O'Brien
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the O'Brien clear sky chart from 2005-11-05 to 2017-12-04.

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
58%
16039
22%
47874
18%
16000
64%
16000
31%
29105

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
41%
717
21%
2327
12%
716
52%
716
26%
1407
January16th to endNight
40%
768
24%
2418
16%
768
50%
768
26%
1513
February1st to 15thNight
41%
701
26%
2106
14%
699
52%
699
32%
1257
February16th to endNight
43%
631
25%
1893
16%
631
53%
631
30%
1147
March1st to 15thNight
48%
720
28%
1990
16%
720
58%
720
38%
1169
March16th to endNight
51%
768
26%
2112
17%
768
58%
768
38%
1233
April1st to 15thNight
54%
718
24%
1976
17%
718
59%
718
37%
1182
April16th to endNight
60%
612
30%
1773
20%
612
68%
612
44%
951
May1st to 15thNight
69%
539
26%
1619
21%
539
73%
539
43%
878
May16th to endNight
75%
561
23%
1682
19%
561
76%
561
40%
948
June1st to 15thNight
69%
540
17%
1620
15%
540
70%
540
29%
1020
June16th to endNight
75%
540
13%
1620
12%
540
76%
540
29%
1029
July1st to 15thNight
77%
510
11%
1530
11%
510
77%
510
29%
985
July16th to endNight
75%
564
8%
1595
9%
531
76%
531
25%
1084
August1st to 15thNight
75%
539
8%
1656
9%
536
76%
536
26%
1091
August16th to endNight
69%
642
12%
1979
13%
642
69%
642
21%
1378
September1st to 15thNight
65%
720
12%
1980
12%
720
65%
720
22%
1397
September16th to endNight
62%
717
19%
1980
17%
717
64%
717
25%
1351
October1st to 15thNight
65%
720
28%
2004
26%
720
67%
720
36%
1202
October16th to endNight
60%
768
32%
2304
28%
768
68%
768
37%
1301
November1st to 15thNight
58%
760
31%
2288
27%
760
65%
760
39%
1244
November16th to endNight
52%
780
30%
2535
23%
780
63%
780
34%
1406
December1st to 15thNight
49%
736
26%
2391
22%
736
56%
736
30%
1406
December16th to endNight
48%
768
23%
2496
19%
768
56%
768
27%
1526

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
9%5%25%6%36%5%6%8%39%
48601
Night
8%5%25%5%245%6%8%45%
48080
TransparencyDay
39%7%13%17%14%7%
48302
Night
34%6%14%19%16%8%
47883
SeeingDay
10%314%21%25%23%
5895
Night
10%318%32%28%6%
16048

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%7%25%42445%7%41%
1611
16th to endDay
13%5%35%425%346%44%
1804
February1st to 15thDay
15%6%245%23335%47%
1750
16th to endDay
13%6%2443343449%
1580
March1st to 15thDay
8%32431446%8%51%
1968
16th to endDay
7%4245%3445%7%50%
2111
April1st to 15thDay
8%5%345%3446%7%47%
1972
16th to endDay
6%3245%245%6%7%51%
2196
May1st to 15thDay
4313425%6%6%9%51%
2331
16th to endDay
5%5%246%47%6%6%8%41%
2431
June1st to 15thDay
8%5%37%8%6%7%6%7%9%29%
2340
16th to endDay
7%5%35%7%47%8%9%11%28%
2340
July1st to 15thDay
6%6%35%8%5%9%8%9%12%23%
2340
16th to endDay
7%447%9%6%10%8%8%11%21%
2465
August1st to 15thDay
9%5%27%9%6%9%8%8%11%20%
2289
16th to endDay
11%8%37%8%5%8%8%7%8%22%
2208
September1st to 15thDay
10%6%48%9%5%6%7%8%8%25%
1980
16th to endDay
11%7%38%9%46%6%6%6%30%
1980
October1st to 15thDay
9%5%35%6%335%6%6%44%
1953
16th to endDay
8%323434445%54%
1920
November1st to 15thDay
6%42442345%8%54%
1898
16th to endDay
8%425%32435%5%53%
1755
December1st to 15thDay
11%6%3442446%7%43%
1651
16th to endDay
11%7%35%5%35%5%5%8%40%
1728
January1st to 15thNight
12%6%25%4245%46%45%
2327
16th to endNight
14%5%25%5%24346%44%
2418
February1st to 15thNight
12%6%25%41323452%
2103
16th to endNight
10%6%25%423446%49%
1893
March1st to 15thNight
7%425%42445%8%50%
1990
16th to endNight
9%313424346%55%
2112
April1st to 15thNight
7%5%24324447%52%
1976
16th to endNight
5%31332346%8%56%
1773
May1st to 15thNight
422342345%10%55%
1619
16th to endNight
43134345%6%10%51%
1682
June1st to 15thNight
8%5%25%5%35%6%9%12%35%
1620
16th to endNight
5%425%5%35%7%9%13%37%
1620
July1st to 15thNight
5%3345%36%6%10%14%35%
1620
16th to endNight
45%26%5%46%7%10%13%31%
1703
August1st to 15thNight
5%325%7%36%8%10%14%32%
1667
16th to endNight
8%6%25%6%47%6%8%11%32%
1979
September1st to 15thNight
9%5%26%7%45%6%8%12%30%
1980
16th to endNight
9%7%36%6%36%6%7%9%35%
1980
October1st to 15thNight
6%5%15%42445%7%50%
2004
16th to endNight
6%424434446%53%
2304
November1st to 15thNight
6%423424346%56%
2288
16th to endNight
8%42442445%7%52%
2535
December1st to 15thNight
11%5%25%5%23348%46%
2391
16th to endNight
11%6%35%4345%6%6%43%
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
40%48%17%17%11%
1612
16th to endDay
40%36%17%20%10%
1804
February1st to 15thDay
40%27%14%19%15%
1752
16th to endDay
38%37%14%23%12%
1580
March1st to 15thDay
28%410%22%22%10%
1968
16th to endDay
32%411%19%20%11%
2112
April1st to 15thDay
35%49%17%22%10%
1972
16th to endDay
31%410%23%19%10%
2196
May1st to 15thDay
27%5%12%24%21%8%
2331
16th to endDay
36%6%13%22%16%4
2435
June1st to 15thDay
47%10%15%16%8%
2340
16th to endDay
44%11%19%18%5%
2340
July1st to 15thDay
43%14%25%14%1
2201
16th to endDay
49%13%21%12%3
2310
August1st to 15thDay
49%13%22%12%1
2276
16th to endDay
53%12%18%11%3
2208
September1st to 15thDay
51%10%17%12%6%1
1980
16th to endDay
50%6%12%16%10%3
1980
October1st to 15thDay
38%49%18%17%11%
1953
16th to endDay
30%37%15%25%17%
1920
November1st to 15thDay
27%39%23%23%12%
1898
16th to endDay
31%48%17%23%14%
1755
December1st to 15thDay
38%410%21%18%6%
1651
16th to endDay
41%410%21%13%8%
1728
January1st to 15thNight
39%310%16%19%10%
2327
16th to endNight
40%37%14%22%11%
2418
February1st to 15thNight
35%37%15%20%16%
2112
16th to endNight
37%38%17%19%13%
1893
March1st to 15thNight
30%411%23%19%10%
1990
16th to endNight
30%410%21%21%11%
2112
April1st to 15thNight
32%49%19%23%10%
1976
16th to endNight
24%412%27%22%9%
1773
May1st to 15thNight
24%6%14%26%19%10%
1620
16th to endNight
26%7%19%24%18%4
1684
June1st to 15thNight
35%9%23%25%6%
1620
16th to endNight
33%11%26%21%7%
1620
July1st to 15thNight
33%12%31%20%2
1530
16th to endNight
35%14%32%13%3
1595
August1st to 15thNight
34%14%33%15%2
1656
16th to endNight
41%13%24%16%4
1979
September1st to 15thNight
42%11%21%15%6%1
1980
16th to endNight
42%7%16%18%10%3
1980
October1st to 15thNight
32%5%12%18%20%11%
2004
16th to endNight
30%47%17%24%16%
2304
November1st to 15thNight
28%37%23%24%12%
2288
16th to endNight
30%48%20%20%15%
2535
December1st to 15thNight
37%311%24%15%6%
2391
16th to endNight
38%5%11%22%14%8%
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
13%14%42%11%10%8%
90
16th to endDay
14%15%35%22%11%
96
February1st to 15thDay
11%25%24%23%14%1
90
16th to endDay
9%9%39%29%9%1
81
March1st to 15thDay
10%7%30%32%17%1
258
16th to endDay
11%426%24%28%3
288
April1st to 15thDay
11%7%26%22%27%5%
270
16th to endDay
6%215%31%30%13%
270
May1st to 15thDay
7%318%25%25%20%
288
16th to endDay
7%36%16%32%33%
331
June1st to 15thDay
12%9%13%27%36%
315
16th to endDay
10%312%28%45%
315
July1st to 15thDay
5%36%23%60%
305
16th to endDay
7%1310%29%47%
326
August1st to 15thDay
14%312%24%44%
313
16th to endDay
10%412%24%46%
332
September1st to 15thDay
15%15%15%29%32%
315
16th to endDay
15%7%17%37%21%
314
October1st to 15thDay
13%213%29%28%12%
315
16th to endDay
7%5%22%32%25%6%
336
November1st to 15thDay
9%218%39%21%8%
316
16th to endDay
5%7%27%31%20%6%
135
December1st to 15thDay
8%10%32%29%17%4
100
16th to endDay
17%6%23%36%11%4
96
January1st to 15thNight
16%7%29%33%12%
720
16th to endNight
16%7%29%34%11%
768
February1st to 15thNight
15%8%29%32%12%
704
16th to endNight
14%6%31%41%6%
631
March1st to 15thNight
8%7%30%39%13%
720
16th to endNight
11%5%25%37%19%1
768
April1st to 15thNight
10%425%41%18%
718
16th to endNight
7%223%39%24%2
612
May1st to 15thNight
6%214%46%26%2
540
16th to endNight
5%29%36%41%4
563
June1st to 15thNight
9%15%28%43%11%
540
16th to endNight
7%320%49%18%
540
July1st to 15thNight
6%216%50%23%
510
16th to endNight
6%115%54%21%
564
August1st to 15thNight
6%211%57%21%
539
16th to endNight
11%5%18%44%20%
642
September1st to 15thNight
12%15%21%44%15%
720
16th to endNight
12%19%29%40%6%
717
October1st to 15thNight
10%213%41%30%3
720
16th to endNight
8%222%37%27%2
768
November1st to 15thNight
8%323%40%22%1
760
16th to endNight
9%327%39%17%1
780
December1st to 15thNight
13%425%36%18%
736
16th to endNight
13%5%24%35%19%
768
Page generated at 2017-12-05 10:19:04. Version ac04

Copyright 2017 A. Danko


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