14%
612
54%
612
32%
1044
May1st to 15thNight
48%
540
16%
1620
8%
540
54%
540
25%
1062
May16th to endNight
61%
561
17%
1684
14%
561
63%
561
27%
1082
June1st to 15thNight
64%
540
14%
1620
11%
540
66%
540
24%
1102
June16th to endNight
67%
540
16%
1620
13%
540
68%
540
26%
1090
July1st to 15thNight
68%
510
10%
1530
9%
510
68%
510
25%
1029
July16th to endNight
69%
564
14%
1595
12%
531
70%
531
25%
1080
August1st to 15thNight
70%
539
13%
1609
12%
536
70%
536
24%
1127
August16th to endNight
66%
651
17%
1809
14%
651
67%
651
26%
1238
September1st to 15thNight
65%
720
18%
1980
15%
720
67%
720
29%
1304
September16th to endNight
52%
717
21%
1980
17%
717
56%
717
27%
1342
October1st to 15thNight
53%
720
29%
2097
25%
720
59%
720
33%
1256
October16th to endNight
51%
768
34%
2303
24%
768
65%
768
38%
1265
November1st to 15thNight
51%
700
29%
2149
23%
700
61%
700
36%
1206
November16th to endNight
45%
720
27%
2340
20%
720
56%
720
28%
1356
December1st to 15thNight
42%
720
23%
2340
16%
720
52%
720
24%
1449
December16th to endNight
36%
768
22%
2496
16%
768
45%
768
20%
1630

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%2442445%7%43%
48329
Night
13%5%2442445%7%44%
47615
TransparencyDay
38%6%12%20%17%4
48030
Night
37%6%11%19%19%5%
47418
SeeingDay
16%418%24%22%13%
5762
Night
16%6%21%30%21%3
15921

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
18%6%2433334444%
1611
16th to endDay
16%5%13324445%47%
1728
February1st to 15thDay
15%4243135%47%46%
1637
16th to endDay
16%5%13423345%47%
1592
March1st to 15thDay
15%424324346%48%
1980
16th to endDay
18%423423447%43%
2111
April1st to 15thDay
11%41332345%8%48%
2011
16th to endDay
15%423424446%46%
2277
May1st to 15thDay
11%5%26%5%25%5%6%7%41%
2331
16th to endDay
10%5%245%2446%8%43%
2431
June1st to 15thDay
8%5%25%5%36%6%7%10%38%
2340
16th to endDay
6%424435%6%8%12%43%
2340
July1st to 15thDay
9%5%35%5%36%7%8%11%33%
2340
16th to endDay
7%4245%48%7%9%11%34%
2465
August1st to 15thDay
12%6%35%6%46%6%7%10%30%
2340
16th to endDay
11%426%8%5%6%6%7%9%32%
2378
September1st to 15thDay
9%5%24435%5%7%8%41%
1980
16th to endDay
14%7%35%5%3445%5%40%
1980
October1st to 15thDay
15%5%1321223456%
1863
16th to endDay
13%31331232360%
1920
November1st to 15thDay
11%423322236%56%
1706
16th to endDay
17%423413345%49%
1620
December1st to 15thDay
15%7%2432445%5%44%
1620
16th to endDay
22%6%24323335%41%
1728
January1st to 15thNight
16%5%2332333449%
2327
16th to endNight
17%424323345%47%
2496
February1st to 15thNight
14%5%1442444449%
2214
16th to endNight
14%5%24434436%46%
1879
March1st to 15thNight
13%424323447%48%
1980
16th to endNight
15%425%434446%43%
2112
April1st to 15thNight
12%5%23413437%50%
1937
16th to endNight
13%41442445%6%48%
1692
May1st to 15thNight
10%6%35%5%35%6%47%41%
1619
16th to endNight
9%425%5%35%47%10%39%
1682
June1st to 15thNight
10%5%25%6%36%6%8%10%33%
1620
16th to endNight
5%425%6%48%6%8%9%38%
1620
July1st to 15thNight
8%4346%37%6%9%11%33%
1620
16th to endNight
5%426%6%48%8%9%11%32%
1703
August1st to 15thNight
9%6%25%6%46%6%7%11%32%
1620
16th to endNight
9%5%35%6%35%6%7%11%34%
1809
September1st to 15thNight
9%5%25%5%25%5%6%10%40%
1980
16th to endNight
15%6%25%5%2445%7%39%
1980
October1st to 15thNight
15%5%24313245%52%
2097
16th to endNight
11%31431224458%
2303
November1st to 15thNight
12%323322336%56%
2149
16th to endNight
14%42342345%6%48%
2340
December1st to 15thNight
15%7%24414345%46%
2340
16th to endNight
22%5%24324445%40%
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
43%46%18%21%4
1612
16th to endDay
38%37%20%21%8%
1728
February1st to 15thDay
36%49%20%23%4
1639
16th to endDay
38%39%22%19%5%
1592
March1st to 15thDay
37%47%22%22%6%
1980
16th to endDay
39%6%11%21%18%3
2112
April1st to 15thDay
32%410%24%21%5%
2011
16th to endDay
38%49%20%19%7%
2277
May1st to 15thDay
39%7%15%20%16%2
2331
16th to endDay
36%7%15%25%13%2
2435
June1st to 15thDay
37%8%16%26%10%
2340
16th to endDay
31%10%19%21%14%2
2340
July1st to 15thDay
38%10%18%19%9%2
2201
16th to endDay
36%12%18%20%10%1
2310
August1st to 15thDay
45%9%16%18%9%1
2327
16th to endDay
44%9%15%18%10%1
2378
September1st to 15thDay
36%9%13%19%17%3
1980
16th to endDay
44%5%10%17%18%4
1980
October1st to 15thDay
33%39%21%26%5%
1863
16th to endDay
29%25%21%29%10%
1920
November1st to 15thDay
31%28%17%30%9%
1706
16th to endDay
37%37%21%23%7%
1620
December1st to 15thDay
40%5%9%20%18%5%
1620
16th to endDay
45%39%17%18%5%
1728
January1st to 15thNight
39%38%17%23%7%
2327
16th to endNight
38%37%19%23%7%
2496
February1st to 15thNight
37%38%20%23%6%
2223
16th to endNight
38%48%21%22%3
1879
March1st to 15thNight
35%410%20%21%8%
1980
16th to endNight
40%411%19%19%5%
2112
April1st to 15thNight
33%5%8%23%23%6%
1937
16th to endNight
35%49%20%21%8%
1692
May1st to 15thNight
40%7%12%19%16%2
1620
16th to endNight
39%7%12%26%13%1
1684
June1st to 15thNight
41%10%15%22%9%1
1620
16th to endNight
37%11%14%20%12%4
1620
July1st to 15thNight
38%11%20%18%8%2
1530
16th to endNight
38%11%19%18%8%2
1595
August1st to 15thNight
41%11%19%15%11%
1609
16th to endNight
39%10%19%19%10%
1809
September1st to 15thNight
36%10%15%18%15%4
1980
16th to endNight
42%6%12%15%19%4
1980
October1st to 15thNight
35%38%21%24%6%
2097
16th to endNight
29%36%19%28%12%
2303
November1st to 15thNight
30%37%16%28%13%
2149
16th to endNight
35%36%19%26%8%
2340
December1st to 15thNight
39%5%9%19%19%7%
2340
16th to endNight
45%39%16%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
23%12%28%31%4
90
16th to endDay
21%16%41%16%3
96
February1st to 15thDay
17%14%54%13%
90
16th to endDay
20%11%38%21%7%
93
March1st to 15thDay
18%10%32%30%7%1
270
16th to endDay
20%9%32%24%11%2
288
April1st to 15thDay
17%9%23%27%19%2
270
16th to endDay
20%422%25%20%8%
270
May1st to 15thDay
13%9%27%22%18%9%
288
16th to endDay
15%212%20%29%19%
331
June1st to 15thDay
12%310%21%27%24%
315
16th to endDay
10%311%25%27%21%
315
July1st to 15thDay
11%16%23%32%24%
305
16th to endDay
9%17%22%31%28%
326
August1st to 15thDay
18%8%18%26%27%
313
16th to endDay
13%9%23%27%25%
332
September1st to 15thDay
15%110%20%30%21%
315
16th to endDay
19%116%22%26%13%
314
October1st to 15thDay
20%315%29%22%7%
315
16th to endDay
14%5%15%33%21%10%
336
November1st to 15thDay
21%419%25%21%7%
214
16th to endDay
12%7%24%30%23%2
90
December1st to 15thDay
22%8%32%24%12%
90
16th to endDay
36%10%30%16%6%
96
January1st to 15thNight
19%13%27%31%7%
720
16th to endNight
19%13%33%30%2
768
February1st to 15thNight
18%11%36%31%2
704
16th to endNight
18%12%39%25%3
631
March1st to 15thNight
16%11%31%32%6%
720
16th to endNight
18%9%29%31%10%
768
April1st to 15thNight
16%9%29%28%14%
718
16th to endNight
15%7%23%32%20%
612
May1st to 15thNight
13%5%24%35%19%1
540
16th to endNight
12%212%32%35%4
563
June1st to 15thNight
12%111%34%33%6%
540
16th to endNight
7%111%28%42%9%
540
July1st to 15thNight
12%7%28%42%8%
510
16th to endNight
8%7%23%48%10%
564
August1st to 15thNight
14%428%44%7%
539
16th to endNight
12%18%24%45%7%
651
September1st to 15thNight
11%110%27%40%8%
720
16th to endNight
20%214%25%31%5%
717
October1st to 15thNight
17%418%26%28%4
720
16th to endNight
14%5%23%29%22%4
768
November1st to 15thNight
13%5%24%34%18%3
700
16th to endNight
16%10%24%32%15%
720
December1st to 15thNight
20%8%22%36%10%1
720
16th to endNight
25%10%22%32%9%
768
Page generated at 2017-11-01 17:23:34. Version ac04

Copyright 2017 A. Danko


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