Brogdon Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brogdon 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
62%
16595
20%
48463
16%
16554
66%
16554
30%
30415

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
48%
778
19%
2522
15%
776
56%
776
27%
1549
January16th to endNight
50%
788
26%
2524
21%
788
60%
788
32%
1456
February1st to 15thNight
48%
701
24%
2103
16%
698
58%
698
33%
1248
February16th to endNight
52%
631
29%
1779
18%
631
62%
631
40%
1017
March1st to 15thNight
55%
720
30%
1980
18%
720
66%
720
47%
1066
March16th to endNight
61%
768
26%
2112
21%
768
66%
768
44%
1166
April1st to 15thNight
61%
718
23%
1976
19%
718
65%
718
44%
1078
April16th to endNight
63%
720
27%
1821
17%
720
68%
720
43%
1077
May1st to 15thNight
68%
666
25%
1746
17%
666
71%
666
46%
1003
May16th to endNight
77%
561
21%
1682
17%
561
78%
561
35%
1016
June1st to 15thNight
66%
540
10%
1620
8%
540
66%
540
21%
1159
June16th to endNight
72%
540
10%
1620
8%
540
72%
540
22%
1155
July1st to 15thNight
72%
510
6%
1530
6%
510
72%
510
19%
1143
July16th to endNight
75%
564
7%
1595
7%
531
75%
531
21%
1166
August1st to 15thNight
78%
549
7%
1619
7%
546
78%
546
24%
1133
August16th to endNight
64%
764
5%
2053
5%
764
64%
764
18%
1545
September1st to 15thNight
64%
720
6%
1980
5%
720
64%
720
18%
1471
September16th to endNight
62%
717
9%
1980
9%
717
62%
717
19%
1465
October1st to 15thNight
66%
720
21%
2072
20%
720
68%
720
28%
1326
October16th to endNight
60%
768
24%
2304
24%
768
64%
768
30%
1435
November1st to 15thNight
65%
760
28%
2281
26%
760
70%
760
37%
1297
November16th to endNight
58%
780
31%
2340
27%
780
65%
780
34%
1400
December1st to 15thNight
59%
780
25%
2520
24%
780
64%
780
31%
1495
December16th to endNight
61%
832
24%
2704
24%
832
65%
832
32%
1549

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%26%7%47%6%7%8%34%
49040
Night
7%425%5%35%5%6%9%43%
48672
TransparencyDay
43%8%14%16%12%4
48741
Night
34%8%16%21%14%4
48475
SeeingDay
8%212%22%26%27%
6376
Night
8%215%32%30%10%
16603

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
10%5%35%5%35%47%8%38%
1746
16th to endDay
9%4235%345%7%9%43%
1801
February1st to 15thDay
10%5%244245%5%8%45%
1750
16th to endDay
7%4145%25%45%8%47%
1691
March1st to 15thDay
5%2245%45%46%9%49%
1980
16th to endDay
7%425%6%35%6%5%9%45%
2111
April1st to 15thDay
5%3245%37%7%7%9%42%
1972
16th to endDay
7%3245%37%5%5%10%43%
2136
May1st to 15thDay
6%4145%46%5%6%9%45%
2212
16th to endDay
9%5%27%8%5%9%7%7%8%29%
2431
June1st to 15thDay
12%7%38%8%6%8%6%8%9%20%
2340
16th to endDay
9%5%48%8%5%9%9%7%9%21%
2340
July1st to 15thDay
10%7%39%9%6%9%9%7%8%19%
2340
16th to endDay
9%6%48%9%6%8%7%9%9%20%
2465
August1st to 15thDay
7%6%27%8%5%9%8%9%10%23%
2316
16th to endDay
10%8%48%9%7%7%6%8%8%20%
2145
September1st to 15thDay
9%7%38%10%6%8%8%8%9%20%
1980
16th to endDay
12%8%39%8%5%8%8%8%7%19%
1980
October1st to 15thDay
9%6%36%8%5%6%5%7%8%32%
1887
16th to endDay
10%5%25%7%45%5%5%8%37%
1920
November1st to 15thDay
6%5%26%6%36%5%5%8%44%
1907
16th to endDay
8%436%5%35%5%6%8%41%
1950
December1st to 15thDay
12%5%245%35%5%5%7%42%
1768
16th to endDay
6%424426%5%6%11%44%
1872
January1st to 15thNight
9%6%25%5%345%6%9%40%
2522
16th to endNight
9%42442445%8%46%
2524
February1st to 15thNight
10%6%2442445%7%48%
2103
16th to endNight
6%3244245%6%7%52%
1779
March1st to 15thNight
431432445%8%57%
1980
16th to endNight
6%31332445%8%56%
2112
April1st to 15thNight
422442345%9%55%
1976
16th to endNight
6%3133245%6%8%53%
1821
May1st to 15thNight
42134235%5%9%55%
1746
16th to endNight
6%324435%6%8%11%44%
1682
June1st to 15thNight
10%7%46%5%46%7%9%10%27%
1620
16th to endNight
6%436%7%47%7%7%10%33%
1620
July1st to 15thNight
10%6%35%6%36%7%8%10%32%
1620
16th to endNight
5%5%27%8%38%8%8%10%31%
1703
August1st to 15thNight
45%26%5%47%6%10%13%33%
1630
16th to endNight
10%5%26%7%36%8%8%12%27%
2053
September1st to 15thNight
7%5%27%8%48%7%8%13%26%
1980
16th to endNight
9%7%37%8%46%7%6%10%28%
1980
October1st to 15thNight
7%5%25%5%35%6%7%9%41%
2072
16th to endNight
10%5%2442446%8%45%
2304
November1st to 15thNight
5%3244245%5%9%50%
2281
16th to endNight
8%4244345%5%8%47%
2340
December1st to 15thNight
9%3245%35%5%5%7%47%
2520
16th to endNight
6%4245%35%5%5%9%47%
2704

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%6%10%19%18%4
1747
16th to endDay
35%5%7%22%19%8%
1801
February1st to 15thDay
34%48%20%22%10%
1752
16th to endDay
32%5%12%21%18%9%
1691
March1st to 15thDay
30%412%25%19%7%
1980
16th to endDay
34%5%10%22%19%7%
2112
April1st to 15thDay
32%7%13%22%18%4
1972
16th to endDay
35%6%10%19%22%6%
2136
May1st to 15thDay
32%6%12%21%19%7%
2212
16th to endDay
47%6%14%19%12%
2435
June1st to 15thDay
55%10%15%13%3
2340
16th to endDay
53%12%20%11%2
2340
July1st to 15thDay
56%14%20%6%1
2201
16th to endDay
54%12%21%11%
2310
August1st to 15thDay
49%12%28%9%
2303
16th to endDay
55%13%22%7%
2145
September1st to 15thDay
54%13%21%9%1
1980
16th to endDay
57%11%17%9%3
1980
October1st to 15thDay
45%7%11%16%14%4
1887
16th to endDay
41%6%8%16%19%9%
1920
November1st to 15thDay
37%5%9%22%17%8%
1907
16th to endDay
38%5%8%19%17%10%
1950
December1st to 15thDay
39%6%12%20%14%6%
1768
16th to endDay
32%5%13%25%16%6%
1872
January1st to 15thNight
38%5%14%21%14%4
2522
16th to endNight
33%410%25%18%7%
2524
February1st to 15thNight
34%38%19%21%11%
2112
16th to endNight
28%5%12%24%21%7%
1779
March1st to 15thNight
23%314%31%20%6%
1980
16th to endNight
24%5%15%25%20%8%
2112
April1st to 15thNight
24%5%18%26%18%6%
1976
16th to endNight
27%5%13%25%22%5%
1821
May1st to 15thNight
24%6%14%29%18%6%
1747
16th to endNight
30%8%19%26%15%
1684
June1st to 15thNight
46%9%22%16%4
1620
16th to endNight
40%14%24%17%3
1620
July1st to 15thNight
44%15%25%12%2
1530
16th to endNight
40%17%27%14%1
1595
August1st to 15thNight
36%16%35%11%
1619
16th to endNight
44%16%27%10%
2053
September1st to 15thNight
45%15%25%11%2
1980
16th to endNight
46%12%21%15%3
1980
October1st to 15thNight
36%9%15%17%17%3
2072
16th to endNight
36%6%10%15%20%10%
2304
November1st to 15thNight
29%5%10%24%22%7%
2281
16th to endNight
34%49%22%18%9%
2340
December1st to 15thNight
34%5%11%25%15%7%
2520
16th to endNight
31%6%15%24%16%5%
2704

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%6%42%23%7%4
135
16th to endDay
11%13%29%23%18%2
109
February1st to 15thDay
6%10%28%24%21%8%
90
16th to endDay
11%327%35%20%
192
March1st to 15thDay
5%426%35%23%3
270
16th to endDay
5%6%21%31%29%5%
288
April1st to 15thDay
4222%30%30%9%
270
16th to endDay
7%112%29%31%17%
270
May1st to 15thDay
6%18%24%38%20%
288
16th to endDay
8%26%17%32%33%
331
June1st to 15thDay
14%16%11%26%38%
315
16th to endDay
7%37%23%58%
315
July1st to 15thDay
5%5%24%62%
305
16th to endDay
9%1210%19%57%
326
August1st to 15thDay
6%39%22%58%
313
16th to endDay
11%25%9%19%51%
332
September1st to 15thDay
7%16%10%20%53%
315
16th to endDay
12%314%26%42%
314
October1st to 15thDay
9%8%29%36%15%
315
16th to endDay
11%220%27%27%11%
336
November1st to 15thDay
7%19%35%34%11%
325
16th to endDay
6%316%43%26%3
330
December1st to 15thDay
13%427%31%16%5%
148
16th to endDay
211%42%32%9%
144
January1st to 15thNight
10%6%25%36%20%2
780
16th to endNight
10%6%26%42%13%
788
February1st to 15thNight
11%428%41%13%
704
16th to endNight
8%328%45%13%
631
March1st to 15thNight
4430%43%15%1
720
16th to endNight
6%321%48%19%
768
April1st to 15thNight
4422%45%22%1
718
16th to endNight
7%319%46%22%
720
May1st to 15thNight
5%117%46%27%2
667
16th to endNight
7%16%34%41%8%
563
June1st to 15thNight
12%1320%46%14%
540
16th to endNight
6%211%48%29%
540
July1st to 15thNight
9%8%47%33%
510
16th to endNight
41110%42%39%
564
August1st to 15thNight
6%29%45%36%
549
16th to endNight
12%15%12%42%26%
764
September1st to 15thNight
9%15%13%44%25%
720
16th to endNight
11%1418%45%17%
717
October1st to 15thNight
9%19%33%37%8%
720
16th to endNight
12%215%32%31%5%
768
November1st to 15thNight
6%216%42%28%3
760
16th to endNight
8%221%41%24%1
780
December1st to 15thNight
9%317%41%25%2
780
16th to endNight
5%320%38%28%3
832
Page generated at 2018-01-21 12:19:21. Version ac04

Copyright 2018 A. Danko


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