Branched Oak Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Branched Oak Observatory clear sky chart from 2005-11-05 to 2018-01-20.

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
42%
16544
23%
48629
13%
16499
51%
16499
34%
28458

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
35%
975
21%
2522
10%
970
43%
970
32%
1599
January16th to endNight
31%
985
27%
2561
11%
985
42%
985
33%
1600
February1st to 15thNight
28%
880
13%
2288
4%
876
33%
876
25%
1600
February16th to endNight
32%
651
26%
1913
8%
651
47%
651
32%
1140
March1st to 15thNight
36%
579
23%
2019
15%
579
46%
579
27%
1143
March16th to endNight
28%
576
15%
2112
11%
576
37%
576
20%
1320
April1st to 15thNight
31%
539
21%
1863
13%
539
44%
539
26%
1084
April16th to endNight
33%
540
21%
1620
15%
540
43%
540
26%
1036
May1st to 15thNight
39%
540
18%
1620
13%
540
47%
540
28%
1013
May16th to endNight
42%
561
15%
1685
8%
561
49%
561
33%
1004
June1st to 15thNight
53%
540
17%
1479
7%
540
57%
540
38%
867
June16th to endNight
59%
540
23%
1513
10%
540
64%
540
53%
749
July1st to 15thNight
68%
510
17%
1530
11%
510
70%
510
44%
817
July16th to endNight
76%
564
25%
1594
22%
531
79%
531
52%
790
August1st to 15thNight
73%
539
22%
1610
25%
536
76%
536
44%
856
August16th to endNight
64%
573
26%
1728
27%
573
69%
573
41%
952
September1st to 15thNight
54%
540
25%
1941
23%
540
64%
540
37%
979
September16th to endNight
53%
537
31%
1980
26%
537
63%
537
39%
943
October1st to 15thNight
38%
658
27%
2098
17%
658
46%
658
30%
1226
October16th to endNight
45%
777
30%
2313
16%
777
54%
777
40%
1243
November1st to 15thNight
41%
950
29%
2470
12%
950
52%
950
41%
1420
November16th to endNight
37%
975
28%
2639
13%
975
48%
975
38%
1526
December1st to 15thNight
29%
975
19%
2730
7%
975
40%
975
28%
1718
December16th to endNight
35%
1040
24%
2801
11%
1040
44%
1040
28%
1833

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
11%6%25%42445%7%45%
48884
Night
9%5%24423347%50%
48824
Cloud CoverDay
10%6%25%42445%7%45%
48882
Night
9%5%24424347%50%
48824
TransparencyDay
38%314%26%14%2
48582
Night
33%313%28%17%2
48629
SeeingDay
13%6%29%30%16%3
6360
Night
12%8%31%35%12%
16546

By Month

Percentage Cloud Cover SW (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
9%6%36%6%34447%45%
1746
16th to endDay
10%9%36%434345%43%
1767
February1st to 15thDay
11%9%47%6%2445%7%36%
1575
16th to endDay
11%6%36%423448%43%
1572
March1st to 15thDay
10%6%36%424446%45%
1940
16th to endDay
15%10%35%434445%38%
2112
April1st to 15thDay
15%7%35%434335%42%
2082
16th to endDay
22%7%26%5%24347%35%
2340
May1st to 15thDay
14%5%35%435%447%40%
2331
16th to endDay
15%5%25%6%3445%8%39%
2430
June1st to 15thDay
10%425%42446%8%45%
2475
16th to endDay
6%324425%5%6%8%50%
2441
July1st to 15thDay
8%41443445%10%48%
2340
16th to endDay
5%3134345%6%9%52%
2466
August1st to 15thDay
6%4245%35%6%7%10%43%
2340
16th to endDay
8%41442445%7%51%
2474
September1st to 15thDay
13%5%23424346%49%
2018
16th to endDay
8%324323246%57%
1980
October1st to 15thDay
13%6%24434335%48%
1849
16th to endDay
11%5%14322336%54%
1910
November1st to 15thDay
8%424323346%55%
1718
16th to endDay
10%6%345%23447%48%
1648
December1st to 15thDay
10%9%35%5%3345%6%43%
1560
16th to endDay
11%9%5%8%5%2445%6%36%
1770
January1st to 15thNight
6%6%35%6%3436%7%45%
2522
16th to endNight
9%7%35%423335%51%
2561
February1st to 15thNight
11%9%36%6%35%445%38%
2278
16th to endNight
8%5%35%43446%6%48%
1913
March1st to 15thNight
10%6%34324335%51%
2019
16th to endNight
16%7%3442445%6%39%
2112
April1st to 15thNight
13%6%245%13347%46%
1863
16th to endNight
17%7%24423347%43%
1620
May1st to 15thNight
13%4245%25%45%8%43%
1619
16th to endNight
12%6%1422345%8%47%
1683
June1st to 15thNight
8%41442346%8%50%
1479
16th to endNight
211232446%9%61%
1513
July1st to 15thNight
43145%1346%9%55%
1620
16th to endNight
31233346%9%60%
1702
August1st to 15thNight
431343445%9%55%
1620
16th to endNight
7%413423346%57%
1728
September1st to 15thNight
8%314223446%57%
1941
16th to endNight
7%313313337%59%
1980
October1st to 15thNight
15%423313335%51%
2098
16th to endNight
10%41331234459%
2313
November1st to 15thNight
7%324324347%56%
2470
16th to endNight
10%424323346%55%
2639
December1st to 15thNight
11%7%35%423347%46%
2730
16th to endNight
11%9%36%42335%6%43%
2801

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
8%6%26%6%44447%44%
1746
16th to endDay
9%9%36%5%35%336%43%
1767
February1st to 15thDay
10%8%5%7%6%3445%8%35%
1575
16th to endDay
11%7%25%5%24448%43%
1572
March1st to 15thDay
9%7%35%5%34447%44%
1940
16th to endDay
15%9%36%424445%38%
2110
April1st to 15thDay
15%7%35%424336%42%
2082
16th to endDay
21%8%26%5%23446%34%
2340
May1st to 15thDay
13%5%36%5%35%45%7%39%
2331
16th to endDay
14%6%25%6%25%45%8%38%
2430
June1st to 15thDay
9%5%245%3445%9%45%
2475
16th to endDay
5%424425%5%6%8%50%
2441
July1st to 15thDay
8%31343446%10%47%
2340
16th to endDay
4323425%5%6%10%52%
2466
August1st to 15thDay
6%4245%35%6%8%10%42%
2340
16th to endDay
8%42443445%7%50%
2474
September1st to 15thDay
12%5%2442345%6%49%
2018
16th to endDay
8%323423346%57%
1980
October1st to 15thDay
13%6%35%42433448%
1849
16th to endDay
11%5%24413346%53%
1910
November1st to 15thDay
8%425%323346%55%
1718
16th to endDay
10%5%35%423447%48%
1648
December1st to 15thDay
10%10%35%5%2345%7%42%
1560
16th to endDay
11%10%48%5%2445%6%35%
1770
January1st to 15thNight
6%6%26%5%35%36%7%45%
2522
16th to endNight
9%7%35%423336%50%
2561
February1st to 15thNight
11%8%47%7%34445%38%
2278
16th to endNight
7%6%3443446%6%48%
1913
March1st to 15thNight
10%6%25%424345%50%
2019
16th to endNight
16%7%35%5%2435%6%38%
2112
April1st to 15thNight
12%6%245%23347%46%
1863
16th to endNight
16%7%3442335%6%43%
1620
May1st to 15thNight
13%415%5%3445%8%43%
1619
16th to endNight
12%6%1432335%9%46%
1683
June1st to 15thNight
8%3235%235%5%9%50%
1479
16th to endNight
121322445%10%61%
1513
July1st to 15thNight
42245%2435%9%55%
1620
16th to endNight
3123245%6%9%59%
1702
August1st to 15thNight
42135%2446%9%54%
1620
16th to endNight
7%5%23423236%57%
1728
September1st to 15thNight
8%314323446%57%
1941
16th to endNight
7%413213347%59%
1980
October1st to 15thNight
14%5%2441333451%
2098
16th to endNight
10%323312445%58%
2313
November1st to 15thNight
6%423423447%56%
2470
16th to endNight
10%423323346%55%
2639
December1st to 15thNight
10%7%35%423347%46%
2730
16th to endNight
10%9%37%41335%6%43%
2801

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%218%25%10%1
1747
16th to endDay
43%316%22%13%
1767
February1st to 15thDay
47%316%22%7%1
1576
16th to endDay
40%415%24%14%2
1572
March1st to 15thDay
40%313%26%15%1
1940
16th to endDay
48%315%22%8%1
2112
April1st to 15thDay
44%212%26%12%1
2082
16th to endDay
50%310%24%10%
2340
May1st to 15thDay
43%312%24%14%
2331
16th to endDay
43%417%23%10%1
2434
June1st to 15thDay
36%5%14%28%14%1
2475
16th to endDay
29%5%15%33%13%3
2441
July1st to 15thDay
32%314%30%13%3
2201
16th to endDay
25%415%33%19%2
2311
August1st to 15thDay
31%6%19%27%13%1
2326
16th to endDay
31%411%29%18%4
2474
September1st to 15thDay
35%310%28%18%3
2018
16th to endDay
29%211%33%22%1
1980
October1st to 15thDay
40%28%24%21%3
1849
16th to endDay
32%213%26%19%5%
1910
November1st to 15thDay
29%214%27%23%1
1718
16th to endDay
37%212%30%15%1
1648
December1st to 15thDay
40%318%25%10%1
1560
16th to endDay
48%215%20%11%
1770
January1st to 15thNight
37%216%26%15%
2522
16th to endNight
36%215%29%14%1
2561
February1st to 15thNight
47%314%22%10%1
2288
16th to endNight
34%313%28%15%4
1913
March1st to 15thNight
35%310%28%18%2
2019
16th to endNight
44%415%23%10%1
2112
April1st to 15thNight
38%210%29%17%1
1863
16th to endNight
41%312%24%16%
1620
May1st to 15thNight
39%313%25%16%1
1620
16th to endNight
34%420%24%15%1
1685
June1st to 15thNight
30%5%16%28%16%2
1479
16th to endNight
18%415%34%23%4
1513
July1st to 15thNight
25%416%30%18%4
1530
16th to endNight
18%5%15%36%20%2
1594
August1st to 15thNight
24%418%32%16%2
1610
16th to endNight
29%311%27%20%7%
1728
September1st to 15thNight
27%311%29%20%7%
1941
16th to endNight
25%211%34%22%4
1980
October1st to 15thNight
35%38%23%24%3
2098
16th to endNight
28%211%28%27%2
2313
November1st to 15thNight
28%212%26%25%4
2470
16th to endNight
30%214%29%20%2
2639
December1st to 15thNight
38%315%29%12%
2730
16th to endNight
41%314%25%12%1
2801

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
17%10%37%25%8%
135
16th to endDay
17%340%26%11%
109
February1st to 15thDay
17%15%40%22%4
90
16th to endDay
11%13%38%22%12%2
81
March1st to 15thDay
17%11%45%18%6%
90
16th to endDay
25%7%37%21%8%
96
April1st to 15thDay
17%11%38%25%6%
201
16th to endDay
27%13%28%20%9%
450
May1st to 15thDay
14%10%32%26%13%2
468
16th to endDay
18%433%28%11%2
517
June1st to 15thDay
10%5%26%33%19%3
495
16th to endDay
6%431%35%20%2
495
July1st to 15thDay
10%222%32%25%6%
475
16th to endDay
4117%41%29%5%
515
August1st to 15thDay
5%220%40%26%4
493
16th to endDay
11%318%33%26%5%
514
September1st to 15thDay
11%226%38%17%4
173
16th to endDay
14%234%30%15%2
135
October1st to 15thDay
21%8%25%28%8%8%
135
16th to endDay
15%8%39%22%12%2
144
November1st to 15thDay
11%8%38%28%7%5%
135
16th to endDay
25%10%33%24%5%
135
December1st to 15thDay
16%15%42%20%22
135
16th to endDay
20%11%42%22%3
144
January1st to 15thNight
10%11%35%33%7%
975
16th to endNight
13%10%37%31%6%
985
February1st to 15thNight
15%8%40%30%5%
880
16th to endNight
11%10%40%30%6%
651
March1st to 15thNight
15%10%34%30%8%
579
16th to endNight
18%8%37%28%5%
576
April1st to 15thNight
14%12%35%31%5%
539
16th to endNight
20%10%30%30%7%
540
May1st to 15thNight
15%9%30%31%12%
540
16th to endNight
14%5%34%32%12%
563
June1st to 15thNight
9%5%25%46%12%
540
16th to endNight
2429%45%17%
540
July1st to 15thNight
4119%43%29%
510
16th to endNight
412%54%27%
564
August1st to 15thNight
5%212%53%24%1
539
16th to endNight
9%216%41%27%3
573
September1st to 15thNight
10%128%34%24%1
540
16th to endNight
9%429%35%20%
537
October1st to 15thNight
18%7%30%28%11%1
658
16th to endNight
12%7%29%37%11%
777
November1st to 15thNight
10%10%34%34%9%
950
16th to endNight
13%9%36%30%9%
975
December1st to 15thNight
15%12%37%28%6%
975
16th to endNight
16%10%31%35%6%
1040
Page generated at 2018-01-21 11:19:20. Version ac04

Copyright 2018 A. Danko


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