Broken Oak Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Broken Oak Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
55%
15896
20%
47014
15%
15855
61%
15855
29%
29606

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
43%
718
20%
2327
14%
716
52%
716
23%
1462
January16th to endNight
39%
768
23%
2418
16%
768
48%
768
25%
1518
February1st to 15thNight
40%
701
24%
2103
16%
698
51%
698
32%
1265
February16th to endNight
36%
631
24%
1858
11%
631
49%
631
29%
1134
March1st to 15thNight
42%
720
29%
1980
13%
720
55%
720
37%
1137
March16th to endNight
45%
768
26%
2112
17%
768
53%
768
38%
1232
April1st to 15thNight
48%
718
23%
1976
15%
718
56%
718
42%
1119
April16th to endNight
53%
705
27%
1854
16%
705
60%
705
41%
1085
May1st to 15thNight
68%
539
25%
1619
19%
539
73%
539
43%
882
May16th to endNight
72%
561
23%
1682
17%
561
75%
561
35%
998
June1st to 15thNight
68%
540
12%
1620
11%
540
69%
540
25%
1115
June16th to endNight
73%
540
8%
1620
7%
540
73%
540
22%
1154
July1st to 15thNight
73%
510
6%
1530
6%
510
73%
510
20%
1143
July16th to endNight
75%
564
6%
1595
5%
531
77%
531
20%
1179
August1st to 15thNight
77%
539
5%
1642
6%
536
77%
536
22%
1180
August16th to endNight
68%
693
10%
2030
10%
693
68%
693
20%
1448
September1st to 15thNight
64%
720
8%
1980
7%
720
64%
720
18%
1470
September16th to endNight
59%
689
15%
1903
14%
689
60%
689
21%
1355
October1st to 15thNight
64%
660
26%
1854
23%
660
68%
660
34%
1136
October16th to endNight
55%
704
28%
2112
24%
704
63%
704
33%
1246
November1st to 15thNight
53%
700
30%
2101
23%
700
63%
700
38%
1159
November16th to endNight
46%
720
28%
2262
20%
720
58%
720
33%
1308
December1st to 15thNight
45%
720
26%
2340
20%
720
55%
720
29%
1392
December16th to endNight
48%
768
23%
2496
21%
768
54%
768
28%
1489

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
8%5%26%7%46%6%6%8%36%
47871
Night
7%5%25%5%35%5%6%9%44%
47223
TransparencyDay
42%9%13%15%13%6%
47572
Night
34%9%15%19%14%6%
47026
SeeingDay
9%415%23%24%23%
5755
Night
9%5%21%31%24%8%
15904

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
11%5%26%5%3445%9%40%
1611
16th to endDay
9%6%25%5%24447%46%
1804
February1st to 15thDay
13%436%4235%36%45%
1750
16th to endDay
7%5%245%34447%48%
1613
March1st to 15thDay
6%425%4245%5%7%51%
1980
16th to endDay
8%425%5%3445%6%48%
2111
April1st to 15thDay
6%425%5%36%5%5%7%46%
1972
16th to endDay
6%3145%36%5%5%9%47%
2114
May1st to 15thDay
5%4145%35%5%5%8%48%
2331
16th to endDay
6%326%7%5%6%5%7%8%38%
2431
June1st to 15thDay
11%6%37%8%5%7%7%7%9%25%
2340
16th to endDay
7%6%38%8%5%10%8%9%9%22%
2340
July1st to 15thDay
8%6%39%9%6%9%8%7%8%20%
2340
16th to endDay
6%6%49%11%5%9%9%8%10%18%
2465
August1st to 15thDay
7%6%28%10%6%9%8%8%11%19%
2302
16th to endDay
9%7%38%9%5%8%7%8%8%21%
2158
September1st to 15thDay
8%6%410%10%6%8%7%7%8%21%
1980
16th to endDay
9%7%48%8%5%9%7%6%7%24%
1894
October1st to 15thDay
8%5%36%6%45%6%5%6%39%
1774
16th to endDay
8%6%34435%45%7%47%
1760
November1st to 15thDay
5%425%425%5%46%53%
1757
16th to endDay
8%5%25%435%45%8%46%
1696
December1st to 15thDay
10%6%35%5%2446%6%42%
1620
16th to endDay
6%5%25%6%35%6%6%7%44%
1728
January1st to 15thNight
11%6%35%43446%9%39%
2327
16th to endNight
12%5%34425%5%5%7%43%
2418
February1st to 15thNight
10%6%2342345%6%50%
2103
16th to endNight
8%5%35%434448%47%
1858
March1st to 15thNight
6%42442345%8%54%
1980
16th to endNight
6%42442346%7%54%
2112
April1st to 15thNight
5%32231347%10%53%
1976
16th to endNight
6%312425%45%8%54%
1854
May1st to 15thNight
432242445%10%55%
1619
16th to endNight
3324435%47%9%50%
1682
June1st to 15thNight
9%5%35%5%37%5%8%11%35%
1620
16th to endNight
6%5%25%6%46%7%9%11%32%
1620
July1st to 15thNight
5%446%6%47%7%10%13%30%
1620
16th to endNight
4326%8%5%8%8%9%13%28%
1703
August1st to 15thNight
3426%6%47%7%10%13%31%
1653
16th to endNight
7%6%36%5%36%7%8%12%31%
2030
September1st to 15thNight
7%6%26%7%5%7%6%8%11%29%
1980
16th to endNight
8%6%27%7%46%6%7%10%31%
1903
October1st to 15thNight
6%6%244345%6%8%48%
1854
16th to endNight
8%6%24423348%51%
2112
November1st to 15thNight
5%42442435%8%53%
2101
16th to endNight
6%336%43445%7%50%
2262
December1st to 15thNight
8%6%25%42445%8%46%
2340
16th to endNight
7%5%25%5%25%6%5%9%44%
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
39%6%9%19%18%6%
1612
16th to endDay
37%49%15%23%10%
1804
February1st to 15thDay
39%5%6%13%19%16%
1752
16th to endDay
35%5%10%15%21%11%
1613
March1st to 15thDay
30%5%10%22%21%9%
1980
16th to endDay
35%5%10%18%19%9%
2112
April1st to 15thDay
34%6%10%17%22%8%
1972
16th to endDay
32%6%11%19%22%8%
2114
May1st to 15thDay
31%6%13%20%18%9%
2331
16th to endDay
40%8%14%18%15%2
2435
June1st to 15thDay
51%11%15%16%4
2340
16th to endDay
52%14%18%11%2
2340
July1st to 15thDay
56%15%18%8%1
2201
16th to endDay
53%16%18%9%1
2310
August1st to 15thDay
51%17%24%6%
2289
16th to endDay
53%15%17%12%1
2158
September1st to 15thDay
55%14%16%9%3
1980
16th to endDay
52%11%13%13%6%2
1894
October1st to 15thDay
41%9%9%14%15%10%
1774
16th to endDay
35%5%8%15%21%12%
1760
November1st to 15thDay
29%5%8%23%22%10%
1757
16th to endDay
34%5%9%18%17%13%
1696
December1st to 15thDay
39%5%12%19%16%6%
1620
16th to endDay
35%7%10%20%17%7%
1728
January1st to 15thNight
39%6%11%19%16%6%
2327
16th to endNight
39%5%9%16%20%9%
2418
February1st to 15thNight
32%6%8%16%21%14%
2112
16th to endNight
35%6%11%16%22%7%
1858
March1st to 15thNight
28%5%12%25%20%7%
1980
16th to endNight
28%6%11%25%19%8%
2112
April1st to 15thNight
24%7%16%23%21%6%
1976
16th to endNight
26%6%14%23%22%6%
1854
May1st to 15thNight
23%7%17%25%18%7%
1620
16th to endNight
28%9%18%22%18%2
1684
June1st to 15thNight
39%11%22%20%5%
1620
16th to endNight
39%15%22%18%3
1620
July1st to 15thNight
39%19%28%10%1
1530
16th to endNight
38%20%28%11%1
1595
August1st to 15thNight
36%19%33%10%
1642
16th to endNight
41%15%25%16%1
2030
September1st to 15thNight
44%16%22%12%4
1980
16th to endNight
43%12%17%17%6%2
1903
October1st to 15thNight
32%7%12%20%18%7%
1854
16th to endNight
32%5%9%16%25%10%
2112
November1st to 15thNight
28%410%23%23%9%
2101
16th to endNight
32%410%20%17%13%
2262
December1st to 15thNight
34%5%10%26%15%6%
2340
16th to endNight
34%6%12%21%15%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
14%17%34%17%13%2
90
16th to endDay
12%21%32%21%10%1
96
February1st to 15thDay
12%22%24%25%12%3
90
16th to endDay
12%14%29%33%9%
114
March1st to 15thDay
8%13%30%29%15%1
270
16th to endDay
10%10%25%29%21%3
288
April1st to 15thDay
8%9%26%26%22%6%
270
16th to endDay
5%5%18%30%28%10%
270
May1st to 15thDay
6%318%31%22%17%
288
16th to endDay
7%29%23%31%25%
331
June1st to 15thDay
16%17%12%30%30%
315
16th to endDay
7%5%15%24%46%
315
July1st to 15thDay
5%49%21%58%
305
16th to endDay
9%7%14%23%45%
326
August1st to 15thDay
11%148%26%48%
313
16th to endDay
10%15%15%26%40%
332
September1st to 15thDay
13%1417%29%34%
315
16th to endDay
12%1420%32%28%
283
October1st to 15thDay
10%112%34%30%10%
255
16th to endDay
11%423%29%20%9%
272
November1st to 15thDay
6%122%33%28%7%
265
16th to endDay
7%431%36%14%4
166
December1st to 15thDay
10%10%43%28%7%
90
16th to endDay
46%23%47%16%1
96
January1st to 15thNight
13%12%26%34%12%
720
16th to endNight
14%12%28%33%10%
768
February1st to 15thNight
12%9%31%32%13%
704
16th to endNight
10%11%34%35%7%
631
March1st to 15thNight
7%8%38%33%11%
720
16th to endNight
7%9%33%35%13%
768
April1st to 15thNight
6%6%33%38%14%
718
16th to endNight
8%5%28%39%17%
705
May1st to 15thNight
5%120%43%25%2
540
16th to endNight
5%113%40%31%7%
563
June1st to 15thNight
12%6%27%38%13%
540
16th to endNight
7%1418%40%27%
540
July1st to 15thNight
8%214%41%33%
510
16th to endNight
3413%48%29%
564
August1st to 15thNight
5%210%49%31%
539
16th to endNight
10%8%15%38%26%
693
September1st to 15thNight
11%9%25%36%16%
720
16th to endNight
11%112%27%38%9%
689
October1st to 15thNight
10%115%40%28%3
660
16th to endNight
11%5%22%33%25%2
704
November1st to 15thNight
7%428%37%17%3
700
16th to endNight
7%6%33%37%14%1
720
December1st to 15thNight
11%8%29%32%16%
720
16th to endNight
10%7%27%35%18%1
768
Page generated at 2017-09-24 09:15:55. Version ac04

Copyright 2017 A. Danko


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